Among the most highly expressed drug transporters in neonatal organs are the organic cation transporters (Octs), which transport drugs, neurotransmitters, metabolites and toxins. Many drug-drug interactions and metabolic derangements due to drugs are thought to occur at the level of the transporter, and certain polymorphisms can lead to drug toxicity. Oct1/SLC22A1 is the prototypical member of the SLC22A family of transporters and along with certain ABC transporters (e.g., MDR), Oats and Oatps, is one of the most important xenobiotic (phase III drug transporter) transporters in the body. The PI's lab identified Organic Anion Transporter 1 (Oat1/NKT/Slc22a6), which, along with Oct1 originally helped define the SLC22 transporter family. We have studied the in vivo function of several SLC22 transporters and performed detailed in vitro analysis and in silico modeling of substrate-transporter interactions. Nevertheless, detailed molecular analyses of substrate-transporter interactions-which are necessary to take a rational approach to diminishing adverse affects of drugs transported by Oct1-are limited by the absence of precise structural information. Here we propose to combine our knowledge of SLC22 transporter biology (and skill with in vitro, ex vivo and in vivo assays) together with the expertise of top-notch investigators in x-ray crystallography, protein and substrate modeling to investigate the molecular mechanisms of the key substrate-transporter interactions involved in Oct1-mediated organic cation xenobiotic handling. Although in this proposal we focus on Oct1, the results will also provide important information relevant to other SLC22 drug transporters. To our knowledge, we are among the very few groups in this field that has a proven ability to combine such diverse areas of expertise, including computationally biology, structural biology and in vivo/in vitro wet-lab biology and is one of the most innovative aspects of the proposed studies. We will crystallize and determine the high-resolution x-ray structure of Oct1 (SA1) in a continuing collaboration with Dr. Geoffrey Chang (involving both his laboratory and TransportPDB, a component of the NIH Protein Structural Initiative of which he is a founding member) to gain key insights into the structural basis of substrate binding and transport. We will use our documented expertise in ligand-based and transporter-based computational approaches (SA2) to identify the molecular determinants of substrates and the Oct1 protein mediating their interactions. Pharmacophore-based virtual screening of chemical structure libraries will be done, and identified structures will be used for molecular dynamic analyses to prioritize compounds. Identified compounds will be obtained and tested in wet-lab studies using in vitro, ex vivo and in vivo approaches well established in the PI's group (SA3). This multifaceted structural- computational-wet-lab strategy will result in major advances in understanding adverse drug reactions in children as well as adults and help move the drug transporter field forward.

Public Health Relevance

Children are particularly vulnerable to toxicity from pharmaceutical drugs. These drugs are distributed throughout the body via drug transporters. Understanding how drugs interact with transporters at the molecular level may help diminish adverse drug reactions in children and adults.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Special Emphasis Panel (ZRG1-CB-L (55))
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Wu, Mary Ann
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University of California San Diego
Schools of Medicine
La Jolla
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Nigam, Sanjay K (2018) The SLC22 Transporter Family: A Paradigm for the Impact of Drug Transporters on Metabolic Pathways, Signaling, and Disease. Annu Rev Pharmacol Toxicol 58:663-687
Bush, Kevin T; Wu, Wei; Lun, Christina et al. (2017) The drug transporter OAT3 (SLC22A8) and endogenous metabolite communication via the gut-liver-kidney axis. J Biol Chem 292:15789-15803
Liu, Henry C; Goldenberg, Anne; Chen, Yuchen et al. (2016) Molecular Properties of Drugs Interacting with SLC22 Transporters OAT1, OAT3, OCT1, and OCT2: A Machine-Learning Approach. J Pharmacol Exp Ther 359:215-29
Liu, Henry C; Jamshidi, Neema; Chen, Yuchen et al. (2016) An Organic Anion Transporter 1 (OAT1)-centered Metabolic Network. J Biol Chem 291:19474-86
Bhatnagar, Vibha; Richard, Erin L; Wu, Wei et al. (2016) Analysis of ABCG2 and other urate transporters in uric acid homeostasis in chronic kidney disease: potential role of remote sensing and signaling. Clin Kidney J 9:444-53
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
Martovetsky, Gleb; Bush, Kevin T; Nigam, Sanjay K (2016) Kidney versus Liver Specification of SLC and ABC Drug Transporters, Tight Junction Molecules, and Biomarkers. Drug Metab Dispos 44:1050-60
Nigam, Sanjay K; Wu, Wei; Bush, Kevin T et al. (2015) Handling of Drugs, Metabolites, and Uremic Toxins by Kidney Proximal Tubule Drug Transporters. Clin J Am Soc Nephrol 10:2039-49
Nigam, Sanjay K (2015) What do drug transporters really do? Nat Rev Drug Discov 14:29-44
Wu, Wei; Bush, Kevin T; Liu, Henry C et al. (2015) Shared Ligands Between Organic Anion Transporters (OAT1 and OAT6) and Odorant Receptors. Drug Metab Dispos 43:1855-63

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