Ketoconazole Binds to Glucocorticoid Receptors

A B S T R A C T We have recently found that ketoconazole inhibits adrenal steroidogenesis; in this paper we investigated whether imidazole antimycotic drugs additionally interact with glucocorticoid receptor sites in target tissues. Our approach was to assess the ability of three drugs: ketoconazole, clotrimazole, and RS 49910, to inhibit [3H]dexamethasone binding to hepatoma tissue culture (HTC) cell cytosol. The results indicated dose-dependent, competitive displacement of [3H]dexamethasone binding that was in the potency sequence: clotrimazole > ketoconazole > RS 49910. We then examined the functional response of this binding by measuring tyrosine aminotransferase (TAT) activity in HTC cells. The antimycotics did not exhibit TAT agonist activity and inhibition of basal enzyme levels was not detected. However, the drugs were potent antagonists of dexamethasone-induced TAT activity and the effect was temporally reversible. This antagonist activity was in the same sequence and closely correlated with the binding potency of the three drugs. We conclude that ketoconazole and other imidazole antimycotic drugs possess glucocorticoid antagonist activity by virtue of occupancy of glucocorticoid receptor sites in target tissues.