Purpose: Our previous pharmacokinetic studies have demonstrated that TR-14035, a novel dual antagonist for alpha4beta1/alpha4beta7 integrin, selectively and strongly accumulated in the liver and was mainly excreted in bile as an unchanged drug. In the present study, we investigated the hepatobiliary transport system in detail.
Materials and methods: Uptake by hepatocytes and organic anion transporting polypeptide (OATP)-expressing Xenopus laevis oocytes or Flp-In-293 cells was performed in vitro. Biliary excretion was investigated in mdr1a/b-knockout mice, Bcrp-knockout mice and Mrp2-defective Eisai hyperbilirubinemic rats (EHBRs).
Results: TR-14035 was taken up by rat and human hepatocytes by an apparently single saturable mechanism with K(m) of 6.7 and 2.1 microM, respectively, and taurocholate and digoxin reduced this uptake. OATP1B1/OATP-C and OATP1B3/OATP8 expressed in oocytes mediated the TR-14035 uptake with K(m) of 7.5 and 5.3 microM, respectively. OATP1B1*15, a genetic variant of OATP1B1, exhibited a decreased transport of TR-14035 compared with OATP1B1*1a. Biliary excretion and total body clearance of unchanged TR-14035 in EHBRs were significantly lower than those in normal rats, while there was no difference in the clearances between wild and mdr1a/b- or Bcrp-knockout mice.
Conclusion: These results indicate that OATP1B1 and OATP1B3 are at least partly responsible for the accumulation of TR-14035 into hepatocytes, and Mrp2 principally mediates the biliary excretion of TR-14035. Furthermore, genetic polymorphisms of OATP1B1 may cause an interindividual variability in the pharmacokinetics of TR-14035.