TAS3681: New class of androgen receptor antagonist with androgen receptor downregulating activity.

266 Background: The persistent activation of the androgen receptor (AR) signaling axis plays a major role in castration-resistant prostate cancer (CRPC). This knowledge has driven the clinical development of new inhibitors of androgen production (e.g., abiraterone) and AR signaling (e.g., enzalutamide). However, in many patients, the efficacy is short-lived and eventually resistance appears. Reactivation of AR signaling occurs by several mechanisms in CRPC. In this study, we report the biological properties of TAS3681, a new AR antagonist with AR downregulating activity, and propose this concept as a potential new approach for the treatment of CRPC. Methods: For assay of AR transactivation, COS-7 cells were transiently transfected with androgen-responsive reporter gene construct and expression vectors encoding wt or mu ARs. The transfected cells were treated with TAS3681 and androgen in steroid depleted media for 24 h, and luciferase activity was measured. For an in vivo pharmacodynamic assay to confirm A...