Abstract 1514: CRISPRi screening reveals RNA editing as a major determinant of platinum sensitivity in high-grade serous ovarian cancer

Abstract Platinum-based chemotherapeutic drugs induce intra- and interstrand purine crosslinks causing DNA damage and tumor cell death. Although these drugs are widely used as front-line treatment for multiple human cancers, particularly high-grade serous ovarian cancer (HGSOC), platinum resistance and tumor recurrence remains a common clinical problem. Here we report results from both a genome-wide CRISPRi screen and an RNA-binding protein-focused CRISPRi screen for modulators of sensitivity and resistance of HGSOC cells to two widely used platinum agents, cisplatin and oxaliplatin, and an microtubule-targeting taxane. Using an in vitro approach that mimics clinical treatment protocols, we found that cell lethality after cisplatin or oxaliplatin treatment in p53-defective ovarian cancer cells is markedly enhanced by suppressing genes in the Fanconi anemia (FA) and homologous recombination (HR) pathways, but considerably less enhanced by suppressing genes in the nucleotide excision repair (NER) pathway, despite the well-established importance of NER in reversing platinum-induced intrastrand crosslinks, particularly for cells in G1. Our findings suggest that cell death induced by platinum-DNA crosslinks results from replication stress, which can be further exacerbated by interference with error-free DNA repair mechanisms known to be particularly active during the S- and G2 phases of the cell cycle. These screens further implicated several known and novel RNA-binding proteins (RBPs) as potent sensitizers of HGSOC to both platinum agents and taxanes, including the RNA-modifying enzyme ADAR1, that catalyzes the deamination of adenosine-to-inosine in RNA, altering mRNA coding potential, modifying RNA structure, and regulating RNA localization. Additionally, ADAR1 has been implicated in controlling the integrated stress response (ISR), a signaling network that allows cells to adapt to changes in environment. These findings suggest that activation of an ADAR1-dependent ISR underlies the resistance of HGSOC cells to both platinum-based agents and anti-microtubule drugs that form the current clinical standard of care for HGSOC treatment. Citation Format: Yi Wen Kong, Erika D. Handly, Robin A. Lu, Molly A. Bird, Jack W. Schaeffer, Samkyu P. Yaffe, Michael B. Yaffe. CRISPRi screening reveals RNA editing as a major determinant of platinum sensitivity in high-grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1514.