Exploration and application of a liver-on-a-chip device in combination with modelling and simulation for quantitative drug metabolism studies.

Microphysiological systems (MPS) are complex and more physiologically realistic cellular in vitro tools that aim to provide more relevant human in vitro data for quantitative prediction of clinical pharmacokinetics while also reducing the need for animal testing. The PhysioMimix liver-on-a-chip integrates medium flow with hepatocyte culture and has the potential to be adopted for in vitro studies investigating the hepatic disposition characteristics of drug candidates. The current study focusses on liver-on-a-chip system exploration for multiple drug metabolism applications. Characterization of cytochrome P450 (CYP), UDP-glucuronosyl transferase (UGT) and aldehyde oxidase (AO) activities was performed using 15 drugs and in vitro to in vivo extrapolation (IVIVE) was assessed for 12 of them. Next, the utility of the liver-on-a-chip for estimation of the fraction metabolized (fm) via specific biotransformation pathways of quinidine and diclofenac was established. Finally, the metabolite identification opportunities were also explored using efavirenz as an example drug with complex primary and secondary metabolism involving a combination of CYP, UGT and sulfotransferase enzymes. A key aspect of these investigations was the application of mathematical modelling for improved parameter calculation. Such approaches will be required for quantitative assessment of metabolism and/or transporter processes in systems where medium flow and system compartments result in non-homogeneous drug concentrations. In particular, modelling was used to explore the effect of evaporation from the medium and it was found that the intrinsic clearance (CLint) might be underestimated by up to 40% for low clearance compounds if evaporation is not accounted for. Modelling of liver-on-a-chip in vitro data also enhanced the approach to fm estimation allowing objective assessment of metabolism models of different complexity. The resultant diclofenac fm,UGT of 0.64 was highly comparable with values reported previously in the literature. The current study demonstrates the integration of mathematical modelling with experimental liver-on-a-chip studies and illustrates how this approach supports generation of high quality of data from complex in vitro cellular systems.

In vivo and in vitro characterization of ethyl methanesulfonate pharmacokinetics in animals and in human.

Pharmacokinetics of ethyl methanesulfonate (EMS) were characterized in mice, rats and in cynomolgus monkeys with unlabelled and (14)C-radiolabelled EMS by either quantification of unchanged EMS or the N-ethyl-valine haemoglobin (Hb) adduct. EMS was well absorbed and exhibited close to 100% oral bioavailability. EMS showed some species differences in systemic clearance (intermediate in mice, low in rats and monkeys) representing only 1-4% of the cardiac output. The volume of distribution (0.5-0.8L/kg) was constant across species and corresponded to extracellular water. As a result of the species differences in clearance, the half-life ranged from 10 min in mouse (at low dose) to 5h in monkey. The systemic exposure of free EMS and the levels of its Hb adduct increased nearly dose proportionately from 1 to 5 and 0.5 to 80 mg/kg, respectively. The persistence of the N-ethyl-valine Hb adduct was much longer than EMS itself, consistent with the long life span of haemoglobin. No species differences were evident for the binding of EMS to Hb in whole blood ex vivo as determined by the second order rate constants. Following administration of Viracept tablets of the contaminated production batches (to monkeys leading to EMS doses of 0.08-27 microg/kg, concentrations of ethyl-valine Hb adducts) were near or below the detection limit of the assay (0.043 nmol/g Hb).