Relative Activity Factor (RAF)-Based Scaling of Uptake Clearance Mediated by Organic Anion Transporting Polypeptide (OATP) 1B1 and OATP1B3 in Human Hepatocytes

In vitro-in vivo extrapolation based on uptake clearance determined in human hepatocytes has been used to predict in vivo hepatic clearance of organic anion transporting polypeptide (OATP) substrates. This study evaluated the relative activity factor (RAF) approach to extrapolate active uptake clearance in transporter-transfected cell systems (CL_uptake) to that in human hepatocyte suspensions (PS_inf,act). RAF values for OATP1B1 and OATP1B3 were determined in two batches of cryopreserved human hepatocytes using estrone-3-sulfate and cholecystokinin octapeptide as reference substrates, respectively. Fourteen OATP1B substrate drugs selected (atorvastatin, bosentan, cerivastatin, fexofenadine, fluvastatin, glibenclamide, irbesartan, nateglinide, pitavastatin, pravastatin, rosuvastatin, telmisartan, torasemide, and valsartan) showed temperature-dependent uptake in human hepatocytes. In transporter-transfected cells, OATP1B1- and OATP1B3-mediated uptake was observed in all compounds except for telmisartan. RAF-based net CL_uptake was mainly accounted for by OATP1B1 (72.3-99.7%) and fell within the 3-fold of PS_inf,act observed in human hepatocytes in 11 out of 13 compounds (excluding telmisartan). This study demonstrated that the RAF approach provides a quantitative index of OATP1B1- and OATP1B3-mediated PS_inf,act in human hepatocytes, which will facilitate the optimization of the pharmacokinetic properties of OATP1B substrates at nonclinical stages of drug development.