Differential responses to selective CDK2 inhibitor BLU-222 is conditioned by tumor suppressors

The selective CDK2 inhibitor BLU-222 was evaluated for mechanisms of response in the context of ovarian and breast cancer models. Using sensors of cellular CDK activity, it was found that sensitivity to either CDK4/6 or CDK2 inhibition is related to the differential dependence on a single CDK for G1/S transition. Unlike CDK4/6 inhibitors, BLU-222 was able to robustly inhibit proliferation through cell cycle inhibition in both G1 and G2 phases. However, it remained possible for cells to re-enter the cell cycle upon drug withdrawal. The anti-proliferative strength and impact on G1/S versus G2/M accumulation was found to be mediated by the RB tumor suppressor, as determined by functional perturbation strategies. To broaden the sensitivity to CDK2 inhibition, combinatorial drug screens were performed that identified both synergistic (e.g., CDK4/6 inhibitors) and antagonistic (e.g., WEE1 inhibitors) relationships. Models that were exceptionally sensitive to CDK2 inhibition displayed coordinate expression of Cyclin E1 and P16INK4A, an endogenous CDK4/6 inhibitor. Functional studies demonstrated that P16INK4A and CDK4/6 activity were key mediators of sensitivity to BLU-222. Clinical gene and protein expression analysis revealed a positive correlation between Cyclin E1 and P16INK4A and that ~25% of ovarian cancers exhibited coordinate expression of Cyclin E, P16INK4A, and RB, indicative of strong sensitivity to CDK2 inhibition. Together, this work advances a precision strategy for the use of CDK2 inhibitors in the context of ovarian and breast cancers.