Bypassing drug-resistance mechanisms of prostate cancer with small-molecules that target androgen receptor chromatin interactions

Human androgen receptor (AR) is a hormone-activated transcription factor that is an important drug-target in the treatment of prostate cancer. Current small molecule AR-antagonists, such as enzalutamide, compete with androgens that bind to the steroid binding pocket of the AR ligand binding domain (LBD). In castration-resistant prostate cancer (CRPC), drug-resistance can manifest through AR-LBD mutations that convert AR-antagonists into agonists, or by expression of AR-variants lacking the LBD. Such treatment resistance underscores the importance of novel ways of targeting the AR.  Previously, we reported the development a series of small molecules that were rationally designed to selectively target the AR DNA binding domain (DBD) and, hence, to directly interfere with AR-DNA interactions. In the current work we have confirmed that the lead AR DBD inhibitor indeed directly interacts with the AR-DBD and tested that substance across multiple clinically relevant CRPC cell lines. We have also performed a series of experiments that revealed that genome-wide chromatin binding of AR was dramatically impacted by the lead compound (although with lesser effect on AR variants). Collectively, these observations confirm the novel mechanism of anti-androgen action of the developed AR-DBD inhibitors, establishing proof-of-principle for targeting DNA-binding domains of nuclear receptors in endocrine cancers.

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