Abstract 1850: Characterizing senescence response to PARP inhibition may provide opportunities for enhanced efficacy through combinations with senolytic agents

Abstract Background: Inhibition of poly (ADP-ribose) polymerase (PARP) is an exciting treatment strategy recently approved for prostate cancer patients with homologous recombination repair defects. Despite this advance in the field, it remains unclear how PARP inhibitor (PARPi) sensitive cells respond to treatment. We previously demonstrated that treatment with the PARPi olaparib induces not only cell death, but also G2/M arrested senescence characterized by activation of the p53 signaling pathway. We hypothesize that targeting PARPi induced senescence may provide a means to enhance the efficacy of PARPi treatment. In our current work, we sought to 1) understand whether senescence induction is a generalized response to all PARPi’s and 2) characterize senescence induction to guide the development of novel treatment strategies combining a PARPi with a senolytic drug. Methods: PARPi sensitive LNCaP and C4-2B prostate tumor cells were treated with olaparib, rucaparib, niraparib, or talazoparib for 5 days to induce senescence. Both vehicle treated and quiescent cells (LNCaP and C4-2B cultured in FBS-low (0.2%) conditions) were used as controls. Cell viability, flow cytometry, and beta-galactosidase activity assays tested response to PARPi’s. Western blot was used to detect PARP activity, apoptosis, and DNA damage response. RNA-sequencing was performed to characterize senescence induced signaling alterations. Results: We found that exposure to rucaparib, niraparib, and talazoparib all induce a robust G2/M arrested senescence response in LNCaP and C4-2B cells, suggesting that senescence induction is a class effect of PARPi’s. PARPi induced senescence is characterized by activation of the p53 signaling pathway and significantly increased expression of the cyclin-dependent kinase inhibitor p21. Furthermore, PARPi induced senescence is distinct from quiescence, suggesting that response to PARP inhibition is phenotypically different from a more general growth arrest. RNA-sequencing revealed several signaling changes associated with senescence which may provide novel treatment opportunities. Conclusions: Senolytics are a class of drugs thought to specifically target senescent cells. Our results demonstrate that PARPi’s induce senescence. Future work will be directed at further characterizing PARPi induced senescence, leading to rationally selected senolytic drug combinations which may enhance the efficacy of PARPi therapy. Citation Format: Alan P. Lombard, Wei Lou, Christopher P. Evans, Allen C. Gao. Characterizing senescence response to PARP inhibition may provide opportunities for enhanced efficacy through combinations with senolytic agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1850.