Comparative RARα, RARβ, and RARγ transactivation of ST1926, CD437, and congeners: correlation with the apoptotic potential. COS-7 cells (150 000/well) were cotransfected with the indicated RAR subtype (0.05 μg) (A,B) or RARγ (C), a retinoic acid–dependent reporter construct (DR5-tk-CAT; 1 μg) and the β-galactosidase expression vector pCH110 (0.5 μg). Twenty-four hours after transfection, cells were treated for an additional 24 hours with vehicle or the indicated concentration of ST1926 (A) and CD437 (B) or the indicated compound (1 μM) (C). At the end of the experiment, cells were harvested and homogenized, and CAT as well as β-galactosidase activities determined. The results are expressed in fold induction of CAT activity following normalization for the amount of β-galactosidase expressed. CAT activity measured in cells treated with vehicle is considered as 1.0. Panel D illustrates the linear correlation between the RARγ transactivating activity of each RRM, as determined at a concentration of 1 μM (C), and the apoptotic potential, as determined at a concentration of 10 μM (Table 1). Results are expressed as the mean ± SD of 3 replicate cultures. The data are representative of at least 2 independent experiments. *Significantly higher than the corresponding vehicle-treated group (P < .01 according to the Student t test).