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Picard N, Yee SW, Woillard JB, Lebranchu Y, Le Meur Y, Giacomini KM, Marquet P. The role of organic anion-transporting polypeptides and their common genetic variants in mycophenolic acid pharmacokinetics. Clin Pharmacol Ther 2009; 87:100-8. [PMID: 19890249 DOI: 10.1038/clpt.2009.205] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The goal of this study was to determine the roles of the organic anion-transporting polypeptides (OATPs) OATP1A2, OATP1B1, and OATP1B3 and their genetic variants in the pharmacokinetics of the immunosuppressive drug mycophenolate mofetil (MMF). Using OATP-transfected human embryonic kidney (HEK) cells, we measured the uptake of mycophenolic acid (MPA) and its glucuronide (MPAG). MPAG, but not MPA, significantly accumulated in cells expressing OATP1B3 or OATP1B1 (P < 0.05). The pharmacokinetics of both MPA and MPAG were significantly influenced by the OATP1B3 polymorphism 334T>G/699G>A in 70 renal transplant patients receiving combination treatment of MMF with either tacrolimus or sirolimus, but not in 115 patients receiving MMF and cyclosporine. The decrease in dose-normalized (dn) MPA exposure and the concomitant increase in the MPAG/MPA metabolic ratio are consistent with reduced enterohepatic cycling in patients carrying the OATP1B3 334G-699A haplotype. Further studies demonstrated that this variant of OATP1B3 exhibited a reduced maximal velocity (V(max)) in transfected HEK cells, thereby providing functional evidence to support our clinical findings.
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152
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Hesselson SE, Matsson P, Shima JE, Fukushima H, Yee SW, Kobayashi Y, Gow JM, Ha C, Ma B, Poon A, Johns SJ, Stryke D, Castro RA, Tahara H, Choi JH, Chen L, Picard N, Sjödin E, Roelofs MJE, Ferrin TE, Myers R, Kroetz DL, Kwok PY, Giacomini KM. Genetic variation in the proximal promoter of ABC and SLC superfamilies: liver and kidney specific expression and promoter activity predict variation. PLoS One 2009; 4:e6942. [PMID: 19742321 PMCID: PMC2735003 DOI: 10.1371/journal.pone.0006942] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2009] [Accepted: 08/05/2009] [Indexed: 12/11/2022] Open
Abstract
Membrane transporters play crucial roles in the cellular uptake and efflux of an array of small molecules including nutrients, environmental toxins, and many clinically used drugs. We hypothesized that common genetic variation in the proximal promoter regions of transporter genes contribute to observed variation in drug response. A total of 579 polymorphisms were identified in the proximal promoters (−250 to +50 bp) and flanking 5′ sequence of 107 transporters in the ATP Binding Cassette (ABC) and Solute Carrier (SLC) superfamilies in 272 DNA samples from ethnically diverse populations. Many transporter promoters contained multiple common polymorphisms. Using a sliding window analysis, we observed that, on average, nucleotide diversity (π) was lowest at approximately 300 bp upstream of the transcription start site, suggesting that this region may harbor important functional elements. The proximal promoters of transporters that were highly expressed in the liver had greater nucleotide diversity than those that were highly expressed in the kidney consistent with greater negative selective pressure on the promoters of kidney transporters. Twenty-one promoters were evaluated for activity using reporter assays. Greater nucleotide diversity was observed in promoters with strong activity compared to promoters with weak activity, suggesting that weak promoters are under more negative selective pressure than promoters with high activity. Collectively, these results suggest that the proximal promoter region of membrane transporters is rich in variation and that variants in these regions may play a role in interindividual variation in drug disposition and response.
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153
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Ianculescu AG, Giacomini KM, Scanlan TS. Identification and characterization of 3-iodothyronamine intracellular transport. Endocrinology 2009; 150:1991-9. [PMID: 19074582 PMCID: PMC2659270 DOI: 10.1210/en.2008-1339] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
3-Iodothyronamine (T(1)AM) is a naturally occurring thyroid hormone metabolite with distinct biological effects that are opposite those of thyroid hormone. The known molecular targets of T(1)AM include both plasma membrane and intracellular proteins, suggesting that intracellular transport of T(1)AM may be an important component of its action, although no uptake mechanism has yet been described. Using various human cell lines, we show that, indeed, cellular uptake of T(1)AM occurs in multiple cell types and that this process involves specific, saturable, and inhibitable transport mechanisms. These mechanisms are sodium and chloride independent, pH dependent, thyronamine specific, and do not involve the likely candidate transporters of other monoamines, organic cations, or thyroid hormones. A large-scale RNA interference screen targeting the entire solute carrier superfamily of transporter genes reveals that the transport of T(1)AM into cells involves multiple transporters, and we identify eight transporters that may contribute to the uptake of T(1)AM in HeLa cells. This type of transporter small interfering RNA screening approach can be used in general to identify the constellation of transporters that participate in the intracellular disposition of compounds.
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154
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Miller WL, Huang N, Agrawal V, Giacomini KM. Genetic variation in human P450 oxidoreductase. Mol Cell Endocrinol 2009; 300:180-4. [PMID: 18930113 DOI: 10.1016/j.mce.2008.09.017] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2008] [Revised: 09/03/2008] [Accepted: 09/15/2008] [Indexed: 11/28/2022]
Abstract
Catalysis by all 50 Type II (microsomal) P450 enzymes, including steroidogenic P450c17, P450c21, and P450aro and hepatic drug-metabolizing enzymes requires electron donation from P450 oxidoreductase (POR). POR knockout mice are embryonic lethal, but human POR mutations cause a complex disorder of steroidogenesis. Disorders of hepatic drug metabolism in human POR deficiency have not yet been described. To understand the potential contribution of POR to pharmacogenetics, we sequenced the POR gene in 842 normal persons from 4 ethnic groups. We detected 140 single nucleotide sequence variants of which 43 were in >1% of alleles, including 15 missense mutants; this brings the total of known POR missense mutants to 35. A503V was found on 28% of alleles, varying from 19% in African Americans to 37% in Chinese Americans. We expressed all 35 missense mutants in E. coli and assayed their activities to: oxidize NADPH, reduce cytochrome c, support the 17alpha-hydroxylase and 17,20 lyase activities of bacterially expressed human P450c17, and support the metabolism of fluorogenic EOMCC by bacterially expressed human CYP1A2 and CYP2C19. These data show that there are great differences in the activities of some POR mutants depending on the electron recipient assayed; for example, Q153R causes severely impaired steroid biosynthesis in human patients and in vitro, but is a gain-of-function mutant with CYP1A2 and 2C19. A503V reduces both activities of P450c17 in half, but had no effect on CYP1A2 or 2C19. POR variants are a previously unappreciated source of genetic variation in patterns of steroid synthesis and drug metabolism.
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155
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Chen Y, Teranishi K, Li S, Yee SW, Hesselson S, Stryke D, Johns SJ, Ferrin TE, Kwok P, Giacomini KM. Genetic variants in multidrug and toxic compound extrusion-1, hMATE1, alter transport function. THE PHARMACOGENOMICS JOURNAL 2009; 9:127-36. [PMID: 19172157 DOI: 10.1038/tpj.2008.19] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
hMATE1 (human multidrug and toxin compound extrusion-1; encoded by SLC47A1) is thought to have an important function in the renal and hepatic elimination of drugs, endogenous compounds and environmental toxins. The goals of this study were to identify genetic variants of hMATE1 and to determine their effects on hMATE1 transport function. We identified four synonymous and six nonsynonymous, coding region variants in DNA samples from 272 individuals (68 Caucasians, 68 African Americans, 68 Asian Americans and 68 Mexican Americans). The overall prevalence of hMATE1 nonsynonymous variants was relatively low with three singleton variants and three variants having allele frequencies > or =2% in a specific ethnic group. The nonsynonymous hMATE1 variants were constructed and stably transfected into HEK-293 cells. Uptake studies using four known hMATE1 substrates (paraquat, metformin, tetraethylammonium and oxaliplatin) were performed in cells transfected with hMATE1 reference or variants. We found that two singleton variants, G64D and V480M, produced a complete loss of function for all four tested substrates whereas three polymorphic variants (allele frequencies > or =2%), L125F, V338I and C497S, significantly altered the transport function in a substrate-dependent manner. Confocal microscopy studies were consistent with functional studies suggesting that the altered function of the variants was due to altered localization to the plasma membrane. These data suggest that nonsynonymous variants in hMATE1 may alter drug disposition and ultimately affect clinical drug response.
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156
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Tahara H, Yee SW, Urban TJ, Hesselson S, Castro RA, Kawamoto M, Stryke D, Johns SJ, Ferrin TE, Kwok PY, Giacomini KM. Functional genetic variation in the basal promoter of the organic cation/carnitine transporters OCTN1 (SLC22A4) and OCTN2 (SLC22A5). J Pharmacol Exp Ther 2009; 329:262-71. [PMID: 19141711 DOI: 10.1124/jpet.108.146449] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The organic cation/ergothioneine transporter OCTN1 (SLC22A4) and the high-affinity carnitine transporter OCTN2 (SLC22A5), play an important role in the disposition of xenobiotics and endogenous compounds. Here, we analyzed the sequence of the proximal promoter regions of OCTN1 and OCTN2 in four ethnic groups and determined the effects of the identified genetic variants on transcriptional activities and mRNA expression. Six variants were found in the proximal promoter of OCTN1, one of which showed high allele frequency ranging from 13 to 34% in samples from individuals with ancestries in Africa, Europe, China, and Mexico. OCTN1 haplotypes had similar activities as the reference in luciferase reporter assays. For OCTN2, three of the seven variants identified in the proximal promoter showed allele frequencies greater than 29.5% in all populations, with the exception of -207C>G (rs2631367) that was monomorphic in Asian Americans. OCTN2 haplotypes containing -207G, present in all populations, were associated with a gain of function in luciferase reporter assays. Consistent with reporter assays, OCTN2 mRNA expression levels in lymphoblastoid cell lines (LCLs) from gene expression analysis were greater in samples carrying a marker for -207G. This SNP seems to contribute to racial differences in OCTN2 mRNA expression levels in LCLs. Our study with healthy subjects (n = 16) homozygous for either -207C or -207G, showed no appreciable effect of this SNP on carnitine disposition. However, there were significant effects of gender on carnitine plasma levels (p < 0.01). Further in vivo studies of OCTN2 promoter variants on carnitine disposition and variation in drug response are warranted.
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157
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Yee SW, Shima JE, Hesselson S, Nguyen L, De Val S, Lafond RJ, Kawamoto M, Johns SJ, Stryke D, Kwok PY, Ferrin TE, Black BL, Gurwitz D, Ahituv N, Giacomini KM. Identification and characterization of proximal promoter polymorphisms in the human concentrative nucleoside transporter 2 (SLC28A2). J Pharmacol Exp Ther 2008; 328:699-707. [PMID: 19098160 DOI: 10.1124/jpet.108.147207] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The human concentrative nucleoside transporter 2 (CNT2) plays an important role in the absorption, disposition, and biological effects of endogenous nucleosides and nucleoside analog drugs. We identified genetic variation in the basal promoter region of CNT2 and characterized the function of the variants. We screened DNA from an ethnically diverse population and identified five basal promoter variants in CNT2. Three major haplotypes in the CNT2 basal promoter region were identified and were found at different allele frequencies in various ethnic groups. The common promoter variants and haplotypes were constructed and characterized for their promoter activity using luciferase reporter assays. One polymorphic variant, rs2413775 (-146T>A), with an allele frequency >20% in all populations, showed a gain of function in luciferase activity. Furthermore, in vivo mouse promoter assays of these nucleotide variants using the hydrodynamic tail vein injection, leading to their expression in the liver, demonstrated similar results. Transcription factor binding site (TFBS) analysis indicated this variant alters a hepatic nuclear factor (HNF) 1 TFBS. Electrophoretic mobility shift assay demonstrated stronger binding of HNF1alpha and weaker binding of HNF1beta to the -146T and -146A regions, whereas the single nucleotide polymorphism (SNP), -146A, exhibited enhanced binding to both HNF1alpha and HNF1beta, consistent with its greater activity in reporter assays. The data collectively suggest that the common variant, -146T>A, in the proximal promoter of CNT2 may result in an enhanced transcription rate of the gene and, thus, expression levels of CNT2. This SNP may play a role in variation in the pharmacokinetics and pharmacological effects of nucleoside analogs.
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158
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Li M, Hays FA, Roe-Zurz Z, Vuong L, Kelly L, Ho CM, Robbins RM, Pieper U, O'Connell JD, Miercke LJW, Giacomini KM, Sali A, Stroud RM. Selecting optimum eukaryotic integral membrane proteins for structure determination by rapid expression and solubilization screening. J Mol Biol 2008; 385:820-30. [PMID: 19061901 DOI: 10.1016/j.jmb.2008.11.021] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Revised: 10/26/2008] [Accepted: 11/12/2008] [Indexed: 10/21/2022]
Abstract
A medium-throughput approach is used to rapidly identify membrane proteins from a eukaryotic organism that are most amenable to expression in amounts and quality adequate to support structure determination. The goal was to expand knowledge of new membrane protein structures based on proteome-wide coverage. In the first phase, membrane proteins from the budding yeast Saccharomyces cerevisiae were selected for homologous expression in S. cerevisiae, a system that can be adapted to expression of membrane proteins from other eukaryotes. We performed medium-scale expression and solubilization tests on 351 rationally selected membrane proteins from S. cerevisiae. These targets are inclusive of all annotated and unannotated membrane protein families within the organism's membrane proteome. Two hundred seventy-two targets were expressed, and of these, 234 solubilized in the detergent n-dodecyl-beta-D-maltopyranoside. Furthermore, we report the identity of a subset of targets that were purified to homogeneity to facilitate structure determinations. The extensibility of this approach is demonstrated with the expression of 10 human integral membrane proteins from the solute carrier superfamily. This discovery-oriented pipeline provides an efficient way to select proteins from particular membrane protein classes, families, or organisms that may be more suited to structure analysis than others.
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159
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Sorani MD, Manley GT, Giacomini KM. Genetic variation in human aquaporins and effects on phenotypes of water homeostasis. Hum Mutat 2008; 29:1108-17. [DOI: 10.1002/humu.20762] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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160
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Sorani MD, Morabito D, Rosenthal G, Giacomini KM, Manley GT. Characterizing the dose-response relationship between mannitol and intracranial pressure in traumatic brain injury patients using a high-frequency physiological data collection system. J Neurotrauma 2008; 25:291-8. [PMID: 18373479 DOI: 10.1089/neu.2007.0411] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Despite the widespread use of mannitol to treat elevated intracranial pressure (ICP), there is no consensus regarding the optimal dosage. The objective of this study was to retrospectively characterize the dose-response relationship between mannitol and ICP using data collected with a continuous high-frequency physiological data collection system. To this end, we measured ICP continuously in 28 patients with traumatic brain injury (TBI) who were given at least one dose of mannitol. Twenty TBI patients were given a total of 85 doses of 50 g of mannitol, and 18 patients were given 50 doses of 100 g. Some patients received both amounts. Cerebral perfusion pressure was maintained above 60 mm Hg. The average ICP was 22.0 +/- 10.6 mm Hg when mannitol was administered, fell immediately after dosing, and continued falling for approximately 30 min to 15.7 +/- 8.1 mm Hg across all patients. After 30 min, ICP was equal in the 100-g group (15.6 +/- 10.9) versus the 50-g group (15.7 +/- 6.3). However, at 100 min, ICP had increased in the 50-g group to nearly its initial value but was still lower in the 100-g group (18.6 +/- 7.6 vs. 14.2 +/- 6.7 mm Hg; p = 0.001). Osmotic agents such as mannitol have been used for decades to treat cerebral edema, but there has been no definitive quantitative information regarding the dosing of mannitol. In a large, retrospective study of high-frequency ICP data, we have quantitatively shown that mannitol's effect on ICP is dose-dependent and that higher doses provide a more durable reduction in ICP.
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161
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Cropp CD, Yee SW, Giacomini KM. Genetic variation in drug transporters in ethnic populations. Clin Pharmacol Ther 2008; 84:412-6. [PMID: 18528433 DOI: 10.1038/clpt.2008.98] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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162
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Sorani MD, Zador Z, Hurowitz E, Yan D, Giacomini KM, Manley GT. Novel variants in human Aquaporin-4 reduce cellular water permeability. Hum Mol Genet 2008; 17:2379-89. [PMID: 18511455 DOI: 10.1093/hmg/ddn138] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Cerebral edema contributes significantly to morbidity and mortality after brain injury and stroke. Aquaporin-4 (AQP4), a water channel expressed in astrocytes, plays a key role in brain water homeostasis. Genetic variants in other aquaporin family members have been associated with disease phenotypes. However, in human AQP4, only one non-synonymous single-nucleotide polymorphism (nsSNP) has been reported, with no characterization of protein function or disease phenotype. We analyzed DNA from an ethnically diverse cohort of 188 individuals to identify novel AQP4 variants. AQP4 variants were constructed by site-directed mutagenesis and expressed in cells. Water permeability assays in the cells were used to measure protein function. We identified 24 variants in AQP4 including four novel nsSNPs (I128T, D184E, I205L and M224T). We did not observe the previously documented M278T in our sample. The nsSNPs found were rare ( approximately 1-2% allele frequency) and heterozygous. Computational analysis predicted reduced function mutations. Protein expression and membrane localization were similar for reference AQP4 and the five AQP4 mutants. Cellular assays confirmed that four variant AQP4 channels reduced normalized water permeability to between 26 and 48% of the reference (P < 0.001), while the M278T mutation increased normalized water permeability (P < 0.001). We identified multiple novel AQP4 SNPs and showed that four nsSNPs reduced water permeability. The previously reported M278T mutation resulted in gain of function. Our experiments provide insight into the function of the AQP4 protein. These nsSNPs may have clinical implications for patients with cerebral edema and related disorders.
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163
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Cropp CD, Komori T, Shima JE, Urban TJ, Yee SW, More SS, Giacomini KM. Organic anion transporter 2 (SLC22A7) is a facilitative transporter of cGMP. Mol Pharmacol 2008; 73:1151-8. [PMID: 18216183 PMCID: PMC2698938 DOI: 10.1124/mol.107.043117] [Citation(s) in RCA: 93] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The second messenger, cGMP, mediates a host of cellular responses to various stimuli, resulting in the regulation of many critical physiologic functions. The existence of specific cGMP transporters on the plasma membrane that participate in the regulation of cGMP levels has been suggested in a large number of studies. In this study, we identified a novel plasma membrane transporter for cGMP. In particular, we showed that hOAT2 (SLC22A7), a member of the solute carrier (SLC) superfamily, was a facilitative transporter for cGMP and other guanine nucleotides. hOAT2, which is ubiquitously expressed at high levels in many cell types, was previously thought to primarily transport organic anions. Among purine and pyrimidine nucleobases, nucleosides, and nucleotides, hOAT2 showed the greatest preference for cGMP, which transported cGMP with a K(m) value of 88 +/- 11 muM and exhibited between 50- and 100-fold enhanced uptake over control cells. Our data revealed that hOAT2 is a bidirectional facilitative transporter that can control both intracellular and extracellular levels of cGMP. In addition, we observed that a common alternatively spliced variant of hOAT2 demonstrated a complete loss of transport function as a result of a low expression level on the plasma membrane. We conclude that hOAT2 is a highly efficient, facilitative transporter of cGMP and may be involved in cGMP signaling in many tissues. Our study suggests that hOAT2 represents a potential new drug target for regulating cGMP levels.
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164
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Abla N, Chinn LW, Nakamura T, Liu L, Huang CC, Johns SJ, Kawamoto M, Stryke D, Taylor TR, Ferrin TE, Giacomini KM, Kroetz DL. The human multidrug resistance protein 4 (MRP4, ABCC4): functional analysis of a highly polymorphic gene. J Pharmacol Exp Ther 2008; 325:859-68. [PMID: 18364470 DOI: 10.1124/jpet.108.136523] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
ABCC4 encodes multidrug resistance protein 4 (MRP4), a member of the ATP-binding cassette family of membrane transporters involved in the efflux of endogenous and xenobiotic molecules. The aims of this study were to identify single nucleotide polymorphisms of ABCC4 and to functionally characterize selected nonsynonymous variants. Resequencing was performed in a large ethnically diverse population. Ten nonsynonymous variants were selected for analysis of transport function based on allele frequencies and evolutionary conservation. The reference and variant MRP4 cDNAs were constructed by site-directed mutagenesis and transiently transfected into human embryonic kidney cells (HEK 293T). The function of MRP4 variants was compared by measuring the intracellular accumulation of two antiviral agents, azidothymidine (AZT) and adefovir (PMEA). A total of 98 variants were identified in the coding and flanking intronic regions of ABCC4. Of these, 43 variants are in the coding region, and 22 are nonsynonymous. In a functional screen of ten variants, there was no evidence for a complete loss of function allele. However, two variants (G187W and G487E) showed a significantly reduced function compared to reference with both substrates, as evidenced by higher intracellular accumulation of AZT and PMEA compared to the reference MRP4 (43 and 69% increase in accumulation for G187W compared with the reference MRP4, with AZT and PMEA, respectively). The G187W variant also showed decreased expression following transient transfection of HEK 293T cells. Further studies are required to assess the clinical significance of this altered function and expression and to evaluate substrate specificity of this functional change.
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165
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Wilke RA, Lin DW, Roden DM, Watkins PB, Flockhart D, Zineh I, Giacomini KM, Krauss RM. Erratum: Identifying genetic risk factors for serious adverse drug reactions: current progress and challenges. Nat Rev Drug Discov 2008. [DOI: 10.1038/nrd2508] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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166
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Zhang S, Lovejoy KS, Shima JE, Lagpacan LL, Shu Y, Lapuk A, Chen Y, Komori T, Gray JW, Chen X, Lippard SJ, Giacomini KM. Organic cation transporters are determinants of oxaliplatin cytotoxicity. Cancer Res 2007; 66:8847-57. [PMID: 16951202 PMCID: PMC2775093 DOI: 10.1158/0008-5472.can-06-0769] [Citation(s) in RCA: 305] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Although the platinum-based anticancer drugs cisplatin, carboplatin, and oxaliplatin have similar DNA-binding properties, only oxaliplatin is active against colorectal tumors. The mechanisms for this tumor specificity of platinum-based compounds are poorly understood but could be related to differences in uptake. This study shows that the human organic cation transporters (OCT) 1 and 2 (SLC22A1 and SLC22A2) markedly increase oxaliplatin, but not cisplatin or carboplatin, accumulation and cytotoxicity in transfected cells, indicating that oxaliplatin is an excellent substrate of these transporters. The cytotoxicity of oxaliplatin was greater than that of cisplatin in six colon cancer cell lines [mean +/- SE of IC(50) in the six cell lines, 3.9 +/- 1.4 micromol/L (oxaliplatin) versus 11 +/- 2.0 micromol/L (cisplatin)] but was reduced by an OCT inhibitor, cimetidine, to a level similar to, or even lower than that of, cisplatin (29 +/- 11 micromol/L for oxaliplatin versus 19 +/- 4.3 micromol/L for cisplatin). Structure-activity studies indicated that organic functionalities on nonleaving groups coordinated to platinum are critical for selective uptake by OCTs. These results indicate that OCT1 and OCT2 are major determinants of the anticancer activity of oxaliplatin and may contribute to its antitumor specificity. They also strongly suggest that expression of OCTs in tumors should be investigated as markers for selecting specific platinum-based therapies in individual patients. The development of new anticancer drugs, specifically targeted to OCTs, represents a novel strategy for targeted drug therapy. The results of the present structure-activity studies indicate specific tactics for realizing this goal.
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167
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Urban TJ, Yang C, Lagpacan LL, Brown C, Castro RA, Taylor TR, Huang CC, Stryke D, Johns SJ, Kawamoto M, Carlson EJ, Ferrin TE, Burchard EG, Giacomini KM. Functional effects of protein sequence polymorphisms in the organic cation/ergothioneine transporter OCTN1 (SLC22A4). Pharmacogenet Genomics 2007; 17:773-82. [PMID: 17700366 DOI: 10.1097/fpc.0b013e3281c6d08e] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
BACKGROUND OCTN1 is a multispecific transporter of organic cations and zwitterions, including several clinically important drugs as well as the antioxidant ergothioneine. OCTN1 is highly expressed in the kidney, where it is thought to aid in active secretion of organic cations, and may facilitate the active reabsorption of ergothioneine. Genetic variation in OCTN1 may help to explain interindividual variability in the pharmacokinetics of many cationic or zwitterionic drugs. METHODS We screened for human genetic variants in the OCTN1 coding region by direct sequencing in a large sample (n=270) of ethnically diverse healthy volunteers. RESULTS Six protein sequence-altering variants were identified, including five-amino-acid substitutions and one nonsense mutation. Two of the variants, T306I and L503F, were polymorphic, occurring at frequencies of 37 and 19%, respectively, in the total sample. Allele frequencies are varied by ethnicity. In biochemical assays, two of the variants (D165G and R282X) resulted in complete loss of transport function, and one variant (M205I) caused a reduction in activity to approximately 50% of the reference sequence protein. One variant, L503F, showed altered substrate specificity; this variant occurred at particularly high allele frequency (42%) in the European-American participants in our sample. Subcellular localization and ergothioneine inhibition kinetics were similar among the common amino-acid sequence variants of OCTN1. CONCLUSIONS The common OCTN1-L503F variant may explain a significant amount of population variation in the pharmacokinetics of OCTN1 substrate drugs. The rare loss-of-function variants provide a rational tool for studying the importance of ergothioneine in humans in vivo.
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168
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Urban TJ, Brown C, Castro RA, Shah N, Mercer R, Huang Y, Brett CM, Burchard EG, Giacomini KM. Effects of genetic variation in the novel organic cation transporter, OCTN1, on the renal clearance of gabapentin. Clin Pharmacol Ther 2007; 83:416-21. [PMID: 17609685 DOI: 10.1038/sj.clpt.6100271] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Gabapentin is an anticonvulsant that is widely prescribed for epilepsy and other neuropathic disorders. The pharmacokinetics, particularly the absorption and renal elimination, of gabapentin appear to involve membrane transporters. In this study, we tested the hypothesis that organic cation transporter 1 (OCTN1), a multispecific transporter expressed at the apical membrane in intestine and kidney, plays a role in gabapentin pharmacokinetics and that the common variant of OCTN1, OCTN1-L503F, contributes to variation in the pharmacokinetics of the drug. We observed that OCTN1 facilitates the Na+-independent transport of gabapentin, and that the OCTN1-L503F variant is deficient in gabapentin transport activity in stably transfected HEK-293 cells (fourfold enhanced uptake of gabapentin by OCTN1-503L vs twofold enhanced uptake by OCTN1-L503F, compared to mock-transfected cells). In clinical studies, we found that in subjects homozygous for the L503F variant, gabapentin renal clearance (CL(R)) approximates the glomerular filtration rate (mean+/-SE: 110+/-12 ml/min, n=9), whereas in subjects homozygous for the reference allele, gabapentin undergoes net secretion in the kidney (141+/-7.8 ml/min, n=11, P<0.05). Creatinine clearance and OCTN1 genotype accounted for 56% of the variation in CL(R) and were the only significant predictors of CL(R) (P<0.05). Importantly, OCTN1 genotype was the only significant predictor of net secretion of gabapentin (P<0.008). Oral bioavailability of gabapentin was not affected by OCTN1 genotype. We conclude that OCTN1 contributes to active tubular secretion of gabapentin, and that this effect may be diminished or absent in individuals carrying the OCTN1-L503F polymorphism. These results provide clinical evidence of the role of genetic variation in renal drug transporters in active drug secretion in vivo.
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169
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Shu Y, Brown C, Castro RA, Shi RJ, Lin ET, Owen RP, Sheardown SA, Yue L, Burchard EG, Brett CM, Giacomini KM. Effect of genetic variation in the organic cation transporter 1, OCT1, on metformin pharmacokinetics. Clin Pharmacol Ther 2007; 83:273-80. [PMID: 17609683 PMCID: PMC2976713 DOI: 10.1038/sj.clpt.6100275] [Citation(s) in RCA: 370] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The goal of this study was to determine the effects of genetic variation in the organic cation transporter 1, OCT1, on the pharmacokinetics of the antidiabetic drug, metformin. Twenty healthy volunteers with known OCT1 genotype agreed to participate in the study. Each subject received two oral doses of metformin followed by collection of blood and urine samples. OCT1 genotypes had a significant (P<0.05) effect on metformin pharmacokinetics, with a higher area under the plasma concentration-time curve (AUC), higher maximal plasma concentration (Cmax), and lower oral volume of distribution (V/F) in the individuals carrying a reduced function OCT1 allele (R61C, G401S, 420del, or G465R). The effect of OCT1 on metformin pharmacokinetics in mice was less than in humans possibly reflecting species differences in hepatic expression level of the transporter. Our studies suggest that OCT1 genotype is a determinant of metformin pharmacokinetics.
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170
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Shu Y, Sheardown SA, Brown C, Owen RP, Zhang S, Castro RA, Ianculescu AG, Yue L, Lo JC, Burchard EG, Brett CM, Giacomini KM. Effect of genetic variation in the organic cation transporter 1 (OCT1) on metformin action. J Clin Invest 2007; 117:1422-31. [PMID: 17476361 PMCID: PMC1857259 DOI: 10.1172/jci30558] [Citation(s) in RCA: 653] [Impact Index Per Article: 38.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2006] [Accepted: 01/30/2007] [Indexed: 02/06/2023] Open
Abstract
Metformin is among the most widely prescribed drugs for the treatment of type 2 diabetes. Organic cation transporter 1 (OCT1) plays a role in the hepatic uptake of metformin, but its role in the therapeutic effects of the drug, which involve activation of AMP-activated protein kinase (AMPK), is unknown. Recent studies have shown that human OCT1 is highly polymorphic. We investigated whether OCT1 plays a role in the action of metformin and whether individuals with OCT1 polymorphisms have reduced response to the drug. In mouse hepatocytes, deletion of Oct1 resulted in a reduction in the effects of metformin on AMPK phosphorylation and gluconeogenesis. In Oct1-deficient mice the glucose-lowering effects of metformin were completely abolished. Seven nonsynonymous polymorphisms of OCT1 that exhibited reduced uptake of metformin were identified. Notably, OCT1-420del (allele frequency of about 20% in white Americans), previously shown to have normal activity for model substrates, had reduced activity for metformin. In clinical studies, the effects of metformin in glucose tolerance tests were significantly lower in individuals carrying reduced function polymorphisms of OCT1. Collectively, the data indicate that OCT1 is important for metformin therapeutic action and that genetic variation in OCT1 may contribute to variation in response to the drug.
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171
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Giacomini KM, Krauss RM, Roden DM, Eichelbaum M, Hayden MR, Nakamura Y. When good drugs go bad. Nature 2007; 446:975-7. [PMID: 17460642 DOI: 10.1038/446975a] [Citation(s) in RCA: 162] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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172
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Chen Y, Zhang S, Sorani M, Giacomini KM. Transport of paraquat by human organic cation transporters and multidrug and toxic compound extrusion family. J Pharmacol Exp Ther 2007; 322:695-700. [PMID: 17495125 DOI: 10.1124/jpet.107.123554] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Paraquat (N,N-dimethyl-4-4'-bipiridinium; PQ), a widely used herbicide, when ingested accidentally or intentionally can cause major organ toxicities in lung, liver, and kidney. Because PQ is primarily eliminated in the kidney, renal elimination, including tubular transport, plays a critical role in controlling systemic exposure to the herbicide. The goal of this study was to determine the molecular identities of the transporters involved in the renal elimination of PQ. Using stably transfected human embryonic kidney (HEK)-293 cells, we examined the role of human organic cation transporters (hOCTs, SLC22A1-3) and human multidrug and toxic compound extrusion (hMATE)1 in the cellular accumulation and cytotoxicity of PQ. We found that overexpression of hOCT2 but not hOCT1 and hOCT3 in HEK-293 cells significantly enhanced the accumulation and cytotoxicity of PQ (-fold increase for uptake was 12 +/- 0.5, p < 0.01; -fold increase of cytotoxicity was 18 +/- 1.5, p < 0.001). The kinetics of PQ transport was altered in cells expressing a genetic polymorphism of hOCT2 (A270S) in comparison with those expressing the reference hOCT2. In addition, the cellular accumulation and cytotoxicity of PQ were also enhanced in cells expressing hMATE1 (-fold increase for uptake was 18 +/- 3.7, p < 0.0001; -fold increase of cytotoxicity was 5.7 +/- 0.5, p < 0.0001). These results suggest that hOCT2 and hMATE1 mediate PQ transport. These transporters may play an important role in the accumulation and renal excretion of PQ, and they may serve as molecular targets for the prevention and treatment of PQ-induced nephrotoxicity.
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173
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Giacomini KM, Brett CM, Altman RB, Benowitz NL, Dolan ME, Flockhart DA, Johnson JA, Hayes DF, Klein T, Krauss RM, Kroetz DL, McLeod HL, Nguyen AT, Ratain MJ, Relling MV, Reus V, Roden DM, Schaefer CA, Shuldiner AR, Skaar T, Tantisira K, Tyndale RF, Wang L, Weinshilboum RM, Weiss ST, Zineh I. The pharmacogenetics research network: from SNP discovery to clinical drug response. Clin Pharmacol Ther 2007; 81:328-45. [PMID: 17339863 PMCID: PMC5006950 DOI: 10.1038/sj.clpt.6100087] [Citation(s) in RCA: 186] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
The NIH Pharmacogenetics Research Network (PGRN) is a collaborative group of investigators with a wide range of research interests, but all attempting to correlate drug response with genetic variation. Several research groups concentrate on drugs used to treat specific medical disorders (asthma, depression, cardiovascular disease, addiction of nicotine, and cancer), whereas others are focused on specific groups of proteins that interact with drugs (membrane transporters and phase II drug-metabolizing enzymes). The diverse scientific information is stored and annotated in a publicly accessible knowledge base, the Pharmacogenetics and Pharmacogenomics Knowledge base (PharmGKB). This report highlights selected achievements and scientific approaches as well as hypotheses about future directions of each of the groups within the PGRN. Seven major topics are included: informatics (PharmGKB), cardiovascular, pulmonary, addiction, cancer, transport, and metabolism.
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Roden DM, Altman RB, Benowitz NL, Flockhart DA, Giacomini KM, Johnson JA, Krauss RM, McLeod HL, Ratain MJ, Relling MV, Ring HZ, Shuldiner AR, Weinshilboum RM, Weiss ST. Pharmacogenomics: challenges and opportunities. Ann Intern Med 2006; 145:749-57. [PMID: 17116919 PMCID: PMC5006954 DOI: 10.7326/0003-4819-145-10-200611210-00007] [Citation(s) in RCA: 172] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The outcome of drug therapy is often unpredictable, ranging from beneficial effects to lack of efficacy to serious adverse effects. Variations in single genes are 1 well-recognized cause of such unpredictability, defining the field of pharmacogenetics (see Glossary). Such variations may involve genes controlling drug metabolism, drug transport, disease susceptibility, or drug targets. The sequencing of the human genome and the cataloguing of variants across human genomes are the enabling resources for the nascent field of pharmacogenomics (see Glossary), which tests the idea that genomic variability underlies variability in drug responses. However, there are many challenges that must be overcome to apply rapidly accumulating genomic information to understand variable drug responses, including defining candidate genes and pathways; relating disease genes to drug response genes; precisely defining drug response phenotypes; and addressing analytic, ethical, and technological issues involved in generation and management of large drug response data sets. Overcoming these challenges holds the promise of improving new drug development and ultimately individualizing the selection of appropriate drugs and dosages for individual patients.
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Owen RP, Badagnani I, Giacomini KM. Molecular Determinants of Specificity for Synthetic Nucleoside Analogs in the Concentrative Nucleoside Transporter, CNT2. J Biol Chem 2006; 281:26675-82. [PMID: 16840788 DOI: 10.1074/jbc.m513421200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Members of the concentrative nucleoside transporter (CNT) family (SLC28) mediate the transport of naturally-occurring nucleosides, and nucleoside analog drugs across the plasma membrane of epithelial cells. Each of the three CNT family members has a distinct specificity for naturally occurring nucleosides, and residues that contribute to the specificity of each transporter have been identified. In contrast, the molecular determinants of specificity for synthetic nucleoside analogs are not known. In this study, we take advantage of the large species difference that exists between human and rat CNT2 (hCNT2 and rCNT2) in their ability to transport the nucleoside analog drug cladribine, 2CdA, (rCNT2 > > > hCNT2) to identify the critical domains and amino acid residues that contribute to the observed difference in specificity between CNT2 orthologs. Using chimeric proteins of human and rat CNT2, we determined that the C-terminal half of CNT2 contained the determinants of 2CdA selectivity. We replaced key residues in the C terminus of hCNT2 with the equivalent residue in rCNT2. One residue in the C-terminal portion of CNT2 was found to significantly contribute to 2CdA selectivity: hCNT2-S354A. This mutant caused an increase of 5-6-fold over hCNT2. The 2-chloro pharmacophore, rather than the 2'-deoxyribose was responsible for the reduced 2CdA uptake by hCNT2. Our data are consistent with a model in which an increased capability for hydrogen bonding in critical amino acids that reside in the C terminus of rCNT2 contributes to its enhanced selectivity for 2CdA.
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