Abstract

Some quinoline containing c-Met kinase inhibitors are aldehyde oxidase (AO) substrates. 3-substituted quinoline triazolopyridine analogues were synthesized to understand the electron donating and steric hindrance effect on AO-mediated metabolism. Metabolic stability studies for these quinoline analogues were carried out in liver cytosol from mice, rats, cyno monkeys, and humans. Several 3-N-substituted analogues were found to be unstable in monkey liver cytosolic incubations (t1/2 < 10 min), and five of them (63, 53, 51, 11, and 71) were chosen for additional mechanistic studies. Monooxygenation on the quinoline ring was identified by LC/MS/MS. Metabolite formation was inhibited by the AO inhibitors menadione and raloxifene, but not by the xanthine oxidase inhibitor allopurinol. It was found that small electron donating groups at the 3-quinoline moiety made the analogues more susceptible to AO metabolism, while large 3-substituents could reverse the trend. Although species differences were observed, this trend was applicable to all species tested. Small electron donating substituents at the 3-quinoline moiety increased both affinity (decreased Km) and Vmax towards AO in kinetic studies, while large substituents decreased both parameters probably due to steric hindrance. Based on our analysis, a common structural feature with high AO liability was proposed. Our finding could provide useful information for chemists to minimize potential AO liability when designing quinoline analogues.