Synthesis and Evaluation of Novel Steroidal Oxime Inhibitors of P450 17 (17α-Hydroxylase/C17−20-Lyase) and 5α-Reductase Types 1 and 2

Abstract

17 alpha-Hydroxylase/C17-20-lyase (P450 17, CYP 17) and 5 alpha-reductase are the key enzymes in androgen biosynthesis and targets for the treatment of prostate cancer and benign prostatic hyperplasia. In the search of inhibitors for both enzymes, 23 pregnenolone- or progesterone-based steroids were synthesized bearing an oxime group connected directly or via a spacer to the steroidal D-ring. Tested for inhibition of human and rat P450 17, some pregnenolone (9, 11, 14) and a series of progesterone compounds (17-20) turned out to be highly active inhibitors of the human enzyme. The most active compound was Z-21-hydroxyiminopregna-5, 17(20)-dien-3 beta-ol (9) showing K(i) values of 44 and 3.4 nM for the human and rat enzymes, respectively, and a type II UV-difference spectrum indicating a coordinate bond between the oxime group and the heme iron. In contrast to the pregnenolones which showed no inhibition of 5 alpha-reductase isozymes 1 and 2, the progesterones 16, 17, 20, 21, and 23 showed marked inhibition, especially toward the type 2 enzyme. Compounds 17 and 20 were identified as potent dual inhibitors of both P450 17 and 5 alpha-reductase. Tested for selectivity, the most potent P450 17 inhibitors 9, 10, and 14 showed no or only marginal inhibition of P450 arom, P450 scc, and P450 TxA(2). Selected compounds were tested for inhibition of the target enzymes using whole-cell assays. Compounds 9-11 strongly inhibited P450 17 being coexpressed with NADPH-P450 reductase in E. coli cells, and 16, 20, and 23 markedly inhibited 5 alpha-reductase expressed in HEK 293 cells. Tested for in vivo activity, 9 (0.019 mmol/kg) decreased the plasma testosterone concentration in rats after 2 and 6 h by 57% and 44%.

Catalysis, Stereochemistry, and Inhibition of Ureidoglycolate Lyase

“…androgens). Competitive P450c17 inhibitors with K I values in the 3-9 nM range have been reported by Hartmann et al (62,63), and Ideyama et al (64) have reported that the nonsteroidal compound 2-(1H-imidazol-4-ylmethyl)-9H-carbazole (named "YM116") competitively inhibits the 17,20-lyase activity with a K I of 0.38 nM. Since prostate cancers typically show androgen-dependent growth, inhibitors for P450c17 may represent promising therapeutic agents for prostate cancer.…”

Synthesis and Evaluation of Steroidal Hydroxamic Acids as Inhibitors of P450 17 (17α-Hydroxylase/C17-20-Lyase)

“…As compound 1 has been shown to be a strong inhibitor of P450 17 [8] , the low activity of 2 (and 3) cannot be due to steric reasons. It is more likely that the hydroxamate group is a low activity monodentate ligand compared to the oxime group, which might be due to the electron withdrawing effect of the carbonyl group or to an inappropriate state of the tautomeric equilibrium (Chart 1).…”

“…Interestingly, the oxime group has been found to be appropriate for the design of potent steroidal inhibitors [8,2] (as an example see compound 1, Chart 1). Structurally related to oximes are hydroxamic acids which exist in solution in two tautomeric forms (Chart 1).…”

17-Oximino-5-androsten-3β-yl esters: synthesis, antiproliferative activity, acute toxicity, and effect on serum androgen level

“…2)-based steroids bearing an oxime group connected directly or via a spacer to the steroidal D ring, where the oxime group is capable to form a coordinate bond with heme iron of enzyme (Hartmann et al, 2000). On the other hand, progesterone esters (3a, 3b) (Fig.…”