Abstract B007: NAD+ metabolism drives PARPi resistance in ovarian cancer cells

Abstract NAD+ is a coenzyme for redox reactions and a cofactor for enzymes such as PARPs and Sirtuins. The nuclear enzyme PARP1 is a major consumer of NAD+, which is cleaved during the catalytic activation of PARP1 in response to DNA damage. PARP1 inhibitors compete with NAD+ for the catalytic site of PARP1 and reduce the catalytic activity of PARP1 and impair DNA damage repair. Recently PARP inhibitors (PARPi) have shown efficacy in the treatment of ovarian cancers and most patients with defects in homologous repair of DNA damage are now on PARPi maintenance. But, heterogeneous responses to PARPi is limiting their clinical efficacy. To identify the mechanisms of PARPi resistance, we generated a panel of ovarian cancer cells with acquired resistance to niraparib (PARPiR), an FDA approved PARP inhibitor. We demonstrated that the PARPiR cells are also resistant to other FDA approved PARP inhibitors rucaparib and olaparib. This data suggested that a common mechanism of resistance underlies poor response to the FDA approved PARP inhibitors. Since PARP1 activity is tightly controlled by the cellular NAD+ levels, we next investigated the role of NAD+ biosynthesis in PARPi resistance. Metabolomic profiling of the parental and PARPiR cells demonstrated that PARPiR cells have elevated levels of NAD+ metabolism. Indeed, treating the PARPiR cells with inhibitors of NAD+ synthesis restored the sensitivity to PARP inhibitors. Moreover, culturing the previously sensitive parental ovarian cancer cells in NAD+ precursors decreased their sensitivity to PARP inhibitors. These data collectively demonstrated that high levels of NAD+ metabolism causes PARP inhibitor resistance in ovarian cancer cells. Complementary to the metabolomic analysis, results from phenotypic assays in PARPiR cells revealed that high levels of NAD+ maintain cellular quiescence in PARPiR cells. In summary, our results demonstrated that high levels of NAD+ biosynthesis causes PARPi resistance by maintaining cellular quiescence. There is an urgent need to identify the mechanisms of resistance to PARP inhibitors to increase their clinical efficacy. Our study identified that maintenance of quiescence is a fundamental mechanism of PARPi resistance. We also demonstrated that inhibiting NAD+ biosynthesis reverses PARP inhibitor resistance. Citation Format: Subin Myong, Hardik Shah, Benedikt Nagele, Reshma Rajesh, Sridevi Challa. NAD+ metabolism drives PARPi resistance in ovarian cancer cells [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr B007.