Abstract

BACKGROUNDCurrently available 5-reductase inhibitors are not completely effective for treatment of benign prostate enlargement, prevention of prostate cancer (CaP), or treatment of advanced castration-recurrent (CR) CaP. We tested the hypothesis that a novel 5-reductase, 5-reductase-3, contributes to residual androgen metabolism, especially in CR-CaP. METHODSA new protein with potential 5-reducing activity was expressed in CHO-K1 cellsandTOP10 E. coli for characterization. Protein lysates and total mRNA were isolated from preclinical and clinical tissues. Androgen metabolism was assessed using androgen precursors and thin layer chromatography or liquid chromatography tandem mass spectrometry. RESULTSThe relative mRNA expression for the three 5-reductase enzymes in clinical samples of CR-CaP was 5-reductase-3 >> 5-reductase-1>5-reductase-2. Recombinant 5-reductase-3 protein incubations converted testosterone, 4-androstene-3,17-dione (androstenedione) and 4-pregnene-3,20-dione (progesterone) to dihydrotestosterone, 5-androstan-3,17-dione, and 5-pregnan-3,20-dione, respectively. 5-Reduced androgen metabolites were measurable in lysates from androgen-stimulated (AS) CWR22 and CR-CWR22 tumors and clinical specimens of AS-CaP and CR-CaP pre-incubated with dutasteride (a bi-specific inhibitor of 5-reductase-1 and 2). CONCLUSIONHuman prostate tissues contain a third 5-reductase that was inhibited poorly by dutasteride at high androgen substrate concentration in vitro, and it may promote DHT formation in vivo, through alternative androgen metabolism pathways when testosterone levels are low. Prostate 74:235-249, 2014. (c) 2013 Wiley Periodicals, Inc.