TY - JOUR T1 - Different Molecular Mechanisms of Vitamin D<sub>3</sub> Receptor Antagonists JF - Molecular Pharmacology JO - Mol Pharmacol SP - 1478 LP - 1485 DO - 10.1124/mol.59.6.1478 VL - 59 IS - 6 AU - Andrea Toell AU - Manuel Macias Gonzalez AU - Dagmar Ruf AU - Andreas Steinmeyer AU - Seiichi Ishizuka AU - Carsten Carlberg Y1 - 2001/06/01 UR - http://molpharm.aspetjournals.org/content/59/6/1478.abstract N2 - Two structurally different antagonists of the nuclear hormone 1α,25-dihydroxyvitamin D3[1α,25(OH)2D3], the 25-carboxylic ester ZK159222 and the 26,23-lactone TEI-9647, have recently been described. In this study, the molecular mechanisms and the efficacy of both antagonists were compared. ZK159222 showed similar potency and sensitivity to 1α,25(OH)2D3 in ligand-dependent gel shift assays using the vitamin D receptor (VDR), the retinoid X receptor, and specific DNA binding sites, whereas TEI-9647 displayed reduced potency and &gt;10-fold lower sensitivity in this assay system. Limited protease digestion and gel shift clipping assays showed that the two antagonists stabilized individual patterns of VDR conformations. Both antagonists prevented the interaction of the VDR with coactivator proteins, as demonstrated by GST-pull-down and supershift assays; like the natural hormone, however, they were able to induce a dissociation of corepressor proteins. Interestingly, ZK159222 demonstrated functional antagonism in reporter gene assays both in HeLa and MCF-7 cells, whereas TEI-9647 functioned as a less sensitive antagonist only in MCF-7 cells. In conclusion, the two 1α,25(OH)2D3 analogs act in part via different molecular mechanisms, which allows us to speculate that ZK159222 is a more complete antagonist and TEI-9647 a more selective antagonist. ER -