Hydrolase activities of cynomolgus monkey liver microsomes and recombinant CES1, CES2, and AADAC

The cynomolgus monkey is a nonhuman primate that is often used for pharmacokinetic and toxicokinetic studies of new chemical entities. Species differences in drug metabolism are obstacles for the extrapolation of animal data to humans. This study aimed to characterize hydrolase activities for typical compounds by cynomolgus monkey liver microsomes and recombinant monkey carboxylesterases (CES1 and CES2) and arylacetamide deacetylase (AADAC) compared with the activities in humans. To estimate the contribution of each hydrolase, the ratios of the expression level of each hydrolase in the liver microsomes and recombinant systems were used. For almost all of the tested human CES1 substrates, hydrolase activities in cynomolgus monkey liver microsomes tended to be lower than those in human liver microsomes, and recombinant cynomolgus monkey CES1 showed catalytic activity, but not for all substrates. For human CES2 substrates, hydrolase activities in cynomolgus monkey liver were higher than those in human liver microsomes, and recombinant monkey CES2 was responsible for their hydrolysis. Among human AADAC substrates, phenacetin was mainly hydrolyzed by monkey AADAC, whereas indiplon and ketoconazole were hydrolyzed by AADAC and other unknown enzymes. Flutamide was hydrolyzed by monkey CES2, not by AADAC. Rifamycins were hardly hydrolyzed in monkey liver microsomes. In conclusion, this study characterized the hydrolase activities of cynomolgus monkeys compared with those in humans. The findings would be helpful for pharmacokinetic or toxicokinetic studies of new chemical entities whose main metabolic pathway is hydrolysis.