3β-Alkyl-androsterones as inhibitors of type 3 17β-hydroxysteroid dehydrogenase: Inhibitory potency in intact cells, selectivity towards isoforms 1, 2, 5 and 7, binding affinity for steroid receptors, and proliferative/antiproliferative activities on AR+

Type 3 17β-hydroxysteroid dehydrogenase (17β-HSD) is involved in the biosynthesis of the potent androgen testosterone (T), which plays an important role in androgen-sensitive diseases. In an attempt to design compounds to lower the level of T, we designed androsterone (ADT) derivatives substituted at the position 3β as inhibitors of type 3 17β-HSD, and then selected the eight most potent ones (compounds 1–8) for additional studies. In an intact cell assay, they inhibited efficiently the conversion of natural substrate 4-androstene-3,17-dione into T, although they were less active in intact cells (IC50 ∼ 1 μM) than in homogenated cells (IC50 = 57–100 nM). A study of the inhibitory potency with four other 17β-HSDs revealed they were selective, since they do not inhibit reductive types 1, 5 and 7, nor oxidative type 2. Interestingly, they did not show any binding affinity for steroid receptors (androgen, estrogen, glucocorticoid and progestin). Only two inhibitors, 3β-phenyl-ADT (5) and 3β-phenylmethyl-ADT (6) showed some proliferative activities on an AR+ cell line and on an ER+ cell line, but their effects were not mediated through the androgen or estrogen receptors. This study identified selective inhibitors of type 3 17β-HSD acting through a mixed-type inhibition, and devoid of non-suitable androgenic and estrogenic proliferative activities. The more potent inhibitors were 3β-hexyl-ADT (2), 3β-cyclohexylethyl-ADT (4) and 3β-phenylethyl-ADT (7).