Abstract PR009: CRISPRi screening reveals RNA editing and the integrated stress response as major determinants of platinum and taxol sensitivity in high-grade serous ovarian cancer

Abstract Platinum-based chemotherapeutic drugs induce intra- and interstrand purine crosslinks that causes DNA damage and tumor cell death. While these drugs are front-line treatments for multiple human cancers – including high-grade serous ovarian cancer (HGSOC) – platinum resistance and tumor recurrence remains a major clinical challenge. Here, we report findings from both a genome-wide CRISPRi screen and an RNA-binding protein (RBP)-focused CRISPRi screen aimed at identifying modulators of sensitivity and resistance of HGSOC cells to two widely used platinum agents, cisplatin and oxaliplatin, as well as to an microtubule-targeting taxane. Using an in vitro treatment regimen designed to mimics clinical treatment protocols, we found that loss of genes in the Fanconi anemia (FA) and homologous recombination (HR) DNA repair pathways markedly increased the killing of p53-deficient HGSOC cells following treatment with cisplatin or oxaliplatin. In contrast, knockdown of genes in the nucleotide excision repair (NER) pathway—despite its known role in repairing platinum-induced intrastrand crosslinks, particularly in G1—had a significantly lesser effect. These results suggest that platinum-induced cytotoxicity in HGSOC is primarily driven by replication stress, which is exacerbated by disruption of error-free DNA repair pathways active during the S- and G2 phases of the cell cycle. Our screens also identified several known and novel RBPs as potent sensitizers to both platinum agents and taxanes. Depletion of these RBPs resulted in substantial activation of interferon signaling, a hallmark of innate immune activation and cellular stress responses. Among them, the RNA-editing enzyme ADAR1 emerged as a key modulator of drug resistance. ADAR1 catalyzes adenosine-to-inosine RNA editing, thereby altering mRNA coding potential, secondary structure, and subcellular localization. Additionally, ADAR1 has been implicated in regulating the integrated stress response (ISR), a signaling network that enables cellular adaptation to environmental stress. As part of this stress adaptation, we observed that platinum and taxol treatment caused a translational shift from canonical cap-dependent translation mediated by eIF4G1 to a cap-independent mechanism reliant on eIF4G2, supporting selective translation of stress-responsive mRNAs. Together, our findings suggest that ADAR1-dependent suppression of interferon signaling and activation of the ISR contributes to resistance to both platinum-based chemotherapy and microtubule-targeting agents, which together comprise the current standard of care for HGSOC. Citation Format: Yi Wen Kong, Erika D. Handly, Robin A. Lu, Molly A. Bird, Jack Schaeffer, Samkyu P. Yaffe, Michael B. Yaffe. CRISPRi screening reveals RNA editing and the integrated stress response as major determinants of platinum and taxol sensitivity in high-grade serous ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Ovarian Cancer Research; 2025 Sep 19-21; Denver, CO. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl):Abstract nr PR009.