R115866

Orally active retinoic acid (RA) metabolism blocking agent (RAMBA) with higher CYP26 specificity and potency than liarozole (R75251).

R115866 (Talarozole) is an orally active all-trans retinoic acid (RA) metabolism blocking agent (RAMBA; IC50 = 4 nM against RA metablism in yeast microsomes expressing human CYP26) with much reduced or little potency against CYP19 (aromatase), CYP17 (17,20-lyase), CYP2C11, CYP3A, and CYP2A1 (IC50 from 1.2 to >10 μM). Plasma and tissue RA upregulation via R115866 oral treatment exhibits in vivo efficacy in several retinoid-responsive rodent models, including vaginal keratinization suppression (ED50 = 1.0 mg/kg/day vs. 5.1 mg/kg/day with RA in rats), pinnal hyperplasia induction (ear epidermis thickness = 35.5 μm with 2.5 mg/kg/day R115866 vs. 16.5 μm in control mice), conversion of caudal para- to ortho-keratosis (90% with 1.25 mg/kg/day R115866 vs. 30.3% in control mice). Comparing to liarozole, R115866 is CYP26-selective and does not inhibit CYP-mediated biosynthesis of adrenal and gonadal steroid hormones.