Search Results (533)

Background: Head and neck squamous cell carcinoma (HNSCC) remains a highly aggressive malignancy with poor clinical outcomes. Although poly(ADP-ribose) polymerase (PARP) inhibitors have shown promising activity in tumors with homologous recombination deficiency, their efficacy in BRCA wild-type HNSCC remains limited. Reactive oxygen species (ROS)-induced DNA damage may increase cellular dependence on DNA repair pathways and thereby enhance sensitivity to PARP inhibition. This study investigated whether ROS-mediated DNA damage could sensitize BRCA wild-type HNSCC cells to the PARP inhibitor olaparib. Methods: BRCA wild-type HSC-3 and SCC-25 HNSCC cell lines were exposed to H₂O₂ to induce oxidative stress. Intracellular ROS levels were quantified using DCFDA assays, DNA double-strand breaks were evaluated by γ-H2AX ELISA, PARP activity was assessed by ELISA, and cell viability was determined using MTT assays. Expression levels of DNA repair genes (PARP1, PARP2, BRCA1, BRCA2, RAD51, and MLH1), checkpoint kinases (ATM, ATR, and CHK1), the homologous recombination regulator FANCD2, and redox defense genes (NQO1, GPX4, and SLC7A11) were analyzed by qRT-PCR. Therapeutic selectivity was assessed using HGF-1 normal human gingival fibroblasts as a normal cell control. Apoptosis was measured through caspase-3/7 activity assays, and drug interactions were evaluated using the Chou–Talalay method. Results: H₂O₂ treatment increased intracellular ROS levels in both cell lines, accompanied by significant induction of DNA damage as demonstrated by elevated γ-H2AX levels. ROS induction markedly enhanced olaparib sensitivity, significantly reducing IC₅₀ values in both HSC-3 and SCC-25 cells. Combined H₂O₂ and olaparib treatment produced strong synergistic cytotoxicity, suppressed DNA repair, checkpoint kinase, and redox defense gene expression, and increased caspase-3/7 activity compared with control cells. Importantly, the combination demonstrated selective cytotoxicity toward cancer cells, with normal HGF-1 cells retaining significantly higher viability. Conclusions: ROS-induced DNA damage significantly enhances the anti-tumor activity of olaparib in BRCA wild-type HNSCC cells through a functional synthetic lethal-like interaction involving the simultaneous collapse of DNA repair capacity, checkpoint activation, and oxidative stress buffering, culminating in apoptosis induction. These findings support the rationale for combining ROS-generating therapies with PARP inhibitors in HNSCC treatment. Full article

Triple-negative breast cancer (TNBC), particularly when associated with breast cancer susceptibility gene 1/2 (BRCA1/2) alterations or homologous recombination deficiency (HRD), remains therapeutically challenging because DNA repair vulnerabilities coexist with molecular heterogeneity, resistance, and toxicity constraints. This narrative review synthesizes mechanistic, preclinical, clinical, and translational evidence on DNA damage response (DDR)-targeted and synthetic lethality-based strategies in TNBC. We summarize TNBC biological heterogeneity, current biomarker-guided treatment options, mechanisms of poly(ADP-ribose) polymerase (PARP) inhibition and resistance, and emerging DDR targets, including ataxia telangiectasia and Rad3-related/checkpoint kinase 1 (ATR/CHK1), WEE1, DNA-dependent protein kinase (DNA-PK), RAD51, DNA polymerase theta (POLQ), neddylation-related pathways, and targeted protein degradation. The review highlights that PARP inhibitors and platinum agents provide clinically validated examples of exploiting HRD in selected populations, whereas most next-generation DDR inhibitors remain preclinical, investigational, or in early clinical trials. Resistance mechanisms, including BRCA reversion, homologous recombination restoration, replication fork stabilization, and checkpoint adaptation, limit durable benefit. Safety, target selectivity, overlapping toxicities, and the lack of standardized functional biomarkers further constrain translation. Future progress will require prospective biomarker validation, dynamic HRD assessment, rational scheduling of combinations, and medicinal chemistry approaches that improve therapeutic index rather than a broad application of DDR inhibition across all TNBC. Full article

Background/Aims: While pathogenic germline variants play a critical role in pediatric cancer susceptibility, traditional clinical genetics primarily focuses on single-gene interpretations. Transitioning to a systems-level analysis of inherited variation can uncover shared biological vulnerabilities, informing genetic counseling, surveillance, and targeted therapeutics. This study aims to implement an unsupervised machine learning framework to identify and characterize Germline Mutation Signatures (GMS) across diverse pediatric malignancies, elucidating latent genomic patterns that reveal shared oncogenic mechanisms. Methods: We analyzed germline whole-exome and whole-genome sequencing (WES/WGS) data from a retrospective cohort of 420 pediatric cancer patients and matched non-cancer controls. Variants were deeply annotated to capture multi-dimensional features, including predicted pathogenicity, splice-site disruption, regulatory impact, population frequency, and sequence context. To enable robust modeling, we integrated an augmented feature set encompassing evolutionary constraint, loss-of-function intolerance, and compositionally normalized substitution spectra. These high-dimensional annotations were processed using a deep autoencoder for non-linear representation learning, followed by Gaussian Mixture Modeling (GMM) of the latent space. Results: The framework delineated 13 signatures (GMS1–GMS13), yielding an optimal Davies–Bouldin index of 1.051. These signatures map to fundamental biological processes, including DNA repair deficiencies, transcription-coupled damage, replication stress, and aberrant RNA regulation. Crucially, these GMSs transcend traditional tissue-of-origin classifications, manifesting across multiple distinct cancer types. This observation indicates convergent germline etiologies and suggests potential shared susceptibilities to pathway-directed therapies. Conclusions: The discovery of these cross-cancer signatures provides a scalable, biologically interpretable framework for decoding inherited pediatric cancer risk. While the therapeutic mapping networks identified are currently exploratory and serve as a hypothesis-generating foundation, this deep learning-driven paradigm establishes a robust basis for stratified precision medicine. Pending prospective clinical validation, this approach holds significant translational potential to move beyond single-gene paradigms toward unified, systems-level precision oncology strategies. Full article

Background/Objectives: White–Sutton syndrome (WHSUS; OMIM 616364) is a rare neurodevelopmental disorder caused by pathogenic variants in the POGZ gene and characterized by developmental delay, intellectual disability, speech impairment, autism spectrum features, and dysmorphic traits. Although most reported cases are sporadic, inherited forms are exceptionally rare. We describe a familial case of WHSUS involving an affected mother and two children carrying a heterozygous POGZ nonsense variant, highlighting marked intra-familial phenotypic variability and expanding the clinical spectrum of the disorder. Methods: Clinical evaluation included multidisciplinary assessments. Genetic testing was performed using clinical exome sequencing (CES) with a virtual neurodevelopmental disorder (NDD) gene panel, followed by Sanger confirmation and segregation analysis in family members. The POGZ transcript reference NM_015100.3 was used for variant nomenclature and verified with the Mutalyzer tool. CNV detection from NGS data was performed using the Alissa CNV caller (Agilent) and visualized via IGV; the Xp11.22 microduplication was confirmed by chromosomal microarray (aCGH) and parental segregation analyses. Results: CES identified the heterozygous pathogenic POGZ variant c.1522C>T (p.Arg508*) in the female proband (III₆), an infant presenting with global developmental delay, hypotonia, speech impairment, gait abnormalities, and characteristic dysmorphic features. Segregation analysis demonstrated maternal inheritance and confirmed the presence of the variant in her affected brother (III₄), who also carries a de novo 1.79 kb microduplication at Xp11.22, while the maternal grandparents tested negative, indicating a de novo origin in the mother. The mother exhibited an attenuated phenotype, including mild neuropsychiatric and gastrointestinal manifestations. The variant is predicted to undergo nonsense-mediated decay (NMD), consistent with a moderate clinical presentation; however, experimental validation was not performed. Conclusions: This report documents a rare familial occurrence of WHSUS with highly variable expressivity. Our findings broaden the phenotypic and molecular characterization of POGZ-related disorders and emphasize the importance of comprehensive segregation studies and early genomic diagnosis. While experimental data link POGZ deficiency to DNA repair defects, no longitudinal clinical studies have demonstrated increased cancer risk in WHSUS; therefore, formal malignancy screening guidelines cannot be established at present, and this issue deserves future study in larger cohorts or registries. Full article

Cancer cells, like yeast, use fermentation despite the presence of oxygen, a phenomenon called aerobic glycolysis. The advantage is that it maintains many C-C bonds of glucose, allowing highly proliferating cells to produce the biomolecules that are necessary for cytokinesis. However, aerobic glycolysis is less energy-efficient than respiration, and it must operate at high frequency and produces large amounts of lactate, which modifies and stimulates DNA repair enzymes via lysine lactylation. This makes cancer cells resistant to radiotherapy, which requires a combination with chemotherapy using drugs that inhibit DNA repair. However, this converts healthy cells to cancer cells, indicating that research is still required regarding the relationship between glycolysis and cancer. Using yeast as a model, we discovered that the glycolytic enzymes TPI and GAPDH (Tpi1p and Tdh1-3p in yeast) interact with the DNA damage-dependent Checkpoint Rad9p (53BP1/BRCA1/MDC1 in humans). We propose that Tpi1p and Tdh1-3p override Rad9p, allowing cells with damaged DNA to proliferate. We isolated tpi and gapdh mutant strains that are deficient in DNA repair. While the tpi mutant strain has lower enzymatic activity, the gapdh mutant strains have normal enzymatic activity, confirming previous reports that GAPDH moonlights in the DNA damage response. Full article

Targeting checkpoints is one of the most promising strategies in cancer chemotherapy. Leukemia, in particular, is expected to yield high therapeutic efficacy due to its high replication stress. However, the DNA damage response factors involved in the vulnerability to checkpoint inhibitors of these hematopoietic cancers remain elusive. In this study, we reveal common factors required for cellular resistance to ATR inhibition in hematopoietic cancer cells. We explored the DNA damage response pathways contributing to cellular tolerance to three types of ATR inhibitors using an isogenic DNA repair factor mutant collection derived from the chicken lymphoma cell line, DT40. We first demonstrated significant ATR inhibition activity of the recently developed Torin2 analogous compounds, SPK67 and SPK98, under stressed replication conditions. We then compared cellular sensitivity patterns of the known ATR inhibitor, VE-821, and the potential ATR inhibitors, SPK67 and SPK98, in 24 types of mutants deficient in genome maintenance systems and found that RAD17^/−, FEN1^−/−, and POLB^−/− cells exhibited hypersensitivity to all these drugs. Consistently, these mutant cells exhibited increased chromosome instability upon treatment with VE-821, SPK67, and SPK98, resulting in apoptosis. These results suggest that Rad17, Fen1, and Polymerase β play roles in responding to DNA damage caused by these drugs. However, ATR inhibition did not result in cell-cycle arrest, Chk1 phosphorylation, or increased γH2AX levels. These results suggest that, although ATR inhibition causes DNA damage, impaired checkpoint function suppresses the appropriate activation of DNA damage signaling pathways, thereby leading to cell death. This study is the first to demonstrate the importance of Rad17, Fen1, and Polymerase β in cellular tolerance to ATR inhibition in hematopoietic cells. Full article

Background: Triple-negative breast cancer (TNBC) remains a clinical challenge due to its aggressive nature and the frequent emergence of therapeutic resistance. While the role of protein-coding genes in DNA repair is well-documented, the regulatory contributions of the non-coding genome, specifically long intergenic non-coding RNAs (lincRNAs), remain largely undefined. Objectives: In this study, we characterize the biological significance of LincRNA-BC7, a novel transcript identified within the breast cancer field effect. Methods: Through a combined in silico and in vitro approach, we investigated the transcriptional dynamics of the LincRNA-BC7/miR-663a/BRCA1 axis in response to the PARP inhibitor, Olaparib. Results: Our results demonstrate that Olaparib induces selective cytotoxicity in BRCA1-deficient MDA-MB-231 cells while sparing non-cancerous HEK293 cells, a response accompanied by a significant downregulation of LincRNA-BC7 and a reciprocal upregulation of BRCA1. Bioinformatics analysis through BLASTN, miRBase, and KEGG revealed that LincRNA-BC7 contains highly complementary binding sites for miR-663a, suggesting it functions as a competing endogenous RNA (ceRNA) or “molecular sponge.” Conclusions: By sequestering miR-663a, LincRNA-BC7 appears to modulate the expression of critical signaling nodes within the PI3K-AKT and TP53 pathways, thereby influencing cellular sensitivity to DNA-damaging agents. These findings suggest that LincRNA-BC7 is a key determinant of the aggressive TNBC phenotype and the response to PARP inhibition. Our study establishes the LincRNA-BC7/miR-663a axis as a novel biomarker for precision risk stratification and a promising therapeutic target to enhance treatment outcomes in BRCA1-associated breast cancers. Full article

Germline loss-of-function mutations in BRCA1 and BRCA2 markedly increase susceptibility to breast, ovarian, and other cancers. Mechanistically, BRCA2 facilitates RAD51 recruitment to sites of DNA damage, whereas BRCA1 regulates homologous recombination repair (HRR) through double-strand break resection and broader DNA damage response signaling. These insights underpin targeted therapies such as poly (ADP-ribose) polymerase inhibitors (PARPis), which induce synthetic lethality in homologous recombination-deficient tumors. Clinically, PARPis have demonstrated significant benefit in BRCA1/2-mutated breast, ovarian, pancreatic, and prostate cancers. However, resistance remains a major obstacle, with secondary intragenic BRCA1/2 mutations restoring partial protein function representing a prominent mechanism. Despite therapeutic advances, critical gaps persist in understanding how specific BRCA1/2 domains and residual protein activities contribute to tumorigenesis and treatment response. In this review, we summarize the structural and functional domains of BRCA1/2, their pathogenic mutation profiles, and therapeutic strategies targeting BRCA1/2-deficient cancers. Despite therapeutic advances, critical gaps persist in understanding how specific BRCA1/2 domains and residual protein activities contribute to tumorigenesis and treatment response. This review emphasizes the need for functional studies of BRCA1/2 variants to refine risk prediction and develop mutation-tailored therapies. Full article

Immune checkpoint receptors (ICRs) play a pivotal role in modulating antitumor immunity and have become central targets in the immunotherapy of genitourinary (GU) malignancies. This review provides a comprehensive overview of the fundamental mechanisms of ICR signaling, the expression and pathophysiological roles of these receptors in GU cancers (kidney, bladder, prostate, testicular, and penile), and the evolving therapeutic landscape. Key ICRs, including PD-1, CTLA-4, LAG-3, TIM-3, and TIGIT, orchestrate complex signaling cascades that can lead to T-cell exhaustion and tumor immune evasion. Their expression varies significantly across GU cancer types, histological subtypes, and tumor stages, influencing prognosis and therapeutic response. Immune checkpoint inhibitors (ICIs) reinvigorate antitumor immunity by disrupting these inhibitory pathways and remodeling the tumor microenvironment (TME); however, resistance mechanisms (primary, adaptive, and acquired) and immune-related adverse events (irAEs) pose significant clinical challenges. Established biomarkers such as PD-L1 expression, tumor mutational burden (TMB), and microsatellite instability (MSI)/deficient mismatch repair (dMMR) status guide ICI use, but their predictive power has limitations. Consequently, emerging tissue-based (e.g., immune cell signatures, multiplex IHC/IF, spatial transcriptomics), liquid biopsy-based (e.g., ctDNA, CTCs, exosomes), and imaging-based (radiomics, AI-driven analysis) biomarkers are under active investigation to refine patient selection and monitor treatment efficacy. The therapeutic armamentarium is rapidly expanding with novel ICIs targeting new receptors, bispecific antibodies, and innovative combination strategies involving ICIs with chemotherapy, targeted therapies, radiotherapy, and other immunotherapies. Furthermore, ICIs are increasingly explored in neoadjuvant, adjuvant, and maintenance settings. This review highlights the dynamic progress in understanding ICR biology and its clinical translation, emphasizing the ongoing efforts to develop more personalized and effective immunotherapeutic strategies for patients with genitourinary tumors. Full article

Locally advanced rectal cancer is commonly treated using total neoadjuvant therapy (TNT), which integrates radiotherapy with systemic chemotherapy to improve tumor downstaging, local control, and long-term oncologic outcomes. Despite its central role in treatment, responses to radiotherapy remain highly heterogeneous. While some tumors undergo complete regression, others exhibit intrinsic or acquired treatment resistance, resulting in incomplete tumor control while experiencing treatment-related toxicity. Understanding the biological determinants that govern radiation sensitivity in rectal cancer, therefore, represents a major clinical challenge. Ionizing radiation induces tumor cell death primarily through the generation of reactive oxygen species (ROS) and DNA damage, particularly DNA double-strand breaks. In addition to nuclear DNA injury, radiation-induced oxidative stress can initiate lipid peroxidation within cellular membranes. When lipid peroxide accumulation exceeds the capacity of cellular antioxidant systems, this process can trigger ferroptosis, an iron-dependent form of regulated cell death driven by phospholipid oxidation. Ferroptotic susceptibility is regulated by interconnected metabolic pathways, including cystine transport through system Xc⁻ (SLC7A11/SLC3A2), glutathione synthesis, glutathione peroxidase-4 (GPX4) activity, iron metabolism, and membrane lipid remodeling. Recent evidence further indicates that ferroptosis intersects with antitumor immunity. Ferroptotic tumor cells release oxidized lipid mediators and damage-associated molecular signals that can influence immune activation, while interferon-γ produced by activated CD8⁺ T cells during immune checkpoint blockade suppresses SLC7A11 expression, limiting cystine uptake and promoting ferroptotic tumor cell death. These findings suggest that ferroptosis represents a mechanistic interface between tumor metabolic vulnerability and immune-mediated cytotoxicity. This interaction is particularly relevant in colorectal cancer biology, where immune checkpoint inhibitors demonstrate clinical benefit primarily in tumors with deficient mismatch repair or microsatellite instability-high (MSI-H) status. The vast majority of rectal cancers are microsatellite stable (MSS) and exhibit limited responsiveness to immunotherapy due to reduced immunogenicity and immune exclusion within the tumor microenvironment. Strategies capable of increasing tumor immunogenicity in this setting are therefore of considerable interest. In this review, we examine the molecular mechanisms linking radiation-induced oxidative stress to ferroptosis and tumor immunity in colorectal cancer, while focusing on the clinical context of radiotherapy in rectal cancer. We discuss how lipid metabolism, iron homeostasis, cysteine-dependent antioxidant systems, and immune signaling pathways converge to regulate ferroptotic vulnerability and radiation response. We further explore the therapeutic potential of integrating radiotherapy, ferroptosis-targeting strategies, and immunotherapy to overcome radioresistance and improve treatment outcomes in colorectal cancer. Full article

Pancreatic ductal adenocarcinoma (PDAC) and biliary tract cancers (BTCs) remain highly lethal gastrointestinal malignancies because of late presentation, marked molecular heterogeneity, and limited durable benefit from conventional systemic therapy. This narrative review summarizes recent advances in both diseases, focusing on practice-informing clinical trials, biomarker-driven treatment strategies, and translational insights into tumor biology and resistance. In PDAC, progress includes refinement of perioperative management, broader germline and somatic testing, recognition of DNA damage repair-deficient subsets, and development of KRAS-directed therapies and rational combination strategies. In BTCs, especially intrahepatic cholangiocarcinoma, comprehensive molecular profiling has expanded precision oncology through actionable alterations such as FGFR2 rearrangements, IDH1 mutations, HER2 amplification/overexpression, BRAF V600E, NTRK fusions, and MSI-high/dMMR status. Immunotherapy has a clearer role in selected BTC populations, whereas in PDAC benefit remains largely restricted to rare biomarker-defined subsets. Across both diseases, circulating tumor DNA is emerging as a promising tool for prognostication, minimal residual disease assessment, response monitoring, and early resistance detection. Contemporary care increasingly depends on early molecular profiling, individualized treatment sequencing, and integration of targeted therapies, biomarker-guided immunotherapy, and clinical trials. Full article

Background/Objectives: Capivasertib is a selective pan-AKT inhibitor recently approved in combination with fulvestrant for the treatment of hormone receptor-positive (HR+)/HER2- breast cancer with alterations in the PI3K/AKT pathway. The PI3K/AKT/mTOR signaling cascade represents a critical indication of endocrine resistance and tumor progression in this subtype of breast cancer. The present review summarizes current clinical data regarding the efficacy of capivasertib, either as monotherapy or in combination with other therapeutic agents and discusses emerging biomarkers and mechanisms of resistance. Methods: A literature search of the PubMed database was conducted to identify clinical trials evaluating capivasertib in breast cancer. Studies on capivasertib as monotherapy or in combination with fulvestrant, paclitaxel, or olaparib were included. Results: Findings from phase I–III clinical trials indicate that capivasertib in combination with fulvestrant significantly prolongs progression-free survival in patients with HR+/HER2- advanced breast cancer, particularly in tumors containing PIK3CA, AKT1, or PTEN alterations. Drug combination approaches with paclitaxel or olaparib have demonstrated additive or synergistic effects in triple-negative and DNA repair-deficient contexts, respectively. Monotherapy studies confirm effective pathway inhibition with modest clinical benefit, primarily in AKT1-mutant tumors. Translational analyses suggest that persistent mTORC1-mediated protein synthesis and compensatory signaling activation contribute to acquired resistance. Conclusions: Capivasertib constitutes a clinically validated therapeutic approach for the inhibition of AKT signaling in breast cancer. Its efficacy is most evident when combined with endocrine therapy; however, optimization of patient selection and rational combination strategies remains necessary to overcome resistance associated with mTORC1 activation and signaling redundancy. Full article

Y-box binding protein 1 (YB-1; encoded by YBX1) is a multifunctional DNA- and RNA-binding protein implicated in cell cycle regulation, DNA repair, stress adaptation, and therapy resistance. Elevated YBX1 expression has been associated with aggressive disease across multiple cancer types; however, its pan-cancer genomic and clinical correlates, and the extent to which these reflect proliferative activity versus genomic instability, remain incompletely defined. Here, we performed an integrative pan-cancer analysis across 53 independent datasets spanning 33 tumour types, incorporating transcriptomic (YBX1 mRNA), proteomic (RPPA), genomic, and clinical data. We found that YBX1 is rarely altered at the genomic level, whereas its mRNA expression is highly variable within tumour cohorts. Tumours with high YBX1 mRNA expression consistently exhibited conserved transcriptional programmes enriched for cell cycle, mitotic, RNA processing, and signalling pathways, patterns that were also reflected at the protein level by concordant pathway associations with elevated YB-1 abundance. These molecular features co-occurred with clinicopathological characteristics indicative of aggressive disease. High YBX1 mRNA expression was associated with increased mutation burden, chromosomal alteration burden, hypoxia, and homologous recombination deficiency at the pan-cancer level, with similar molecular associations observed in tumours stratified by elevated YB-1 protein levels. The association between YBX1 expression and chromosomal alteration burden was largely attenuated after accounting for proliferative activity, particularly G2/M-associated transcriptional programmes used as a proxy for mitotic activity. While the relationship with mutation burden was heterogeneous across tumour types, this pattern suggests that links between YBX1 expression and chromosomal instability primarily reflect shared proliferative and mitotic tumour biology rather than an independent genomic instability programme. Clinically, high YBX1 mRNA expression was associated with advanced disease stage, higher histologic grade, reduced progression-free survival, and poorer overall survival. Elevated YB-1 protein levels were also associated with advanced disease stage and poorer survival outcomes and demonstrated a similar, although non-significant, directional trend with histologic grade. Collectively, these findings demonstrate that elevated YBX1 expression marks proliferative and clinically aggressive tumour states within which genomic instability-related features arise in a context-dependent manner, providing a clarified pan-cancer framework for interpreting YB-1-associated tumour biology. Full article

Colorectal cancer remains a leading cause of morbidity and mortality worldwide with diverse pathways of carcinogenesis. Deficiencies in the DNA mismatch repair and resultant microsatellite instability are thought to make up roughly 15% of localized and 5% of metastatic cancers of the colon and rectum. Cancers arising through this pathway are characterized by poor response to traditional chemotherapies, but have demonstrated unprecedented responses to immunotherapy over the last decade. Thus, the management of mismatch repair-deficient/microsatellite-unstable colorectal cancer is a rapidly evolving field. In this review we provide a clinician-oriented update on the diagnosis and management of mismatch repair-deficient/microsatellite-unstable colorectal cancer. We explore the tools used for diagnosis as well as the causes and implications of the failure of these tools, along with practical recommendations to mitigate and circumvent such errors. Furthermore, we examine the changing treatment paradigm in the advanced setting with the implementation of mono and dual immunotherapy approaches and explore who is most likely to benefit from such strategies, and how to address treatment failures. Finally, we explore how immunotherapy may allow for non-surgical approaches in the localized setting and discuss the evolving evidence for neoadjuvant and adjuvant approaches when surgery is used. 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