Predicted values for human total clearance of a variety of typical compounds with differently humanized-liver mouse plasma data

Cytochrome P450s in chimeric mice with humanized liver

Chimeric mice with humanized livers (humanized liver mice) are attractive experimental animal models for drug metabolism and pharmacokinetic studies. The "humanized liver" is a mature and functional liver with zonal position-specific expressions of human cytochrome P450 (P450) enzymes and a global gene expression pattern consistent with that of the mature human liver. Most P450-dependent drug oxidation activities were comparable between microsomes from livers of human and humanized liver mice based on similar expression levels of human P450 enzymes; however, some differences were observed between the two species, including considerable variations in activities of bufuralol 1'-hydroxylation and propafenone 4'-hydroxylation. Human disproportionate and/or unique metabolites of P450 substrate drugs were produced in humanized liver mice. Plasma concentration profiles of typical P450 substrate drugs in humans could be extrapolated from the corresponding data in humanized liver mice using simplified physiologically based pharmacokinetic modeling. Drug-drug interaction-mediated hepatic human CYP3A/2C induction by rifampicin (a human pregnane X receptor agonist) was observed in humanized liver mice. The major role of human CYP2C9 in in vivo diclofenac 4'-hydroxylation were determined using human CYP2C9-inactivated chimeric mice using a mechanism-based inhibitor, tienilic acid. Overall, based on the functional characteristics of hepatic human P450 enzymes, humanized liver mice are valuable experimental animals for studying metabolite profiling, pharmacokinetics, and drug interactions.

Empirical and theoretical approaches for the prediction of human hepatic clearance using chimeric mice with humanised liver: the use of physiologically based scaling, a novel solution for potential overprediction due to coexisting mouse metabolism

Chimeric mice are immunodeficient mice in which the majority of the hepatic parenchymal cells are replaced with human hepatocytes.Following intravenous administration of 24 model compounds to control and chimeric mice, human hepatic clearance (CL_h) was predicted using the single-species allometric scaling (SSS) method. Predictability of the chimeric mice was better than that of the control mice.Human CL_h was predicted by the physiologically based scaling (PBS) method, wherein observed CL_h in chimeric mice was first converted to intrinsic CL_h (CL_h,int). As the liver of chimeric mice contains remaining mouse hepatocytes, CL_h,int was corrected by in vitro CL_h ratios of the mouse to human hepatocytes according to their hepatocyte replacement index. Further, predicted human CL_h was calculated based on an assumption that CL_h,int in chimeric mice normalised for their liver weight was equal to CL_h,int per liver weight in humans. Consequently, better prediction performance was observed with the use of the PBS method than the SSS method.SSS method is an empirical method, and the effects of coexisting mouse metabolism cannot be avoided. However, the PBS method with in vitro CL_h correction might be a potential solution and may expand the application of chimeric mice in new drug development.

Characterization of plasma protein binding in two mouse models of humanized liver, PXB mouse and humanized TK-NOG mouse

The unbound fractions in plasma (f _up) in two mouse models of humanized liver mice, PXB and humanized TK-NOG mice, were compared with human f _up values using equilibrium dialysis method. A good relationship between f _up values obtained from PXB mice and humans was observed; the f _up of 34/39 compounds (87.2%) in PXB mice were within 3-fold of human f _up. In contrast, a weak correlation was observed between human and humanized TK-NOG mouse f _up values; the f _up of 15/24 compounds (62.5%) in humanized TK-NOG mice were within 3-fold of human f _up. As different profiles of plasma protein binding (PPB) profiles were observed between PXB and humanized TK-NOG mice, f _up evaluation is necessary in each mouse model to utilize these humanized liver mice for pharmacological, drug-drug interaction (DDI), and toxicity studies. The unbound fraction in the mixed plasma of human and SCID mouse plasma (85:15) was well correlated with f _up in PXB mice (38/39 compounds within a 3-fold). Thus, this artificial PXB mouse plasma could be used to evaluate PPB.