Evaluation of the Interplay between Uptake Transport and CYP3A4 Induction in Micropatterned Cocultured Hepatocytes

Previously we assessed the inductive response of prototypical inducers in hepatocyte monocultures and the long-term coculture model HepatoPac using cryopreserved hepatocytes from the same donors. We noted that the rifampicin EC₅₀ generated using the HepatoPac model corresponded better to the EC₅₀ based on clinical data compared with data generated in the monoculture system. We postulated that there may be differences in the functioning of uptake transporters between the two systems that may have led to the EC₅₀ difference. In this study, we characterized the functional activity of multiple uptake transporters in the two systems using cryopreserved hepatocytes from the same donors. Our data suggest that uptake transporter activity is higher in HepatoPac compared with the monoculture system. As a follow up to this study, we measured the intracellular concentrations of rifampicin and bosentan, which are known substrates of uptake transporters; we observed significantly higher intracellular concentrations of both compounds in HepatoPac relative to the monoculture system. This finding equated to lower cytochrome P450 isoform 3A4 (CYP3A4) EC₅₀ values in the HepatoPac system compared with the monoculture system for both mRNA and activity. In parallel, no significant EC₅₀ shift was observed for carbamazepine and phenytoin, which are not known to be substrates of uptake transporters. Our data suggest that next generation liver models such as HepatoPac may be a useful in vitro tool to quantitatively predict drug-drug interactions when it is known that the perpetrator is also a substrate of drug transporters.