Next Article in Journal
A Specific Oligodeoxynucleotide Promotes the Differentiation of Osteoblasts via ERK and p38 MAPK Pathways
Next Article in Special Issue
The Tricyclodecan-9-yl-xanthogenate D609 Triggers Ceramide Increase and Enhances FasL-Induced Caspase-Dependent and -Independent Cell Death in T Lymphocytes
Previous Article in Journal
Synthesis and Electrochemical Proprieties of Novel Unsymmetrical Bis-Tetrathiafulvalenes and Electrical Conductivity of Their Charge Transfer Complexes with Tetracyanoquinodimethane (TCNQ)
Previous Article in Special Issue
Apoptosis Signaling Is Altered in CD4+CD25+FoxP3+ T Regulatory Lymphocytes in Pre-Eclampsia

Int. J. Mol. Sci. 2012, 13(7), 7886-7901; doi:10.3390/ijms13077886

Review
Molecular Targets of TRAIL-Sensitizing Agents in Colorectal Cancer
Carmine Stolfi *, Francesco Pallone and Giovanni Monteleone
Department of Systems Medicine, University of “Tor Vergata”, Via Montpellier 1, Rome 00133, Italy; E-Mails: pallone@uniroma2.it (F.P.); gi.monteleone@med.uniroma2.it (G.M.)
*
Author to whom correspondence should be addressed; E-Mail: carmine.stolfi@uniroma2.it; Tel.: +39-06-72596158; Fax: +39-06-72596391.
Received: 1 June 2012; in revised form: 18 June 2012 / Accepted: 20 June 2012 /
Published: 25 June 2012

Abstract

: Tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL), a member of the TNF superfamily, interacts with its functional death receptors (DRs) and induces apoptosis in a wide range of cancer cell types. Therefore, TRAIL has been considered as an attractive agent for cancer therapy. However, many cancers are resistant to TRAIL-based therapies mainly due to the reduced expression of DRs and/or up-regulation of TRAIL pathway-related anti-apoptotic proteins. Compounds that revert such defects restore the sensitivity of cancer cells to TRAIL, suggesting that combined therapies could help manage neoplastic patients. In this article, we will focus on the TRAIL-sensitizing effects of natural products and synthetic compounds in colorectal cancer (CRC) cells and discuss the molecular mechanisms by which such agents enhance the response of CRC cells to TRAIL.
Keywords:
DR4; DR5; caspase-8; p53; CHOP; survivin; extrinsic pathway; intrinsic pathway; chemotherapeutics; natural products

1. Introduction

Induction of programmed cell death or apoptosis in tumor cells is a pivotal mechanism for most anti-cancer approaches including chemotherapy, radiation or immunotherapy [1]. However, conventional anti-cancer strategies are associated with several adverse effects due to their toxicity also in non-transformed cells [1]. Since its discovery in 1995, tumor necrosis factor (TNF)-related apoptosis inducing ligand (TRAIL/Apo2L), a member of the TNF superfamily [2], has been involved in cancer biology. TRAIL induces apoptosis in malignant cells both in vitro [3] and in pre-clinical models of cancer [4,5]. Moreover, mutations in genes of the TRAIL pathway machinery are associated with human tumorigenesis [69]. TRAIL shows very little or no toxicity towards normal cells [4]. The reason why normal cells are resistant to TRAIL-induced apoptosis is not yet known, but there is evidence that non-neoplastic cells express high levels of decoy receptors (DcR)s for TRAIL, which could interfere with TRAIL signaling [10]. Nonetheless, cells derived from many human cancers, such as colorectal cancer (CRC), are resistant against TRAIL-driven apoptosis due to defects in the TRAIL signaling machinery (e.g., down-regulation and/or impaired functionality of TRAIL receptors, increased level of anti-apoptotic proteins) [11]. Restoring the susceptibility of CRC cells to TRAIL could thus help improve the ways we manage patients with this neoplasia.

In this article, we discuss the molecular mechanisms by which various natural products and synthetic compounds increase the susceptibility of CRC cells to TRAIL-induced apoptosis.

2. TRAIL Signaling Pathway and Mechanisms of TRAIL Resistance

TRAIL is known to bind five different receptors [12]. Two of these receptors, DR4 (also named TRAIL-R1) and DR5 (also named TRAIL-R2 or KILLER), are coined DRs due to the presence of a cytoplasmic death domain which allows triggering of apoptosis upon TRAIL binding [13]. DcR1, also termed TRAIL-R3 or TRID, and DcR2 (TRAIL-R4, TRUNDD) are expressed on the cell surface but lack a functional intracellular death domain. Both receptors confer protection against TRAIL-induced apoptosis rather than delivering apoptotic signals [14] and may be up-regulated by p53 or hypoxia in CRC cells [15,16]. The fifth TRAIL-receptor is osteoprotegerin, a secreted, low affinity receptor for TRAIL, suggested to mediate TRAIL resistance even though its physiological relevance is still a matter of debate [17]. Binding of TRAIL to DR4 and DR5 leads to caspase-8 activation through Fas-associated death domain (FADD) in the death-inducing signaling complex (DISC) [3]. Activated caspase-8 can induce apoptosis through the so-called extrinsic pathway by directly triggering downstream effector caspases (i.e., caspase-3, -6 and -7) [18]. DRs can also indirectly activate effector caspases through the intrinsic mitochondria-mediated apoptotic pathway [19]. In this later case, activated caspase-8 cleaves Bid thereby generating truncated Bid (tBid). tBid in turn translocates to the mitochondria where it interacts with Bax and Bak, thereby promoting the release of pro-apoptotic factors, such as cytochrome c and Smac/DIABLO [19]. Cytochrome c together with Apaf-1 and caspase-9 form a functional apoptosome that results in cleavage and activation of caspase 9 [20]. Active caspase-9 cleaves and activates executioner caspases (e.g., caspases-3) leading to apoptosis [19]. In parallel, Smac/DIABLO can bind to and dampen the activity of cellular inhibitor of apoptosis protein (IAP) members [21] which are powerful caspase inhibitors.

Many cancer cells are resistant to apoptotic signals triggered by TRAIL. The mechanism underlying TRAIL resistance is not fully understood, but it is supposed to rely on defects occurring at various levels in the TRAIL signaling pathway. The first mechanism involves DR expression/function. For example, malignant cells may have diminished expression of DR4 and DR5 due to defective p53 given that p53 directly regulates the transcription of both DRs through specific p53 binding sites [22]. Down-regulation of DR surface expression could be also due to impaired transport from ribosomes [23]. Plasma membrane microdomains enriched in cholesterol and glycosphingolipids (i.e., lipid rafts) play an important role in clustering or aggregating surface DRs into membrane complexes at specific sites and in the initiation of DR–induced apoptosis [24,25]. Therefore defective redistribution/relocalization of DR4 and DR5 in lipid rafts on the outer membrane could contribute further to the weak response of cells to TRAIL [26]. Finally, impaired DR functionality due either to loss-of-function mutations or epigenetic changes has been documented in neoplastic cells [27]. A second mechanism relates to defects in the expression/activity of molecules which control DISC function. These include down-regulation, degradation or inactivation of the initiator caspase-8 [28] as well as perturbations of the physiological level of cellular FLICE-like inhibitory protein (c-FLIP), a molecule that is co-recruited with caspase-8 to the DISC and inhibits caspase-8 release-dependent pro-apoptotic signals [29,30]. A low ratio caspase-8/c-FLIP has been described in many CRC cell lines and coupled with increased resistance to TRAIL-induced apoptosis [31]. Further defects involve intrinsic pathway-related pro-apoptotic proteins (e.g., Bim, Bid, Bax, Bak, PUMA) and molecules able to prevent mitochondria outer-membrane permeabilization and cytochrome c release, such as the anti-apoptotic Bcl-2 family members [e.g., Bcl-2, Bcl-xL and myeloid cell leukemia sequence 1 (Mcl-1)] [31]. Finally, resistance of cancer cells to TRAIL could be secondary to enhanced expression of IAPs. Indeed, members of the IAP family [e.g., X-linked IAP (XIAP), cellular IAP1 (c-IAP1), c-IAP2, survivin] prevent activation of both caspase-3 and caspase-9 thus inhibiting at the same time both the extrinsic and intrinsic apoptotic pathway [32]. IAPs, and particularly survivin and XIAP, are up-regulated in CRC [33,34] and thought to represent a major hurdle for TRAIL-based therapies in this neoplasia. Figure 1 summarizes the TRAIL signaling pathway and the above-mentioned mechanisms of TRAIL resistance.

3. TRAIL-Sensitizing Agents in CRC

In recent years numerous chemotherapeutics, natural products and newly synthesized molecules have been screened for their ability to restore TRAIL sensitivity in cancer cells with encouraging results. Table 1 summarizes the agents reported to overcome TRAIL resistance and synergize with TRAIL in inducing CRC cell death.

3.1. Chemotherapeutics–DNA Damage Agents

Chemotherapeutic drugs are widely used in clinical oncology and have been extensively studied as TRAIL sensitizing agents. Enhanced TRAIL DISC formation by several chemotherapeutics allows restoration of TRAIL-induced apoptosis in CRC cells. In particular, cisplatin, VP16 and 5-fluorouracil (5-FU) sensitize HCT-116 and SW480 cells to TRAIL mainly by increasing caspase-8 recruitment and activation at the DISC [39]. Enhanced FADD and pro-caspase-8 recruitment to the DISC as well as activation of the mitochondria-dependent death pathway underlie the TRAIL-sensitizing effect of cisplatin, 5-FU and doxorubicin in HT-29 cells [35,36]. Among the above-mentioned cytotoxic drugs, only 5-FU induces c-FLIP degradation both in HCT-116 [37,39] and HT-29 cells [36] thus contributing to TRAIL sensitization. Additionally, a recent paper indicated that 5-FU sensitizes HCT-116 cells to TRAIL through the induction of DR4 [38]. Knock-down experiments showed that 5-FU requires both p53-dependent and -independent mechanisms to efficiently trigger apoptosis as well as a functional FADD/caspase-8/Bid axis [38]. Otherwise, the specific cyclo-oxygenase-2 inhibitor DuP-697 overcomes TRAIL resistance in HT-29 cells by inducing DR5 clustering at the cell surface and the redistribution of the DISC components (i.e., DR5, FADD, and pro-caspase-8) in peculiar lipid rafts called caveolae [25]. TRAIL also synergizes with irinotecan (CPT-11), an analog of the DNA topoisomerase I inhibitor camptothecin, in inducing apoptosis in HCT-116 cells [40]. This later event associates with DR4 and DR5 up-regulation and enhanced degradation of p21, a negative regulator of the apoptotic process. Semisynthetic retinoid fenretinide promotes DR5 up-regulation through the endoplasmic reticulum (ER) stress-related CAAT/enhancer-binding protein homologous protein (CHOP) thus sensitizing CRC cells to TRAIL-driven apoptosis [41]. More recently, lapatinib, a dual inhibitor of EGFR and HER2, was reported to increase TRAIL-induced cell death in CRC cells by promoting JNK/c-Jun-driven DR over-expression [42]. Modulation of molecules involved in the intrinsic/mitochondrial pathway accounts for the sensitization of TRAIL resistant CRC cells to sunitinib, a tyrosine kinase inhibitor, and oxaliplatin, a third-generation platinum agent [43,44]. In particular, sunitinib decreases the expression of the anti-apoptotic proteins Mcl-1 and XIAP [43] while the oxaliplatin-mediated TRAIL sensitization increases phosphorylation of Bcl-xL, thus reducing the anti-apoptotic activity of this protein [44]. However, it is noteworthy to underline that CRC cells harboring functional p53 (e.g., HCT-116) fail to trigger apoptosis upon oxaliplatin and TRAIL treatments due to a strong p53-dependent, oxaliplatin-mediated, up-regulation of DcR1 [75].

3.2. Natural Products

Since chemotherapeutic drugs lead to DNA damage in cells, combination treatment of TRAIL with these cytotoxic agents, even at lower doses than those used in conventional chemotherapy, can result in severe side effects [76]. Therefore in the last decade, numerous researchers have focused attention on natural products, which exhibit TRAIL sensitizing effects at concentrations easy to obtain and which appear to be safe [77].

3.2.1. Polyphenols and Related Compounds

Among natural products, polyphenols, and in particular the subgroup of flavonoids, constitute the major category of molecules used in combination with TRAIL in CRC cells. Food polyphenols sensitize CRC cells to TRAIL-driven cell death mainly by increasing the expression of DR5 and to a lesser extent DR4. One such compound is apigenin, a flavonoid widely distributed in many fruits and vegetables. Apigenin increases DR5 expression and synergistically acts with TRAIL in inducing DLD-1 cell death [45]. DR5 up-regulation also accounts for the TRAIL-sensitizing effect of both baicalein and isoliquiritigenin in SW480 and HT-29 cells, respectively [46,47]. Kaempferol, a flavonoid isolated from many plant sources (e.g., tea, broccoli, propolis, grapefruit), also shows TRAIL sensitizing effect in SW480 cells. Kaempferol up-regulates the expression of both DR4 and DR5 but knock-down of DR5 and not DR4 by siRNA effectively abrogates apoptosis induced by the combined treatment of this compound with TRAIL [48]. DR modulation partly underlies the TRAIL sensitizing effect of quercetin and wogonin [49,50]. Quercetin, a flavonoid found in vegetables, fruits and tea, aggregates DRs into lipid rafts thus facilitating the DISC formation without increasing DR expression at the cell surface [49]. Wogonin, an active ingredient of Chinese herb medicine Scutellaria baicalensis, up-regulates DR5 and decreases c-FLIP expression in HT-29 cells [50]. The TRAIL-sensitizing properties of other tested polyphenols are associated with modulation of different intracellular pro- and anti-apoptotic proteins. For example, cycloartenyl ferulate, a phenolic compound present in γ-oryzanol (a component of the rice bran oil), up-regulates DRs and increases caspase-8 activation as well as Bid cleavage leading to mitochondrial pathway activation in both SW480 and SW620 cells [51]. In the same cells, the flavonolignan silibinin used in combination with TRAIL synergistically induces cell death through both a p53-independent DR5 up-regulation and down-regulation of Mcl-1 and XIAP [52]. Another polyphenol recently reported to have TRAIL sensitizing properties in CRC cells is gossypol. Gossypol is derived from cottonseed oil and commonly designated as a BH3 mimetic due to its ability to bind the BH3 binding pockets of Bcl-2 and Bcl-xL thus inhibiting their function [78]. Beside the down-regulation of anti-apoptotic proteins involved in TRAIL resistance (e.g., Bcl-2, Bcl-xL, survivin), this molecule potentiates TRAIL-driven apoptosis in HCT-116 cells by increasing DR5 expression through the ROS-mediated induction of CHOP [53]. In the same cells, the ROS-CHOP-mediated up-regulation of DR4 and DR5 is needed for TRAIL sensitization by cardamonin. The potentiation of TRAIL-induced apoptosis by this chalcone also correlates with DcR1 down-regulation and modulation of both pro-apoptotic (i.e., Bax) and pro-survival (e.g., Bcl-2, c-IAP1) intracellular proteins [54].

3.2.2. Terpenoids

Terpenoids are one of the largest families of natural products. Terpenoids contained in many plants, and in particular the subclasses of monoterpenes, diterpenes and tetraterpenes (including carotenoids), play a role in traditional herbal medicine and are currently under investigation for their antitumor activities [79,80]. Zerumbone, a sesquiterpene isolated from the rhizome of a tropical ginger, shows anticancer activity against different tumor cell types but very little or no cytotoxic effect on normal human endothelial cells and dermal fibroblasts [81]. In HCT-116 cells, which possess a functional p53, treatment with zerumbone generates ROS and subsequently activates the MAPK ERK1/2 leading to DR4/DR5 induction and TRAIL sensitization [55]. Interestingly, zerumbone-mediated DR up-regulation as well as the increased TRAIL-induced apoptosis is abolished by ROS scavenging compounds thus suggesting a key role of free radicals in these processes. Additionally, zerumbone markedly down-regulates the expression of c-FLIP without affecting other anti-apoptotic proteins (i.e., Bcl-2, Bcl-xL, XIAP, survivin) [55]. However, zerumbone shows no sensitizing effect on HT-29 cells that express mutant p53 [55]. An increased susceptibility to TRAIL-induced apoptosis is observed in both HCT-116 and HT-29 cells when treated with nimbolide, a tetranortriterpenoid isolated from the leaves and flowers of the tree Azadirachta indica [56]. Several mechanisms are proposed for this effect. First, nimbolide up-regulates the expression of DRs through ROS production and MAPK pathway activation in a p53-independent fashion. This up-regulation is due to the increase of both transcription and protein stability and is critical for the TRAIL sensitization by this compound. Indeed, knock-down of DRs, and in particular of DR5, significantly hampers the TRAIL-sensitizing effect of nimbolide. Second, nimbolide up-regulates Bax and potentiates the intrinsic pathway of apoptosis. Finally, nimbolide down-regulates the expression of critical anti-apoptotic proteins (i.e., c-FLIP, Bcl-2, Bcl-xL, c-IAP1, c-IAP2, survivin and XIAP) [56]. TRAIL-sensitizing properties are also reported for halocynthiaxanthin, a dietary carotenoid contained in oysters and sea squirts, in DLD-1 and HT-29 cells. This effect is associated with DR5 up-regulation further confirming the key role of this DR in the TRAIL apoptotic pathway [57].

3.2.3. Other Natural Products

TRAIL-sensitizing effects in CRC cells are also reported for other natural products not belonging either to polyphenols or terpenoids, such as vitamin-related compounds. Among these compounds γ-Tocotrienol (γ-T3), an unsaturated tocopherol found in palm oil, rice bran, barley, and wheat germ, enhances TRAIL-induced apoptosis in HCT-116 cells through ERK1/2-driven ROS-dependent DR4/DR5 up-regulation [58]. Despite p53 not being activated by γ-T3, it is required in the DR up-regulation process as evidenced by the failure of γ-T3 to induce DRs both in p53 knockout HCT-116 cells and in the p53 mutated HT-29 cells [58]. A different mechanism, independent of the modulation of CHOP, p53, Bax and mitogen-activated protein kinases (MAPK), underlies both DR4 and DR5 up-regulation in CRC cells by garcinol, a compound derived from the dried rind of the fruit Garcinia indica. Moreover, garcinol diminishes expression of c-FLIP, Bcl-2, survivin and XIAP [59]. The down-regulation of anti-apoptotic proteins also account for the sensitization of CRC cells to TRAIL by combretastatin A-4 and the plant stress hormone methyl jasmonate [60,61]. Combined treatment of HT-29 cells with TRAIL and the polyunsaturated fatty acid docosahexaenoic acid (DHA) markedly increases cell death compared to the agents used alone [62]. On the molecular level, DHA dose-dependently induces ROS production, enhances caspase-8 activation and the formation of tBid [62]. HT-29 cells are sensitized to TRAIL-induced cell death also when exposed to diosgenin, a steroid saponin present in fenugreek (Trigonella foenum graecum) and other plants, through the increase of DR5 expression [63]. Zhang and colleagues demonstrated that the combination of TRAIL and the vitamin A-related compound all-trans-retinyl acetate (RAc) restores apoptosis in APC-deficient premalignant cells in vivo without affecting normal cells [64]. A similar effect was observed in vitro as RAc sensitizes human colon epithelial cells (NCM356) with altered APC function to TRAIL. Specifically, in these cells, RAc-mediated TRAIL sensitization is associated with DR up-regulation and suppression of both DcR1 and DcR2 thus leading to enhanced caspase-8 activation [64].

3.3. Other TRAIL-Sensitizing Agents

Other TRAIL-sensitizing molecules discussed in this article include proteasome inhibitors, ER stress inducers and molecules controlling p53, AMP-activated protein kinase, protein kinase C and the molecular chaperone Hsp90.

3.3.1. Proteasome Inhibitors

Inhibition of the proteasome, a multicatalytic enzyme complex that recognizes and degrades poly-ubiquitinated proteins, has been proposed as a possible therapeutic strategy to manage human malignancies [82]. In this context, the proteasome inhibitor MG132 cooperates with TRAIL in inducing HCT-116 apoptosis through DR5 up-regulation [65]. Another proteasome inhibitor, PS-341, synergizes with TRAIL to enhance HCT-116 and HC4 cell death through DR up-regulation and the following activation of both extrinsic and intrinsic apoptotic pathways [66].

3.3.2. ER Stress Inducers

Disruption of ER homeostasis due to various stress conditions leads to accumulation and aggregation of unfolded and/or misfolded proteins in the lumen of this organelle and to activation of an ER stress response termed unfolded protein response [83]. A large body of evidence indicates that ER stress inducing agents exert antitumor properties [84]. 15-Deoxy-delta (12,14)-prostaglandin J2 (15dPGJ2), a known ER stress inducer, increases DR5 expression thus sensitizing HCT-116 cells to TRAIL-induced apoptosis. DR5 up-regulation by 15dPGJ(2) is independent of PPAR-γ and p53 but relies on ROS-mediated CHOP induction [67]. Likewise, ROS and CHOP are critical for dibenzylideneacetone (DBA) to sensitize HCT-116 to TRAIL through DR4 and DR5 induction and down-regulation of anti-apoptotic proteins [68]. Moreover, DcR2 but not DcR1 is decreased by DBA probably contributing to TRAIL sensitization [68]. ER stress is also one of the mechanisms by which 2-Methoxy-5-Amino-N-Hydroxybenzamide (termed 2–14), a derivative of mesalamine, restores the susceptibility of CRC cells to TRAIL [69]. We have also shown that 2–14 inhibits CRC cell growth both in vitro and in vivo without affecting the proliferation of normal colonic cells, intraepithelial lymphocytes and fibroblasts [85]. The 2–14-mediated TRAIL sensitization is seen in the p53-mutant DLD-1 and HT-29 cells and this phenomenon is in part dependent on ERK1/2-driven CHOP-mediated DR5 up-regulation [69]. Additionally, 2–14 promotes the proteasome-mediated degradation of survivin, a major hurdle to TRAIL signaling in these CRC cell lines [69]. Both CHOP-mediated DR5 increase and survivin down-regulation are also the major mechanisms by which dipyridamole, a thromboxane synthase inhibitor widely used as an antiplatelet, sensitizes SW480 cells to TRAIL [70].

3.3.3. Molecules Controlling p53, AMP-Activated Protein Kinase, Protein Kinase C and the Molecular Chaperone Hsp90

p53 activation can contribute to sensitize tumor cells to TRAIL-induced apoptosis [86]. Nutlin-3, a cis-imidazoline derivative, interferes with Mdm2-mediated p53 degradation with the downstream effect of promoting p53-dependent up-regulation of DR5 and enhancing HCT-116 susceptibility to TRAIL. The pro-apoptotic effect of nutlin-3 is also mediated by Bcl-2 and XIAP down-regulation [71]. A p53-dependent TRAIL sensitization is also reported in HCT-116 cells treated with 5-Aminoimidazole-4-carboxamide riboside (AICAR), an activator of AMP-activated protein kinase [72]. Co-treatment of these cells with AICAR and TRAIL reduces Bcl-2 expression and increases Bid cleavage thus potentiating the intrinsic mitochondrial pathway [72]. Furthermore, rottlerin and 17-allylamino-17-demethoxygeldanamycin (17-AAG), known to inhibit the protein kinase C and the molecular chaperone Hsp90 respectively, are effective in overcoming TRAIL resistance in HT-29 and RKO cells. This is achieved via direct effects at the level of the mitochondria and by reducing the expression of IAPs, and in particular XIAP [73,74].

4. Conclusions

Accumulating evidence indicates TRAIL is a promising anti-cancer agent due to its ability to selectively induce apoptosis in transformed cells. However, cancer cells including CRC cells often develop resistance to TRAIL-induced apoptosis and this issue has strongly limited the use of TRAIL-based therapies. Chemotherapeutic drugs are reported to overcome resistance of CRC cells to TRAIL but unfortunately their wide use is limited by the risk of side-effects. Therefore, the validation of effective TRAIL-sensitizing agents which exhibit diminished toxicity is worth pursuing. Several natural and synthetic compounds, which revert various cellular defects contributing to TRAIL resistance, have already been tested with success in CRC cell systems. An important issue relates to the choice of which compound should be used. Since resistance of CRC cells to TRAIL can rely on the presence of multiple defects, we can speculate that compounds that target more pathways simultaneously may have higher potential for anticancer therapy. It would be also useful to better characterize such defects in single patients in order to personalize TRAIL-based therapy. Another concern deals with compounds which increase p53 expression. Indeed, up-regulation of DcRs by p53 may result in a significantly delay of TRAIL-induced killing thus limiting the use of such agents in CRC tumors bearing functional p53. Additionally, hypoxic conditions, easily found in solid tumors, may render CRC cells resistant to some therapeutic agents and attenuate TRAIL-induced cell death. All these drawbacks should be taken into account before designing combined therapies involving TRAIL. Further experimentation is however needed to confirm the in vitro data in pre-clinical models of CRC and ascertain the profile of safety and tolerability of such compounds.

Acknowledgements

This work received support from the “Fondazione Umberto di Mario ONLUS”, Rome, AIRC (IG-9148 to GM and MFAG-12108 to CS), and Giuliani SpA, Milan, Italy.

  • Conflict of InterestThe authors declare no conflict of interest.

References

  1. Johnstone, R.W.; Ruefli, A.A.; Lowe, S.W. Apoptosis: A link between cancer genetics and chemotherapy. Cell 2002, 108, 153–164. [Google Scholar]
  2. Wiley, S.R.; Schooley, K.; Smolak, P.J.; Din, W.S.; Huang, C.P.; Nicholl, J.K.; Sutherland, G.R.; Smith, T.D.; Rauch, C.; Smith, C.A.; et al. Identification and characterization of a new member of the tnf family that induces apoptosis. Immunity 1995, 3, 673–682. [Google Scholar]
  3. Almasan, A.; Ashkenazi, A. Apo2l/trail: Apoptosis signaling, biology, and potential for cancer therapy. Cytokine Growth Factor Rev 2003, 14, 337–348. [Google Scholar]
  4. Ashkenazi, A.; Pai, R.C.; Fong, S.; Leung, S.; Lawrence, D.A.; Marsters, S.A.; Blackie, C.; Chang, L.; McMurtrey, A.E.; Hebert, A.; et al. Safety and antitumor activity of recombinant soluble apo2 ligand. J. Clin. Invest 1999, 104, 155–162. [Google Scholar]
  5. Walczak, H.; Miller, R.E.; Ariail, K.; Gliniak, B.; Griffith, T.S.; Kubin, M.; Chin, W.; Jones, J.; Woodward, A.; Le, T.; et al. Tumoricidal activity of tumor necrosis factor-related apoptosis-inducing ligand in vivo. Nat. Med 1999, 5, 157–163. [Google Scholar]
  6. Hopkins-Donaldson, S.; Bodmer, J.L.; Bourloud, K.B.; Brognara, C.B.; Tschopp, J.; Gross, N. Loss of caspase-8 expression in highly malignant human neuroblastoma cells correlates with resistance to tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis. Cancer Res 2000, 60, 4315–4319. [Google Scholar]
  7. Lee, S.H.; Shin, M.S.; Kim, H.S.; Lee, H.K.; Park, W.S.; Kim, S.Y.; Lee, J.H.; Han, S.Y.; Park, J.Y.; Oh, R.R.; et al. Somatic mutations of trail-receptor 1 and trail-receptor 2 genes in non-hodgkin’s lymphoma. Oncogene 2001, 20, 399–403. [Google Scholar]
  8. Lee, S.H.; Shin, M.S.; Kim, H.S.; Lee, H.K.; Park, W.S.; Kim, S.Y.; Lee, J.H.; Han, S.Y.; Park, J.Y.; Oh, R.R.; et al. Alterations of the dr5/trail receptor 2 gene in non-small cell lung cancers. Cancer Res 1999, 59, 5683–5686. [Google Scholar]
  9. Fisher, M.J.; Virmani, A.K.; Wu, L.; Aplenc, R.; Harper, J.C.; Powell, S.M.; Rebbeck, T.R.; Sidransky, D.; Gazdar, A.F.; El-Deiry, W.S. Nucleotide substitution in the ectodomain of trail receptor dr4 is associated with lung cancer and head and neck cancer. Clin. Cancer Res 2001, 7, 1688–1697. [Google Scholar]
  10. Strater, J.; Hinz, U.; Walczak, H.; Mechtersheimer, G.; Koretz, K.; Herfarth, C.; Moller, P.; Lehnert, T. Expression of trail and trail receptors in colon carcinoma: Trail-r1 is an independent prognostic parameter. Clin. Cancer Res 2002, 8, 3734–3740. [Google Scholar]
  11. Zhang, L.; Fang, B. Mechanisms of resistance to trail-induced apoptosis in cancer. Cancer Gene Ther 2005, 12, 228–237. [Google Scholar]
  12. LeBlanc, H.N.; Ashkenazi, A. Apo2l/trail and its death and decoy receptors. Cell Death Differ 2003, 10, 66–75. [Google Scholar]
  13. Carlo-Stella, C.; Lavazza, C.; Locatelli, A.; Vigano, L.; Gianni, A.M.; Gianni, L. Targeting trail agonistic receptors for cancer therapy. Clin. Cancer Res 2007, 13, 2313–2317. [Google Scholar]
  14. Sheridan, J.P.; Marsters, S.A.; Pitti, R.M.; Gurney, A.; Skubatch, M.; Baldwin, D.; Ramakrishnan, L.; Gray, C.L.; Baker, K.; Wood, W.I.; et al. Control of trail-induced apoptosis by a family of signaling and decoy receptors. Science 1997, 277, 818–821. [Google Scholar]
  15. Pei, G.T.; Wu, C.W.; Lin, W.W. Hypoxia-induced decoy receptor 2 gene expression is regulated via a hypoxia-inducible factor 1alpha-mediated mechanism. Biochem. Biophys. Res. Commun 2010, 391, 1274–1279. [Google Scholar]
  16. Meng, R.D.; McDonald, E.R., 3rd; Sheikh, M.S.; Fornace, A.J., Jr.; El-Deiry, W.S. The trail decoy receptor trundd (dcr2, trail-r4) is induced by adenovirus-p53 overexpression and can delay trail-, p53-, and killer/dr5-dependent colon cancer apoptosis. Mol. Ther 2000, 1, 130–144. [Google Scholar]
  17. De Toni, E.N.; Thieme, S.E.; Herbst, A.; Behrens, A.; Stieber, P.; Jung, A.; Blum, H.; Goke, B.; Kolligs, F.T. Opg is regulated by beta-catenin and mediates resistance to trail-induced apoptosis in colon cancer. Clin. Cancer Res 2008, 14, 4713–4718. [Google Scholar]
  18. Scaffidi, C.; Fulda, S.; Srinivasan, A.; Friesen, C.; Li, F.; Tomaselli, K.J.; Debatin, K.M.; Krammer, P.H.; Peter, M.E. Two cd95 (apo-1/fas) signaling pathways. EMBO J 1998, 17, 1675–1687. [Google Scholar]
  19. Ashkenazi, A.; Dixit, V.M. Death receptors: Signaling and modulation. Science 1998, 281, 1305–1308. [Google Scholar]
  20. Zou, H.; Henzel, W.J.; Liu, X.; Lutschg, A.; Wang, X. Apaf-1, a human protein homologous to c. Elegans CED-4, participates in cytochrome c-dependent activation of caspase-3. Cell 1997, 90, 405–413. [Google Scholar]
  21. Verhagen, A.M.; Ekert, P.G.; Pakusch, M.; Silke, J.; Connolly, L.M.; Reid, G.E.; Moritz, R.L.; Simpson, R.J.; Vaux, D.L. Identification of diablo, a mammalian protein that promotes apoptosis by binding to and antagonizing iap proteins. Cell 2000, 102, 43–53. [Google Scholar]
  22. Elrod, H.A.; Sun, S.Y. Modulation of death receptors by cancer therapeutic agents. Cancer Biol. Ther 2008, 7, 163–173. [Google Scholar]
  23. Jin, Z.; McDonald, E.R., 3rd; Dicker, D.T.; El-Deiry, W.S. Deficient tumor necrosis factor-related apoptosis-inducing ligand (trail) death receptor transport to the cell surface in human colon cancer cells selected for resistance to trail-induced apoptosis. J. Biol. Chem 2004, 279, 35829–35839. [Google Scholar]
  24. Muppidi, J.R.; Tschopp, J.; Siegel, R.M. Life and death decisions: Secondary complexes and lipid rafts in tnf receptor family signal transduction. Immunity 2004, 21, 461–465. [Google Scholar]
  25. Martin, S.; Phillips, D.C.; Szekely-Szucs, K.; Elghazi, L.; Desmots, F.; Houghton, J.A. Cyclooxygenase-2 inhibition sensitizes human colon carcinoma cells to trail-induced apoptosis through clustering of dr5 and concentrating death-inducing signaling complex components into ceramide-enriched caveolae. Cancer Res 2005, 65, 11447–11458. [Google Scholar]
  26. Delmas, D.; Rebe, C.; Micheau, O.; Athias, A.; Gambert, P.; Grazide, S.; Laurent, G.; Latruffe, N.; Solary, E. Redistribution of cd95, dr4 and dr5 in rafts accounts for the synergistic toxicity of resveratrol and death receptor ligands in colon carcinoma cells. Oncogene 2004, 23, 8979–8986. [Google Scholar]
  27. Pai, S.I.; Wu, G.S.; Ozoren, N.; Wu, L.; Jen, J.; Sidransky, D.; El-Deiry, W.S. Rare loss-of-function mutation of a death receptor gene in head and neck cancer. Cancer Res 1998, 58, 3513–3518. [Google Scholar]
  28. Van Geelen, C.M.; Pennarun, B.; Ek, W.B.; Le, P.T.; Spierings, D.C.; de Vries, E.G.; de Jong, S. Downregulation of active caspase 8 as a mechanism of acquired trail resistance in mismatch repair-proficient colon carcinoma cell lines. Int. J. Oncol 2010, 37, 1031–1041. [Google Scholar]
  29. Micheau, O.; Thome, M.; Schneider, P.; Holler, N.; Tschopp, J.; Nicholson, D.W.; Briand, C.; Grutter, M.G. The long form of flip is an activator of caspase-8 at the fas death-inducing signaling complex. J. Biol. Chem 2002, 277, 45162–45171. [Google Scholar]
  30. Chang, D.W.; Xing, Z.; Pan, Y.; Algeciras-Schimnich, A.; Barnhart, B.C.; Yaish-Ohad, S.; Peter, M.E.; Yang, X. C-flip(l) is a dual function regulator for caspase-8 activation and cd95-mediated apoptosis. EMBO J 2002, 21, 3704–3714. [Google Scholar]
  31. Van Geelen, C.M.; de Vries, E.G.; de Jong, S. Lessons from trail-resistance mechanisms in colorectal cancer cells: Paving the road to patient-tailored therapy. Drug Resist. Updat 2004, 7, 345–358. [Google Scholar]
  32. Deveraux, Q.L.; Reed, J.C. Iap family proteins—Suppressors of apoptosis. Genes Dev 1999, 13, 239–252. [Google Scholar]
  33. Kim, P.J.; Plescia, J.; Clevers, H.; Fearon, E.R.; Altieri, D.C. Survivin and molecular pathogenesis of colorectal cancer. Lancet 2003, 362, 205–209. [Google Scholar]
  34. Takeuchi, H.; Kim, J.; Fujimoto, A.; Umetani, N.; Mori, T.; Bilchik, A.; Turner, R.; Tran, A.; Kuo, C.; Hoon, D.S. X-linked inhibitor of apoptosis protein expression level in colorectal cancer is regulated by hepatocyte growth factor/c-met pathway via akt signaling. Clin. Cancer Res 2005, 11, 7621–7628. [Google Scholar]
  35. Lacour, S.; Hammann, A.; Wotawa, A.; Corcos, L.; Solary, E.; Dimanche-Boitrel, M.T. Anticancer agents sensitize tumor cells to tumor necrosis factor-related apoptosis-inducing ligand-mediated caspase-8 activation and apoptosis. Cancer Res 2001, 61, 1645–1651. [Google Scholar]
  36. Lacour, S.; Micheau, O.; Hammann, A.; Drouineaud, V.; Tschopp, J.; Solary, E.; Dimanche-Boitrel, M.T. Chemotherapy enhances tnf-related apoptosis-inducing ligand disc assembly in ht29 human colon cancer cells. Oncogene 2003, 22, 1807–1816. [Google Scholar]
  37. Galligan, L.; Longley, D.B.; McEwan, M.; Wilson, T.R.; McLaughlin, K.; Johnston, P.G. Chemotherapy and trail-mediated colon cancer cell death: The roles of p53, trail receptors, and c-flip. Mol. Cancer Ther 2005, 4, 2026–2036. [Google Scholar]
  38. Henry, R.E.; Andrysik, Z.; Paris, R.; Galbraith, M.D.; Espinosa, J.M. A dr4:Tbid axis drives the p53 apoptotic response by promoting oligomerization of poised bax. EMBO J 2012, 31, 1266–1278. [Google Scholar]
  39. Morizot, A.; Merino, D.; Lalaoui, N.; Jacquemin, G.; Granci, V.; Iessi, E.; Lanneau, D.; Bouyer, F.; Solary, E.; Chauffert, B.; et al. Chemotherapy overcomes trail-r4-mediated trail resistance at the disc level. Cell Death Differ 2011, 18, 700–711. [Google Scholar]
  40. Xiang, H.; Fox, J.A.; Totpal, K.; Aikawa, M.; Dupree, K.; Sinicropi, D.; Lowe, J.; Escandon, E. Enhanced tumor killing by apo2l/trail and cpt-11 co-treatment is associated with p21 cleavage and differential regulation of apo2l/trail ligand and its receptors. Oncogene 2002, 21, 3611–3619. [Google Scholar]
  41. Kouhara, J.; Yoshida, T.; Nakata, S.; Horinaka, M.; Wakada, M.; Ueda, Y.; Yamagishi, H.; Sakai, T. Fenretinide up-regulates dr5/trail-r2 expression via the induction of the transcription factor chop and combined treatment with fenretinide and trail induces synergistic apoptosis in colon cancer cell lines. Int. J. Oncol 2007, 30, 679–687. [Google Scholar]
  42. Dolloff, N.G.; Mayes, P.A.; Hart, L.S.; Dicker, D.T.; Humphreys, R.; El-Deiry, W.S. Off-target lapatinib activity sensitizes colon cancer cells through trail death receptor up-regulation. Sci. Transl. Med 2011, 3. [Google Scholar] [CrossRef]
  43. Ding, W.; Cai, T.; Zhu, H.; Wu, R.; Tu, C.; Yang, L.; Lu, W.; He, Q.; Yang, B. Synergistic antitumor effect of trail in combination with sunitinib in vitro and in vivo. Cancer Lett 2010, 293, 158–166. [Google Scholar]
  44. El Fajoui, Z.; Toscano, F.; Jacquemin, G.; Abello, J.; Scoazec, J.Y.; Micheau, O.; Saurin, J.C. Oxaliplatin sensitizes human colon cancer cells to trail through jnk-dependent phosphorylation of bcl-xl. Gastroenterology 2011, 141, 663–673. [Google Scholar]
  45. Horinaka, M.; Yoshida, T.; Shiraishi, T.; Nakata, S.; Wakada, M.; Sakai, T. The dietary flavonoid apigenin sensitizes malignant tumor cells to tumor necrosis factor-related apoptosis-inducing ligand. Mol. Cancer Ther 2006, 5, 945–951. [Google Scholar]
  46. Taniguchi, H.; Yoshida, T.; Horinaka, M.; Yasuda, T.; Goda, A.E.; Konishi, M.; Wakada, M.; Kataoka, K.; Yoshikawa, T.; Sakai, T. Baicalein overcomes tumor necrosis factor-related apoptosis-inducing ligand resistance via two different cell-specific pathways in cancer cells but not in normal cells. Cancer Res 2008, 68, 8918–8927. [Google Scholar]
  47. Yoshida, T.; Horinaka, M.; Takara, M.; Tsuchihashi, M.; Mukai, N.; Wakada, M.; Sakai, T. Combination of isoliquiritigenin and tumor necrosis factor-related apoptosis-inducing ligand induces apoptosis in colon cancer ht29 cells. Environ. Health Prev. Med 2008, 13, 281–287. [Google Scholar]
  48. Yoshida, T.; Konishi, M.; Horinaka, M.; Yasuda, T.; Goda, A.E.; Taniguchi, H.; Yano, K.; Wakada, M.; Sakai, T. Kaempferol sensitizes colon cancer cells to trail-induced apoptosis. Biochem. Biophys. Res. Commun 2008, 375, 129–133. [Google Scholar]
  49. Psahoulia, F.H.; Drosopoulos, K.G.; Doubravska, L.; Andera, L.; Pintzas, A. Quercetin enhances trail-mediated apoptosis in colon cancer cells by inducing the accumulation of death receptors in lipid rafts. Mol. Cancer Ther 2007, 6, 2591–2599. [Google Scholar]
  50. Ding, J.; Polier, G.; Kohler, R.; Giaisi, M.; Krammer, P.H.; Li-Weber, M. Wogonin and related natural flavones overcome tumor necrosis factor-related apoptosis-inducing ligand (trail) protein resistance of tumors by down-regulation of c-flip protein and up-regulation of trail receptor 2 expression. J. Biol. Chem 2012, 287, 641–649. [Google Scholar]
  51. Kong, C.K.; Lam, W.S.; Chiu, L.C.; Ooi, V.E.; Sun, S.S.; Wong, Y.S. A rice bran polyphenol, cycloartenyl ferulate, elicits apoptosis in human colorectal adenocarcinoma sw480 and sensitizes metastatic sw620 cells to trail-induced apoptosis. Biochem. Pharmacol 2009, 77, 1487–1496. [Google Scholar]
  52. Kauntz, H.; Bousserouel, S.; Gosse, F.; Raul, F. Silibinin triggers apoptotic signaling pathways and autophagic survival response in human colon adenocarcinoma cells and their derived metastatic cells. Apoptosis 2011, 16, 1042–1053. [Google Scholar]
  53. Sung, B.; Ravindran, J.; Prasad, S.; Pandey, M.K.; Aggarwal, B.B. Gossypol induces death receptor-5 through activation of the ros-erk-chop pathway and sensitizes colon cancer cells to trail. J. Biol. Chem 2010, 285, 35418–35427. [Google Scholar]
  54. Yadav, V.R.; Prasad, S.; Aggarwal, B.B. Cardamonin sensitizes tumour cells to trail through ros- and chop-mediated up-regulation of death receptors and down-regulation of survival proteins. Br. J. Pharmacol 2012, 165, 741–753. [Google Scholar]
  55. Yodkeeree, S.; Sung, B.; Limtrakul, P.; Aggarwal, B.B. Zerumbone enhances trail-induced apoptosis through the induction of death receptors in human colon cancer cells: Evidence for an essential role of reactive oxygen species. Cancer Res 2009, 69, 6581–6589. [Google Scholar]
  56. Gupta, S.C.; Reuter, S.; Phromnoi, K.; Park, B.; Hema, P.S.; Nair, M.; Aggarwal, B.B. Nimbolide sensitizes human colon cancer cells to trail through reactive oxygen species- and erk-dependent up-regulation of death receptors, p53, and bax. J. Biol. Chem 2011, 286, 1134–1146. [Google Scholar]
  57. Yoshida, T.; Maoka, T.; Das, S.K.; Kanazawa, K.; Horinaka, M.; Wakada, M.; Satomi, Y.; Nishino, H.; Sakai, T. Halocynthiaxanthin and peridinin sensitize colon cancer cell lines to tumor necrosis factor-related apoptosis-inducing ligand. Mol. Cancer Res 2007, 5, 615–625. [Google Scholar]
  58. Kannappan, R.; Ravindran, J.; Prasad, S.; Sung, B.; Yadav, V.R.; Reuter, S.; Chaturvedi, M.M.; Aggarwal, B.B. Gamma-tocotrienol promotes trail-induced apoptosis through reactive oxygen species/extracellular signal-regulated kinase/p53-mediated upregulation of death receptors. Mol. Cancer Ther 2010, 9, 2196–2207. [Google Scholar]
  59. Prasad, S.; Ravindran, J.; Sung, B.; Pandey, M.K.; Aggarwal, B.B. Garcinol potentiates trail-induced apoptosis through modulation of death receptors and antiapoptotic proteins. Mol. Cancer Ther 2010, 9, 856–868. [Google Scholar]
  60. Zhang, C.; Wu, R.; Zhu, H.; Hu, Y.Z.; Jiang, H.; Lin, N.M.; He, Q.J.; Yang, B. Enhanced anti-tumor activity by the combination of trail/apo-2l and combretastatin a-4 against human colon cancer cells via induction of apoptosis in vitro and in vivo. Cancer Lett 2011, 302, 11–19. [Google Scholar]
  61. Raviv, Z.; Zilberberg, A.; Cohen, S.; Reischer-Pelech, D.; Horrix, C.; Berger, M.R.; Rosin-Arbesfeld, R.; Flescher, E. Methyl jasmonate down-regulates survivin expression and sensitizes colon carcinoma cells towards trail-induced cytotoxicity. Br. J. Pharmacol 2011, 164, 1433–1444. [Google Scholar]
  62. Vaculova, A.; Hofmanova, J.; Andera, L.; Kozubik, A. Trail and docosahexaenoic acid cooperate to induce ht-29 colon cancer cell death. Cancer Lett 2005, 229, 43–48. [Google Scholar]
  63. Lepage, C.; Leger, D.Y.; Bertrand, J.; Martin, F.; Beneytout, J.L.; Liagre, B. Diosgenin induces death receptor-5 through activation of p38 pathway and promotes trail-induced apoptosis in colon cancer cells. Cancer Lett 2011, 301, 193–202. [Google Scholar]
  64. Zhang, L.; Ren, X.; Alt, E.; Bai, X.; Huang, S.; Xu, Z.; Lynch, P.M.; Moyer, M.P.; Wen, X.F.; Wu, X. Chemoprevention of colorectal cancer by targeting apc-deficient cells for apoptosis. Nature 2010, 464, 1058–1061. [Google Scholar]
  65. He, Q.; Huang, Y.; Sheikh, M.S. Proteasome inhibitor mg132 upregulates death receptor 5 and cooperates with apo2l/trail to induce apoptosis in bax-proficient and -deficient cells. Oncogene 2004, 23, 2554–2558. [Google Scholar]
  66. Johnson, T.R.; Stone, K.; Nikrad, M.; Yeh, T.; Zong, W.X.; Thompson, C.B.; Nesterov, A.; Kraft, A.S. The proteasome inhibitor ps-341 overcomes trail resistance in bax and caspase 9-negative or bcl-xl overexpressing cells. Oncogene 2003, 22, 4953–4963. [Google Scholar]
  67. Su, R.Y.; Chi, K.H.; Huang, D.Y.; Tai, M.H.; Lin, W.W. 15-deoxy-delta12,14-prostaglandin j2 up-regulates death receptor 5 gene expression in hct116 cells: Involvement of reactive oxygen species and c/ebp homologous transcription factor gene transcription. Mol. Cancer Ther 2008, 7, 3429–3440. [Google Scholar]
  68. Prasad, S.; Yadav, V.R.; Ravindran, J.; Aggarwal, B.B. Ros and chop are critical for dibenzylideneacetone to sensitize tumor cells to trail through induction of death receptors and downregulation of cell survival proteins. Cancer Res 2011, 71, 538–549. [Google Scholar]
  69. Stolfi, C.; Caruso, R.; Franze, E.; Rizzo, A.; Rotondi, A.; Monteleone, I.; Fantini, M.C.; Pallone, F.; Monteleone, G. 2-methoxy-5-amino-n-hydroxybenzamide sensitizes colon cancer cells to trail-induced apoptosis by regulating death receptor 5 and survivin expression. Mol. Cancer Ther 2011, 10, 1969–1981. [Google Scholar]
  70. Goda, A.E.; Yoshida, T.; Horinaka, M.; Yasuda, T.; Shiraishi, T.; Wakada, M.; Sakai, T. Mechanisms of enhancement of trail tumoricidal activity against human cancer cells of different origin by dipyridamole. Oncogene 2008, 27, 3435–3445. [Google Scholar]
  71. Hori, T.; Kondo, T.; Kanamori, M.; Tabuchi, Y.; Ogawa, R.; Zhao, Q.L.; Ahmed, K.; Yasuda, T.; Seki, S.; Suzuki, K.; et al. Nutlin-3 enhances tumor necrosis factor-related apoptosis-inducing ligand (trail)-induced apoptosis through up-regulation of death receptor 5 (DR5) in human sarcoma hos cells and human colon cancer hct116 cells. Cancer Lett 2010, 287, 98–108. [Google Scholar]
  72. Su, R.Y.; Chao, Y.; Chen, T.Y.; Huang, D.Y.; Lin, W.W. 5-aminoimidazole-4-carboxamide riboside sensitizes trail- and tnf{alpha}-induced cytotoxicity in colon cancer cells through amp-activated protein kinase signaling. Mol. Cancer Ther 2007, 6, 1562–1571. [Google Scholar]
  73. Tillman, D.M.; Izeradjene, K.; Szucs, K.S.; Douglas, L.; Houghton, J.A. Rottlerin sensitizes colon carcinoma cells to tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis via uncoupling of the mitochondria independent of protein kinase c. Cancer Res 2003, 63, 5118–5125. [Google Scholar]
  74. Vasilevskaya, I.A.; O’Dwyer, P.J. 17-allylamino-17-demethoxygeldanamycin overcomes trail resistance in colon cancer cell lines. Biochem. Pharmacol 2005, 70, 580–589. [Google Scholar]
  75. Toscano, F.; Fajoui, Z.E.; Gay, F.; Lalaoui, N.; Parmentier, B.; Chayvialle, J.A.; Scoazec, J.Y.; Micheau, O.; Abello, J.; Saurin, J.C. P53-mediated upregulation of dcr1 impairs oxaliplatin/trail-induced synergistic anti-tumour potential in colon cancer cells. Oncogene 2008, 27, 4161–4171. [Google Scholar]
  76. Wu, X.X.; Ogawa, O.; Kakehi, Y. Trail and chemotherapeutic drugs in cancer therapy. Vitam. Horm 2004, 67, 365–383. [Google Scholar]
  77. Siu, D. Natural products and their role in cancer therapy. Med. Oncol 2011, 28, 888–900. [Google Scholar]
  78. Oliver, C.L.; Bauer, J.A.; Wolter, K.G.; Ubell, M.L.; Narayan, A.; O’Connell, K.M.; Fisher, S.G.; Wang, S.; Wu, X.; Ji, M.; et al. In vitro effects of the bh3 mimetic, (−)-gossypol, on head and neck squamous cell carcinoma cells. Clin. Cancer Res 2004, 10, 7757–7763. [Google Scholar]
  79. Rabi, T.; Bishayee, A. Terpenoids and breast cancer chemoprevention. Breast Cancer Res. Treat 2009, 115, 223–239. [Google Scholar]
  80. Thoppil, R.J.; Bishayee, A. Terpenoids as potential chemopreventive and therapeutic agents in liver cancer. World J. Hepatol 2011, 3, 228–249. [Google Scholar]
  81. Kirana, C.; McIntosh, G.H.; Record, I.R.; Jones, G.P. Antitumor activity of extract of zingiber aromaticum and its bioactive sesquiterpenoid zerumbone. Nutr. Cancer 2003, 45, 218–225. [Google Scholar]
  82. Sterz, J.; von Metzler, I.; Hahne, J.C.; Lamottke, B.; Rademacher, J.; Heider, U.; Terpos, E.; Sezer, O. The potential of proteasome inhibitors in cancer therapy. Expert Opin. Investig. Drugs 2008, 17, 879–895. [Google Scholar]
  83. Schroder, M.; Kaufman, R.J. Er stress and the unfolded protein response. Mutat. Res 2005, 569, 29–63. [Google Scholar]
  84. Martin-Perez, R.; Niwa, M.; Lopez-Rivas, A. Er stress sensitizes cells to trail through down-regulation of flip and mcl-1 and perk-dependent up-regulation of trail-r2. Apoptosis 2012, 17, 349–363. [Google Scholar]
  85. Stolfi, C.; Sarra, M.; Caruso, R.; Fantini, M.C.; Fina, D.; Pellegrini, R.; Palmieri, G.; Macdonald, T.T.; Pallone, F.; Monteleone, G. Inhibition of colon carcinogenesis by 2-methoxy-5-amino-n-hydroxybenzamide, a novel derivative of mesalamine. Gastroenterology 2010, 138, 221–230. [Google Scholar]
  86. Zhao, J.; Lu, Y.; Shen, H.M. Targeting p53 as a therapeutic strategy in sensitizing trail-induced apoptosis in cancer cells. Cancer Lett 2012, 314, 8–23. [Google Scholar]
Ijms 13 07886f1 1024
Figure 1. TRAIL signaling pathway and mechanisms of TRAIL resistance. Binding of TRAIL to DR4 or DR5 leads to activation of caspase-8 through FADD. Activated caspase-8 can directly activate effector caspase-3, -6, and -7 via the extrinsic pathway or cleave Bid and activate the intrinsic mitochondria-mediated pathway. Initiation of the latter pathway leads to activation of effector caspases through caspase-9. Activation of caspase-3, -6, and -7 leads to apoptosis. TRAIL resistance can occur at several levels. At the outer membrane, TRAIL sensitivity can be reduced by DcR1 and/or DcR2 over-expression as well as by defective expression/function of DR4 and/or DR5 (1). At the DISC, down-regulation, degradation or inactivation of the initiator caspase-8 and/or increased expression of c-FLIP can lead to TRAIL resistance (2). At the mitochondria, defects in pro-apoptotic molecules (e.g., Bid, Bax, Bak, PUMA, Bim) and/or up-regulation of proteins able to prevent cytochrome c and Smac/DIABLO release (e.g., Bcl-2, Bcl-xL and Mcl-1) also interfere with TRAIL signaling (3). Finally, members of the IAP family prevent the activation of both caspase-9 and caspase-3, -6 and -7 (4). →indicates activation, ⊥ indicates inhibition.

Click here to enlarge figure

Figure 1. TRAIL signaling pathway and mechanisms of TRAIL resistance. Binding of TRAIL to DR4 or DR5 leads to activation of caspase-8 through FADD. Activated caspase-8 can directly activate effector caspase-3, -6, and -7 via the extrinsic pathway or cleave Bid and activate the intrinsic mitochondria-mediated pathway. Initiation of the latter pathway leads to activation of effector caspases through caspase-9. Activation of caspase-3, -6, and -7 leads to apoptosis. TRAIL resistance can occur at several levels. At the outer membrane, TRAIL sensitivity can be reduced by DcR1 and/or DcR2 over-expression as well as by defective expression/function of DR4 and/or DR5 (1). At the DISC, down-regulation, degradation or inactivation of the initiator caspase-8 and/or increased expression of c-FLIP can lead to TRAIL resistance (2). At the mitochondria, defects in pro-apoptotic molecules (e.g., Bid, Bax, Bak, PUMA, Bim) and/or up-regulation of proteins able to prevent cytochrome c and Smac/DIABLO release (e.g., Bcl-2, Bcl-xL and Mcl-1) also interfere with TRAIL signaling (3). Finally, members of the IAP family prevent the activation of both caspase-9 and caspase-3, -6 and -7 (4). →indicates activation, ⊥ indicates inhibition.
Ijms 13 07886f1 1024
Table Table 1. Mechanism(s) of action of TRAIL-sensitizing agents in CRC cells.

Click here to display table

Table 1. Mechanism(s) of action of TRAIL-sensitizing agents in CRC cells.
TherapeuticsCellsMechanism(s)Reference
Chemotherapeutics
CisplatinHT-29, SW480Caspase-8 activation, Bid cleavage[35,36]
5-FUHCT-116, HT-29Caspase-8 activation, ↓c-FLIP, Bid cleavage[3538]
VP16HCT-116, SW480Caspase-8 activation[39]
DoxorubicinHT-29, SW480Caspase-8 activation, Bid cleavage[35,36]
DuP-697HT-29DR5 and DISC component redistribution in lipid rafts[25]
CPT-11HCT-116↑DR4, ↑DR5[40]
FenretinideHT-29, SW480↑DR5, Bid cleavage[41]
LapatinibHCT-116, SW480, SW620, DLD-1, HT-29↑DR4, ↑DR5[42]
SunitinibSW620↓c-FLIP, ↓Mcl-1, ↓XIAP[43]
OxaliplatinHT-29, V9P↓Bcl-xL anti-apoptotic activity[44]
Natural products
ApigeninDLD1↑DR5[45]
BaicaleinSW480↑DR5[46]
IsoliquiritigeninHT-29↑DR5[47]
KaempferolSW480↑DR5[48]
QuercetinHT-29, SW620, CACO-2DR4 and DR5 redistribution in lipid rafts[49]
WogoninHT-29↑DR5, ↓c-FLIP[50]
Cycloartenyl ferulateSW480, SW620↑DR4, ↑DR5, Bid cleavage, Bcl-2, Bax[51]
SilibininSW480, SW620↑DR5, ↓Mcl-1, ↓XIAP[52]
GossypolHCT-116↑DR5, ↓Bcl-2, ↓Bcl-xL, ↓survivin[53]
CardamoninHCT-116↑DR4, ↑DR5, ↓DcR1, ↑Bax, ↓Bcl-2, ↓c-IAP1[54]
ZerumboneHCT-116↑DR4, ↑DR5, ↓c-FLIP[55]
NimbolideHCT-116, HT-29↑DR4, ↑DR5, ↓c-FLIP, ↑Bax, ↓Bcl-2, ↓Bcl-xL, ↓c-IAP1, ↓c-IAP2, ↓survivin, ↓XIAP[56]
HalocynthiaxanthinDLD1, HT-29↑DR5[57]
γ-T3HCT-116↑DR4, ↑DR5[58]
GarcinolHCT-116, HT-29↑DR4, ↑DR5, Bid cleavage ↓c-FLIP, ↓Bcl-2, ↓XIAP, ↓survivin[59]
Combretastatin A-4HCT-116, SW620↓c-FLIP, ↓Mcl-1[60]
Methyl jasmonateHCT-116, SW480Bid cleavage, ↓survivin[61]
DHAHT-29Caspase-8 activation, Bid cleavage[62]
DiosgeninHT-29↑DR5[63]
RAcAPC-deleted NCM356↑DR4, ↑DR5, ↓DcR1, ↓DcR2[64]
Other agents
MG-132HCT-116↑DR5[65]
PS-341HCT-116, HC-4↑DR4, ↑DR5, caspase-8 activation, Bid cleavage[66]
15dPGJ2HCT-116↑DR5[67]
DBAHCT-116↑DR4, ↑DR5, ↓DcR2, ↓Bcl-2, ↓XIAP, ↓survivin[68]
2–14DLD1, HT-29↑DR5, ↓survivin[69]
DipyridamoleSW480↑DR5, ↓survivin[70]
Nutlin-3HCT-116↑DR5, ↓Bcl-2, ↓XIAP[71]
AICARHCT-116Bid cleavage, ↓Bcl-2[72]
RottlerinHT-29, RKOCytochrome c and Smac/DIABLO release, ↓XIAP
↓c-IAP1
[73]
17-AAGHT-29, RKOBid cleavage, ↓XIAP[74]
Int. J. Mol. Sci. EISSN 1422-0067 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert