Abstract

The current studies assessed the utility of freshly plated hepatocytes, cryopreserved plated hepatocytes, and cryopreserved plated HepaRG cells for the estimation of inactivation parameters k_inact and K_I for CYP3A. This was achieved using a subset of CYP3A time-dependent inhibitors (fluoxetine, verapamil, clarithromycin, troleandomycin, and mibefradil) representing a range of potencies. The estimated k_inact and K_I values for each time-dependent inhibitor were compared to those obtained using human liver microsomes, and used to estimate the magnitude of clinical pharmacokinetic DDI. The inactivation kinetic parameter, k_inact was most consistent across systems tested for clarithromycin, verapamil, and troleandomycin, with a high k_inact of 0.91 min^-1 observed for mibefradil in HepaRG cells. The apparent K_I estimates derived from the various systems displayed a range of variability from 3-fold for clarithromycin (5.4-17.7 μM) up to 6-fold for verapamil (1.9-12.6 μM). In general, the inactivation kinetic parameters derived from the cell systems tested fairly replicated what was observed in TDI studies using HLMs. Despite some of the observed differences in inactivation kinetic parameters, the estimated DDIs derived from each of the tested systems generally agreed with the clinically reported DDI within approximately 2-fold. In addition, a plated cell approach offered the ability to conduct longer primary incubations (greater than 30 minutes), which afforded improved ability to identify the weak time-dependent inhibitor fluoxetine. Overall, results from these studies suggest that in vitro inactivation parameters generated from plated cell systems may be a practical approach for identifying time-dependent inhibitors, and estimating the magnitude of clinical DDIs.