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PubMed2024

Activated NAD+ biosynthesis pathway induces olaparib resistance in BRCA1 knockout pancreatic cancer cells.

PARP inhibitors have been developed as anti-cancer agents based on synthetic lethality in homologous recombination deficient cancer cells. However, resistance to PARP inhibitors such as olaparib remains a problem in clinical use, and the mechanisms of resistance are not fully understood. To investigate mechanisms of PARP inhibitor resistance, we established a BRCA1 knockout clone derived from the pancreatic cancer MIA PaCa-2 cells, which we termed C1 cells, and subsequently isolated an olaparib-resistant C1/OLA cells. We then performed RNA-sequencing and pathway analysis on olaparib-treated C1 and C1/OLA cells. Our results revealed activation of cell signaling pathway related to NAD+ metabolism in the olaparib-resistant C1/OLA cells, with increased expression of genes encoding the NAD+ biosynthetic enzymes NAMPT and NMNAT2. Moreover, intracellular NAD+ levels were significantly higher in C1/OLA cells than in the non-olaparib-resistant C1 cells. Upregulation of intracellular NAD+ levels by the addition of nicotinamide also induced resistance to olaparib and talazoparib in C1 cells. Taken together, our findings suggest that upregulation of intracellular NAD+ is one of the factors underlying the acquisition of PARP inhibitor resistance.

Humans↗
PubMed2026

Real-World Outcomes of Olaparib in Japanese Patients With BRCA-Mutated Metastatic Castration-Resistant Prostate Cancer: Exploratory Analysis of BRCA2 Loss and Microsatellite Instability Status.

OBJECTIVES: Metastatic castration-resistant prostate cancer has a poor prognosis. Although olaparib has demonstrated efficacy in patients with BRCA1/2 mutations, real-world data in Japanese patients remain limited. We aimed to evaluate the efficacy and safety of olaparib in patients with BRCA-mutated metastatic castration-resistant prostate cancer and explore the association of BRCA2 loss and microsatellite instability status with treatment outcomes. METHODS: We conducted a multicenter retrospective study of 34 patients with BRCA-mutated metastatic castration-resistant prostate cancer treated with olaparib between December 2020 and December 2024. The primary endpoint was progression-free survival. Secondary endpoints included overall survival, prostate-specific antigen-50 response rate, and safety. Exploratory analyses were performed. RESULTS: Among the 34 patients, 33 had a BRCA2 mutation and one had a BRCA1 mutation. Prostate-specific antigen reduction was observed in 76.4% of patients; prostate-specific antigen-50 response rate was 58.8%. Median progression-free and overall survival were 15.8 and 35.1 months, respectively. Grade ≥ 3 adverse events (most commonly anemia) occurred in 17.6% of patients. Treatment discontinuation due to adverse events occurred in one patient. Exploratory analyses were performed in 23 BRCA2-mutated patients who underwent comprehensive genomic profiling. BRCA2 loss was observed in 39.1% of patients and showed a trend toward prolonged progression-free survival, whereas microsatellite instability-high status was observed in 13.0% and was associated with shorter progression-free survival. CONCLUSIONS: Olaparib demonstrated efficacy and safety in Japanese patients with BRCA-mutated metastatic castration-resistant prostate cancer. Exploratory analyses revealed that BRCA2 loss may be associated with prolonged progression-free survival, whereas microsatellite instability-high status may be associated with shorter progression-free survival. These findings require validation in larger cohorts.

Humans↗
PubMed2026

Rationale and Study Design of the GUIDANCE trial: A Multicenter Phase II Trial of Maintenance Durvalumab and Olaparib After Standard Fist Line Treatment (Carboplatin/Cisplatin, Etoposide, and Durvalumab) in HRD Positive Extensive Disease (ED) Small-cell Lung Cancer (SCLC) (AIO-TRK-0124/ass).

BACKGROUND: Small-cell lung cancer (SCLC) is an aggressive malignancy with poor prognosis and limited therapeutic progress over recent decades. Although PD-L1 inhibitors have modestly improved survival, responses are not durable. There are no predictive biomarkers that would allow for a personalized treatment strategy. Targeting DNA damage repair deficiencies represents a promising treatment strategy in various solid tumors. Poly (ADP-ribose) polymerase (PARP) inhibitors such as olaparib have demonstrated efficacy in homologous recombination deficiency (HRD)-positive tumors, and preclinical data suggest synergistic activity with immune checkpoint blockade. METHODS: GUIDANCE is a biomarker-driven, multicenter, single-arm, open-label phase II trial evaluating maintenance therapy with durvalumab and olaparib in patients with advanced or metastatic SCLC without progression after first-line therapy with platinum, etoposide and durvalumab. Patients are prospectively selected for HRD based on homologous recombination repair gene alterations and/or a genomic instability score. Following central prescreening, 29 patients will be enrolled. Patients receive durvalumab (1500 mg every 4 weeks) and olaparib (300 mg twice daily) until progression or unacceptable toxicity. The primary endpoint is progression-free survival (PFS) by RECIST 1.1. Secondary endpoints are overall survival, safety and tolerability. Exploratory analyses include circulating tumor DNA (ctDNA) monitoring of individual TP53 mutations, assessment of SLFN11 expression, and characterization of immune cell composition via multiplex immunohistochemistry. DISCUSSION: This trial investigates a chemotherapy-free, genomically stratified maintenance strategy targeting both DNA damage repair deficiency and immune evasion in SCLC. By integrating HRD-based patient selection with concurrent PARP and immune checkpoint inhibition, GUIDANCE aims to establish a more individualized therapeutic approach and to generate a signal for further evaluation in biomarker-defined patient populations. Trial registration number EuraCT 2024-512373-27-00.

DNA-damage repair↗
PubMed2026

A Novel BRCA1 Pathogenic Variant in Tunisian Patient With High Grade Ovarian Cancer: Favorable Therapeutic Response to Olaparib.

BACKGROUND: Ovarian cancer is one of the leading causes of death from gynecological cancer worldwide. Genetic mutations in genes involved in key cellular functions such as BRCA1/2 play a central role in tumorigenesis and have major implications for targeted therapeutic strategies, especially the use of poly (ADP-ribose) polymerase (PARP) inhibitors. CASE: Herein, we described a case of a 50-year-old woman diagnosed with severe anemia secondary to heavy menometrorrhagia. Initial gynecological evaluation, including transvaginal ultrasound, was unremarkable, and endometrial biopsy was not indicated. Imaging revealed no ovarian abnormalities; however, exploratory laparotomy identified a peritoneal nodule, leading to further investigation. Targeted NGS was performed on somatic and germline DNA samples and showed a frame shift deletion of 10 bp (c.1256_1265del: p.R419Ter) in the BRCA1 gene. This variant, identified only in tumor tissues, is novel and classified as pathogenic in ClinVar and ACMG databases. Additional somatic alterations were detected in TP53 and MSH6, while germline testing revealed only a variant of uncertain significance in BARD1. After first-line chemotherapy, the patient benefited from olaparib and achieved a progression-free survival of 23 months with good tolerance and no evidence of disease recurrence. CONCLUSION: This finding highlights the importance of integrating tumor-based genomic profiling with germline testing to identify actionable mutations and guide precision oncology. The identification of a novel somatic BRCA1 mutation expands the mutational spectrum of HGSOC and underscores the need to include underrepresented populations, such as those from North Africa, in genomic studies.

Humans↗
PubMed2025

The cGAS-STING pathway is a master regulator of OCT4 expression in persistent sarcoma cells and enhances cellular immunotherapy with NK and CIK lymphocytes.

Advanced sarcomas have a poor prognosis and limited therapeutic options. Disease recurrence is caused by persistent cells that survive drug treatments. The alkylating agent trabectedin, when combined with the poly (ADP-ribose) polymerase 1 (PARP1) inhibitor olaparib, exhibits variable antitumor effects in advanced sarcomas. In this study, we demonstrate that the expression of the transcription factor OCT4 is upregulated in persistent cells that survive treatment with trabectedin and olaparib, through the cGAS-STING-IRF3-IFNβ pathway. This route also leads to the upregulation of natural killer (NK) and cytokine-induced killer (CIK) lymphocyte activating ligands. These molecular events enhance the antitumor efficacy of immunotherapy with NK and CIK cells, targeting both the bulk population and residual drug-tolerant cells. In conclusion, the activation of the cGAS-STING pathway has a double-edged effect, enriching the OCT4+ persistent cell population while increasing the expression of NK/CIK ligands. The addition of olaparib to trabectedin potentiates the cGAS-STING pathway activation and the upregulation of NKG2DLs, while simultaneously counteracting the OCT4 overexpression. Therefore, sequential treatment with trabectedin and olaparib followed by NK/CIK immunotherapy represents a promising strategy against advanced sarcomas and warrants further investigation.

Humans↗
PubMed2026

CRISPR screen identifies autophagy inhibition (GNS561) as a PARP inhibitor (AZD5305) combination strategy in small cell lung cancer.

BACKGROUND: Small cell lung cancer (SCLC) is a deadly cancer with few treatment options and poor prognosis, creating a dire need for improving therapies. Poly (ADP-ribose) polymerase inhibitors (PARPi) have been tested as a treatment strategy, but patient response varies. We aimed to identify novel approaches to sensitize SCLC to PARPi through a genome-wide CRISPR dropout screen. METHODS: Genome-wide CRISPR dropout screening was conducted in two SCLC cell lines using the PARPi, olaparib, as the selection pressure. Stable shRNA-mediated knockdown cell lines were validated by Western blotting and tested for olaparib sensitivity by assaying for cell viability. Synergy between PARPi and autophagy inhibition was tested by treating SCLC cell lines and analyzing cell viability using SynergyFinder+. The therapeutic strategy combining AZD5305 (PARPi) and GNS561 (novel autophagy inhibitor) was tested in cell line-derived xenograft mouse models. RESULTS: CRISPR screening identified the loss of mTOR negative regulators as a mechanism of PARPi sensitivity in SCLC, and knockdown of TSC1 and TSC2 sensitized SCLC cell lines to olaparib. Therapeutic strategies combining PARPi and autophagy inhibition demonstrated synergy in SCLC cell lines, and combination therapy with AZD5305 and GNS561 was effective in cell line-derived xenograft mouse models. CONCLUSIONS: Autophagy inhibition downstream of the mTOR pathway is a mechanism of PARPi sensitivity in SCLC. This suggests that a therapeutic combination of autophagy inhibition and PARPi is a promising treatment strategy in SCLC, paving the way for the adoption of novel treatments in this disease context.

Autophagy↗
PubMed2025

Role of GDH and PARP inhibitors as novel treatments for SDHB-deficient PPGLs.

SDHB, one of the four genes encoding the subunits of the Krebs cycle enzyme succinate dehydrogenase (SDH), acts as a tumor suppressor in several human cancers, including pheochromocytomas/paragangliomas. Mutations in SDHB lead to a reduction or complete loss of enzymatic activity, linking SDHB to paraganglioma malignancy. Given the difficulty in curing metastatic paragangliomas and the limited value of surgery, new treatments are needed. Glutamine dehydrogenase 1 (GDH1), a key regulator of glutathione metabolism, and poly (ADP-ribose) polymerase (PARP), essential for repairing single- or double-stranded DNA breaks, are crucial in cancer initiation and progression. We treated the human pheochromocytoma cell line (hPheo1) with knocked-down SDHB using radiation, the GDH inhibitor 'R162', and the PARP inhibitor 'olaparib'. Combining R162 with radiation enhances anticancer effectiveness, reduces cell proliferation, and causes G2/M phase arrest in the wild-type and KD-SDHB hPheo1 cell line. KD-SDHB hPheo1 cells treated with olaparib alone were more resistant than wild-type cells but were more sensitive in combination with radiation, activated repair mechanisms, and halted cell cycle progression at the G2/M phase. These results suggest that enhancing radiation-induced DNA damage could be a potential treatment strategy for metastatic pheochromocytomas/paragangliomas. Inhibiting GDH1 and PARP activities, with radiation, may represent promising strategies for the treatment of SDHB-deficient pheochromocytoma/paraganglioma; however, their effects do not appear to be specific to SDHB-deficient cells and require further validation.

Humans↗
PubMed2026

Brazilian Society of Surgical Oncology Analysis in Cost-Effectiveness of Population-Based BRCA Testing for Ovarian Cancer in the Public Health System.

Although ovarian cancer is the most lethal among gynecological cancers, access to massive BRCA testing is still limited. Its cost-effectiveness is still a topic of discussion in several countries. In Brazil, olaparib was recently incorporated into the public health system, access to BRCA testing is still limited. In this article, we aim to review the cost-effectiveness of offering BRCA testing to the at-risk population. A working group composed of 14 specialists in surgical oncology and cancer genetics was established to discuss the cost-effectiveness of population-based BRCA testing for ovarian cancer. The project was divided into five main areas, each with subtopics assigned among the 14 participants. They were: the existing clinical testing guidelines, the current healthcare infrastructure in the Brazilian public health system, cost-effectiveness analysis, challenges in implementing prophylactic surgeries, and family counseling and risk communication. A comprehensive literature review was conducted, followed by a series of meetings among the article's contributors to reach consensus on unresolved issues. These discussions aimed to build recommendations based on the best available scientific evidence. Using as a basis the current structure already existing within the Brazilian public health service (SUS [Sistema Único de Saude]), and based on the testing of the at-risk population chosen by our experts, we estimated savings. The net savings for a population of 100 000 women would range from BRL 7030.30 (US$1255.41) to BRL 1853.92 (US$331.05). And these costs could have an even greater impact when public service PARP inhibitors are incorporated. The working group of the Brazilian Society of Surgical Oncology understands that large-scale BRCA testing is cost-effective, especially when risk-reducing surgery is implemented. Other measures are important, such as training teams of non-specialists to recognize the population at risk, in addition to creating an entire line of care for patients with ovarian cancer in the SUS.

Humans↗
PubMed2026

Prognostic and predictive value of HRD in early triple negative breast cancer (TNBC).

This review explores the emerging role of homologous recombination deficiency (HRD) as both a prognostic and predictive biomarker in early-stage triple-negative breast cancer (TNBC). HRD arises from the defective repair of DNA double-strand breaks through homologous recombination, resulting in genomic instability and increased sensitivity to DNA-damaging agents such as platinum compounds. The review outlines the biological basis of HRD, including genomic signatures such as loss of heterozygosity, telomeric allelic imbalance, and large-scale state transitions, and highlights its prevalence in TNBC compared with other breast cancer subtypes. Clinical trials have shown that HRD-positive patients often achieve higher pathological complete response rates and improved disease-free survival when treated with chemotherapy. However, conflicting evidence across trials underscores the need for more reliable and standardized methods for HRD assessment. The review also explores the therapeutic potential of poly(ADP-ribose) polymerase inhibitors in TNBC, particularly in BRCA-mutated or HRD-positive tumors. Agents such as olaparib, talazoparib, and niraparib have demonstrated promising efficacy in both neoadjuvant and adjuvant settings with some trials suggesting that selected patients may avoid chemotherapy. Furthermore, HRD-positive tumors are characterized by increased genomic instability and a higher neoantigen burden, promoting immune cell infiltration, particularly of tumor-infiltrating lymphocytes, which may enhance responsiveness to immune checkpoint inhibitors. Overall, current evidence supports the role of HRD as a promising biomarker in TNBC. However, further research is required to refine its clinical utility and to integrate HRD testing into personalized treatment strategies, especially in combination with emerging therapies such as immunotherapy.

Humans↗
PubMed2026

CRISPR Screen Identifies HDAC3 as a Novel Radiosensitizing Target in Small Cell Lung Cancer.

Small cell lung cancer (SCLC) is an aggressive malignancy, with most patients presenting with prognostically poor extensive-stage disease. Limited progress in standard care stresses the urgent need for novel therapies. Radiotherapy offers some survival benefit for selected patients with SCLC but could be enhanced with radiosensitizers. In this study, we identify HDAC3 as a novel radiosensitizing target in SCLC using a CRISPR knockout screen and demonstrate its efficacy and mechanism. SBC5 cells were transduced with a custom EpiDrug single-guide RNA library and treated with ionizing radiation (IR) to identify radiosensitizing genes. HDAC3 emerged as a candidate and was validated through genetic knockdown and pharmacologic inhibition (RGFP966) in multiple SCLC cell lines. Both approaches enhanced radiosensitivity, as shown by cell viability (dose modification factor10 = 1.14-1.69) and clonogenic assays (dose modification factor10 = 1.16-1.41). We assessed changes in chromatin accessibility by assay for transposase-accessible chromatin using sequencing and IR-induced DNA damage and repair using γH2AX foci detection, double-strand break (DSB) repair assays, and immunoblotting of repair proteins. HDAC3-deficient cells exhibited increased chromatin accessibility, greater IR-induced DSBs, and impaired repair capacity, resulting in persistent DNA damage. This repair defect sensitized cells to PARP inhibitors, for which combining RGFP966 with olaparib or talazoparib produced additive to synergistic effects. In SCLC xenograft models, HDAC3 knockdown or RGFP966, combined with IR, achieved significant tumor growth inhibition. Collectively, we identified HDAC3 as a novel radiosensitizing target in SCLC. Its functional loss increased the generation and persistence of IR-induced DNA DSBs, effectively sensitizing SCLC cell lines and xenografts to IR, providing a potential radiosensitization strategy to treat SCLC.

Humans↗
PubMed2026

Patient-derived organoids predict responses to chemotherapy and PARP inhibitors in advanced ovarian cancer.

BACKGROUND: While tumor organoids hold promise for personalized medicine, clinical validation of epithelial ovarian cancer (EOC) organoids as predictors of therapeutic efficacy-particularly for PARP inhibitors (PARPi)-remains unestablished. METHODS: Patient-derived organoids (PDOs) were established from treatment-naive EOC specimens and characterized by H&E staining, immunohistochemistry, and whole-exome sequencing. Drug sensitivity testing (DST) was performed using carboplatin, paclitaxel, and PARPi (olaparib and niraparib). Clinical homologous recombination deficiency (HRD) status was assessed by tumor sequencing. Organoid responses were prospectively compared to patient outcomes after first-line chemotherapy (carboplatin/paclitaxel) and PARPi maintenance. RESULTS: PDOs were successfully established from 21 of 30 patients (70%) across multiple EOC subtypes and preserved the histopathological features and genomic landscapes of their corresponding primary tumors. Organoid-based DST accurately predicted responses to first-line carboplatin/paclitaxel, with a sensitivity of 100% (95% CI 62.88-100%), specificity of 66.67% (95% CI 12.53-98.23%), accuracy of 91.67% (95% CI 61.52-99.79%), AUC of 0.95 (95% CI 0.85-1.00), and Cohen's kappa of 0.75 (95% CI 0.30-1.00). In evaluating PARPi response, organoids revealed discrepancies between genomic HRD status and actual drug responses. One HRD-positive PDO was PARPi-resistant, consistent with patient non-response, while two HRR-proficient PDOs showed PARPi sensitivity and corresponding clinical benefit. CONCLUSIONS: EOC-derived PDOs provide a robust platform for predicting chemotherapy response and offer added value in assessing PARPi efficacy beyond genomic profiling. Combination of organoid-based testing with genomic analysis may improve precision treatment strategies in EOC.

Humans↗
PubMed2026

Systemic treatment of advanced pancreatic cancer: A Comprehensive Review.

IMPORTANCE: Pancreatic adenocarcinoma (PDAC) is an uncommon but potentially catastrophic diagnosis with historically poor prognosis. It is the tenth most prevalent cancer in the US & UK. Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies worldwide, with a five-year survival rate of approximately 10%. Despite increasing understanding of its molecular biology, systemic treatment options for advanced disease remain limited, and survival outcomes have improved only modestly over the past decade. OBSERVATIONS: This narrative review traces the evolution of systemic therapy for advanced PDAC from gemcitabine monotherapy through the landmark FOLFIRINOX (PRODIGE trial) and gemcitabine/nab-paclitaxel (MPACT trial) combination regimens, which remain the standard of care. Second-line options including liposomal irinotecan plus 5-FU/LV (NAPOLI-1) and maintenance olaparib for germline BRCA1/2-mutated disease (POLO) are also reviewed. Emerging data on sequential treatment strategies (SEQUENCE trial), biomarker-driven treatment selection (PRIMUS-001, PASS-01), and precision medicine approaches targeting actionable molecular subgroups, including dMMR/MSI-H, NTRK fusions, and homologous recombination deficiency are discussed. Real-world evidence comparing FOLFIRINOX and gemcitabine/nab-paclitaxel is critically appraised, including the challenges of patient selection, tolerance, and applicability outside clinical trial settings. CONCLUSION AND RELEVANCE: Despite incremental progress, the treatment landscape of advanced PDAC remains challenging. Molecular stratification and biomarker-driven precision oncology represent the most promising path forward. This review serves as a clinical reference for physicians managing advanced pancreatic cancer, highlighting current evidence, evidence limitations, and future research priorities including prospective biomarker-driven trials and improved access to genomic testing.

Biomarkers↗
PubMed2026

STN1 upregulation promotes PARPi resistance in BRCA2-deficient cancer cells via replication fork protection and suppression of ssDNA gap formation.

PARPi are effective therapy for BRCA1/2 mutant cancers, yet recurrent PARPi resistance frequently develops. The underlying mechanism of PARPi resistance remains largely unresolved. Here, we identify STN1, a component of the CTC1/STN1/TEN1 (CST) complex, as a modulator of PARPi resistance in BRCA2-deficient cells. RNA-seq analysis of PARPi-resistant cancer cells from BRCA2-mutated backgrounds shows largely distinct transcriptomic profiles with limited overlap, suggesting multiple routes to resistance. Notably, STN1 is consistently upregulated in resistant cells. We observe that overexpression of STN1 enhances Olaparib resistance in multiple BRCA2-deficient cell lines and alleviates DNA damage under replication stress. Mechanistically, we find that STN1 overexpression increases RAD51 loading to stalled replication forks while restricting MRE11 recruitment in BRCA2-deficient cells, thereby protecting stalled forks from nascent-strand degradation. Furthermore, STN1 overexpression rescues the accumulation of ssDNA gaps, a major determinant of PARPi sensitivity in BRCA2-deficient cells. Taken together, these findings suggest that elevated STN1 levels can partially compensate for BRCA2 loss by stabilizing stalled replication forks and limiting ssDNA gap accumulation. Our study uncovers a STN1-dependent pathway of replication stress tolerance that promotes PARPi resistance independently of homologous recombination restoration, highlighting STN1 as a potential biomarker and mechanistic contributor to therapeutic resistance in BRCA2-mutated cancers.

PARPi resistance↗