20-Amino and 20,21-aziridinyl pregnene steroids: Development of potent inhibitors of 17α-hydroxylase/C17,20-lyase (P450 17) Original Research Article

In the search for potent inhibitors of P450 17, the key enzyme of androgen biosynthesis, the 20,21-aziridinyl- and 20-aminopregnene steroids 1–11 were synthesized and tested toward rat testicular P450 17. Only the aziridinyl-substituted pregnenolones (1 and 2) and progesterones (3 and 4), respectively, showed inhibitory activity, which strongly depends on C20 stereochemistry. The most active compound 1 [20(S)-20,21-aziridinylpregn-5-en-3β-ol; IC50 0.21 μM, progesterone 25 μM; Ki = 1.7 nM, Km progesterone = 7.0 μM] is the strongest inhibitor of rat P450 17 described so far. Using UV-vis difference spectroscopy, complexation of the aziridinyl nitrogen to the heme iron, Fe3+, of P450 17 was observed, which could not be reversed by high concentrations of substrate. Preincubation of the enzyme with 1 in the absence and presence of NADPH followed by charcoal treatment results in a strong decrease of enzyme activity within 30 s. However, a recovery of enzyme activity was observed: 90 min after charcoal treatment 75% of the activity was restored.