Combined in vitro-in vivo approach to assess the hepatobiliary disposition of a novel oral thrombin inhibitor.

ABSTRACT

Two clinical trials and a large set of in vitro transporter experiments were performed to investigate if the hepatobiliary disposition of the direct thrombin inhibitor prodrug AZD0837 is the mechanism for the drug-drug interaction with ketoconazole observed in a previous clinical study. In Study 1, [(3)H]AZD0837 was administered to healthy male volunteers (n = 8) to quantify and identify the metabolites excreted in bile. Bile was sampled directly from the jejunum by duodenal aspiration via an oro-enteric tube. In Study 2, the effect of ketoconazole on the plasma and bile pharmacokinetics of AZD0837, the intermediate metabolite (AR-H069927), and the active form (AR-H067637) was investigated (n = 17). Co-administration with ketoconazole elevated the plasma exposure to AZD0837 and the active form approximately 2-fold compared to placebo, which may be explained by inhibited CYP3A4 metabolism and reduced biliary clearance, respectively. High concentrations of the active form was measured in bile with a bile-to-plasma AUC ratio of approximately 75, indicating involvement of transporter-mediated excretion of the compound. AZD0837 and its metabolites were further investigated as substrates of hepatic uptake and efflux transporters in vitro. Studies in MDCK-MDR1 cell monolayers and P-glycoprotein (P-gp) expressing membrane vesicles identified AZD0837, the intermediate, and the active form as substrates of P-gp. The active form was also identified as a substrate of the multidrug and toxin extrusion 1 (MATE1) transporter and the organic cation transporter 1 (OCT1), in HEK cells transfected with the respective transporter. Ketoconazole was shown to inhibit all of these three transporters; in particular, inhibition of P-gp and MATE1 occurred in a clinically relevant concentration range. In conclusion, the hepatobiliary transport pathways of AZD0837 and its metabolites were identified in vitro and in vivo. Inhibition of the canalicular transporters P-gp and MATE1 may lead to enhanced plasma exposure to the active form, which could, at least in part, explain the clinical interaction with ketoconazole.