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

Plasma and urinary CP I and CP III concentrations in chimeric mice with human hepatocytes after rifampicin administration

The interest in transporter-mediated drug interactions has been increasing in the field of drug development. In this study, we measured the plasma and urinary concentrations of coproporphyrin (CP) I and CP III as endogenous substrates for organic anion-transporting polypeptide (OATP) using chimeric mice with human hepatocytes (PXB mice) and examined the influence of an OATP inhibitor, rifampicin (RIF). CP I and CP III were actively taken up intracellularly, and RIF inhibited the uptake in a concentration-dependent manner for both CP I and CP III in human hepatocytes (PXB-cells). Single doses of RIF at 10 and 30 mg/kg were orally or intravenously administered to PXB mice and wild-type ICR mice. Plasma concentrations (AUC0-8h) of CP I increased in both mice. However, a marked increase in CP III was only observed in ICR mice, after intravenous administration of RIF at 30 mg/kg. The IC50 values of RIF for intracellular CP I/III uptake and the unbound plasma concentrations of RIF suggested that the increase in plasma CP I is associated with the exposure of RIF to OATPs. The 24-h cumulative urinary excretions of CP I and CP III increased in both mice, but more markedly in PXB mice. Thus, RIF increased the plasma and urinary concentrations of CP I and CP III in the mice, as reported in humans, and CP I may be a more sensitive biomarker of OATP-mediated drug interactions in PXB mice.

Preclinical models of idiosyncratic drug-induced liver injury (iDILI): Moving towards prediction

Idiosyncratic drug-induced liver injury (iDILI) encompasses the unexpected harms that prescription and non-prescription drugs, herbal and dietary supplements can cause to the liver. iDILI remains a major public health problem and a major cause of drug attrition. Given the lack of biomarkers for iDILI prediction, diagnosis and prognosis, searching new models to predict and study mechanisms of iDILI is necessary. One of the major limitations of iDILI preclinical assessment has been the lack of correlation between the markers of hepatotoxicity in animal toxicological studies and clinically significant iDILI. Thus, major advances in the understanding of iDILI susceptibility and pathogenesis have come from the study of well-phenotyped iDILI patients. However, there are many gaps for explaining all the complexity of iDILI susceptibility and mechanisms. Therefore, there is a need to optimize preclinical human in vitro models to reduce the risk of iDILI during drug development. Here, the current experimental models and the future directions in iDILI modelling are thoroughly discussed, focusing on the human cellular models available to study the pathophysiological mechanisms of the disease and the most used in vivo animal iDILI models. We also comment about in silico approaches and the increasing relevance of patient-derived cellular models.

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.

Prediction of human pharmacokinetics for low-clearance compounds using pharmacokinetic data from chimeric mice with humanized livers

Development of low-clearance (CL) compounds that can be slowly metabolized is a major goal in the pharmaceutical industry. However, the pursuit of low intrinsic CL (CL_int ) often leads to significant challenges in evaluating the pharmacokinetics of such compounds. Although in vitro-in vivo extrapolation is widely used to predict human CL, its application has been limited for low-CL_int compounds because of the low turnover of parent compounds in metabolic stability assays. To address this issue, we focused on chimeric mice with humanized livers (PXB-mice), which have been increasingly reported to accurately predict human CL in recent years. The predictive accuracy for nine low-CL_int compounds with no significant turnover in a human hepatocyte assay was investigated using PXB-mouse methods such as single-species allometric scaling (PXB-SSS) approach and a novel physiologically based scaling (PXB-PBS) approach that assumes that the CL_int per hepatocyte is equal between humans and PXB-mice. The percentages of compounds with predicted CL within 2- and 3-fold ranges of the observed CL for low-CL_int compounds were 89% and 100%, respectively, for both PXB-SSS and PXB-PBS approaches. Moreover, the predicted CL was mostly consistent among the methods. Conversely, percentages of compounds with predicted CL within 2- and 3-fold ranges of the observed CL for low-CL_int compounds were 50% and 63%, respectively for multispecies allometric scaling (MA). Overall, these PXB-mouse methods were much more accurate than conventional MA approaches, suggesting that PXB-mice are useful tool for predicting the human CL of low-CL_int compounds that are slowly metabolized.