Inhibition Of DNA Damage Repair Research Articles

Wogonin inhibits radiation-induced DNA damage repair in hepatocellular carcinoma cells by upregulating p21.

Wogonin has been shown to exhibit anti-tumor effects by regulating the growth and inducing cell death in hepatocellular carcinoma (HCC) cells. However, its impact on radiotherapy for HCC remains unclear. This study aimed to elucidate the mechanisms and effects of wogonin in enhancing radiotherapy for HCC. The viability and cell cycle of HCC cells were assessed using CCK-8, trypan blue dye exclusion, and flow cytometry. RNA sequencing was performed to explore the genomic effects of wogonin on HCC cells. Immunofluorescence staining was employed to detect γ-H2AX distribution, and Western blot was used to evaluate the expression of γ-H2AX and p21. Wogonin induced cell cycle arrest and inhibited DNA damage repair in SMMC-7721 and HCC-LM3 cells following irradiation. RNA sequencing analysis of wogoninand radiation-treated cells revealed significant enrichment of genes related to cell cycle progression, with notable changes in CDK inhibitor expression. Furthermore, wogonin in combination with irradiation increased the expression of γ-H2AX and p21 in HCC cells. Notably, p21 interference partially abrogated the anti-tumor effects of wogonin and radiation. Wogonin enhances the efficacy of radiotherapy in HCC by promoting cell cycle arrest and inhibiting DNA damage repair through upregulation of p21.

Overexpression of miR-124 enhances the therapeutic benefit of TMZ treatment in the orthotopic GBM mice model by inhibition of DNA damage repair

Glioblastoma (GBM) is the most common malignant primary brain cancer with poor prognosis due to the resistant to current treatments, including the first-line drug temozolomide (TMZ). Accordingly, it is urgent to clarify the mechanism of chemotherapeutic resistance to improve the survival rate of patients. In the present study, by integrating comprehensive non-coding RNA-seq data from multiple cohorts of GBM patients, we identified that a series of miRNAs are frequently downregulated in GBM patients compared with the control samples. Among them, a high level of miR-124 is closely associated with a favorable survival rate in the clinical patients. In the phenotype experiment, we demonstrated that miR-124 overexpression increases responsiveness of GBM cells to TMZ-induced cell death, and vice versa. In the mechanistic study, we for the first time identified that RAD51, a key functional molecule in DNA damage repair, is a novel and bona fide target of miR-124 in GBM cells. Given that other miR-124-regulated mechanisms on TMZ sensitivity have been reported, we performed recue experiment to demonstrate that RAD51 is essential for miR-124-mediated sensitivity to TMZ in GBM cells. More importantly, our in vivo functional experiment showed that combinational utilization of miR-124 overexpression and TMZ presents a synergetic therapeutic benefit in the orthotopic GBM mice model. Taken together, we rationally explained a novel and important mechanism of the miR-124-mediated high sensitivity to TMZ-induced cell death in GBM and provided evidence to support that miR-124-RAD51 regulatory axis could be a promising candidate in the comprehensive treatment with TMZ in GBM.

Abstract A012: Development of a translational tumoroid-organoid platform revealing tumor-specific radiosensitization in rectal cancer using matched patient-derived models

Abstract Background: Radiation therapy in rectal cancer treatment is limited by variable tumor responses among patients and harmful effects on normal tissues. We developed a translational human tumoroid-organoid platform to assess novel tumor-specific strategies for radiation sensitization using matched patient-derived models. Methods: Fifteen rectal cancer-derived tumoroids and three matched normal tissue-derived organoids were established from patients, representing primary tumors, metastases, and recurrences. Four tumoroids were derived from a single patient, encompassing different disease stages: primary tumor and splenic metastasis (pre-progression), and rectal and vaginal recurrences (post-progression). To evaluate tumor-specific radiation sensitizers, both tumoroids and their matched normal organoids were treated with 5-fluorouracil (5-FU), one of four DNA damage repair inhibitors (DDRis; ATMi, DNA-PKi, PARPi, or ATRi), or a DMSO control. Following treatment, samples were irradiated, and cell viability was measured. We assessed intrinsic radiation sensitivity under control conditions and radiosensitizer efficacy using a linear regression model with log-transformed cell viability as the outcome. Whole-exome sequencing characterized the mutation profiles of the tumoroids. Results: Intrinsic radiosensitivity was heterogeneous among tumoroids, with a 10–28% decrease in cell growth per unit increase in radiation dose. Critically, when comparing tumoroids to their matched normal organoids, we observed greater sensitization in tumoroids across all cases and for all DDRis, demonstrating tumor-specific radiosensitization. The most potent radiosensitizer relative to DMSO was DNA-PKi in 7 tumoroids, ATMi in 4 tumoroids, and PARPi in 1 tumoroid. Tumoroids derived after disease progression exhibited increased resistance to radiation and a diminished degree of sensitization with DDRi treatment compared to pre-progression tumoroids. Despite variations in radiation sensitivity and DDRi responses, the genetic profiles of the tumoroids remained largely unchanged. Conclusion: We developed a translational ex vivo tumoroid-organoid platform using matched patient-derived models to test tumor-specific radiation sensitizers in rectal cancer. This platform allowed us to determine tumor-specific sensitization by directly comparing tumoroids with matched normal organoids, demonstrating greater sensitization in tumoroids. Our findings highlight the potential of this platform to uncover precise, tumor-selective treatment options, improve patient responses, reduce toxicity, and address resistant tumors in patients with disease progression. Citation Format: Wini Zambare, Chao Wu, Hannah Kalvin, Hanchen Huang, Sara Yoder, Michael Del Latto, Maria Kierstead, Satoru Meguro, Xi Steven Chen, Mithat Gonen, J. Joshua Smith, Paul B. Romesser. Development of a translational tumoroid-organoid platform revealing tumor-specific radiosensitization in rectal cancer using matched patient-derived models. [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Targeted Therapies in Combination with Radiotherapy; 2025 Jan 26-29; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(2_Suppl):Abstract nr A012.

A Multipotent PROX1+ Tumor Stem/Progenitor Cell Population Emerges During Intestinal Tumorigenesis and Mediates Radioresistance in Colorectal Cancer.

Colorectal carcinoma (CRC) progression is associated with an increase in PROX1+ tumor cells, which exhibit features of CRC stem cells and contribute to metastasis. Here, we aimed to provide a better understanding to the function of PROX1+ cells in CRC, investigating their progeny and their role in therapy resistance. PROX1+ cells in intestinal adenomas of ApcMin/+ mice expressed intestinal epithelial and CRC stem cell markers, and cells with high PROX1 expression could both self-renew tumor stem/progenitor cells and contribute to differentiated tumor cells. Most PROX1-lineage traced tumor cells were stem/progenitor cells, which can supply cells to multiple intestinal tumor cell lineages, whereas most lineage-traced LGR5+ tumor cells were enterocytes, indicating that PROX1+ and LGR5+ tumor stem cells have distinct differentiation programs. Although the PROX1+ tumor cells proliferated slower than PROX1- cells, irradiation increased the proportion of PROX1+ cells in human CRC cell lines, patient-derived organoids, and tumor xenografts. Furthermore, transcripts related to DNA damage repair (DDR) were enriched in PROX1+ vs. PROX1- cells in adenomas and in CRC tumor cells from patients. Experiments with PROX1 silencing and overexpression indicated that PROX1 expression enhances CRC cell colony formation following irradiation. PROX1 interacted with DDR proteins, including components of non-homologous end-joining (NHEJ) and base excision repair, and inhibition of NHEJ repair led to a decreased proportion of PROX1+ cells following irradiation. In conclusion, PROX1+ cells are irradiation-resistant tumor stem/progenitor cells capable of self-renewal and differentiation. DDR inhibitors could represent a strategy to target the treatment-resistant PROX1+ tumor stem cells.

Advancements in Cancer Therapeutics: Emerging Agents and Combination Strategies in Drug Discovery

In the last few years, there have been significant advances in cancer agent research, most of which entered clinical trials after succeeding in initial preclinical studies. Here, we discuss successful accomplishments in the promising approaches of targeted therapies, immunotherapies, and combination therapies. The development in these areas includes sotorasib - targeting the mutation of KRAS for lung and pancreatic cancer and pembrolizumab - an immune checkpoint inhibitor for melanoma therapy; the latter has been synergistic with chemotherapy. In addition, exciting results emerge from trials with the DNA damage repair inhibitor olaparib in BRCA-mutated cancers and the tyrosine kinase inhibitor osimertinib for EGFR-mutant lung cancer. Bevacizumab continues to establish itself as an evolving therapy in colorectal cancer, and niraparib enters Phase III in ovarian cancer. New combinations will include alpelisib and PD-1 inhibitors and nanoparticle-based Abraxane for triple-negative breast cancers leading toward precision medicine. These would improve the survival rates and quality of life in patients with advanced or refractory malignancies.

Enhancement Of High-Dose Chemotherapy and Autologous SCT with the PARP Inhibitor Olaparib for Refractory Lymphoma.

More active high-dose chemotherapy (HDC) regimens are needed for autologous stem-cell transplantation (ASCT) for refractory lymphomas. Seeking HDC enhancement with a poly(ADP-ribose) polymerase (PARP) inhibitor, we observed marked synergy between olaparib and vorinostat/gemcitabine/busulfan/melphalan (GemBuMel) against lymphoma cell lines, mediated by inhibition of DNA damage repair. Our preclinical work led us to clinically study olaparib/vorinostat/GemBuMel with ASCT. Patients ages 15-65 with refractory lymphoma and adequate end-organ function were eligible for this phase I trial. The olaparib dose was escalated from 25 mg PO BID on days (d)-11 to -3, plus vorinostat (1,000 mg PO/d, d-10 to -3), gemcitabine (2,475 mg/m2/d IV, d-8 and -3), busulfan (target AUC 4,000 μM.min-1/d IV, d-8 to -5), melphalan (60 mg/m2/d IV, d-3 and -2), and rituximab (CD20+ tumors) (375 mg/m2, d-10), with ASCT. Fifty patients were enrolled (23 Hodgkin, 18 DLBCL, 9 T-NHL); median age 35 (range, 20-61); median 3 prior lines of therapy (range, 2-7); 17 patients had previously relapsed after CAR-T or other cellular immunotherapies; 23 patients had PET-positive tumors at HDC (9 in progression). An olaparib dose of 150 mg PO BID was identified as the recommended phase 2 dose. The main extramedullary toxicity was mucositis. The ORR/CR rates were 100%/90%. At median follow-up of 30 months (range, 12-56) months, the EFS/OS rates were 72%/82%, and 71%/88% in patients with prior CAR-T cell failure. In this first trial combining a PARP inhibitor with HDC, olaparib/vorinostat/GemBuMel was safe and showed promising activity in refractory lymphomas, including post-CAR-T relapses.

Insecticide chlorfenapyr confers induced toxicity in human cells through mitochondria-dependent pathways of apoptosis.

Pesticides are always used in the environment, the unexpected effects of pesticides on the environment and non-target organisms need to be continuously studied. Insecticide chlorfenapyr (Chl) is widely used in agriculture and also recommended for public health use (e.g., providing protection from malaria). Here we study toxic effects of Chl on human alveolar carcinoma cells (A549) and human normal liver cells (L02) in vitro. Chl's ability to induce DNA damage and apoptosis in human cells was confirmed through alkaline comet assay, immunofluorescence assay, and flow cytometric analysis. Further research showed that Chl induced mitochondrial damage (the collapse of mitochondrial membrane potential and the opening of mitochondrial permeability transition pore) with up-regulated expression of Bax/Bcl-2 leads to the release of cytochrome c from mitochondria which in turn activated the apoptotic pathway. Meanwhile, the key protein PARP is cleaved during apoptosis, resulting in the inhibition of DNA damage repair. In short, human A549 and L02 cells exposed to Chl were experiencing DNA damage and apoptosis linked to mitochondria. The results of this study supply theoretical understanding of Chl's toxicity on human cells, and can attract attention on the potential threat of insecticide Chl to human health.

Nanoparticulate drug combination inhibits DNA damage repair and PD-L1 expression in BRCA-mutant and wild type triple-negative breast cancer

The high mortality rate associated with metastatic breast cancer presents a significant global challenge. Inherent and chemotherapy-induced DNA damage repair, alongside immunosuppression, drastically contribute to triple-negative breast cancer (TNBC) relapse and metastasis. While poly (ADP-ribose) polymerase (PARP) inhibitors such as olaparib show effectiveness against BRCA1-mutant TNBC, they may lead to drug resistance and reduced efficacy due to increased programmed death-ligand 1 (PD-L1) expression. Our study explored the use of polymer-lipid nanoparticles (PLN) loaded with doxorubicin (DOX) and oligomeric hyaluronic acid (oHA), functionalized iRGD-peptide for integrins targeting (iRGD-DOX-oHA-PLN), to prevent TNBC immunosuppression, DNA repair, and metastasis. The results demonstrate that the iRGD-DOX-oHA-PLNs efficiently downregulated single and double-strand DNA repair proteins and enhanced DNA damage while decreasing PD-L1 expression compared to olaparib. Accordingly, iRGD-DOX-oHA-PLN treatment showed significantly higher efficiency in reducing levels of primary tumor growth and numbers of metastases to the lung and liver compared to olaparib in vitro and in vivo in both BRCA1-mutant and wild type TNBC orthotopic xenograft models.

Metabolizable alloy clusters assemble nanoinhibitor for enhanced radiotherapy of tumor by hypoxia alleviation and intracellular PD-L1 restraint

BackgroundCancer radiotherapy (RT) still has limited clinical success because of the obstacles including radioresistance of hypoxic tumors, high-dose X-ray–induced damage to adjacent healthy tissue, and DNA-damage repair by intracellular PD-L1 in tumor.ResultsTherefore, to overcome these obstacles multifunctional core–shell BMS@Pt2Au4 nanoparticles (NPs) are prepared using nanoprecipitation followed by electrostatic assembly. Pt2Au4 clusters are released from BMS@Pt2Au4 NPs to alleviate tumor hypoxia by catalyzing the decomposition of endogenous H2O2 to generate O2 as well as by enhancing X-ray deposition at the tumor site, which thereby reduce the required X-ray dose. The released BMS-202 molecules simultaneously blockade PD-L1 on and in tumor cells, causing the activation of effector T cells and the inhibition of DNA-damage repair. Consequently, radiotherapy based on BMS@Pt2Au4 NPs enhance the expression of calreticulin on cancer cells, transposition of HMGB1 from the nucleus to the cytoplasm, generation of reactive oxygen species (ROS), DNA breakage and apoptosis of cancer cells in vitro. The tumor inhibition rate reached 92.5% under three cycles of 1-Gy X-ray irradiation in vivo.ConclusionIn conclusion, the therapeutic outcome supports the high-efficiency of radiotherapy based on BMS@Pt2Au4 NPs in hypoxic tumors expressing PD-L1.Graphical

DNAR-12. STEAROYL-COA DESATURASE REGULATES DNA DAMAGE REPAIR IN GBM BY MODULATING PARP1 ACTIVITY

Abstract Glioblastoma (GBM) is the most prevalent malignant brain cancer in adults, notorious for its aggressiveness and resistance to therapy. GBM patients commonly receive radiation therapy combined with temozolomide (TMZ), which engages tumor cells to promote lethal DNA damage and subsequent cytotoxicity. Active DNA repair mechanisms, particularly in a subset population of GBM stem-like cells (GSCs), drive therapeutic resistance, thus largely contributing to the bleak prognosis of GBM. Poly (ADP-ribose) polymerases (PARPs) are essential in various cellular processes, including DNA repair. We have previously reported that fatty acid desaturation mediated by Stearoyl-CoA desaturase 1 (SCD1) plays a cytoprotective role in GSCs. Inhibiting SCD prevents tumor initiation and inhibits DNA damage repair, hence sensitizing to radiation and TMZ. Yet, the mechanistic role of SCD in DNA damage regulation remained unknown. Here, we found that the expression of both human isoforms of SCD, SCD1, and SCD5, directly correlates with PARP protein levels and subcellular localization. Downregulating SCD1/5 in GSCs resulted in significantly lower levels of PARP1, coupled with increased DNA damage, as well as reduced DNA damage repair and chromosome assembly. Conversely, cells overexpressing SCD1/5 exhibited higher PARP1 expression and lower levels of basal DNA damage compared to control GSCs. Notably, SCD1/5 overexpression also led to increased resistance to TMZ. We show that SCD1/5 regulates PARP activity by controlling PARP1 subcellular localization. In addition to decreased total levels of PARP following SCD1/5 downregulation, we also found increased PARP1 self-PARylation. Using confocal microscopy, we show that when SCD1/5 is repressed, PARylated PARP translocates from the nucleus to the cytosol, rendering it unable to bind DNA and recruit DNA-repairing machinery. In conclusion, our study provides a direct link between fatty acid metabolism and PARP1-mediated DNA damage repair.

The cGAS-STING pathway is an in vivo modifier of genomic instability syndromes.

Mutations in genes involved in DNA damage repair (DDR) often lead to premature aging syndromes. While recent evidence suggests that inflammation, alongside mutation accumulation and cell death, may drive disease phenotypes, its precise contribution to in vivo pathophysiology remains unclear. Here, by modeling Ataxia Telangiectasia (A-T) and Bloom Syndrome in the African turquoise killifish ( N. furzeri ), we replicate key phenotypes of DDR syndromes, including infertility, cytoplasmic DNA fragments, and reduced lifespan. The link between DDR defects and inflammation is attributed to the activation of the cGAS-STING pathway and interferon signaling by cytoplasmic DNA. Accordingly, mutating cGAS partially rescues germline defects and senescence in A-T fish. Double mutants also display reversal of telomere abnormalities and suppression of transposable elements, underscoring cGAS's non-canonical role as a DDR inhibitor. Our findings emphasize the role of interferon signaling in A-T pathology and identify the cGAS-STING pathway as a potential therapeutic target for genomic instability syndromes.

P1.03G.01 Lurbinectedin Synergizes with Selinexor by Inhibiting DNA Damage Repair and Enhancing Immune Cell Infiltration in Neuroendocrine Lung Tumors

P1.03G.01 Lurbinectedin Synergizes with Selinexor by Inhibiting DNA Damage Repair and Enhancing Immune Cell Infiltration in Neuroendocrine Lung Tumors

YAP1 Status Defines Two Intrinsic Subtypes of LCNEC with Distinct Molecular Features and Therapeutic Vulnerabilities.

Large cell neuroendocrine carcinoma (LCNEC) is a high-grade neuroendocrine malignancy that, like small cell lung cancer (SCLC), is associated with the absence of druggable oncogenic drivers and dismal prognosis. In contrast to SCLC, however, there is little evidence to guide optimal treatment strategies, which are often adapted from SCLC and non-small cell lung cancer approaches. To better define the biology of LCNEC, we analyzed cell line and patient genomic data and performed IHC and single-cell RNA sequencing of core needle biopsies from patients with LCNEC and preclinical models. In this study, we demonstrate that the presence or absence of YAP1 distinguishes two subsets of LCNEC. The YAP1-high subset is mesenchymal and inflamed and is characterized, alongside TP53 mutations, by co-occurring alterations in CDKN2A/B and SMARCA4. Therapeutically, the YAP1-high subset demonstrates vulnerability to MEK- and AXL-targeting strategies, including a novel preclinical AXL chimeric antigen receptor-expressing T cell. Meanwhile, the YAP1-low subset is epithelial and immune-cold and more commonly features TP53 and RB1 co-mutations, similar to those observed in pure SCLC. Notably, the YAP1-low subset is also characterized by the expression of SCLC subtype-defining transcription factors, especially ASCL1 and NEUROD1, and as expected, given its transcriptional similarities to SCLC, exhibits putative vulnerabilities reminiscent of SCLC, including delta-like ligand 3 and CD56 targeting, as is with novel preclinical delta-like ligand 3 and CD56 chimeric antigen receptor-expressing T cells, and DNA damage repair inhibition. YAP1 defines distinct subsets of LCNEC with unique biology. These findings highlight the potential for YAP1 to guide personalized treatment strategies for LCNEC.

Dose-rate effects and tumor control probability in 177Lu-based targeted radionuclide therapy: a theoretical analysis

Objective.177Lu-based targeted radionuclide therapy (TRT) has become an important cancer treatment option in recent years, in particular in the treatment of advanced prostate cancer and metastasized neuroendocrine tumors. Although it is known from conventional radiotherapy that the temporal dynamics of the dose-rate can be of relevance for tumor cell survival, the analysis of TRT efficacy usually considers only the absorbed dose. Thus, the aim of this theoretical analysis is to shed light on the possible effects of the pattern of dose-rate in TRT on tumor control probability (TCP).Approach.For this purpose, TCP is studied numerically in a typical four-cycle treatment regime based on the mechanistic lethal-potentially lethal model and the Zaider-Minerbo model for TCP including repopulation of tumor cells.Main results.It is shown that the dose-rate pattern in TRT can have a substantial effect on TCP even though the absorbed dose in the tumor lesion is unchanged. These dose-rate effects are particularly evident when repair of potentially lethal lesions is slow.Significance.The results indicate that in some situations in the analysis of the efficacy of TRT it is necessary to consider the full dose-rate pattern instead of the absorbed dose alone. This can be highly relevant for optimization and further development of TRTs. In particular, it could be of relevancy in studying the efficacy of newly emerging treatment concepts that combine the use of TRT and drugs that inhibit DNA damage repair.

359 (PB347): Neoplastic small extracellular vesicles cause DNA damage and inhibit DNA damage repair in Barrett’s esophagus cells: A model for synthetic lethality by PARP inhibitors

359 (PB347): Neoplastic small extracellular vesicles cause DNA damage and inhibit DNA damage repair in Barrett’s esophagus cells: A model for synthetic lethality by PARP inhibitors

FACT inhibitor CBL0137, administered in an optimized schedule, potentiates radiation therapy for glioblastoma by suppressing DNA damage repair.

Standard-of-care for glioblastoma remains surgical debulking followed by temozolomide and radiation. However, many tumors become radio-resistant while radiation damages surrounding brain tissue. Novel therapies are needed to increase the effectiveness of radiation and reduce the required radiation dose. Drug candidate CBL0137 is efficacious against glioblastoma by inhibiting histone chaperone FACT, known to be involved in DNA damage repair. We investigated the combination of CBL0137 and radiation on glioblastoma. In vitro, we combined CBL0137 with radiation on U87MG and A1207 glioblastoma cells using the clonogenic assay to evaluate the response to several treatment regimens, and the Fast Halo Assay to examine DNA repair. In vivo, we used the optimum combination treatment regimen to evaluate the response of orthotopic tumors in nude mice. In vitro, the combination of CBL0137 and radiation is superior to either alone and administering CBL0137 two hours prior to radiation, having the drug present during and for a prolonged period post-radiation, is an optimal schedule. CBL0137 inhibits DNA damage repair following radiation and affects the subcellular distribution of histone chaperone ATRX, a molecule involved in DNA repair. In vivo, one dose of CBL0137 is efficacious and the combination of CBL0137 with radiation increases median survival over either monotherapy. CBL0137 is most effective with radiation for glioblastoma when present at the time of radiation, immediately after and for a prolonged period post-radiation, by inhibiting DNA repair caused by radiation. The combination leads to increased survival making it attractive as a dual therapy.

FACT inhibitor CBL0137, administered in an optimized schedule, potentiates radiation therapy for glioblastoma by suppressing DNA damage repair.

Standard-of-care for glioblastoma remains surgical debulking followed by temozolomide and radiation. However, many tumors become radio-resistant while radiation damages surrounding brain tissue. Novel therapies are needed to increase the effectiveness of radiation and reduce the required radiation dose. Drug candidate CBL0137 is efficacious against glioblastoma by inhibiting histone chaperone FACT, known to be involved in DNA damage repair. We investigated the combination of CBL0137 and radiation on glioblastoma. In vitro, we combined CBL0137 with radiation on U87MG and A1207 glioblastoma cells using the clonogenic assay to evaluate the response to several treatment regimens, and the Fast Halo Assay to examine DNA repair. In vivo, we used the optimum combination treatment regimen to evaluate the response of orthotopic tumors in nude mice. In vitro, the combination of CBL0137 and radiation is superior to either alone and administering CBL0137 two hours prior to radiation, having the drug present during and for a prolonged period post-radiation, is an optimal schedule. CBL0137 inhibits DNA damage repair following radiation and affects the subcellular distribution of histone chaperone ATRX, a molecule involved in DNA repair. In vivo, one dose of CBL0137 is efficacious and the combination of CBL0137 with radiation increases median survival over either monotherapy. CBL0137 is most effective with radiation for glioblastoma when present at the time of radiation, immediately after and for a prolonged period post-radiation, by inhibiting DNA repair caused by radiation. The combination leads to increased survival making it attractive as a dual therapy.

Aberrant SWI/SNF Complex Members Are Predominant in Rare Ovarian Malignancies-Therapeutic Vulnerabilities in Treatment-Resistant Subtypes.

SWI/SNF (SWItch/Sucrose Non-Fermentable) is the most frequently mutated chromatin-remodelling complex in human malignancy, with over 20% of tumours having a mutation in a SWI/SNF complex member. Mutations in specific SWI/SNF complex members are characteristic of rare chemoresistant ovarian cancer histopathological subtypes. Somatic mutations in ARID1A, encoding one of the mutually exclusive DNA-binding subunits of SWI/SNF, occur in 42-67% of ovarian clear cell carcinomas (OCCC). The concomitant somatic or germline mutation and epigenetic silencing of the mutually exclusive ATPase subunits SMARCA4 and SMARCA2, respectively, occurs in Small cell carcinoma of the ovary, hypercalcaemic type (SCCOHT), with SMARCA4 mutation reported in 69-100% of SCCOHT cases and SMARCA2 silencing seen 86-100% of the time. Somatic ARID1A mutations also occur in endometrioid ovarian cancer (EnOC), as well as in the chronic benign condition endometriosis, possibly as precursors to the development of the endometriosis-associated cancers OCCC and EnOC. Mutation of the ARID1A paralogue ARID1B can also occur in both OCCC and SCCOHT. Mutations in other SWI/SNF complex members, including SMARCA2, SMARCB1 and SMARCC1, occur rarely in either OCCC or SCCOHT. Abrogated SWI/SNF raises opportunities for pharmacological inhibition, including the use of DNA damage repair inhibitors, kinase and epigenetic inhibitors, as well as immune checkpoint blockade.

Radiosensitizing Effect of PARP Inhibition on Chondrosarcoma and Chondrocyte Cells Is Dependent on Radiation LET.

Chondrosarcoma is a rare malignant tumor that forms in bone and cartilage. The primary treatment involves surgical removal of the tumor with a margin of healthy tissue. Especially if complete surgical removal is not possible, radiation therapy and chemotherapy are used in conjunction with surgery, but with a generally low efficiency. Ongoing researches are focused on understanding the genetic and molecular basis of chondrosarcoma following high linear energy transfer (LET) irradiation, which may lead to treatments that are more effective. The goal of this study is to evaluate the differential effects of DNA damage repair inhibitors and high LET irradiation on chondrosarcoma versus chondrocyte cells and the LET-dependency of the effects. Two chondrosarcoma cell lines with different IDH mutation status and one chondrocyte cell line were exposed to low LET (X-ray) and high LET (carbon ion) irradiation in combination with an Olaparib PARP inhibitor. Cell survival and DNA repair mechanisms were investigated. High LET irradiation drastically reduced cell survival, with a biological efficiency three times that of low LET. Olaparib significantly inhibited PARylation in all the tested cells. A significant reduction in cell survival of both chondrosarcoma and chondrocyte cells was observed following the treatment combining Olaparib and X-ray. PARP inhibition induced an increase in PARP-1 expression and a reduced effect on the cell survival of WT IDH chondrosarcoma cells. No radiosensitizing effect was observed in cells exposed to Olaparib paired with high LET irradiation. NHEJ was activated in response to high LET irradiation, neutralizing the PARP inhibition effect in both chondrosarcoma cell lines. When high LET irradiation is not available, PARP inhibition could be used in combination with low LET irradiation, with significant radiosensitizing effects on chondrosarcoma cells. Chondrocytes may be affected by the treatment combination too, showing the need to preserve normal tissues from radiation fields when this kind of treatment is suggested.

The PARP1 selective inhibitor saruparib (AZD5305) elicits potent and durable antitumor activity in patient-derived BRCA1/2-associated cancer models

BackgroundPoly (ADP-ribose) polymerase 1 and 2 (PARP1/2) inhibitors (PARPi) are targeted therapies approved for homologous recombination repair (HRR)-deficient breast, ovarian, pancreatic, and prostate cancers. Since inhibition of PARP1 is sufficient to cause synthetic lethality in tumors with homologous recombination deficiency (HRD), PARP1 selective inhibitors such as saruparib (AZD5305) are being developed. It is expected that selective PARP1 inhibition leads to a safer profile that facilitates its combination with other DNA damage repair inhibitors. Here, we aimed to characterize the antitumor activity of AZD5305 in patient-derived preclinical models compared to the first-generation PARP1/2 inhibitor olaparib and to identify mechanisms of resistance.MethodsThirteen previously characterized patient-derived tumor xenograft (PDX) models from breast, ovarian, and pancreatic cancer patients harboring germline pathogenic alterations in BRCA1, BRCA2, or PALB2 were used to evaluate the efficacy of AZD5305 alone or in combination with carboplatin or an ataxia telangiectasia and Rad3 related (ATR) inhibitor (ceralasertib) and compared it to the first-generation PARPi olaparib. We performed DNA and RNA sequencing as well as protein-based assays to identify mechanisms of acquired resistance to either PARPi.ResultsAZD5305 showed superior antitumor activity than the first-generation PARPi in terms of preclinical complete response rate (75% vs. 37%). The median preclinical progression-free survival was significantly longer in the AZD5305-treated group compared to the olaparib-treated group (> 386 days vs. 90 days). Mechanistically, AZD5305 induced more replication stress and genomic instability than the PARP1/2 inhibitor olaparib in PARPi-sensitive tumors. All tumors at progression with either PARPi (39/39) showed increase of HRR functionality by RAD51 foci formation. The most prevalent resistance mechanisms identified were the acquisition of reversion mutations in BRCA1/BRCA2 and the accumulation of hypomorphic BRCA1. AZD5305 did not sensitize PDXs with acquired resistance to olaparib but elicited profound and durable responses when combined with carboplatin or ceralasertib in 3/6 and 5/5 models, respectively.ConclusionsCollectively, these results show that the novel PARP1 selective inhibitor AZD5305 yields a potent antitumor response in PDX models with HRD and delays PARPi resistance alone or in combination with carboplatin or ceralasertib, which supports its use in the clinic as a new therapeutic option.