Aurora-A kinase inhibition is synthetic lethal with loss of the RB1 tumor suppressor gene.

Loss-of-function mutations in the retinoblastoma gene RB1 are common in several treatment-refractory cancers such as small-cell lung cancer and triple-negative breast cancer. To identify drugs synthetic lethal with RB1 mutation (RB1mut), we tested 36 cell-cycle inhibitors using a cancer cell panel profiling approach optimized to discern cytotoxic from cytostatic effects. Inhibitors of the Aurora kinases, AurA and AurB, showed the strongest RB1 association in this assay. LY3295668, an AurA inhibitor with over 1000-fold selectivity versus AurB, is distinguished by minimal toxicity to bone marrow cells at concentrations active against RB1mut cancer cells and leads to durable regression of RB1mut tumor xenografts at exposures that are well tolerated in rodents. Genetic suppression screens identified enforcers of the spindle assembly checkpoint (SAC) as essential for LY3295668 cytotoxicity in Rb-deficient cancers and suggest a model in which a primed SAC creates a unique dependency on AurA kinase for mitotic exit and survival.