Abstract 14035: Renal Tubular Secretion and Cardiac Distribution of Dofetilide is Dependent on MATE1 Function

Introduction: Dofetilide is a delayed rectifier potassium channel inhibitor used to treat patients with atrial fibrillation and flutter, and its use is associated with a risk of QT prolongation and Torsades de Pointes . The mechanisms involved in dofetilide’s renal tubular secretion and its uptake into cardiomyocytes remain unknown. Previously reported drug-drug interaction (DDI) studies suggest the involvement of organic cation transporters. Here, we investigated the contribution of organic cation transporters (OCT2 and MATE1) to the pharmacokinetics of dofetilide to gain insight into its DDI potential. Hypothesis: Based on known DDIs with dofetilide, we hypothesize that OCT2 and/or MATE1 play a key role in the inter-individual variability in pharmacokinetics and pharmacodynamics of dofetilide. Methods: In vitro and ex vivo transport kinetics of dofetilide were determined in HEK293 cells stably transfected with OCT2 or MATE1, and in isolated cardiomyocytes, respectively. In vivo studies were performed in wild-type, OCT2-, and MATE1-deficient mice (n=5) receiving dofetilide (5 mg/kg, p.o., 2.5 mg/kg, i.v.), with or without several contraindicated drugs. Dofetilide concentrations in plasma and urine were determined by UPLC-MS/MS. Results: In vitro studies demonstrated that dofetilide is a good substrate of MATE1 but not OCT2. Deficiency of MATE1 was associated with increased plasma concentrations of dofetilide and with a significantly reduced urinary excretion (3-fold in females and 5-fold in males, respectively). Dofetilide accumulation in cardiomyocytes was increased by 2-fold in MATE1-deficient females, and pre-incubation with the MATE1 inhibitor cimetidine significantly reduced dofetilide uptake in wild-type cardiomyocytes. Several contraindicated drugs listed in the dofetilide prescribing information, including cimetidine, ketoconazole, increased dofetilide plasma exposure in wild-type mice by >2.8-fold. Conclusion: Renal secretion of dofetilide is mediated by MATE1 and is highly sensitive to inhibition by many widely used prescription drugs that can cause clinically relevant DDIs. Deficiency of MATE1 also increases accumulation in the heart which may contribute to individual variation in response to dofetilide.

Molecular Mechanism of Renal Tubular Secretion of the Antimalarial Drug Chloroquine

ABSTRACTThe antimalarial drug chloroquine is eliminated to a significant extent by renal tubular secretion. The molecular mechanism of renal chloroquine secretion remains unknown. We hypothesized that organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1), localized in the basolateral and luminal membranes of proximal tubule cells, respectively, are involved in chloroquine transport. The interaction of chloroquine with both transporters was investigated using single-transfected human embryonic kidney 293 (HEK293)-MATE1 cells in uptake experiments and single-transfected Madin-Darby canine kidney II (MDCK)-OCT2 and MDCK-MATE1 cells as well as double-transfected MDCK-OCT2-MATE1 cells grown as polarized monolayers on transwell filters. In HEK293-MATE1 cells, chloroquine competitively inhibited MATE1-mediated metformin uptake (Ki= 2.8 μM). Cellular accumulation of chloroquine was significantly lower (P< 0.001) and transcellular chloroquine transport was significantly increased (P< 0.001) in MDCK-MATE1 and MDCK-OCT2-MATE1 cells compared to vector control cells after basal addition of chloroquine (0.1 to 10 μM). In contrast, no difference in cellular accumulation or transcellular transport of chloroquine was observed between MDCK-OCT2 and vector control cells. In line with an oppositely directed proton gradient acting as a driving force for MATE1, basal-to-apical transport of chloroquine by MDCK-OCT2-MATE1 cells increased with decreasing apical pH from 7.8 to 6.0. Transcellular transport of chloroquine by MDCK-OCT2-MATE1 cells was inhibited by cimetidine, trimethoprim, and amitriptyline. Our data demonstrate that chloroquine is a substrate and potent competitive inhibitor of MATE1, whereas OCT2 seems to play no role in chloroquine uptake. Concomitantly administered MATE1 inhibitors are likely to modify the renal secretion of chloroquine.