We are excited to share the Takeda team’s study results generated with the support of PhoenixBio through the Chimeric Mouse with Humanized Liver (CMHL) Consortium. The paper titled “Prediction of Human Disproportionate and Biliary Excreted Metabolites Using Chimeric Mice with Humanized Liver” is published in Drug Metabolism and Disposition (open access publication).
Understanding a drug candidate’s biotransformation and circulating metabolites in humans prior to first-in-human dosing is an essential part of drug development. As a routine practice, human hepatocytes are used in vitro for the prediction of human metabolism. And of course, preclinical animal models are used for the in vivo evaluation. Unfortunately, it is a known fact that the in vitro systems lack reliable correlation with clinical outcomes in humans. On the other hand, preclinical in vivo models are not reliable predictors either, due to the species differences. As such, having a preclinical in vivo model that would minimize such a difference would be the best available solution for human metabolite profiling and identification. The PXB-mouse® is a proven model to mitigate the species difference and it has a significant potential to being incorporated into the routine human metabolism assessment more widely.
The biotransformation of four compounds with disproportionate human metabolites was evaluated in the reported study.
The disproportionate metabolite in this study refers to a metabolite present only in human or present at a much higher level in any human biomatrix than that in the regularly used preclinical safety species.
The comprehensive investigation of three radiolabeled compounds ([14C]desloratadine, [3H]mianserin and [3H]carbazeran) and one not radiolabeled compound cyproheptadine was performed. The use of radioisotope allows capturing virtually all drug related materials in radiochromatographic profiles of all matrices used in study: plasma, urine, bile and feces.
The compounds were selected based on their known species-dependent metabolic profiles: disproportionate circulating and/or excreted metabolites of each of these compounds have been reported in humans compared to preclinical safety species. It is also important to mention that these model compounds cover a variety of metabolic pathways, involving cytochrome P450 (CYP450), uridine diphosphate glucuronosyltransferase (UGT)-, and aldehyde oxidase (AO)-mediated metabolism.
The absorption, metabolism and excretion of these compounds were studied, and metabolite profiling of the selected compounds was monitored in plasma, urine, bile and feces. Each compound was dosed to intact or bile-duct cannulated PXB-mice or control mice. As bile samples are typically not available in human ADME (absorption, distribution, metabolism, and excretion) studies, the proposed approach using the PXB-mouse is beneficial in helping to understand the biliary clearance mechanism of drugs in development.
Considering the metabolic pathways of mianserin and cyproheptadine and based on the data generated with them, it is useful to mention that PXB-mice may be able to accurately predict the quaternary N-glucuronidation observed in humans and be the best available model when compared to the other preclinical animals in this regard.
The results indicate the possibility of predicting potential presence of human disproportionate metabolites prior to conducting clinical studies when the PXB-mouse® is implemented in preclinical evaluations. Unfortunately, other extensively used preclinical species lack this predictive capability which is shown in the example of the evaluated drugs: desloratadine, mianserin, cyproheptadine, and carbazeran. The possibility of collecting bile samples from PXB-mice during metabolic profile evaluation is another benefit for timely characterization of human circulating metabolites. A better understanding of biotransformation and clearance mechanisms of evaluated drugs is one of the important outcomes of the performed work.
This study was performed with the support of Chimeric Mouse with Humanized Liver (CMHL) consortium, which is acknowledged in the paper.