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KAT2B-Mediated Epigenetic Suppression of RAD51C Enhances Olaparib Sensitivity in Colorectal Cancer

ABSTRACT: By blocking poly ADP ribose polymerase (PARP), olaparib prevents DNA damage repair, particularly in tumors that have a BRCA1/2 mutation or are BRCA-positive. Nevertheless, a Phase II study of 33 CRC patients receiving mono-Olaparib therapy revealed that some of these individuals still had resistance to Olaparib while having poor DNA damage repair. RAD51 reversion mutations are a frequent cause of resistance to PARP inhibitors in cancers that do not have BRCA mutations. Though little is known, a number of tactics have been studied when combining PARPi with other inhibitors. Here, we introduce the enzyme KAT2B as a protein involved in transcription that is connected to RAD51C, reducing the levels of RAD51C by lowering the acetylation of Histone H3 (H3K27) at the beginning of the RAD51C gene. Consequently, colorectal cancer cells become more vulnerable to Olaparib therapy. The H3K27ac binding domain is necessary for the transcription of RAD51C. We find that a subpopulation of tumor cells expressing RAD51C have reduced endogenous KAT2B expression. This expression leads to increased DNA damage accumulation and decreased PARPi resistance in RAD51C-expressing cells. According to our findings, RAD51C-expressing cells' RAD51C and PARPi responses are significantly regulated by KAT2B and histone acetylation. This information offers vital new understandings into the molecular requirements for focusing on BRCA-functional malignancies.

ORGANISM(S): Homo sapiens

PROVIDER: GSE267911 | GEO | 2026/03/18

REPOSITORIES: GEO

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Project description:Background: PARP inhibition (PARPi) has demonstrated potent therapeutic efficacy in patients with BRCA-mutant ovarian cancer. However, acquired resistance to PARPi remains a major challenge in the clinic. Methods: PARPi-resistant ovarian cancer mouse models were generated by long-term treatment of olaparib in syngeneic Brca1-deficient ovarian tumors. STAT3-mediated immunosuppression was investigated in vitro by co-culture experiments and in vivo by analysis of immune cells in the TME of human and mouse PARPi-resistant tumors. Whole genome transcriptome analysis was performed to assess the anti-tumor immunomodulatory effect of STING (stimulator of interferon genes) agonists on myeloid cells in the TME of PARPi-resistant ovarian tumors. A STING agonist was used to overcome STAT3-mediated immunosuppression and acquired PARPi resistance in syngeneic and PDX models of ovarian cancer. Results: In this study, we uncover an adaptive resistance mechanism to PARP inhibition mediated by tumor associated macrophages (TAMs) in the tumor microenvironment (TME). Markedly increased populations of pro-tumor macrophages are found in BRCA-deficient ovarian tumors that rendered resistance to PARPi in both murine models and patients. Mechanistically, PARP inhibition elevates the STAT3 signaling pathway in tumor cells, which in turn promotes pro-tumor polarization of TAMs. STAT3 ablation in tumor cells mitigates polarization of pro-tumor macrophages and increases tumor-infiltrating T-cells upon PARP inhibition. These findings are corroborated in patient-derived, PARPi-resistant BRCA1-mutant ovarian tumors. Importantly, STING agonists reshape the immunosuppressive TME by reprogramming myeloid cells and overcome the TME-dependent adaptive resistance to PARPi in ovarian cancer. This effect is further enhanced by addition of PD-1 blockade. Conclusions: We elucidate an adaptive immunosuppression mechanism rendering resistance to PARPi in BRCA1-mutant ovarian tumors. This is mediated by enrichment of pro-tumor TAMs propelled by PARPi-induced STAT3 activation in tumor cells. We also provide a new strategy to reshape the immunosuppressive TME with STING agonist and overcome PARPi resistance in ovarian cancer.

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KAT2B-Mediated Epigenetic Suppression of RAD51C Enhances Olaparib Sensitivity in Colorectal Cancer

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