Pharmacophore analysis of the nuclear oxysterol receptor LXR alpha

A cell-free assay was developed for the orphan nuclear receptor LXR alpha t hat measures the ligand-dependent recruitment of a peptide from the steroid receptor coactivator 1 (SRC1) to the nuclear receptor. Using this ligand-s ensing assay (LiSA), the structural requirements for activation of the rece ptor by oxysterols and related compounds were studied. The minimal pharmaco phore for receptor activation was shown to be a sterol with a hydrogen bond acceptor at C24. 24(S),25-Epoxycholesterol (1), which meets this criterion , is among the most efficacious of the oxysterols and is an attractive cand idate as the LXR alpha natural hormone. Cholenic acid dimethylamide (14) sh owed increased efficacy compared to 1, whereas the unnatural oxysterol 22(S )-hydroxycholesterol (4) was shown to be an antagonist of 1 in the LiSA. Th e structural requirements for SRC1 recruitment in the LiSA correlated with the transcriptional activity of compounds in a cell-based reporter assay em ploying LXR alpha -GAL4 chimeric receptors. Site-directed mutagenesis ident ified Trp(443) as an amino acid critical for activation of LXR alpha by oxy sterol ligands. This information was combined with the structure-activity r elationship developed from the LiSA to develop a 3D homology model of LXR a lpha. This model may aid the design of synthetic drugs targeted at this tra nscriptional regulator of cholesterol homeostasis.