Identification of rat urinary and biliary metabolites of esonarimod, a novel antirheumatic drug, using liquid chromatography/electrospray ionization tandem mass spectrometry with postcolumn addition of 2- (2-methoxyethoxy) ethanol, a signal-enhancing modifier
Yamaguchi, J.; Ohmichi, M.; Hasegawa, M.; Yoshida, H.; Ogawa, N.; Higuchi, S.
Drug Metabolism and Disposition the Biological Fate of Chemicals 29(6): 806-812
2001
ISSN/ISBN: 0090-9556 PMID: 11353748 Document Number: 526328
The biotransformation of esonarimod (KE-298) ((+-)-2-acetylthio-methyl-4-(4-methylphenyl)-4-oxobutanoic acid), a new antirheumatic drug, was investigated in rats. Urinary and biliary excretions within 24 h after oral administration of 5 mg/kg (14C)esonarimod accounted for 89 and 10% of the dose, respectively. Initial metabolite analysis by liquid chromatography/electrospray ionization tandem mass spectrometry with negative ion mode, in which a mobile phase of 20 mM ammonium acetate (pH 4.6)/methanol with gradient-elution mode was used, failed to obtain any structural information on most of the metabolites due to poor sensitivity. To overcome this problem, postcolumn addition of 2-(2-methoxy-ethoxy)ethanol, a powerful signal-enhancing modifier, to the mobile phase was used, allowing pronounced signal enhancement and structural elucidation of urinary and biliary metabolites. The results of metabolite analysis suggested that esonarimod is pre-dominantly biotransformed to a pharmacologically active metabolite, thiol-containing deacetyl-esonarimod (M-I), and subsequently undergoes extensive metabolism, mainly S-methylation followed by the combination of S-oxidation and oxidative conversion of the aromatic methyl group. No disulfide metabolites, such as M-I-cysteine mixed disulfide and M-I-dimer, were found in the excreta. This finding is probably evidence supporting the notion that the reactivity of the thiol moiety of M-I with macromolecules in vivo is extremely lower than that of common thiol-containing drugs.