Genome-wide CRISPR Screening in FBXW7-mutant Cells Uncovers Multiple Druggable Synthetic Lethal Interactions Involving Cell Cycle Control
Current standard of care chemotherapeutics broadly target actively dividing cells, with both healthy and cancerous cells being damaged, causing toxic side effects. Personalized oncology aims to selectively target cancerous cells based on their mutational status, minimizing toxic and life-altering side effects, while effectively blocking the cancer’s growth and proliferation. Understanding what is an essential gene or essential process selectively required for the growth of cells with specific mutations is a challenging task. Leveraging genome-wide knockout screens using paired isogenic cell lines that only differ in a cancer-causing mutation of interest provides a path forward to understanding these processes. In this thesis we generated several isogenic cell lines to identify genetic interactions that are synthetic lethal with common cancer-associated mutations in the Wnt signalling pathway and that could therefore represent new therapeutic targets. From this work we identified two novel druggable synthetic lethal interactions with the commonly mutated tumour suppressor gene, FBXW7. We first identified that FBXW7-/- cells require CCNL1 for growth, and discovered that CCNL1 is a novel substrate of FBXW7, tasked with a role controlling progression through mitosis. FBXW7-/- cells, due to their requirement of CCNL1, were more sensitive to the novel CDK11-inhibitor OTS964. The second SL interaction identified in FBXW7-/- cells was the requirement for DNA damage response genes. We identified high levels of replication stress in FBXW7-/- cells and organoids, resulting in increased sensitivity to an inhibitor of the ATR kinase - a mediator of the cellular response to replication stress. We hypothesize that activation of DNA damage response in FBXW7-/- cells leads to persistent ATR activation to mitigate replication stress and that ATR inhibition will force mitotic entry leading to mitotic catastrophe.
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