Abstract 5280: Minimizes T cells DNA damage induced by PARP inhibitors and enhances its anti-tumor efficacy

Abstract Background: Poly (ADP-ribose) polymerase (PARP) inhibitors have emerged as promising targeted therapies for ovarian and breast cancer. The sustained remission induced by PARP inhibitors largely depends on T cell activity. However, the direct effects of PARP inhibitors on T cells, as well as their precise impact on T cell DNA integrity and subsequent anti-tumor immune responses, have not been fully elucidated. Method & Result: Following treatment with 25 μM olaparib or 15 μM niraparib for 48 hours, T cell viability decreased by 39.20% and 41.89%, respectively. Reduced proliferation and increased cell death were also observed, as indicated by reduced Ki-67 and elevated cleaved Caspase-3 levels. RNA sequencing further revealed a significant enrichment of DNA damage pathways in T cells after olaparib treatment, which was validated by elevated γH2AX levels in T cells using western blots and immunofluorescence. To assess PARP inhibitor-induced DNA damage in clinical settings, paired ovarian cancer samples pre- and post-niraparib monotherapy were obtained from the NANT trial (NCT04507841). Post-treatment tumor samples exhibited a higher number of γH2AX+ T cells compared to their pre-treatment counterparts. To identify the key protein mediating T cell inhibition induced by PARP inhibitors, a whole genomic CRISPR knock-out screening was conducted in human T cells, revealing an enrichment of sgRNAs targeting PARP1 after PARP inhibitor treatment. This outcome was further confirmed by the knockout of PARP1 in human T cells in vitro, leading to the restored viability and reduced levels of DNA damage after olaparib treatment. Importantly, following cytosine base editors (CBEs) of PARP1 in CAR-T cells, improved anticancer activity was observed both in vitro and in two ovarian cancer patient-derived xenografts (PDX) models when combined with PARP inhibitors. Conclusion: This study observed that PARP inhibitors can cause significant DNA damage in human T cells, resulting in cell death, inhibited proliferation, and impairment of anti-cancer immunity. PARP1 was identified as the target for PARP inhibitor-induced T cell death, and its knockout or point mutation led to improved anticancer efficacy of T cells when used in combination with PARP inhibitors. [JH Liu and XF Jiao contributed equally as co-first authors.] Citation Format: Jiahao Liu, Xiaofei Jiao, Wei Mu, Huayi Li, Li Zhu, Xuejiao Zhao, Gordon B. Mills, Qinglei Gao, Yong Fang. Minimizes T cells DNA damage induced by PARP inhibitors and enhances its anti-tumor efficacy [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(6_Suppl):Abstract nr 5280.