Search

Two isozymes (types 1 and 2) of 5alpha-reductase (5alphaR; EC 1.3.99.5), with differential tissue distribution, catalyze the reduction of testosterone (T) to dihydrotestosterone (DHT) in humans. This study examined sequentially increasing oral doses of MK-386 (4,7beta-dimethyl-4-aza-5alpha-cholestan-3-one), an azasteroid that specifically inhibits the human 5alphaR1 isozyme in vitro. Finasteride, a selective inhibitor of 5alphaR2, was included for comparison. One hundred men were evaluated in a double blind, randomized, placebo-controlled, sequential, increasing dose, parallel group trial. Ten to 20 subjects received MK-386, and 2 to 5 received placebo in each of 6 panels. In 1 panel, 10 subjects received finasteride (5 mg), and 5 received placebo. Treatments were given once daily for 14 days, except in 1 panel in which MK-386 was administered 10 mg twice daily for comparison to 20 mg daily. Serum, sebum, and semen DHT concentrations and serum and sebum T concentrations were measured before and after treatment. The mean changes from baseline on day 14 for serum DHT after placebo and 0.1, 0.5, 5, 20, and 50 mg MK-386 were 6.9%, 4.6%, -2.7%, -1.2%, -14.1% (P < 0.05 vs. placebo), and -22.2% (P < 0.05 vs. placebo), respectively. No significant alterations in serum T were observed after any dose of MK-386. Serum DHT fell 65.8% from the baseline 14 days after finasteride treatment (P < 0.05 vs. placebo). The mean changes from baseline on day 14 in sebum DHT were 5.0%, 3.0%, -25.4% (P < 0.05 vs. placebo), -30.1% (P < 0.05 vs. placebo), and -49.1% (P < 0.05 vs. placebo) for the placebo and 0.5, 5, 20, and 50 mg MK-386 groups, respectively. Finasteride also reduced sebum DHT, but to a lesser extent (- 14.9%; P < 0.05 vs. placebo). Reciprocal increases in sebum T concentration were noted at doses of 5 mg or more of MK-386, but not with finasteride. The mean reduction in semen DHT with 5 mg finasteride was approximately 88% (P < 0.01 vs. placebo); no significant change in semen DHT was noted with 20 or 50 mg MK-386. Serum 3alpha-androstanediol glucuronide values were also reduced after the 20- and 50-mg MK-386 treatments in parallel with the changes in serum DHT. No meaningful changes were observed in serum LH after MK-386 treatment. MK-386 was generally well tolerated by all subjects; reversible aspartate aminotransferase/alanine aminotransferase elevations were observed in two subjects at the 50-mg dose. The differential responses in serum, sebum, and semen DHT concentrations associated with MK-386 and finasteride treatments are consistent with those changes anticipated for selective inhibitors of the human 5alphaR isozymes. Dose-dependent suppression of sebum DHT by a 5alphaR1 inhibitor suggests the potential utility of such compounds in the treatment of acne.

Two isozymes (types 1 and 2) of 5 alpha-reductase (5 alpha R; EC 1.3.99.5), with differential tissue distribution, have been identified in humans. These enzymes catalyze the reduction of testosterone (T) to dihydrotestosterone (DHT). The contributions of each of these isozymes to serum and tissue concentrations of DHT remain to be fully defined. Finasteride, a selective inhibitor of type 2 5 alpha R, lowers circulating DHT levels by approximately 70% in men after treatment with 5 mg daily. MK-386 (4,7 beta-dimethyl-4-aza-5 alpha-cholestan-3-one) is a new selective inhibitor of type 1 5 alpha R. A single rising dose, alternating panel, trial in 16 healthy males (age range, 21-25 yr) studied the effect of 0.1-100 mg MK-386. DHT was maximally reduced by 20-30% relative to placebo at MK-386 doses of 10 mg or more, orally, by 24 h posttreatment (P < 0.01 vs. placebo). No consistent effect on T concentrations was evident. In a second trial, finasteride (5 mg) was given for 19 days to 10 healthy young men (age range, 24-47 yr); a 25-mg dose of MK-386 was added for 2 days of combination therapy after at least 10 days of finasteride treatment. Withdrawal of MK-386 was followed by 5-6 days of finasteride follow-up treatment. Finasteride alone reduced DHT, on the average, by 68.7% (SE = 3.4%). Addition of MK-386 suppressed DHT by 89.5% (SE = 1.4%) relative to baseline (P < 0.01 vs. effect of finasteride alone). Small increases in serum T were observed with finasteride alone and in combination with MK-386 (approximately 10% and 19%, respectively). These data are consistent with selective 5 alpha R type 1 inhibition in man by MK-386 and the prediction that types 1 and 2 5 alpha R account for all, or nearly all, of circulating DHT. Further clinical trials are needed to assess the therapeutic utility of type 1 5 alpha R inhibition as well as that of combined inhibition of types 1 and 2 5 alpha R.