Discovery of potent and orally bioavailable 17β-hydroxysteroid dehydrogenase type 3 inhibitors

We have previously reported the discovery of a new class of potent inhibitors of 17 beta-hydroxysteroid dehydrogenase type 3 (17 beta-HSD3) derived from benzylidene oxazolidinedione and thiazolidinedione scaffolds. In this study, these analogs were designed, synthesized, and evaluated in a human cell-based assay. The detailed structure-activity relationship (SAR) surrounding this pharmacophore were developed, and consequently a number of compounds from this series demonstrated single-digit nanomolar 17 beta-HDS3 inhibitory activity in vitro. Subsequent optimization work in pursuit of the improvement of oral bioavailability demonstrated in vivo proof-of-concept by prodrug strategy based on phosphate esters for these 17 beta-HSD3 inhibitors. When a phosphate ester 16 was administered orally at a high dose of 100 mg/kg, 16 showed approximately two times more potent testosterone (T)-lowering effect against a positive control in the luteinizing hormone-releasing hormone (LH-RH)-induced T production assay. The T-lowering effect continued at ca 10% level of control over 4 h after administration. The nonsteroidal molecules based on this series have the potential to provide unique and effective clinical opportunities for treatment of prostate cancer. (C) 2012 Elsevier Ltd. All rights reserved.