Abstract

The wealth of information that has emerged in recent years detailing the substrate specificity of hepatic transporters necessitates an investigation into their potential role in drug elimination. 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 subset of 36 AstraZeneca 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 underestimation 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 × 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 hepatocytes. 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.