Abstract 5941: Small molecule NSC59984 synergizes with PARP inhibitors in BRCA1 wild type ovarian cancer

Abstract PARP inhibitors (PARPi) targeting poly (ADP-ribose) polymerase are the first clinically approved drugs designed to apply synthetic lethality in BRCA1 mutant/deficient cancer. However, the treatment can cause reversion of BRCA mutation which results in drug resistance. To explore new strategies to improve antitumor efficacy of PARPi, we applied PARPi in combination with a small molecule NSC59984 for cancer therapy. NSC59984 is a small molecular targeting mutant p53 degradation and activating p73 via ROS-ERK2-MDM2 pathway. The treatments with radiation or hydrogen peroxide showed that NSC59984 enhanced DNA comet tails and gamma-H2AX, correlated to reduction of rad51 foci in cancer cells. These results suggest that NSC59984 impairs DNA damage repair via abrogation of homologous recombination (HR). We further applied the combinational treatment of NSC59984 and PARPi in BRCA1 wild-type ovarian cancer cells and found that NSC59984 synergized with PARPi to reduce cell viability, inhibit colony formation, and increase cell death. The combination treatment enhanced DNA damage and correlated with reduction of BRCA1 at the protein level. These results, taken together, suggest that the induction of BRCAness causes a synthetical lethality with PARPi in BRCA1 wild-type cancer cells. Cell cycle profiling showed that the cells were arrested at the G2/M phase in response to combinational treatment. At the G2 phase arrest, the high doses of the combinational drugs led to cell death via mitotic catastrophe, and the intermediate doses induced cellular senescence defined by senescence phenotypic hallmarks including senescence-associated beta-gal staining and a secretome consistent with senescence-associated secretory phenotype (SASP). Therapy-induced senescence (TIS) in cancer cells is considered as one of the mechanisms of tumor recurrence and drug resistance. To reduce the risk of TIS in treatment, we applied senolytic treatment to target senescent cells in the combinational treatment. The senolytic drug ABT263 treatment eliminated the senescent cancer cells from the combinational treatment. ABT263, NSC59984 + PARPi combinational treatment further reduced cell viability. Our study provides a rationale for small molecular compounds targeting HR deficiency in combination with PARPi to treat BRCA1wild-type ovarian cancer cells, and additional senolytic treatment may be required to limit resistance by removal of the TIS. Citation Format: Shengliang Zhang, Lanlan Zhou, Leiqing Zhang, Maximilian Pinho-Schwermann, Benedito Carneiro, John Sedivy, Wafik S. El-Deiry. Small molecule NSC59984 synergizes with PARP inhibitors in BRCA1 wild type ovarian cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 5941.