TY - JOUR T1 - Substrate specificity and ligand interactions of CYP26A1, the human liver retinoic acid hydroxylase JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.111.072413 SP - mol.111.072413 AU - Jayne E Thatcher AU - Brian Buttrick AU - Scott A Shaffer AU - Jakob A Shimshoni AU - David R Goodlett AU - Wendel L Nelson AU - Nina Isoherranen Y1 - 2011/04/26 UR - http://molpharm.aspetjournals.org/content/early/2011/04/26/mol.111.072413.abstract N2 - All-trans retinoic acid (atRA) is the active metabolite of vitamin A. atRA is also used as a drug, and synthetic atRA analogues and inhibitors of RA metabolism have been developed. The hepatic clearance of atRA is mediated primarily by CYP26A1, but design of CYP26A1 inhibitors is hindered by lack of information on CYP26A1 structure and structure activity relationships of its ligands. This study was aimed at identifying the primary metabolites of atRA formed by CYP26A1 and at characterizing the ligand selectivity and ligand interactions of CYP26A1. Based on high resolution MS/MS data, the four primary metabolites formed from atRA by CYP26A1 were identified as 4OH-RA, 4oxo-RA, 16OH-RA and 18OH-RA. 9-cisRA and 13-cisRA were also substrates of CYP26A1. Forty-two compounds with diverse structural properties were tested for CYP26A1 inhibition using 9-cisRA as a probe, and IC50 values for ten inhibitors were determined. The imidazole and triazole containing inhibitors R116010 and R115866 were the most potent inhibitors of CYP26A1 with IC50 values of 4.3 and 5.1nM, respectively. Liarozole and ketoconazole were significantly less potent with IC50 values of 2100 and 550nM, respectively. The RARγ agonist CD1530 was as potent inhibitor of CYP26A1 as ketoconazole with an IC50 of 530nM, whereas the tested RARα and RARβ agonists did not significantly inhibit CYP26A1. The pan-RAR agonist TTNPB and the PPAR ligands rosiglitazone and pioglitazone inhibited CYP26A1 with IC50 values of 3.7, 4.2 and 8.6μM respectively. These data demonstrate that CYP26A1 has high ligand selectivity but accepts structurally related nuclear receptor agonists as inhibitors. ER -