Search Results (170)

Tyrosyl-DNA phosphodiesterase 1 (TDP1) represents a compelling pharmacological target for the development of agents designed to circumvent tumor resistance to topoisomerase 1 (TOP1) inhibitors, a major class of clinically relevant antineoplastic drugs. This paper describes the design and synthesis of novel hybrid TDP1 inhibitors combining coumarin and monoterpene moieties via rigid isoxazole and 1,2,3-triazole heterocyclic linkers. The synthesis was accomplished via [3 + 2] cycloaddition of nitrile oxides to alkynes and copper-catalyzed click chemistry. Biological tests have demonstrated the crucial role of linker nature in the activity of the compounds. Isoxazole-linked conjugates showed strong inhibitory effects on TDP1, with IC₅₀ values in the submicromolar to low micromolar range (0.8–3.2 μM). Overall, these values slightly surpassed those of the triazole-linked analogues, whose IC₅₀ values ranged from 1.1 to 23.3 μM. At noncytotoxic doses, compounds 26e and 16b enhanced the sensitivity of human cervical cancer (HeLa) cells to the antitumor agent topotecan, a TOP1 inhibitor, thereby supporting the promise of this structural class as components of combination chemotherapy. Full article

Objectives: Transient Receptor Potential Ankyrin 1 (TRPA1) has emerged as a stress-responsive ion channel involved in calcium homeostasis, redox signaling, migration, and cancer cell survival; however, the therapeutic relevance of TRPA1 activation versus inhibition remains poorly understood. In this study, we comparatively investigated the anticancer potential of the TRPA1 agonist ASP7663 and the TRPA1 antagonist HC030031 across a broad panel of human cancer cell lines. Methods: Antiproliferative and cytotoxic effects were evaluated using MTT and LDH assays, while apoptotic signaling, DNA fragmentation, mitochondrial membrane potential, migration inhibition, DNA/BSA interactions, topoisomerase I inhibition, and molecular docking analyses were comprehensively assessed. Results: ASP7663 exhibited markedly lower GI₅₀ values than HC030031 in most cancer models and demonstrated favorable tumor selectivity relative to normal cells. Mechanistically, ASP7663 induced robust apoptotic activation characterized by significant upregulation of Caspase-3, Caspase-8, and Caspase-9, together with enhanced DNA fragmentation and pronounced nuclear condensation. Rhodamine-123 staining further revealed substantial mitochondrial membrane depolarization, indicating activation of intrinsic apoptotic pathways. In addition, ASP7663 produced selective membrane damage in malignant cells, stronger inhibition of migration in osteosarcoma and chondrosarcoma models, enhanced CT-DNA/BSA binding affinity, partial topoisomerase I inhibition, and superior docking interactions with apoptosis-related targets, including Caspase-3, Caspase-8, Caspase-9, Bax, and Bcl-2. Conclusions: Collectively, these findings suggest that ASP7663 is a promising multi-target candidate for anticancer therapy and support further investigation of TRPA1-associated pathways as potential therapeutic targets in cancer. Full article

Redox homeostasis is the balance between oxidative processes and antioxidant defenses and is fundamental to cellular integrity. This review critically synthesizes current evidence on the phytochemical composition, redox-modulating mechanisms, and therapeutic bioactivities of Fagonia cretica L. (F. cretica), with the aim of evaluating its translational potential as a natural antioxidant and anticancer agent. F. cretica has emerged as a phytochemically rich candidate containing highly bioactive secondary metabolite for redox-targeted therapeutic applications. Its diverse secondary metabolite profile, including alkaloids, flavonoids, tannins, saponins, terpenoids, glycosides, and phenolic compounds, confers broad biological activity. Bioactive constituents, particularly kaempferol, catechin, quercetin, and arbutin, directly neutralize reactive oxygen species (ROS) and modulate inflammatory pathways through inhibition of COX-1, COX-2, and nitric oxide production. These compounds influence important major ROS-sensitive redox signaling pathways: activation of the Keap1/Nrf2/ARE axis to upregulate cytoprotective genes such as HO-1, NQO1, and GCL, suppression of the NF-κB pathway to attenuate pro-inflammatory cytokine transcription, including TNF-α, IL-1β, and IL-6, and interference with the MAPK-PI3K/Akt cascade to disrupt aberrant cancer cell survival and proliferation. Bioactive compound-rich extracts of F. cretica exhibit anticancer activity in MCF-7 breast cancer cells by inducing DNA damage, cell cycle arrest, and apoptotic signaling through the FOXO3a/p53 pathways. Similar effects have been reported in colorectal (HCT-116) and prostate (PC-3) cancer cells through DNA (cytosine-5)-methyltransferase 1 (DNMT1) downregulation, oxidative stress induction, and ER-β activation. Moreover, these extracts demonstrate cytotoxic effects in HepG2 and Caco-2 intestinal cancer cells, often associated with topoisomerase inhibition and caspase activation. Despite encouraging preclinical evidence, systematic studies encompassing pharmacokinetic profiling, toxicological characterization, and human clinical trials remain essential to translate these findings into safe, evidence-based therapeutic applications. Full article

Epithelial ovarian cancer (EOC) remains one of the most aggressive gynecological malignancies, largely due to late-stage diagnosis, therapeutic resistance, and molecular heterogeneity. This study aimed to identify biologically relevant hub genes and evaluate potential dual-target compounds against Cyclin-Dependent Kinase 1 (CDK1) and DNA Topoisomerase II Alpha (TOP2A) through an integrated computational framework. Transcriptomic datasets from GSE28799, GSE54388, and GSE14407 were analyzed to identify overlapping differentially expressed genes, followed by protein–protein interaction analysis, functional enrichment, survival assessment, molecular docking, ADMET profiling, and molecular dynamics simulations. Mechanistically, CDK1 and TOP2A participate in coordinated cell-cycle regulation associated with G2/M progression and chromosomal dynamics in ovarian cancer. Among the identified hub genes, CDK1 and TOP2A demonstrated marked overexpression and central topological importance within the interaction network. Functional enrichment analyses highlighted significant associations with mitotic cell-cycle regulation, DNA replication, and proliferative signaling pathways. Molecular docking analyses identified Naringin as a potential dual-target candidate with favorable binding affinity toward both CDK1 and TOP2A. ADMET profiling suggested acceptable pharmacokinetic and toxicity characteristics, while molecular dynamics simulations supported stable protein–ligand interactions under dynamic conditions. Although survival analyses did not demonstrate statistically significant independent prognostic associations, the findings support the biological relevance of CDK1 and TOP2A in EOC progression. Collectively, this study provides an integrated computational perspective on CDK1/TOP2A-associated oncogenic signaling and prioritizes Naringin as a preliminary candidate for future experimental investigation in epithelial ovarian cancer. Full article

Cardiac safety assessment is an integral part of drug discovery and development. Drug candidates that adversely affect cardiac or hemodynamic function should be discontinued early unless a favorable benefit-risk ratio for patients can be justified. In this hypothesis-generating work, we aimed to develop a conceptual framework for informing early safety risk assessment based on in vitro drug affinities to pharmacological targets. For illustration, we used the drug-induced cardiotoxicity rank (DICTrank) data comprising 1318 drugs with cardiac safety concerns according to FDA labeling. The data was enriched with information on affinity to the most plausible mechanistic targets, clinical drug exposure, and human plasma protein binding. We descriptively identified 18 target classes potentially associated with elevated cardiovascular risk: potassium channels (accounting alone for 20% of the ‘most concern’ safety group); adrenergic, dopamine, serotonin, androgen, sex hormone, and opioid receptors; cyclooxygenase; sodium and calcium channels; muscarinic and glucocorticoid receptors; phosphodiesterase; topoisomerase; angiotensin-converting enzyme; angiotensin II type 1 receptor; monoamine transporters, and acetylcholinesterase. Overall, 80% of the ‘most concern’ drugs compared with only 12% of the ‘no concern’ drugs were associated with these targets in this exploratory descriptive analysis. Concentration–response analyses revealed differences in target potency and free drug exposure that appeared associated with variability in the severity of cardiotoxicity among drugs acting on the same target. This framework demonstrates how in vitro data can be used to benchmark new compounds early in development, enabling the timely discontinuation of candidates associated with substantial risk. Full article

The bactericidal mechanisms of fluoroquinolones extend beyond their canonical inhibition of DNA topoisomerases, yet the associated metabolic perturbations remain incompletely understood. In this study, we systematically investigated the metabolic responses of Escherichia coli to three representative FQs—ofloxacin, enrofloxacin, and ciprofloxacin—using untargeted UPLC–Q Exactive Orbitrap–MS-based metabolomics. Bacterial cells were exposed to bactericidal concentrations (2 × MIC) for a single-time point (1 h), followed by comprehensive metabolomic profiling with six biological replicates per group. Our findings demonstrate that FQ-induced metabolic reprogramming serves as a primary driver of oxidative stress and nucleic acid damage, rather than a mere secondary effect. All three FQs induced substantial metabolic reprogramming characterized by disruptions in nucleotide biosynthesis, central carbon metabolism, and redox-related pathways, with notable drug-specific differences. Ciprofloxacin exhibited the most pronounced suppression of energy metabolism and antioxidant systems, whereas ofloxacin and enrofloxacin showed partial compensatory metabolic responses. Consistently, intracellular ROS levels were significantly elevated in all treatment groups, and this effect was attenuated by antioxidant supplementation. Furthermore, increased accumulation of 8-hydroxydeoxyguanosine and 8-hydroxyguanosine confirmed the occurrence of oxidative DNA and RNA damage. Collectively, these findings indicate that FQs induce distinct metabolic perturbations that are closely associated with oxidative stress and nucleic acid damage, providing a metabolic perspective on their bactericidal activity and suggesting potential targets for metabolic adjuvant strategies. Full article

Tyrosyl-DNA phosphodiesterase 1 (TDP1) is a key enzyme for the repair of stalled topoi-somerase 1 (TOP1)-DNA complexes. We have previously developed a TDP1 inhibitor, compound OL9-116, which is capable of enhancing the action of the anticancer drug topotecan (TPC), a TOP1 poison, in vitro and in vivo. In this study, the inhibition mode of OL9-116 (uncompetitive) was investigated. We have shown that N-terminal domain of TDP1, which is important for the cell function of TDP1 but is not involved in catalysis directly, reduced the inhibitory potency of OL9-116 probably by influencing the conformation of the enzyme. OL9-116 did not reduce cell viability and did not affect mitochondrial membrane potential. OL9-116 enhanced the cytotoxic/antiproliferative effect of TPC on the panel of tumor cells. This effect was not observed on nontumor cells or TDP1-deficient cells. OL9-116 and TPC had different effects on TDP1 and TOP1 gene expression detected by PCR depending on the cell type and the presence of functional TDP1. The direct relation between the effects of the compounds on the gene expression and cell survival was not found. The obtained data indicated a synergistic effect of OL9-116 and TPC, which appeared to be mediated by TDP1 inhibition rather than by an effect on TDP1 gene expression. Full article

Quercetin, a naturally occurring flavonoid, exhibits antiproliferative and pro-apoptotic effects across various cancer models. Topotecan, a topoisomerase I inhibitor, is used in the treatment of retinoblastoma; however, its clinical utility is limited by dose-dependent toxicity. This study aimed to investigate whether quercetin is associated with enhanced topotecan-induced cytotoxicity in retinoblastoma and to explore the underlying mechanisms under both two-dimensional (2D) and three-dimensional (3D) conditions. Cell viability was assessed using the MTT assay, and drug interactions were evaluated using the combination index (CI) based on the Chou–Talalay method. Apoptosis was analyzed by Annexin V-FITC/PI staining and flow cytometry. Reactive oxygen species (ROS) levels and mitochondrial membrane potential were evaluated using fluorometric methods, and N-acetyl-L-cysteine (NAC) was used for functional modulation of oxidative stress. Three-dimensional tumor spheroid models were used to assess treatment effects under conditions that partially recapitulate tumor architecture. Gene expression levels of apoptosis-related markers and PI3K/Akt/mTOR pathway components were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). The combination of quercetin and topotecan was associated with synergistic cytotoxic effects in Y79 cells (CI < 1), accompanied by increased ROS levels, mitochondrial membrane depolarization, and elevated apoptotic cell death. NAC co-treatment partially attenuated ROS levels and restored cell viability. In 3D spheroid models, combination treatment induced structural disruption, reduced viability, and increased cell death, effects that were partially reversed by NAC. Gene expression analysis revealed upregulation of pro-apoptotic genes and downregulation of survival-related genes, along with increased PTEN expression. Quercetin is associated with enhanced topotecan-induced cytotoxicity in retinoblastoma cells under both 2D and 3D conditions. These effects were associated with ROS-associated cellular stress, mitochondrial dysfunction, and modulation of apoptotic and survival-related pathways. The partial rescue by NAC supports a contributory, but not exclusive, role of oxidative stress. These findings should be interpreted within a preclinical context and suggest that quercetin may represent a potential adjunct strategy warranting further validation in translational and in vivo models. Full article

Cancer is an alarming health concern and economic burden in both developed and developing countries. Recently, there has been a growing demand for new alternative medications with more effectiveness and fewer harmful effects. During the past decades, a set of chemotherapeutic agents has been developed to fight against a large spectrum of cancer types. Unfortunately, their use is associated with a high level of toxicity; they are expensive, also, and their deployment is restricted by the emergence of cellular resistance. Plant-based components are garnering attention due to their low toxicity, selectivity, efficiency, and ease of accessibility. Alkaloids are one of these targeted compounds. Indeed, they are a highly diverse group with basic heterocyclic nitrogen-containing alkaloids that exhibit potent anticancer effects against a large panel of solid and liquid tumors, such as lung, breast, leukemia, liver, and colon cancer. The main molecular mechanisms involved in alkaloids’ anticancer effect are the induction of apoptosis via the extrinsic and intrinsic pathways, DNA damage, and the inhibition of cell cycle progression. Amazingly, these auspicious compounds exhibited strenuous inhibitory effects against a whole range of key enzymes involved in cancer progression and metastasis, such as Cytochrome P450 (CYP450), Cyclooxygenase-2 (Cox-2), Lysine-Specific Demethylase 1 (LSD1), Poly [ADP-ribose] polymerase (PARP), and topoisomerase, mainly through two action modes, namely irreversible and reversible inhibition. Furthermore, several conventional extraction methods have been developed to extract bioactive compounds from natural matrices, such as Soxhlet and hot water extraction. However, these techniques have many drawbacks, as they require a large amount of organic solvents, which not only affect human health but also generate severe environmental issues. To overcome these limitations, multiple eco-extraction techniques have emerged as potential alternatives to traditional extraction methods such as ultrasonic extraction, microwave-assisted extraction, and supercritical fluid extraction. In fact, they are considered eco-friendly and efficient technologies with less time and solvent consumption. Overall, this review aims to provide an updated overview of the most prominent anticancer alkaloids that have not been well reviewed already, as well as the main green extraction techniques relevant to the extraction of antineoplastic alkaloids. Full article

Background: Oral squamous cell carcinoma (OSCC) is an aggressive cancer closely associated with smoking and alcohol consumption, with a higher incidence in men. Despite changes in treatment strategies, poor survival persists in most patients, highlighting the need for novel and improved therapeutic options. Naphthoquinone analogs are being investigated because of their active redox structure and broad pharmacological profile; they demonstrate cytotoxic antitumor activity, making them potential candidates for new drug agents. Objective: This study investigated new benzyl-naphthoquinone compounds as potential anticancer agents for various genotypes of oral squamous cell carcinoma (OSCC) and other cancer cells. Methods: This study reports the synthesis and evaluation of a series of eight benzyl-naphthoquinone compounds against oral squamous cell carcinoma. Results: Four compounds 1–4 showed the best cytotoxic profiles, with a selectivity index ≥ 3 for all OSCC cell lines tested. Compound 1 was the most selective compound in all OSCC models, showing a higher selectivity index than both carboplatin and shikonin. Furthermore, compound 1 induced DNA fragmentation, cell-cycle arrest, and caspase-3/7 activation, changes consistent with apoptosis, and time-lapse imaging corroborated the apoptotic phenotype. Hemolysis assays showed minimal toxicity in human erythrocytes, and acute in vivo evaluation in mice revealed no evident adverse effects under the conditions tested, indicating low acute toxicity, although more detailed histopathological and biochemical studies will be required to fully establish the safety profile. Molecular modeling suggested that compound 1 may interact with topoisomerase II, RSK2, and PKM2, which could contribute to the activation of apoptotic pathways, although these interactions remain predictive and require biochemical validation. Finally, in silico analysis of physicochemical and ADMET parameters indicated properties compatible with oral absorption and systemic exposure, together with predicted low toxicity; however, these results are model-based and should be confirmed experimentally. Conclusions: Based on these findings, compound 1 emerges as a promising lead candidate for the development of a novel chemotherapeutic agent against OSCC, with potential therapeutic efficacy against other cancer types. Full article

Background/Objectives: TP53 mutation or deletion status is important for determining cellular responses to DNA-damaging drugs. Oxaliplatin (OXA) is combined with the fluoropyrimidine (FP) drug 5-fluorouracil (5-FU) in the FOLFOX regimen used to treat advanced colorectal cancer (CRC). However, the effects of TP53 deletion on 5-FU + OXA synergy are not well known. We investigated potential synergy between OXA and 5-FU and compared it with OXA synergy with a novel polymeric FP, CF10, in four cell lines harboring either wild-type (WT) or TP53-null status. Methods: Using CompuSyn and the highest single agent (HSA) models, we compared synergy between CF10 and OXA (COXA) and between 5-FU and OXA (FOXA). Cell cycle analysis was performed, as was Western blot quantification of canonical DNA damage pathway proteins. Likewise, immunofluorescent and confocal analysis allowed us to compare topoisomerase 1 cleavage complex and double-strand DNA break formation. Results: COXA synergy displayed minimal TP53 dependence with greatly improved potency compared to FOXA. COXA synergy resulted from OXA increasing: (i) Topoisomerase 1 (Top1) cleavage complex formation; (ii) DNA double-strand breaks (DSBs), and (iii) Checkpoint Kinase 1 and 2 (p-Chk1/2) phosphorylation, consistent with increased replication stress. Additionally, increased S-phase entry in TP53-null cells enhanced synergy between CF10, 5-FU, and OXA as S-phase drugs. Conclusions: Our results demonstrate that OXA synergizes with CF10 more effectively than with 5-FU through enhanced replication stress in both WT and TP53-null cells by causing greater Top1-mediated DNA double-strand breaks. Our studies provide a foundation for further testing of this combination in an orthotopic liver metastatic setting and eventual clinical development. Full article

Naphthyridine derivatives have emerged as privileged scaffolds with diverse pharmacological activities, particularly in anticancer and antiviral drug discovery. In this study, a series of naphthyridine-based derivatives (1–10b) was designed, synthesized, and structurally characterized using IR, ¹H/¹³C NMR, and mass spectrometry, and evaluated as dual-function antiproliferative and anti-fowlpox virus agents supported by integrated computational analyses. The synthesized compounds were screened for in vitro antiproliferative activity against HeLa, HCT-116, and MCF-7 cancer cell lines, as well as normal WI-38 lung fibroblasts. Several derivatives exhibited potent cytotoxic activity with enhanced selectivity toward cancer cells. Compound 5b showed the highest activity against HeLa cells, compound 1 was most effective against HCT-116 cells, while compounds 7 and 8 displayed remarkable activity against MCF-7 cells, with compound 7 surpassing doxorubicin and compound 8 demonstrating excellent selectivity toward normal cells. Mechanistic investigations revealed that compounds 7 and 8 acted as dual topoisomerase I/IIβ inhibitors, inducing G2/M cell cycle arrest and intrinsic apoptosis associated with caspase-9 activation and downregulation of topoisomerase II protein expression. Selected derivatives were further evaluated for antiviral activity against fowlpox virus using in ovo and in vivo SPF embryonated chicken egg models, where compounds 2 and 9a exhibited the highest therapeutic indices, comparable to ribavirin, and compound 9a markedly suppressed viral replication and titers in vivo. ADMET profiling, molecular docking, molecular dynamics simulations, and DFT calculations supported the experimental findings and identified compound 10a as the most favorable theoretical candidate. Overall, this integrated experimental–computational approach establishes naphthyridine derivatives as a rationally designed multifunctional chemotype for simultaneous anticancer and antiviral drug development. Full article

Objectives: Lung transplantation (LT) is a rescue therapy for end-stage pulmonary diseases, including systemic autoimmune diseases. The aim of this study was to analyse the evolution of patients with systemic sclerosis (SSc) who, after undergoing LT, become negative for antinuclear antibodies (ANA) and to assess whether they have different clinical and prognostic characteristics than patients who do not become negative. Material and Methods: A retrospective, descriptive analysis was performed over a cohort of patients with a diagnosis of SSc, who underwent unilateral or bilateral LT between 2006 and 2021 at the Vall d’Hebron University Hospital. Clinical and analytical data were obtained from these patients by reviewing their electronic medical records. Two groups of patients were compared: those who tested negative for ANA after LT and those who did not. Statistical analysis was performed with SPSS Statistics 20.0. Results: Eighteen patients were included. The most frequent indication for LT was interstitial lung disease (ILD) combined with pulmonary hypertension (PH), in 13 (72%) patients. All had ANA before the LT (n = 18), and regarding specific SSc autoantibodies, anti-topoisomerase I was presented in 44% (n = 8), anti-U11/U12RNP in 17% (n = 3), anti-RNA Polymerase III in 11.1% (n = 2), anti-Ro52 in 11% (n = 2) and anti-centromere in 6% of individuals (n = 1). 39% (n = 7) of the patients had negative post-LT ANA, 44% (n = 8) had declining titres, and 17% (n = 3) had stable ANA titres. Titres did not increase in any case after LT. Those patients who became ANA-negative after LT were those who had significantly lower titres before LT. No statistically significant differences between groups were found related to pre-LT clinical characteristics, immunosuppressive regimen applied after LT, or in post-LT outcomes. A non-significant trend towards better survival was observed in patients who became ANA negative, with a cumulative survival at 5 years of 85.7% compared to 72.7% among those who remained ANA-positive. Conclusions: Most patients with SSc clear ANA or reduce their levels after LT. A trend towards better survival was observed in this group, compared to the group of transplanted patients who remained positive. Full article

Anthraquinones are molecules with numerous biological properties that can act as DNA intercalators and topoisomerase IIa inhibitors. In this work, the development of technetium-99m radiotracers was pursued via the technetium-tricarbonyl “2 + 1” mixed-ligand approach, fac-[^99mTc][Tc^I(CO)₃(NN′)(N)]⁺, with a (N,N′) bidentate chelator and a N co-ligand. In one approach, the ligands used were 2,2′-bipyridine (bpy) and N-functionalized-imidazole, where imidazole was conjugated to an anthraquinone moiety. In the other approach, 2-picolylamine and imidazole were used as the mixed-ligand system, where picolylamine was conjugated to an anthraquinone moiety. The synthesis of the ligands was achieved by reaction of 2-picolylamine with a suitably functionalized anthraquinone (Aqpa) or anthrapyrazole (Appa) and imidazole with a suitably functionalized anthraquinone (Aqim). The rhenium reference compounds, fac-[Re^I(CO)₃(bpy)(Aqim)]⁺ with bpy as a bidentate chelator and fac-[Re^I(CO)₃(Aqpa or Appa)(Im)]⁺, with imidazole (Im) as a co-ligand, were synthesized and characterized with spectroscopic methods. The radiotracer technetium-99m complexes fac-[^99mTc][Tc(CO)₃(bpy)(Aqim)]⁺ and fac-[^99mTc][Tc(CO)₃(Aqpa or Appa)(Im)]⁺ were prepared and characterized with standard methods. The purified radiotracers displayed high stability (≥90%) after incubation 24 h in 1 mM L-histidine or rat plasma. The tracers’ cell uptake was evaluated in vitro in CT-26 cells, and their pharmacokinetic properties and tumor uptake were evaluated in vivo in CT26-tumor-bearing mice. The “2 + 1” technetium-tricarbonyl approach leads to in vitro stable tracers, and this mixed-ligand system shows promise for further evaluation. Full article

Tyrosyl-DNA phosphodiesterase 1 (TDP1) is an important DNA repair enzyme and its functioning is considered as one of the possible reasons for tumor resistance to topoisomerase 1 (TOP1) poisons such as topotecan. Thus, TDP1 inhibitors in combination with topotecan may improve the effectiveness of anticancer therapy. TDP1 acts somehow in a phospholipase manner, depleting the phosphodiester bond between lipophilic tyrosine residue and 3′ end of DNA; therefore, lipophilic molecules bearing aromatic substituents can interact with TDP1 and even possess high inhibitory activity, which is evidenced by data from the literature. Previously, we identified lipophilic nucleoside derivative (compound 6d, IC₅₀ = 0.82 µM) as an effective inhibitor of the purified enzyme TDP1 that enhances the cytotoxic, DNA-damaging, and antitumor effects of topotecan. However, the role of TDP1 inhibition in this synergistic effect remained not fully understood. In the present study, we have tested the hypothesis of a TDP1-dependent mechanism of action for compound 6d, showing that it sensitizes wild-type A549 lung cancer cells, but not TDP1 knockout cells, to the cytotoxic effects of topotecan. The sensitizing effect was absent in non-cancerous HEK293A cells regardless of TDP1 status. Additionally, we analyzed the effect of compound 6d and topotecan on the expression level of TOP1 and TDP1 to determine whether the observed synergy was due to direct TDP1 inhibition and/or changes in regulation of these enzymes. The data obtained shows that compound 6d did not affect TDP1 gene expression level in HEK293A and A549 WT cells. Thus, compound 6d most probably does not suppress the transcription or mRNA stability of TDP1, and the synergistic action of 6d with topotecan is related to TDP1 inhibtion. Full article