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The in vitro-in vivo extrapolation (IVIVE) methods used currently to predict the hepatic clearance of new chemical entities are plagued by poorly understood inaccuracies. To begin identifying plausible sources, we challenge two of core hypotheses. Hypothesis-1: the intralobular micro-anatomical organization of hepatocytes (HPCs) can be abstracted away. By accepting that hypothesis, one can assume that intrinsic clearance per HPC is essentially the same in vitro and in vivo, and thus an IVIVE method can employ a simplified liver model, typically the “well-stirred” liver model. Hypothesis-2: when the simplified liver model is the “parallel tube model,” drug concentration decreases exponentially from portal to central vein. When either simplified liver model is used, a core assumption is that intrinsic clearance is directly proportional to the unbound fraction of drug. A barrier to progress has been the fact that it is currently infeasible to challenge the two hypotheses using wet-lab experiments. In this work, we challenge virtual counterparts of the two hypotheses by experimenting on virtual mice in which hepatic disposition and clearance are consequences of concretized model mechanisms that have met several demanding requirements, including the following. The virtual liver’s structure and organization are strongly analogous to those of an actual liver, and the hepatic disposition and clearance of several virtual compounds have achieved quantitative validation targets. We study two virtual compounds. Compound-1 simulates the extreme of low-clearance, highly permeable compounds. Compound-2 simulates a highly permeable compound exhibiting maximum intrinsic clearance. We simulate changes in unbound fraction by changing the probability (pEnter) that a Compound-1 or -2 will enter an adjacent HPC during a simulation cycle. Compound-1 and -2 HPC EPiC Series in Computing Volume 70, 2020, Pages 198–207 Proceedings of the 12th International Conference on Bioinformatics and Computational Biology Q. Ding, O. Eulenstein and H. Al-Mubaid (eds.), BICOB 2020 (EPiC Series in Computing, vol. 70), pp. 198–207 exposure rates do not decrease from portal to central vein: they increase, and that contradicts both hypotheses. Further, the relationship between exposure rates and pEnter is nonlinear. The insights achieved help explain the frequently reported underprediction of in vivo hepatic clearance values. We suggest that IVIVE methods can be improved by utilizing a liver model that couples a biomimetic representation of intralobular HPC organization with biomimetic representations of intrahepatic disposition dynamics.

Exposure Measurements on Biomimetic Lobules Using Virtual Experiments to Help Improve IVIVE