CDK7 inhibition suppresses Castration-Resistant Prostate Cancer through MED1 inactivation

Metastatic castration-resistant prostate cancer (CRPC) is a fatal disease, primarily resulting from the transcriptional addiction driven by Androgen Receptor (AR). First-line CRPC treatments typically target AR-signaling, but are rapidly bypassed, resulting in only a modest survival benefit with the anti-androgens. Therapeutic approaches that more effectively block the AR-transcriptional axis are urgently needed. Here, we investigated the molecular mechanism underlying the association between the transcriptional co-activator MED1 and AR as a vulnerability in AR-driven CRPC. MED1 undergoes CDK7-dependent phosphorylation at T1457 and physically engages AR at super-enhancer sites, and is essential for AR-mediated transcription. Additionally, a CDK7 specific inhibitor THZ1 blunts AR-dependent neoplastic growth by blocking AR/MED1 co-recruitment genome-wide, as well as reverses the hyper-phosphorylated MED1 associated enzalutamide resistant phenotype. In vivo, THZ1 induces tumor regression of AR amplified castration-resistant human prostate cancer in xenograft mouse model. Together, we demonstrate that CDK7 inhibition selectively targets MED1-mediated, AR-dependent oncogenic transcriptional amplification, thus representing a potential new approach for the treatment of CRPC.