Inhibition of 5 alpha-reductase, receptor binding, and nuclear uptake of androgens in the prostate by a 4-methyl-4-aza-steroid.

17 beta-N,N-Diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one (DMAA) is a potent reversible inhibitor of 5 alpha-reductase. The inhibition by DMAA of the conversion of testosterone to 5 alpha-dihydrotestosterone by rat prostate 5 alpha-reductase is competitive with testosterone, the apparent Ki being 5 nM, and uncompetitive with NADPH, DMAA inhibited both membrane-bound and solubilized 5 alpha-reductase. DMAA has moderate affinity for the prostate cytosol androgen receptor: 3 X 10(-6) M gives 50% inhibition of the binding of 10(-9) M 5 alpha-[3H]dihydrotestosterone to this receptor. This affinity to the androgen receptor is 1,000-, 500-, 120-, and 40-fold lower than that of 5 alpha-dihydrotestosterone, testosterone, spironolactone, and cyproterone acetate, respectively, and 7-fold higher than that of cimetidine. After incubation of [3H]testosterone with minced prostate, more than 90% of the radioactivity extracted from the nuclei co-chromatographed with 5 alpha-dihydrotestosterone and the rest with testosterone. DMAA at low concentrations decreased the ratio of 5 alpha-dihydrotestosterone to testosterone in the nuclei without significantly reducing the total uptake. DMAA at high concentrations also reduced the total radioactivity in the nuclei. This differential effect may reflect a higher affinity of DMAA for 5 alpha-reductase than for the androgen receptor. When 5 alpha-[3H]dihydrotestosterone was used in the tissue incubations, all radioactivity extracted from nuclei co-chromatographed with 5 alpha-dihydrotestosterone, regardless of whether or not DMAA was present. This nuclear uptake of 5 alpha-dihydrotestosterone is inhibited only by high concentrations of DMAA. In a cell-free system, the nuclear uptake of 5 alpha-[3H]dihydrotestosterone prebound to the cytosol receptor was not inhibited by DMAA. These results suggest that DMAA may inhibit nuclear uptake of 5 alpha-dihydrotestosterone by inhibiting the receptor binding. Sucrose gradient centrifugation of the radioactive KCl nuclear extracts prepared from the tissue incubations showed that the nuclear [3H]testosterone-receptor complex has a greater rate of dissociation than does the nuclear 5 alpha-[3H]dihydrotestosterone-receptor complex. [3H]Testosterone prebound to the prostate cytosol receptor also dissociates faster than 5 alpha-[3H]dihydrotestosterone prebound to the cytosol receptor.