Organic Cation Transporters (OCTs) influence the plasma concentration of many endogenous molecules, and of an even wider array of xenobiotic compounds (incl. pharmacologically and toxicologically active agents). Although expressed in many tissues, the highest levels of expression are typically found in barrier epithelia, including the kidney, liver and intestine where they influence drug bioavailability; drug resistance; excretion of drugs and their metabolites; drug toxicity; and drug pharmacokinetics and pharmacodynamics. Thus, OCT transporters play a critical role in fundamental cellular processes in health and disease, and function as important mediators governing all aspects of drug therapy. Despite the apparent physiological and clinical importance of OCT proteins, knowledge of their structure and mechanism of action has lagged far behind the knowledge of these properties of proteins in general. In this proposal, we outline four Specific Aims that will apply a series of experimental and computational approaches to address the structure of a prototypical organic cation transporter, OCT2: (1) Define the membrane topology of OCT transporters using a series of topology scanning approaches; (2) Define the functional regions of OCTs by site-directed mutagenesis; (3) Construct a comprehensive structural and predictive model of OCT2 that can correlate structural point mutations to changes in substrate affinity and transport,"""""""" and (4) Determine the substrate binding domains of OCT transporters by mass spectrometry employing selective photoaffinity labels to determine peptide sequences structurally associated with the binding site. The results will be used to develop a model of the structural factors that influence binding of substrates to human OCT2. Application of the information gained through these studies holds the promise of predicting potential drug-interactions and the basis of genetic differences in renal secretion of cationic xenobiotics.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK058251-08
Application #
7264501
Study Section
Xenobiotic and Nutrient Disposition and Action Study Section (XNDA)
Program Officer
Ketchum, Christian J
Project Start
2000-08-15
Project End
2008-07-31
Budget Start
2007-08-01
Budget End
2008-07-31
Support Year
8
Fiscal Year
2007
Total Cost
$220,490
Indirect Cost
Name
University of Arizona
Department
Physiology
Type
Schools of Medicine
DUNS #
806345617
City
Tucson
State
AZ
Country
United States
Zip Code
85721
Sandoval, Philip J; Zorn, Kimberley M; Clark, Alex M et al. (2018) Assessment of Substrate-Dependent Ligand Interactions at the Organic Cation Transporter OCT2 Using Six Model Substrates. Mol Pharmacol 94:1057-1068
Severance, Alyscia Cory; Sandoval, Philip J; Wright, Stephen H (2017) Correlation between Apparent Substrate Affinity and OCT2 Transport Turnover. J Pharmacol Exp Ther 362:405-412
He, Xiao; Garza, Denisse; Nigam, Sanjay K et al. (2016) Multispecific Organic Cation Transporter 1 (OCT1) from Bos taurus Has High Affinity and Slow Binding Kinetics towards Prostaglandin E2. PLoS One 11:e0152969
Martínez-Guerrero, L J; Evans, K K; Dantzler, W H et al. (2016) The multidrug transporter MATE1 sequesters OCs within an intracellular compartment that has no influence on OC secretion in renal proximal tubules. Am J Physiol Renal Physiol 310:F57-67
Shibayama, Takahiro; Morales, Mark; Zhang, Xiaohong et al. (2015) Unstirred Water Layers and the Kinetics of Organic Cation Transport. Pharm Res 32:2937-49
Ekins, Sean; Clark, Alex M; Wright, Stephen H (2015) Making Transporter Models for Drug-Drug Interaction Prediction Mobile. Drug Metab Dispos 43:1642-5
Pelis, Ryan M; Wright, Stephen H (2014) SLC22, SLC44, and SLC47 transporters--organic anion and cation transporters: molecular and cellular properties. Curr Top Membr 73:233-61
Belzer, Mathew; Morales, Mark; Jagadish, Bhumasamudram et al. (2013) Substrate-dependent ligand inhibition of the human organic cation transporter OCT2. J Pharmacol Exp Ther 346:300-10
Harper, Jaclyn N; Wright, Stephen H (2013) Multiple mechanisms of ligand interaction with the human organic cation transporter, OCT2. Am J Physiol Renal Physiol 304:F56-67
Pelis, Ryan M; Dangprapai, Yodying; Cheng, Yaofeng et al. (2012) Functional significance of conserved cysteines in the human organic cation transporter 2. Am J Physiol Renal Physiol 303:F313-20

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