Novel 17-azolyl steroids, potent inhibitors of human cytochrome 17 alpha-hydroxylase-C17,20-lyase (P450(17) alpha): potential agents for the treatment of prostate cancer.

A new synthetic route to a variety of novel delta 16-17-azolyl steroids is described: it involves the nucleophilic vinylic "addition-elimination" substitution reaction of 3 beta-acetoxy-17-chloro-16-formylandrosta-5,16-diene (2) and azolyl nucleophiles. Some of these novel delta 16-17-azolyl steroids, 6, 17, 19, and 27-29, prepared in good overall yields, are very potent inhibitors of human and rat testicular P450(17) alpha. They are shown to be noncompetitive and appear to be slow-binding inhibitors of human P450(17) alpha. The most potent compounds are 3 beta-hydroxy-17-(1H-imidazol-1-yl)androsta-5,16-diene (17), 3 beta-hydroxy-17-(1H-1,2,3-triazol-1-yl)androsta-5,-16-diene (19), and 17-(1H-imidazol-1-yl)androsta-4,16-dien-3-one (28), with Ki values of 1.2, 1.4, and 1.9 nM, respectively, being 20-32 times more potent than ketoconazole (Ki = 38 nM). Spectroscopic studies with a modified form of human P450(17) alpha indicate that the inhibition process involves binding of steroidal azole nitrogen to the heme iron of the enzyme. Furthermore, some of these potent P450(17) alpha inhibitors (27-29) are also powerful inhibitors of steroid 5 alpha-reductase, and others (17 and 19) appear to exhibit strong antiandrogenic activity in cultures of the LNCaP human prostatic cancer cell line. These novel compounds with impressive dual biological activities make them strong candidates for development as therapeutic agents for treatment of prostate cancer and other disease states which depend on androgens.