Metabolism of c-Met Kinase Inhibitors Containing Quinoline by Aldehyde Oxidase, Electron Donating, and Steric Hindrance Effect.

Some quinoline-containing c-Met kinase inhibitors are aldehyde oxidase (AO) substrates. 3-Substituted quinoline triazolopyridine analogs were synthesized to understand the electron-donating and steric hindrance effects on AO-mediated metabolism. Metabolic stability studies for these quinoline analogs were carried out in liver cytosol from mice, rats, cynomolgus monkeys, and humans. Several 3-N-substituted analogs were found to be unstable in monkey liver cytosolic incubations (half-life, <10 minutes), and five of them (63, 53, 51, 11, and 71) were chosen for additional mechanistic studies. Mono-oxygenation on the quinoline ring was identified by liquid chromatography tandem mass spectrometry. 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 analogs more susceptible to AO metabolism, whereas 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 Michaelis constant) and V max maximum velocity toward AO in kinetic studies, whereas large substituents decreased both parameters probably as a result of 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 analogs.

Molecular dynamics simulations of CYP2E1.

CYP2E1, as a member of the cytochrome P450s (CYPs) super-family, is in charge of six percent drug metabolism involving a diversity of drugs distinct in structures and chemical properties, such as alcohols, monocyclic compounds (e.g., acetaminophen, benzene, p-nitrophenol), bicyclic heterocycles (e.g., coumarin, caffeine) and even fatty acids. The aromatic molecules form a vital species catalyzed by CYP2E1. To investigate the mechanism of metabolizing a diversity of aromatic molecules, five representative aromatic substrates were selected: (1) benzene, the non-polar simple ring; (2) aniline, the monocyclic substrate with smallest substitution on the phenyl ring; (3) acetaminophen, a large monocyclic substrate with highly active reactivity; (4) chlorzoxazone, and (5) theophylline, the bicyclic substrates with low or high catalytic activities. They were docked into X-ray structure of CYP2E1, after which all-atom molecular dynamics simulations of 5 ns were performed on each model. It was found that the active site interact with the aromatic substrates mainly through π-π stacking, supplied by five hydrophobic phenylalanines in the active site. Our simulations also illustrated the specific movement of different kinds of aromatic substrates in the pocket. Small monocyclic substrates show highly frequent self-rotation and limited translation movement. Substrates with single catalytic position are less movable in the pocket than substrates with multiple products. All these findings are quite useful for understanding the catalytic mechanism of CYP2E1, stimulating novel strategies for conducting further mutagenesis studies for specific drug design.