Inhibition of Mps1 kinase enhances taxanes efficacy in castration resistant prostate cancer

Androgen ablation therapy is the standard of care for newly diagnosed prostate cancer (PC) patients. PC that relapsed after hormonal therapy, referred to as castration-resistant PC (CRPC), often presents with metastasis (mCRPC) and is the major cause of disease lethality. The few available therapies for mCRPC include the Taxanes Docetaxel (DTX) and Cabazitaxel (CBZ). Alas, clinical success of Taxanes in mCRPC is limited by high intrinsic and acquired resistance. Therefore, it remains essential to develop rationally designed treatments for managing therapy-resistant mCRPC disease. The major effect of Taxanes on microtubule hyper-polymerization is a prolonged mitotic block due to activation of the Spindle Assembly Checkpoint (SAC). Taxane-sensitive cells eventually inactivate SAC and exit mitosis by mitotic catastrophe, resulting in genome instability and blockade of proliferation. Resistant cells remain in mitotic block, and, upon drug decay, resume mitosis and proliferation, underlying one resistance mechanism. In our study we explored the possibility of forced mitotic exit to elevate Taxane efficacy. Inactivation of the SAC component, mitotic checkpoint kinase Mps1/TTK with a small molecule inhibitor (Msp1i), potentiated efficacy of Taxanes treatment in both 2D cell culture and 3D prostasphere settings. Mechanistically, Mps1 inhibition forced mitotic catastrophe in cells blocked in mitosis by Taxanes. Androgen receptor (AR), the main driver of PC, is often mutated or truncated in mCRPC. Remarkably, Mps1i significantly potentiated CBZ cytotoxicity regardless of AR status, in both AR-WT and in AR-truncated CRPC cells. Overall, our data demonstrate that forced mitotic exit by Mps1 inhibition potentiates Taxanes efficacy. Given that several Mps1i's are currently in different stages of clinical trials, our results point to Mps1 as a new therapeutic target to potentiate efficacy of Taxanes in mCRPC patients.