Next Article in Journal
Distinct Effects of a High Fat Diet on Bone in Skeletally Mature and Developing Male C57BL/6J Mice
Next Article in Special Issue
Role of CD38 in Adipose Tissue: Tuning Coenzyme Availability?
Previous Article in Journal
Differences in Adolescents’ Food Habits Checklist (AFHC) Scores before and during Pandemic in a Population-Based Sample: Polish Adolescents’ COVID-19 Experience (PLACE-19) Study
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:

Advances in NAD-Lowering Agents for Cancer Treatment

Department of Internal Medicine and Medical Specialties (DIMI), University of Genoa, Viale Benedetto XV 6, 16132 Genoa, Italy
Ospedale Policlinico San Martino IRCCS, Largo Rosanna Benzi 10, 16132 Genova, Italy
Author to whom correspondence should be addressed.
Nutrients 2021, 13(5), 1665;
Received: 22 March 2021 / Revised: 4 May 2021 / Accepted: 8 May 2021 / Published: 14 May 2021
(This article belongs to the Special Issue Nicotinamide Adenine Dinucleotide (NAD) in Human Health and Disease)


Nicotinamide adenine dinucleotide (NAD) is an essential redox cofactor, but it also acts as a substrate for NAD-consuming enzymes, regulating cellular events such as DNA repair and gene expression. Since such processes are fundamental to support cancer cell survival and proliferation, sustained NAD production is a hallmark of many types of neoplasms. Depleting intratumor NAD levels, mainly through interference with the NAD-biosynthetic machinery, has emerged as a promising anti-cancer strategy. NAD can be generated from tryptophan or nicotinic acid. In addition, the “salvage pathway” of NAD production, which uses nicotinamide, a byproduct of NAD degradation, as a substrate, is also widely active in mammalian cells and appears to be highly exploited by a subset of human cancers. In fact, research has mainly focused on inhibiting the key enzyme of the latter NAD production route, nicotinamide phosphoribosyltransferase (NAMPT), leading to the identification of numerous inhibitors, including FK866 and CHS-828. Unfortunately, the clinical activity of these agents proved limited, suggesting that the approaches for targeting NAD production in tumors need to be refined. In this contribution, we highlight the recent advancements in this field, including an overview of the NAD-lowering compounds that have been reported so far and the related in vitro and in vivo studies. We also describe the key NAD-producing pathways and their regulation in cancer cells. Finally, we summarize the approaches that have been explored to optimize the therapeutic response to NAMPT inhibitors in cancer.

Graphical Abstract

1. Introduction

Cancer cells share common distinctive features that dictate their aberrant behavior in the body. Hanahan and Weinberg described six capabilities that tumor cells acquire which enable their growth and proliferation, and named them “the hallmarks of cancer”. These hallmark features consist in the ability of malignant cells to sustain the self-supply of growth signals, escape anti-growth signals, evade programmed cell death, maintain the formation of new blood vessels, possess an infinite replicative potential, and, finally, to invade and metastasize into distant tissues [1]. More than a decade later, the same authors added additional features as emerging hallmarks of cancer. The reprogramming of cellular metabolism is among these “next-generation” hallmarks that ultimately support malignant cell survival [2].
Among the major reprogrammed metabolic processes in cancer cells, there is what is named the Warburg’s effect (or aerobic glycolysis) after the name of its discoverer [3]. Typically, in non-malignant cells, in the presence of oxygen, glucose undergoes glycolysis to produce pyruvate which is then converted to acetyl Co-A and enters the citric acid cycle in the mitochondria to produce CO2 and energy in the form of adenosine triphosphate (ATP) via oxidative phosphorylation. However, in cancerous cells, glucose metabolism is rewired and, even in the presence of oxygen, glycolysis predominates while oxidative phosphorylation is reduced, leading to the fermentation of pyruvate to lactate [3]. This so-called Warburg effect is closely related to the need that cancer cells have to sustain a higher production of nicotinamide adenine dinucleotide (NAD), a central molecule required not only at the physiological level but also by neoplastic cells to support numerous crucial cellular processes [4].
NAD is a pyridine nucleotide essential coenzyme that plays a major role in the oxidation–reduction reactions taking place inside the cell, and is also responsible for energy production. Through behaving as an electron acceptor/donor that shuttles between oxidized and reduced forms, NAD supports various metabolic pathways such as glycolysis, Krebs cycle (citric acid cycle), oxidative phosphorylation, and fatty acid oxidation [5,6]. Beyond its role in bioenergetics and cellular metabolism, NAD possesses a prominent cell regulatory function. NAD serves as a substrate for NAD-dependent enzymes such as mono (ADP-ribosyl) transferases (MARTs), poly (ADP-ribose) polymerases (PARPs), sirtuins (SIRT1-7), and cyclic ADP-ribose (cADPR) synthases (CD38 and CD157) [7,8,9]. Indeed, NAD is degraded during the poly-ADP ribosylation reactions carried out by PARPs (e.g., PARP1/2), during protein deacetylation reactions through sirtuins (e.g., SIRT1), and by the hydrolase and ADP-ribosyl cyclase activities of CD38 and CD157 [8,9]. These NAD-consuming reactions orchestrate a series of fundamental biological processes including gene expression, transcription, calcium signaling, DNA repair, apoptosis, circadian rhythm, and cell cycle progression [8,10]. Importantly, many of these cellular events were found to be implicated in malignant transformation and cancer cell survival. For instance, cancer cells frequently face DNA-damaging insults and thus, typically rely on elevated PARP activity to carry out their DNA repair, overcome stress signals, and thereupon sustain their survival. As opposed to its fate as a coenzyme, NAD becomes rapidly degraded by the enzymatic reactions that use it as a substrate, potentially leading to a net NAD deficit [8]. As a consequence, a nonstop generation of NAD is required in normal tissues, and more in neoplastic cells, to compensate for the high NAD degradation. In light of the above findings, dysregulating NAD homeostasis through interfering with the NAD biosynthetic machinery and consequently reducing NAD pools within cancer cells has been conceived as a promising strategy for cancer treatment [8].
In this review, we provide an overview of NAD production routes in eukaryotic cells, the milestone findings, and studies in the development of NAD-depleting agents in the context of oncology therapeutics. In addition, the obstacles in the field and the most recent advances, including the ongoing clinical studies of NAD biosynthesis inhibitors, will also be highlighted.

2. NAD Biosynthesis in Mammals

Overall, mammalian cells utilize the following three biosynthetic pathways to generate NAD: the de novo pathway, the Preiss–Handler (PH) pathway, and the salvage pathway (Figure 1) [8,9]. In the de novo pathway, also referred to as the kynurenine pathway, the essential amino acid tryptophan serves as the starting molecule. It undergoes a cascade of enzymatic reactions that yield quinolinic acid (QA), which is then converted by the enzyme quinolinic acid phosphoribosyltransferase (QAPRT/QPRT) to nicotinic acid mononucleotide (NAMN) [11]. NAMN is also generated in the PH pathway by transferring a phosphoribosyl moiety from phosphoribosyl pyrophosphate (PRPP) to nicotinic acid (NA) with the help of another phosphoribosyltransferase enzyme called nicotinic acid phosphoribosyltransferase (NAPRT). NA is thus considered the precursor unit in the PH pathway of NAD synthesis [12,13]. Noticeably, PRPP, the provider of the NAD-sugar moiety, is synthesized from ribose-5-phosphate, which is a central product of the pentose phosphate pathway (PPP). In such a way, PRPP can be regarded as a linking molecule between glucose metabolism and NAD biosynthesis. The third biosynthetic pathway that contributes to maintaining the NAD supply is the salvage pathway, where NAD is generated starting from the end product of NAD-consuming enzymes, nicotinamide (NAM). Another phosphoribosyltransferase enzyme named nicotinamide phosphoribosyltransferase (NAMPT) controls the rate-limiting step in this pathway. NAMPT catalyzes the transfer of a phosphoribosyl group from the co-substrate PRPP to NAM, yielding nicotinamide mononucleotide (NMN) and pyrophosphate as a byproduct. Alternatively, the two mononucleotides NMN and NAMN can also be produced from the phosphorylation of the nucleosides nicotinamide riboside (NR) and nicotinic acid riboside (NAR) by nicotinamide riboside kinases (NMRK1/2) [14,15]. NAMN and NMN are converted to their corresponding dinucleotides nicotinic acid adenine dinucleotide (NAAD) and NAD through reactions governed by nicotinamide/nicotinic acid mononucleotide adenylyltransferases (NMNATs), of which three mammalian isoforms exist (NMNAT 1–3) [16,17]. In the final step of the PH pathway, NAD synthetase (NADSYN) catalyzes the amidation of NAAD into NAD using glutamine as a nitrogen donor.
NA, NAM and NR (collectively referred to as vitamin B3), as well as tryptophan, can all be obtained through diet, e.g., through cow milk in the case of NR [11,18]. As anticipated above, NAM is also largely produced “endogenously” in virtually every tissue as a byproduct of NAD-degrading enzymes, such as PARPs, sirtuins and CD38. NR can also be produced in bodily tissues starting from its reduced form, NRH, via NRH:quinone oxidoreductase 2 (NQO2), which utilizes NRH as an electron donor [19]. NRH was shown to be endogenously present in the liver by metabolomic analysis [20] and it was proposed to come from NADH degradation via NUDIX hydrolases, such as NUDIX5, 12, and 13 [21,22]. Notably, exogenously supplemented NRH can also stimulate NAD production independent of NMRK enzymes, through a mechanism that foresees its phosphorylation to NMNH, the reduced form of NMN, by adenosine kinase followed by the subsequent conversion to NADH and, ultimately, to NAD [20,23,24]. NRH and NMNH have indeed been identified as important NAD precursors both in vitro and in vivo [22,23,24].
Recent work by Shats et al. showed that gut bacteria convert NAM into NA through their nicotinamidase (PncA) and thereby contribute to NAD production in several mouse tissues, as well as in cancer cells growing the mouse, making them resistant to NAMPT inhibition (an effect that was shown to be dependent on NAPRT expression in cancer cells) [25]. These findings indicate that at least some amounts of gut microbiota- and diet-derived NA do reach bodily tissues despite the extensive metabolism NA undergoes in the liver (here, NA undergoes first-pass metabolism, being conjugated with glycine to form nicotinuric acid, which is then excreted in the urine, and being converted to nicotinamide—assumingly, via NA-mediated NAD generation and subsequent degradation with consequent NAM release). Indeed, circulating NA levels in the nanomolar range can be physiologically detected in mammals and such levels are increased by NA infusion [26] as well as by oral, pharmacological NA doses (gram doses of NA have been used for decades as a lipid-lowering approach). Thus, these observations suggest a role for dietary NA intake as well as for NA produced by the intestinal flora in fueling the PH pathway in NAPRT-expressing tissues (including NAPRT-positive tumors).
The role of NADH in the maintenance of the NAD pool should also not be overlooked. In this context, the enzyme NAD(P)H:quinone oxidoreductase (NQO1) oxidizes NADH into NAD, helping to maintain NAD levels [27]. Indeed, pharmacologically activating NQO1 was shown to augment the NAD/NADH ratio in the kidney tissues, meanwhile, NQO1−/− mice demonstrated higher NADH:NAD and NADPH:NADP ratios as compared to the wild-type mice [28,29].
Since many body tissues don’t express the complete set of the kynurenine pathway enzymes, the contribution of tryptophan to the overall NAD pool has long been thought to be less important. Nevertheless, a recent analysis of NAD synthesis and breakdown fluxes revealed that the liver mainly produces NAD from tryptophan, that it consumes NAD, producing NAM, and that the latter gets secreted in large amounts into the circulation to be used by other tissues [26]. This raises the interesting possibility that tryptophan might strongly contribute to the NAD pool of bodily tissues, not so much directly via de novo synthesis but rather indirectly through multistep inter-tissue cooperation. The latter involves (i) liver-dependent de novo synthesis, followed by (ii) the conversion of NAD into NAM (always in the liver), (iii) NAM excretion into the circulation, and (iv) finally, NAM uptake and utilization by the tissues to produce NAD via the canonical salvage pathway.
Recently published work proposes that the enzyme α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD) acts as a metabolic gatekeeper of the de novo NAD biosynthetic route [30]. ACMSD is expressed mainly by the liver and kidney and it catalyzes the decarboxylation of α-amino-β-carboxymuconate-ε-semialdehyde (ACMS) to α-amino-β-muconate-ε-semialdehyde (AMS), thus rerouting tryptophan metabolism to picolinic acid and acetyl Co-A synthesis rather than towards NAD production [5,30]. Indeed, enhancement of de novo NAD synthesis and SIRT1 activity was observed in response to ACMSD inhibition [30]. In line with these findings, another study reported that mice overexpressing ACMSD show reduced blood and tissue NAD levels, as compared to their counterparts with normal ACMSD expression, when both groups were fed with niacin-free diets [31].
Finally, nicotinamide N-methyltransferase (NNMT) is another important modulating enzyme of NAD homeostasis. NNMT catalyzes the methyl transfer from S-adenosyl methionine (SAM) to NAM, yielding 1-methylnicotinamide, which is subsequently metabolized and excreted in urine [10]. NNMT derails NAM away from being recycled into NAD and curbs the NAM accumulation and inhibition of NAD-dependent signaling pathways by excessive NAM [32]. NNMT was found to regulate histone methylation and NAD-dependent SIRT1 signaling in adipose tissue and NNMT knockout was associated with elevated NAMPT, NMNAT2 expression, and NAD levels in adipocytes, but not in the liver [33]. Notably, numerous cancer types and stromal cells upregulate NNMT expression, which epigenetically reprograms gene expression and causes a state of histone hypomethylation by consuming SAM methyl groups which, in turn, depletes SAM and creates a methyl sink [34,35]. Similarly, NNMT was shown to promote DNA hypomethylation in mesenchymal glioblastoma stems cells (GSCs) and to drive alterations in DNA methylation within the promoter regions of several genes in cancer-associated fibroblasts [35,36].

3. Regulation of NAD Production in Cancer Cells

The molecular basis and genetic mechanisms that underly the selection of the NAD biosynthetic pathway in cancer cells have not been fully uncovered. However, a recent and extensive analysis for thousands of tumors and their corresponding normal tissues of origin has revealed that the choice of the NAD-producing pathway in cancer cells is based upon the healthy tissues from which they originate [37]. Accordingly, tumors were classified into the following two broad categories: PH-dependent tumors and salvage-dependent tumors where NAPRT gene amplification and NAMPT enhancer remodeling, respectively, are the key hallmarks. Tissues with high basal NAPRT expression become dependent on NAPRT for survival upon malignant transformation. On the other hand, salvage-dependent tumors originate from tissues that lack NAPRT expression, and consequently, their NAD supply is primarily hinged upon NAMPT. This conclusion was further substantiated by the observation that neither the overexpression of NAPRT in salvage-dependent cancer cells nor the overexpression of NAMPT in PH-amplified cancer cells has reversed their predestined NAD metabolic pathway [37]. Notably, when NAMPT was depleted in salvage-dependent tumors, they were still able to maintain the NAD supply through the alternative salvage NR-NMRK1 pathway, and dual NMRK1 and NAMPT inhibition resulted in more effective NAD reduction and significant tumor suppression in vivo [37]. This finding provides insights into the role of NMRK1 in mediating resistance to NAMPT inhibition. In this section, we describe how the rate-limiting enzyme in each NAD synthetic pathway is regulated in cancer cells (Table 1).

3.1. NAMPT Regulation

Several transcriptional and post-transcriptional mechanisms tightly regulate NAMPT expression and activity in tumors. Chowdhry and colleagues recently reported on a putative NAMPT enhancer located 65 kb upstream of the NAMPT transcription start site, which controls NAMPT expression and activity [37]. Chromatin immunoprecipitation and further experiments revealed that this NAMPT enhancer is marked by H3K27 acetylation, is bound by the transcription factors c-MYC and MAX that regulate its activity, and that it is required solely by salvage-dependent tumors for their survival [37]. Consistent with a role for c-MYC in NAMPT expression, an earlier study described a c-MYC–NAMPT–SIRT1 positive feedback loop, in which c-MYC directly interacts with the NAMPT promoter and induces NAMPT expression, which in turn leads to SIRT1 activation through enhanced NAD provision [38]. SIRT1, in turn, stabilizes c-MYC and enhances its transcriptional activity, and promotes tumorigenesis through the attenuation of p53 activity and the inhibition of c-MYC-induced apoptosis [38]. This c-MYC–NAMPT–SIRT1 positive feedback loop was found to be activated in colorectal carcinoma and its interruption was proposed as a viable therapeutic intervention [59,60]. Additionally, the high-mobility group A (HMGA1) protein was reported to be another protein regulating NAMPT expression through a different enhancer element [39]. The HMGA1–NAMPT–NAD signaling axis was shown to drive the proinflammatory senescence-associated secretory phenotype (SASP) via NAD-mediated enhancement of nuclear-factor kappa B (NF-κB) activity, to promote an inflammatory environment and to drive tumor progression [39]. Indeed, numerous cancer types overexpress HMGA proteins and their overexpression is often associated with poor prognosis [61]. On the contrary, the transcription factor and tumor suppressor forkhead box O1 (Foxo1) binds to the 5′-flanking region of the NAMPT gene and downregulates NAMPT expression in breast cancer cells, an effect that is reversed by the insulin–PI3K–AKT signaling pathway [42]. Additionally, NAMPT-AS “RP11-22N19.2”, a new promoter-associated long non-coding RNA (Lnc-RNA), epigenetically regulates NAMPT expression in triple-negative breast cancer (TNBC) [43]. NAMPT-AS activates NAMPT expression at the transcriptional and post-transcriptional level, and promotes tumor progression and invasiveness in TNBC [43]. Similarly, in gliomas, gastric cancer-associated transcript 3 (GACAT3), another long non-coding RNA, regulates NAMPT expression and promotes glioma progression by acting as a molecular sponge to miR-135a, inhibiting its interaction with its target, NAMPT [44]. Several studies report on NAMPT expression being regulated at the post-transcriptional level by microRNAs. Specifically, NAMPT mRNA was found to be a target of miR-381 [45], miR-206 [46], miR-494 [47], and miR-154 [48] in breast cancer cells, of miR-23b in melanoma [51], of mir-206 in pancreatic cancer [50] and miR-26b [49] in colorectal cancer. Generally, increased expression of these microRNAs was shown to suppress NAMPT expression and it was associated with reduced cancer cell viability, suggesting the potential use of these microRNAs as anti-cancer agents. In this context, we have recently shown that, in addition to being regulated at the gene level, NAMPT enzymatic activity can also be regulated by other enzymes. Specifically, we found that SIRT6 enhances NAMPT enzymatic activity through direct protein deacetylation, protecting cancer cells against oxidative stress [40]. Similarly, a previous study found that also SIRT1 deacetylates NAMPT, predisposing it to secretion in adipocytes [41]. Mesenchymal glioblastoma stem cells were found to preferentially upregulate NAMPT and NMMT expression through the transcription factor C/EBPβ, which interacts with NAMPT and NNMT gene regulatory regions. Of note, in these cells subtypes, NNMT induced a state of DNA hypomethylation and downregulated the expression of DNA methyltransferases in a methionine-dependent fashion [36]. Whether NNMT epigenetically affects NAMPT expression requires further studies.

3.2. NAPRT Regulation

An increased NAPRT gene copy number is the major hallmark in the PH-dependent tumors and their matched tissues of origin [37,62]. By contrast, tumors exist that show NAPRT promoter hypermethylation and thus, lose NAPRT expression [52]. The treatment of these tumors with NAMPT inhibitors (NAMPTi) results in synthetic lethality, which could not be reversed by adding NA due to the dysfunctional NA–NAPRT route [52]. In addition to promoter hypermethylation, other mechanisms that regulate NAPRT gene expression include alternative splicing and mutations in the transcription factor binding sites [63]. Mounting evidence indicates that NAPRT is a central regulator of NAD metabolism and a critical determinant of the therapeutic success of NAMPT inhibitors. For instance, we demonstrated that NAPRT-expressing ovarian and pancreatic cancers are resistant to NAMPT inhibition, but downregulation of NAPRT significantly depletes intracellular NAD stores and sensitizes these tumors to NAMPT inhibitors [62]. On the other side, cancers displaying genetic alterations that suppress NAPRT activity are exquisitely vulnerable to NAMPT inhibitors’ monotherapy. For example, carcinomas with isocitrate dehydrogenase 1 (IDH1) mutations, such as gliomas and sarcomas, tend to downregulate NAPRT levels through hypermethylation of the NAPRT promoter, thereby blocking the NA–NAPRT pathway, which makes them dependent on NAMPT for NAD replenishment [53]. As a direct result, NAMPT inhibition was shown to result in a metabolic crisis in these types of tumors, blunting NAD pools and causing AMPK-mediated autophagy and cytotoxicity [53]. In keeping with this notion, mutations in the protein phosphatase Mg2+/Mn2+-dependent 1D (PPM1D) gene in pediatric gliomas also drive NAPRT gene silencing through the hypermethylation of CpG islands in the NAPRT promoter, thus, again conferring unique sensitivity to NAMPT inhibitors [54]. Additionally, extreme susceptibility to NAMPT inhibition was also seen with gastric cancer cell lines, which show markers of epithelial-to-mesenchymal transition (EMT), where this EMT subtype was associated with loss of NAPRT expression [64]. Collectively, these findings emphasize that NAPRT expression could be a useful biomarker of sensitivity to NAMPT inhibitors.

3.3. QAPRT Regulation

Given that many cancer cells lack the expression of the complete chain of enzymes of the de novo NAD biosynthetic pathway, they are unable to use tryptophan as a precursor for NAD production [65]. Nevertheless, elevated expression of QAPRT, the rate-limiting enzyme in the de novo NAD pathway, has been reportedly associated with resistance to NAMPT inhibitors, but also to chemotherapeutic agents in multiple types of cancer [66,67,68,69,70]. For instance, glioma cells were found to express QAPRT and utilize QA as a NAD precursor to protect themselves from oxidative stress and NAMPT inhibition, thereby drawing attention to the de novo NAD synthesis pathway as a potential therapeutic target [70]. Similar to NAMPT regulation, the RNA molecules miR-654-3p and the Down syndrome cell adhesion molecule antisense RNA 1 (DSCAM-AS1) were recently found to control the expression of QAPRT in ovarian and breast cancer cells, respectively [56,57]. Alternatively, the transcription factor Wilms’ tumor protein 1 (WT1) is a positive regulator for QAPRT transcription in leukemia cells through binding to conserved regions in the QAPRT promoter [58].

4. Chemical Inhibitors of NAD Biosynthesis

As mentioned earlier, NAMPT is the bottleneck enzyme in the NAD salvage pathway. Elevated NAMPT expression levels were extensively reported in numerous solid and hematological malignancies, including pancreatic cancer [50], gastric cancer [71], prostate cancer [72], breast cancer [73,74], colorectal cancer [75,76,77], gliomas [78], ovarian cancer [79], melanoma [80], thyroid carcinoma [81], sarcomas [82], and lymphomas [83]. Indeed, NAMPT is implicated in driving pro-oncogenic and more aggressive phenotypes, and its overexpression has been associated with poor prognosis in different types of cancer [74,75,76,78,84,85]. In addition to existing as an intracellular protein (intracellular NAMPT, iNAMPT), NAMPT also gets secreted extracellularly and this form of the protein is known as extracellular NAMPT (eNAMPT), but also as visfatin or as pre-B-cell colony-enhancing factor (PBEF). In fact, eNAMPT was originally identified as PBEF, a modulatory cytokine during B-cell development [86]. The eNAMPT also exerts pro-oncogenic effects by modulating the tumor microenvironment, enhancing tumor metabolism, and promoting EMT [87,88]. In melanoma, NAMPT is secreted by the cancer cells and NAMPT silencing was shown to reduce tumor progression and was accompanied by lower levels of circulating eNAMPT [89]. In line with this finding, eNAMPT levels were increased in the mice bearing melanoma cells that acquired resistance to BRAF inhibitors as well as in patients with BRAF-mutated metastatic melanoma, and high eNAMPT levels showed a negative correlation with patients’ overall survival [90]. Patients with invasive prostate cancer also showed higher plasma eNAMPT levels and neutralizing circulating eNAMPT was proven to markedly attenuate cancer invasiveness in prostate cancer mice models [91].
Moreover, a proinflammatory function of eNAMPT has already been established [92]. Consistently, serum levels of eNAMPT were found to be elevated in inflammatory bowel disease (IBD) patients who showed resistance to anti-TNFα therapy, and eNAMPT neutralization, with an anti-eNAMPT monoclonal antibody, ameliorated acute and chronic colitis in experimental mice models [93]. Notably, NAPRT was also found to exist as an extracellular protein (eNAPRT), which mediates inflammation by binding to toll-like receptor 4 (TLR4) and by activating the NF-κB pathway [94]. Consistent with these findings, NAPRT serum levels were strikingly elevated in septic patients [94]. Whether, similar to eNAMPT, eNAPRT also plays a pro-oncogenic role remains to be understood. Nonetheless, primary clues from 312 cancer patients diagnosed with solid or hematological malignancies just indicated mild elevations in their serum eNAPRT levels as compared to healthy donors (median serum eNAPRT was 1.4  ±  0.07 ng/mL in healthy donors, 2.4  ±  0.15 ng/mL in cancer patients and 27.1  ±  4.9 ng/mL in septic individuals) [94]. For a broader overview of the roles of eNAMPT and eNAPRT, we refer the reader to other recent articles [87,95,96].
Given its pleiotropic role in cancer pathogenesis, NAMPT has long been considered an attractive therapeutic target for cancer treatment. In this section, we provide a brief overview of some of the key NAMPT inhibitors that have been discovered so far (Figure 2), as well as of other inhibitors of NAD biosynthesis reported over the last years. The advances in medicinal chemistry and the pharmacology of small molecule NAMPT inhibitors are beyond the scope of this review. They have recently been reviewed by Sampath et al. [97] and by Galli et al. [98].

4.1. Specific NAMPT Inhibitors

4.1.1. FK866 (also known as APO866, (E)-Daporinad, and WK175)

It is the first chemical compound reported as an NAMPT inhibitor. It shows a potency in the low nanomolar range (cellular IC50 of about 1 nM) [99]. An early study from 2002 showed that FK866 markedly reduced intracellular NAD levels which, in turn, triggered delayed apoptotic cell death in human leukemia cells [100]. One year later, FK866 was demonstrated to cause NAD depletion and to induce apoptosis in HEPG2 liver cancer cells via NAMPT inhibition [99]. Based on kinetic studies, FK866 was initially identified to be a non-competitive NAMPT inhibitor [99]. Later on, crystallographic studies of the NAMPT–FK866 complex revealed how FK866 binds within the enzyme catalytic domain [101,102,103] and suggested that FK866 could be a tight-binding competitive NAMPT inhibitor [103]. Up until now, FK866 has been extensively employed in preclinical cancer research and demonstrated robust antineoplastic efficacy across a wide variety of solid and hematological cancers both in vitro and in vivo.

4.1.2. CHS-828 (GMX1778)

It is a pyridyl cyanoguanidine anticancer agent that was developed by Leo Pharma AS. It was first reported in 1997 and 1999 where it demonstrated potent antitumor activity in breast cancer and lung cancer cell lines, and in mice experiments the treatment with CHS-828 resulted in regression of human breast cancer and lung cancer tumors [104,105]. In fact, CHS-828 was evaluated in clinical trials even before FK866 [106]. However, it was not until 2008 that Olesen et al. showed that CHS-828 kills cancer cells mainly through NAD depletion in a similar fashion to FK866 and suggested that CHS-828 acts as an NAMPT inhibitor [107].

4.1.3. GMX1777 (EB1627)

It is a prodrug of the compound CHS-828 that was developed in 2005 to improve the pharmacokinetic and solubility profile of the parent compound [108]. GMX1777 showed potent in vivo tumor-killing action as a single agent and potentiated the effect of etoposide in small-cell lung cancer mice models [108].

4.1.4. OT-82

It is a novel NAMPT inhibitor developed by OncoTaris, Inc. It is a lead compound identified through the cell-based high-throughput screening of chemical libraries comprising more than 200,000 small molecules, followed by hit validation and structural optimization [109]. Its activity was further assessed in a cell panel of 12 hematological and 17 non-hematological malignancies. OT-82 demonstrated stronger activity towards hematopoietic malignancies with an average IC50 of 2.89  ±  0.47 nM compared to an average IC50 of 13.03  ±  2.94 nM in non-hematopoietic cancers [109]. OT-82 was shown to cause NAMPT inhibition with subsequent NAD and ATP depletion, and to induce apoptotic cell death [109]. For optimal OT-82 efficacy, the authors recommended adherence to diets that do not contain more than 100% of the recommended daily amount of niacin [109].
Besides, additional examples of reported NAMPT inhibitors include GNE-617 [110] and GNE-618 (Genentech) [111], MV87 [112], A-1293201 and A-1326133 (AbbVie) [113], STF-118804 [114], LSN3154567 (Eli Lilly) [115], and antibody–drug conjugates (ADCs) with NAMPT inhibitors [116,117].

4.2. Dual NAMPT Inhibitors

4.2.1. KPT-9274 (ATG-019)

It is a dual inhibitor of NAMPT and of the serine/threonine p21-activated kinase 4 (PAK4) that was developed by Karyopharm Therapeutics. Its anticancer activity was primarily tested in human renal cell carcinoma where KPT-974 reduced cancer cell viability, invasion and migration, and induced apoptosis [118]. The downstream effects of PAK4 inhibition included reduced G2-M transition, nuclear β-catenin, and downregulation of c-MYC and cyclin D1. NAMPT inhibition caused significant NAD depletion and downregulation of SIRT1 activity [118]. KPT-9274 showed minimal cytotoxicity in vitro on normal primary renal cells and no significant weight loss in mice [118]. It is currently evaluated in phase I trials enrolling patients with solid tumors or lymphomas.

4.2.2. STF-31

It is a hybrid inhibitor of NAMPT and glucose transporter 1 (GLUT1). It was initially reported to specifically bind to GLUT1, which in turn impairs glucose uptake and confers synthetic lethality against renal cell carcinomas that show loss of the von Hippel–Lindau (VHL) tumor suppressor gene, and become highly reliant on elevated glucose uptake and aerobic glycolysis [119]. Later on, cancer cell line profiling and genomic profiling of compound-resistant clones identified NAMPT as the target enzyme of STF-31 [120].

4.2.3. Chidamide

It is a histone deacetylase (HDAC) inhibitor that is used for the treatment of cutaneous T-cell lymphoma [121]. Interestingly, NAMPT was very recently found to be a novel target of chidamide where it demonstrated NAMPT inhibitory activity (IC50 = 2.1 µM) and reduction in NAD levels in HCT116 cells [122]. This finding introduces a new mode of action of chidamide as a dual NAMPT/HDAC inhibitor. Notably, a number of dual NAMPT/HDAC inhibitors have been developed in earlier studies using pharmacophore fusion approaches [123,124]. Particularly, one compound (7f) demonstrated potent dual-target inhibition in the low nanomolar range [124].

4.3. Inhibitors of Other NAD-Producing Enzymes

4.3.1. Vacor

It is an old rat poison [125]. It was recently shown to have cytotoxic activity against NMNAT2-expressing cancer cells [126]. Mechanistically, Vacor is converted via NAMPT and then via NMNAT2 into the NAD analog, Vacor adenine dinucleotide (VAD) and Vacor metabolism results in the inhibition of NMNAT2, NAMPT, and also NAD-dependent dehydrogenases [126]. This extensively and immediately depletes NAD, impairs glycolysis, prompts energy failure, and ultimately kills NMNAT2-proficient cancer cells by necrosis [126]. In vivo, Vacor suppressed tumor growth of NMNAT2-expressing xenografts of neuroblastoma and melanoma [126]. Similarly, gallotannin was also found to be a potent inhibitor of all NMNAT isoforms, with NMNAT3 being the most sensitive (IC50 = 2 µM) followed by NMNAT1 (IC50 = 10 µM) and finally NMNAT2 (IC50 = 55 µM) [16].

4.3.2. 2-Hydroxy Nicotinic Acid (2-HNA)

It is a competitive inhibitor of NAPRT with an apparent inhibitory constant (Ki) of 0.23 mM [127]. It was primarily identified as a potent structural analog of nicotinic acid, which inhibited the accumulation of radioactivity in blood platelets incubated with radiolabeled [14C7] nicotinic acid (10 µM) [128]. It showed 95% inhibition at 1 mM with a direct relationship between the extent of inhibition and the 2-HNA concentration [128]. In NAPRT-expressing ovarian and pancreatic cancer cells, 2-HNA recapitulated the effects of NAPRT silencing and sensitized cells to FK866 [62]. In addition to 2-HNA, other reported NAPRT inhibitors include non-steroidal anti-inflammatory compounds such as flufenamic acid, salicylic acid, mefenamic acid, phenylbutazone, and indomethacin [129]. Furthermore, NAPRT was reported to be inhibited by several metabolites involved in glucose and fatty acid metabolisms such as glyceraldehyde 3-phosphate, phosphoenolpyruvate, fructose 1,6-bisphosphate, Co-A, acetyl-CoA, glutaryl-CoA, and succinyl-CoA. Of note, Co-A was the most effective among them and manifested an IC50 of about 0.85 mM [130].

4.3.3. N-(3,4-dichlorophenyl)-4-{[(4-nitrophenyl)carbamoyl]amino}benzenesulfonamide (Compound 5824)

It is an inhibitor of the bacterial NAD synthetase, the enzyme that catalyzes the amidation of NAAD to NAD in the PH pathway. Brouillette’s group primarily focused on developing chemical inhibitors of the bacterial NAD synthetase (NadE) for their potential use as antibacterial compounds [131,132]. In silico screening and docking studies followed by high-throughput assays of enzyme inhibition and antibacterial activity identified the molecule 5824 as a lead compound acting as a bacterial NAD synthetase inhibitor (IC50 = 10 µM) [133]. Given that compound 5824 was suggested to bind to the NAAD binding site in the NAD synthetase of B. subtilis [133,134], which was found to share a very high degree of residue conservation with the NAAD binding site of the human NAD synthetase 1 (NADSYN1), Chowdhry and colleagues employed compound 5824 as a human NADSYN1 inhibitor in cancer models [37]. Interestingly, this compound showed a significant and dose-dependent reduction in NAD levels and suppressed the growth of PH-amplified (OV4) xenografts but not of salvage-dependent (H460) tumors [37].

5. Effects of NAD Production Inhibition in Cancer

Deregulating NAD homeostasis in the cancer cells through NAD synthesis inhibitors was shown to result in antiproliferative and cytotoxic effects via different mechanisms. In this section, we report the downstream effects of NAD deprivation in cancer cells and combination strategies that were shown to potentiate the NAMPT inhibitors, eliciting a more pronounced antitumor response (Table 2).

5.1. NAD Depletion and Cancer Cell Death

Several mechanisms were reported to trigger cancer cell death in response to NAD depletion by NAMPT inhibitors. Initially, FK866 was reported to deplete intracellular NAD and to kill cancer cells by inducing apoptosis [99,100]. Similarly, OT-82 and KPT-9274 were also found to induce their antileukemic effect through apoptosis [109,169]. In primary chronic lymphocytic leukemia (CLL) cells, FK866 was demonstrated to induce apoptotic signaling and caspase activation at doses that triggered cell death [135]. However, in the same models, indicators for autophagy induction were also observed at low doses of FK866 and/or at early time points [135]. Several studies linked NAMPTi-induced cell death to autophagy. In multiple myeloma cells, FK866 triggered autophagic cell death via (i) the inhibition of PI3K/mTORC1 activity (a transcription-independent mechanism) and (ii) the inhibition of MAP kinase (MAPK), which permits nuclear translocation of the transcription factor EB (TFEB) that coordinates lysosomal biogenesis and drives the expression of autophagy-related genes [170,171]. Additionally, no evidence of apoptotic cell death was detected in multiple myeloma cells in response to FK866 treatment [170]. Consistent with this observation, autophagy, but not apoptosis, was associated with FK866-induced cytotoxicity in neuroblastoma and hematological cancers [172,173]. In neuroblastoma cells, FK866-induced autophagy was potentiated or antagonized by chloroquine and by 3-methyl adenine (3-MA), respectively, lending support to the notion that aberrant autophagy is involved in FK866-mediated cancer cell demise [138]. Furthermore, NAMPTi-induced NAD depletion in IDH1-mutant cancers was associated with inducing AMP kinase (AMPK) and initiating autophagy, and the autophagy inhibitor 3-MA rescued the cells from the cytotoxic effects of NAMPTi-mediated NAD depletion [53]. Intriguingly, FK866 simultaneously activated apoptosis and autophagy and markedly reduced the viability of HTLV-1-infected, adult T-cell leukemia/lymphoma (ATL) cell lines [174]. Furthermore, we showed that autophagy-mediated FK866 antileukemic activity was potentiated by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) [162]. Another group postulated that oncosis is the critical pathway leading to cancer cell death in response to the NAMPT inhibitor, GNE-617, in several non-hematological cancer cell lines irrespective of the appearance of signs of apoptosis or autophagy [175]. This group also showed that oncosis was driven by dramatic ATP depletion and subsequent loss of plasma membrane integrity, which typically marks the late phases of NAD depletion via NAMPT inhibition [175]. Taken together, the mechanism underlying cancer cell death in response to NAMPT inhibitors might be cancer type-specific and regulated in a dose and time-dependent manner.

5.2. NAD Depletion and Oxidative Stress

Oxidative stress is caused by an imbalance between reactive oxygen species (ROS) and the cellular antioxidant capacity in favor of the former. Excessive ROS accumulation is detrimental to cell viability. NADPH is a critical molecule in oxidative homeostasis as it provides the reductive power for glutathione reductase and thioredoxin reductase in glutathione and thioredoxin ROS scavenging systems [10,176]. NADPH is mainly produced via the PPP and accordingly, cancer cells have evolved mechanisms to enhance glucose flux into the PPP to combat oxidative stress [177,178]. As a consequence, building blocks for nucleotide biosynthesis are also more available to cancer cells. Besides, around 10% of the total NAD(H) pool is phosphorylated to NADP(H) by NAD kinases [10,27]. Several studies described a strong link between NAD inhibition and oxidative stress in cancer cells. For instance, enhanced ROS production in MDA-MB-231 breast cancer cells was noted when FK866 was added to ROS-containing plasma-activated medium (PAM) [179]. Also, recently FK866 was reported to exert its antileukemia activity through ROS and reactive nitrogen species generation as a consequence of NAD depletion [136]. Mitochondrial depolarization, ATP loss, and cell death were also reported as downstream effects of FK866-induced oxidative stress in this study [136]. Increased ROS levels were also reported with other NAMPT inhibitors, such as GMX1778 and OT-82 [154,180]. In support of the above insights, combining FK866 with β-lapachone, an NQO1 substrate that generates ROS and exerts anticancer effects, was shown to cause dramatic NAD depletion and cytotoxic effects in NQO1-expressing pancreatic ductal adenocarcinoma (PDAC) and non-small cell lung cancer (NSCLC) cells [164,165,166]. Curiously, in renal and in cochlear tissues, β-lapachone was reported to augment NAD levels and to reverse the drop in the NAD/NADH ratio caused by cisplatin treatment. [28,181]. This different and apparently contrasting behavior of β-lapachone seems to be attributable to the preferential accumulation of ROS species via this compound in NQO1-overexpressing cancers, but not in normal cells (that are protected by low NQO1 expression and by high catalase levels). In NQO1-overexpressing cancer cells, ROS production in response to β-lapachone causes DNA damage and thereby triggers PARP-mediated NAD degradation to such an extent that it outweighs the possible increase in NAD caused by NQO1, ultimately causing cancer cell demise via NAD and ATP shortage [182,183]. Similarly, paracetamol was found to bind to NQO2 as an off-target effect and NQO2 expression modulated paracetamol-induced ROS production in HeLA cells [184]. Therefore, combining paracetamol with NAD-depleting agents in NQO2-overexpressing cancers might be a promising approach. Last but not least, NAMPT inhibitors augmented oxidative stress induced by temozolomide (TMZ) in glioblastoma cells, and this sensitization effect was reversed by the ROS scavenger tocopherol [149].

5.3. NAD Depletion and DNA Damage and Repair

The crosstalk between NAMPT, PARPs, and DNA damage has been thoroughly investigated over the past decades. While NAMPT produces NAD, activated PARPs consume the majority of NAD to support their DNA repair activity in response to DNA-damaging insults [10]. In line with this notion, excision repair cross-complementation group 1 (ERCC1)-deficient NSCLC cells, a DNA-repair defective cancer model, showed reduced basal NAMPT and NAD levels, presumably as a result of chronic PARP1 activation, and FK866 treatment resulted in a catastrophic NAD drop and profound synthetic lethality in vitro and in vivo [185]. Chemo-potentiation was seen when NAMPT inhibitors were combined with agents that cause DNA damage, such as 5-fluorouracil (5-FU) in gastric cancer [71], fludarabine and cytarabine in leukemia [135,154], cisplatin or etoposide in neuroblastoma [138], temozolomide in gliomas [149,150], gemcitabine, paclitaxel and etoposide in pancreatic cancer cells [144,145], pemetrexed in NSCLC [143], and bendamustine and melphalan in Waldenstrom macroglobulinemia (WM) [159]. In addition, NAMPT inhibitors potentiated the efficacy of the radionuclide 177Lu-DOTATATE in neuroendocrine tumors [147], and sensitized head and neck cancer and prostate cancer models to radiotherapy [186,187]. Also, it was hypothesized that combining NAMPT inhibitors with PARP inhibitors would further downregulate PARP activity leading to persistent DNA lesions and ultimately cell death. Indeed, a potentiating effect was shown between NAMPT inhibitors and the PARP inhibitors olaparib or niraparib in triple-negative breast cancer and Ewing sarcoma [151,152,153]. In opposition, a recent study demonstrated that the FK866 cytotoxic effect against hematological malignant cells is reliant on PARP integrity since PARP1 deletion reversed ROS accumulation, mitochondria depolarization and ATP loss, and abolished FK866-induced cell death [136]. Similar results were previously reported by our group in human activated T-cells and T-cell acute lymphoblastic leukemia (ALL) models [188]. The proposed explanation for these findings is that PARP inhibitors, by blocking NAD consumption, elevate NAD levels and this antagonizes NAMPTi-induced NAD depletion and its downstream effects.

5.4. NAD Depletion and Targeted Therapy

Owing to their particular mode of action, NAMPT inhibitors lend themselves to be used in combination regimes, enhancing the antitumor activity of targeted therapies such as histone deacetylase inhibitors [146] and tyrosine kinase inhibitors in leukemia [154] and WM [142], proteasome inhibitors in multiple myeloma [141], and mTOR inhibitors in pancreatic neuroendocrine tumors [160]. Finally, we demonstrated that cyclosporin-A and verapamil sensitized leukemia cells to FK866 by inhibiting P-glycoprotein 1 (Pgp), the multidrug resistance transporter, thereby permitting the intracellular accumulation of FK866, which in turn led to ER stress and cell demise [140].

6. In Vivo Studies of NAD Production Inhibitors in Mice

6.1. Efficacy of NAMPT Inhibitors In Vivo

The short-term treatment with NAMPT inhibitors, including multitarget NAMPT inhibitors or NAMPTi-ADCs, displayed marked antineoplastic efficacy across a wide spectrum of tumor murine models, either as single-agent therapy or in combination with other anticancer treatments.
For instance, FK866 demonstrated antitumor, antiangiogenic, and antimetastatic effects in renal cancer murine models [189]. GNE-617 showed robust antitumor activity in NAPRT-deficient xenograft mouse models, including prostate (PC3) cancer, fibrosarcoma (HT1080), and pancreatic (MiaPaCa-2) cancer, and resulted in more than 98% of the NAD reduction in tumors in vivo [190]. Likewise, its structurally related derivative, GNE-618, demonstrated to suppress tumor growth in A549 NSCLC xenografts as well as in patient-derived gastric cancer and sarcoma xenografts [65,190].
Given that IDH1-mutant cancers are exquisitely reliant on NAMPT for their NAD supplies (as they downregulate NAPRT expression), NAMPT inhibitors were found to exhibit remarkable antitumor activity against IDH1-mutant glioma and fibrosarcoma xenografts [53]. Alternatively, a recent study aimed to achieve NAD depletion in IDH-mutant cancer cells, not by interfering with NAD synthesis but by blocking the regeneration of the mono ADP-ribose moieties from poly(ADP-ribose) (PAR) through the inhibition of poly(ADP-ribose) glycohydrolase (PARG), the enzyme responsible for PAR breakdown, with the simultaneous enhancement of PARP-mediated NAD consumption via DNA-damaging agents administration. As hypothesized, in an IDH-mutant fibrosarcoma (HT1080) mouse model, temozolomide combination with PARG knockout depleted freely available NAD by preventing PAR breakdown, leading to hyperPARylation, NAD sequestration, metabolic collapse and, indeed, significant tumor growth suppression was noted [191].
Although cellular senescence is an antitumor mechanism, the so-called senescence-associated secretory phenotype (SASP) sees senescent cells secrete several pro-inflammatory and pro-angiogenic factors, and was implicated in creating a tumor-promoting microenvironment and promoting cancer stemness [192,193]. In mice bearing epithelial ovarian cancer xenografts, the addition of FK866 to cisplatin prolonged mouse survival and delayed the outgrowth of cisplatin-treated tumors upon treatment cessation [139]. NAMPT inhibition was shown to mediate this additional anticancer benefit by i) NAD-mediated inhibition of the cisplatin-induced SASP in epithelial ovarian cancer and ii) suppression of the platinum-induced senescence-associated cancer stem cells [139].
Concerning the antileukemic activity of NAMPT inhibitors, OT-82 showed in vivo efficacy against hematological malignancies in a dose-dependent manner [109]. OT-82 suppressed the tumor growth of subcutaneous xenografts of acute myeloid leukemia (AML) (MV4-11), erythroleukemia (HEL92.1.7), Burkitt lymphoma (Ramos), and multiple myeloma (RPMI 8226), and prolonged survival of mice with systemic xenografts of AML (MV4-11), erythroleukemia (HEL92.1.7), infant MLL-arranged ALL (MLL-2) and with patient-derived xenografts (PDX) of high risk ALL [109,154]. In the latter model, OT-82 was found to delay leukemia growth in 95% (20/21), and cause disease regression in 86% (18/21), of the pediatric ALL PDXs [154]. Additionally, OT-82 alone showed comparable efficacy to an induction-type chemotherapeutic regimen used to treat pediatric ALL and improved the efficacy of cytarabine and dasatinib against pediatric ALL in mice [154]. Consistent with these reports, earlier studies had shown that FK866 elicited potent in vivo antitumor activity in human xenograft models of ATL, AML, Burkitt leukemia, and lymphoma [173,174]. Additionally, in a Burkitt lymphoma (Ramos) xenograft model, combining FK866 with rituximab resulted in prolonged mouse survival and reduced tumor burden as compared to mice receiving the single agents [148]. In addition, FK866 plus bortezomib were shown to act synergistically in multiple myeloma (MM1S) xenograft models [141].
OT-82 was also reported to reduce tumor growth and to prolong mouse survival in Ewing sarcoma xenograft (TC71 and TC32)-bearing mice, although tumors were found to grow again upon treatment discontinuation [153]. Notably, the combination of low doses of OT-82 and drugs that augment DNA damage, such as irinotecan or niraparib, improved the anticancer efficacy of OT-82 in orthotopic xenografts (TC32) and patient-derived xenografts of Ewing sarcoma [153].
The novel NAMPT/PAK4 inhibitor, KPT-9274, elicited remarkable antitumor effects in a broad panel of tumor mouse models, including models of renal cell carcinoma [118], B-cell acute lymphoblastic leukemia [194], acute myeloid leukemia [169], melanoma [158], colon cancer [158], triple-negative breast cancer [195], pancreatic ductal adenocarcinoma [161], pancreatic neuroendocrine tumors [160], rhabdomyosarcoma [196], Ewing sarcoma [197], multiple myeloma [198], and Waldenstrom macroglobulinemia [159]. It should be mentioned that the antitumor activity of KPT-9274 in rhabdomyosarcoma, Ewing sarcoma, multiple myeloma, breast cancer, pancreatic ductal adenocarcinoma, colon carcinoma, and melanoma was shown to be substantially driven by PAK4 inhibition [158,161,195,196,197,198,199]. Overall, compelling results from preclinical studies of KPT-9274 and OT-82 (summarized in Table 3) built a strong rationale for the evaluation of these two inhibitors in the clinic.
Combining NAMPT inhibition with cancer immunotherapy (e.g., by anti-PD1 antibodies) has been put forward as a promising therapeutic opportunity. This, in the first place, in view of studies showing that once secreted in the extracellular environment, NAMPT promotes the polarization of macrophages towards the “immunosuppressive” M2 phenotype [200]. In glioblastoma-bearing mice, the local delivery of microparticles loaded with the NAMPT inhibitor GMX1778, combined with a systemic anti-PD1 checkpoint blockade, resulted in higher T-cell recruitment and prolonged mice survival compared to monotherapy [155]. Of note, one animal survived 100 days and was confirmed tumor-free at the end of the experiment. The mice bearing renal carcinoma and melanoma tumors demonstrated an improved antitumor response when cotreated with anti-PD1 and KPT-9274 in comparison with either anti-PD1 or KPT-9274 monotherapy [157,158]. Interestingly, in the renal carcinoma model, KPT-9274 monotherapy was found to significantly reduce NAD + NADH levels, while the combined KPT-9274 and anti-PD1 treatment did not result in an overall reduction in the total NAD + NADH levels [157]. In support of the above findings, enhanced antitumor activity was seen when combining the NAMPT inhibitor MV87 and an anti-PD1 antibody compared to the single therapies in a fibrosarcoma model [156]. Strikingly, NAD replenishment through exogenous NMN supplementation sensitized anti-PD-(L)1 therapy-resistant (PD-L1 low) tumors to immunotherapy in mice models representing immunotherapy-tolerant lung cancer, pancreatic cancer, and hepatic cancer [201]. The latter effect was ascribed to the finding that NAD metabolism drives interferon γ (IFNγ)-induced PD-L1 expression in tumor cells via an activated NAMPT–TET1–pSTAT1–IRF1–PD-L1 axis, which in turn promotes tumor immune invasion in a CD8+ T cell-dependent manner [201]. However, this finding is in contradiction with another study that reported that NAD depletion via NAMPT inhibitors upregulated PD-L1 expression in glioblastoma cells [155]. Altogether, these results imply that further understanding of the crosstalk between NAMPT and PD-L1 is warranted.
With respect to the development of multitarget NAMPT inhibitors, compounds 35 and 7f are two recently discovered dual NAMPT/HDAC inhibitors, which demonstrated superior or comparable antitumor efficacy in comparison with FK866 or vorinostat monotherapy in HCT116 xenograft mice models [123,124]. Very recently, Zhang et al. applied molecular hybridization techniques using CHS-828 and erlotinib as templates and designed several first-in-class compounds that inhibit both NAMPT and epidermal growth factor receptor (EGFR) simultaneously [202]. Notably, the most active NAMPT/EGFR inhibitor showed a potent reduction in cell viability across several cancer cell lines and markedly suppressed tumor growth in a human H1975 lung cancer mouse model [202].
Lastly, the single-dose administration (20 mg/kg) of two novel anti-c-KIT antibody–drug conjugates, with novel NAMPT inhibitors as payloads, efficiently blocked in vivo tumor proliferation in c-Kit-positive gastrointestinal stromal tumor GIST-T1 mouse xenografts [117]. In agreement with these results, another group reported the strong in vivo antitumor activity of NAMPTi-ADCs in xenograft models of AML, Hodgkin lymphoma, and non-Hodgkin lymphoma [116].

6.2. Impact of NA on the Efficacy of NAMPT Inhibitors In Vivo

While normal tissues express NAPRT and can utilize NA to produce NAD, many cancer cells lack the PH pathway for NAD biosynthesis. Consequently, coadministration of NA with NAMPT inhibitors was proposed as a strategy to mitigate the off-target toxicity of NAMPT inhibitors, thereby widening their therapeutic index. According to this approach, NAPRT expression within tumor cells is the key determinant of the cancer types that might benefit from it [52]. Indeed, NA supplementation was shown to rescue NAPRT-proficient cancer cell lines from NAMPTi-induced cytotoxicity, while it was unable to reverse NAMPTi-induced toxicity in NAPRT-deficient cells [52,53,64,115,118,180,190,203].
Nevertheless, the results from mice experiments with NAPRT-negative tumors reflected a more complex situation. In agreement with the aforementioned in vitro results, early studies reported that NA cotreatment abolished the antitumor effects of FK866, GNE-617, and GMX1777 in mice bearing xenografts of NAPRT-proficient tumors (ML-2 and HCT-116) [190,203,204], while not affecting the efficacy of GMX1777 (24 h IV infusion 150 mg/kg and 650 mg/kg) or LSN3154567 (20 mg/kg; BID) in xenografts of NAPRT-deficient cancer cells (HT-1080 and NCI-H1155) [115,203]. However, in other experiments, the in vivo antitumor effects of the NAMPT inhibitors, GNE-617 and GNE-618, were found to be abrogated by NA supplementation even in the xenografts of NAPRT-deficient cell lines and patient-derived xenograft tumor models [190]. This rescue effect of supplemented NA was proposed to be achieved through partial NAD replenishment in the tumors, occurring independently of the PH pathway [190]. In another study, NA reversed the antiproliferative effect of FK866 in NAPRT-deficient A2780 xenografts at the standard 15 mg/kg dose, and the sensitivity to FK866 in the presence of NA was restored at the 50 mg/kg dose, which demonstrated an even more significant anticancer benefit compared to the standard FK866 (15 mg/kg) regimen [204]. Interestingly, in a multiple myeloma (IM-9) model, NA abrogated the antitumor effect of GMX1777 (150 mg/kg) when infused immediately after the end of the GMX1777 infusion, but when it was administered after 24 h from the end of GMX1777 infusion, the antitumor activity of GMX1777 persisted [205]. More recently, Shats and colleagues reported that mycoplasma-contaminated colon cancer cells were resistant to the NAMPT inhibitor STF-118804 in culture, but also in vivo once xenografted into nude mice, and a similar effect was seen with E.coli in vitro [25]. The authors proved that cancer cells were protected from NAMPTi-induced NAD depletion by the ability of the bacteria to convert NAM into NA, via their bacterial enzyme nicotinamidase (PncA), and thereby supply the precursors of the PH pathway [25]. Likewise, gut microbiota were demonstrated to deamidate exogenous NAM to NA and mediate NAD production in mammalian tissues, postulating that the microbial flora could mediate tumor resistance to NAMPT inhibitors through endogenous NA provision and PH pathway engagement [25]. In addition, it was found that the NA content of a diet is a key determinant of NAMPT inhibitor efficacy. For instance, one study showed that the efficacy of OT-82 was inversely correlated with the niacin (NA) dietary content in leukemia-bearing mice [109]. Thus, the complex systemic coordination of NAD production, as well as the metabolite exchange mechanisms, make so that the in vivo effects of NAD biosynthesis inhibition strategies can hardly be anticipated. In addition, albeit NA supplementation could potentially enhance the tolerability of NAMPT inhibitors, caution must be taken with this intervention as NA might, at least in part, attenuate their antitumor action.

6.3. Toxicity of NAMPT Inhibitors In Vivo

The adverse effects associated with NAMPT inhibitors have been comprehensively investigated in animal models. In an acute toxicological study, treatment of mice with high doses of FK866 (60 mg/kg bid for 4 days) resulted in thrombocytopenia and severe lymphopenia which were reverted by NA cotreatment [204]. In the same study, histological signs of drug-related toxicities were observed in the testis and spleen but not in the retina, lungs, heart, or brain. Similar hematological results were obtained in another study, which showed that rats treated with various NAMPT inhibitors, including FK866 and GM1778, for periods up to 15 days demonstrated lymphopenia and reticulocytopenia (reduced lymphocytes and reticulocytes counts) but not thrombocytopenia [206].
In non-tumor-bearing mice, NA infusion reduced the mortality associated with the administration of toxic doses of GMX1777 (650 mg/kg and 750 mg/kg) [203,205]. Similarly, NA protected B6D2F1 mice from toxic doses of FK866 [204]. These results strengthen the rationale for using NA as an antidote for NAMPT inhibitors and to widen their therapeutic index.
GNE-617 and GMX1778 were associated with retinal toxicity and fatal cardiac toxicity in short-term safety studies in rodents, and these effects were reproducible in human- and rat-relevant cell systems [97,207,208]. Of note, systemic NA treatment did not mitigate the retinal toxicity associated with GNE-617 and GMX1778 in rodents and only partially protected them from the NAMPTi (GNE-617)-induced cardiotoxicity [207,208]. The NAMPT inhibitors A-1326133 and A-1293201 were also reported to cause retinal damage in rats and dogs [209]. On the other hand, LSN3154567 did not cause retinopathy in rats treated with 20, 40, and 80 mg/kg of this compound for 4 days [115]. Yet, retinal toxicity was still observed in dogs that received LSN3154567 (1 and 2.5 mg/kg/day) for 4 days [115]. As opposed to what was observed with GMX1778 and GNE- 617, the co-administration of NA with LSN3154567 (5 mg/kg) did protect the dogs from retinopathy [115]. Altogether, these findings suggest that NAMPTi-induced retinal damage and its mitigation by NA could be chemotype-specific and might show species variability depending on the used animal model. Lastly, the recently reported NAMPT inhibitor OT-82 showed a favorable toxicological profile with no cardiac, neurological, or retinal toxicities in mice and cynomolgus monkeys (non-human primates), thus apparently avoiding the side effects of other NAMPT inhibitors [109]. Noteworthy, a combined low-dose OT-82 and niraparib therapy for one month led to several unexpected deaths in Ewing sarcoma-bearing mice, raising the concern of potential toxicities associated with prolonged combination treatments with this compound [153]. Finally, NAMPTi-ADCs were shown to have a remarkably improved toxicological profile. For example, IgG-8, a non-binding NAMPTi-ADC, was well tolerated at a dose of 100 mg/kg in a single-dose rat toxicity study and was only associated with mild acute cytopenias that were recovered four weeks post-injection with no reported thrombocytopenia, retinal toxicity, or cardiac toxicity [116]. This dose is 10-folds higher than the dose of the targeted ADCs (αCD19-8 and αCD30-8) at which antitumor activity was typically seen [116].

7. Perspectives and Obstacles for Clinical Uses of NAD Biosynthesis Inhibitors

Based on the encouraging preclinical data, the early-generation NAMPT inhibitors, FK866 (APO-866), GMX1778 (CHS-828), and its prodrug GMX1777, were investigated in early-phase clinical trials. Thrombocytopenia was the common dose-limiting toxicity associated with the three NAMPT inhibitors [210,211,212]. Additionally, several gastrointestinal (GI) adverse effects and high intra- and inter-patient pharmacokinetic variability were reported with CHS-828 [106,210,213]. GI hemorrhage and skin rash were other dose-limiting toxicities that accompanied GMX1777 [211,214]. Regrettably, the lack of objective tumor response and unfavorable side effect profile upon treatment with NAMPT inhibitors have halted their further progression in clinical trials so far [106,210,211,212,213,214,215].
The failure of NAMPT inhibitors in clinical trials has fueled research endeavors to overcome the limited clinical outcome of these agents. Indeed, numerous approaches have been sought to reduce their toxicities and re-sensitize cancer cells to NAMPT inhibitors, which can be summarized as the following (Figure 3):
Developing safer and more effective “next-generation” NAMPT inhibitors;
Using NAMPT inhibitors against a subset of cancers that show unique sensitivity to NAMPT inhibitors, such as hematological cancers or IDH-mutant cancers. NA might be administered simultaneously to protect normal tissues (circumventing NAMPT inhibition by the PH pathway to sustain adequate NAD stores). Although NA might alleviate the systemic toxicity and widen the therapeutic index of NAMPT inhibitors, abrogation of antitumor efficacy could represent a caveat to this approach;
Combining NAMPT inhibitors with chemotherapy, immunotherapy, or radiation to achieve a synergistic effect;
Combining NAMPT inhibitors with NAPRT inhibitors against NAPRT-positive cancer subtypes [62];
Development of “broad-spectrum” NAMPT inhibitors such as the dual NAMPT-PAK inhibitors, NAMPT-HDAC inhibitors, NAMPT-GLUT1 inhibitors, and recently the NAMPT-EGFR inhibitors;
Development of NAMPTi-ADCs that selectively target NAMPT in cancer cells through antibody binding to cancer-specific cell surface markers, thereby sparing the normal cells from systemic NAD depletion.
Notably, two compounds of the second wave of NAMPT inhibitors (OT-82 and KPT-9274) are being currently investigated in phase I trials. In a two-stage (dose escalation and dose expansion) phase 1 study, the safety and efficacy of OT-82 are being evaluated in participants with relapsed or refractory lymphoma (NCT03921879). In the PANAMA (NCT02702492) and TEACH (NCT04281420) phase 1 trials, the safety, efficacy, and tolerability of KPT-9274 will be evaluated in patients with advanced solid tumors and malignancies or non-Hodgkin’s lymphoma. In both studies, the experimental arms include KPT-9274 alone or in combination with niacin ER. In the PANAMA trial, additionally, a third arm will also assess the combination of KPT-9274 and the immune checkpoint inhibitor nivolumab (anti-PD1). So far, no results have been disclosed.

8. Future Outlook

In summary, NAD-producing enzymes represent a collection of targets that could be exploited to combat cancer proliferation. Even though NAMPT is the most extensively NAD-producing enzyme targeted by chemical inhibitors, limited objective responses and unacceptable toxicities in the clinical trials have hampered faster progressions in the field. Given its pleiotropic roles in energy metabolism, promoting DNA repair in response to genomic insults, epithelial to mesenchymal transition, oncogenic signaling, and suppressing the immune surveillance within the tumor milieu, NAMPT remains an attractive target in cancer therapy [216]. As mentioned earlier, two NAMPT inhibitors are being currently evaluated in clinical trials. Nevertheless, in light of accumulating evidence that substantiated the significance of NAPRT expression as a parallel regulator of NAD metabolism in cancer and as a biomarker for NAMPT inhibitor therapy [37,62], the development of NAPRT inhibitors also represents a promising therapeutic approach. To our best knowledge, no potent NAPRT inhibitor has been identified so far. As a consequence, an important future challenge will be to develop NAPRT inhibitors with a higher potency than that of the currently available compounds (e.g., 2-hydroxy nicotinic acid) and with optimized drug-like properties. Additionally, given the recently emerging function of the gut microbiota as a key contributor to NAD metabolism, manipulation of the intestinal microbiome, presumably through antibiotics, might be exploited to modulate systemic and tumor NAD biosynthesis [25]. Furthermore, recent studies show that limiting dietary intake of niacin and tryptophan creates NAD deficiency in mouse models that recapitulate human physiology [31]. Consistent with this finding, curbing the content of NAD precursors in diets, together with NAD-depleting agents, might allow to more effectively lower NAD levels in cancer cells and thus, provide enhanced antitumor activity. In addition, processes such as polyunsaturated fatty acid (PUFA) desaturation and lactate fermentation prompt regeneration of NAD from NADH, and permit glycolytic NAD recycling and cell survival when the NAD/NADH ratio decreases in the cytosol [217]. These findings raise the possibility that such processes might be targeted to improve NAMPT inhibitors’ efficacy in malignant cells. Lastly, nicotinamide mononucleotide adenylyltransferase (NMNAT 1–3), nicotinamide riboside kinase (NMRK1/2), and NAD synthetase (NADSYN) stand out as additional understudied enzymes that warrant further exploration as targets in oncology.

Author Contributions

Conceptualization, A.N. and M.S.G.; methodology, M.S.G.; software, not applicable; validation, not applicable; formal analysis, not applicable; investigation, not applicable; resources, not applicable; data curation, not applicable; writing—original draft preparation, M.S.G.; writing—review and editing, A.N. and F.M.; visualization, M.S.G.; supervision, A.N.; project administration, not applicable; funding acquisition, A.N. and M.S.G. All authors have read and agreed to the published version of the manuscript.


This work was supported in part by the Associazione Italiana per la Ricerca sul Cancro (AIRC; IG#22098) and by the Italian Ministry of Health grants PE-2016-02362694 and PE-2016-02363073. In addition, this project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 813284.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.


The authors would like to thank Irene Caffa (Department of Internal Medicine and Medical Specialties, University of Genoa) and Francesco Piacente (Department of Experimental Medicine, University of Genoa) for the helpful discussion. In addition, the graphical abstract was created with

Conflicts of Interest

The authors declare no conflict of interest.


  1. Hanahan, D.; Weinberg, R.A. The Hallmarks of Cancer. Cell 2000, 100, 57–70. [Google Scholar] [CrossRef][Green Version]
  2. Hanahan, D.; Weinberg, R.A. Hallmarks of Cancer: The Next Generation. Cell 2011, 144, 646–674. [Google Scholar] [CrossRef] [PubMed][Green Version]
  3. Warburg, O. On Respiratory Impairment in Cancer Cells. Science 1956, 124, 269–270. [Google Scholar] [PubMed]
  4. Garten, A.; Schuster, S.; Penke, M.; Gorski, T.; de Giorgis, T.; Kiess, W. Physiological and Pathophysiological Roles of NAMPT and NAD Metabolism. Nat. Rev. Endocrinol. 2015, 11, 535–546. [Google Scholar] [CrossRef] [PubMed]
  5. Cantó, C.; Menzies, K.J.; Auwerx, J. NAD+ Metabolism and the Control of Energy Homeostasis: A Balancing Act between Mitochondria and the Nucleus. Cell Metab. 2015, 22, 31–53. [Google Scholar] [CrossRef][Green Version]
  6. Yaku, K.; Okabe, K.; Nakagawa, T. NAD Metabolism: Implications in Aging and Longevity. Ageing Res. Rev. 2018, 47, 1–17. [Google Scholar] [CrossRef] [PubMed]
  7. Houtkooper, R.H.; Cantó, C.; Wanders, R.J.; Auwerx, J. The Secret Life of NAD+: An Old Metabolite Controlling New Metabolic Signaling Pathways. Endocr. Rev. 2010, 31, 194–223. [Google Scholar] [CrossRef][Green Version]
  8. Chiarugi, A.; Dölle, C.; Felici, R.; Ziegler, M. The NAD Metabolome—A Key Determinant of Cancer Cell Biology. Nat. Rev. Cancer 2012, 12, 741–752. [Google Scholar] [CrossRef] [PubMed]
  9. Verdin, E. NAD+ in Aging, Metabolism, and Neurodegeneration. Science 2015, 350, 1208–1213. [Google Scholar] [CrossRef]
  10. Xie, N.; Zhang, L.; Gao, W.; Huang, C.; Huber, P.E.; Zhou, X.; Li, C.; Shen, G.; Zou, B. NAD+ Metabolism: Pathophysiologic Mechanisms and Therapeutic Potential. Signal Transduct. Target. Ther. 2020, 5, 1–37. [Google Scholar] [CrossRef]
  11. Bogan, K.L.; Brenner, C. Nicotinic Acid, Nicotinamide, and Nicotinamide Riboside: A Molecular Evaluation of NAD+ Precursor Vitamins in Human Nutrition. Annu. Rev. Nutr. 2008, 28, 115–130. [Google Scholar] [CrossRef][Green Version]
  12. Preiss, J.; Handler, P. Biosynthesis of Diphosphopyridine Nucleotide. I. Identification of Intermediates. J. Biol. Chem. 1958, 233, 488–492. [Google Scholar] [CrossRef]
  13. Preiss, J.; Handler, P. Biosynthesis of Diphosphopyridine Nucleotide. II. Enzymatic Aspects. J. Biol. Chem. 1958, 233, 493–500. [Google Scholar] [CrossRef]
  14. Bieganowski, P.; Brenner, C. Discoveries of Nicotinamide Riboside as a Nutrient and Conserved NRK Genes Establish a Preiss-Handler Independent Route to NAD+ in Fungi and Humans. Cell 2004, 117, 495–502. [Google Scholar] [CrossRef][Green Version]
  15. Tempel, W.; Rabeh, W.M.; Bogan, K.L.; Belenky, P.; Wojcik, M.; Seidle, H.F.; Nedyalkova, L.; Yang, T.; Sauve, A.A.; Park, H.-W.; et al. Nicotinamide Riboside Kinase Structures Reveal New Pathways to NAD+. PLoS Biol. 2007, 5, e263. [Google Scholar] [CrossRef]
  16. Berger, F.; Lau, C.; Dahlmann, M.; Ziegler, M. Subcellular Compartmentation and Differential Catalytic Properties of the Three Human Nicotinamide Mononucleotide Adenylyltransferase Isoforms. J. Biol. Chem. 2005, 280, 36334–36341. [Google Scholar] [CrossRef] [PubMed][Green Version]
  17. Lau, C.; Niere, M.; Ziegler, M. The NMN/NaMN Adenylyltransferase (NMNAT) Protein Family. Front. Biosci. J. Virtual Libr. 2009, 14, 410–431. [Google Scholar] [CrossRef]
  18. Trammell, S.A.; Yu, L.; Redpath, P.; Migaud, M.E.; Brenner, C. Nicotinamide Riboside Is a Major NAD+ Precursor Vitamin in Cow Milk. J. Nutr. 2016, 146, 957–963. [Google Scholar] [CrossRef][Green Version]
  19. Long, D.J.; Jaiswal, A.K. NRH:Quinone Oxidoreductase2 (NQO2). Chem. Biol. Interact. 2000, 129, 99–112. [Google Scholar] [CrossRef]
  20. Yang, Y.; Zhang, N.; Zhang, G.; Sauve, A.A. NRH Salvage and Conversion to NAD+ Requires NRH Kinase Activity by Adenosine Kinase. Nat. Metab. 2020, 2, 364–379. [Google Scholar] [CrossRef]
  21. Kulikova, V.A.; Nikiforov, A.A. Role of NUDIX Hydrolases in NAD and ADP-Ribose Metabolism in Mammals. Biochem. Mosc. 2020, 85, 883–894. [Google Scholar] [CrossRef] [PubMed]
  22. Zapata-Pérez, R.; Tammaro, A.; Schomakers, B.V.; Scantlebery, A.M.L.; Denis, S.; Elfrink, H.L.; Giroud-Gerbetant, J.; Cantó, C.; López-Leonardo, C.; McIntyre, R.L.; et al. Reduced Nicotinamide Mononucleotide Is a New and Potent NAD+ Precursor in Mammalian Cells and Mice. FASEB J. 2021, 35, e21456. [Google Scholar] [CrossRef] [PubMed]
  23. Giroud-Gerbetant, J.; Joffraud, M.; Giner, M.P.; Cercillieux, A.; Bartova, S.; Makarov, M.V.; Zapata-Pérez, R.; Sánchez-García, J.L.; Houtkooper, R.H.; Migaud, M.E.; et al. A Reduced Form of Nicotinamide Riboside Defines a New Path for NAD+ Biosynthesis and Acts as an Orally Bioavailable NAD+ Precursor. Mol. Metab. 2019, 30, 192–202. [Google Scholar] [CrossRef] [PubMed]
  24. Yang, Y.; Mohammed, F.S.; Zhang, N.; Sauve, A.A. Dihydronicotinamide Riboside Is a Potent NAD+ Concentration Enhancer in Vitro and in Vivo. J. Biol. Chem. 2019, 294, 9295–9307. [Google Scholar] [CrossRef]
  25. Shats, I.; Williams, J.G.; Liu, J.; Makarov, M.V.; Wu, X.; Lih, F.B.; Deterding, L.J.; Lim, C.; Xu, X.; Randall, T.A.; et al. Bacteria Boost Mammalian Host NAD Metabolism by Engaging the Deamidated Biosynthesis Pathway. Cell Metab. 2020, 31, 564–579.e7. [Google Scholar] [CrossRef]
  26. Liu, L.; Su, X.; Quinn, W.J.; Hui, S.; Krukenberg, K.; Frederick, D.W.; Redpath, P.; Zhan, L.; Chellappa, K.; White, E.; et al. Quantitative Analysis of NAD Synthesis-Breakdown Fluxes. Cell Metab. 2018, 27, 1067–1080.e5. [Google Scholar] [CrossRef] [PubMed][Green Version]
  27. Katsyuba, E.; Romani, M.; Hofer, D.; Auwerx, J. NAD+ Homeostasis in Health and Disease. Nat. Metab. 2020, 2, 9–31. [Google Scholar] [CrossRef]
  28. Oh, G.-S.; Kim, H.-J.; Choi, J.-H.; Shen, A.; Choe, S.-K.; Karna, A.; Lee, S.H.; Jo, H.-J.; Yang, S.-H.; Kwak, T.H.; et al. Pharmacological Activation of NQO1 Increases NAD+ Levels and Attenuates Cisplatin-Mediated Acute Kidney Injury in Mice. Kidney Int. 2014, 85, 547–560. [Google Scholar] [CrossRef][Green Version]
  29. Gaikwad, A.; Long, D.J.; Stringer, J.L.; Jaiswal, A.K. In Vivo Role of NAD(P)H:Quinone Oxidoreductase 1 (NQO1) in the Regulation of Intracellular Redox State and Accumulation of Abdominal Adipose Tissue. J. Biol. Chem. 2001, 276, 22559–22564. [Google Scholar] [CrossRef][Green Version]
  30. Katsyuba, E.; Mottis, A.; Zietak, M.; De Franco, F.; van der Velpen, V.; Gariani, K.; Ryu, D.; Cialabrini, L.; Matilainen, O.; Liscio, P.; et al. De Novo NAD+ Synthesis Enhances Mitochondrial Function and Improves Health. Nature 2018, 563, 354–359. [Google Scholar] [CrossRef]
  31. Palzer, L.; Bader, J.J.; Angel, F.; Witzel, M.; Blaser, S.; McNeil, A.; Wandersee, M.K.; Leu, N.A.; Lengner, C.J.; Cho, C.E.; et al. Alpha-Amino-Beta-Carboxy-Muconate-Semialdehyde Decarboxylase Controls Dietary Niacin Requirements for NAD+ Synthesis. Cell Rep. 2018, 25, 1359–1370.e4. [Google Scholar] [CrossRef][Green Version]
  32. Bockwoldt, M.; Houry, D.; Niere, M.; Gossmann, T.I.; Reinartz, I.; Schug, A.; Ziegler, M.; Heiland, I. Identification of Evolutionary and Kinetic Drivers of NAD-Dependent Signaling. Proc. Natl. Acad. Sci. USA 2019, 116, 15957–15966. [Google Scholar] [CrossRef] [PubMed][Green Version]
  33. Kraus, D.; Yang, Q.; Kong, D.; Banks, A.S.; Zhang, L.; Rodgers, J.T.; Pirinen, E.; Pulinilkunnil, T.C.; Gong, F.; Wang, Y.; et al. Nicotinamide N-Methyltransferase Knockdown Protects against Diet-Induced Obesity. Nature 2014, 508, 258–262. [Google Scholar] [CrossRef][Green Version]
  34. Ulanovskaya, O.A.; Zuhl, A.M.; Cravatt, B.F. NNMT Promotes Epigenetic Remodeling in Cancer by Creating a Metabolic Methylation Sink. Nat. Chem. Biol. 2013, 9, 300–306. [Google Scholar] [CrossRef] [PubMed][Green Version]
  35. Eckert, M.A.; Coscia, F.; Chryplewicz, A.; Chang, J.W.; Hernandez, K.M.; Pan, S.; Tienda, S.M.; Nahotko, D.A.; Li, G.; Blaženović, I.; et al. Proteomics Reveals NNMT as a Master Metabolic Regulator of Cancer Associated Fibroblasts. Nature 2019, 569, 723–728. [Google Scholar] [CrossRef] [PubMed]
  36. Jung, J.; Kim, L.J.; Wang, X.; Wu, Q.; Sanvoranart, T.; Hubert, C.G.; Prager, B.C.; Wallace, L.C.; Jin, X.; Mack, S.C.; et al. Nicotinamide Metabolism Regulates Glioblastoma Stem Cell Maintenance. JCI Insight 2017, 2. [Google Scholar] [CrossRef][Green Version]
  37. Chowdhry, S.; Zanca, C.; Rajkumar, U.; Koga, T.; Diao, Y.; Raviram, R.; Liu, F.; Turner, K.; Yang, H.; Brunk, E.; et al. NAD Metabolic Dependency in Cancer Is Shaped by Gene Amplification and Enhancer Remodelling. Nature 2019, 569, 570–575. [Google Scholar] [CrossRef]
  38. Menssen, A.; Hydbring, P.; Kapelle, K.; Vervoorts, J.; Diebold, J.; Luscher, B.; Larsson, L.-G.; Hermeking, H. The C-MYC Oncoprotein, the NAMPT Enzyme, the SIRT1-Inhibitor DBC1, and the SIRT1 Deacetylase Form a Positive Feedback Loop. Proc. Natl. Acad. Sci. USA 2012, 109, E187–E196. [Google Scholar] [CrossRef][Green Version]
  39. Nacarelli, T.; Lau, L.; Fukumoto, T.; Zundell, J.; Fatkhutdinov, N.; Wu, S.; Aird, K.M.; Iwasaki, O.; Kossenkov, A.V.; Schultz, D.; et al. NAD+ Metabolism Governs the Proinflammatory Senescence-Associated Secretome. Nat. Cell Biol. 2019, 21, 397–407. [Google Scholar] [CrossRef]
  40. Sociali, G.; Grozio, A.; Caffa, I.; Schuster, S.; Becherini, P.; Damonte, P.; Sturla, L.; Fresia, C.; Passalacqua, M.; Mazzola, F.; et al. SIRT6 Deacetylase Activity Regulates NAMPT Activity and NAD(P)(H) Pools in Cancer Cells. FASEB J. Off. Publ. Fed. Am. Soc. Exp. Biol. 2019, 33, 3704–3717. [Google Scholar] [CrossRef]
  41. Yoon, M.J.; Yoshida, M.; Johnson, S.; Takikawa, A.; Usui, I.; Tobe, K.; Nakagawa, T.; Yoshino, J.; Imai, S. SIRT1-Mediated ENAMPT Secretion from Adipose Tissue Regulates Hypothalamic NAD+ and Function in Mice. Cell Metab. 2015, 21, 706–717. [Google Scholar] [CrossRef] [PubMed][Green Version]
  42. Jeong, B.; Park, J.W.; Kim, J.G.; Lee, B.J. FOXO1 Functions in the Regulation of Nicotinamide Phosphoribosyltransferase (Nampt) Expression. Biochem. Biophys. Res. Commun. 2019, 511, 398–403. [Google Scholar] [CrossRef]
  43. Zhang, H.; Zhang, N.; Liu, Y.; Su, P.; Liang, Y.; Li, Y.; Wang, X.; Chen, T.; Song, X.; Sang, Y.; et al. Epigenetic Regulation of NAMPT by NAMPT-AS Drives Metastatic Progression in Triple-Negative Breast Cancer. Cancer Res. 2019, 79, 3347–3359. [Google Scholar] [CrossRef] [PubMed][Green Version]
  44. Wang, J.; Zhang, M.; Lu, W. Long Noncoding RNA GACAT3 Promotes Glioma Progression by Sponging MiR-135a. J. Cell. Physiol. 2019, 234, 10877–10887. [Google Scholar] [CrossRef] [PubMed]
  45. Bolandghamat Pour, Z.; Nourbakhsh, M.; Mousavizadeh, K.; Madjd, Z.; Ghorbanhosseini, S.S.; Abdolvahabi, Z.; Hesari, Z.; Mobaser, S.E. Up-Regulation of MiR-381 Inhibits NAD+ Salvage Pathway and Promotes Apoptosis in Breast Cancer Cells. EXCLI J. 2019, 18, 683–696. [Google Scholar] [CrossRef]
  46. Hesari, Z.; Nourbakhsh, M.; Hosseinkhani, S.; Abdolvahabi, Z.; Alipour, M.; Tavakoli-Yaraki, M.; Ghorbanhosseini, S.S.; Yousefi, Z.; Jafarzadeh, M.; Yarahmadi, S. Down-Regulation of NAMPT Expression by Mir-206 Reduces Cell Survival of Breast Cancer Cells. Gene 2018, 673, 149–158. [Google Scholar] [CrossRef] [PubMed]
  47. Ghorbanhosseini, S.S.; Nourbakhsh, M.; Zangooei, M.; Abdolvahabi, Z.; Bolandghamtpour, Z.; Hesari, Z.; Yousefi, Z.; Panahi, G.; Meshkani, R. MicroRNA-494 Induces Breast Cancer Cell Apoptosis and Reduces Cell Viability by Inhibition of Nicotinamide Phosphoribosyltransferase Expression and Activity. EXCLI J. 2019, 18, 838–851. [Google Scholar] [CrossRef]
  48. Bolandghamat Pour, Z.; Nourbakhsh, M.; Mousavizadeh, K.; Madjd, Z.; Ghorbanhosseini, S.S.; Abdolvahabi, Z.; Hesari, Z.; Ezzati Mobasser, S. Suppression of Nicotinamide Phosphoribosyltransferase Expression by MiR-154 Reduces the Viability of Breast Cancer Cells and Increases Their Susceptibility to Doxorubicin. BMC Cancer 2019, 19, 1027. [Google Scholar] [CrossRef][Green Version]
  49. Zhang, C.; Tong, J.; Huang, G. Nicotinamide Phosphoribosyl Transferase (Nampt) Is a Target of MicroRNA-26b in Colorectal Cancer Cells. PLoS ONE 2013, 8, e69963. [Google Scholar] [CrossRef][Green Version]
  50. Ju, H.-Q.; Zhuang, Z.-N.; Li, H.; Tian, T.; Lu, Y.-X.; Fan, X.-Q.; Zhou, H.-J.; Mo, H.-Y.; Sheng, H.; Chiao, P.J.; et al. Regulation of the Nampt-Mediated NAD Salvage Pathway and Its Therapeutic Implications in Pancreatic Cancer. Cancer Lett. 2016, 379, 1–11. [Google Scholar] [CrossRef]
  51. Lv, R.; Yu, J.; Sun, Q. Anti-Angiogenic Role of MicroRNA-23b in Melanoma by Disturbing NF-ΚB Signaling Pathway via Targeted Inhibition of NAMPT. Future Oncol. Lond. Engl. 2020, 16, 541-458. [Google Scholar] [CrossRef]
  52. Shames, D.S.; Elkins, K.; Walter, K.; Holcomb, T.; Du, P.; Mohl, D.; Xiao, Y.; Pham, T.; Haverty, P.M.; Liederer, B.; et al. Loss of NAPRT1 Expression by Tumor-Specific Promoter Methylation Provides a Novel Predictive Biomarker for NAMPT Inhibitors. Clin. Cancer Res. 2013, 19, 6912–6923. [Google Scholar] [CrossRef] [PubMed][Green Version]
  53. Tateishi, K.; Wakimoto, H.; Iafrate, A.J.; Tanaka, S.; Loebel, F.; Lelic, N.; Wiederschain, D.; Bedel, O.; Deng, G.; Zhang, B.; et al. Extreme Vulnerability of IDH1 Mutant Cancers to NAD+ Depletion. Cancer Cell 2015, 28, 773–784. [Google Scholar] [CrossRef] [PubMed][Green Version]
  54. Fons, N.R.; Sundaram, R.K.; Breuer, G.A.; Peng, S.; McLean, R.L.; Kalathil, A.N.; Schmidt, M.S.; Carvalho, D.M.; Mackay, A.; Jones, C.; et al. PPM1D Mutations Silence NAPRT Gene Expression and Confer NAMPT Inhibitor Sensitivity in Glioma. Nat. Commun. 2019, 10, 3790. [Google Scholar] [CrossRef] [PubMed][Green Version]
  55. LI, H.; FENG, Z.; WU, W.; LI, J.; ZHANG, J.; XIA, T. SIRT3 Regulates Cell Proliferation and Apoptosis Related to Energy Metabolism in Non-Small Cell Lung Cancer Cells through Deacetylation of NMNAT2. Int. J. Oncol. 2013, 43, 1420–1430. [Google Scholar] [CrossRef][Green Version]
  56. Niu, Y.-C.; Tong, J.; Shi, X.-F.; Zhang, T. MicroRNA-654-3p Enhances Cisplatin Sensitivity by Targeting QPRT and Inhibiting the PI3K/AKT Signaling Pathway in Ovarian Cancer Cells. Exp. Ther. Med. 2020, 20, 1467–1479. [Google Scholar] [CrossRef] [PubMed]
  57. Yue, Z.; Shusheng, J.; Hongtao, S.; Shu, Z.; Lan, H.; Qingyuan, Z.; Shaoqiang, C.; Yuanxi, H. Silencing DSCAM-AS1 Suppresses the Growth and Invasion of ER-Positive Breast Cancer Cells by Downregulating Both DCTPP1 and QPRT. Aging 2020, 12, 14754–14774. [Google Scholar] [CrossRef]
  58. Ullmark, T.; Montano, G.; Järvstråt, L.; Jernmark Nilsson, H.; Håkansson, E.; Drott, K.; Nilsson, B.; Vidovic, K.; Gullberg, U. Anti-Apoptotic Quinolinate Phosphoribosyltransferase (QPRT) Is a Target Gene of Wilms’ Tumor Gene 1 (WT1) Protein in Leukemic Cells. Biochem. Biophys. Res. Commun. 2017, 482, 802–807. [Google Scholar] [CrossRef][Green Version]
  59. Brandl, L.; Kirstein, N.; Neumann, J.; Sendelhofert, A.; Vieth, M.; Kirchner, T.; Menssen, A. The C-MYC/NAMPT/SIRT1 Feedback Loop Is Activated in Early Classical and Serrated Route Colorectal Cancer and Represents a Therapeutic Target. Med. Oncol. 2018, 36, 5. [Google Scholar] [CrossRef]
  60. Brandl, L.; Zhang, Y.; Kirstein, N.; Sendelhofert, A.; Boos, S.L.; Jung, P.; Greten, F.; Rad, R.; Menssen, A. Targeting C-MYC through Interference with NAMPT and SIRT1 and Their Association to Oncogenic Drivers in Murine Serrated Intestinal Tumorigenesis. Neoplasia 2019, 21, 974–988. [Google Scholar] [CrossRef]
  61. Sumter, T.F.; Xian, L.; Huso, T.; Koo, M.; Chang, Y.-T.; Almasri, T.N.; Chia, L.; Inglis, C.; Reid, D.; Resar, L.M.S. The High Mobility Group A1 (HMGA1) Transcriptome in Cancer and Development. Curr. Mol. Med. 2016, 16, 353–393. [Google Scholar] [CrossRef] [PubMed][Green Version]
  62. Piacente, F.; Caffa, I.; Ravera, S.; Sociali, G.; Passalacqua, M.; Vellone, V.G.; Becherini, P.; Reverberi, D.; Monacelli, F.; Ballestrero, A.; et al. Nicotinic Acid Phosphoribosyltransferase Regulates Cancer Cell Metabolism, Susceptibility to NAMPT Inhibitors, and DNA Repair. Cancer Res. 2017, 77, 3857–3869. [Google Scholar] [CrossRef] [PubMed][Green Version]
  63. Duarte-Pereira, S.; Pereira-Castro, I.; Silva, S.S.; Correia, M.G.; Neto, C.; da Costa, L.T.; Amorim, A.; Silva, R.M. Extensive Regulation of Nicotinate Phosphoribosyltransferase (NAPRT) Expression in Human Tissues and Tumors. Oncotarget 2016, 7, 1973–1983. [Google Scholar] [CrossRef] [PubMed][Green Version]
  64. Lee, J.; Kim, H.; Lee, J.E.; Shin, S.-J.; Oh, S.; Kwon, G.; Kim, H.; Choi, Y.Y.; White, M.A.; Paik, S.; et al. Selective Cytotoxicity of the NAMPT Inhibitor FK866 Toward Gastric Cancer Cells With Markers of the Epithelial-Mesenchymal Transition, Due to Loss of NAPRT. Gastroenterology 2018, 155, 799–814.e13. [Google Scholar] [CrossRef] [PubMed]
  65. Xiao, Y.; Elkins, K.; Durieux, J.K.; Lee, L.; Oeh, J.; Yang, L.X.; Liang, X.; DelNagro, C.; Tremayne, J.; Kwong, M.; et al. Dependence of Tumor Cell Lines and Patient-Derived Tumors on the NAD Salvage Pathway Renders Them Sensitive to NAMPT Inhibition with GNE-618. Neoplasia 2013, 15, 1151-IN23. [Google Scholar] [CrossRef]
  66. Thongon, N.; Zucal, C.; D’Agostino, V.G.; Tebaldi, T.; Ravera, S.; Zamporlini, F.; Piacente, F.; Moschoi, R.; Raffaelli, N.; Quattrone, A.; et al. Cancer Cell Metabolic Plasticity Allows Resistance to NAMPT Inhibition but Invariably Induces Dependence on LDHA. Cancer Metab. 2018, 6, 1. [Google Scholar] [CrossRef]
  67. Guo, J.; Lam, L.T.; Longenecker, K.L.; Bui, M.H.; Idler, K.B.; Glaser, K.B.; Wilsbacher, J.L.; Tse, C.; Pappano, W.N.; Huang, T.-H. Identification of Novel Resistance Mechanisms to NAMPT Inhibition via the de Novo NAD+ Biosynthesis Pathway and NAMPT Mutation. Biochem. Biophys. Res. Commun. 2017, 491, 681–686. [Google Scholar] [CrossRef]
  68. Jane, E.P.; Premkumar, D.R.; Thambireddy, S.; Golbourn, B.; Agnihotri, S.; Bertrand, K.C.; Mack, S.C.; Myers, M.I.; Chattopadhyay, A.; Taylor, D.L.; et al. Targeting NAD+ Biosynthesis Overcomes Panobinostat and Bortezomib-Induced Malignant Glioma Resistance. Mol. Cancer Res. MCR 2020, 18, 1004–1017. [Google Scholar] [CrossRef][Green Version]
  69. Chung, C.-T.; Yeh, K.-C.; Lee, C.-H.; Chen, Y.-Y.; Ho, P.-J.; Chang, K.-Y.; Chen, C.-H.; Lai, Y.-K.; Chen, C.-T. Molecular Profiling of Afatinib-Resistant Non-Small Cell Lung Cancer Cells in Vivo Derived from Mice. Pharmacol. Res. 2020, 161, 105183. [Google Scholar] [CrossRef]
  70. Sahm, F.; Oezen, I.; Opitz, C.A.; Radlwimmer, B.; von Deimling, A.; Ahrendt, T.; Adams, S.; Bode, H.B.; Guillemin, G.J.; Wick, W.; et al. The Endogenous Tryptophan Metabolite and NAD+ Precursor Quinolinic Acid Confers Resistance of Gliomas to Oxidative Stress. Cancer Res. 2013, 73, 3225–3234. [Google Scholar] [CrossRef][Green Version]
  71. Bi, T.-Q.; Che, X.-M.; Liao, X.-H.; Zhang, D.-J.; Long, H.-L.; Li, H.-J.; Zhao, W. Overexpression of Nampt in Gastric Cancer and Chemopotentiating Effects of the Nampt Inhibitor FK866 in Combination with Fluorouracil. Oncol. Rep. 2011, 26, 1251–1257. [Google Scholar] [CrossRef][Green Version]
  72. Wang, B.; Hasan, M.K.; Alvarado, E.; Yuan, H.; Wu, H.; Chen, W.Y. NAMPT Overexpression in Prostate Cancer and Its Contribution to Tumor Cell Survival and Stress Response. Oncogene 2011, 30, 907–921. [Google Scholar] [CrossRef][Green Version]
  73. Zhu, Y.; Guo, M.; Zhang, L.; Xu, T.; Wang, L.; Xu, G. Biomarker Triplet NAMPT/VEGF/HER2 as a de Novo Detection Panel for the Diagnosis and Prognosis of Human Breast Cancer. Oncol. Rep. 2016, 35, 454–462. [Google Scholar] [CrossRef] [PubMed]
  74. Zhou, S.-J.; Bi, T.-Q.; Qin, C.-X.; Yang, X.-Q.; Pang, K. Expression of NAMPT Is Associated with Breast Invasive Ductal Carcinoma Development and Prognosis. Oncol. Lett. 2018, 15, 6648–6654. [Google Scholar] [CrossRef] [PubMed][Green Version]
  75. Li, X.; Lei, J.; Mao, L.; Wang, Q.; Xu, F.; Ran, T.; Zhou, Z.; He, S. NAMPT and NAPRT, Key Enzymes in NAD Salvage Synthesis Pathway, Are of Negative Prognostic Value in Colorectal Cancer. Front. Oncol. 2019, 9, 736. [Google Scholar] [CrossRef] [PubMed][Green Version]
  76. Ye, C.; Qi, L.; Li, X.; Wang, J.; Yu, J.; Zhou, B.; Guo, C.; Chen, J.; Zheng, S. Targeting the NAD+ Salvage Pathway Suppresses APC Mutation-Driven Colorectal Cancer Growth and Wnt/β-Catenin Signaling via Increasing Axin Level. Cell Commun. Signal. CCS 2020, 18, 16. [Google Scholar] [CrossRef] [PubMed][Green Version]
  77. Van Beijnum, J.R.; Moerkerk, P.T.M.; Gerbers, A.J.; De Bruïne, A.P.; Arends, J.-W.; Hoogenboom, H.R.; Hufton, S.E. Target Validation for Genomics Using Peptide-Specific Phage Antibodies: A Study of Five Gene Products Overexpressed in Colorectal Cancer. Int. J. Cancer 2002, 101, 118–127. [Google Scholar] [CrossRef] [PubMed]
  78. Lucena-Cacace, A.; Otero-Albiol, D.; Jiménez-García, M.P.; Peinado-Serrano, J.; Carnero, A. NAMPT Overexpression Induces Cancer Stemness and Defines a Novel Tumor Signature for Glioma Prognosis. Oncotarget 2017, 8, 99514–99530. [Google Scholar] [CrossRef][Green Version]
  79. Shackelford, R.E.; Bui, M.M.; Coppola, D.; Hakam, A. Over-Expression of Nicotinamide Phosphoribosyltransferase in Ovarian Cancers. Int. J. Clin. Exp. Pathol. 2010, 3, 522–527. [Google Scholar]
  80. Maldi, E.; Travelli, C.; Caldarelli, A.; Agazzone, N.; Cintura, S.; Galli, U.; Scatolini, M.; Ostano, P.; Miglino, B.; Chiorino, G.; et al. Nicotinamide Phosphoribosyltransferase (NAMPT) Is over-Expressed in Melanoma Lesions. Pigment Cell Melanoma Res. 2013, 26, 144–146. [Google Scholar] [CrossRef]
  81. Sawicka-Gutaj, N.; Waligórska-Stachura, J.; Andrusiewicz, M.; Biczysko, M.; Sowiński, J.; Skrobisz, J.; Ruchała, M. Nicotinamide Phosphorybosiltransferase Overexpression in Thyroid Malignancies and Its Correlation with Tumor Stage and with Survivin/Survivin DEx3 Expression. Tumour Biol. J. Int. Soc. Oncodev. Biol. Med. 2015, 36, 7859–7863. [Google Scholar] [CrossRef] [PubMed][Green Version]
  82. Vora, M.; Ansari, J.; Shanti, R.M.; Veillon, D.; Cotelingam, J.; Coppola, D.; Shackelford, R.E. Increased Nicotinamide Phosphoribosyltransferase in Rhabdomyosarcomas and Leiomyosarcomas Compared to Skeletal and Smooth Muscle Tissue. Anticancer Res. 2016, 36, 503–507. [Google Scholar]
  83. Olesen, U.H.; Hastrup, N.; Sehested, M. Expression Patterns of Nicotinamide Phosphoribosyltransferase and Nicotinic Acid Phosphoribosyltransferase in Human Malignant Lymphomas. APMIS Acta Pathol. Microbiol. Immunol. Scand. 2011, 119, 296–303. [Google Scholar] [CrossRef] [PubMed]
  84. Audrito, V.; Messana, V.G.; Moiso, E.; Vitale, N.; Arruga, F.; Brandimarte, L.; Gaudino, F.; Pellegrino, E.; Vaisitti, T.; Riganti, C.; et al. NAMPT Over-Expression Recapitulates the BRAF Inhibitor Resistant Phenotype Plasticity in Melanoma. Cancers 2020, 12, 3855. [Google Scholar] [CrossRef]
  85. Lucena-Cacace, A.; Otero-Albiol, D.; Jiménez-García, M.P.; Muñoz-Galvan, S.; Carnero, A. NAMPT Is a Potent Oncogene in Colon Cancer Progression That Modulates Cancer Stem Cell Properties and Resistance to Therapy through Sirt1 and PARP. Clin. Cancer Res. 2018, 24, 1202–1215. [Google Scholar] [CrossRef] [PubMed][Green Version]
  86. Samal, B.; Sun, Y.; Stearns, G.; Xie, C.; Suggs, S.; McNiece, I. Cloning and Characterization of the CDNA Encoding a Novel Human Pre-B-Cell Colony-Enhancing Factor. Mol. Cell. Biol. 1994, 14, 1431–1437. [Google Scholar] [CrossRef] [PubMed]
  87. Carbone, F.; Liberale, L.; Bonaventura, A.; Vecchiè, A.; Casula, M.; Cea, M.; Monacelli, F.; Caffa, I.; Bruzzone, S.; Montecucco, F.; et al. Regulation and Function of Extracellular Nicotinamide Phosphoribosyltransferase/Visfatin. Compr. Physiol. 2017, 7, 603–621. [Google Scholar] [CrossRef]
  88. Soncini, D.; Caffa, I.; Zoppoli, G.; Cea, M.; Cagnetta, A.; Passalacqua, M.; Mastracci, L.; Boero, S.; Montecucco, F.; Sociali, G.; et al. Nicotinamide Phosphoribosyltransferase Promotes Epithelial-to-Mesenchymal Transition as a Soluble Factor Independent of Its Enzymatic Activity. J. Biol. Chem. 2014, 289, 34189–34204. [Google Scholar] [CrossRef][Green Version]
  89. Grolla, A.A.; Torretta, S.; Gnemmi, I.; Amoruso, A.; Orsomando, G.; Gatti, M.; Caldarelli, A.; Lim, D.; Penengo, L.; Brunelleschi, S.; et al. Nicotinamide Phosphoribosyltransferase (NAMPT/PBEF/Visfatin) Is a Tumoural Cytokine Released from Melanoma. Pigment Cell Melanoma Res. 2015, 28, 718–729. [Google Scholar] [CrossRef]
  90. Audrito, V.; Managò, A.; Zamporlini, F.; Rulli, E.; Gaudino, F.; Madonna, G.; D’Atri, S.; Antonini Cappellini, G.C.; Ascierto, P.A.; Massi, D.; et al. Extracellular Nicotinamide Phosphoribosyltransferase (ENAMPT) Is a Novel Marker for Patients with BRAF-Mutated Metastatic Melanoma. Oncotarget 2018, 9, 18997–19005. [Google Scholar] [CrossRef][Green Version]
  91. Sun, B.L.; Sun, X.; Casanova, N.; Garcia, A.N.; Oita, R.; Algotar, A.M.; Camp, S.M.; Hernon, V.R.; Gregory, T.; Cress, A.E.; et al. Role of Secreted Extracellular Nicotinamide Phosphoribosyltransferase (ENAMPT) in Prostate Cancer Progression: Novel Biomarker and Therapeutic Target. EBioMedicine 2020, 61, 103059. [Google Scholar] [CrossRef] [PubMed]
  92. Moschen, A.R.; Kaser, A.; Enrich, B.; Mosheimer, B.; Theurl, M.; Niederegger, H.; Tilg, H. Visfatin, an Adipocytokine with Proinflammatory and Immunomodulating Properties. J. Immunol. Baltim. Md 1950 2007, 178, 1748–1758. [Google Scholar] [CrossRef] [PubMed][Green Version]
  93. Colombo, G.; Clemente, N.; Zito, A.; Bracci, C.; Colombo, F.S.; Sangaletti, S.; Jachetti, E.; Ribaldone, D.G.; Caviglia, G.P.; Pastorelli, L.; et al. Neutralization of Extracellular NAMPT (Nicotinamide Phosphoribosyltransferase) Ameliorates Experimental Murine Colitis. J. Mol. Med. Berl. Ger. 2020, 98, 595–612. [Google Scholar] [CrossRef] [PubMed]
  94. Managò, A.; Audrito, V.; Mazzola, F.; Sorci, L.; Gaudino, F.; Gizzi, K.; Vitale, N.; Incarnato, D.; Minazzato, G.; Ianniello, A.; et al. Extracellular Nicotinate Phosphoribosyltransferase Binds Toll like Receptor 4 and Mediates Inflammation. Nat. Commun. 2019, 10, 4116. [Google Scholar] [CrossRef]
  95. Audrito, V.; Messana, V.G.; Deaglio, S. NAMPT and NAPRT: Two Metabolic Enzymes With Key Roles in Inflammation. Front. Oncol. 2020, 10, 358. [Google Scholar] [CrossRef][Green Version]
  96. Dakroub, A.; Nasser, S.A.; Younis, N.; Bhagani, H.; Al-Dhaheri, Y.; Pintus, G.; Eid, A.A.; El-Yazbi, A.F.; Eid, A.H. Visfatin: A Possible Role in Cardiovasculo-Metabolic Disorders. Cells 2020, 9, 2444. [Google Scholar] [CrossRef]
  97. Sampath, D.; Zabka, T.S.; Misner, D.L.; O’Brien, T.; Dragovich, P.S. Inhibition of Nicotinamide Phosphoribosyltransferase (NAMPT) as a Therapeutic Strategy in Cancer. Pharmacol. Ther. 2015, 151, 16–31. [Google Scholar] [CrossRef] [PubMed]
  98. Galli, U.; Colombo, G.; Travelli, C.; Tron, G.C.; Genazzani, A.A.; Grolla, A.A. Recent Advances in NAMPT Inhibitors: A Novel Immunotherapic Strategy. Front. Pharmacol. 2020, 11, 656. [Google Scholar] [CrossRef] [PubMed]
  99. Hasmann, M.; Schemainda, I. FK866, a Highly Specific Noncompetitive Inhibitor of Nicotinamide Phosphoribosyltransferase, Represents a Novel Mechanism for Induction of Tumor Cell Apoptosis. Cancer Res. 2003, 63, 7436–7442. [Google Scholar] [PubMed]
  100. Wosikowski, K.; Mattern, K.; Schemainda, I.; Hasmann, M.; Rattel, B.; Löser, R. WK175, a Novel Antitumor Agent, Decreases the Intracellular Nicotinamide Adenine Dinucleotide Concentration and Induces the Apoptotic Cascade in Human Leukemia Cells. Cancer Res. 2002, 62, 1057–1062. [Google Scholar]
  101. Kim, M.-K.; Lee, J.H.; Kim, H.; Park, S.J.; Kim, S.H.; Kang, G.B.; Lee, Y.S.; Kim, J.B.; Kim, K.K.; Suh, S.W.; et al. Crystal Structure of Visfatin/Pre-B Cell Colony-Enhancing Factor 1/Nicotinamide Phosphoribosyltransferase, Free and in Complex with the Anti-Cancer Agent FK-866. J. Mol. Biol. 2006, 362, 66–77. [Google Scholar] [CrossRef] [PubMed]
  102. Kang, G.B.; Bae, M.-H.; Kim, M.-K.; Im, I.; Kim, Y.-C.; Eom, S.H. Crystal Structure of Rattus Norvegicus Visfatin/PBEF/Nampt in Complex with an FK866-Based Inhibitor. Mol. Cells 2009, 27, 667–671. [Google Scholar] [CrossRef] [PubMed]
  103. Khan, J.A.; Tao, X.; Tong, L. Molecular Basis for the Inhibition of Human NMPRTase, a Novel Target for Anticancer Agents. Nat. Struct. Mol. Biol. 2006, 13, 582–588. [Google Scholar] [CrossRef] [PubMed]
  104. Hjarnaa, P.J.; Jonsson, E.; Latini, S.; Dhar, S.; Larsson, R.; Bramm, E.; Skov, T.; Binderup, L. CHS 828, a Novel Pyridyl Cyanoguanidine with Potent Antitumor Activity in Vitro and in Vivo. Cancer Res. 1999, 59, 5751–5757. [Google Scholar]
  105. Schou, C.; Ottosen, E.R.; Petersen, H.J.; Björkling, F.; Latini, S.; Hjarnaa, P.V.; Bramm, E.; Binderup, L. Novel Cyanoguanidines with Potent Oral Antitumour Activity. Bioorg. Med. Chem. Lett. 1997, 7, 3095–3100. [Google Scholar] [CrossRef]
  106. Hovstadius, P.; Larsson, R.; Jonsson, E.; Skov, T.; Kissmeyer, A.-M.; Krasilnikoff, K.; Bergh, J.; Karlsson, M.O.; Lönnebo, A.; Ahlgren, J. A Phase I Study of CHS 828 in Patients with Solid Tumor Malignancy. Clin. Cancer Res. Off. J. Am. Assoc. Cancer Res. 2002, 8, 2843–2850. [Google Scholar]
  107. Olesen, U.H.; Christensen, M.K.; Björkling, F.; Jäättelä, M.; Jensen, P.B.; Sehested, M.; Nielsen, S.J. Anticancer Agent CHS-828 Inhibits Cellular Synthesis of NAD. Biochem. Biophys. Res. Commun. 2008, 367, 799–804. [Google Scholar] [CrossRef]
  108. Binderup, E.; Björkling, F.; Hjarnaa, P.V.; Latini, S.; Baltzer, B.; Carlsen, M.; Binderup, L. EB1627: A Soluble Prodrug of the Potent Anticancer Cyanoguanidine CHS828. Bioorg. Med. Chem. Lett. 2005, 15, 2491–2494. [Google Scholar] [CrossRef]
  109. Korotchkina, L.; Kazyulkin, D.; Komarov, P.G.; Polinsky, A.; Andrianova, E.L.; Joshi, S.; Gupta, M.; Vujcic, S.; Kononov, E.; Toshkov, I.; et al. OT-82, a Novel Anticancer Drug Candidate That Targets the Strong Dependence of Hematological Malignancies on NAD Biosynthesis. Leukemia 2020, 34, 1828–1839. [Google Scholar] [CrossRef][Green Version]
  110. Zheng, X.; Bauer, P.; Baumeister, T.; Buckmelter, A.J.; Caligiuri, M.; Clodfelter, K.H.; Han, B.; Ho, Y.-C.; Kley, N.; Lin, J.; et al. Structure-Based Discovery of Novel Amide-Containing Nicotinamide Phosphoribosyltransferase (Nampt) Inhibitors. J. Med. Chem. 2013, 56, 6413–6433. [Google Scholar] [CrossRef]
  111. Zheng, X.; Bair, K.W.; Bauer, P.; Baumeister, T.; Bowman, K.K.; Buckmelter, A.J.; Caligiuri, M.; Clodfelter, K.H.; Feng, Y.; Han, B.; et al. Identification of Amides Derived from 1H-Pyrazolo[3,4-b]Pyridine-5-Carboxylic Acid as Potent Inhibitors of Human Nicotinamide Phosphoribosyltransferase (NAMPT). Bioorg. Med. Chem. Lett. 2013, 23, 5488–5497. [Google Scholar] [CrossRef]
  112. Travelli, C.; Aprile, S.; Rahimian, R.; Grolla, A.A.; Rogati, F.; Bertolotti, M.; Malagnino, F.; di Paola, R.; Impellizzeri, D.; Fusco, R.; et al. Identification of Novel Triazole-Based Nicotinamide Phosphoribosyltransferase (NAMPT) Inhibitors Endowed with Antiproliferative and Antiinflammatory Activity. J. Med. Chem. 2017, 60, 1768–1792. [Google Scholar] [CrossRef]
  113. Wilsbacher, J.L.; Cheng, M.; Cheng, D.; Trammell, S.A.J.; Shi, Y.; Guo, J.; Koeniger, S.L.; Kovar, P.J.; He, Y.; Selvaraju, S.; et al. Discovery and Characterization of Novel Nonsubstrate and Substrate NAMPT Inhibitors. Mol. Cancer Ther. 2017, 16, 1236–1245. [Google Scholar] [CrossRef][Green Version]
  114. Matheny, C.J.; Wei, M.C.; Bassik, M.C.; Donnelly, A.J.; Kampmann, M.; Iwasaki, M.; Piloto, O.; Solow-Cordero, D.E.; Bouley, D.M.; Rau, R.; et al. Next-Generation NAMPT Inhibitors Identified by Sequential High-Throughput Phenotypic Chemical and Functional Genomic Screens. Chem. Biol. 2013, 20, 1352–1363. [Google Scholar] [CrossRef] [PubMed][Green Version]
  115. Zhao, G.; Green, C.F.; Hui, Y.-H.; Prieto, L.; Shepard, R.; Dong, S.; Wang, T.; Tan, B.; Gong, X.; Kays, L.; et al. Discovery of a Highly Selective NAMPT Inhibitor That Demonstrates Robust Efficacy and Improved Retinal Toxicity with Nicotinic Acid Coadministration. Mol. Cancer Ther. 2017, 16, 2677–2688. [Google Scholar] [CrossRef][Green Version]
  116. Neumann, C.S.; Olivas, K.C.; Anderson, M.E.; Cochran, J.H.; Jin, S.; Li, F.; Loftus, L.V.; Meyer, D.W.; Neale, J.; Nix, J.C.; et al. Targeted Delivery of Cytotoxic NAMPT Inhibitors Using Antibody–Drug Conjugates. Mol. Cancer Ther. 2018, 17, 2633–2642. [Google Scholar] [CrossRef][Green Version]
  117. Karpov, A.S.; Abrams, T.; Clark, S.; Raikar, A.; D’Alessio, J.A.; Dillon, M.P.; Gesner, T.G.; Jones, D.; Lacaud, M.; Mallet, W.; et al. Nicotinamide Phosphoribosyltransferase Inhibitor as a Novel Payload for Antibody–Drug Conjugates. ACS Med. Chem. Lett. 2018, 9, 838–842. [Google Scholar] [CrossRef]
  118. Abu Aboud, O.; Chen, C.-H.; Senapedis, W.; Baloglu, E.; Argueta, C.; Weiss, R.H. Dual and Specific Inhibition of NAMPT and PAK4 By KPT-9274 Decreases Kidney Cancer Growth. Mol. Cancer Ther. 2016, 15, 2119–2129. [Google Scholar] [CrossRef] [PubMed][Green Version]
  119. Chan, D.A.; Sutphin, P.D.; Nguyen, P.; Turcotte, S.; Lai, E.W.; Banh, A.; Reynolds, G.E.; Chi, J.-T.; Wu, J.; Solow-Cordero, D.E.; et al. Targeting GLUT1 and the Warburg Effect in Renal Cell Carcinoma by Chemical Synthetic Lethality. Sci. Transl. Med. 2011, 3, 94ra70. [Google Scholar] [CrossRef] [PubMed][Green Version]
  120. Adams, D.J.; Ito, D.; Rees, M.G.; Seashore-Ludlow, B.; Puyang, X.; Ramos, A.H.; Cheah, J.H.; Clemons, P.A.; Warmuth, M.; Zhu, P.; et al. NAMPT Is the Cellular Target of STF-31-Like Small-Molecule Probes. ACS Chem. Biol. 2014, 9, 2247–2254. [Google Scholar] [CrossRef] [PubMed]
  121. Moskowitz, A.J.; Horwitz, S.M. Targeting Histone Deacetylases in T-Cell Lymphoma. Leuk. Lymphoma 2017, 58, 1306–1319. [Google Scholar] [CrossRef] [PubMed]
  122. Wu, Y.; Wang, L.; Huang, Y.; Chen, S.; Wu, S.; Dong, G.; Sheng, C. Nicotinamide Phosphoribosyltransferase (NAMPT) Is a New Target of Antitumor Agent Chidamide. ACS Med. Chem. Lett. 2019, 11, 40–44. [Google Scholar] [CrossRef] [PubMed]
  123. Dong, G.; Chen, W.; Wang, X.; Yang, X.; Xu, T.; Wang, P.; Zhang, W.; Rao, Y.; Miao, C.; Sheng, C. Small Molecule Inhibitors Simultaneously Targeting Cancer Metabolism and Epigenetics: Discovery of Novel Nicotinamide Phosphoribosyltransferase (NAMPT) and Histone Deacetylase (HDAC) Dual Inhibitors. J. Med. Chem. 2017, 60, 7965–7983. [Google Scholar] [CrossRef] [PubMed]
  124. Chen, W.; Dong, G.; Wu, Y.; Zhang, W.; Miao, C.; Sheng, C. Dual NAMPT/HDAC Inhibitors as a New Strategy for Multitargeting Antitumor Drug Discovery. ACS Med. Chem. Lett. 2018, 9, 34–38. [Google Scholar] [CrossRef] [PubMed]
  125. LeWitt, P.A. The Neurotoxicity of the Rat Poison Vacor. A Clinical Study of 12 Cases. N. Engl. J. Med. 1980, 302, 73–77. [Google Scholar] [CrossRef] [PubMed]
  126. Buonvicino, D.; Mazzola, F.; Zamporlini, F.; Resta, F.; Ranieri, G.; Camaioni, E.; Muzzi, M.; Zecchi, R.; Pieraccini, G.; Dölle, C.; et al. Identification of the Nicotinamide Salvage Pathway as a New Toxification Route for Antimetabolites. Cell Chem. Biol. 2018, 25, 471–482.e7. [Google Scholar] [CrossRef][Green Version]
  127. Gaut, Z.N.; Solomon, H.M. Inhibition of Nicotinate Phosphoribosyltransferase in Human Platelet Lysate by Nicotinic Acid Analogs. Biochem. Pharmacol. 1971, 20, 2903–2906. [Google Scholar] [CrossRef]
  128. Gaut, Z.N.; Solomon, H.M. Uptake and Metabolism of Nicotinic Acid by Human Blood Platelets. Effects of Structure Analogs and Metabolic Inhibitors. Biochim. Biophys. Acta 1970, 201, 316–322. [Google Scholar] [CrossRef]
  129. Gaut, Z.N.; Solomon, H.M. Inhibition of Nicotinate Phosphoribosyl Transferase by Nonsteroidal Anti-Inflammatory Drugs: A Possible Mechanism of Action. J. Pharm. Sci. 1971, 60, 1887–1888. [Google Scholar] [CrossRef]
  130. Galassi, L.; Di Stefano, M.; Brunetti, L.; Orsomando, G.; Amici, A.; Ruggieri, S.; Magni, G. Characterization of Human Nicotinate Phosphoribosyltransferase: Kinetic Studies, Structure Prediction and Functional Analysis by Site-Directed Mutagenesis. Biochimie 2012, 94, 300–309. [Google Scholar] [CrossRef] [PubMed]
  131. Velu, S.E.; Cristofoli, W.A.; Garcia, G.J.; Brouillette, C.G.; Pierson, M.C.; Luan, C.-H.; DeLucas, L.J.; Brouillette, W.J. Tethered Dimers as NAD Synthetase Inhibitors with Antibacterial Activity. J. Med. Chem. 2003, 46, 3371–3381. [Google Scholar] [CrossRef] [PubMed]
  132. Velu, S.E.; Luan, C.-H.; Delucas, L.J.; Brouillette, C.G.; Brouillette, W.J. Tethered Dimer Inhibitors of NAD Synthetase: Parallel Synthesis of an Aryl-Substituted SAR Library. J. Comb. Chem. 2005, 7, 898–904. [Google Scholar] [CrossRef] [PubMed]
  133. Moro, W.B.; Yang, Z.; Kane, T.A.; Brouillette, C.G.; Brouillette, W.J. Virtual Screening to Identify Lead Inhibitors for Bacterial NAD Synthetase (NADs). Bioorg. Med. Chem. Lett. 2009, 19, 2001–2005. [Google Scholar] [CrossRef][Green Version]
  134. Wang, X.; Ahn, Y.-M.; Lentscher, A.G.; Lister, J.S.; Brothers, R.C.; Kneen, M.M.; Gerratana, B.; Boshoff, H.I.; Dowd, C.S. Design, Synthesis, and Evaluation of Substituted Nicotinamide Adenine Dinucleotide (NAD+) Synthetase Inhibitors as Potential Antitubercular Agents. Bioorg. Med. Chem. Lett. 2017, 27, 4426–4430. [Google Scholar] [CrossRef]
  135. Gehrke, I.; Bouchard, E.D.J.; Beiggi, S.; Poeppl, A.G.; Johnston, J.B.; Gibson, S.B.; Banerji, V. On-Target Effect of FK866, a Nicotinamide Phosphoribosyl Transferase Inhibitor, by Apoptosis-Mediated Death in Chronic Lymphocytic Leukemia Cells. Clin. Cancer Res. 2014, 20, 4861–4872. [Google Scholar] [CrossRef][Green Version]
  136. Cloux, A.-J.; Aubry, D.; Heulot, M.; Widmann, C.; ElMokh, O.; Piacente, F.; Cea, M.; Nencioni, A.; Bellotti, A.; Bouzourène, K.; et al. Reactive Oxygen/Nitrogen Species Contribute Substantially to the Antileukemia Effect of APO866, a NAD Lowering Agent. Oncotarget 2019, 10, 6723–6738. [Google Scholar] [CrossRef] [PubMed]
  137. Grohmann, T.; Penke, M.; Petzold-Quinque, S.; Schuster, S.; Richter, S.; Kiess, W.; Garten, A. Inhibition of NAMPT Sensitizes MOLT4 Leukemia Cells for Etoposide Treatment through the SIRT2-P53 Pathway. Leuk. Res. 2018, 69, 39–46. [Google Scholar] [CrossRef][Green Version]
  138. Travelli, C.; Drago, V.; Maldi, E.; Kaludercic, N.; Galli, U.; Boldorini, R.; Lisa, F.D.; Tron, G.C.; Canonico, P.L.; Genazzani, A.A. Reciprocal Potentiation of the Antitumoral Activities of FK866, an Inhibitor of Nicotinamide Phosphoribosyltransferase, and Etoposide or Cisplatin in Neuroblastoma Cells. J. Pharmacol. Exp. Ther. 2011, 338, 829–840. [Google Scholar] [CrossRef]
  139. Nacarelli, T.; Fukumoto, T.; Zundell, J.A.; Fatkhutdinov, N.; Jean, S.; Cadungog, M.G.; Borowsky, M.E.; Zhang, R. NAMPT Inhibition Suppresses Cancer Stem-like Cells Associated with Therapy-Induced Senescence in Ovarian Cancer. Cancer Res. 2020, 80, 890–900. [Google Scholar] [CrossRef][Green Version]
  140. Cagnetta, A.; Caffa, I.; Acharya, C.; Soncini, D.; Acharya, P.; Adamia, S.; Pierri, I.; Bergamaschi, M.; Garuti, A.; Fraternali, G.; et al. APO866 Increases Antitumor Activity of Cyclosporin-A by Inducing Mitochondrial and Endoplasmic Reticulum Stress in Leukemia Cells. Clin. Cancer Res. 2015, 21, 3934–3945. [Google Scholar] [CrossRef][Green Version]
  141. Cagnetta, A.; Cea, M.; Calimeri, T.; Acharya, C.; Fulciniti, M.; Tai, Y.-T.; Hideshima, T.; Chauhan, D.; Zhong, M.Y.; Patrone, F.; et al. Intracellular NAD+ Depletion Enhances Bortezomib-Induced Anti-Myeloma Activity. Blood 2013, 122, 1243–1255. [Google Scholar] [CrossRef][Green Version]
  142. Cea, M.; Cagnetta, A.; Acharya, C.; Acharya, P.; Tai, Y.-T.; Yang, G.; Lovera, D.; Soncini, D.; Miglino, M.; Fraternali-Orcioni, G.; et al. Dual NAMPT and BTK Targeting Leads to Synergistic Killing of Waldenstrom’s Macroglobulinemia Cells Regardless of MYD88 and CXCR4 Somatic Mutations Status. Clin. Cancer Res. Off. J. Am. Assoc. Cancer Res. 2016, 22, 6099–6109. [Google Scholar] [CrossRef] [PubMed][Green Version]
  143. Chan, M.; Gravel, M.; Bramoullé, A.; Bridon, G.; Avizonis, D.; Shore, G.C.; Roulston, A. Synergy between the NAMPT Inhibitor GMX1777(8) and Pemetrexed in Non-Small Cell Lung Cancer Cells Is Mediated by PARP Activation and Enhanced NAD Consumption. Cancer Res. 2014, 74, 5948–5954. [Google Scholar] [CrossRef][Green Version]
  144. Barraud, M.; Garnier, J.; Loncle, C.; Gayet, O.; Lequeue, C.; Vasseur, S.; Bian, B.; Duconseil, P.; Gilabert, M.; Bigonnet, M.; et al. A Pancreatic Ductal Adenocarcinoma Subpopulation Is Sensitive to FK866, an Inhibitor of NAMPT. Oncotarget 2016, 7, 53783–53796. [Google Scholar] [CrossRef]
  145. Espindola-Netto, J.M.; Chini, C.C.S.; Tarragó, M.; Wang, E.; Dutta, S.; Pal, K.; Mukhopadhyay, D.; Sola-Penna, M.; Chini, E.N. Preclinical Efficacy of the Novel Competitive NAMPT Inhibitor STF-118804 in Pancreatic Cancer. Oncotarget 2017, 8, 85054–85067. [Google Scholar] [CrossRef] [PubMed][Green Version]
  146. Cea, M.; Soncini, D.; Fruscione, F.; Raffaghello, L.; Garuti, A.; Emionite, L.; Moran, E.; Magnone, M.; Zoppoli, G.; Reverberi, D.; et al. Synergistic Interactions between HDAC and Sirtuin Inhibitors in Human Leukemia Cells. PLoS ONE 2011, 6, e22739. [Google Scholar] [CrossRef]
  147. Elf, A.-K.; Bernhardt, P.; Hofving, T.; Arvidsson, Y.; Forssell-Aronsson, E.; Wängberg, B.; Nilsson, O.; Johanson, V. NAMPT Inhibitor GMX1778 Enhances the Efficacy of 177Lu-DOTATATE Treatment of Neuroendocrine Tumors. J. Nucl. Med. Off. Publ. Soc. Nucl. Med. 2017, 58, 288–292. [Google Scholar] [CrossRef][Green Version]
  148. Nahimana, A.; Aubry, D.; Breton, C.S.; Majjigapu, S.R.; Sordat, B.; Vogel, P.; Duchosal, M.A. The Anti-Lymphoma Activity of APO866, an Inhibitor of Nicotinamide Adenine Dinucleotide Biosynthesis, Is Potentialized When Used in Combination with Anti-CD20 Antibody. Leuk. Lymphoma 2014, 55, 2141–2150. [Google Scholar] [CrossRef] [PubMed]
  149. Feng, J.; Yan, P.-F.; Zhao, H.; Zhang, F.-C.; Zhao, W.-H.; Feng, M. Inhibitor of Nicotinamide Phosphoribosyltransferase Sensitizes Glioblastoma Cells to Temozolomide via Activating ROS/JNK Signaling Pathway. BioMed Res. Int. 2016, 2016. [Google Scholar] [CrossRef] [PubMed]
  150. Tateishi, K.; Higuchi, F.; Miller, J.J.; Koerner, M.V.A.; Lelic, N.; Shankar, G.M.; Tanaka, S.; Fisher, D.E.; Batchelor, T.T.; Iafrate, A.J.; et al. The Alkylating Chemotherapeutic Temozolomide Induces Metabolic Stress in IDH1 -Mutant Cancers and Potentiates NAD+ Depletion–Mediated Cytotoxicity. Cancer Res. 2017, 77, 4102–4115. [Google Scholar] [CrossRef] [PubMed][Green Version]
  151. Bajrami, I.; Kigozi, A.; Van Weverwijk, A.; Brough, R.; Frankum, J.; Lord, C.J.; Ashworth, A. Synthetic Lethality of PARP and NAMPT Inhibition in Triple-Negative Breast Cancer Cells. EMBO Mol. Med. 2012, 4, 1087–1096. [Google Scholar] [CrossRef]
  152. Heske, C.M.; Davis, M.I.; Baumgart, J.T.; Wilson, K.; Gormally, M.V.; Chen, L.; Zhang, X.; Ceribelli, M.; Duveau, D.Y.; Guha, R.; et al. Matrix Screen Identifies Synergistic Combination of PARP Inhibitors and Nicotinamide Phosphoribosyltransferase (NAMPT) Inhibitors in Ewing Sarcoma. Clin. Cancer Res. Off. J. Am. Assoc. Cancer Res. 2017, 23, 7301–7311. [Google Scholar] [CrossRef] [PubMed][Green Version]
  153. Gibson, A.E.; Yeung, C.; Issaq, S.H.; Collins, V.J.; Gouzoulis, M.; Zhang, Y.; Ji, J.; Mendoza, A.; Heske, C.M. Inhibition of Nicotinamide Phosphoribosyltransferase (NAMPT) with OT-82 Induces DNA Damage, Cell Death, and Suppression of Tumor Growth in Preclinical Models of Ewing Sarcoma. Oncogenesis 2020, 9, 80. [Google Scholar] [CrossRef] [PubMed]
  154. Somers, K.; Evans, K.; Cheung, L.; Karsa, M.; Pritchard, T.; Kosciolek, A.; Bongers, A.; El-Ayoubi, A.; Forgham, H.; Middlemiss, S.; et al. Effective Targeting of NAMPT in Patient-Derived Xenograft Models of High-Risk Pediatric Acute Lymphoblastic Leukemia. Leukemia 2020, 34, 1524–1539. [Google Scholar] [CrossRef]
  155. Li, M.; Kirtane, A.R.; Kiyokawa, J.; Nagashima, H.; Lopes, A.; Tirmizi, Z.A.; Lee, C.K.; Traverso, G.; Cahill, D.P.; Wakimoto, H. Local Targeting of NAD+ Salvage Pathway Alters the Immune Tumor Microenvironment and Enhances Checkpoint Immunotherapy in Glioblastoma. Cancer Res. 2020. [Google Scholar] [CrossRef] [PubMed]
  156. Travelli, C.; Consonni, F.M.; Sangaletti, S.; Storto, M.; Morlacchi, S.; Grolla, A.A.; Galli, U.; Tron, G.C.; Portararo, P.; Rimassa, L.; et al. Nicotinamide Phosphoribosyltransferase Acts as a Metabolic Gate for Mobilization of Myeloid-Derived Suppressor Cells. Cancer Res. 2019, 79, 1938–1951. [Google Scholar] [CrossRef] [PubMed][Green Version]
  157. Trott, J.F.; Abu Aboud, O.; McLaughlin, B.; Anderson, K.L.; Modiano, J.F.; Kim, K.; Jen, K.-Y.; Senapedis, W.; Chang, H.; Landesman, Y.; et al. Anti-Cancer Activity of PAK4/NAMPT Inhibitor and Programmed Cell Death Protein-1 Antibody in Kidney Cancer. Kidney360 2020, 1, 376–388. [Google Scholar] [CrossRef][Green Version]
  158. Abril-Rodriguez, G.; Torrejon, D.Y.; Liu, W.; Zaretsky, J.M.; Nowicki, T.S.; Tsoi, J.; Puig-Saus, C.; Baselga-Carretero, I.; Medina, E.; Quist, M.J.; et al. PAK4 Inhibition Improves PD-1 Blockade Immunotherapy. Nat. Cancer 2020, 1, 46–58. [Google Scholar] [CrossRef][Green Version]
  159. Li, N.; Lopez, M.A.; Linares, M.; Kumar, S.; Oliva, S.; Martinez-Lopez, J.; Xu, L.; Xu, Y.; Perini, T.; Senapedis, W.; et al. Dual PAK4-NAMPT Inhibition Impacts Growth and Survival, and Increases Sensitivity to DNA-Damaging Agents in Waldenström Macroglobulinemia. Clin. Cancer Res. Off. J. Am. Assoc. Cancer Res. 2019, 25, 369–377. [Google Scholar] [CrossRef][Green Version]
  160. Mpilla, G.; Aboukameel, A.; Muqbil, I.; Kim, S.; Beydoun, R.; Philip, P.A.; Mohammad, R.M.; Kamgar, M.; Shidham, V.; Senapedis, W.; et al. PAK4-NAMPT Dual Inhibition as a Novel Strategy for Therapy Resistant Pancreatic Neuroendocrine Tumors. Cancers 2019, 11, 1902. [Google Scholar] [CrossRef][Green Version]
  161. Aboukameel, A.; Muqbil, I.; Senapedis, W.; Baloglu, E.; Landesman, Y.; Shacham, S.; Kauffman, M.; Philip, P.A.; Mohammad, R.M.; Azmi, A.S. Novel P21-Activated Kinase 4 (PAK4) Allosteric Modulators Overcome Drug Resistance and Stemness in Pancreatic Ductal Adenocarcinoma. Mol. Cancer Ther. 2017, 16, 76–87. [Google Scholar] [CrossRef] [PubMed][Green Version]
  162. Zoppoli, G.; Cea, M.; Soncini, D.; Fruscione, F.; Rudner, J.; Moran, E.; Caffa, I.; Bedognetti, D.; Motta, G.; Ghio, R.; et al. Potent Synergistic Interaction between the Nampt Inhibitor APO866 and the Apoptosis Activator TRAIL in Human Leukemia Cells. Exp. Hematol. 2010, 38, 979–988. [Google Scholar] [CrossRef]
  163. Yang, H.-J.; Yen, M.-C.; Lin, C.-C.; Lin, C.-M.; Chen, Y.-L.; Weng, T.-Y.; Huang, T.-T.; Wu, C.-L.; Lai, M.-D. A Combination of the Metabolic Enzyme Inhibitor APO866 and the Immune Adjuvant L-1-Methyl Tryptophan Induces Additive Antitumor Activity. Exp. Biol. Med. 2010, 235, 869–876. [Google Scholar] [CrossRef] [PubMed]
  164. Moore, Z.; Chakrabarti, G.; Luo, X.; Ali, A.; Hu, Z.; Fattah, F.J.; Vemireddy, R.; DeBerardinis, R.J.; Brekken, R.A.; Boothman, D.A. NAMPT Inhibition Sensitizes Pancreatic Adenocarcinoma Cells to Tumor-Selective, PAR-Independent Metabolic Catastrophe and Cell Death Induced by β-Lapachone. Cell Death Dis. 2015, 6, e1599. [Google Scholar] [CrossRef] [PubMed][Green Version]
  165. Liu, H.-Y.; Li, Q.-R.; Cheng, X.-F.; Wang, G.-J.; Hao, H.-P. NAMPT Inhibition Synergizes with NQO1-Targeting Agents in Inducing Apoptotic Cell Death in Non-Small Cell Lung Cancer Cells. Chin. J. Nat. Med. 2016, 14, 582–589. [Google Scholar] [CrossRef]
  166. Breton, C.S.; Aubry, D.; Ginet, V.; Puyal, J.; Heulot, M.; Widmann, C.; Duchosal, M.A.; Nahimana, A. Combinative Effects of β-Lapachone and APO866 on Pancreatic Cancer Cell Death through Reactive Oxygen Species Production and PARP-1 Activation. Biochimie 2015, 116, 141–153. [Google Scholar] [CrossRef]
  167. Le, A.; Cooper, C.R.; Gouw, A.M.; Dinavahi, R.; Maitra, A.; Deck, L.M.; Royer, R.E.; Vander Jagt, D.L.; Semenza, G.L.; Dang, C.V. Inhibition of Lactate Dehydrogenase A Induces Oxidative Stress and Inhibits Tumor Progression. Proc. Natl. Acad. Sci. USA 2010, 107, 2037–2042. [Google Scholar] [CrossRef] [PubMed][Green Version]
  168. Pogrebniak, A.; Schemainda, I.; Azzam, K.; Pelka-Fleischer, R.; Nüssler, V.; Hasmann, M. Chemopotentiating Effects of a Novel NAD Biosynthesis Inhibitor, FK866, in Combination with Antineoplastic Agents. Eur. J. Med. Res. 2006, 11, 313–321. [Google Scholar]
  169. Mitchell, S.R.; Larkin, K.; Grieselhuber, N.R.; Lai, T.-H.; Cannon, M.; Orwick, S.; Sharma, P.; Asemelash, Y.; Zhang, P.; Goettl, V.M.; et al. Selective Targeting of NAMPT by KPT-9274 in Acute Myeloid Leukemia. Blood Adv. 2019, 3, 242–255. [Google Scholar] [CrossRef][Green Version]
  170. Cea, M.; Cagnetta, A.; Fulciniti, M.; Tai, Y.-T.; Hideshima, T.; Chauhan, D.; Roccaro, A.; Sacco, A.; Calimeri, T.; Cottini, F.; et al. Targeting NAD+ Salvage Pathway Induces Autophagy in Multiple Myeloma Cells via MTORC1 and Extracellular Signal-Regulated Kinase (ERK1/2) Inhibition. Blood 2012, 120, 3519–3529. [Google Scholar] [CrossRef][Green Version]
  171. Cea, M.; Cagnetta, A.; Patrone, F.; Nencioni, A.; Gobbi, M.; Anderson, K.C. Intracellular NAD+ Depletion Induces Autophagic Death in Multiple Myeloma Cells. Autophagy 2013, 9, 410–412. [Google Scholar] [CrossRef] [PubMed][Green Version]
  172. Billington, R.A.; Genazzani, A.A.; Travelli, C.; Condorelli, F. NAD Depletion by FK866 Induces Autophagy. Autophagy 2008, 4, 385–387. [Google Scholar] [CrossRef][Green Version]
  173. Nahimana, A.; Attinger, A.; Aubry, D.; Greaney, P.; Ireson, C.; Thougaard, A.V.; Tjørnelund, J.; Dawson, K.M.; Dupuis, M.; Duchosal, M.A. The NAD Biosynthesis Inhibitor APO866 Has Potent Antitumor Activity against Hematologic Malignancies. Blood 2009, 113, 3276–3286. [Google Scholar] [CrossRef]
  174. Kozako, T.; Aikawa, A.; Ohsugi, T.; Uchida, Y.; Kato, N.; Sato, K.; Ishitsuka, K.; Yoshimitsu, M.; Honda, S. High Expression of NAMPT in Adult T-Cell Leukemia/Lymphoma and Anti-Tumor Activity of a NAMPT Inhibitor. Eur. J. Pharmacol. 2019, 865, 172738. [Google Scholar] [CrossRef]
  175. Del Nagro, C.; Xiao, Y.; Rangell, L.; Reichelt, M.; O’Brien, T. Depletion of the Central Metabolite NAD Leads to Oncosis-Mediated Cell Death. J. Biol. Chem. 2014, 289, 35182–35192. [Google Scholar] [CrossRef] [PubMed][Green Version]
  176. Yang, Y.; Sauve, A.A. NAD+ Metabolism: Bioenergetics, Signaling and Manipulation for Therapy. Biochim. Biophys. Acta 2016, 1864, 1787–1800. [Google Scholar] [CrossRef] [PubMed][Green Version]
  177. Jiang, P.; Du, W.; Wu, M. Regulation of the Pentose Phosphate Pathway in Cancer. Protein Cell 2014, 5, 592–602. [Google Scholar] [CrossRef][Green Version]
  178. Patra, K.C.; Hay, N. The Pentose Phosphate Pathway and Cancer. Trends Biochem. Sci. 2014, 39, 347–354. [Google Scholar] [CrossRef][Green Version]
  179. Nagaya, M.; Hara, H.; Kamiya, T.; Adachi, T. Inhibition of NAMPT Markedly Enhances Plasma-Activated Medium-Induced Cell Death in Human Breast Cancer MDA-MB-231 Cells. Arch. Biochem. Biophys. 2019, 676, 108155. [Google Scholar] [CrossRef]
  180. Cerna, D.; Li, H.; Flaherty, S.; Takebe, N.; Coleman, C.N.; Yoo, S.S. Inhibition of Nicotinamide Phosphoribosyltransferase (NAMPT) Activity by Small Molecule GMX1778 Regulates Reactive Oxygen Species (ROS)-Mediated Cytotoxicity in a P53- and Nicotinic Acid Phosphoribosyltransferase1 (NAPRT1)-Dependent Manner. J. Biol. Chem. 2012, 287, 22408–22417. [Google Scholar] [CrossRef] [PubMed][Green Version]
  181. Kim, H.-J.; Oh, G.-S.; Shen, A.; Lee, S.-B.; Choe, S.-K.; Kwon, K.-B.; Lee, S.; Seo, K.-S.; Kwak, T.H.; Park, R.; et al. Augmentation of NAD+ by NQO1 Attenuates Cisplatin-Mediated Hearing Impairment. Cell Death Dis. 2014, 5, e1292. [Google Scholar] [CrossRef] [PubMed][Green Version]
  182. Silvers, M.A.; Deja, S.; Singh, N.; Egnatchik, R.A.; Sudderth, J.; Luo, X.; Beg, M.S.; Burgess, S.C.; DeBerardinis, R.J.; Boothman, D.A.; et al. The NQO1 Bioactivatable Drug, β-Lapachone, Alters the Redox State of NQO1+ Pancreatic Cancer Cells, Causing Perturbation in Central Carbon Metabolism. J. Biol. Chem. 2017, 292, 18203–18216. [Google Scholar] [CrossRef][Green Version]
  183. Li, L.S.; Bey, E.A.; Dong, Y.; Meng, J.; Patra, B.; Yan, J.; Xie, X.-J.; Brekken, R.A.; Barnett, C.C.; Bornmann, W.G.; et al. Modulating Endogenous NQO1 Levels Identifies Key Regulatory Mechanisms of Action of β-Lapachone for Pancreatic Cancer Therapy. Clin. Cancer Res. Off. J. Am. Assoc. Cancer Res. 2011, 17, 275–285. [Google Scholar] [CrossRef][Green Version]
  184. Miettinen, T.P.; Björklund, M. NQO2 Is a Reactive Oxygen Species Generating Off-Target for Acetaminophen. Mol. Pharm. 2014, 11, 4395–4404. [Google Scholar] [CrossRef][Green Version]
  185. Touat, M.; Sourisseau, T.; Dorvault, N.; Chabanon, R.M.; Garrido, M.; Morel, D.; Krastev, D.B.; Bigot, L.; Adam, J.; Frankum, J.R.; et al. DNA Repair Deficiency Sensitizes Lung Cancer Cells to NAD+ Biosynthesis Blockade. J. Clin. Investig. 2018, 128, 1671–1687. [Google Scholar] [CrossRef]
  186. Zerp, S.F.; Vens, C.; Floot, B.; Verheij, M.; van Triest, B. NAD+ Depletion by APO866 in Combination with Radiation in a Prostate Cancer Model, Results from an in Vitro and in Vivo Study. Radiother. Oncol. J. Eur. Soc. Ther. Radiol. Oncol. 2014, 110, 348–354. [Google Scholar] [CrossRef] [PubMed]
  187. Kato, H.; Ito, E.; Shi, W.; Alajez, N.M.; Yue, S.; Lee, C.; Chan, N.; Bhogal, N.; Coackley, C.L.; Vines, D.; et al. Efficacy of Combining GMX1777 with Radiation Therapy for Human Head and Neck Carcinoma. Clin. Cancer Res. Off. J. Am. Assoc. Cancer Res. 2010, 16, 898–911. [Google Scholar] [CrossRef][Green Version]
  188. Bruzzone, S.; Fruscione, F.; Morando, S.; Ferrando, T.; Poggi, A.; Garuti, A.; D’Urso, A.; Selmo, M.; Benvenuto, F.; Cea, M.; et al. Catastrophic NAD+ Depletion in Activated T Lymphocytes through Nampt Inhibition Reduces Demyelination and Disability in EAE. PLoS ONE 2009, 4, e7897. [Google Scholar] [CrossRef]
  189. Drevs, J.; Löser, R.; Rattel, B.; Esser, N. Antiangiogenic Potency of FK866/K22.175, a New Inhibitor of Intracellular NAD Biosynthesis, in Murine Renal Cell Carcinoma. Anticancer Res. 2003, 23, 4853–4858. [Google Scholar] [PubMed]
  190. O’Brien, T.; Oeh, J.; Xiao, Y.; Liang, X.; Vanderbilt, A.; Qin, A.; Yang, L.; Lee, L.B.; Ly, J.; Cosino, E.; et al. Supplementation of Nicotinic Acid with NAMPT Inhibitors Results in Loss of In Vivo Efficacy in NAPRT1-Deficient Tumor Models. Neoplasia 2013, 15, 1314-IN3. [Google Scholar] [CrossRef][Green Version]
  191. Nagashima, H.; Lee, C.K.; Tateishi, K.; Higuchi, F.; Subramanian, M.; Rafferty, S.; Melamed, L.; Miller, J.J.; Wakimoto, H.; Cahill, D.P. Poly(ADP-Ribose) Glycohydrolase Inhibition Sequesters NAD+ to Potentiate the Metabolic Lethality of Alkylating Chemotherapy in IDH-Mutant Tumor Cells. Cancer Discov. 2020, 10, 1672–1689. [Google Scholar] [CrossRef] [PubMed]
  192. Coppé, J.-P.; Desprez, P.-Y.; Krtolica, A.; Campisi, J. The Senescence-Associated Secretory Phenotype: The Dark Side of Tumor Suppression. Annu. Rev. Pathol. 2010, 5, 99–118. [Google Scholar] [CrossRef][Green Version]
  193. Muñoz-Galván, S.; Lucena-Cacace, A.; Perez, M.; Otero-Albiol, D.; Gomez-Cambronero, J.; Carnero, A. Tumor Cell-Secreted PLD Increases Tumor Stemness by Senescence-Mediated Communication with Microenvironment. Oncogene 2019, 38, 1309–1323. [Google Scholar] [CrossRef]
  194. Takao, S.; Chien, W.; Madan, V.; Lin, D.-C.; Ding, L.-W.; Sun, Q.-Y.; Mayakonda, A.; Sudo, M.; Xu, L.; Chen, Y.; et al. Targeting the Vulnerability to NAD+ Depletion in B-Cell Acute Lymphoblastic Leukemia. Leukemia 2018, 32, 616–625. [Google Scholar] [CrossRef] [PubMed]
  195. Rane, C.; Senapedis, W.; Baloglu, E.; Landesman, Y.; Crochiere, M.; Das-Gupta, S.; Minden, A. A Novel Orally Bioavailable Compound KPT-9274 Inhibits PAK4, and Blocks Triple Negative Breast Cancer Tumor Growth. Sci. Rep. 2017, 7, 42555. [Google Scholar] [CrossRef] [PubMed]
  196. Dasgupta, A.; Sierra, L.; Tsang, S.V.; Kurenbekova, L.; Patel, T.; Rajapakshe, K.; Shuck, R.L.; Rainusso, N.; Landesman, Y.; Unger, T.; et al. Targeting PAK4 Inhibits Ras-Mediated Signaling and Multiple Oncogenic Pathways in High-Risk Rhabdomyosarcoma. Cancer Res. 2020. [Google Scholar] [CrossRef]
  197. Qasim, S.L.; Sierra, L.; Shuck, R.; Kurenbekova, L.; Patel, T.D.; Rajapakshe, K.; Wulff, J.; Nakahata, K.; Kim, H.R.; Landesman, Y.; et al. P21-Activated Kinases as Viable Therapeutic Targets for the Treatment of High-Risk Ewing Sarcoma. Oncogene 2021, 1–15. [Google Scholar] [CrossRef]
  198. Fulciniti, M.; Martinez-Lopez, J.; Senapedis, W.; Oliva, S.; Lakshmi Bandi, R.; Amodio, N.; Xu, Y.; Szalat, R.; Gulla, A.; Samur, M.K.; et al. Functional Role and Therapeutic Targeting of P21-Activated Kinase 4 in Multiple Myeloma. Blood 2017, 129, 2233–2245. [Google Scholar] [CrossRef]
  199. Cordover, E.; Wei, J.; Patel, C.; Shan, N.L.; Gionco, J.; Sargsyan, D.; Wu, R.; Cai, L.; Kong, A.-N.; Jacinto, E.; et al. KPT-9274, an Inhibitor of PAK4 and NAMPT, Leads to Downregulation of MTORC2 in Triple Negative Breast Cancer Cells. Chem. Res. Toxicol. 2020, 33, 482–491. [Google Scholar] [CrossRef]
  200. Audrito, V.; Serra, S.; Brusa, D.; Mazzola, F.; Arruga, F.; Vaisitti, T.; Coscia, M.; Maffei, R.; Rossi, D.; Wang, T.; et al. Extracellular Nicotinamide Phosphoribosyltransferase (NAMPT) Promotes M2 Macrophage Polarization in Chronic Lymphocytic Leukemia. Blood 2015, 125, 111–123. [Google Scholar] [CrossRef]
  201. Lv, H.; Lv, G.; Chen, C.; Zong, Q.; Jiang, G.; Ye, D.; Cui, X.; He, Y.; Xiang, W.; Han, Q.; et al. NAD+ Metabolism Maintains Inducible PD-L1 Expression to Drive Tumor Immune Evasion. Cell Metab. 2020. [Google Scholar] [CrossRef]
  202. Zhang, W.; Zhang, K.; Yao, Y.; Liu, Y.; Ni, Y.; Liao, C.; Tu, Z.; Qiu, Y.; Wang, D.; Chen, D.; et al. Dual Nicotinamide Phosphoribosyltransferase and Epidermal Growth Factor Receptor Inhibitors for the Treatment of Cancer. Eur. J. Med. Chem. 2020, 113022. [Google Scholar] [CrossRef] [PubMed]
  203. Watson, M.; Roulston, A.; Bélec, L.; Billot, X.; Marcellus, R.; Bédard, D.; Bernier, C.; Branchaud, S.; Chan, H.; Dairi, K.; et al. The Small Molecule GMX1778 Is a Potent Inhibitor of NAD+ Biosynthesis: Strategy for Enhanced Therapy in Nicotinic Acid Phosphoribosyltransferase 1-Deficient Tumors. Mol. Cell. Biol. 2009, 29, 5872–5888. [Google Scholar] [CrossRef] [PubMed][Green Version]
  204. Olesen, U.H.; Thougaard, A.V.; Jensen, P.B.; Sehested, M. A Preclinical Study on the Rescue of Normal Tissue by Nicotinic Acid in High-Dose Treatment with APO866, a Specific Nicotinamide Phosphoribosyltransferase Inhibitor. Mol. Cancer Ther. 2010, 9, 1609–1617. [Google Scholar] [CrossRef] [PubMed][Green Version]
  205. Beauparlant, P.; Bédard, D.; Bernier, C.; Chan, H.; Gilbert, K.; Goulet, D.; Gratton, M.-O.; Lavoie, M.; Roulston, A.; Turcotte, E.; et al. Preclinical Development of the Nicotinamide Phosphoribosyl Transferase Inhibitor Prodrug GMX1777. Anticancer. Drugs 2009, 20, 346–354. [Google Scholar] [CrossRef] [PubMed]
  206. Tarrant, J.M.; Dhawan, P.; Singh, J.; Zabka, T.S.; Clarke, E.; DosSantos, G.; Dragovich, P.S.; Sampath, D.; Lin, T.; McCray, B.; et al. Preclinical Models of Nicotinamide Phosphoribosyltransferase Inhibitor-Mediated Hematotoxicity and Mitigation by Co-Treatment with Nicotinic Acid. Toxicol. Mech. Methods 2015, 25, 201–211. [Google Scholar] [CrossRef]
  207. Zabka, T.S.; Singh, J.; Dhawan, P.; Liederer, B.M.; Oeh, J.; Kauss, M.A.; Xiao, Y.; Zak, M.; Lin, T.; McCray, B.; et al. Retinal Toxicity, in Vivo and in Vitro, Associated with Inhibition of Nicotinamide Phosphoribosyltransferase. Toxicol. Sci. 2015, 144, 163–172. [Google Scholar] [CrossRef][Green Version]
  208. Misner, D.L.; Kauss, M.A.; Singh, J.; Uppal, H.; Bruening-Wright, A.; Liederer, B.M.; Lin, T.; McCray, B.; La, N.; Nguyen, T.; et al. Cardiotoxicity Associated with Nicotinamide Phosphoribosyltransferase Inhibitors in Rodents and in Rat and Human-Derived Cells Lines. Cardiovasc. Toxicol. 2017, 17, 307–318. [Google Scholar] [CrossRef]
  209. Cassar, S.; Dunn, C.; Olson, A.; Buck, W.; Fossey, S.; Ramos, M.F.; Sancheti, P.; Stolarik, D.; Britton, H.; Cole, T.; et al. From the Cover: Inhibitors of Nicotinamide Phosphoribosyltransferase Cause Retinal Damage in Larval Zebrafish. Toxicol. Sci. 2018, 161, 300–309. [Google Scholar] [CrossRef]
  210. Ravaud, A.; Cerny, T.; Terret, C.; Wanders, J.; Bui, B.N.; Hess, D.; Droz, J.-P.; Fumoleau, P.; Twelves, C. Phase I Study and Pharmacokinetic of CHS-828, a Guanidino-Containing Compound, Administered Orally as a Single Dose Every 3 Weeks in Solid Tumours: An ECSG/EORTC Study. Eur. J. Cancer Oxf. Engl. 1990 2005, 41, 702–707. [Google Scholar] [CrossRef]
  211. Pishvaian, M.J.; Marshall, J.L.; Hwang, J.H.; Malik, S.M.; He, A.R.; Deeken, J.F.; Kelso, C.B.; Dorsch-Vogel, K.; Berger, M.S. A Phase 1 Trial of GMX1777: An Inhibitor of Nicotinamide Phosphoribosyl Transferase (NAMPRT). J. Clin. Oncol. 2008, 26, 14568. [Google Scholar] [CrossRef]
  212. Holen, K.; Saltz, L.B.; Hollywood, E.; Burk, K.; Hanauske, A.-R. The Pharmacokinetics, Toxicities, and Biologic Effects of FK866, a Nicotinamide Adenine Dinucleotide Biosynthesis Inhibitor. Investig. New Drugs 2008, 26, 45–51. [Google Scholar] [CrossRef]
  213. von Heideman, A.; Berglund, Å.; Larsson, R.; Nygren, P. Safety and Efficacy of NAD Depleting Cancer Drugs: Results of a Phase I Clinical Trial of CHS 828 and Overview of Published Data. Cancer Chemother. Pharmacol. 2010, 65, 1165–1172. [Google Scholar] [CrossRef][Green Version]
  214. Pishvaian, M.J.; Marshall, J.L.; Hwang, J.J.; Malik, S.; He, A.R.; Deeken, J.F.; Kelso, C.B.; Cotarla, I.; Berger, M.S. A Phase I Trial of GMX1777, an Inhibitor of Nicotinamide Phosphoribosyl Transferase (NAMPRT), given as a 24-Hour Infusion. J. Clin. Oncol. 2009, 27, 3581. [Google Scholar] [CrossRef]
  215. Goldinger, S.M.; Gobbi Bischof, S.; Fink-Puches, R.; Klemke, C.-D.; Dréno, B.; Bagot, M.; Dummer, R. Efficacy and Safety of APO866 in Patients With Refractory or Relapsed Cutaneous T-Cell Lymphoma: A Phase 2 Clinical Trial. JAMA Dermatol. 2016, 152, 837–839. [Google Scholar] [CrossRef][Green Version]
  216. Heske, C.M. Beyond Energy Metabolism: Exploiting the Additional Roles of NAMPT for Cancer Therapy. Front. Oncol. 2019, 9, 1514. [Google Scholar] [CrossRef][Green Version]
  217. Kim, W.; Deik, A.; Gonzalez, C.; Gonzalez, M.E.; Fu, F.; Ferrari, M.; Churchhouse, C.L.; Florez, J.C.; Jacobs, S.B.R.; Clish, C.B.; et al. Polyunsaturated Fatty Acid Desaturation Is a Mechanism for Glycolytic NAD+ Recycling. Cell Metab. 2019, 29, 856–870.e7. [Google Scholar] [CrossRef][Green Version]
Figure 1. Schematic representation of the NAD biosynthetic pathways. NAD, nicotinamide adenine dinucleotide; NAMPT, nicotinamide phosphoribosyltransferase; NAPRT, nicotinic acid phosphoribosyltransferase; PncA, bacterial nicotinamidase; NMNAT, nicotinamide mononucleotide adenylyltransferase; NMRK, nicotinamide riboside kinase; NADSYN, NAD synthetase; QAPRT, quinolinic acid phosphoribosyltransferase; IDO, indoleamine-2,3-dioxygenase; TDO, tryptophan-2,3-dioxygenase; AFMID, arylformamidase; KMO, kynurenine 3-monooxygenase; KYNU, kynureninase; HAAO, 3-hydroxyanthranilate 3,4-dioxygenase; ACMSD, α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase; MARTs, mono(ADP-ribosyl) transferases; PARPs, poly(ADP-ribose) polymerases; SARM 1, sterile alpha and TIR motif-containing 1; NQO1, NAD(P)H:quinone oxidoreductase; NQO2, NRH:quinone oxidoreductase; AK, adenosine kinase; NNMT, nicotinamide N-methyltransferase; and TCA, tricarboxylic acid.
Figure 1. Schematic representation of the NAD biosynthetic pathways. NAD, nicotinamide adenine dinucleotide; NAMPT, nicotinamide phosphoribosyltransferase; NAPRT, nicotinic acid phosphoribosyltransferase; PncA, bacterial nicotinamidase; NMNAT, nicotinamide mononucleotide adenylyltransferase; NMRK, nicotinamide riboside kinase; NADSYN, NAD synthetase; QAPRT, quinolinic acid phosphoribosyltransferase; IDO, indoleamine-2,3-dioxygenase; TDO, tryptophan-2,3-dioxygenase; AFMID, arylformamidase; KMO, kynurenine 3-monooxygenase; KYNU, kynureninase; HAAO, 3-hydroxyanthranilate 3,4-dioxygenase; ACMSD, α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase; MARTs, mono(ADP-ribosyl) transferases; PARPs, poly(ADP-ribose) polymerases; SARM 1, sterile alpha and TIR motif-containing 1; NQO1, NAD(P)H:quinone oxidoreductase; NQO2, NRH:quinone oxidoreductase; AK, adenosine kinase; NNMT, nicotinamide N-methyltransferase; and TCA, tricarboxylic acid.
Nutrients 13 01665 g001
Figure 2. Timeline summary for the development of NAMPT inhibitors and their entry for evaluation in clinical studies. * the trial years are the years in which the study started according to
Figure 2. Timeline summary for the development of NAMPT inhibitors and their entry for evaluation in clinical studies. * the trial years are the years in which the study started according to
Nutrients 13 01665 g002
Figure 3. Schematic overview of the different strategies to improve the overall performance of NAMPT inhibitors.
Figure 3. Schematic overview of the different strategies to improve the overall performance of NAMPT inhibitors.
Nutrients 13 01665 g003
Table 1. Overview of the regulation of the major enzymes involved in NAD biosynthesis.
Table 1. Overview of the regulation of the major enzymes involved in NAD biosynthesis.
RegulatorTargetMechanismEffectCancer/Tissue Type
c-MYC and Max [37]NAMPT-Binding to and regulating the activity of the distal 4.6 kb putative NAMPT enhancer 65 kb downstream the NAMPT transcription start site specifically through the 1 kb “B-region” within the NAMPT enhancer.UpregulationSalvage-dependent cancer cells
c-MYC [38]NAMPT-Binding to the NAMPT promoter.UpregulationMCF-7 cells (breast cancer)
C/EBPβ [36]NAMPT-Interaction with NAMPT regulatory regions.UpregulationMesenchymal GSCs
HMGA proteins [39]NAMPT-Binding to an NAMPT enhancer element during oncogene-induced senescence (OIS).UpregulationOncogenic Ras-induced senescent IMR90 cells (lung fibroblasts)
SIRT6 [40]NAMPT-Regulation of NAMPT enzymatic activity through lysine deacetylation.UpregulationHEK293 cells (human embryonic kidney cells)
SIRT1 [41]NAMPT-Regulation of NAMPT activity through lysine deacetylation and secretion of eNAMPT.UpregulationAdipocytes
Foxo1 [42]NAMPT-Binding to conserved insulin response elements (IREs) in the NAMPT 5′-flanking promoter region.DownregulationMCF-7 cells (breast cancer)
“RP11-22N19.2” Lnc-RNA [43]
NAMPT-Recruitment of the transcription factor POU2F2 to the promoter region of NAMPT to enhance NAMPT transcription.
-Competitive binding to miR-548b-3p leading to increasing the NAMPT mRNA pool.
UpregulationMDA-MB-231 and MDA-MB-468 cells (triple-negative breast cancer)
GACAT3 [44]
NAMPT-Competitive binding to miR-135a, whose target gene is NAMPT.UpregulationU87 and U251 cells (glioma)
miR-381 [45]NAMPT-Post-transcriptional binding to the 3′- untranslated region (UTR) of NAMPT.DownregulationMDA-MB-231 and MCF-7 cells (breast cancer)
miR-206 [46]NAMPT-Binding to the 3′-UTR of NAMPT.DownregulationMDA-MB-231 and MCF-7 cells (breast cancer)
miR-494 [47]NAMPT-Binding to the 3’-UTR of NAMPT.DownregulationMDA-MB-231 and MCF-7 cells (breast cancer)
miR-154 [48]NAMPT-Binding to the 3’-UTR of NAMPT.DownregulationMDA-MB-231 and MCF-7 cells (breast cancer)
miR-26b [49]NAMPT-Binding to the 3′-UTR of NAMPT.DownregulationSW480 cells (colorectal cancer)
miR-206 [50]NAMPT-Regulation of NAMPT expression most probably through targeting the 3′-UTR of NAMPT.DownregulationMiaPaCa-2 and Panc-1 cells (pancreatic cancer)
miR-23b [51]NAMPT-Regulation of NAMPT expression.Downregulationmelanoma cells
Gene Amplification [37]NAPRT/
-Regulation of NAPRT or NADSYN expression.UpregulationPH-dependent tumors and cancer cell lines
Gene Silencing [52]NAPRT-Hypermethylation of NAPRT promoter region.DownregulationSeveral cancer cell lines
Mutant IDH1 [53]NAPRT-Hypermethylation of the CpG islands in the NAPRT promoter region and thus reprogramming NAD metabolism.
-IDH1-mutant cancers are uniquely sensitive to NAMPT inhibitors via NAD depletion.
DownregulationIDH1-mutant cancer cells (MGG119, MGG152, BT142, BT142, HT1080, 30T, SW1353)
Mutant PPM1D [54]NAPRT-Hypermethylation of the CpG islands in the genome and epigenetic silencing of NAPRT gene.
-PPM1D mutant cancer cells are uniquely sensitive to NAMPT inhibitors.
DownregulationPPM1D mutant astrocytes and diffuse intrinsic pontine glioma (DIPG) cell lines
SIRT3 [55]NMNAT2-Regulation of NMNAT2 activity through deacetylation.UpregulationA549 cells (non-small cell lung cancer)
miR-654-3p [56]QAPRT-Binding to the 3′-UTR of QAPRT.DownregulationIgrov-1 cells (ovarian cancer)
DSCAM-AS1 [57]
QAPRT-Competitive binding of miRNA-150-5p and miRNA-2467-3p.UpregulationT47D and MCF-7 cells (breast cancer)
WT1 [58]QAPRT-Binding to a conserved site on the QAPRT promoter.UpregulationK562 cells (leukemia)
Table 2. Summary of the reported combinations of NAMPT inhibitors with other agents in cancer therapy.
Table 2. Summary of the reported combinations of NAMPT inhibitors with other agents in cancer therapy.
The Combination Agent/DrugClassApproval as an Anti-CancerCancer TypeIn Vitro EfficacyIn Vivo EfficacyRef.
FK8665-fluorouracilAntimetaboliteYesGastric cancerYesn/a 1[71]
FK866FludarabineAntimetaboliteYesLeukemia (CLL)Yesn/a[135]
FK866EtoposideTopoisomerase II inhibitorYesLeukemiaYesn/a[136,137]
GMX1777EtoposideTopoisomerase II inhibitorYesLung cancern/aYes[108]
FK866EtoposideTopoisomerase II inhibitorYesNeuroblastomaYesn/a[138]
FK866CisplatinAlkylating agentYesNeuroblastomaYesn/a[138]
CisplatinAlkylating agentYesOvarian cancerYesYes
FK866Cyclosporin A
Pgp inhibitor
Pgp inhibitor
FK866BortezomibProteasome inhibitorYesMultiple myelomaYesYes[141]
FK866IbrutinibBruton’s tyrosine kinase inhibitorYesWaldenstrom
YesNon-small-cell lung cancer (NSCLC)YesYes[143]
FK866GemcitabineAntimetaboliteYesPancreatic cancer (PDAC)Yesn/a[144]
Topoisomerase II inhibitor
Antimicrotubular agent
Valproic acid
HDAC inhibitor
HDAC inhibitor
GMX1778177Lu-DOTATATERadiolabeled somatostatin analogYesNeuroendocrine tumorsn/aYes[147]
TemozolomideAlkylating agentYesGlioblastomaYesn/a[149]
TemozolomideAlkylating agentYesIDH1-mutant cancersYesYes
FK866OlaparibPARP inhibitorYesTriple-negative breast cancer (TNBC)YesYes[151]
NiraparibPARP inhibitorYesEwing sarcomaYesYes
OT-82NiraparibPARP InhibitorYesEwing sarcomaYesYes[153]
OT-82Irinotecan & its metabolite SN-38topoisomerase I inhibitorsYes
Ewing sarcomaYes
OT-82CytarabineAntimetaboliteYesAcute lymphoblastic leukemia (ALL)YesYes[154]
OT-82DasatinibTyrosine kinase inhibitorYesALLn/aYes[154]
OT-82EtoposideTopoisomerase II inhibitorYesALLYesn/a[154]
GMX1778Anti-mouse PD-1 antibodyImmune checkpoint inhibitorHuman
anti-PD1: Yes
MV87Anti-mouse PD-1 antibodyImmune checkpoint inhibitorHuman
anti-PD1: Yes
KPT-9274Anti-mouse PD-1 antibodyImmune checkpoint inhibitorHuman
anti-PD1: Yes
Renal cell carcinoman/aYes[157]
KPT-9274Anti-mouse PD-1 antibodyImmune checkpoint inhibitorHuman
anti-PD1: Yes
Colon adenocarcinoma
n/aYes (PAK4)[158]
Alkylating agent
Alkylating agent
KPT-9274EverolimusmTOR inhibitorYesPancreatic neuroendocrine tumorYesn/a[160]
Alkylating agent
Yes (PAK4)
FK866TRAILApoptosis activatorNot approved as a drugLeukemiaYesn/a[162]
FK8662-HNANAPRT inhibitorNot approved as a drugOvarian cancer
Pancreatic cancer
(sodium salt of 2-HNA)
FK866L-1-methyl-tryptophanIndoleamine 2,3-dioxygenase (IDO) inhibitorNot approved as a drugGastric cancer
Bladder cancer
n/aYes (only in immuno-competent mice)[163]
FK866β-LapachoneROS generator &
NQO1 substrate
Not approved as a drugPDAC
FK866FX11Lactate dehydrogenase A (LDHA) inhibitorNot approved as a drugLymphomaYesYes[167]
FK8661-methyl-3-nitro-1-nitrosoguanidinium (MNNG)Alkylating agentNot approved as a drugLeukemiaYesn/a[168]
1 n/a: not available (i.e., not reported in the referred article).
Table 3. Summary of the reported preclinical studies of the NAMPT inhibitors that are currently being evaluated in clinical trials.
Table 3. Summary of the reported preclinical studies of the NAMPT inhibitors that are currently being evaluated in clinical trials.
CompoundCancer TypeCancer Cell LinesIn Vitro EffectsMouse ModelIn Vivo ModelIn Vivo EffectsReported Mode of Action
KPT-9274Renal cell carcinoma (RCC) [118]RCC cell lines:
-Attenuation of viability, invasion, and migration in several RCC cell lines.
-Limited toxicity in normal human renal epithelial cells.
-Induction of apoptosis.
-Decrease in G2-M transition.
-Reduced NAD and SIRT1 levels.
-NA rescued NAD levels in normal renal epithelial cells but not in 786-O and Caki-1 “NAPRT deficient” cells.
-Reduction in nuclear β-catenin and of the Wnt/β-catenin targets c-MYC and cyclin D1 as a result of PAK4 inhibition.
nude mice
RCC xenograft model:
786-O cells
-Reduced tumor growth.
-No significant animal weight loss.
PAK4 and NAMPT inhibition
KPT-9274Renal cell carcinoma (RCC) [157] Ex vivo:
-Reduced tumor expression of PAK4 and phospho-β-catenin.
-NAD + NADH levels in tumors decreased by KPT-9274 and increased by anti-PD1 antibody.
Male BALB/cJ miceRCC allograft model:
Mouse RENCA-luciferase (RENCA-Luc) cells
-Significant reduction in tumor growth with KPT-9274 and anti-PD1 combination compared to each agent alone.
-No significant animal weight loss.
PAK4 and
NAMPT inhibition
KPT-9274Pancreatic ductal adenocarcinoma (PDAC) [161]PDAC cell lines:
MiaPaCa-2 cancer stem cells
-Inhibition of proliferation of PDAC cells.
-Limited toxicity in normal pancreatic human epithelial cells.
-Cancer-selective induction of apoptosis and cell-cycle arrest.
-Suppression of cancer migration.
-Overcoming stemness (PDAC cancer stem cells) and downregulation of EMT markers.
-Synergistic effect with gemcitabine and oxaliplatin.
Female SCID
PDAC xenograft model:
L3.6pl cells
AsPc-1 cells
PDAC cancer stem cell xenograft model:
CD44+/CD133+/EpCAM+ MiaPaCa-2 cells
-Remarkable antitumor activity as a single agent.
-Marginal antitumor activity in combination with gemcitabine.
-No signs of toxicity.
-Suppression of growth of highly resistant PDAC cancer stem cell-derived tumors.
PAK4 inhibition
KPT-9274Acute myeloid leukemia (AML) [169]AML cell lines:
Primary AML cells
-Inhibition of proliferation of AML cells.
-Cell cycle arrest.
-Induction of apoptosis.
-Reduction in NAD levels, disruption of mitochondrial activity, and cellular respiration.
-Limited toxicity on normal hematopoietic cells.
NSG miceAML xenograft model: luciferase-positive MV4-11 cells

Patient-derived xenograft (PDX) model of AML
-Improved overall survival.
-Reduced disease progression and tumor burden.
NAMPT inhibition
KPT-9274B-cell acute
lymphoblastic leukemia
(B-ALL) [194]
B-ALL cell lines: KOPN-8
PDX B-ALL cells
-Strong inhibition of cell growth.
-Induction of apoptosis.
-Intracellular NAD depletion and modulation of NAD-dependent pathways.
-NA supplementation reversed KPT-9274-mediated growth inhibition in three sensitive B-ALL cell lines.
NSG micePDX model of B-ALL:
luciferase-transduced LAX2 cells
-Effective suppression of leukemia progression.
-Significantly improved survival.
-Acceptable adverse effect profile (normal mice activity, no significant difference in body weight between groups).
NAMPT inhibition
KPT-9274Triple-negative breast cancer
(TNBC) [195]
BC cell lines:
-Inhibition of cell proliferation in several BC cell lines.
-Reduction in viability was more pronounced in TNBC cell lines (almost complete inhibition).
-Stimulation of apoptosis.
nude mice
TNBC xenograft models:
MDA-MB-231 cells
MDA-MB-468 cells
SUM159 cells
-Significant reduction in tumor weights and volumes.
-No significant effect on the body weights of the mice.
-Reduced PAK4 protein levels in tumors.
PAK4 inhibition
KPT-9274Melanoma [158]Melanoma cell lines:
Murine B16 cells
C57BL/6 miceMelanoma model:
B16 cells
-Significant decrease in tumor growth with KPT-9274 and anti-PD1 combination compared to each agent alone.PAK4 inhibition
KPT-9274Colon cancer
Colon cancer cell lines:
Murine MC38
C57BL/6 miceColon adenocarcinoma model:
MC38 cells
-Significant decrease in tumor growth with KPT-9274 alone or combined with anti-PD1
compared to anti-PD1 alone.
PAK4 inhibition
KPT-9274Pancreatic neuro-endocrine tumors (PNET) [160]PNET cell lines:
-Reduction in growth and survival of PNET cells.
-Reduced NAD and ATP levels and ATP collapse was reversed by NA.
-Synergistic effect with everolimus.
Female SCID micePNET xenograft model:
BON-1 cells
-Significant reduction in tumor growth as monotherapy.PAK4 and NAMPT inhibition
macroglobulinemia (WM) [159]
WM cell lines:
Primary WM cells
-Reduction in cell viability.
-NA rescued BCWM-1 cells from KPT-9274-mediated growth inhibition.
-Impairment of DNA repair and induction of DNA damage.
-Induction of apoptosis.
-Synergistic effect in combination with DNA-damaging agents (bendamustine & melphalan).
SCID miceWM xenograft model:
BCMW-1 cells
-Significant inhibition of tumor growth as a single agent.
-Significant reduction in tumor volume with KPT-9274 and bendamustine combination compared with either agent alone.
PAK4 and
NAMPT inhibition
KPT-9274Multiple myeloma (MM) [198]Many human myeloma cell lines
Primary MM cells
-Reduction in cell growth and survival in a large panel of MM cell lines and primary MM cells.
-Suppression of the promoting effects of the bone marrow microenvironment.
-No significant effect on bone marrow mononuclear cells or PBMCS.
-Induction of apoptosis and deregulation of the MEK/ERK pathway.
Nude miceMM xenograft models:
MM1S cells
OPM2 cells
-Significant single-agent antitumor activity in both MM xenograft models.
-Higher sensitivity to KPT-9274 was seen with t(4:14) FGFR3-mutated OPM2 tumors
compared to MM1S xenografts.
PAK4 inhibition
KPT-9274Ewing sarcoma (EWS) [197]EWS cell lines:
-Suppression in cell proliferation.
-Reduction in invasive and migratory characteristics.
-Potential synergistic effect with doxorubicin and vincristine.
NSG miceEWS xenograft models:
A673 cells
TC71 cells
PDX and metastatic models of EWS
-Significant reduction in tumor growth as a single agent.
-Reduced metastatic burden in the EWS metastatic model.
PAK4 inhibition
KPT-9274Rhabdomyosarcoma (RMS) [196]RMS cell lines:
-Reduction in cell proliferation in multiple RMS cell lines (IC50 ranges from 40 to 80 nM).
-Limited toxicity in normal skeletal muscle myoblast cells (IC50 values were 8–10 times higher).
-Induction of apoptosis and G1-S arrest.
-Inhibition of cell motility and invasive properties.
-Reduced PAK4 activity and β-catenin activation.
NSG miceRMS orthotopic xenograft models:
RH30 cells
RD cells

PDX model of relapsed RMS

Metastatic model of RMS:
RD cells
-Significant reduction in tumor growth in the orthotopic and PDX models with KPT-9274 alone compared to vehicle.
-No significant changes in body weight.
-Reduced metastatic burden in the liver with KPT-9274 in the metastatic model.
PAK4 inhibition
OT-82Pediatric acute lymphoblastic leukemia
(ALL) [154]
ALL cell lines:
Pediatric PDX ALL cells
-Potent dose-dependent reduction in cell viability.
-Reduction in NAD levels, ATP levels, and PARP activity.
-Higher DNA damage.
-Induction of apoptosis.
-Synergistic effect with cytarabine and etoposide in PER-485 cell line.
NSG mice
21 PDX models of high-risk pediatric
-Significant extension of the survival in 20/21 (95%) PDXs and objective response in 18/21 (86%) PDXs→ significant leukemia regression.
-Therapeutic enhancement when combined with cytarabine in 2 aggressive MLLr-ALL PDX models and with dasatinib in one Ph+ ALL PDX model.
OT-82Ewing sarcoma (EWS) [153]EWS cell lines:
-Potent inhibition in cell growth and proliferation.
-Reduction in NAD levels and PARP activity.
-Higher DNA damage.
-G2 arrest and induction of apoptosis.
-Enhanced antiproliferative effects when combined with niraparib or SN-38.
SCID beige mice
NOG mice
Orthotopic xenograft models of EWS:
TC71 cells
TC32 cells

PDX model of EWS
-Significant reduction in tumor growth and prolongation of survival with doses of 25 mg/kg and 50 mg/kg.
-Cessation of treatment resulted in tumor regrowth.
-Improved OT-82 efficacy when combined with irinotecan or niraparib (slower tumor growth and prolongation of median survival).
-Several unexpected deaths occurred with OT-82/niraparib combination.
OT-82Acute myeloid leukemia
(AML) [109]
AML cell lines:
-Potent reduction in cell viability.
-Depletion of NAD and ATP levels.
-Induction of apoptosis.
-NA addition rescued MV4-11 cells from OT-82-mediated cytotoxicity.
SCID miceSubcutaneous (SC) and systemic xenograft models of AML:
MV4-11 cells
-Significant dose-dependent reduction in tumor volume→ SC model.
-Significant prolongation of mice survival at 25 and 40 mg/kg → systemic model.
-Improved survival with the optimized OT-82 regimen→ systemic model.
OT-82Erythroleukemia [109]Erythroleukemia cell line:
-Potent reduction in cell viability.SCID miceSC and systemic xenograft models of erythroleukemia: HEL92.1.7 cells-Significant reduction in tumor volume at 50 mg/kg dose→ SC model.
-Significant prolongation of mice survival at 40 mg/kg→ systemic model.
OT-82Burkitt lymphoma (BL) [109]BL cell lines:
-Potent reduction in cell viability.SCID miceSC xenograft model of BL:
Ramos cells
-Significant reduction in tumor volume with the optimized OT-82 regimen.
OT-82Multiple myeloma (MM) [109] SCID miceSC xenograft model of MM:
RPMI 8226 cells
-Significant reduction in tumor volume with the optimized OT-82 regimen.
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Ghanem, M.S.; Monacelli, F.; Nencioni, A. Advances in NAD-Lowering Agents for Cancer Treatment. Nutrients 2021, 13, 1665.

AMA Style

Ghanem MS, Monacelli F, Nencioni A. Advances in NAD-Lowering Agents for Cancer Treatment. Nutrients. 2021; 13(5):1665.

Chicago/Turabian Style

Ghanem, Moustafa S., Fiammetta Monacelli, and Alessio Nencioni. 2021. "Advances in NAD-Lowering Agents for Cancer Treatment" Nutrients 13, no. 5: 1665.

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop