Antimineralocorticoid 11β-Substituted Spirolactones Exhibit Androgen Receptor Agonistic Activity: A Structure Function Study

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Abstract
In humans, spironolactone and mespirenone are well known antimineralocorticoids without C-11β substituents. These compounds display antagonist properties by acting through the human androgen receptor (hAR). In contrast, we demonstrate here that synthetic mineralocorticoid antagonists bearing hydrophobic C-11β substituents and C-17γ-lactone are potent hAR agonists in vitro. The three-dimensional construction of both the ligand binding domain (LBD) of the hAR and the human mineralocorticoid receptor (hMR), based on the crystal structure of the LBD of the human progesterone receptor, revealed not only that the interactions with the steroidal A- and D-rings seemed to be crucial for stabilization of active hMR or hAR conformation, but that other steroidal substitutions could influence the agonist versus antagonist activity of ligands. The docking of synthetic compounds bearing C-11β hydrophobic substituents within the ligand binding pocket of hAR demonstrated that precise positions of the steroid, such as C-11 and C-17, are in close contact with some residues on the receptor, C-11 with Gly 708 and C-17 with Asn705 and Thr877. These contacts are crucial for the stabilization of the active receptor conformation. Mutation of Asn705 by alanine altered the 11β-substituted spirolactone-mediated trans-activation function of hAR, suggesting an anchoring of the C-17-lactone carbonyl group (C-22) with this residue. The stabilizing effect of the H12 helix in its active conformation is also induced by hydrophobic contacts between the Gly708 and C-11β substituents, as recently observed with the A773G-hMR mutant in the presence of similar drugs. The study of the role of these substituents suggests efficient new directions for the drug design of selective androgen agonists.