Antimineralocorticoid 11 beta-substituted spirolactones exhibit androgen receptor agonistic activity: A structure function study

In humans, spironolactone and mespirenone are well known antimineralocortic oids without C-11 beta substituents. These compounds display antagonist pro perties by acting through the human androgen receptor (hAR). In contrast, w e demonstrate here that synthetic mineralocorticoid antagonists bearing hyd rophobic C-11 beta substituents and C-17 gamma -lactone are potent hAR agon ists in vitro. The three-dimensional construction of both the ligand bindin g domain (LBD) of the hAR and the human mineralocorticoid receptor (hMR), b ased 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 a ntagonist activity of ligands. The docking of synthetic compounds bearing C -11 beta hydrophobic substituents within the ligand binding pocket of hAR d emonstrated that precise positions of the steroid, such as C-11 and C-17, a re in close contact with some residues on the receptor, C-11 with Gly 708 a nd C-17 with Asn705 and Thr877. These contacts are crucial for the stabiliz ation of the active receptor conformation. Mutation of Asn705 by alanine al tered the 11 beta -substituted spirolactone-mediated trans-activation funct ion of hAR, suggesting an anchoring of the C-17-lactone carbonyl group (C-2 2) with this residue. The stabilizing effect of the H12 helix in its active conformation is also induced by hydrophobic contacts between the Gly708 an d C-11 beta 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 androge n agonists.