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Ali SS, Raj R, Kaur T, Weadick B, Nayak D, No M, Protos J, Odom H, Desai K, Persaud AK, Wang J, Govindarajan R. Solute Carrier Nucleoside Transporters in Hematopoiesis and Hematological Drug Toxicities: A Perspective. Cancers (Basel) 2022; 14:cancers14133113. [PMID: 35804885 PMCID: PMC9264962 DOI: 10.3390/cancers14133113] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Revised: 06/18/2022] [Accepted: 06/22/2022] [Indexed: 02/04/2023] Open
Abstract
Simple Summary Anticancer nucleoside analogs are promising treatments that often result in damaging toxicities and therefore ineffective treatment. Mechanisms of this are not well-researched, but cellular nucleoside transport research in mice might provide additional insight given transport’s role in mammalian hematopoiesis. Cellular nucleoside transport is a notable component of mammalian hematopoiesis due to how mutations within it relate to hematological abnormities. This review encompasses nucleoside transporters, focusing on their inherent properties, hematopoietic role, and their interplay in nucleoside drug treatment side effects. We then propose potential mechanisms to explain nucleoside transport involvement in blood disorders. Finally, we point out and advocate for future research areas that would improve therapeutic outcomes for patients taking nucleoside analog therapies. Abstract Anticancer nucleoside analogs produce adverse, and at times, dose-limiting hematological toxicities that can compromise treatment efficacy, yet the mechanisms of such toxicities are poorly understood. Recently, cellular nucleoside transport has been implicated in normal blood cell formation with studies from nucleoside transporter-deficient mice providing additional insights into the regulation of mammalian hematopoiesis. Furthermore, several idiopathic human genetic disorders have revealed nucleoside transport as an important component of mammalian hematopoiesis because mutations in individual nucleoside transporter genes are linked to various hematological abnormalities, including anemia. Here, we review recent developments in nucleoside transporters, including their transport characteristics, their role in the regulation of hematopoiesis, and their potential involvement in the occurrence of adverse hematological side effects due to nucleoside drug treatment. Furthermore, we discuss the putative mechanisms by which aberrant nucleoside transport may contribute to hematological abnormalities and identify the knowledge gaps where future research may positively impact treatment outcomes for patients undergoing various nucleoside analog therapies.
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Affiliation(s)
- Syed Saqib Ali
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Ruchika Raj
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Tejinder Kaur
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Brenna Weadick
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Debasis Nayak
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Minnsung No
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Jane Protos
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Hannah Odom
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Kajal Desai
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Avinash K. Persaud
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
| | - Joanne Wang
- Department of Pharmaceutics, College of Pharmacy, University of Washington, Seattle, WA 98195, USA;
| | - Rajgopal Govindarajan
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA; (S.S.A.); (R.R.); (T.K.); (B.W.); (D.N.); (M.N.); (J.P.); (H.O.); (K.D.); (A.K.P.)
- Translational Therapeutics, The Ohio State University Comprehensive Cancer Center, Columbus, OH 43210, USA
- Correspondence: ; Tel.: +1-614-247-8269; Fax: +1-614-292-2588
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Vaskó B, Juhász V, Tóth B, Kurunczi A, Fekete Z, Krisjanis Zolnerciks J, Kis E, Magnan R, Bidon-Chanal Badia A, Pastor-Anglada M, Hazai E, Bikadi Z, Fülöp F, Krajcsi P. Inhibitor selectivity of CNTs and ENTs. Xenobiotica 2018; 49:840-851. [PMID: 30022699 DOI: 10.1080/00498254.2018.1501832] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The concentrative nucleoside transporters (CNT; solute carrier family 28 (SLC28)) and the equilibrative nucleoside transporters (ENT; solute carrier family 29 (SLC29)) are important therapeutic targets but may also mediate toxicity or adverse events. To explore the relative role of the base and the monosaccharide moiety in inhibitor selectivity we selected compounds that either harbor an arabinose moiety or a cytosine moiety, as these groups had several commercially available drug members. The screening data showed that more compounds harboring a cytosine moiety displayed potent interactions with the CNTs than compounds harboring the arabinose moiety. In contrast, ENTs showed a preference for compounds with an arabinose moiety. The correlation between CNT1 and CNT3 was good as five of six compounds displayed IC50 values within the threefold threshold and one displayed a borderline 4-fold difference. For CNT1 and CNT2 as well as for CNT2 and CNT3 only two of six IC50 values correlated and one displayed a borderline 4-fold difference. Interestingly, of the six compounds that potently interacted with both ENT1 and ENT2 only nelarabine displayed selectivity. Our data show differences between inhibitor selectivities of CNTs and ENTs as well as differences within the CNT family members.
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Affiliation(s)
| | | | - Beáta Tóth
- b SOLVO Biotechnology , Budaörs , Hungary
| | | | | | | | - Emese Kis
- a SOLVO Biotechnology , Szeged , Hungary
| | | | - Axel Bidon-Chanal Badia
- c Departament de Nutrició, Ciències de l'Alimentació i Gastronomia, Facultat de Farmàcia i Ciències de l'Alimentació and Institute of Biomedicine (IBUB), Campus de l'Alimentació de Torribera , Universitat de Barcelona , Santa Coloma de Gramenet , Spain
| | - Marçal Pastor-Anglada
- d Departament de Bioquímica i Biomedicina Molecular, Facultat de Biologia and Institute of Biomedicine (IBUB) , Universitat de Barcelona , Barcelona , Spain.,e Oncology Program , National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER EHD), Instituto de Salud Carlos III , Madrid , Spain
| | | | | | - Ferenc Fülöp
- g Institute of Pharmaceutical Chemistry, University of Szeged , Szeged , Hungary
| | - Peter Krajcsi
- a SOLVO Biotechnology , Szeged , Hungary.,h Department of Morphology and Physiology, Faculty of Health Sciences , Semmelweis University , Budapest , Hungary.,i Faculty of Information Technology and Bionics , Pázmány Péter Catholic University , Budapest , Hungary
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Pastor-Anglada M, Urtasun N, Pérez-Torras S. Intestinal Nucleoside Transporters: Function, Expression, and Regulation. Compr Physiol 2018; 8:1003-1017. [PMID: 29978890 DOI: 10.1002/cphy.c170039] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The gastrointestinal tract is the absorptive organ for nutrients found in foods after digestion. Nucleosides and, to a lesser extent nucleobases, are the late products of nucleoprotein digestion. These metabolites are absorbed by nucleoside (and nucleobase) transporter (NT) proteins. NTs are differentially distributed along the gastrointestinal tract showing also polarized expression in epithelial cells. Concentrative nucleoside transporters (CNTs) are mainly located at the apical side of enterocytes, whereas equilibrative nucleoside transporters (ENTs) facilitate the basolateral efflux of nucleosides and nucleobases to the bloodstream. Moreover, selected nucleotides and the bioactive nucleoside adenosine act directly on intestinal cells modulating purinergic signaling. NT-polarized insertion is tightly regulated. However, not much is known about the modulation of intestinal NT function in humans, probably due to the lack of appropriate cell models retaining CNT functional expression. Thus, the possibility of nutritional regulation of intestinal NTs has been addressed using animal models. Besides the nutrition-related role of NT proteins, orally administered drugs also need to cross the intestinal barrier, this event being a major determinant of drug bioavailability. In this regard, NT proteins might also play a role in pharmacology, thereby allowing the absorption of nucleoside- and nucleobase-derived drugs. The relative broad selectivity of these membrane transporters also suggests clinically relevant drug-drug interactions when using combined therapies. This review focuses on all these physiological and pharmacological aspects of NT protein biology. © 2017 American Physiological Society. Compr Physiol 8:1003-1017, 2018.
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Affiliation(s)
- Marçal Pastor-Anglada
- Biochemistry and Molecular Pharmacology Section, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine (IBUB), University of Barcelona, Barcelona, Spain.,Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER EHD), Instituto de Salud Carlos III, Barcelona, Spain.,Genetics, Molecular Biology and Gene Therapy Program, Institut de Recerca Sant Joan de Déu (IR SJD), Esplugues de Llobregat, Barcelona, Spain
| | - Nerea Urtasun
- Biochemistry and Molecular Pharmacology Section, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine (IBUB), University of Barcelona, Barcelona, Spain.,Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER EHD), Instituto de Salud Carlos III, Barcelona, Spain.,Genetics, Molecular Biology and Gene Therapy Program, Institut de Recerca Sant Joan de Déu (IR SJD), Esplugues de Llobregat, Barcelona, Spain
| | - Sandra Pérez-Torras
- Biochemistry and Molecular Pharmacology Section, Department of Biochemistry and Molecular Biomedicine, Institute of Biomedicine (IBUB), University of Barcelona, Barcelona, Spain.,Oncology Program, National Biomedical Research Institute on Liver and Gastrointestinal Diseases (CIBER EHD), Instituto de Salud Carlos III, Barcelona, Spain.,Genetics, Molecular Biology and Gene Therapy Program, Institut de Recerca Sant Joan de Déu (IR SJD), Esplugues de Llobregat, Barcelona, Spain
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4
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Xu D, You G. Loops and layers of post-translational modifications of drug transporters. Adv Drug Deliv Rev 2017; 116:37-44. [PMID: 27174152 DOI: 10.1016/j.addr.2016.05.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Accepted: 05/03/2016] [Indexed: 12/19/2022]
Abstract
Drug transporters encoded by solute carrier (SLC) family are distributed in multiple organs including kidney, liver, placenta, brain, and intestine, where they mediate the absorption, distribution, and excretion of a diverse array of environmental toxins and clinically important drugs. Alterations in the expression and function of these transporters play important roles in intra- and inter-individual variability of the therapeutic efficacy and the toxicity of many drugs. Consequently, the activity of these transporters must be highly regulated to carry out their normal functions. While it is clear that the regulation of these transporters tightly depends on genetic mechanisms, many studies have demonstrated that these transporters are the target of various post-translational modifications. This review article summarizes the recent advances in identifying the posttranslational modifications underlying the regulation of the drug transporters of SLC family. Such mechanisms are pivotal not only in physiological conditions, but also in diseases.
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Kumar Deokar H, Barch HP, Buolamwini JK. Homology Modeling of Human Concentrative Nucleoside Transporters (hCNTs) and Validation by Virtual Screening and Experimental Testing to Identify Novel hCNT1 Inhibitors. ACTA ACUST UNITED AC 2017; 6. [PMID: 29167753 DOI: 10.4172/2169-0138.1000146] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Objective The nucleoside transporter family is an emerging target for cancer, viral and cardiovascular diseases. Due to the difficulty in the expression, isolation and crystallization of membrane proteins, there is a lack of structural information on any of the mammalian and for that matter the human proteins. Thus the objective of this study was to build homology models for the three cloned concentrative nucleoside transporters hCNT1, hCNT2 and hCNT3 and validate them for screening towards the discovery of much needed inhibitors and probes. Methods The recently reported crystal structure of the Vibrio cholerae concentrative nucleoside transporter (vcCNT), has satisfactory similarity to the human CNT orthologues and was thus used as a template to build homology models of all three hCNTs. The Schrödinger modeling suite was used for the exercise. External validation of the homology models was carried out by docking a set of recently reported known hCNT1 nucleoside class inhibitors at the putative binding site using induced fit docking (IDF) methodology with the Glide docking program. Then, the hCNT1 homology model was subsequently used to conduct a virtual screening of a 360,000 compound library, and 172 compounds were obtained and biologically evaluated for hCNT 1, 2 and 3 inhibitory potency and selectivity. Results Good quality homology models were obtained for all three hCNTs as indicated by interrogation for various structural parameters and also external validated by docking of known inhibitors. The IDF docking results showed good correlations between IDF scores and inhibitory activities; particularly for hCNT1. From the top 0.1% of compounds ranked by virtual screening with the hCNT1 homology model, 172 compounds selected and tested for against hCNT1, hCNT2 and hCNT3, yielded 14 new inhibitors (hits) of (i.e., 8% success rate). The most active compound exhibited an IC50 of 9.05 μM, which shows a greater than 25-fold higher potency than phlorizin the standard CNT inhibitor (IC50 of 250 μM). Conclusion We successfully undertook homology modeling and validation for all human concentrative nucleoside transporters (hCNT 1, 2 and 3). The proof-of-concept that these models are promising for virtual screening to identify potent and selective inhibitors was also obtained using the hCNT1 model. Thus we identified a novel potent hCNT1 inhibitor that is more potent and more selective than the standard inhibitor phlorizin. The other hCNT1 hits also mostly exhibited selectivity. These homology models should be useful for virtual screening to identify novel hCNT inhibitors, as well as for optimization of hCNT inhibitors.
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Affiliation(s)
- Hemant Kumar Deokar
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, 847 Monroe Avenue, Suite 327, Memphis, Tennessee, 38163, USA.,Department of Pharmaceutical Sciences, College of Pharmacy, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, 60064, USA
| | - Hilaire Playa Barch
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, 847 Monroe Avenue, Suite 327, Memphis, Tennessee, 38163, USA
| | - John K Buolamwini
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, 847 Monroe Avenue, Suite 327, Memphis, Tennessee, 38163, USA.,Department of Pharmaceutical Sciences, College of Pharmacy, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, 60064, USA
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6
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Host-based ribavirin resistance influences hepatitis C virus replication and treatment response. J Virol 2011; 85:7273-83. [PMID: 21543469 DOI: 10.1128/jvi.00629-11] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Many individuals infected with hepatitis C virus (HCV) develop a chronic infection, and of those who are treated with pegylated interferon and ribavirin (RBV), many do not respond. While the nucleoside analog RBV improves treatment outcome, and will likely be an important component of therapy with next-generation viral inhibitors, RBV's mechanism is controversial. Most of RBV's proposed mechanisms require RBV import into cells. Therefore, we explored whether host-based RBV resistance develops through reduced cellular uptake, akin to chemotherapy resistance in some cancers. We examined the effect of host-based RBV resistance on HCV replication in cultured hepatoma Huh7.5 liver cells and whether RBV resistance develops in HCV patients. When Huh7.5 cells were exposed to RBV, resistance developed through reduced RBV uptake via the ENT1 nucleoside transporter and antiviral efficacy was reduced. The uptake defect in RBV-resistant cells was specific to RBV, since transport of another ENT1 substrate, cytidine, was unaffected. Importantly, RBV uptake significantly declined in HCV patient peripheral blood mononuclear cells (PBMCs) following 4 weeks of therapy. Furthermore, maintenance of RBV uptake correlated with rapid treatment response. Our results uncovered a novel form of antiviral drug resistance and suggest that host-based RBV resistance develops in HCV patients undergoing therapy and that maintenance of RBV uptake may contribute to rapid viral clearance.
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Klaassen CD, Aleksunes LM. Xenobiotic, bile acid, and cholesterol transporters: function and regulation. Pharmacol Rev 2010; 62:1-96. [PMID: 20103563 PMCID: PMC2835398 DOI: 10.1124/pr.109.002014] [Citation(s) in RCA: 561] [Impact Index Per Article: 40.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Transporters influence the disposition of chemicals within the body by participating in absorption, distribution, and elimination. Transporters of the solute carrier family (SLC) comprise a variety of proteins, including organic cation transporters (OCT) 1 to 3, organic cation/carnitine transporters (OCTN) 1 to 3, organic anion transporters (OAT) 1 to 7, various organic anion transporting polypeptide isoforms, sodium taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter, peptide transporters (PEPT) 1 and 2, concentrative nucleoside transporters (CNT) 1 to 3, equilibrative nucleoside transporter (ENT) 1 to 3, and multidrug and toxin extrusion transporters (MATE) 1 and 2, which mediate the uptake (except MATEs) of organic anions and cations as well as peptides and nucleosides. Efflux transporters of the ATP-binding cassette superfamily, such as ATP-binding cassette transporter A1 (ABCA1), multidrug resistance proteins (MDR) 1 and 2, bile salt export pump, multidrug resistance-associated proteins (MRP) 1 to 9, breast cancer resistance protein, and ATP-binding cassette subfamily G members 5 and 8, are responsible for the unidirectional export of endogenous and exogenous substances. Other efflux transporters [ATPase copper-transporting beta polypeptide (ATP7B) and ATPase class I type 8B member 1 (ATP8B1) as well as organic solute transporters (OST) alpha and beta] also play major roles in the transport of some endogenous chemicals across biological membranes. This review article provides a comprehensive overview of these transporters (both rodent and human) with regard to tissue distribution, subcellular localization, and substrate preferences. Because uptake and efflux transporters are expressed in multiple cell types, the roles of transporters in a variety of tissues, including the liver, kidneys, intestine, brain, heart, placenta, mammary glands, immune cells, and testes are discussed. Attention is also placed upon a variety of regulatory factors that influence transporter expression and function, including transcriptional activation and post-translational modifications as well as subcellular trafficking. Sex differences, ontogeny, and pharmacological and toxicological regulation of transporters are also addressed. Transporters are important transmembrane proteins that mediate the cellular entry and exit of a wide range of substrates throughout the body and thereby play important roles in human physiology, pharmacology, pathology, and toxicology.
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Affiliation(s)
- Curtis D Klaassen
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160-7417, USA.
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Interaction of benzopyranone derivatives and related compounds with human concentrative nucleoside transporters 1, 2 and 3 heterologously expressed in porcine PK15 nucleoside transporter deficient cells. Structure–activity relationships and determinants of transporter affinity and selectivity. Biochem Pharmacol 2010; 79:307-20. [DOI: 10.1016/j.bcp.2009.08.028] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2009] [Revised: 08/26/2009] [Accepted: 08/28/2009] [Indexed: 11/23/2022]
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Johnson DE, Ai HW, Wong P, Young JD, Campbell RE, Casey JR. Red fluorescent protein pH biosensor to detect concentrative nucleoside transport. J Biol Chem 2009; 284:20499-511. [PMID: 19494110 PMCID: PMC2742814 DOI: 10.1074/jbc.m109.019042] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2009] [Indexed: 11/06/2022] Open
Abstract
Human concentrative nucleoside transporter, hCNT3, mediates Na+/nucleoside and H+/nucleoside co-transport. We describe a new approach to monitor H+/uridine co-transport in cultured mammalian cells, using a pH-sensitive monomeric red fluorescent protein variant, mNectarine, whose development and characterization are also reported here. A chimeric protein, mNectarine fused to the N terminus of hCNT3 (mNect.hCNT3), enabled measurement of pH at the intracellular surface of hCNT3. mNectarine fluorescence was monitored in HEK293 cells expressing mNect.hCNT3 or mNect.hCNT3-F563C, an inactive hCNT3 mutant. Free cytosolic mNect, mNect.hCNT3, and the traditional pH-sensitive dye, BCECF, reported cytosolic pH similarly in pH-clamped HEK293 cells. Cells were incubated at the permissive pH for H(+)-coupled nucleoside transport, pH 5.5, under both Na(+)-free and Na(+)-containing conditions. In mNect.hCNT3-expressing cells (but not under negative control conditions) the rate of acidification increased in media containing 0.5 mm uridine, providing the first direct evidence for H(+)-coupled uridine transport. At pH 5.5, there was no significant difference in uridine transport rates (coupled H+ flux) in the presence or absence of Na+ (1.09 +/- 0.11 or 1.18 +/- 0.32 mm min(-1), respectively). This suggests that in acidic Na(+)-containing conditions, 1 Na+ and 1 H+ are transported per uridine molecule, while in acidic Na(+)-free conditions, 1 H+ alone is transported/uridine. In acid environments, including renal proximal tubule, H+/nucleoside co-transport may drive nucleoside accumulation by hCNT3. Fusion of mNect to hCNT3 provided a simple, self-referencing, and effective way to monitor nucleoside transport, suggesting an approach that may have applications in assays of transport activity of other H(+)-coupled transport proteins.
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Affiliation(s)
- Danielle E. Johnson
- From the Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7 and
| | - Hui-wang Ai
- the Department of Chemistry, University of Alberta, Edmonton T6G 2G2, Canada
| | - Peter Wong
- the Department of Chemistry, University of Alberta, Edmonton T6G 2G2, Canada
| | - James D. Young
- From the Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7 and
| | - Robert E. Campbell
- the Department of Chemistry, University of Alberta, Edmonton T6G 2G2, Canada
| | - Joseph R. Casey
- From the Membrane Protein Research Group, Department of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7 and
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Reduced ribavirin antiviral efficacy via nucleoside transporter-mediated drug resistance. J Virol 2009; 83:4538-47. [PMID: 19244331 DOI: 10.1128/jvi.02280-08] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Treatment for hepatitis C virus infection currently consists of pegylated interferon and ribavirin (RBV), a nucleoside analog. Although RBV clearly plays a role in aiding the treatment response, its antiviral mechanism is unclear. Regardless of the specific mechanism of RBV, we hypothesize that differences in levels of cellular uptake of RBV may affect antiviral efficacy and treatment success and that cells may become RBV resistant through reduced uptake. We monitored RBV uptake in various cell lines and determined the effect of uptake capacity on viral replication. RBV-resistant cells demonstrated reduced RBV uptake and increased growth of a model RNA virus, poliovirus, in the presence of RBV. Overexpression of equilibrative nucleoside transporter 1 (ENT1) or concentrative nucleoside transporter 3 (CNT3) increased RBV uptake in RBV-sensitive cell lines and restored the uptake defect in most RBV-resistant cell lines. However, CNT3 is not expressed in Huh-7 liver cells, and inhibition of concentrative transport did not affect RBV uptake. Blocking equilibrative transport using the inhibitor nitrobenzylmercaptopurine riboside recapitulated the RBV-resistant phenotype in RBV-sensitive cell lines, with a reduction in RBV uptake and increased poliovirus growth. Taken together, these results indicate that RBV uptake is restricted primarily to ENT1 in the cell lines examined. Interestingly, some RBV-resistant cell lines may compensate for reduced ENT1-mediated nucleoside uptake by increasing the activity of an alternative nucleoside transporter, ENT2. It is possible that RBV uptake affects the antiviral treatment response, either through natural differences in patients or through acquired resistance.
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Gupte A, Buolamwini JK. Synthesis and biological evaluation of phloridzin analogs as human concentrative nucleoside transporter 3 (hCNT3) inhibitors. Bioorg Med Chem Lett 2008; 19:917-21. [PMID: 19097778 DOI: 10.1016/j.bmcl.2008.11.112] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Revised: 11/24/2008] [Accepted: 11/26/2008] [Indexed: 11/16/2022]
Abstract
Nucleoside transporter inhibitors have potential therapeutic applications as anticancer, antiviral, cardioprotective and neuroprotective agents. Although quite a few potent inhibitors of the equilibrative nucleoside transporters are known, largely missing are the concentrative nucleoside transporter inhibitors. Phloridzin (3, K(i)=16.00 microM) is a known moderate inhibitor of the concentrative nucleoside transporters. We have synthesized and evaluated analogs of phloridzin at the hCNT3 nucleoside transporter. Within the series of synthesized analogs compound 16 (K(i)=2.88 microM), possessing a ribofuranose sugar unit instead of a glucopyranose as present in phloridzin, exhibited the highest binding affinity at the hCNT3 transporter. Phloridzin and compound 16 have also been shown to be selective for the hCNT3 transporter as compared with the hENT1 transporter. Compound 16 can serve as a new lead which after further modifications could yield selective and potent hCNT3 inhibitors.
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Affiliation(s)
- Amol Gupte
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Sciences Center, 847 Monroe Avenue Suite 327, Memphis, TN 38163, USA
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Pastor-Anglada M, Cano-Soldado P, Errasti-Murugarren E, Casado FJ. SLC28 genes and concentrative nucleoside transporter (CNT) proteins. Xenobiotica 2008; 38:972-94. [PMID: 18668436 DOI: 10.1080/00498250802069096] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
The human concentrative nucleoside transporter (hCNT) protein family has three members, hCNT1, 2, and 3, encoded by SLC28A1, A2, and A3 genes, respectively. hCNT1 and hCNT2 translocate pyrimidine- and purine-nucleosides, respectively, by a sodium-dependent mechanism, whereas hCNT3 shows broad substrate selectivity and the unique ability of translocating nucleosides both in a sodium- and a proton-coupled manner. hCNT proteins are also responsible for the uptake of most nucleoside-derived antiviral and anticancer drugs. Thus, hCNTs are key pharmacological targets. This review focuses on several crucial aspects of hCNT biology and pharmacology: protein structure-function, structural determinants for transportability, pharmacogenetics of hCNT-encoding genes, role of hCNT proteins in nucleoside-based therapeutics, and finally hCNT physiology.
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Affiliation(s)
- M Pastor-Anglada
- Facultat de Biologia, Departament de Bioquimica i Biologia Molecular, Institut de Biomedicina de la Universitat de Barcelona (IBUB), Universitat de Barcelona, Barcelona, Spain.
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Errasti‐Murugarren E, Molina‐Arcas M, Casado FJ, Pastor‐Anglada M. A splice variant of the
SLC28A3
gene encodes a novel human concentrative nucleoside transporter‐3 (hCNT3) protein localized in the endoplasmic reticulum. FASEB J 2008; 23:172-82. [DOI: 10.1096/fj.08-113902] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Ekaitz Errasti‐Murugarren
- Departament de Bioquímica i Biologia Molecular, Facultat de BiologiaInstitut de Biomedicina, CIBER EHD, Universitat de BarcelonaBarcelonaSpain
| | - Miriam Molina‐Arcas
- Departament de Bioquímica i Biologia Molecular, Facultat de BiologiaInstitut de Biomedicina, CIBER EHD, Universitat de BarcelonaBarcelonaSpain
| | - Fco Javier Casado
- Departament de Bioquímica i Biologia Molecular, Facultat de BiologiaInstitut de Biomedicina, CIBER EHD, Universitat de BarcelonaBarcelonaSpain
| | - Marcal Pastor‐Anglada
- Departament de Bioquímica i Biologia Molecular, Facultat de BiologiaInstitut de Biomedicina, CIBER EHD, Universitat de BarcelonaBarcelonaSpain
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14
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Leung GPH, Tse CM. The role of mitochondrial and plasma membrane nucleoside transporters in drug toxicity. Expert Opin Drug Metab Toxicol 2008; 3:705-18. [PMID: 17916056 DOI: 10.1517/17425255.3.5.705] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Many anticancer and antiviral drugs are nucleoside analogues, which interfere with nucleotide metabolism and DNA replication to produce pharmacological effects. Clinical efficacy and toxicity of nucleoside drugs are closely associated with nucleoside transporters because they mediate the transport of nucleoside drugs across biological membranes. Two families of human nucleoside transporters (equilibrative nucleoside transporters and concentrative nucleoside transporters) have been extensively studied for several decades. They are widely distributed, from the plasma membrane to membranes of organelles such as mitochondria, and the distribution differs in different tissues. In addition, they have different specificities to nucleoside drugs. The characteristics of equilibrative and concentrative nucleoside transporters affect the therapeutic outcomes achieved with anticancer and antiviral nucleoside drugs. In this review, an overview of the role of mitochondrial and plasma membrane nucleoside transporters in nucleoside drug toxicity is provided. Rational design and therapeutic application of nucleoside analogues are also discussed.
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Affiliation(s)
- George P H Leung
- The University of Hong Kong, Department of Pharmacology, Hong Kong.
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15
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Errasti-Murugarren E, Cano-Soldado P, Pastor-Anglada M, Casado FJ. Functional Characterization of a Nucleoside-Derived Drug Transporter Variant (hCNT3C602R) Showing Altered Sodium-Binding Capacity. Mol Pharmacol 2007; 73:379-86. [DOI: 10.1124/mol.107.041848] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
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16
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Zhang J, Visser F, King KM, Baldwin SA, Young JD, Cass CE. The role of nucleoside transporters in cancer chemotherapy with nucleoside drugs. Cancer Metastasis Rev 2007; 26:85-110. [PMID: 17345146 DOI: 10.1007/s10555-007-9044-4] [Citation(s) in RCA: 178] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Nucleoside analogs are important components of treatment regimens for various malignancies. Nucleoside-specific membrane transporters mediate plasma membrane permeation of physiologic nucleosides and most nucleoside analogs, for which the initial event is cellular conversion of nucleosides to active agents. Understanding of the roles of nucleoside transporters in nucleoside drug toxicity and resistance will provide opportunities for potentiating anticancer efficacy and avoiding resistance. Because transportability is a possible determinant of toxicity and resistance of many nucleoside analogs, nucleoside transporter abundance might be a prognostic marker to assess drug resistance. Elucidation of the structural determinants of nucleoside analogs for interaction with transporter proteins as well as the structural features of transporter proteins required for permeant interaction and translocation will lead to "transportability guidelines" for the rational design and therapeutic application of nucleoside analogs as anticancer drugs. It should eventually be possible to develop clinical assays that predict sensitivity and/or resistance to nucleoside anti-cancer drugs and thus to identify those patient populations that will most likely benefit from optimal nucleoside analog treatments. This review discusses recent results from structure/function studies of human nucleoside transporters, the role of nucleoside transport processes in the cytotoxicity and resistance of several anticancer nucleoside analogs and strategies to improve the nucleoside transporter-related anticancer effects of nucleoside analogs.
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Affiliation(s)
- Jing Zhang
- Membrane Protein Research Group, University of Alberta, Edmonton, AB, Canada
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17
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Hansen JE, Tse CM, Chan G, Heinze ER, Nishimura RN, Weisbart RH. Intranuclear protein transduction through a nucleoside salvage pathway. J Biol Chem 2007; 282:20790-3. [PMID: 17525162 DOI: 10.1074/jbc.c700090200] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Regulation of gene expression by intranuclear transduction of macromolecules such as transcription factors is an alternative to gene therapy for the treatment of numerous diseases. The identification of an effective intranuclear delivery vehicle and pathway for the transport of therapeutic macromolecules across plasma and nuclear membranes, however, has posed a significant challenge. The anti-DNA antibody fragment 3E10 Fv has received attention as a novel molecular delivery vehicle due to its penetration into living cells with specific nuclear localization, absence of toxicity, and successful delivery of therapeutic cargo proteins in vitro and in vivo. Elucidation of the pathway that allows 3E10 Fv to cross cell membranes is critical to the development of new molecular therapies. Here we show that 3E10 Fv penetrates cells through a nucleoside salvage transporter. 3E10 Fv is unable to penetrate into cells deficient in the equilibrative nucleoside transporter ENT2, and reconstitution of ENT2 into ENT2-deficient cells restores 3E10 Fv transport into cell nuclei. Our results represent the first demonstration of protein transport through a nucleoside salvage pathway. We expect that our finding will facilitate a variety of methods of gene regulation in the treatment of human diseases, open up new avenues of research in nucleoside salvage pathways, and enhance our understanding of the pathophysiology of autoimmune diseases.
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Affiliation(s)
- James E Hansen
- Veterans Affairs Greater Los Angeles Healthcare System (VAGLAHS), Sepulveda, California 91343, USA
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18
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Li RWS, Tse CM, Man RYK, Vanhoutte PM, Leung GPH. Inhibition of human equilibrative nucleoside transporters by dihydropyridine-type calcium channel antagonists. Eur J Pharmacol 2007; 568:75-82. [PMID: 17512522 DOI: 10.1016/j.ejphar.2007.04.033] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2006] [Revised: 04/12/2007] [Accepted: 04/17/2007] [Indexed: 10/23/2022]
Abstract
Dihydropyridine-type calcium channel antagonists, in addition to having a vasodilatory effect, are known to inhibit cellular uptake of nucleosides such as adenosine. However, the nucleoside transporter subtypes involved and the mechanism by which this occurs are not known. Therefore, we have studied the inhibitory effects of dihydropyridines on both human equilibrative nucleoside transporters, hENT-1 and hENT-2, which are the major transporters mediating nucleoside transport in most tissues. Among the dihydropyridines tested, nimodipine proved to be the most potent inhibitor of hENT-1, with an IC(50) value of 60+/-31 muM, whereas nifedipine, nicardipine, nitrendipine, and felodipine exhibited 100-fold less effective inhibitory activity. Nifedipine, nitrendipine, and nimodipine inhibited hENT-2 with IC(50) values in the micromolar range; however, nicardipine and felodipine had no significant effect on hENT-2. Removal of the 4-aryl ring or changing the nitro group at the 4-aryl ring proved not to be detrimental to the inhibitory effects of dihydropyridines on hENT-1, but resulted in a drastic decrease in their inhibitory effects on hENT-2. Kinetic studies revealed that nimodipine and nifedipine reduced V(max) of [(3)H]uridine transport without affecting K(m). The inhibitory effects of nimodipine and nifedipine could be washed out. In addition, nimodipine and nifedipine inhibited the rate of NBTGR-induced dissociation of [(3)H]NBMPR from hENT-1 cell membrane. We conclude that dihydropyridines are non-competitive inhibitors of hENT-1 and hENT-2, probably working through reversible interactions with the allosteric sites. The inhibitory potencies of dihydropyridines may be associated with the structure of the 4-aryl ring, as well as the ester groups at the C-3 and C-5 positions.
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Affiliation(s)
- Rachel W S Li
- Department of Pharmacology, The University of Hong Kong, Hong Kong
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19
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Errasti-Murugarren E, Pastor-Anglada M, Casado FJ. Role of CNT3 in the transepithelial flux of nucleosides and nucleoside-derived drugs. J Physiol 2007; 582:1249-60. [PMID: 17412768 PMCID: PMC2075247 DOI: 10.1113/jphysiol.2007.130138] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
We examined the role of the concentrative nucleoside transporter CNT3 in the establishment of a transepithelial flux of natural nucleosides and their pharmacologically active derivatives in renal epithelial cell lines. Murine PCT cells grown on a transwell dish showed endogenous CNT3 activity at their apical membrane that was responsible for the sodium-dependent transepithelial flux of both purine and pyrimidine nucleosides. hCNT3 was also identified in human kidney and its role in the transport of nucleosides was tested. To this end, MDCK cells, lacking endogenous CNT3 activity, were genetically engineered to express the human orthologue of CNT3 (hCNT3-MDCK cells). In these cells, hCNT3 was inserted into the apical membrane, thus generating, as for PCT cells, a transepithelial flux of both nucleosides and nucleoside-derived drugs. Apical-to-basolateral transepithelial flux was present in all cells expressing a functional CNT3 transporter and was significantly higher than that found either in PCT cells in absence of sodium or in mock-transfected MDCK cells. Nevertheless in all cases a significant amount of the transported nucleoside was retained and transformed inside cells. However release to the opposite compartment was CNT3 dependent, not only in terms of absolute flux (much higher when an apical CNT3 transporter was active) but also regarding metabolic transformations of the apically absorbed nucleosides. These results underline a critical role of CNT3 in the renal reabsorption of nucleosides and their derivatives as well as in their intracellular metabolism.
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Affiliation(s)
- Ekaitz Errasti-Murugarren
- Departament de Bioquímica i Biologia Molecular, Facultat de Biologia, Universitat de Barcelona, Avda Diagonal 645, Edifici annex, Planta-1, E-08028 Barcelona, Spain
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20
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Yamamoto T, Kuniki K, Takekuma Y, Hirano T, Iseki K, Sugawara M. Ribavirin uptake by cultured human choriocarcinoma (BeWo) cells and Xenopus laevis oocytes expressing recombinant plasma membrane human nucleoside transporters. Eur J Pharmacol 2006; 557:1-8. [PMID: 17140564 DOI: 10.1016/j.ejphar.2006.10.062] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2006] [Revised: 10/23/2006] [Accepted: 10/30/2006] [Indexed: 01/23/2023]
Abstract
We investigated the mechanism of the transport of ribavirin (1-beta-D-ribofuranosyl-1,2,4-trizole-3-carboxamide) into placental epithelial cells using human choriocarcinoma (BeWo) cells and Xenopus oocytes expressing human nucleoside transporters. In BeWo cells, when a relatively low concentration (123 nM) of ribavirin was used, both Na(+)-dependent uptake and -independent uptake of ribavirin were observed. On the other hand, when a higher concentration (100 microM) of ribavirin was used, Na(+)-independent uptake was observed, but there was only a slight Na(+)-dependent uptake. In Xenopus oocytes, influxes of ribavirin mediated by hCNT2 (concentrative nucleoside transporter 2), hCNT3 (concentrative nucleoside transporter 3), hENT1 (equilibrative nucleoside transporter 1) and hENT2 (equilibrative nucleoside transporter 2) were saturable, and apparent K(m) values were 18.0 microM, 14.2 microM, 3.46 mM and 3.71 mM, respectively. These data indicate that hCNT2 and hCNT3 have higher affinity for ribavirin than do hENT1 and hENT2. Moreover, analysis by RT-PCR showed that BeWo cells express mRNA of hCNT3, hENT1 and hENT2. These results suggest that ribavirin is taken up by BeWo cells via both the high-affinity Na(+)-dependent transporter hCNT3 and the low-affinity Na(+)-independent transporters hENT1 and hENT2.
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Affiliation(s)
- Takashi Yamamoto
- Department of Pharmacy, Hokkaido University Hospital, Sapporo 060-8648, Japan
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21
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Leung GPH, Tse CM, Man RYK. Characterization of adenosine transport in H9c2 cardiomyoblasts. Int J Cardiol 2006; 116:186-93. [PMID: 16824629 DOI: 10.1016/j.ijcard.2006.03.044] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/26/2005] [Revised: 03/20/2006] [Accepted: 03/25/2006] [Indexed: 11/20/2022]
Abstract
Adenosine plays a significant role in various physiological processes including cardioprotection. Nucleoside transporters modulate adenosine levels in the vicinity of adenosine receptors, which in turn modulate adenosine functional efficacy. In the current study, adenosine transport in the rat heart myoblast cell line H9c2 was characterized. Kinetic analysis of adenosine transport in H9c2 cells revealed a Km of 8.9+/-0.001 microM and a Vmax of 32.1+/-0.65 pmol/mg protein/min. Adenosine transport in H9c2 cells was Na+-independent. About 6% of the total adenosine uptake was sensitive to nitrobenzylmercaptopurine riboside (NBMPR); however, 94% was insensitive, suggesting that adenosine uptake by H9c2 cells was predominantly mediated by the equilibrative nucleoside transporter (ENT)-2 and only mildly by ENT-1. Results of RT-PCR demonstrated the presence of mRNA for ENT-1, ENT-2 and ENT-3. Upon culture in a cell differentiation medium containing fetal bovine serum (1%) and retinoic acid (10 nM), both the activity and mRNA expression of ENT-1 increased 3-fold, however, ENT-2 was unaffected. Pharmacological studies revealed that ENT-1 activity was stimulated by PKA and PKC-delta/epsilon, however, ENT-2 activity was unaffected. Taken together, the exceptionally high expression level of ENT-2 in H9c2 cells raises questions regarding the use of H9c2 cells as a model for physiological adenosine activity in the heart. Furthermore, this study may form the basis for further investigation into the effect of cell differentiation and protein kinases on the regulation of nucleoside transporters.
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Affiliation(s)
- George P H Leung
- Department of Pharmacology, The University of Hong Kong, Hong Kong.
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22
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Hu H, Endres CJ, Chang C, Umapathy NS, Lee EW, Fei YJ, Itagaki S, Swaan PW, Ganapathy V, Unadkat JD. Electrophysiological Characterization and Modeling of the Structure Activity Relationship of the Human Concentrative Nucleoside Transporter 3 (hCNT3). Mol Pharmacol 2006; 69:1542-53. [PMID: 16446384 DOI: 10.1124/mol.105.018945] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We characterized the electrophysiology, kinetics, and quantitative structure-activity relationship (QSAR) of the human concentrative nucleoside transporter 3 (hCNT3) expressed in Xenopus laevis oocytes by measuring substrate-induced inward currents using a two-microelectrode voltage-clamp system. At membrane potentials between -30 and -150 mV, sodium activation of gemcitabine transport was sigmoidal, with a K0.5 of 8.5+/-0.3 mM for Na+ and a Hill coefficient of 2.2+/-0.25 independent of membrane potential. We measured the Imax and K0.5 for substrate at -50 mV for the nucleoside analog drugs gemcitabine (638+/-58 nA, 59.7+/-17.5 microM), ribavirin (546+/-37 nA, 61.0+/-13.2 microM), AZT (420+/-4 nA, 310+/-9 microM), and 3-deazauridine (506+/-30 nA, 50.8+/-9.90 microM). K0.5 and Imax for substrate were dependent on membrane potential (both increasing as the membrane became more hyperpolarized) for all four drugs. hCNT3 also exhibited pre-steady-state currents. The quantitative structure-activity relationship (QSAR) was examined using comparative molecular field analysis and comparative molecular similarity indices analysis of the inward currents induced by 27 nucleoside analogs with substitutions at both the ribose and the nucleobase. Two statistically significant QSAR models identified electrostatic interaction as the major force in hCNT3 transport and attributed a critical role to the 3'-hydroxyl position of hCNT3 substrates. Steric hindrance at the 3-position and positive charge at the 5-position of the pyrimidine ring were favorable for transport. Two hCNT3 pharmacophore models revealed the minimal features required for hCNT3 transport as two hydrogen bond acceptors at 3'-OH and 5'-O and the hydrophobic center occupied by the base ring.
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Affiliation(s)
- Huankai Hu
- Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta, USA
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23
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Damaraju S, Zhang J, Visser F, Tackaberry T, Dufour J, Smith KM, Slugoski M, Ritzel MWL, Baldwin SA, Young JD, Cass CE. Identification and functional characterization of variants in human concentrative nucleoside transporter 3, hCNT3 (SLC28A3), arising from single nucleotide polymorphisms in coding regions of the hCNT3 gene. Pharmacogenet Genomics 2005; 15:173-82. [PMID: 15861042 DOI: 10.1097/01213011-200503000-00006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
INTRODUCTION Human concentrative nucleoside transporter 3, hCNT3 (SLC28A3), which mediates transport of purine and pyrimidine nucleosides and a variety of antiviral and anticancer nucleoside drugs, was investigated to determine if there are single nucleotide polymorphisms in the coding regions of the hCNT3 gene. METHODS AND RESULTS Ninety-six DNA samples from Caucasians (Coriell Panel) were sequenced and sixteen variants in exons and flanking intronic regions were identified, of which five were coding variants; three of these were non-synonymous (S5N, L131F, Y513F) and were further investigated for functional alterations of the resulting recombinant proteins in Saccharomyces cerevisiae and Xenopus laevis oocytes. In yeast, immunostaining and fluorescence quantitation of the reference (wild-type) and variant CNT3 proteins showed similar levels of expression. Kinetic studies were undertaken in yeast with a high through-put semi-automated assay process; reference hCNT3 exhibited Km values of 1.7+/-0.3, 3.6+/-1.3, 2.2+/-0.7, and 2.1+/-0.6 muM and Vmax values of 1402+/-286, 1310+/-113, 1020+/-44, and 1740+/-114 pmol/mg/min, respectively, for uridine, cytidine, adenosine and inosine. Similar Km and Vmax values were obtained for the three variant proteins assayed in yeast under identical conditions. All of the characterized hCNT3 variants produced in oocytes retained sodium and proton dependence of uridine transport based on measurements of radioisotope flux and two-electrode voltage-clamp studies. CONCLUSION These results suggested a high degree of conservation of function for hCNT3 in the Caucasian population.
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Badagnani I, Chan W, Castro RA, Brett CM, Huang CC, Stryke D, Kawamoto M, Johns SJ, Ferrin TE, Carlson EJ, Burchard EG, Giacomini KM. Functional analysis of genetic variants in the human concentrative nucleoside transporter 3 (CNT3; SLC28A3). THE PHARMACOGENOMICS JOURNAL 2005; 5:157-65. [PMID: 15738947 DOI: 10.1038/sj.tpj.6500303] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The human concentrative nucleoside transporter, CNT3 (SLC28A3), plays an important role in mediating the cellular entry of a broad array of physiological nucleosides and synthetic anticancer nucleoside analog drugs. As a first step toward understanding the genetic basis for interindividual differences in the disposition and response to antileukemic nucleoside analogs, we examined the genetic and functional diversity of CNT3. In all, 56 variable sites in the exons and flanking intronic region of SLC28A3 were identified in a collection of 270 DNA samples from US populations (80 African-Americans, 80 European-Americans, 60 Asian-Americans, and 50 Mexican-Americans). Of the 16 coding region variants, 12 had not been previously reported. Also, 10 resulted in amino-acid changes and three of these had total allele frequencies of >/=1%. Nucleotide diversity (pi) at nonsynonymous and synonymous sites was estimated to be 1.81 x 10(4) and 18.13 x 10(4), respectively, suggesting that SLC28A3 is under negative selection. All nonsynonymous variants, constructed by site-directed mutagenesis and expressed in Xenopus laevis oocytes, transported purine and pyrimidine model substrates, except for c. 1099G>A (p. Gly367Arg). This rare variant alters an evolutionarily conserved site in the putative substrate recognition domain of CNT3. The presence of three additional evolutionarily conserved glycine residues in the vicinity of p. Gly367Arg that are also conserved in human paralogs suggest that these glycine residues are critical in the function of the concentrative nucleoside transporter family. The genetic analysis and functional characterization of CNT3 variants suggest that this transporter does not tolerate nonsynonymous changes and is important for human fitness.
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Affiliation(s)
- I Badagnani
- Department of Biopharmaceutical Sciences, University of California, San Francisco, CA 94143-0446, USA
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Leung GPH, Man RYK, Tse CM. D-Glucose upregulates adenosine transport in cultured human aortic smooth muscle cells. Am J Physiol Heart Circ Physiol 2005; 288:H2756-62. [PMID: 15695555 DOI: 10.1152/ajpheart.00921.2004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The etiology of the atherosclerosis that occurs in diabetes mellitus is unclear. Adenosine has been shown to inhibit growth of rat aortic smooth muscle cells. Nucleoside transporters play an integral role in adenosine function by regulating adenosine levels in the vicinity of adenosine receptors. Therefore, we studied the effect of 25 mM d-glucose, which mimics hyperglycemia of diabetes, on adenosine transport in cultured human aortic smooth muscle cells (HASMCs). Although RT-PCR demonstrated the presence of equilibrative nucleoside transporter-1 (ENT-1) and ENT-2 mRNA, functional studies revealed that adenosine transport in HASMCs was predominantly mediated by ENT-1 and inhibited by nitrobenzylmercaptopurine riboside (NBMPR, IC(50) = 0.69 +/- 0.05 nM). Adenosine transport in HASMCs was increased by >30% after treatment for 48 h with 25 mM d-glucose, but not with equimolar d-mannitol and l-glucose. Kinetic studies showed that d-glucose increased V(max) of adenosine transport without affecting K(m). Similarly, d-glucose increased B(max) of high-affinity [(3)H]NBMPR binding, while the dissociation constant (K(d)) was not changed. Consistent with these observations, 25 mM d-glucose increased mRNA and protein expression of ENT-1. Treatment of serum-starved cells with the selective inhibitors of MAPK/ERK, PD-98059 (40 microM) and U-0126 (10 microM), abolished the effect of d-glucose on ENT-1. We conclude that d-glucose upregulates the protein and message expression and functional activity of ENT-1 in HASMCs, possibly via MAPK/ERK-dependent pathways. Pathologically, the increase in ENT-1 activity in diabetes may affect the availability of adenosine in the vicinity of adenosine receptors and, thus, alter vascular functions in diabetes.
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