Received for publication December 20, 2006.
Revised February 27, 2007.
Accepted for publication March 1, 2007.

Use of Hepatocytes to Assess the Contribution of Hepatic Uptake to Clearance In Vivo

Abstract

The wealth of information which has emerged in recent years detailing the substrate specificity of hepatic transporters necessitates an investigation into their potential role in the elimination of drugs. Therefore an assay in which the loss of parent compound from the incubation medium into hepatocytes ('media loss' assay) was developed to assess the impact of hepatic uptake on unbound drug intrinsic clearance in vivo (CL_{int ub in vivo}). Studies using conventional hepatocyte incubations for a sub-set of 36 AZ new chemical entities (NCEs) resulted in a poor projection of CL_{int ub in vivo} (r² = 0.25, p = 0.002, average fold error = 57). This significant under-estimation of CL_{int ub in vivo} suggested that metabolism was not the dominant clearance mechanism for the majority of compounds examined. However CL_{int ub in vivo}was described well for this dataset using an initial compound 'disappearance' CL_int obtained from 'media loss' assays (r² = 0.72, p = 6.3 x 10^-11, average fold error = 3). Subsequent studies, using this method for the same 36 NCEs, suggested that the active uptake into human hepatocytes was generally slower (3-fold on average) than that observed with rat hepatocyes. The accurate prediction of human CL_{int ub in vivo} (within 4 fold) for the marketed drug transporter substrates montelukast, bosentan, atorvastatin and pravastatin confirmed further the utility of this assay. This work has described a simple method, amenable for use within a drug discovery setting, for predicting the in vivo clearance of drugs with significant hepatic uptake.

Key words: active transport, drug clearance, drug transport, hepatic uptake, hepatocytes, in vitro-in vivo prediction, in vitro-in vivo scaling