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Functional Characterization of the Human Organic Cation Transporter 2 Variant p.270Ala>Ser

Institute of Experimental and Clinical Pharmacology and Toxicology, University of Erlangen-Nuremberg, Erlangen, Germany

The organic cation transporter 2 (OCT2, SLC22A2) plays an important role for renal drug elimination. Recent clinical studies indicate an impact of the frequent nonsynonymous c.808G>T (p.270Ala>Ser) polymorphism on renal clearance of metformin and the extent of the metformin-cimetidine interaction. The role of this polymorphism for renal disposition of endogenous compounds and drugs other than metformin has not been investigated. In addition, it is unclear whether the observed genotype dependence of an OCT2-mediated drug-drug interaction might occur also with other OCT inhibitors. To address these issues, we generated human embryonic kidney cells stably expressing wild-type OCT2 or the p.270Ala>Ser variant. No differences in protein expression levels and membrane incorporation pattern were observed between the two cell lines. The p.270Ala>Ser variant significantly impaired uptake kinetics of 1-methyl-4-phenylpyridinium, dopamine, norepinephrine, and propranolol. V_max values were significantly reduced for uptake of all four compounds mediated by the p.270Ala>Ser variant compared with wild-type OCT2. In addition, a significant difference in the affinity to wild-type and mutant OCT2 was observed for dopamine (K_m dopamine: 932 ± 77 versus 1285 ± 132 µM). Moreover, out of a set of 27 compounds p.270Ala>Ser OCT2 was significantly less sensitive to inhibition by cimetidine, flurazepam, metformin, mexiletine, propranolol, and verapamil than wild-type OCT2 (e.g., for propranolol: IC₅₀ wild type versus p.270Ala>Ser 189 versus 895 µM, P < 0.001). Our results indicate that the common OCT2 c.808G>T single nucleotide polymorphism significantly alters uptake of endogenous compounds and drugs. Moreover, for selected compounds the extent of OCT2-mediated drug interactions could depend on OCT2 c.808G>T genotype.