Identification of novel functional inhibitors of 17β-hydroxysteroid dehydrogenase type III (17β-HSD3)

BACKGROUND. Endocrine therapy of prostate cancer (PCa) relies on agents which disrupt the biosynthesis of testosterone in the testis and/or by direct antagonism of active hormone on the androgen receptor (AR) in non-gonadal target tissues of hormone action such as the prostate. METHODS. In an effort to evaluate new therapies which could inhibit gonadal or non-gonadal testosterone biosynthesis, we developed high throughput biochemical and cellular screening assays to identify inhibitors of 17 beta-hydroxysteroid dehydrogenase type III (17 beta-HSD3), the enzyme catalyzing the conversion of androstenedione (AdT) to testosterone. RESULTS. Initial screening efforts identified a natural product, 18 beta-glycyrrhetinic acid, and a novel derivative of AdT, 3-O-benzylandrosterone, as potent inhibitors of the enzyme. Further efforts led to the identification of several classes of non-steroidal, low molecular weight compounds that potently inhibited 17 beta-HSD3 enzymatic activity. One of the most potent classes of 17 beta-HSD3 inhibitors was a series of anthranilamide small molecules identified from a collection of compounds related to non-steroidal modulators of nuclear hormone receptors. The anthranilamide based 17 beta-HSD3 inhibitors were exemplified by BMS-856, a compound displaying low nanomolar inhibition of 17 beta-HSD3 enzymatic activity. In addition, this series of compounds displayed potent inhibition of 17 beta-HSD3-mediated cellular conversion of AdT to testosterone and inhibited the 17 beta-HSD3-mediated conversion of testosterone necessary to promote AR-dependent transcription. CONCLUSIONS. The identification of non-steroidal functional inhibitors of 17 beta-HSD3 may be a useful complementary approach for the disruption of testosterone biosynthesis in the treatment of PCa.