Hitoshi Mizuo

Unique Metabolic Pathway of [14C]Lenvatinib after Oral Administration to Male Cynomolgus Monkey

Lenvatinib, a potent inhibitor of multiple tyrosine kinases, including vascular endothelial growth factor receptors 2 and 3, generated unique metabolites after oral administration of [14C]lenvatinib (30 mg/kg) to a male cynomolgus monkey. Lenvatinib was found to be transformed to a GSH conjugate, through displacement of an O-aryl moiety, at the quinoline part of the molecule in the liver and kidneys. The GSH conjugate underwent further hydrolysis by γ-glutamyltranspeptidase and dipeptidases, followed by intramolecular rearrangement, to form N-cysteinyl quinoline derivatives, which were dimerized to form disulfide dimers and also formed an N,S-cysteinyl diquinoline derivative. In urine, a thioacetic acid conjugate of the quinoline was also observed as one of the major metabolites of lenvatinib. Lenvatinib is a 4-O-aryl quinoline derivative, and such compounds have been known to undergo conjugation with GSH, accompanied by release of the O-aryl moiety. Because of intramolecular rearrangement in the case of lenvatinib, hydrolysis of the GSH conjugate yielded N-cysteinylglycine and N-cysteine conjugates instead of the corresponding S-conjugates. Because the N-substituted derivatives possess free sulfhydryl groups, dimerization through disulfide bonds and another nucleophilic substitution reaction with lenvatinib resulted in the formation of disulfanyl dimers and an N,S-cysteinyl diquinoline derivative, respectively. Characteristic product ions at m/z 235 and m/z 244, which were associated with thioquinoline and N-ethylquinoline derivatives, respectively, were used to differentiate S- and N-derivatives in this study. On the basis of accurate mass and NMR measurements, a unique metabolic pathway for lenvatinib in monkey and the proposed formation mechanism have been elucidated.

Oxidative Metabolic Pathway of Lenvatinib Mediated by Aldehyde Oxidase

Lenvatinib is a multityrosine kinase inhibitor that inhibits vascular endothelial growth factor receptors, and is being developed as an anticancer drug. P450s are involved in one of the elimination pathways of lenvatinib, and mono-oxidized metabolites, such as N-oxide (M3) and desmethylated metabolite (M2), form in rats, dogs, monkeys, and humans. Meanwhile, two other oxidative metabolites are produced only in monkey and human liver S9 fractions, and their structures have been identified using high-resolution mass spectrometry as a quinolinone form of lenvatinib (M3′) and a quinolinone form of desmethylated lenvatinib (M2′). The formation of M3′ from lenvatinib occurred independently of NADPH and was effectively inhibited by typical inhibitors of aldehyde oxidase, indicating the involvement of aldehyde oxidase, but not P450s, in this pathway. M2′ was a dioxidized metabolite arising from a combination of mono-oxidation and desmethylation and could only be produced from M2 in a NADPH-independent manner; M2′ could not be generated from M3 or M3′. These results suggested that M2′ is formed from lenvatinib by a unique two-step pathway through M2. Although both lenvatinib and M2 were substrates for aldehyde oxidase, an enzyme kinetic study indicated that M2 was a much more favorable substrate than lenvatinib. No inhibitory activities of lenvatinib, M2′, or M3′ and no significant inhibitory activities of M2 or M3 on aldehyde oxidase were observed, suggesting a low possibility of drug-drug interactions in combination therapy with substrates of aldehyde oxidase.