Synthesis and evaluation of 17-aliphatic heterocycle-substituted steroidalinhibitors of 17 alpha-hydroxylase/C17-20-lyase (P450 17)

In the search for potent inhibitors of P450 17, the key enzyme in androgen biosynthesis, a series of steroidal inhibitors were synthesized and tested toward rat and human P450 17. Small aliphatic heterocycles (aziridine, oxir ane, thiirane, diaziridine, diazirine, azetidine) were introduced into the 17 beta -position of anstrost-5-en-3 beta -ol. After identifying that aziri dine is the most suitable functional group to coordinate with the heme iron , modifications of the steroidal skeleton were performed for further optimi zation. A wide range of inhibitory potencies toward P450 17 were found for the 21 test compounds. The most potent inhibitors toward the human and rat enzyme were aziridine compounds 3 (IC50 rat: 0.21 muM, K-i = 3 nM; IC50 hum an: 0.54 muM, K-i = 8 nM), 5 (IC50 rat: 0.43 muM, K-i = 7 nM; IC50 human: 0 .29 muM, K-i = 4 nM), and 8 (21R:21S = 1:1; IC50 rat: 0.53 muM, K-i = 9 nM; IC50 human: 0.40 muM, K-i = 6 nM) which were more potent than the referenc e ketoconazole (IC50 rat: 67 muM; IC50 human: 0.74 muM), The inhibitory pot ency depends markedly on the stereochemistry at C20 of the inhibitors. This effect is more pronounced for the rat enzyme. Tested for selectivity, the highly potent inhibitors show poor inhibitory activity toward P450 arom, P4 50 sec, P450 TxA(2), and 5 alpha -reductase. Tested for in vivo activity, 3 and 8 (0.019 mmol/kg) decreased the plasma testosterone concentration in r ats by 81% and 84% after 2 h.