Lithocholic Acid Derivatives as Potent Vitamin D Receptor Agonists

Lithocholic acid ( ) was identified as a second endogenous ligand of vitamin D receptor (VDR), though its activity is very weak. In this study, we designed novel lithocholic acid derivatives based on the crystal structure of VDR-ligand-binding domain (LBD) bound to . Among the synthesized compounds, bearing a 2-hydroxy-2-methylprop-1-yl group instead of the 3-hydroxy group at the 3α-position of showed dramatically increased activity in HL-60 cell differentiation assay, being at least 10 000 times more potent than lithocholic acid ( ) and 3 times more potent than 1α,25-dihydroxyvitamin D ( ). Although the binding affinities of and its epimer were less than that of , their transactivation activities were greater than that of . X-ray structure analyses of VDR LBD bound to or showed that the binding positions of these compounds in the ligand-binding pocket are similar to that of .