Effect of megestrol acetate (Megace) on steroid metabolism and steroid-protein binding in the human prostate.

Megestrol acetate (Megace), an antiandrogen, was administered in a dosage of 80 mg daily to 6 patients with benign prostatic hypertrophy (BPH) for 4 to 25 days prior to transurethral resection of the prostate (TURP). Surgical tissue from drug-treated patients was compared to untreated controls in regard to: 1) the enzymatic reduction of testosterone (T) and dihydrotestosterone (DHT); 2) DHT binding to a cytosol receptor protein; 3) tissue levels of endogenous dihydrotestosterone and androstanediols (diols). When minced prostate was incubated with 3H-T and 14C-androstenedione for 1 h at 37 C, prostate 5alpha-reductase activity, measured as reduced products formed from substrate, decreased to 31% and 39%, respectively, of the control values. Prostate 3-oxido-reductase enzyme activity, measured as diols formed from 3H-DHT, was decreased to neglible values in Megace-treated patients compared to an 8.7% conversion to diols in controls. No 3H-DHT binding to a cytosol receptor protein could be demonstrated in 4 out of 5 prostates from Megace-treated patients, whereas the presence of such a receptor was noted in 14 out of 17 untreated controls. Endogenous DHT levels in Megace-treated patients averaged 1.1 ng/g (SE = 0.26), significantly less than the average of 3.9 ng/g (SE = 0.49) found in controls (P less than 0.001). No significant difference was noted in endogenous diols. In addition to these effects on tissue, Megace significantly decreased plasma levels of T, LH, and FSH at the end of the 4- to 25-day period; plasma prolactin levels did not change. Continued studies of Megace for the possible treatment of benign prostatic hypertrophy may be warranted since the drug appears to block several important biochemical steps which mediate the effects of androgen on the human prostate.