ABSTRACT
Cynomolgus monkeys are a commonly used species in preclinical drug discovery, and have high genetic similarity to humans, especially for the drug-metabolizing cytochrome P450s. However, species differences are frequently observed in the metabolism of drugs between cynomolgus monkeys and humans, and delineating these differences requires expressed CYPs. Toward this end, cynomolgus monkey CYP3A4 (c3A4) was cloned and expressed in a novel human embryonic kidney 293-6E cell suspension system. Following the preparation of microsomes, the kinetic profiles of five known human CYP3A4 (h3A4) substrates (midazolam, testosterone, terfenadine, nifedipine, and triazolam) were determined. All five substrates were found to be good substrates of c3A4, although some differences were observed in the Km values. Overall, the data suggest a strong substrate similarity between c3A4 and h3A4. Additionally, c3A4 exhibited no activity against non-h3A4 probe substrates, except for a known human CYP2D6 substrate (bufuralol), which suggests potential metabolism of human cytochrome CYP2D6-substrates by c3A4. Ketoconazole and troleandomycin showed similar inhibitory potencies toward c3A4 and h3A4, whereas non-h3A4 inhibitors did not inhibit c3A4 activity. The availability of a c3A4 preparation, in conjunction with commercially available monkey liver microsomes, will support further characterization of the cynomolgus monkey as a model to assess CYP3A-dependent clearance and drug-drug interactions.
