FBXW7-loss sensitizes cells to ATR inhibition through induced mitotic catastrophe.

FBXW7 is a commonly mutated tumor suppressor gene that functions to regulate numerous oncogenes involved in cell cycle regulation. Genome-wide CRISPR fitness screens identified a signature of DNA repair and DNA damage response genes as required for the growth of FBXW7-knockout cells. Guided by these findings, we show that FBXW7 mutant cells have high levels of replication stress, which results in a genotype-specific vulnerability to inhibition of the ATR signaling pathway, as these mutant cells become heavily reliant on a robust S-G2 checkpoint. ATR-inhibition induces an accelerated S-phase, leading to mitotic catastrophe and cell death caused by the high replication stress present in FBXW7-/- cells. In addition, we provide evidence in cell and organoid studies, and mining of publicly available high throughput drug screening efforts, that this genotype-specific vulnerability extends to multiple types of cancer, providing a rational means of identifying responsive patients for targeted therapy.