[(3)H]metyrapol and 4-[(131)i]iodometomidate label overlapping, but not identical, binding sites on rat adrenal membranes.

Metyrapone, metyrapol, and etomidate are competitive inhibitors of 11-deoxycorticosterone hydroxylation by 11ß-hydroxylase. [(3)H]Metyrapol and 4-[(131)I]iodometomidate bind with high affinity to membranes prepared from bovine and rat adrenals. Here we report inhibitory potencies of several compounds structurally related to one or both of these adrenostatic drugs, against the binding of both radioligands to rat adrenal membranes. While derivatives of etomidate inhibited the binding of both radioligands with similar potencies, derivatives of metyrapone inhibited the binding of 4-[(131)I]iodometomidate about 10 times weaker than the binding of [(3)H]metyrapol. By X-ray structure analysis the absolute configuration of (+)-1-(2-fluorophenyl)-2-methyl-2-(pyridin-3-yl)-1-propanol [(+)-11, a derivative of metyrapol] was established as (R). We introduce 1-(2-fluorophenyl)-2-methyl-2-(pyridin-3-yl)-1-propanone (9; Ki = 6 nM), 2-(1-imidazolyl)-2-methyl-1-phenyl-1-propanone (13; 2 nM), and (R)-(+)-[1-(4-iodophenyl)ethyl]-1H-imidazole (34; 4 nM) as new high affinity ligands for the metyrapol binding site on 11ß-hydroxylase and discuss our results in relation to a proposed active site model of 11ß-hydroxylase.

New selective inhibitors of steroid 11beta-hydroxylation in the adrenal cortex. Synthesis and structure-activity relationship of potent etomidate analogues.

Derivatives of etomidate were evaluated as inhibitors of adrenal steroid 11beta-hydroxylations. Stereoselective coupling by Mitsunobu produced chirally pure analogues to study the effect of configuration, modification of the ester, and substitution in the phenyl ring, with the aim to probe specific sites for introducing a radionuclide. Iodophenyl metomidate (IMTO) labeled with iodine-131 served as radioligand for structure-affinity relationship studies. We have characterized the kinetic parameters of specific (131)I-IMTO binding on rat adrenal membranes and used the displacement of (131)I-IMTO binding to evaluate functionalized MTO analogues. Our results indicated that (1) ( R)-configuration is essential for high affinity, (2) highest potency resides in the ethyl, 2-propyl, and 2-fluoroethyl esters, and (3) substitution of the phenyl ring is well tolerated. The clinically used inhibitors metyrapone and ketoconazole inhibited (131)I-IMTO binding with low affinity. Incubation of selected analogues with human adrenocortical NCI-h295 cells demonstrated a high correlation with the inhibitory effect on cortisol secretion.