Abstract
Aldehyde oxidase (AO) and xanthine oxidase (XO) are molybdo-flavoenzymes that catalyze oxidation of aromatic azaheterocycles. Differences in AO activity have been reported among various species including rat, human, and monkey. Herein we report a species difference in the enzymes responsible for metabolism of mGlu5 NAM VU0424238 (VU238, auglurant). Hepatic S9 incubations with AO and XO specific inhibitors hydralazine and allopurinol indicated that rat and cynomolgus monkey both oxidized VU238 to the 6-oxopyrimidine metabolite M1 via an AO-mediated pathway, whereas secondary oxidation to the 2,6-dioxopyrimidine metabolite M2 was mediated predominantly by AO in monkey and XO in rat. Despite differences in enzymatic pathways, intrinsic clearance (CLint) of M1 was similar between species (cynomolgus and rat CLint = 2.00±0.040 and 2.19±0.201 μL/min/mg protein, respectively). Inhibitor studies in multiple species' S9 indicated oxidation of VU238 to M1 was mediated predominantly by AO in human, cynomolgus and rhesus monkey, rat, mouse, guinea pig, and minipig. Interestingly, oxidation of M1 to M2 was predominantly mediated by XO in rat and mouse and by AO in monkeys and guinea pig, while low turnover prevented enzyme phenotyping in human and minipig. Additionally, inhibitor experiments indicated oxidation at the 2-position of the pyrimidine ring of the known AO substrate, BIBX1382, was mediated by AO in all species, although production of this metabolite was comparatively low in rat and mouse. These data may suggest low reactivity of rat AO toward 2-oxidation of pyrimidine-containing compounds and highlight the importance of thoroughly characterizing AO-metabolized drug candidates in multiple preclinical species.
- aldehyde oxidases
- animal/nonclinical/preclinical
- drug development/discovery
- metabolite identification
- xanthine oxidase
- The American Society for Pharmacology and Experimental Therapeutics