Fluorinated oxysterol analogues: synthesis, molecular modelling and LXRß activity

RODRIGUEZ, C; ALVAREZ, L; DANSEY, M.V.; PAOLO, L. S.; VELEIRO, A.; PECCI, A; BURTON, G

JOURNAL OF STEROID BIOCHEMISTRY AND MOLECULAR BIOLOGY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2017 vol. 165 p. 268 - 276

0960-0760

Liver X receptors (LXRs) are nuclear receptors that playcentral roles in the transcriptional control of lipid metabolism. Theability of LXRs to integrate metabolic and inflammation signaling makesthem attractive targets for intervention in human metabolic diseases.Several oxidized metabolites of cholesterol (oxysterols) are endogenousLXR ligands, that modulate their transcriptional responses. While 25Rcholestenoicacid is an agonist of the LXRs, the synthetic analogue 27-norcholestenoic acid that lacks the 25-methyl is an inverse agonist. Thischange in the activity profile is triggered by a disruption of a keyinteraction between residues His435 and Trp457 that destabilizes the H11-H12 region of the receptor and favors the binding of corepressors. Theintroduction of fluorine atoms on the oxysterol side chain can favor bothhydrophobic interactions as well as hydrogen bonds with the fluorineatoms and may thus induce changes in the receptor that may lead tochanges in the activity profile. To evaluate these effects we havesynthesized two fluorinated 27-nor-steroids, analogues of 27-norcholestenoic acid, the 25,25-difluoroacid and the corresponding 26-alcohol. The key step was a Reformatsky reaction on the C-24cholenaldehyde, with ethyl bromodifluoroacetate under high intensityultrasound (HIU) irradiation, followed by a Barton-McCombie typedeoxygenation. Activity was evaluated in a luciferase reporter assay inthe human HEK293T cells co-transfected with full length human LXRβexpression vector. The 25,25-difluoro-27-norcholestenoic acid was aninverse agonist and antagonist similar to its non-fluorinated analoguewhile its reduced derivative 25,25-difluoro-27-norcholest-5-ene- -diol was an agonist. Molecular dynamics simulation of the ligand-receptorcomplexes showed that the difluoroacid disrupted the His435-Trp457interaction although the resulting conformational changes were differentfrom those induced by the non-fluorinated analogue. In the case of thedifluoroalcohol, the fluorine atoms actively participated in theinteraction with several residues in the ligand binding pocket leading toa stabilization of the active receptor conformation