Inhibition of steroid-protein interactions by dicyclohexane derivatives.

Sixteen dicyclohexane derivatives including the parent compound d,1-3,4-bis (4-oxocyclohexyl)-hexane (PRDX) have been synthesized and studied for putative interference with androgen binding to transport proteins, metabolizing enzymes, and receptors from rat tissues. Several of these analogues inhibited competitively the binding of dihydrotestosterone to ABP, the epididymal androgen transport protein. One compound had an affinity for ABP as high as Kd = 70 nM. Some dicyclohexanes also inhibited the aromatase enzyme which catalyses conversion of androgens into estrogens, as well as the NADPH-dependent, particulate form of 3 alpha(beta)-hydroxysteroid dehydrogenase, the enzyme that converts dihydrotestosterone into 5 alpha-androstanediol. For both enzymes the inhibition potency Ki of PRDX was about equal to the Km of the substrate. All of these interactions were specific in that they were modulated by single substitutions on the dicyclohexane molecule and they did not occur with other steroid binding proteins such as 5 alpha-reductase and the intracellular androgen receptor. A conformational study showed that dicyclohexanes can assume a 'steroidoid' conformation that differs from the crystal structure and which could account for the specific interactions with the steroid binding sites described here.

Effects of dicyclohexane derivatives on androgen metabolism in the rat prostate.

Dicyclohexane derivatives, which inhibit the binding of testosterone and dihydrotestosterone (DHT) to the androgen-binding protein (ABP) of rat epididymis without interfering with their binding to the androgen receptor, show a similar selectivity in their effects on androgen metabolism. Their ability to inhibit the aromatization of testosterone has been reported previously. This paper demonstrates that they are potent inhibitors of 3 alpha(beta)-hydroxysteroid:NAD(P)+ oxidoreductase activity (3-HSD) in the particulate fraction from rat prostate gland; the values of Ki for their inhibition of this enzyme are similar to that of the Km for DHT as substrate. The dicyclohexane derivatives are markedly less effective against the cytosolic NADPH-dependent 3-HSD, and they do not appear to inhibit testosterone 5 alpha-reductase activity. These characteristics are likely to complicate the proposed use of the dicyclohexane derivatives as probes for the role of ABP in vivo. However, they may be of interest in the study of structure-activity relationships in androgen-metabolizing enzymes, particularly in the examination of the different forms of 3-HSD.