Abstract A035: Genome-wide CRISPRi screening reveals determinants of platinum sensitivity and resistance in high-grade serous ovarian cancer

Abstract Platinum-based chemotherapeutic drugs induce intra- and interstrand crosslinks between purine residues, resulting in 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), the development of platinum resistance and tumor recurrence remains a common clinical problem due to an incomplete understanding of what governs the cellular response to platinum-induced DNA damage. Here we report the results from genome-wide CRISPRi-screens for modulators of sensitivity and resistance to two widely used platinum agents, cisplatin and oxaliplatin, using a cell-based approach that mimics clinical treatment protocols. Using this unbiased genomic approach, we demonstrate that 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. Loss of NER activity, however, can markedly increase tumor cell death from cisplatin-induced DNA damage, if the cell cycle checkpoint kinase MK2 is co-targeted, indicating an augmented synthetic lethal relationship between XPA, MK2, and mutant p53 in the presence of DNA crosslinks. A second targeted CRISPRi screen 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. Together, these findings indicate that (1) platinum-induced interstrand DNA crosslinks, which require repair by FA and HR, rather than intrastrand crosslinks repaired by NER, are the primary determinants of tumor cell survival following treatment, (2) loss of NER function alone, which only modestly sensitizes cells to platinum-induced DNA crosslinks, results in a markedly enhanced dependence of the DNA-damaged tumor cells on sustained cell cycle checkpoint arrest mediated by MK2 for tumor cell survival, and that (3) a small subset of RBPs control the sensitivity of ovarian cancer cells to both platinum-based agents and anti-microtubule drugs that form the current clinical standard of care for HGSOC. Citation Format: Yi Wen Kong, Erika D. Handly, Robin A. Lu, Molly A. Bird, Hannah-Lou Schilling, Samkyu P. Yaffe, Michael B. Yaffe, David H. Koch. Genome-wide CRISPRi screening reveals determinants of platinum sensitivity and resistance in high-grade serous ovarian cancer 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 Suppl₂): Abstract nr A035.