The antiglucocorticoid, cortexolone, fails to promote in vitro activation of cytoplasmic glucocorticoid receptors from the human leukemic cell line CEM-C7.

Cortexolone functions as an antiglucocorticoid in the human leukemic cell line CEM-C7, since it blocks the growth inhibition and cell lysis mediated by the potent agonist triamcinolone acetonide (TA). At high concentrations (10(-5) M) cortexolone alone is inactive. The ability of cortexolone to block the TA-mediated biological effects is reflected in its ability (1000-fold molar excess) to effectively block the binding of [3H]TA to the cytoplasmic unactivated form of the receptors eluted from DEAE-cellulose at approx. 180 mM potassium phosphate (KP). Likewise a 1000-fold molar excess of TA inhibits the specific binding of [3H]cortexolone to the unactivated receptors and to a peak which elutes at low salt concentration (35 mM KP) but does not appear to represent activated [3H]cortexolone-receptor complexes. Thermal activation/transformation (25 degrees C for 30 min +/- 10 mM ATP) of the [3H]TA-receptor complexes significantly enhances the subsequent DNA-cellulose binding capacity of these complexes and also results in their elution from DEAE-cellulose at the low salt (50 mM KP) activated position. In contrast, exposure of the cytoplasmic [3H]cortexolone-receptor complexes to identical in vitro activating (transforming) conditions fails to enhance subsequent DNA-cellulose binding capacity or to result in the appropriate shift in DEAE-cellulose elution profile. This inability of [3H]cortexolone to facilitate activation/transformation of receptors was also verified using cytosol prepared from the glucocorticoid-resistant 'activation-labile' mutant, 3R7. Taken collectively the data suggest that cortexolone, unlike an agonist such as TA, fails to promote in vitro activation/transformation, a conformational change which also occurs in vivo under physiological conditions and is a prerequisite for nuclear binding.