Comparison of finasteride (Proscar), a 5 alpha reductase inhibitor, and various commercial plant extracts in in vitro and in vivo 5 alpha reductase inhibition.

Human prostate was used as a source of 5 alpha reductase. Compounds were incubated with an enzyme preparation and [3H]testosterone. [3H]-dihydrotestosterone production was measured to calculate 5 alpha reductase activity. IC50 values (ng/ml) were finasteride = 1; Permixon = 5,600; Talso = 7,000; Strogen Forte = 31,000; Prostagutt = 40,000; and Tadenan = 63,000. Bazoton and Harzol had no activity at concentrations up to 500,000 ng/ml. In castrate rats stimulated with testosterone (T) or dihydrotestosterone (DHT), finasteride, but not Permixon or Bazoton, inhibited T stimulated prostate growth, while none of the three compounds inhibited DHT stimulated growth. These results demonstrate that finasteride inhibits 5 alpha reductase, while Permixon and Bazoton have neither anti-androgen nor 5 alpha reductase inhibitory activity. In addition, in a 7 day human clinical trial, finasteride, but not Permixon or placebo, decreased serum DHT in men, further confirming the lack of 5 alpha reductase inhibition by Permixon. Finasteride and the plant extracts listed above do not inhibit the binding of DHT to the rat prostatic androgen receptor (concentrations to 100 micrograms/ml). Based on these results, it is unlikely that these plant extracts would shrink the prostate by inhibiting androgen action or 5 alpha reductase.

Topical anti-androgenicity of a new 4-azasteroid in the hamster.

The topical anti-androgenic activity of L-651,580 (methyl 3-oxo-4-methyl-4-aza-5 alpha-androst-1-ene-17 beta-carboxylate) was established in a series of for experiments using castrated male hamsters. During each 21-day experiment, the animals received a daily subcutaneous injection of 40 micrograms testosterone propionate or 20 micrograms dihydrotestosterone propionate. Test compound in 25 microliters of gel was applied daily to the left flank organ. Compounds assayed included L-651,580, WIN 17,665 (17 alpha-propyltestosterone), and SH-434 (17 beta-hydroxy-1 alpha-methyl-17 alpha-propyl-5 alpha-androstan-3-one). Endpoints were flank organ area, sebaceous gland area, and prostate weight. Very similar results were obtained with L-651,580 and WIN 17,665. Daily doses of 0.25 mg or more of either compound usually produced a significant reduction in the areas of treated flank organs and sebaceous glands underlying treated flank organs. Neither compound caused significant changes in the area of the contralateral flank organs and sebaceous glands, which indicated they possess little or no systemic activity at topically effective treatment levels. In direct comparisons, SH-434 was less anti-androgenic than L-651,580 or WIN 17,665, although in one experiment, 0.5 mg/d of SH-434 significantly reduced the area of treated flank organs and sebaceous glands. Neither WIN 17,665 nor SH-434 caused a change in prostate weight; however, in one of four tests, a significant decrease was induced by the 0.5 mg/d level of L-651,580. The results of these experiments show that the topical anti-androgenicity of L-651,580 compares very favorably with that of WIN 17,665 and SH-434. They also indicate that the topical administration of effective dosage levels of L-651,580 causes few, if any, systemic effects.

Effect of castration, DES, flutamide, and the 5 alpha-reductase inhibitor, MK-906, on the growth of the Dunning rat prostatic carcinoma, R-3327.

Male rats bearing implants of the Dunning rat prostatic carcinoma, R-3327, were used in a 42-day study to determine the effect of castration or orally administered flutamide (FL), DES (diethylstilbestrol) or the 5 alpha-reductase inhibitor, MK-906, on the growth of this androgen-responsive cancer. The rate of growth and final weights of the tumor and the ventral prostate (VP) were all reduced (P less than 0.05) by castration. Flutamide (25 mg/kg/day) significantly decreased tumor and VP weights in intact rats and castrates given 100 micrograms/day (SC) of testosterone propionate (TP) or dihydrotestosterone propionate (DHTP). It also significantly retarded tumor growth rate in TP- or DHTP-treated castrates and was marginally effective in intact animals. DES (100 micrograms/kg/day) reduced (P less than 0.05) tumor and VP weights of intact rats but did not significantly affect tumor growth rate or weight in castrates given TP or DHTP. These results indicated that the effect of DES on tumor growth is caused by its inhibition of the secretion or release of the gonadotropins necessary for testicular androgen production. MK-906 (25 mg/kg/day) affected neither the gross nor the histomorphology of the tumor in intact rats or castrates given TP or DHTP. Further, it caused no histological changes in the testes of intact rats. It did, however, significantly reduce VP weight in intact animals and TP-treated castrates but not in those given DHTP. This illustrates that the anti-androgenicity of MK-906 stems from its inhibition of DHT formation. The failure of MK-906 to influence tumor growth in the TP-treated castrates strongly suggests that the R-3327 tumor can respond to testosterone directly. If that is true, then its growth is unlikely to be affected by a pure 5 alpha-reductase inhibitor such as MK-906. In ancillary experiments, tumors from MK-906-treated animals were found to have reduced levels of DHT and, when assayed in vitro, to have a reduced capacity to convert [3H]-T to [3H]-DHT.

Prostatic effects induced in dogs by chronic or acute oral administration of 5 alpha-reductase inhibitors.

A series of 4-azasteroidal 5 alpha-reductase inhibitors was tested in dogs to determine the effect of chronic (35-44 day) oral administration on prostate size and histology and acute oral administration on prostatic concentrations of testosterone (T) and dihydrotestosterone (DHT). The extent to which the results of the two tests were correlated was also studied in order to see whether the acute test could be used to predict activity in the chronic test. Six delta 1 analogs of the potent 5 alpha-reductase inhibitor, 4-MA (17 beta-N,N-diethylcarbamoyl-4-aza-4-methyl-5 alpha-androstan-3-one) were uniformly active at low dosage levels (less than or equal to 3 mg/kg) in both types of assay whereas several C1-C2 saturated analogs exhibited little activity in the chronic test. The nature of the side chain and whether there was a methyl or a proton at 4-N did not dramatically influence the activity of delta 1 compounds. There was a broad general agreement between the results of the two kinds of test in that if a compound acutely decreased the prostatic concentration of DHT it was likely to reduce prostate size and alter prostatic histology when given on a chronic basis.

5 Alpha-reductase inhibitory and anti-androgenic activities of some 4-azasteroids in the rat.

Inhibition of 5 alpha-reductase and anti-androgenicity were studied in rats treated with various 4-azasteroids. The known inhibitor, N,N-diethyl-4-methyl-3-oxo-4-aza-5 alpha-androstane-17 beta-carboxamide (4-MA) served as a reference compound, and analogs of this basic molecule were assayed. Enhancement of enzyme inhibitory potency was usually seen with delta 1 analogs, whereas reduction in activity was noted with substitutuents such as delta 5, a spirotetrahydrofuran ring at C-17 or 4-deaza groups. Many of the 4-azasteroids had a much greater oral anti-androgenic effect against testosterone propionate (TP) than dihydrotestosterone propionate (DHTP). This difference in activity versus the two androgens is believed to reflect the necessity for TP to undergo reduction to DHT before becoming capable of stimulating prostatic growth. Inhibition of 5 alpha-reductase by active compounds prevented the conversion, thereby producing an anti-androgenic effect. In this regard, certain delta 1 analogs of 4-MA, particularly those bearing a 17 beta-(N-tert butylcarbamoyl) group, proved very effective against TP but were relatively inactive versus DHTP.

Azasteroids as inhibitors of rat prostatic 5 alpha-reductase.

A series of A-ring heterocyclic steroids has been prepared and tested for inhibition of rat prostatic steroid 5 alpha-reductase in vitro. Strikingly high inhibitory activity was found with a group of 17 beta-substituted 4-methyl-4-aza-5 alpha-androstan-3-ones. These compounds were prepared from 3-keto-delta 4-precursors by oxidative (O3 or NaIO4-KMnO4) A-ring cleavage followed, in turn, by ring closure with an amine and hydrogenation over platinum catalyst. Other A-ring azasteroids were made by Beckmann rearrangement of oximes of 2-oxo-A-nor, 3-oxo- and 4-oxo-5 alpha-androstanes. An A-nor-2-oxo-3-azasteroid was prepared by oxidative decarbonylation of a precursor 2,3-dioxo-4-azasteroid with m-chloroperbenzoic acid. A-ring modifications of the 4-azasteroids included delta 1-unsaturation, 2- and 4-substituents, and 3-carbonyl replacements. Side chains at the 17-position were varied with an emphasis on carboxylate derivatives (salts, esters, and amides).

Effect of a new 5 alpha-reductase inhibitor on size, histologic characteristics, and androgen concentrations of the canine prostate.

Mature male beagles were used in studies designed to determine the effect of the steroidal 5 alpha-reductase inhibitor 17 beta-N,N-diethylcarbamoyl-4-aza-4-methyl-5 alpha-androstan-3-one (4-MA) on size, histology, and androgen concentration of the prostate. Subcutaneous administration of 3 or 15 mg/kg/day for 43 days caused a sharp decline in prostate volume. flattening of prostatic epithelial cells, vacuolization of the cytoplasm and pycnosis of the nuclei. Whereas serum testosterone levels remained normal in dogs injected with 3 mg/kg/day, they were lower in those that received 15 mg/kg/day. Concentration of both testosterone and 5 alpha-dihydrotestosterone were reduced in the prostates of dogs that had received either 3 or 15 mg/kg/day of 4-MA. The 15 mg/kg/day level also appeared to adversely affect spermatogenesis. In a 43-day study, 4-MA given orally once each day at levels of 0.1, 0.3, or 1 mg/kg failed to cause a significant decrease in prostate volume. However, daily divided oral doses totaling 1 or 3 mg/kg were given in a 42-day test and both treatment levels produced significant reductions in prostate size.