Inhibitors of vitamin D hydroxylases: structure-activity relationships

Aiming at new drugs to efficiently treat diseases, in which either increased or decreased levels of active vitamin D are desirable, we have designed some 400 structurally different azole-type inhibitors and examined their capacity to selectively block vitamin D metabolism by CYP24 or synthesis by CYP27B, in human keratinocytes. Based on resulting data, we built pharmacophore models of the active sites using commercial software. The overlay of potent selective compounds indicated similar docking modes in the two-substrate pockets and allowed for identification of bioactive conformations. Superimposing these bioactive conformations with low energy conformers of 25(OH)D(3) suggested that the substrate-mimicked by strong inhibitors in size, shape and lipophilic character-binds to both enzymes in 6s-trans configuration. Pharmacophoric models implied a similar geometry of the substrate sites, nevertheless specific features of CYP24 and CYP27B could be defined. Bulky substituents in alpha-position to the azole caused selectivity for CYP24, whereas bulky substituents in beta-position could result in selectivity for CYP27B. Moreover, studies with small sterically restricted inhibitors revealed a probable location of the 3-OH-group of 25(OH)D(3) in CYP27B. In the absence of crystal structures, our inhibitors are valuable tools to model and understand the active sites of vitamin D hydroxylases, resulting in the design of powerful, selective therapeutics.