Expression and functional activity of cytochrome P450 enzymes in human hepatocytes with sustainable reproducibility for in vitro phenotyping studies

Abstract

Primary human hepatocytes are an essential in vitro tool for evaluating drug metabolism, drug-drug interactions, and hepatotoxicity. This model is considered as the gold standard in matter of DMPK studies in both industrial and academic research. The primary human hepatocytes are used either in suspension or in monolayer, as fresh or frozen cells. However, the use of this model is limited due to the lack of availability, rapid loss of functionality, high cost as well as the variable hepatocyte plating efficiencies in culture and the limited stock of hepatocytes derived from the same origin. Chimeric TK-NOG mice with humanized livers (humanized liver mice) are an attractive platform for drug metabolism and toxicity, which were produced by transplanting human hepatocytes into immunodeficient mice with injured livers. Here, we show that, using humanized mouse liver, in vivo human hepatocyte repopulation was over ~100-fold enabling the continuous and abundant use of human hepatocytes of the same origin and improving their plateability. In our latest cell preparations, hepatocytes isolated from humanized liver mice (Hu-Liver cells) exhibited high purity (ratio of HLA-positive cells: 92±3%), good viability (75±12%), and yield (1.0×10 8 cells/mouse). Human hepatic drug metabolizing enzymes, transporters, and nuclear receptors genes were expressed in humanized mouse liver. Drug-metabolizing activities in Hu-Liver cells were comparable to or higher than those in primary human hepatocytes. An extensive P450-dependent human drug metabolism was observed in Hu-Liver cells. CYP1A2, CYP2B6, and CYP3A4/5 activities/mRNA in Hu-Liver cells were induced by the hepatocyte exposure to typical human P450 inducers, omeprazole, phenobarbital, and rifampicin, respectively. Finally, Human albumin secretion and CYP3A-mediated drug oxidation activity were maintained over 4-weeks. Altogether, the expression level of pharmacokinetics-related genes, enzyme activity, human-typed drug metabolism, and inducibility of P450 in Hu-Liver cells make from humanized mouse liver a relevant and robust model for in vitro preclinical studies, including drug metabolism, pharmacokinetics, and toxicology studies.