STRUCTURAL VARIANTS OF THE VITAMIN-D ANALOG EB1089 REDUCE ITS LIGAND SENSITIVITY AND PROMOTER SELECTIVITY

The nuclear hormone 1 alpha,25-dihydroxyvitamin D-3 (VD) has important cell-regulatory functions but also a strong calcemic effect. Therefor e, various VD analogues have been synthesized and screened for their b iological profile. In order to gain more insight into the molecular ba sis of the high antiproliferative but low calcemic action of the VD an alogue EB1089, we characterized this compound in comparison to five st ructurally related VD analogues. The activities of the six VD analogue s in in vitro assays (limited protease digestion assays for determinin g interaction with monomeric vitamin D receptor (VDR), ligand-dependen t gel shift assays for showing the increase of DNA binding of VDR-reti noid X receptor (RXR) heterodimers, and reporter gene assays on differ ent types of VD response elements for demonstrating the efficacy in nu clear VD signalling) were found to represent their biological potency (antiproliferative effect on different malignant cell lines). In this series, EB1089 proved to be the most potent VD analogue; that is, ever y structural modification (20-epi configuration, cis-configuration at position C24, or changes at the ethyl groups at position C25) appeared to reduce the determined activities mediated through the VDR of these analogues. Moreover, the modifications of EB1089 resulted in a loss o f VD response element selectivity, suggesting that this parameter is v ery critical for the biological profile of this VD analogue. I. Cell. Biochem. 71 :340-350, 1998. (C) 1998 Wiley-Liss, Inc.