17β-Hydroxysteroid dehydrogenase 2 (17β-HSD2) catalyzes the inactivation of estradiol into estrone. This enzyme is expressed only in a few tissues, and therefore its inhibition is considered as a treatment option for osteoporosis to ameliorate estrogen deficiency. In this study, ligand-based pharmacophore models for 17β-HSD2 inhibitors were constructed and employed for virtual screening. From the virtual screening hits, 29 substances were evaluated in vitro for 17β-HSD2 inhibition. Seven compounds inhibited 17β-HSD2 with low micromolar IC50 values. To investigate structure–activity relationships (SAR), 30 more derivatives of the original hits were tested. The three most potent hits, 12, 22, and 15, had IC50 values of 240 nM, 1 μM, and 1.5 μM, respectively. All but 1 of the 13 identified inhibitors were selective over 17β-HSD1, the enzyme catalyzing conversion of estrone into estradiol. Three of the new, small, synthetic 17β-HSD2 inhibitors showed acceptable selectivity over other related HSDs, and six of them did not affect other HSDs.

Bupropion is widely used for treatment of depression and as a smoking-cessation drug. Despite more than 20 years of therapeutic use, its metabolism is not fully understood. While CYP2B6 is known to form hydroxybupropion, the enzyme(s) generating erythro-and threohydrobupropion have long remained unclear. Previous experiments using microsomal preparations and the nonspecific inhibitor glycyrrhetinic acid suggested a role for 11b-hydroxysteroid dehydrogenase 1 (11b-HSD1) in the formation of both erythro-and threohydrobupropion. 11b-HSD1 catalyzes the conversion of inactive glucocorticoids (cortisone, prednisone) to their active forms (cortisol, prednisolone). Moreover, it accepts several other substrates. Here, we used for the first time recombinant 11b-HSD1 to assess its role in the carbonyl reduction of bupropion. Furthermore, we applied human, rat, and mouse liver microsomes and a selective inhibitor to characterize species-specific differences and to estimate the relative contribution of 11b-HSD1 to bupropion metabolism. The results revealed 11b-HSD1 as the major enzyme responsible for threohydrobupropion formation. The reaction was stereoselective and no erythrohydrobupropion was formed. Human liver microsomes showed 10 and 80 times higher activity than rat and mouse liver microsomes, respectively. The formation of erythrohydrobupropion was not altered in experiments with microsomes from 11b-HSD1-deficient mice or upon incubation with 11b-HSD1 inhibitor, indicating the existence of another carbonyl reductase that generates erythrohydrobupropion. Molecular docking supported the experimental findings and suggested that 11b-HSD1 selectively converts R-bupropion to threohydrobupropion. Enzyme inhibition experiments suggested that exposure to bupropion is not likely to impair 11b-HSD1-dependent glucocorticoid activation but that pharmacological administration of cortisone or prednisone may inhibit 11b-HSD1-dependent bupropion metabolism.

Inhibition of 17β-HSD2 is an attractive mechanism for the treatment of osteoporosis. We report here the optimization of human 17β-HSD2 inhibitors in the 2,5-thiophene amide class by varying the size of the linker (n equals 0 and 2) between the amide moiety and the phenyl group. While none of the phenethylamides (n = 2) were active, most of the anilides (n = 0) turned out to moderately or strongly inhibit 17β-HSD2. The four most active compounds showed an IC₅₀ of around 60 nM and a very good selectivity toward 17β-HSD1, 17β-HSD4, 17β-HSD5, 11β-HSD1, 11β-HSD2 and the estrogen receptors α and β. The investigated compounds inhibited monkey 17β-HSD2 moderately, and one of them showed good inhibitory activity on mouse 17β-HSD2. SAR studies allowed a first characterization of the human 17β-HSD2 active site, which is predicted to be considerably larger than that of 17β-HSD1.