Jianxin Wang

p16 expression confers sensitivity to CDK2 inhibitors in cyclin E1–driven ovarian cancers

Blocking the cell cycle is a promising avenue for cancer therapy, with cyclin-dependent kinase 2 (CDK2) emerging as a key target. However, in multiple cell types, the activities of CDK4 and CDK6 (CDK4/6) compensate for CDK2 inhibition and sustain tumor cell proliferation, enabling CDK2 reactivation. Thus, we hypothesized that sensitivity to CDK2 inhibition is linked to the absence of this CDK4/6-mediated compensatory mechanism. We found that cyclin E1–driven ovarian cancers often coexpressed the tumor suppressor p16, which inhibited CDK4/6 signaling. Single-cell time-lapse imaging showed that high abundance of p16 conferred increased sensitivity to CDK2 inhibitors, whereas depletion of p16 rendered cells more resistant to CDK2 inhibition through CDK4/6-dependent compensation. Concordantly, acquired resistance to CDK2 inhibitors correlated with reduced p16 and increased cyclin D1 protein abundance. Multiplexed immunofluorescence of 225 ovarian tumors from patients revealed that 18% of the tumors had high cyclin E1 and p16 expression. Thus, p16 may be a useful biomarker for identifying patients most likely to benefit from CDK2 inhibitors.

Tumor Suppressors Condition Differential Responses to the Selective CDK2 Inhibitor BLU-222

Abstract Cyclin-dependent kinase 2 (CDK2) inhibitors have recently been developed and have entered clinical trials. Combination approaches can help broaden the use of therapeutic agents and establish more effective treatments. Here, we evaluated the selective CDK2 inhibitor BLU-222 for mechanisms of response in the context of ovarian and breast cancer models. Sensors of cellular CDK activity indicated that sensitivity to either CDK4/6 or CDK2 inhibition was 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 reenter the cell cycle upon drug withdrawal. The antiproliferative strength and impact on G1–S versus G2–M accumulation was mediated by the RB tumor suppressor. 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 analyses revealed a positive correlation between cyclin E1 and P16INK4A and identified 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. Significance: The CDK2-specific inhibitor BLU-222 shows preclinical efficacy in breast and ovarian cancer with select determinants of response and holds promise in combinatorial strategies. See related article by House and colleagues, p. 1297