OATP1B1-mediated uptake of statins, estrone 3-sulfate and estradiol 17beta-glucuronide in HEK293-OATP1B1 cells and inhibition by rifamycin SV, gemfibrozil and an investigational drug

Abstract

OATP1B1 is an important hepatic uptake transporter shown to effect the therapeutic efficacy, drug-drug interaction potential, pharmacogenetics and toxicity of drugs [1]. Among the most commonly prescribed medications for older patients are lipid lowering HMG-CoA inhibitors (statins) which are substrates of OATP1B1, making this transporter important for close scrutiny during drug discovery and development. We have previously published an approach using the HEK293-OATP1B1 cell line for studying compounds as substrates and inhibitors of OATP1B1 [2]. Here we describe the use of this cell line to investigate kinetics of six statins (simvastatin, atorvastatin, pravastatin, rosuvastatin, pitavas-tatin, fluvastatin), estradiol 17beta-glucuronide and estrone 3-sulfate and inhibition of their OATP1B1-mediated transport by investigational compound and known prototypical inhibitors (gemfibrozil and rifamycin SV). The study included determination of time linearity of substrates, apparent Michaelis-Menten constant (apparent K m) and IC 50 values. The results obtained demonstrated that K m values of statins were in range of 0.6-29 muM, with atorvastatin exhibiting highest and pravastatin exhibiting the lowest affinity for OATP1B1. Estrone 3-sulfate exhibited biphasic transport kinetics comprising both high affinity (K m = 0.4 muM) and low affinity components (K m = 42 muM). The Michaelis-Menten constant (K m) of simvastatin could not be determined due to its high passive permeability. The investigational drug inhibited OATP1B1 mediated transport of all statins and estradiol 17beta-glucuronide and weakly inhibited estrone 3-sulfate. Rifamcycin SV significantly inhibited OATP1B1-mediated transport of all substrates while gemfibrozil exhibited weak inhibition for all statins, estradiol 17beta-glucuronide and estrone 3-sulfate. Based on results obtained estradiol 17betaglucuronide appears to be a good surrogate probe substrate to predict OATP1B1 based statin DDIs in vitro using this cell line. These studies have also helped shape the future clinical DDI program of the investigational compound.