title: Substrate-dependent ligand inhibition of the human organic cation transporter OCT2.
abstract: Organic cation transporter 2 (OCT2) mediates the initial step in renal secretion of organic cations: uptake from the blood, across the basolateral membrane, and into the renal proximal tubule cells. Because of its potential as a target for unwanted drug-drug interactions (DDIs), considerable attention has been directed toward understanding the basis of OCT2 selectivity. These studies typically assess selectivity based on ligand inhibition profiles for OCT2-mediated transport of a probe substrate. However, little attention has been given to the potential influence of the substrate on the profile of ligand inhibition. Here we compared the IC50 values obtained for a set of structurally distinct inhibitors against OCT2-mediated transport of three structurally distinct substrates: 1-methyl-4-phenylpyridinium (MPP); metformin; and a novel fluorescent substrate, N,N,N-trimethyl-2-[methyl(7-nitrobenzo[c][l,2,5]oxadiazol-4-yl)amino]ethanaminium iodide (NBD-MTMA). The median IC50 value for inhibition of MPP transport was 9-fold higher than that for inhibition of metformin transport. Similarly, the median IC50 value for inhibition of MPP transport was 5-fold higher than that for NBD-MTMA transport. However, this was not a systematic difference in inhibitory efficacy; the ratio of IC50 values, MPP versus NBD-MTMA, ranged from 88-fold (ipratropium) to 0.3-fold (metformin). These data show that 1) the choice of OCT2 substrate significantly influences both quantitative and qualitative inhibitory interactions with cationic drugs; and 2) ligand interactions with OCT2 are not restricted to competition for a common ligand binding site, consistent with a binding surface characterized by multiple, possibly overlapping interaction sites. Development of predictive models of DDIs with OCT2 must take into account the substrate dependence of ligand interaction with this protein.
authors.affiliation: Department of Physiology, University of Arizona, Tucson, AZ 85724, USA.
authors.forename: Mathew
authors.initials: M
authors.lastname: Belzer
authors.forename: Mark
authors.initials: M
authors.lastname: Morales
authors.forename: Bhumasamudram
authors.initials: B
authors.lastname: Jagadish
authors.forename: Eugene A
authors.initials: EA
authors.lastname: Mash
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Wright
mesh_terms: D015655:1-Methyl-4-phenylpyridinium / Q000378:metabolism / Q000494:pharmacology; D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D016466:CHO Cells; D002412:Cations; D006224:Cricetinae; D003412:Cricetulus; D005456:Fluorescent Dyes / Q000378:metabolism / Q000494:pharmacology; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D008687:Metformin / Q000378:metabolism / Q000494:pharmacology; D027701:Organic Cation Transport Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000075102:Organic Cation Transporter 2; D000644:Quaternary Ammonium Compounds / Q000378:metabolism / Q000494:pharmacology
chemical_list: D002412:Cations; D005456:Fluorescent Dyes; D008024:Ligands; C583572:N,N,N-trimethyl-2-(methyl(7-nitrobenzo(c)(l,2,5)oxadiazol-4-yl)amino)ethanaminium; D027701:Organic Cation Transport Proteins; D000075102:Organic Cation Transporter 2; D000644:Quaternary Ammonium Compounds; C491013:SLC22A2 protein, human; D008687:Metformin; D009327:4-Chloro-7-nitrobenzofurazan; D015655:1-Methyl-4-phenylpyridinium