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Daniels G. Augustine Blood Group System and Equilibrative Nucleoside Transporter 1. Transfus Med Hemother 2022; 49:25-29. [PMID: 35221865 PMCID: PMC8832251 DOI: 10.1159/000520596] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2021] [Accepted: 10/27/2021] [Indexed: 10/02/2023] Open
Abstract
Augustine (AUG) is a blood group system comprising four antigens: AUG1, AUG2 (Ata), and AUG4 are of very high frequency; AUG3 is of very low frequency. These antigens are located on ENT1, an equilibrative nucleoside transporter encoded by SLC19A1. AUG antibodies are of clinical relevance in blood transfusion and pregnancy: anti-AUG2 have caused haemolytic transfusion reactions; the only anti-AUG3 was associated with severe haemolytic disease of the fetus and newborn. ENT1 is present in almost all human tissues. It facilitates the transfer of purine and pyrimidine nucleosides and is responsible for the majority of adenosine transport across plasma membranes. Adenosine transport appears to be an important factor in the regulation of bone metabolism. The AUGnull phenotype (AUG:-1,-2,-3,-4) has been found in three siblings, who are homozygous for an inactivating splice-site mutation in SLC29A1. Although ENT1 is very likely to be absent from all cells in these three individuals, they were apparently healthy with normal lifestyles. However, they suffered frequent attacks of pseudogout, a form of arthritis, in various joints with multiple calcifications around their hand joints. Ectopic calcification in the hips, pubic symphysis, and lumbar discs was present in the propositus. The three AUGnull individuals had misshapen red cells with deregulated protein phosphorylation, but no anaemia or shortening of red cell lifespan. Defective in vitro erythropoiesis in the absence of ENT1 was confirmed by shRNA-mediated knockdown of ENT1 during in vitro erythropoiesis of CD34+ progenitor cells from individuals with normal ENT1. Nucleoside transporters, such as ENT1, are vital in the uptake of synthetic nucleoside analogue drugs, used in cancer and viral chemotherapy. It is feasible that the efficacy of these drugs would be compromised in patients with the extremely rare AUGnull phenotype.
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Equilibrative Nucleoside Transporter 2: Properties and Physiological Roles. BIOMED RESEARCH INTERNATIONAL 2020; 2020:5197626. [PMID: 33344638 PMCID: PMC7732376 DOI: 10.1155/2020/5197626] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 11/05/2020] [Accepted: 11/16/2020] [Indexed: 02/06/2023]
Abstract
Equilibrative nucleoside transporter 2 (ENT2) is a bidirectional transporter embedded in the biological membrane and is ubiquitously found in most tissue and cell types. ENT2 mediates the uptake of purine and pyrimidine nucleosides and nucleobase besides transporting a variety of nucleoside-derived drugs, mostly in anticancer therapy. Since high expression of ENT2 has been correlated with advanced stages of different types of cancers, consequently, this has gained significant interest in the role of ENT2 as a potential therapeutic target. Furthermore, ENT2 plays critical roles in signaling pathway and cell cycle progression. Therefore, elucidating the physiological roles of ENT2 and its properties may contribute to a better understanding of ENT2 roles beyond their transportation mechanism. This review is aimed at highlighting the main roles of ENT2 and at providing a brief update on the recent research.
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Meal for Two: Human Cytomegalovirus-Induced Activation of Cellular Metabolism. Viruses 2019; 11:v11030273. [PMID: 30893762 PMCID: PMC6466105 DOI: 10.3390/v11030273] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 03/12/2019] [Accepted: 03/13/2019] [Indexed: 12/18/2022] Open
Abstract
Viruses are parasites that depend on the host cell’s metabolic resources to provide the energy and molecular building blocks necessary for the production of viral progeny. It has become increasingly clear that viruses extensively modulate the cellular metabolic network to support productive infection. Here, we review the numerous ways through which human cytomegalovirus (HCMV) modulates cellular metabolism, highlighting known mechanisms of HCMV-mediated metabolic manipulation and identifying key outstanding questions that remain to be addressed.
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Holmes AP, Ray CJ, Pearson SA, Coney AM, Kumar P. Ecto-5'-nucleotidase (CD73) regulates peripheral chemoreceptor activity and cardiorespiratory responses to hypoxia. J Physiol 2018; 596:3137-3148. [PMID: 28560821 PMCID: PMC6068227 DOI: 10.1113/jp274498] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 05/25/2017] [Indexed: 12/17/2022] Open
Abstract
KEY POINTS Carotid body dysfunction is recognized as a cause of hypertension in a number of cardiorespiratory diseases states and has therefore been identified as a potential therapeutic target. Purinergic transmission is an important element of the carotid body chemotransduction pathway. We show that inhibition of ecto-5'-nucleotidase (CD73) in vitro reduces carotid body basal discharge and responses to hypoxia and mitochondrial inhibition. Additionally, inhibition of CD73 in vivo decreased the hypoxic ventilatory response, reduced the hypoxia-induced heart rate elevation and exaggerated the blood pressure decrease in response to hypoxia. Our data show CD73 to be a novel regulator of carotid body sensory function and therefore suggest that this enzyme may offer a new target for reducing carotid body activity in selected cardiovascular diseases. ABSTRACT Augmented sensory neuronal activity from the carotid body (CB) has emerged as a principal cause of hypertension in a number of cardiovascular related pathologies, including obstructive sleep apnoea, heart failure and diabetes. Development of new targets and pharmacological treatment strategies aiming to reduce CB sensory activity may thus improve outcomes in these key patient cohorts. The present study investigated whether ecto-5'-nucleotidase (CD73), an enzyme that generates adenosine, is functionally important in modifying CB sensory activity and cardiovascular respiratory responses to hypoxia. Inhibition of CD73 by α,β-methylene ADP (AOPCP) in the whole CB preparation in vitro reduced basal discharge frequency by 76 ± 5% and reduced sensory activity throughout graded hypoxia. AOPCP also significantly attenuated elevations in sensory activity evoked by mitochondrial inhibition. These effects were mimicked by antagonism of adenosine receptors with 8-(p-sulfophenyl) theophylline. Infusion of AOPCP in vivo significantly decreased the hypoxic ventilatory response (Δ V ̇ E control 74 ± 6%, Δ V ̇ E AOPCP 64 ± 5%, P < 0.05). AOPCP also modified cardiovascular responses to hypoxia, as indicated by reduced elevations in heart rate and exaggerated changes in femoral vascular conductance and mean arterial blood pressure. Thus we identify CD73 as a novel regulator of CB sensory activity. Future investigations are warranted to clarify whether inhibition of CD73 can effectively reduce CB activity in CB-mediated cardiovascular pathology.
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Affiliation(s)
| | - Clare J. Ray
- Institute of Clinical SciencesUniversity of BirminghamEdgbastonBirminghamUK
| | - Selina A. Pearson
- Mouse Pipelines, Wellcome Trust Sanger InstituteWellcome Genome CampusHinxtonCambridgeUK
| | - Andrew M. Coney
- Institute of Clinical SciencesUniversity of BirminghamEdgbastonBirminghamUK
| | - Prem Kumar
- Institute of Clinical SciencesUniversity of BirminghamEdgbastonBirminghamUK
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Conde SV, Monteiro EC, Sacramento JF. Purines and Carotid Body: New Roles in Pathological Conditions. Front Pharmacol 2017; 8:913. [PMID: 29311923 PMCID: PMC5733106 DOI: 10.3389/fphar.2017.00913] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Accepted: 11/29/2017] [Indexed: 01/28/2023] Open
Abstract
It is known that adenosine and adenosine-5′-triphosphate (ATP) are excitatory mediators involved in carotid body (CB) hypoxic signaling. The CBs are peripheral chemoreceptors classically defined by O2, CO2, and pH sensors. When hypoxia activates the CB, it induces the release of neurotransmitters from chemoreceptor cells leading to an increase in the action potentials frequency at the carotid sinus nerve (CSN). This increase in the firing frequency of the CSN is integrated in the brainstem to induce cardiorespiratory compensatory responses. In the last decade several pathologies, as, hypertension, diabetes, obstructive sleep apnea and heart failure have been associated with CB overactivation. In the first section of the present manuscript we review in a concise manner fundamental aspects of purine metabolism. The second section is devoted to the role of purines on the hypoxic response of the CB, providing the state-of-the art for the presence of adenosine and ATP receptors in the CB; for the role of purines at presynaptic level in CB chemoreceptor cells, as well as, its metabolism and regulation; at postsynaptic level in the CSN activity; and on the ventilatory responses to hypoxia. Recently, we have showed that adenosine is involved in CB hypersensitization during chronic intermittent hypoxia (CIH), which mimics obstructive sleep apnea, since caffeine, a non-selective adenosine receptor antagonist that inhibits A2A and A2B adenosine receptors, decreased CSN chemosensory activity in animals subjected to CIH. Apart from this involvement of adenosine in CB sensitization in sleep apnea, it was recently found that P2X3 ATP receptor in the CB contributes to increased chemoreflex hypersensitivity and hypertension in spontaneously hypertension rats. Therefore the last section of this manuscript is devoted to review the recent findings on the role of purines in CB-mediated pathologies as hypertension, diabetes and sleep apnea emphasizing the potential clinical importance of modulating purines levels and action to treat pathologies associated with CB dysfunction.
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Affiliation(s)
- Silvia V Conde
- Centro de Estudos de Doenças Crónicas, NOVA Medical School - Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisboa, Portugal
| | - Emilia C Monteiro
- Centro de Estudos de Doenças Crónicas, NOVA Medical School - Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisboa, Portugal
| | - Joana F Sacramento
- Centro de Estudos de Doenças Crónicas, NOVA Medical School - Faculdade de Ciências Médicas, Universidade NOVA de Lisboa, Lisboa, Portugal
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Resistance of leukemia cells to cytarabine chemotherapy is mediated by bone marrow stroma, involves cell-surface equilibrative nucleoside transporter-1 removal and correlates with patient outcome. Oncotarget 2017; 8:23073-23086. [PMID: 28160570 PMCID: PMC5410286 DOI: 10.18632/oncotarget.14981] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Accepted: 01/06/2017] [Indexed: 12/18/2022] Open
Abstract
The interaction between acute myeloid leukemia cells (AML) with the bone marrow stroma cells (BMSCs) determines a protective environment that favors tumor development and resistance to conventional chemotherapy. We showed that BMSCs secrete soluble factors that protect AML cells from Ara-C induced cytotoxicity. This leukemia chemoresistance is associated with a decrease in the equilibrative nucleoside transporter (ENT1) activity by inducing removal of ENT1 from the cell surface. Reduction of cell proliferation was also observed with activation of AKT and mTOR-dependent cell survival pathways, which may also contribute to the tumor chemoprotection. Analysis of primary BMSC cultures has demonstrated that AML patients with stroma capable to confer Ara-C resistance in vitro compared to AML patients without this stroma capacity were associated with a worse prognosis. The two year overall survival rate was 0% versus 80% respectively (p=0.0001). This is the first report of a chemoprotection mechanism based on the removal of a drug transporter from the cell surface and most importantly the first time that a stroma phenotype has correlated with prognostic outcome in cancer.
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The Adenosinergic System as a Therapeutic Target in the Vasculature: New Ligands and Challenges. Molecules 2017; 22:molecules22050752. [PMID: 28481238 PMCID: PMC6154114 DOI: 10.3390/molecules22050752] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Revised: 04/24/2017] [Accepted: 05/02/2017] [Indexed: 12/20/2022] Open
Abstract
Adenosine is an adenine base purine with actions as a modulator of neurotransmission, smooth muscle contraction, and immune response in several systems of the human body, including the cardiovascular system. In the vasculature, four P1-receptors or adenosine receptors—A1, A2A, A2B and A3—have been identified. Adenosine receptors are membrane G-protein receptors that trigger their actions through several signaling pathways and present differential affinity requirements. Adenosine is an endogenous ligand whose extracellular levels can reach concentrations high enough to activate the adenosine receptors. This nucleoside is a product of enzymatic breakdown of extra and intracellular adenine nucleotides and also of S-adenosylhomocysteine. Adenosine availability is also dependent on the activity of nucleoside transporters (NTs). The interplay between NTs and adenosine receptors’ activities are debated and a particular attention is given to the paramount importance of the disruption of this interplay in vascular pathophysiology, namely in hypertension., The integration of important functional aspects of individual adenosine receptor pharmacology (such as in vasoconstriction/vasodilation) and morphological features (within the three vascular layers) in vessels will be discussed, hopefully clarifying the importance of adenosine receptors/NTs for modulating peripheral mesenteric vascular resistance. In recent years, an increase interest in purine physiology/pharmacology has led to the development of new ligands for adenosine receptors. Some of them have been patented as having promising therapeutic activities and some have been chosen to undergo on clinical trials. Increased levels of endogenous adenosine near a specific subtype can lead to its activation, constituting an indirect receptor targeting approach either by inhibition of NT or, alternatively, by increasing the activity of enzymes responsible for ATP breakdown. These findings highlight the putative role of adenosinergic players as attractive therapeutic targets for cardiovascular pathologies, namely hypertension, heart failure or stroke. Nevertheless, several aspects are still to be explored, creating new challenges to be addressed in future studies, particularly the development of strategies able to circumvent the predicted side effects of these therapies.
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Role of Genetic Polymorphisms of Deoxycytidine Kinase and Cytidine Deaminase to Predict Risk of Death in Children with Acute Myeloid Leukemia. BIOMED RESEARCH INTERNATIONAL 2015; 2015:309491. [PMID: 26090398 PMCID: PMC4450239 DOI: 10.1155/2015/309491] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 09/02/2014] [Accepted: 09/10/2014] [Indexed: 11/17/2022]
Abstract
Cytarabine is one of the most effective antineoplastic agents among those used for the treatment of acute myeloid leukemia. However, some patients develop resistance and/or severe side effects to the drug, which may interfere with the efficacy of the treatment. The polymorphisms of some Ara-C metabolizing enzymes seem to affect outcome and toxicity in AML patients receiving cytarabine. We conducted this study in a cohort of Mexican pediatric patients with AML to investigate whether the polymorphisms of the deoxycytidine kinase and cytidine deaminase enzymes are implicated in clinical response and toxicity. Bone marrow and/or peripheral blood samples obtained at diagnosis from 27 previously untreated pediatric patients with de novo AML were processed for genotyping and in vitro chemosensitivity assay, and we analyzed the impact of genotypes and in vitro sensitivity on disease outcome and toxicity. In the multivariate Cox regression analysis, we found that age at diagnosis, wild-type genotype of the CDA A79C polymorphism, and wild-type genotype of the dCK C360G polymorphism were the most significant prognostic factors for predicting the risk of death.
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Boswell-Casteel RC, Johnson JM, Duggan KD, Roe-Žurž Z, Schmitz H, Burleson C, Hays FA. FUN26 (function unknown now 26) protein from saccharomyces cerevisiae is a broad selectivity, high affinity, nucleoside and nucleobase transporter. J Biol Chem 2014; 289:24440-51. [PMID: 25035431 DOI: 10.1074/jbc.m114.553503] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Equilibrative nucleoside transporters (ENTs) are polytopic integral membrane proteins that transport nucleosides and, to a lesser extent, nucleobases across cell membranes. ENTs modulate efficacy for a range of human therapeutics and function in a diffusion-controlled bidirectional manner. A detailed understanding of ENT function at the molecular level has remained elusive. FUN26 (function unknown now 26) is a putative ENT homolog from S. cerevisiae that is expressed in vacuole membranes. In the present system, proteoliposome studies of purified FUN26 demonstrate robust nucleoside and nucleobase uptake into the luminal volume for a broad range of substrates. This transport activity is sensitive to nucleoside modifications in the C(2')- and C(5')-positions on the ribose sugar and is not stimulated by a membrane pH differential. [(3)H]Adenine nucleobase transport efficiency is increased ∼4-fold relative to nucleosides tested with no observed [(3)H]adenosine or [(3)H]UTP transport. FUN26 mutational studies identified residues that disrupt (G463A or G216A) or modulate (F249I or L390A) transporter function. These results demonstrate that FUN26 has a unique substrate transport profile relative to known ENT family members and that a purified ENT can be reconstituted in proteoliposomes for functional characterization in a defined system.
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Affiliation(s)
| | | | - Kelli D Duggan
- From the Department of Biochemistry and Molecular Biology and
| | - Zygy Roe-Žurž
- the Department of Biochemistry and Biophysics, University of California, San Francisco, California 94143
| | - Hannah Schmitz
- From the Department of Biochemistry and Molecular Biology and
| | - Carter Burleson
- From the Department of Biochemistry and Molecular Biology and
| | - Franklin A Hays
- From the Department of Biochemistry and Molecular Biology and the Stephenson Oklahoma Cancer Center, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104 and
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Wang C, Lin W, Playa H, Sun S, Cameron K, Buolamwini J. Dipyridamole analogs as pharmacological inhibitors of equilibrative nucleoside transporters. Identification of novel potent and selective inhibitors of the adenosine transporter function of human equilibrative nucleoside transporter 4 (hENT4). Biochem Pharmacol 2013; 86:1531-40. [PMID: 24021350 PMCID: PMC3866046 DOI: 10.1016/j.bcp.2013.08.063] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 08/27/2013] [Accepted: 08/27/2013] [Indexed: 01/04/2023]
Abstract
To identify needed human equilibrative nucleoside transporter 4 (hENT4) inhibitors, we cloned and stably expressed the recombinant protein in PK15NTD (nucleoside transporter deficient) cells, and, investigated its interaction with a series of dipyridamole analogs synthesized in our laboratory. Compounds were tested in this newly established hENT4 expressing system as well in previous stably expressed hENT1 and hENT2 expressing systems. Of the dipyridamole analogs evaluated, about one fourth of the compounds inhibited hENT4 with higher potencies than dipyridamole. The most potent of them, Compound 30 displayed an IC₅₀ of 74.4 nM, making it about 38 times more potent than dipyridamole (IC₅₀=2.8 μM), and selectivities of about 80-fold and 20-fold relative to ENT1 and ENT2, respectively. Structure-activity relationship showed nitrogen-containing monocyclic rings and noncyclic substituents at the 4- and 8-positions of the pyrimido[5,4-d]pyrimidine were important for the inhibitory activity against hENT4. The most potent and selective hENT4 inhibitors tended to have a 2,6-di(N-monohydroxyethyl) substitution on the pyrimidopyrimidine ring system. The inhibitors of hENT4 identified in this study are the most selective and potent inhibitors of hENT4 adenosine transporter function to date, and should serve as useful pharmacological/biochemical tools and/or potential leads for ENT4-based therapeutics. Also, the new hENT4-expressing PK15 cell line established will serve as a useful screening tool for the discovery and design of hENT4 ligands.
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Affiliation(s)
- Chunmei Wang
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
| | | | - Hilaire Playa
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
| | - Shan Sun
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
| | - Kenyuna Cameron
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
| | - John Buolamwini
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
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Sjuvarsson E, Damaraju VL, Mowles D, Sawyer MB, Tiwari R, Agarwal HK, Khalil A, Hasabelnaby S, Goudah A, Nakkula RJ, Barth RF, Cass CE, Eriksson S, Tjarks W. Cellular influx, efflux, and anabolism of 3-carboranyl thymidine analogs: potential boron delivery agents for neutron capture therapy. J Pharmacol Exp Ther 2013; 347:388-97. [PMID: 24006340 DOI: 10.1124/jpet.113.207464] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
3-[5-{2-(2,3-Dihydroxyprop-1-yl)-o-carboran-1-yl}pentan-1-yl]thymidine (N5-2OH) is a first generation 3-carboranyl thymidine analog (3CTA) that has been intensively studied as a boron-10 ((10)B) delivery agent for neutron capture therapy (NCT). N5-2OH is an excellent substrate of thymidine kinase 1 and its favorable biodistribution profile in rodents led to successful preclinical NCT of rats bearing intracerebral RG2 glioma. The present study explored cellular influx and efflux mechanisms of N5-2OH, as well as its intracellular anabolism beyond the monophosphate level. N5-2OH entered cultured human CCRF-CEM cells via passive diffusion, whereas the multidrug resistance-associated protein 4 appeared to be a major mediator of N5-2OH monophosphate efflux. N5-2OH was effectively monophosphorylated in cultured murine L929 [thymidine kinase 1 (TK1(+))] cells whereas formation of N5-2OH monophosphate was markedly lower in L929 (TK1(-)) cell variants. Further metabolism to the di- and triphosphate forms was not observed in any of the cell lines. Regardless of monophosphorylation, parental N5-2OH was the major intracellular component in both TK1(+) and TK1(-) cells. Phosphate transfer experiments with enzyme preparations showed that N5-2OH monophosphate, as well as the monophosphate of a second 3-carboranyl thymidine analog [3-[5-(o-carboran-1-yl)pentan-1-yl]thymidine (N5)], were not substrates of thymidine monophosphate kinase. Surprisingly, N5-diphosphate was phosphorylated by nucleoside diphosphate kinase although N5-triphosphate apparently was not a substrate of DNA polymerase. Our results provide valuable information on the cellular metabolism and pharmacokinetic profile of 3-carboranyl thymidine analogs.
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Affiliation(s)
- Elena Sjuvarsson
- Department of Anatomy, Physiology, and Biochemistry, The Swedish University of Agricultural Sciences, Biomedical Center, Uppsala, Sweden (E.S., S.E.); Department of Oncology, University of Alberta, Edmonton, Alberta, Canada (V.L.D., D.M., M.B.S., C.E.C); Division of Medicinal Chemistry and Pharmacognosy, The Ohio State University, Columbus, Ohio (R.T., H.K.A., A.K., S.H., A.G., W.T.); Chemistry Department, Faculty of Science, Zagazig University, Zagazig, Egypt (A.K.); Division of Pharmaceutical Organic Chemistry, College of Pharmacy, Helwan University, Ain Helwan, Cairo, Egypt (S.H.); Division of Pharmacology, College of Veterinary Medicine, Cairo University, Giza, Egypt (A.G.); and Department of Pathology, The Ohio State University, Columbus, Ohio (R.J.N., R.F.B.)
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Paproski RJ, Yao SYM, Favis N, Evans D, Young JD, Cass CE, Zemp RJ. Human concentrative nucleoside transporter 3 transfection with ultrasound and microbubbles in nucleoside transport deficient HEK293 cells greatly increases gemcitabine uptake. PLoS One 2013; 8:e56423. [PMID: 23441192 PMCID: PMC3575408 DOI: 10.1371/journal.pone.0056423] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Accepted: 01/09/2013] [Indexed: 02/06/2023] Open
Abstract
Gemcitabine is a hydrophilic clinical anticancer drug that requires nucleoside transporters to cross plasma membranes and enter cells. Pancreatic adenocarcinomas with low levels of nucleoside transporters are generally resistant to gemcitabine and are currently a clinical problem. We tested whether transfection of human concentrative nucleoside transporter 3 (hCNT3) using ultrasound and lipid stabilized microbubbles could increase gemcitabine uptake and sensitivity in HEK293 cells made nucleoside transport deficient by pharmacologic treatment with dilazep. To our knowledge, no published data exists regarding the utility of using hCNT3 as a therapeutic gene to reverse gemcitabine resistance. Our ultrasound transfection system - capable of transfection of cell cultures, mouse muscle and xenograft CEM/araC tumors - increased hCNT3 mRNA and 3H-gemcitabine uptake by >2,000– and 3,400–fold, respectively, in dilazep-treated HEK293 cells. Interestingly, HEK293 cells with both functional human equilibrative nucleoside transporters and hCNT3 displayed 5% of 3H-gemcitabine uptake observed in cells with only functional hCNT3, suggesting that equilibrative nucleoside transporters caused significant efflux of 3H-gemcitabine. Efflux assays confirmed that dilazep could inhibit the majority of 3H-gemcitabine efflux from HEK293 cells, suggesting that hENTs were responsible for the majority of efflux from the tested cells. Oocyte uptake transport assays were also performed and provided support for our hypothesis. Gemcitabine uptake and efflux assays were also performed on pancreatic cancer AsPC-1 and MIA PaCa-2 cells with similar results to that of HEK293 cells. Using the MTS proliferation assay, dilazep-treated HEK293 cells demonstrated 13-fold greater resistance to gemcitabine compared to dilazep-untreated HEK293 cells and this resistance could be reversed by transfection of hCNT3 cDNA. We propose that transfection of hCNT3 cDNA using ultrasound and microbubbles may be a method to reverse gemcitabine resistance in pancreatic tumors that have little nucleoside transport activity which are resistant to almost all current anticancer therapies.
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Affiliation(s)
- Robert J. Paproski
- Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
| | - Sylvia Y. M. Yao
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada
- Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada
| | - Nicole Favis
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada
| | - David Evans
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada
| | - James D. Young
- Department of Physiology, University of Alberta, Edmonton, Alberta, Canada
- Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada
| | - Carol E. Cass
- Department of Oncology, Cross Cancer Institute, University of Alberta, Edmonton, Alberta, Canada
- Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta, Canada
| | - Roger J. Zemp
- Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada
- * E-mail:
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Macanas-Pirard P, Leisewitz A, Broekhuizen R, Cautivo K, Barriga FM, Leisewitz F, Gidi V, Riquelme E, Montecinos VP, Swett P, Besa P, Ramirez P, Ocqueteau M, Kalergis AM, Holt M, Rettig M, DiPersio JF, Nervi B. Bone marrow stromal cells modulate mouse ENT1 activity and protect leukemia cells from cytarabine induced apoptosis. PLoS One 2012; 7:e37203. [PMID: 22629369 PMCID: PMC3358339 DOI: 10.1371/journal.pone.0037203] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2011] [Accepted: 04/16/2012] [Indexed: 01/05/2023] Open
Abstract
Background Despite a high response rate to chemotherapy, the majority of patients with acute myeloid leukemia (AML) are destined to relapse due to residual disease in the bone marrow (BM). The tumor microenvironment is increasingly being recognized as a critical factor in mediating cancer cell survival and drug resistance. In this study, we propose to identify mechanisms involved in the chemoprotection conferred by the BM stroma to leukemia cells. Methods Using a leukemia mouse model and a human leukemia cell line, we studied the interaction of leukemia cells with the BM microenvironment. We evaluated in vivo and in vitro leukemia cell chemoprotection to different cytotoxic agents mediated by the BM stroma. Leukemia cell apoptosis was assessed by flow cytometry and western blotting. The activity of the equilibrative nucleoside transporter 1 (ENT1), responsible for cytarabine cell incorporation, was investigated by measuring transport and intracellular accumulation of 3H-adenosine. Results Leukemia cell mobilization from the bone marrow into peripheral blood in vivo using a CXCR4 inhibitor induced chemo-sensitization of leukemia cells to cytarabine, which translated into a prolonged survival advantage in our mouse leukemia model. In vitro, the BM stromal cells secreted a soluble factor that mediated significant chemoprotection to leukemia cells from cytarabine induced apoptosis. Furthermore, the BM stromal cell supernatant induced a 50% reduction of the ENT1 activity in leukemia cells, reducing the incorporation of cytarabine. No protection was observed when radiation or other cytotoxic agents such as etoposide, cisplatin and 5-fluorouracil were used. Conclusion The BM stroma secretes a soluble factor that significantly protects leukemia cells from cytarabine-induced apoptosis and blocks ENT1 activity. Strategies that modify the chemo-protective effects mediated by the BM microenvironment may enhance the benefit of conventional chemotherapy for patients with AML.
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MESH Headings
- Animals
- Antimetabolites, Antineoplastic/pharmacology
- Antimetabolites, Antineoplastic/therapeutic use
- Apoptosis/drug effects
- Apoptosis/physiology
- Bone Marrow Cells/drug effects
- Bone Marrow Cells/metabolism
- Cell Line, Tumor
- Cell Proliferation/drug effects
- Cell Survival/drug effects
- Cytarabine/pharmacology
- Cytarabine/therapeutic use
- Equilibrative Nucleoside Transporter 1/metabolism
- Humans
- Leukemia, Myeloid, Acute/drug therapy
- Leukemia, Myeloid, Acute/metabolism
- Leukemia, Myeloid, Acute/pathology
- Mice
- Stromal Cells/drug effects
- Stromal Cells/metabolism
- Tumor Cells, Cultured
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Affiliation(s)
- Patricia Macanas-Pirard
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Andrea Leisewitz
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Richard Broekhuizen
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Kelly Cautivo
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Francisco M. Barriga
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Francisco Leisewitz
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Victoria Gidi
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Erick Riquelme
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Viviana P. Montecinos
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Pilar Swett
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Pelayo Besa
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Pablo Ramirez
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Mauricio Ocqueteau
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Alexis M. Kalergis
- Departamento de Reumatología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Millennium Institute on Immunology and Immunotherapy, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Matthew Holt
- Oncology Division, Washington University School of Medicine, Saint Louis, Missouri, United States of America
| | - Michael Rettig
- Oncology Division, Washington University School of Medicine, Saint Louis, Missouri, United States of America
| | - John F. DiPersio
- Oncology Division, Washington University School of Medicine, Saint Louis, Missouri, United States of America
| | - Bruno Nervi
- Departamento de Hematología y Oncología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile
- * E-mail:
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14
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Bonavia A, Franti M, Pusateri Keaney E, Kuhen K, Seepersaud M, Radetich B, Shao J, Honda A, Dewhurst J, Balabanis K, Monroe J, Wolff K, Osborne C, Lanieri L, Hoffmaster K, Amin J, Markovits J, Broome M, Skuba E, Cornella-Taracido I, Joberty G, Bouwmeester T, Hamann L, Tallarico JA, Tommasi R, Compton T, Bushell SM. Identification of broad-spectrum antiviral compounds and assessment of the druggability of their target for efficacy against respiratory syncytial virus (RSV). Proc Natl Acad Sci U S A 2011; 108:6739-44. [PMID: 21502533 PMCID: PMC3084118 DOI: 10.1073/pnas.1017142108] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The search for novel therapeutic interventions for viral disease is a challenging pursuit, hallmarked by the paucity of antiviral agents currently prescribed. Targeting of viral proteins has the inextricable challenge of rise of resistance. Safe and effective vaccines are not possible for many viral pathogens. New approaches are required to address the unmet medical need in this area. We undertook a cell-based high-throughput screen to identify leads for development of drugs to treat respiratory syncytial virus (RSV), a serious pediatric pathogen. We identified compounds that are potent (nanomolar) inhibitors of RSV in vitro in HEp-2 cells and in primary human bronchial epithelial cells and were shown to act postentry. Interestingly, two scaffolds exhibited broad-spectrum activity among multiple RNA viruses. Using the chemical matter as a probe, we identified the targets and identified a common cellular pathway: the de novo pyrimidine biosynthesis pathway. Both targets were validated in vitro and showed no significant cell cytotoxicity except for activity against proliferative B- and T-type lymphoid cells. Corollary to this finding was to understand the consequences of inhibition of the target to the host. An in vivo assessment for antiviral efficacy failed to demonstrate reduced viral load, but revealed microscopic changes and a trend toward reduced pyrimidine pools and findings in histopathology. We present here a discovery program that includes screen, target identification, validation, and druggability that can be broadly applied to identify and interrogate other host factors for antiviral effect starting from chemical matter of unknown target/mechanism of action.
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Affiliation(s)
- Aurelio Bonavia
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Michael Franti
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Erin Pusateri Keaney
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Kelli Kuhen
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Mohindra Seepersaud
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Branko Radetich
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Jian Shao
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Ayako Honda
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Janetta Dewhurst
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Kara Balabanis
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - James Monroe
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Karen Wolff
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Colin Osborne
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Leanne Lanieri
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Keith Hoffmaster
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Jakal Amin
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Judit Markovits
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Michelle Broome
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Elizabeth Skuba
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Ivan Cornella-Taracido
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Gerard Joberty
- Cellzome AG, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Tewis Bouwmeester
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Lawrence Hamann
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - John A. Tallarico
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Ruben Tommasi
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Teresa Compton
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Simon M. Bushell
- Novartis Institutes for Biomedical Research, Inc., 250 Massachusetts Avenue, Cambridge, MA 02139; and
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15
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Costa MA, Barbosa A, Neto E, Sá-e-Sousa A, Freitas R, Neves JM, Magalhães-Cardoso T, Ferreirinha F, Correia-de-Sá P. On the role of subtype selective adenosine receptor agonists during proliferation and osteogenic differentiation of human primary bone marrow stromal cells. J Cell Physiol 2011; 226:1353-66. [PMID: 20945394 DOI: 10.1002/jcp.22458] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Purines are important modulators of bone cell biology. ATP is metabolized into adenosine by human primary osteoblast cells (HPOC); due to very low activity of adenosine deaminase, the nucleoside is the end product of the ecto-nucleotidase cascade. We, therefore, investigated the expression and function of adenosine receptor subtypes (A(1) , A(2A) , A(2B) , and A(3) ) during proliferation and osteogenic differentiation of HPOC. Adenosine A(1) (CPA), A(2A) (CGS21680C), A(2B) (NECA), and A(3) (2-Cl-IB-MECA) receptor agonists concentration-dependently increased HPOC proliferation. Agonist-induced HPOC proliferation was prevented by their selective antagonists, DPCPX, SCH442416, PSB603, and MRS1191. CPA and NECA facilitated osteogenic differentiation measured by increases in alkaline phosphatase (ALP) activity. This contrasts with the effect of CGS21680C which delayed HPOC differentiation; 2-Cl-IB-MECA was devoid of effect. Blockade of the A(2B) receptor with PSB603 prevented osteogenic differentiation by NECA. In the presence of the A(1) antagonist, DPCPX, CPA reduced ALP activity at 21 and 28 days in culture. At the same time points, blockade of A(2A) receptors with SCH442416 transformed the inhibitory effect of CGS21680C into facilitation. Inhibition of adenosine uptake with dipyridamole caused a net increase in osteogenic differentiation. The presence of all subtypes of adenosine receptors on HPOC was confirmed by immunocytochemistry. Data show that adenosine is an important regulator of osteogenic cell differentiation through the activation of subtype-specific receptors. The most abundant A(2B) receptor seems to have a consistent role in cell differentiation, which may be balanced through the relative strengths of A(1) or A(2A) receptors determining whether osteoblasts are driven into proliferation or differentiation.
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Affiliation(s)
- M Adelina Costa
- Laboratório de Farmacologia e Neurobiologia, UMIB, Instituto de Ciências Biomédicas Abel Salazar - Universidade do Porto (ICBAS-UP), Portugal
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16
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Graham K, Yao S, Johnson L, Mowles D, Ng A, Wilkinson J, Young JD, Cass CE. Nucleoside transporter gene expression in wild-type and mENT1 knockout miceThis paper is one of a selection of papers published in a Special Issue entitled CSBMCB 53rd Annual Meeting — Membrane Proteins in Health and Disease, and has undergone the Journal’s usual peer review process. Biochem Cell Biol 2011; 89:236-45. [DOI: 10.1139/o10-152] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Owing to the overlapping and redundant roles of the seven mammalian nucleoside transporters (NTs), which belong to two protein families (ENTs and CNTs), the physiological importance of individual NTs has been difficult to assess. Mice that have NT genes knocked out can be a valuable tool in gaining an understanding of the NT proteins. We have generated a strain of mice that is homozygous for a disruption mutation between exons 2 and 3 of the mouse equilibrative nucleoside transporter, mENT1. We have undertaken a quantitative survey of NT gene expression in 10 tissues, as well as microarray analysis of heart and kidney, from wild-type and mENT1 knockout mice. Rather than a consistent change in expression of NT genes in all tissues of mENT1 knockout mice, a complex pattern of changes was found. Some genes, such as those encoding mCNT1 and mCNT3 in colon tissue, exhibited increased expression, whereas other genes, such as those encoding mCNT2 and mENT4 in lung tissue, exhibited decreased expression. Although mCNT3 has been shown to be important in human and rat kidney tissue, we were unable to detect mCNT3 transcripts in the kidney of either the wild-type or mENT1 knockout mice, suggesting differences in renal nucleoside resorption between species.
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Affiliation(s)
- Kathryn Graham
- Cross Cancer Institute, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada
- Department of Oncology, School of Cancer, Engineering & Imaging Sciences, University of Alberta, Edmonton, AB T6G 1Z2, Canada
- Department of Physiology, School of Molecular & Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Sylvia Yao
- Cross Cancer Institute, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada
- Department of Oncology, School of Cancer, Engineering & Imaging Sciences, University of Alberta, Edmonton, AB T6G 1Z2, Canada
- Department of Physiology, School of Molecular & Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Lorelei Johnson
- Cross Cancer Institute, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada
- Department of Oncology, School of Cancer, Engineering & Imaging Sciences, University of Alberta, Edmonton, AB T6G 1Z2, Canada
- Department of Physiology, School of Molecular & Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Delores Mowles
- Cross Cancer Institute, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada
- Department of Oncology, School of Cancer, Engineering & Imaging Sciences, University of Alberta, Edmonton, AB T6G 1Z2, Canada
- Department of Physiology, School of Molecular & Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Amy Ng
- Cross Cancer Institute, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada
- Department of Oncology, School of Cancer, Engineering & Imaging Sciences, University of Alberta, Edmonton, AB T6G 1Z2, Canada
- Department of Physiology, School of Molecular & Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Jodi Wilkinson
- Cross Cancer Institute, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada
- Department of Oncology, School of Cancer, Engineering & Imaging Sciences, University of Alberta, Edmonton, AB T6G 1Z2, Canada
- Department of Physiology, School of Molecular & Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - James D. Young
- Cross Cancer Institute, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada
- Department of Oncology, School of Cancer, Engineering & Imaging Sciences, University of Alberta, Edmonton, AB T6G 1Z2, Canada
- Department of Physiology, School of Molecular & Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Carol E. Cass
- Cross Cancer Institute, 11560 University Avenue, Edmonton, AB T6G 1Z2, Canada
- Department of Oncology, School of Cancer, Engineering & Imaging Sciences, University of Alberta, Edmonton, AB T6G 1Z2, Canada
- Department of Physiology, School of Molecular & Systems Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
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17
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Peng XX, Shi Z, Tiwari AK, Damaraju VL, Fu L, Cass CE, Ashby CR, Kruh GD, Chen ZS. Up-regulation of P-glycoprotein confers acquired resistance to 6-mercaptopurine in human chronic myeloid leukemia cells. Oncol Lett 2011; 2:549-556. [PMID: 22866119 DOI: 10.3892/ol.2011.288] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2010] [Accepted: 03/11/2011] [Indexed: 11/05/2022] Open
Abstract
To investigate the mechanisms of cellular resistance to 6-mercaptopurine (6-MP) in chronic myeloid leukemia (CML), a 6-MP resistant cell line (K562-MP5) was established by stepwise selection of the CML cell line (K562). The results of the drug sensitivity analysis of the K562-MP5 cell line revealed the cells to be 339-fold more resistant to 6-MP compared with the parental K562 cells. K562-MP5 cells exhibited decreased accumulation and increased efflux of [(14)C]6-MP and its metabolites. In addition, K562-MP5 cells showed increased [(3)H]MTX transport. K562-MP5 cells over-expressed P-glycoprotein (P-gp) and up-regulated MDR1 mRNA levels. Taken together, these results suggest that the up-regulation of P-gp, which contributes to the decreased accumulation by increasing the efflux of 6-MP and its metabolites, underlies the mechanism of 6-MP resistance in K562 cells.
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Affiliation(s)
- Xing-Xiang Peng
- Department of Pharmaceutical Sciences, College of Pharmacy and Allied Health Professions, St. John's University, Queens, NY 11439, USA
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18
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Sharma R, Engemann S, Sahota P, Thakkar MM. Role of adenosine and wake-promoting basal forebrain in insomnia and associated sleep disruptions caused by ethanol dependence. J Neurochem 2010; 115:782-94. [PMID: 20807311 PMCID: PMC2970767 DOI: 10.1111/j.1471-4159.2010.06980.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Insomnia is a severe symptom of alcohol withdrawal; however, the underlying neuronal mechanism is yet unknown. We hypothesized that chronic ethanol exposure will impair basal forebrain (BF) adenosinergic mechanism resulting in insomnia-like symptoms. We performed a series of experiments in Sprague-Dawley rats to test our hypothesis. We used Majchrowicz's chronic binge ethanol protocol to induce ethanol dependency. Our first experiment verified the effects of ethanol withdrawal on sleep-wakefulness. Significant increase in wakefulness was observed during ethanol withdrawal. Next, we examined c-Fos expression (marker of neuronal activation) in BF wake-promoting neurons during ethanol withdrawal. There was a significant increase in the number of BF wake-promoting neurons with c-Fos immunoreactivity. Our third experiment examined the effects of ethanol withdrawal on sleep deprivation induced increase in BF adenosine levels. Sleep deprivation did not increase BF adenosine levels in ethanol dependent rats. Our last experiment examined the effects of ethanol withdrawal on equilibrative nucleoside transporter 1 and A1 receptor expression in the BF. There was a significant reduction in A1 receptor and equilibrative nucleoside transporter 1 expression in the BF of ethanol dependent rats. Based on these results, we suggest that insomnia observed during ethanol withdrawal is caused because of impaired adenosinergic mechanism in the BF.
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Affiliation(s)
- Rishi Sharma
- Harry S. Truman Memorial Veterans Hospital and Department of Neurology, University of Missouri, Columbia, Missouri 65210, USA
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19
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Plotnik DA, Emerick LE, Krohn KA, Unadkat JD, Schwartz JL. Different modes of transport for 3H-thymidine, 3H-FLT, and 3H-FMAU in proliferating and nonproliferating human tumor cells. J Nucl Med 2010; 51:1464-71. [PMID: 20720049 DOI: 10.2967/jnumed.110.076794] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
UNLABELLED The basis for the use of nucleoside tracers in PET is that activity of the cell-growth-dependent enzyme thymidine kinase 1 is the rate-limiting factor driving tracer retention in tumors. Recent publications suggest that nucleoside transporters might influence uptake and thereby affect the tracer signal in vivo. Understanding transport mechanisms for different nucleoside PET tracers is important for evaluating clinical results. This study examined the relative role of different nucleoside transport mechanisms in uptake and retention of [methyl-(3)H]-3'-deoxy-3'-fluorothymidine ((3)H-FLT), [methyl-(3)H]-thymidine ((3)H-thymidine), and (3)H-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-methyluracil ((3)H-FMAU). METHODS Transport of (3)H-FLT, (3)H-thymidine, and (3)H-FMAU was examined in a single human adenocarcinoma cell line, A549, under both nongrowth and exponential-growth conditions. RESULTS (3)H-Thymidine transport was dominated by human equilibrative nucleoside transporter 1 (hENT1) under both growth conditions. (3)H-FLT was also transported by hENT1, but passive diffusion dominated its transport. (3)H-FMAU transport was dominated by human equilibrative nucleoside transporter 2. Cell membrane levels of hENT1 increased in cells under exponential growth, and this increase was associated with a more rapid rate of uptake for both (3)H-thymidine and (3)H-FLT. (3)H-FMAU transport was not affected by changes in growth conditions. All 3 tracers concentrated in the plateau phase, nonproliferating cells at levels many-fold greater than their concentration in buffer, in part because of low levels of nucleoside metabolism, which inhibited tracer efflux. CONCLUSION Transport mechanisms are not the same for (3)H-thymidine, (3)H-FLT, and (3)H-FMAU. Levels of hENT1, an important transporter of (3)H-FLT and (3)H-thymidine, increase as proliferating cells enter the cell cycle.
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Affiliation(s)
- David A Plotnik
- Department of Radiation Oncology, University of Washington, Seattle, Washington 98195, USA
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20
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Scharf MT, Naidoo N, Zimmerman JE, Pack AI. The energy hypothesis of sleep revisited. Prog Neurobiol 2008; 86:264-80. [PMID: 18809461 DOI: 10.1016/j.pneurobio.2008.08.003] [Citation(s) in RCA: 135] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2007] [Revised: 06/08/2008] [Accepted: 08/27/2008] [Indexed: 01/09/2023]
Abstract
One of the proposed functions of sleep is to replenish energy stores in the brain that have been depleted during wakefulness. Benington and Heller formulated a version of the energy hypothesis of sleep in terms of the metabolites adenosine and glycogen. They postulated that during wakefulness, adenosine increases and astrocytic glycogen decreases reflecting the increased energetic demand of wakefulness. We review recent studies on adenosine and glycogen stimulated by this hypothesis. We also discuss other evidence that wakefulness is an energetic challenge to the brain including the unfolded protein response, the electron transport chain, NPAS2, AMP-activated protein kinase, the astrocyte-neuron lactate shuttle, production of reactive oxygen species and uncoupling proteins. We believe the available evidence supports the notion that wakefulness is an energetic challenge to the brain, and that sleep restores energy balance in the brain, although the mechanisms by which this is accomplished are considerably more complex than envisaged by Benington and Heller.
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Affiliation(s)
- Matthew T Scharf
- Center for Sleep and Respiratory Neurobiology, University of Pennsylvania School of Medicine, Translational Research Building, Suite 2100, 125 S. 31st Street, Philadelphia, PA 19104-3403, USA.
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21
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Brown RA, Spina D, Page CP. Adenosine receptors and asthma. Br J Pharmacol 2008; 153 Suppl 1:S446-56. [PMID: 18311158 PMCID: PMC2268070 DOI: 10.1038/bjp.2008.22] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2007] [Revised: 11/16/2007] [Accepted: 12/13/2007] [Indexed: 12/20/2022] Open
Abstract
The accumulation of evidence implicating a role for adenosine in the pathogenesis of asthma has led to investigations into all adenosine receptor subtypes as potential therapeutic targets for the treatment of asthma. Selective A(1) receptor antagonists are currently in preclinical development since adenosine has been shown experimentally to mediate various features of asthma through this receptor such as bronchoconstriction, mucus secretion and inflammation. The A(2A) receptor is expressed on most inflammatory cells implicated in asthma, and as A(2A) stimulation activates adenylate cyclase and consequently elevates cAMP, selective A(2A) receptor agonists have now reached clinical development. However, initial reports concerning their efficacy are inconclusive. A(2B) receptor antagonists are also under investigation based on the rationale that inhibiting the effects of adenosine on mast cells would be beneficial, in addition to other reported pro-inflammatory effects mediated by the A(2B) receptor on cells such as airway smooth muscle, epithelial cells and fibroblasts. Whilst the effects in pre-clinical models are promising, their efficacy in the clinical setting has also yet to be reported. Finally, adenosine A(3) receptor stimulation has been demonstrated to mediate inhibitory effects on eosinophils since it also elevates cAMP. However, some experimental reports suggest that A(3) antagonists mediate anti-inflammatory effects, thus the rationale for A(3) receptor ligands as therapeutic agents remains to be determined. In conclusion, establishing the precise role of adenosine in the pathogenesis of asthma and developing appropriate subtype selective agonists/antagonists represents an exciting opportunity for the development of novel therapeutics for the treatment of asthma.
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Affiliation(s)
- R A Brown
- King's College London, Sackler Institute of Pulmonary Pharmacology, Division of Biomedical and Health Sciences, London, UK
| | - D Spina
- King's College London, Sackler Institute of Pulmonary Pharmacology, Division of Biomedical and Health Sciences, London, UK
| | - C P Page
- King's College London, Sackler Institute of Pulmonary Pharmacology, Division of Biomedical and Health Sciences, London, UK
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22
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Abstract
An account is given of how a sensitive bioassay system for measurement of the neurotransmitter acetylcholine serendipitously led to the identification of adenosine triphosphate (ATP) released in vitro from active skeletal muscle. Subsequent application of the identification procedures to exercising human muscle in vivo, cardiac muscle cells in vitro, and human erythrocytes exposed to hypoxia gave rise to the general concept of ATP as a molecule that could influence cell function from the extracellular direction. Mechanisms of ATP release from cells in terms of “trigger” events such as mechanical distortion of the membrane, depolarization of the membrane, and exposure to hypoxia are discussed. Potential therapeutic uses of extracellular ATP in cancer therapy, radiation therapy, and a possible influence upon aging are discussed. Possible roles (distant and local) of extracellular ATP released from muscle during whole body exercise are discussed.
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23
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Wang Z, Do CW, Avila MY, Stone RA, Jacobson KA, Civan MM. Barrier qualities of the mouse eye to topically applied drugs. Exp Eye Res 2007; 85:105-12. [PMID: 17490649 PMCID: PMC2151915 DOI: 10.1016/j.exer.2007.03.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2006] [Revised: 03/02/2007] [Accepted: 03/09/2007] [Indexed: 11/20/2022]
Abstract
The mouse eye displays unusually rapid intraocular pressure (IOP) responses to topically applied drugs as measured by the invasive servo-null micropipette system (SNMS). To learn if the time course reflected rapid drug transfer across the thin mouse cornea and sclera, we monitored a different parameter, pupillary size, following topical application of droplets containing 40 microM (0.073 microg) carbachol. No miosis developed from this low carbachol concentration unless the cornea was impaled with an exploring micropipette as used in the SNMS. We also compared the mouse IOP response to several purinergic drugs, measured by the invasive SNMS and non-invasive pneumotonometry. Responses to the previously studied non-selective adenosine-receptor (AR) agonist adenosine, the A(3)-selective agonist Cl-IB-MECA and the A(3)-selective antagonist MRS 1191 were all enhanced to varying degrees, in time and magnitude, by corneal impalement. We conclude that the thin ocular coats of the mouse eye actually present a substantial barrier to drug penetration. Corneal impalement with even fine-tipped micropipettes can significantly enhance entry of topically-applied drugs into the mouse aqueous humor, reflecting either direct diffusion around the tip or a more complex impalement-triggered change in ocular barrier properties. Comparison of invasive and non-invasive measurement methods can document drug efficacy at intraocular target sites even if topical drug penetration is too slow to manifest convincing physiologic effects in intact eyes.
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Affiliation(s)
- Zhao Wang
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085
| | - Chi Wai Do
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085
- School of Optometry, The Hong Kong Polytechnic University, Kowloon, Hong Kong
| | - Marcel Y. Avila
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085
- Department of Physiological Sciences, Facultad de Medicina, Universidad Nacional de Colombia, Bogota, Colombia
| | - Richard A. Stone
- Department of Ophthalmology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085
| | | | - Mortimer M. Civan
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085
- Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085
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Nagai K, Nagasawa K, Kyotani Y, Hifumi N, Fujimoto S. Mouse Equilibrative Nucleoside Transporter 2 (mENT2) Transports Nucleosides and Purine Nucleobases Differing from Human and Rat ENT2. Biol Pharm Bull 2007; 30:979-81. [PMID: 17473446 DOI: 10.1248/bpb.30.979] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Several mammalian nucleoside transporters have been identified at the molecular level. Human and rat equilibrative nucleoside transporter 2 (hENT2 and rENT2, respectively) was previously reported to have the dual ability of transporting both nucleosides and nucleobases. In the present study, we characterized the transport of a variety of nucleosides and nucleobases via recombinant mouse ENT2 (mENT2). Cloned mENT2 mediated the uptake of nucleosides and purine nucleobases, but not pyrimidine nucleobases. The mENT2-mediated uptake of adenosine was significantly inhibited by nucleosides and nucleobases, irrespective of purine and pyrimidine. The K(m) values for the uptake of nucleosides and purine nucleobases mediated by mENT2 varied between 1.24 and 16.3 microM, and the transport clearances of adenosine and hypoxanthine via the transporter were greater than those of other substrates. Therefore, we concluded that mENT2 is nucleoside and purine nucleobase transporter, and pyrimidine nucleobases are blockers for the transporter, differing from hENT2 and rENT2 that were reported to also transport pyrimidine nucleobases.
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Affiliation(s)
- Katsuhito Nagai
- Department of Environmental Biochemistry, Kyoto Pharmaceutical University, Kyoto, Japan.
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Elwi AN, Damaraju VL, Baldwin SA, Young JD, Sawyer MB, Cass CE. Renal nucleoside transporters: physiological and clinical implicationsThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease. Biochem Cell Biol 2006; 84:844-58. [PMID: 17215872 DOI: 10.1139/o06-198] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Renal handling of physiological and pharmacological nucleosides is a major determinant of their plasma levels and tissue availabilities. Additionally, the pharmacokinetics and normal tissue toxicities of nucleoside drugs are influenced by their handling in the kidney. Renal reabsorption or secretion of nucleosides is selective and dependent on integral membrane proteins, termed nucleoside transporters (NTs) present in renal epithelia. The 7 known human NTs (hNTs) exhibit varying permeant selectivities and are divided into 2 protein families: the solute carrier (SLC) 29 (SLC29A1, SLC29A2, SLC29A3, SLC29A4) and SLC28 (SLC28A1, SLC28A2, SLC28A3) proteins, otherwise known, respectively, as the human equilibrative NTs (hENTs, hENT1, hENT2, hENT3, hENT4) and human concentrative NTs (hCNTs, hCNT1, hCNT2, hCNT3). The well characterized hENTs (hENT1 and hENT2) are bidirectional facilitative diffusion transporters in plasma membranes; hENT3 and hENT4 are much less well known, although hENT3, found in lysosomal membranes, transports nucleosides and is pH dependent, whereas hENT4–PMAT is a H+-adenosine cotransporter as well as a monoamine–organic cation transporter. The 3 hCNTs are unidirectional secondary active Na+-nucleoside cotransporters. In renal epithelial cells, hCNT1, hCNT2, and hCNT3 at apical membranes, and hENT1 and hENT2 at basolateral membranes, apparently work in concert to mediate reabsorption of nucleosides from lumen to blood, driven by Na+ gradients. Secretion of some physiological nucleosides, therapeutic nucleoside analog drugs, and nucleotide metabolites of therapeutic nucleoside and nucleobase drugs likely occurs through various xenobiotic transporters in renal epithelia, including organic cation transporters, organic anion transporters, multidrug resistance related proteins, and multidrug resistance proteins. Mounting evidence suggests that hENT1 may have a presence at both apical and basolateral membranes of renal epithelia, and thus may participate in both selective secretory and reabsorptive fluxes of nucleosides. In this review, the renal handling of nucleosides is examined with respect to physiological and clinical implications for the regulation of human kidney NTs and adenosine signaling, intracellular nucleoside transport, and nephrotoxicities associated with some nucleoside drugs.
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Affiliation(s)
- Adam N Elwi
- Department of Oncology and the Membrane Protein Research Group, University of Alberta, Edmonton, Alta., Canada
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26
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Gurley KA, Reimer RJ, Kingsley DM. Biochemical and genetic analysis of ANK in arthritis and bone disease. Am J Hum Genet 2006; 79:1017-29. [PMID: 17186460 PMCID: PMC1698704 DOI: 10.1086/509881] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2006] [Accepted: 09/26/2006] [Indexed: 01/11/2023] Open
Abstract
Mutations in the progressive ankylosis gene (Ank/ANKH) cause surprisingly different skeletal phenotypes in mice and humans. In mice, recessive loss-of-function mutations cause arthritis, ectopic crystal formation, and joint fusion throughout the body. In humans, some dominant mutations cause chondrocalcinosis, an adult-onset disease characterized by the deposition of ectopic joint crystals. Other dominant mutations cause craniometaphyseal dysplasia, a childhood disease characterized by sclerosis of the skull and abnormal modeling of the long bones, with little or no joint pathology. Ank encodes a multiple-pass transmembrane protein that regulates pyrophosphate levels inside and outside tissue culture cells in vitro, but its mechanism of action is not yet clear, and conflicting models have been proposed to explain the effects of the human mutations. Here, we test wild-type and mutant forms of ANK for radiolabeled pyrophosphate-transport activity in frog oocytes. We also reconstruct two human mutations in a bacterial artificial chromosome and test them in transgenic mice for rescue of the Ank null phenotype and for induction of new skeletal phenotypes. Wild-type ANK stimulates saturable transport of pyrophosphate ions across the plasma membrane, with half maximal rates attained at physiological levels of pyrophosphate. Chondrocalcinosis mutations retain apparently wild-type transport activity and can rescue the joint-fusion phenotype of Ank null mice. Craniometaphyseal dysplasia mutations do not transport pyrophosphate and cannot rescue the defects of Ank null mice. Furthermore, microcomputed tomography revealed previously unappreciated phenotypes in Ank null mice that are reminiscent of craniometaphyseal dysplasia. The combination of biochemical and genetic analyses presented here provides insight into how mutations in ANKH cause human skeletal disease.
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Affiliation(s)
- Kyle A Gurley
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
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27
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Abstract
During the past several years, there has been increasing interest in the role of the blood-brain barrier (BBB) in epilepsy. Advances in neuroradiology have enhanced our ability to image and study the human cerebrovasculature, and further developments in the research of metabolic deficiencies linked to seizure disorders (e.g., GLUT1 deficiency), neuroinflammation, and multiple drug resistance to antiepileptic drugs (AEDs) have amplified the significance of the BBB's relationship to epilepsy. Prior to 1986, BBB research in epilepsy focused on three main areas: ultrastructural studies, brain glucose availability and transport, and clinical uses of AEDs. However, contrast-based imaging techniques and medical procedures such as BBB disruption provided a framework that demonstrated that the BBB could be reversibly disrupted by pathologic or iatrogenic manipulations, with important implications in terms of CNS drug delivery to "multiple drug resistant" brain. This concept of BBB breakdown for therapeutic purposes has also unveiled a previously unrecognized role for BBB failure as a possible etiologic mechanism in epileptogenesis. Finally, a growing body of evidence has shown that inflammatory mechanisms may participate in the pathological changes observed in epileptic brain, with increasing awareness that blood-borne cells or signals may participate in epileptogenesis by virtue of a leaky BBB. In this article we will review the relationships between BBB function and epilepsy. In particular, we will illustrate consensus and divergence between clinical reality and animal studies.
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Affiliation(s)
- Emily Oby
- Cleveland Clinic Foundation, Department of Neurological Surgery, Cerebrovascular Research, Ohio 44195, USA
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Hubeek I, Stam RW, Peters GJ, Broekhuizen R, Meijerink JPP, van Wering ER, Gibson BES, Creutzig U, Zwaan CM, Cloos J, Kuik DJ, Pieters R, Kaspers GJL. The human equilibrative nucleoside transporter 1 mediates in vitro cytarabine sensitivity in childhood acute myeloid leukaemia. Br J Cancer 2006; 93:1388-94. [PMID: 16333246 PMCID: PMC2361532 DOI: 10.1038/sj.bjc.6602881] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
Cytarabine (ara-C) is the most effective agent for the treatment of acute myeloid leukaemia (AML). Aberrant expression of enzymes involved in the transport/metabolism of ara-C could explain drug resistance. We determined mRNA expression of these factors using quantitative-real-time-PCR in leukemic blasts from children diagnosed with de novo AML. Expression of the inactivating enzyme pyrimidine nucleotidase-I (PN-I) was 1.8-fold lower in FAB-M5 as compared to FAB-M1/2 (P=0.007). In vitro sensitivity to deoxynucleoside analogues was determined using the MTT-assay. Human equilibrative nucleoside transporter-1 (hENT1) mRNA expression and ara-C sensitivity were significantly correlated (rp=−0.46; P=0.001), with three-fold lower hENT1 mRNA levels in resistant patients (P=0.003). hENT1 mRNA expression also seemed to correlate inversely with the LC50 values of cladribine (rp=−0.30; P=0.04), decitabine (rp=−0.29; P=0.04) and gemcitabine (rp=−0.33; P=0.02). Deoxycytidine kinase (dCK) and cytidine deaminase (CDA) mRNA expression seemed to correlate with in vitro sensitivity to gemcitabine (rp=−0.31; P=0.03) and decitabine (rp=0.33; P=0.03), respectively. The dCK/PN-I ratio correlated inversely with LC50 values for gemcitabine (rp=−0.45, P=0.001) and the dCK/CDA ratio seemed to correlate with LC50 values for decitabine (rp=−0.29; 0.04). In conclusion, decreased expression of hENT1, which transports ara-C across the cell membrane, appears to be a major factor in ara-C resistance in childhood AML.
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Affiliation(s)
- I Hubeek
- Department of Pediatric Hematology/Oncology, VU University Medical Center, De Boelelaan 1117, Postbus 7057, 1007 MB, Amsterdam, The Netherlands.
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29
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Sun W, Khoo HE, Tan CH. Adenosine induced apoptosis in BHK cells via P1 receptors and equilibrative nucleoside transporters. BMB Rep 2005; 38:314-9. [PMID: 15943907 DOI: 10.5483/bmbrep.2005.38.3.314] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Adenosine, as a ubiquitous metabolite, mediates many physiological functions via activation of plasma membrane receptors. Mechanisms of most of its physiological roles have been studied extensively, but research on adenosine-induced apoptosis (AIA) has only started recently. In this study we demonstrate that adenosine dose-dependently triggered apoptosis of cultured baby hamster kidney (BHK) cells. Adenosine-induced apoptotic cell death was characterized by DNA laddering, changes in nuclear chromatin morphology and phosphatidylserine staining. Apoptosis was also quantified by flow cytometry. Results suggest the involvement of adenosine A1 and A3 receptors as well as equilibrative nucleoside transporters in apoptosis induced by adenosine. These results indicate a receptor-transporter co-signaling mechanism in AIA in BHK cells. The involvement of A1 and A3 receptors also implies a possible apoptotic pathway mediated by G protein-coupled receptors.
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Affiliation(s)
- Wentian Sun
- Department of Biochemistry, Faculty of Medicine, National University of Singapore, 10 Kent Ridge Crescent, Singapore, 119260, Republic of Singapore
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30
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Pfeiffer JK, Kirkegaard K. Ribavirin resistance in hepatitis C virus replicon-containing cell lines conferred by changes in the cell line or mutations in the replicon RNA. J Virol 2005; 79:2346-55. [PMID: 15681435 PMCID: PMC546591 DOI: 10.1128/jvi.79.4.2346-2355.2005] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Ribavirin (RBV), used in combination with alpha interferon to treat hepatitis C virus (HCV) infections, is a guanosine nucleotide analog that can increase the error rate of viral RNA-dependent RNA polymerases, imbalance intracellular nucleotide pools, and cause toxicity in many cell types. To determine potential mechanisms of RBV resistance during HCV RNA replication, we passaged HCV replicon-containing cell lines in the presence of increasing concentrations of RBV. RBV-resistant, HCV replicon-containing cell lines were generated, and the majority of RBV resistance was found to be conferred by changes in the cell lines. The resistant cell lines were defective in RBV import, as measured by [(3)H]RBV uptake experiments. These cell lines displayed reduced RBV toxicity and reduced error accumulation during infection with poliovirus, whose replication is known to be sensitive to RBV-induced error. For one RBV-resistant isolate, two mutations in the replicon RNA contributed to the observed phenotype. Two responsible mutations resided in the C-terminal region of NS5A, G404S, and E442G and were each sufficient for low-level RBV resistance. Therefore, RBV resistance in HCV replicon cell lines can be conferred by changes in the cell line or by mutations in the HCV replicon.
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Affiliation(s)
- Julie K Pfeiffer
- Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, CA 94305, USA
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31
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Anderle P, Sengstag T, Mutch DM, Rumbo M, Praz V, Mansourian R, Delorenzi M, Williamson G, Roberts MA. Changes in the transcriptional profile of transporters in the intestine along the anterior-posterior and crypt-villus axes. BMC Genomics 2005; 6:69. [PMID: 15882471 PMCID: PMC1145182 DOI: 10.1186/1471-2164-6-69] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2005] [Accepted: 05/10/2005] [Indexed: 01/03/2023] Open
Abstract
Background The purpose of this work was to characterize the expression of drug and nutrient carriers along the anterior-posterior and crypt-villus axes of the intestinal epithelium and to study the validity of utilizing whole gut tissue rather than purified epithelial cells to examine regional variations in gene expression. Results We have characterized the mRNA expression profiles of 76 % of all currently known transporters along the anterior-posterior axis of the gut. This is the first study to describe the expression profiles of the majority of all known transporters in the intestine. The expression profiles of transporters, as defined according to the Gene Ontology consortium, were measured in whole tissue of the murine duodenum, jejunum, ileum and colon using high-density microarrays. For nine transporters (Abca1, Abcc1, Abcc3, Abcg8, Slc10a2, Slc28a2, Slc2a1, Slc34a2 and Slc5a8), the mRNA profiles were further measured by RT-PCR in laser micro-dissected crypt and villus epithelial cells corresponding to the aforementioned intestinal regions. With respect to differentially regulated transporters, the colon had a distinct expression profile from small intestinal segments. The majority (59 % for p cutoff ≤ 0.05) of transporter mRNA levels were constant across the intestinal sections studied. For the transporter subclass "carrier activity", which contains the majority of known carriers for biologically active compounds, a significant change (p ≤ 0.05) along the anterior-posterior axis was observed. Conclusion All nine transporters examined in laser-dissected material demonstrated good replication of the region-specific profiles revealed by microarray. Furthermore, we suggest that the distribution characteristics of Slc5a8 along the intestinal tract render it a suitable candidate carrier for monocarboxylate drugs in the posterior portion of the intestine. Our findings also predict that there is a significant difference in the absorption of carrier-mediated compounds in the different intestinal segments. The most pronounced differences can be expected between the adjoining segments ileum and colon, but the differences between the other adjoining segments are not negligible. Finally, for the examined genes, profiles measured in whole intestinal tissue extracts are representative of epithelial cell-only gene expression.
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Affiliation(s)
- Pascale Anderle
- ISREC, Swiss Institute for Experimental Cancer Research, 1066 Epalinges s/Lausanne, Switzerland
| | - Thierry Sengstag
- Swiss Institute for Experimental Cancer Research (ISREC) and Swiss Institute of Bioinformatics (SIB), NCCR Molecular Oncology, CH-1066 Epalinges s/Lausanne, Switzerland
| | - David M Mutch
- Nestle Research Center, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland
| | - Martin Rumbo
- ISREC, Swiss Institute for Experimental Cancer Research, 1066 Epalinges s/Lausanne, Switzerland
| | - Viviane Praz
- ISREC and Swiss Institute of Bioinformatics, 1066 Epalinges s/Lausanne, Switzerland
| | - Robert Mansourian
- Nestle Research Center, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland
| | - Mauro Delorenzi
- Swiss Institute for Experimental Cancer Research (ISREC) and Swiss Institute of Bioinformatics (SIB), NCCR Molecular Oncology, CH-1066 Epalinges s/Lausanne, Switzerland
| | - Gary Williamson
- Nestle Research Center, Vers-chez-les-Blanc, 1000 Lausanne 26, Switzerland
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Huang M, Wang Y, Mitchell BS, Graves LM. Regulation of equilibrative nucleoside uptake by protein kinase inhibitors. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2005; 23:1445-50. [PMID: 15571274 DOI: 10.1081/ncn-200027667] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The uptake of nucleosides and nucleoside analogs into human leukemia K562 cells is facilitated by the equilibrative transporters ENT1 and ENT2. Incubation of K562 cells with a variety of protein kinase inhibitors inhibited the transport of both uridine (ARA-C) and cytidine (CPEC) analogs. These inhibitory effects were observed for a large number of kinase inhibitors including those against p38 MAPK, the EGF receptor kinase, protein kinase C, TOR and others. Thus these results suggest that the nucleoside transporters are unexpected targets for kinase inhibitors and may influence the design and application of combinatorial approaches of nucleoside analogs and kinase inhibitors in clinical applications.
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Affiliation(s)
- Min Huang
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA
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Kato R, Maeda T, Akaike T, Tamai I. Nucleoside Transport at the Blood-Testis Barrier Studied with Primary-Cultured Sertoli Cells. J Pharmacol Exp Ther 2004; 312:601-8. [PMID: 15547112 DOI: 10.1124/jpet.104.073387] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nucleosides are essential for nucleotide synthesis in testicular spermatogenesis. In the present study, the mechanism of the supply of nucleosides to the testicular system across the blood-testis barrier was studied using primary-cultured Sertoli cells from rats and TM4 cells from mice. Uptake of uridine by these cells was time- and concentration-dependent. Uridine uptake was decreased under Na(+)-free conditions, and the system was presumed to be high affinity, indicating an Na(+)-dependent concentrative nucleoside transporter (CNT) is involved. On the other hand, nitrobenzylthioinosine, a potent inhibitor of Na(+)-independent equilibrative nucleoside transporters (ENTs), inhibited uridine uptake by the Sertoli cells in a concentration-dependent manner. Expression of nucleoside transporters ENT1, ENT2, ENT3, CNT1, CNT2, and CNT3 was detected in Sertoli cells by reverse transcriptase-polymerase chain reaction analysis. Inhibition studies of the uptake of uridine by various nucleosides both in the presence and absence of Na(+) indicated that the most of those expressed nucleoside transporters, ENTs and CNTs, are involved functionally. These results demonstrated that Sertoli cells are equipped with multiple nucleoside transport systems, including ENT1, ENT2, and CNTs, to provide nucleosides for spermatogenesis.
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Affiliation(s)
- Ryo Kato
- Department of Molecular Biopharmaceutics, Faculty of Pharmaceutical Sciences, Tokyo University of Science, 2641 Yamasaki, Noda, Chiba 278-8510, Japan
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Wormit A, Traub M, FLöRCHINGER M, Neuhaus H, MöHLMANN T. Characterization of three novel members of the Arabidopsis thaliana equilibrative nucleoside transporter (ENT) family. Biochem J 2004; 383:19-26. [PMID: 15228386 PMCID: PMC1134039 DOI: 10.1042/bj20040389] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2004] [Revised: 06/29/2004] [Accepted: 06/30/2004] [Indexed: 11/17/2022]
Abstract
Research on metabolism of nucleotides and their derivatives has gained increasing interest in the recent past. This includes de novo synthesis, analysis of salvage pathways, breakdown and transport of nucleotides, nucleosides and nucleobases. To perform a further step towards the analysis of nucleoside transport in Arabidopsis, we incubated leaf discs with various radioactively labelled nucleosides. Leaf cells imported labelled nucleosides and incorporated these compounds into RNA, but not into DNA. Furthermore, we report on the biochemical properties of three so far uncharacterized members of the Arabidopsis ENT (equilibrative nucleoside transporter) family (AtENT4, AtENT6 and AtENT7). After heterologous expression in yeast, all three proteins exhibited broad substrate specificity and transported the purine nucleosides adenosine and guanosine, as well as the pyrimidine nucleosides cytidine and uridine. The apparent K(m) values were in the range 3-94 microM, and transport was inhibited most strongly by deoxynucleosides, and to a smaller extent by nucleobases. Typical inhibitors of mammalian ENT proteins, such as dilazep and NBMPR (nitrobenzylmercaptopurine ribonucleoside, also known as nitrobenzylthioinosine) surprisingly exerted almost no effect on Arabidopsis ENT proteins. Transport mediated by the AtENT isoforms differed in pH-dependency, e.g. AtENT7 was not affected by changes in pH, AtENT3, 4 and 6 exhibited a less pronounced pH-dependency, and AtENT1 activity was clearly pH-dependent. Using a GFP (green fluorescent protein)-fusion protein transiently expressed in tobacco leaf protoplasts, a localization of AtENT6 in the plant plasma membrane has been revealed.
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Affiliation(s)
- Alexandra Wormit
- Universität Kaiserslautern, Pflanzenphysiologie, Postfach 3049, D-67653 Kaiserslautern, Germany
| | - Michaela Traub
- Universität Kaiserslautern, Pflanzenphysiologie, Postfach 3049, D-67653 Kaiserslautern, Germany
| | - Martin FLöRCHINGER
- Universität Kaiserslautern, Pflanzenphysiologie, Postfach 3049, D-67653 Kaiserslautern, Germany
| | - H. Ekkehard Neuhaus
- Universität Kaiserslautern, Pflanzenphysiologie, Postfach 3049, D-67653 Kaiserslautern, Germany
| | - Torsten MöHLMANN
- Universität Kaiserslautern, Pflanzenphysiologie, Postfach 3049, D-67653 Kaiserslautern, Germany
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Abstract
Neuronal responses to alcohol involve several hormone- and neurotransmitter-activated signal transduction pathways. Recent studies suggest that the adenosine A2 receptor (A2) mediates important actions of alcohol. Ethanol inhibits adenosine reuptake, increases extracellular adenosine, and promotes activation of A2. This leads to enhanced cAMP/protein kinase A (PKA) signaling ranging from increases in cAMP to stimulation of cAMP-dependent cAMP response element (CRE)-mediated gene expression. Medium spiny neurons in the striatum/nucleus accumbens (NAc) express A2 and dopamine D2 receptor (D2) on the same cells. Studies in model neuronal cell lines and primary neurons in culture expressing A2 and D2 provide evidence for synergy between ethanol/A2 and D2. Subthreshold concentrations of ethanol or a D2 agonist, without effect separately, synergistically activate cAMP/PKA signaling. Thus, neurons expressing A2 and D2 on the same cells, like in the NAc, are characterized by hypersensitivity to ethanol with a simultaneous activation of dopaminergic signaling. Synergy requires adenosine and appears to be mediated by the release of free betagamma dimers from G(i/o) via D2 activation. The release of free betagamma has pathophysiological significance in the drinking animal because specific blockade of betagamma signaling in the NAc strikingly reduces voluntary alcohol consumption. These findings suggest that signaling pathways, which regulate synergy between A2 and D2, might contain molecular targets for the prevention and treatment of alcoholism and alcohol abuse.
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Affiliation(s)
- William S Mailliard
- Ernest Gallo Clinic and Research Center, University of California, San Francisco, 5858 Horton Street, Suite 200, , Emeryville, CA 94608, USA
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Abstract
Many cell types in the kidney express adenosine receptors, and adenosine has multiple effects on renal function. Although adenosine is produced within the kidney by several biochemical reactions, recent studies support a novel mechanism for renal adenosine production, the extracellular cAMP-adenosine pathway. This extracellular cAMP-adenosine pathway is initiated by efflux of cAMP from cells following activation of adenylyl cyclase. Extracellular cAMP is then converted to adenosine by the serial actions of ecto-phosphodiesterase and ecto-5'-nucleotidase. When extracellular cAMP is converted to adenosine near the biophase of cAMP production and efflux, this local extracellular cAMP-adenosine pathway permits tight coupling of the site of adenosine production to the site of adenosine receptors. cAMP in renal compartments may also be formed by tissues/organs remote from the kidney. For example, stimulation of hepatic adenylyl cyclase by the pancreatic hormone glucagon increases circulating cAMP, which is filtered at the glomerulus and concentrated in the tubular lumen as water is extracted from the ultrafiltrate. Conversion of hepatic-derived cAMP to adenosine in the kidney completes a pancreatohepatorenal cAMP-adenosine pathway that may serve as an endocrine link between the pancreas, liver, and kidney.
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Affiliation(s)
- Edwin K Jackson
- Center for Clinical Pharmacology, Department of Pharmacology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA. edj+@pitt.edu
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Lang TT, Young JD, Cass CE. Interactions of Nucleoside Analogs, Caffeine, and Nicotine with Human Concentrative Nucleoside Transporters 1 and 2 Stably Produced in a Transport-Defective Human Cell Line. Mol Pharmacol 2004; 65:925-33. [PMID: 15044622 DOI: 10.1124/mol.65.4.925] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Pharmacologically important drugs were examined as potential inhibitors or permeants of human concentrative nucleoside transporters 1 (hCNT1)- and 2 (hCNT2)-producing stable transfectants by assessing their abilities to inhibit uridine transport. hCNT1 exhibited high affinities for uridine analogs (5-fluorouridine, 2'-deoxyuridine, 5-fluoro-2'-deoxyuridine, and 5-fluoro-5'-deoxyuridine) with K(i) values of 22 to 33 microM, whereas hCNT2 exhibited moderate affinities for 5-fluoro-2'-deoxyuridine, high affinities for 2'-deoxyuridine and 5-fluorouridine, and low affinity for 5-fluoro-5'-deoxyuridine. The uridine analogs were transported at 2-fold higher rates (at 10 microM) by hCNT1 than by hCNT2. Enantiomeric configuration and the 3'-hydroxyl group of the ribose ring were important determinants for interaction with hCNTs, whereas the 2'-hydroxyl group was less important. Both transporters bound N(6)-(p-aminobenzyl)adenosine with affinities similar to those of adenosine (K(i) = 28-39 microM). Other adenosine receptor ligands, including caffeine, bound better to hCNT1 than to hCNT2 (K(i) = 46 versus 103 microM, respectively), whereas 2-chloroadenosine bound better to hCNT2 than to hCNT1 (K(i) = 37 and 101 microM, respectively). There was a greater than 3-fold difference in binding affinities between hCNT1 and hCNT2 for nicotine (K(i) = 63 versus 227 microM). However, direct measurements of nicotine and caffeine uptake rates (10 microM) failed to demonstrate mediated uptake by either transporter. Although hCNT1 bound several adenosine analogs relatively well, it did not transport 2-chloro-2'-deoxyadenosine (cladribine) or 2-fluoro-9-beta-d-arabinofuranosyladenine (fludarabine), whereas hCNT2 transported both, albeit with low activities. The results indicated that although hCNT1 and hCNT2 possess some overlap in transport of several uridine and adenosine analogs, they also exhibit distinct differences in capacity to interact with some adenosine receptor ligands, adenosine-based drugs, and nicotine.
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Affiliation(s)
- Thack T Lang
- Canadian Institutes of health Research Molecular Biology of membranes Group, University of Alberta, Alberta, Canada T6G 1Z2
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Chang C, Swaan PW, Ngo LY, Lum PY, Patil SD, Unadkat JD. Molecular requirements of the human nucleoside transporters hCNT1, hCNT2, and hENT1. Mol Pharmacol 2004; 65:558-70. [PMID: 14978234 DOI: 10.1124/mol.65.3.558] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Concentrative nucleoside transporters (CNTs) and equilibrative nucleoside transporters (ENTs) are important in physiological and pharmacological activity and disposition of nucleosides and nucleoside drugs. A better understanding of the structural requirements of inhibitors for these transporters will aid in designing therapeutic agents. To define the relative and unified structural requirements of nucleoside analogs for interaction with hCNT1, hCNT2, and hENT1, we applied an array of structure-activity techniques. Unique pharmacophore models for each respective nucleoside transporter were generated. These models reveal that hCNT2 affinity is dominated by hydrogen bonding features, whereas hCNT1 and hENT1 displayed mainly electrostatic and steric features. Hydrogen bond formation over 3'-OH is essential for all nucleoside transporters. Inhibition of nucleoside transporters by a series of uridine and adenosine analogs and a variety of drugs was analyzed by comparative molecular field analysis. Cross-validated r2 (q2) values were 0.65, 0.52, and 0.74 for hCNT1, hCNT2, and hENT1, respectively. The predictive quality of the models was further validated by successful prediction of the inhibition of a set of test compounds. Addition of a hydroxyl group around the 2-position of purine (or 3-position of pyrimidine) may increase inhibition to hCNT2 transporter; addition of hydroxyl group around the 2,7-position of purine (or the 3,5-position of pyrimidine) would increase the inhibition to hENT1 transporter. Utilization of these models should assist the design of high-affinity nucleoside transporter inhibitors and substrates for both anticancer and antiviral therapy.
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Affiliation(s)
- C Chang
- Biophysics Program, the Ohio State University, Columbus, USA
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Duarte-Araújo M, Nascimento C, Alexandrina Timóteo M, Magalhães-Cardoso T, Correia-de-Sá P. Dual effects of adenosine on acetylcholine release from myenteric motoneurons are mediated by junctional facilitatory A(2A) and extrajunctional inhibitory A(1) receptors. Br J Pharmacol 2004; 141:925-34. [PMID: 14993098 PMCID: PMC1574269 DOI: 10.1038/sj.bjp.0705697] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2003] [Revised: 11/30/2003] [Accepted: 01/13/2004] [Indexed: 11/08/2022] Open
Abstract
1. The coexistence of both inhibitory A(1) and facilitatory A(2) adenosine receptors in the rat myenteric plexus prompted the question of how adenosine activates each receptor subtype to regulate cholinergic neurotransmission. 2. Exogenously applied adenosine (0.3-300 microm) decreased electrically evoked [(3)H]acetylcholine ([(3)H]ACh) release. Blocking A(1) receptors with 1,3-dipropyl-8-cyclopentylxanthine (10 nm) transformed the inhibitory action of adenosine into a facilitatory effect. Adenosine-induced inhibition was mimicked by the A(1) receptor agonist R-N(6)-phenylisopropyladenosine (0.3 microm), but the A(2A) agonist CGS 21680C (0.003 microm) produced a contrasting facilitatory effect. 3. Increasing endogenous adenosine levels, by the addition of (1) the adenosine precursor AMP (30-100 microm), (2) the adenosine kinase inhibitor 5'-iodotubercidin (10 microm) or (3) inhibitors of adenosine uptake (dipyridamole, 0.5 microm) and of deamination (erythro-9(2-hydroxy-3-nonyl)adenine, 50 microm), enhanced electrically evoked [(3)H]ACh release (5 Hz for 40 s). Release facilitation was prevented by adenosine deaminase (ADA, 0.5 U ml(-1)) and by the A(2A) receptor antagonist ZM 241385 (50 nm); these compounds decreased [(3)H]ACh release by 31+/-6% (n=7) and 37+/-10% (n=6), respectively. 4. Although inhibition of ecto-5'-nucleotidase by alpha,beta-methylene ADP (200 microm) or by concanavalin A (0.1 mg ml(-1)) attenuated endogenous adenosine formation from AMP, analysed by HPLC, the corresponding reduction in [(3)H]ACh release only became evident when stimulation of the myenteric plexus was prolonged to over 250 s. 5. In summary, we found that endogenously generated adenosine plays a predominantly tonic facilitatory effect mediated by prejunctional A(2A) receptors. Extracellular deamination and cellular uptake may restrict endogenous adenosine actions to the neuro-effector region near the release/production sites.
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Affiliation(s)
- Margarida Duarte-Araújo
- Laboratório de Farmacologia/UMIB, Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, L. Prof. Abel Salazar, 2, 4099-003 Porto, Portugal
| | - Carlos Nascimento
- Laboratório de Farmacologia/UMIB, Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, L. Prof. Abel Salazar, 2, 4099-003 Porto, Portugal
| | - M Alexandrina Timóteo
- Laboratório de Farmacologia/UMIB, Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, L. Prof. Abel Salazar, 2, 4099-003 Porto, Portugal
| | - Teresa Magalhães-Cardoso
- Laboratório de Farmacologia/UMIB, Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, L. Prof. Abel Salazar, 2, 4099-003 Porto, Portugal
| | - Paulo Correia-de-Sá
- Laboratório de Farmacologia/UMIB, Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, L. Prof. Abel Salazar, 2, 4099-003 Porto, Portugal
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Abstract
Carrier-mediated processes, often referred to as transporters, play key roles in the reabsorption and secretion of many endogenous and xenobiotic compounds by the kidney. The renal proximal tubule is the primary site of active transport for a wide variety of substrates, including organic anions/cations, peptides, and nucleosides. During the past decade, significant advances in molecular identification and characterization of transporter proteins have been made. Although it is generally noted that these transporters significantly contribute to renal drug handling and variability in drug disposition, the extent of our knowledge regarding the specific roles of such transporters in drug disposition and drug-drug interactions remains, for the most part, limited. In this review, we summarize recent progress in terms of molecular and functional characterization of renal transporters and their clinical relevance to drug therapy.
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Affiliation(s)
- Wooin Lee
- Division of Clinical Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-6602, USA
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41
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de Boer AG, van der Sandt ICJ, Gaillard PJ. The role of drug transporters at the blood-brain barrier. Annu Rev Pharmacol Toxicol 2003; 43:629-56. [PMID: 12415123 DOI: 10.1146/annurev.pharmtox.43.100901.140204] [Citation(s) in RCA: 140] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The blood-brain barrier (BBB) is a dynamic interface between the blood and the brain. It eliminates (toxic) substances from the endothelial compartment and supplies the brain with nutrients and other (endogenous) compounds. It can be considered as an organ protecting the brain and regulating its homeostasis. Until now, many transport systems have been discovered that play an important role in maintaining BBB integrity and brain homeostasis. In this review, we focus on the role of carrier- and receptor-mediated transport systems (CMT, RMT) at the BBB. These include CMT systems, such as P-glycoprotein, multidrug-resistance proteins 1-7, nucleoside transporters, organic anion transporters, and large amino-acid transporters; RMT systems, such as the transferrin-1 and -2 receptors; and the scavenger receptors SB-AI and SB-BI.
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Affiliation(s)
- A G de Boer
- Blood-Brain Barrier Research Group, Division of Pharmacology, Leiden/Amsterdam Center for Drug Research, University of Leiden, The Netherlands.
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42
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Abstract
The tubuloglomerular feedback response, the change in afferent arteriolar tone caused by a change in NaCl concentration at the macula densa, is likely initiated by the generation of a vasoactive mediator within the confines of the juxtaglomerular apparatus. Substantial progress has been made in identifying the nature of this mediator and the factors that modulate its effect on vascular tone. In support of earlier studies using P1 purinergic antagonists, the application of the knockout technique has shown that adenosine 1 receptors are absolutely required for eliciting TGF responses. The background level of angiotensin II appears to be an important cofactor determining the efficiency of A1AR-induced vasoconstriction, probably through a synergistic interaction at the level of the G protein-dependent transduction mechanism. The source of the adenosine is still unclear, but it is conceivable that adenosine is generated extracellularly from released ATP through a cascade of ecto-nucleotidases. There is also evidence that ATP may activate P2 receptors in preglomerular vessels, which may contribute to autoregulation of renal vascular resistance. Nitric oxide (NO), generated by the neuronal isoform of nitric oxide synthase in macula densa cells, reduces the constrictor effect of adenosine, but the regulation of NO release and its exact role in states of TGF-induced hyperfiltration are still unclear.
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Affiliation(s)
- Jürgen Schnermann
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-1370, USA.
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Nagai K, Nagasawa K, Ishimoto A, Fujimoto S. Pirarubicin is taken up by a uridine-transportable sodium-dependent concentrative nucleoside transporter in Ehrlich ascites carcinoma cells. Cancer Chemother Pharmacol 2003; 51:512-8. [PMID: 12679883 DOI: 10.1007/s00280-003-0569-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2002] [Accepted: 12/13/2002] [Indexed: 11/28/2022]
Abstract
PURPOSE We evaluated the contribution of a nucleoside transporter (NT) consisting of an equilibrative NT (ENT) and a concentrative Na(+)/nucleoside cotransporter (CNT) to the uptake of THP and DOX by mouse Ehrlich ascites carcinoma cells. METHODS. Transport experiments were performed using a silicone layer method. The expression of CNT isoforms was confirmed by RT-PCR analysis. RESULTS The effects of inhibition of the ENT inhibitors, nitrobenzylthioinosine (NBMPR) and nitrobenzylthioguanosine, on THP and DOX uptake by Ehrlich cells was negligible. THP uptake, but not DOX uptake, partially depended on an inwardly directed Na(+) gradient, and the uptake was inhibited by all the inhibitors of CNT examined. Furthermore, efflux of [(3)H]uridine from Ehrlich cells was stimulated by the addition of THP to the extracellular compartment, which was definitive evidence of CNT-mediated uptake of THP. The mRNA for CNT2, but not that for CNT3, was detected in Ehrlich cells, which is consistent with the characteristics of [(3)H]uridine uptake. In the cells, formycin B, a representative CNT2 ligand, had cis-inhibitory and trans-stimulatory effects on THP uptake. CONCLUSION These results demonstrate that THP, but not DOX, is taken up into Ehrlich cells partially via a uridine-transportable CNT.
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Affiliation(s)
- Katsuhito Nagai
- Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, 607-8414, Kyoto, Japan
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Flanagan SA, Meckling KA. All- trans-retinoic acid increases cytotoxicity of 1-beta-D-arabinofuranosylcytosine in NB4 cells. Cancer Chemother Pharmacol 2003; 51:363-75. [PMID: 12736759 DOI: 10.1007/s00280-002-0561-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2002] [Accepted: 11/01/2002] [Indexed: 10/25/2022]
Abstract
PURPOSE Clinically, the benefits of combining all- trans-retinoic acid (ATRA) with chemotherapy have been well documented in the treatment of acute promyelocytic leukemia (APL). Changes in nucleoside transporter expression and activity have been shown to occur in NB4 cells in vitro following treatment with ATRA. In this study we investigated whether ATRA treatment increases sensitivity to ara-C in NB4 cells. Specifically, we examined the role of ATRA-associated changes in nucleoside transporter expression and activity in eliciting ara-C cytotoxicity. METHODS Cellular uptake of [(3)H]-ara-C and nucleoside transporter abundance were determined in untreated cells and cells treated with 1 microM ATRA for 12-72 h using an inhibitor and oil stop procedure, and an equilibrium [(3)H]-NBMPR binding assay, respectively. Cytotoxicity of ara-C and the apoptotic response prior to and following ATRA treatment were determined using the MTT viability assay and the TUNEL assay, respectively. RESULTS ATRA treatment increased ara-C cytotoxicity and potency, ara-C transport, and augmented ara-C-induced apoptosis. The combination effect was supraadditive under some conditions and sequence-dependent whereby the maximum effect was seen when the addition of ATRA preceded the addition of ara-C, and when ara-C administration closely followed ATRA administration. CONCLUSIONS The ATRA-induced increase in cytotoxicity of ara-C was, in part, the result of an increase in the functional expression of nucleoside transporters, and a role for bcl-2 was also indicated. Our results would suggest that timing of ara-C therapy should be tied to maximal es transporter expression, which is likely to be 24 h after ATRA treatment begins. It remains to be seen whether the response in the clinic can be further enhanced in APL by taking advantage of ara-C transporter regulation by ATRA.
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Affiliation(s)
- S A Flanagan
- Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
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Alcorn J, Lu X, Moscow JA, McNamara PJ. Transporter gene expression in lactating and nonlactating human mammary epithelial cells using real-time reverse transcription-polymerase chain reaction. J Pharmacol Exp Ther 2002; 303:487-96. [PMID: 12388627 DOI: 10.1124/jpet.102.038315] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Transporter-mediated processes in the lactating mammary gland may explain the significant accumulation of certain drugs in breast milk. The purpose of this study was to identify potential candidate drug transport proteins involved in drug accumulation in milk. Quantitative reverse transcription-polymerase chain reaction methods were developed to determine the relative RNA levels of 30 different drug transporter genes. Transporter gene RNA levels in lactating mammary epithelial cells (MEC) purified from pooled fresh breast milk samples were compared with levels in nonlactating MEC, liver, and kidney tissue. Transcripts were detected in lactating MEC for OCT1, OCT3, OCTN1, OCTN2, OATP-A, OATP-B, OATP-D, OATP-E, MRP1, MRP2, MRP5, MDR1, CNT1, CNT3, ENT1, ENT3, NCBT1, PEPT1, and PEPT2. No transcripts were detected for OCT2, OAT1, OAT2, OAT3, OAT4, OATP-C, MRP3, MRP4, CNT2, ENT2, and NCBT2. Lactating MEC demonstrated more than 4-fold higher RNA levels of OCT1, OCTN1, PEPT2, CNT1, CNT3, and ENT3, and more than 4-fold lower RNA levels of MDR1 and OCTN2 relative to nonlactating MEC. Lactating MEC showed significantly higher RNA levels of CNT3 relative to liver and kidney, increased PEPT2 RNA levels relative to liver, and increased OATP-A RNA levels relative to kidney. These data imply CNT3 may play a specialized role in nucleoside accumulation in milk and may identify an important role for PEPT2 and OATP-A transporters at the lactating mammary epithelium. Furthermore, transporters expressed in lactating MEC identify a potential role for these transporters in drug disposition at the mammary gland.
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Affiliation(s)
- J Alcorn
- Division of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Rose Street, Lexington, KY 40536-0082, USA
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46
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Gerk PM, Hanson L, Neville MC, McNamara PJ. Sodium dependence of nitrofurantoin active transport across mammary epithelia and effects of dipyridamole, nucleosides, and nucleobases. Pharm Res 2002; 19:299-305. [PMID: 11934237 DOI: 10.1023/a:1014495018640] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE The sodium dependence and effects of nucleoside and nucleobase transport inhibitors were determined to ascertain the role of sodium dependent nucleoside or nucleobase transporters in nitrofurantoin active transport across mammary epithelia. METHODS Five lactating female rats received steady-state intravenous infusions of nitrofurantoin with and without the broad-based inhibitor dipyridamole. In the CIT3 murine model of lactation, 14C-nitrofurantoin basolateral to apical permeability was examined in the presence of varying sodium concentrations, purine and pyrimidine nucleosides and nucleobases, and dipyridamole. RESULTS Dipyridamole effectively inhibited 14C-nitrofurantoin flux across CIT3 cells, with Ki = 0.78 microM (95% C.I. = 0.11 to 5.3 microM) and significantly decreased the milk-to-serum ratio of nitrofurantoin from 29.2 +/- 5.0 to 11.0 +/- 6.3 without changing systemic clearance. Nitrofurantoin active transport was significantly inhibited by complete sodium replacement. Adenosine and guanosine significantly inhibited nitrofurantoin permeability (54.5 +/- 2.6 (microl/hr)/cm2 and 50.7 +/- 0.6 (microl/hr)/cm2, respectively, vs. control 90.5 +/- 4.6 (microl/hr)/cm2) but uridine, thymidine, and the nucleobases had no effect. CONCLUSIONS Nitrofurantoin active transport was sodium dependent and inhibited by dipyridamole, adenosine, and guanosine, but known sodium dependent nucleoside or nucleobase transporters were not involved.
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Affiliation(s)
- Phillip M Gerk
- University of Kentucky College of Pharmacy, Division of Pharmaceutical Science Lexington, 40536-0082, USA
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47
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Koshiba M, Kosaka H, Nakazawa T, Hayashi N, Saura R, Kitamura N, Kumagai S. 2-Chloroadenosine but not adenosine induces apoptosis in rheumatoid fibroblasts independently of cell surface adenosine receptor signalling. Br J Pharmacol 2002; 135:1477-86. [PMID: 11906961 PMCID: PMC1573274 DOI: 10.1038/sj.bjp.0704612] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. The apoptotic effect of adenosine and its analogues was studied in fibroblast-like synoviocytes derived from rheumatoid arthritis patients (RA-FLSs). Evoked cell death was quantitatively examined by assessing DNA fragmentation using an enzyme-liked immunosorbent assay and by measuring phosphatidylserine exposure through flow cytometric analysis of annexin V binding. 2. Exposing cells for 24 h to 2-chloroadenosine (2-CADO), a nonspecific, adenosine deaminase (ADA)-resistant, adenosine receptor (AdoR) agonist, induced DNA fragmentation, and thus apoptosis, in RA-FLSs at concentrations > or =50 microM. By contrast, incubation with adenosine for up to 72 h did not evoke DNA fragmentation, even in the presence of ADA inhibitor coformycin and nucleoside transporter inhibitor nitrobenzylmercaptopurin (NBMPR). Transcription of all four AdoR isoforms was detected in RA-FLSs; nevertheless selective AdoR agonists similarly failed to induce DNA fragmentation. 3. DNA fragmentation evoked by 2-CADO was inhibited by NBMPR and by 5'-iodotubercidin, an adenosine kinase inhibitor, but not by xanthine amine congener, an A(1) and A(2) receptor antagonist, or by selective AdoR antagonists. 4. The nonspecific caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone abolished the apoptotic effect of 2-CADO. 5. These results suggest that 2-CADO induces apoptosis in RA-FLSs independently of AdoR-mediated signalling. Instead, 2-CADO, but not adenosine, is taken up into RA-FLSs via human equilibrative nucleoside transporter-1, where it is phosphorylated by adenosine kinase. The resultant phospho-2-CADO induces DNA fragmentation by activating a caspase pathway.
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Affiliation(s)
- Masahiro Koshiba
- Clinical Pathology and Immunology, Department of Biomedical Informatics, Kobe University Graduate School of Medicine, Kobe, Japan.
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48
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Tenser RB, Gaydos A, Hay KA. Inhibition of herpes simplex virus reactivation by dipyridamole. Antimicrob Agents Chemother 2001; 45:3657-9. [PMID: 11709364 PMCID: PMC90893 DOI: 10.1128/aac.45.12.3657-3659.2001] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Herpes simplex virus (HSV) reactivation from latency was investigated. Reactivation of thymidine kinase-negative HSV, which is defective for reactivation, was greatly enhanced by thymidine (TdR). The reactivation-enhancing effect of TdR was blocked by dipyridamole (DPM), a known nucleoside transport inhibitor. DPM also inhibited wild-type HSV reactivation, suggesting potential antiviral use.
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Affiliation(s)
- R B Tenser
- Division of Neurology and Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
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Sinclair CJD, Powell AE, Xiong W, LaRivière CG, Baldwin SA, Cass CE, Young JD, Parkinson FE. Nucleoside transporter subtype expression: effects on potency of adenosine kinase inhibitors. Br J Pharmacol 2001; 134:1037-44. [PMID: 11682452 PMCID: PMC1573041 DOI: 10.1038/sj.bjp.0704349] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1. Adenosine kinase (AK) inhibitors can enhance adenosine levels and potentiate adenosine receptor activation. As the AK inhibitors 5' iodotubercidin (ITU) and 5-amino-5'-deoxyadenosine (NH(2)dAdo) are nucleoside analogues, we hypothesized that nucleoside transporter subtype expression can affect the potency of these inhibitors in intact cells. 3. Three nucleoside transporter subtypes that mediate adenosine permeation of rat cells have been characterized and cloned: equilibrative transporters rENT1 and rENT2 and concentrative transporter rCNT2. We stably transfected rat C6 glioma cells, which express rENT2 nucleoside transporters, with rENT1 (rENT1-C6 cells) or rCNT2 (rCNT2-C6 cells) nucleoside transporters. 3. We tested the effects of ITU and NH(2)dAdo on [(3)H]-adenosine uptake and conversion to [(3)H]-adenine nucleotides in the three cell types. NH(2)dAdo did not show any cell type selectivity. In contrast, ITU showed significant inhibition of [(3)H]-adenosine uptake and [(3)H]-adenine nucleotide formation at concentrations < or =100 nM in rENT1-C6 cells, while concentrations > or =3 microM were required for C6 or rCNT2-C6 cells. 4. Nitrobenzylthioinosine (NBMPR; 100 nM), a selective inhibitor of rENT1, abolished the effects of nanomolar concentrations of ITU in rENT1-C6 cells. 5. This study demonstrates that the effects of ITU, but not NH(2)dAdo, in whole cell assays are dependent upon nucleoside transporter subtype expression. Thus, cellular and tissue differences in expression of nucleoside transporter subtypes may affect the pharmacological actions of some AK inhibitors.
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Affiliation(s)
- C J D Sinclair
- Department of Pharmacology and Therapeutics, University of Manitoba; Winnipeg, Canada R3E 0T6
| | - A E Powell
- Department of Pharmacology and Therapeutics, University of Manitoba; Winnipeg, Canada R3E 0T6
| | - W Xiong
- Department of Pharmacology and Therapeutics, University of Manitoba; Winnipeg, Canada R3E 0T6
| | - C G LaRivière
- Department of Pharmacology and Therapeutics, University of Manitoba; Winnipeg, Canada R3E 0T6
| | - S A Baldwin
- School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT
| | - C E Cass
- Membrane Transport Group, University of Alberta, Edmonton, Canada T6G 2H7
| | - J D Young
- Membrane Transport Group, University of Alberta, Edmonton, Canada T6G 2H7
| | - F E Parkinson
- Department of Pharmacology and Therapeutics, University of Manitoba; Winnipeg, Canada R3E 0T6
- Author for correspondence:
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50
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Lang TT, Selner M, Young JD, Cass CE. Acquisition of human concentrative nucleoside transporter 2 (hcnt2) activity by gene transfer confers sensitivity to fluoropyrimidine nucleosides in drug-resistant leukemia cells. Mol Pharmacol 2001; 60:1143-52. [PMID: 11641443 DOI: 10.1124/mol.60.5.1143] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
CEM-ARAC leukemia cells with resistance to cytarabine were shown to lack equilibrative transporter (hENT1) expression and activity. Stable transfer of hCNT2 cDNA into CEM-ARAC enabled Na(+)-dependent transport of purine and pyrimidine nucleoside analogs and provided a unique in vitro model for studying hCNT2. Analysis of [(3)H]uridine inhibitory activity by test substances in hCNT2 transfectant ARAC/D2 revealed structural requirements for interaction with hCNT2: 1) ribosyl and 2'-deoxyribosyl nucleosides were better inhibitors than 3'-deoxyribosyl, 2',3'-dideoxyribosyl or arabinosyl nucleosides; 2) uridine analogs with halogens at position 5 were better inhibitors than 5-methyluridine or thymidine; 3) 2-chloroadenosine was a better inhibitor than 2-chloro-2'-deoxyadenosine (cladribine); and 4) cytosine-containing nucleosides, 7-deazaadenosine and nucleobases were not inhibitors. Quantification of inhibitory capacity yielded K(i) values of 34-50 microM (5-halogenated uridine analogs, 2'-deoxyuridine), 82 microM (5-fluoro-2'-deoxyuridine), 197-246 microM (5-methyluridine < 5-bromo-2'-deoxyuridine < 5-iodo-2'-deoxyuridine), and 411 microM (5-fluoro-5'-deoxyuridine, capecitabine metabolite). Comparisons of hCNT2-mediated transport rates indicated halogenated uridine analogs were transported more rapidly than halogenated adenosine analogs, even though hCNT2 exhibited preference for physiologic purine nucleosides over uridine. Kinetics of hCNT2-mediated transport of 5-fluorouridine and uridine were similar (K(m) values, 43-46 microM). The impact of hCNT2-mediated transport on chemosensitivity was assessed by comparing antiproliferative activity of nucleoside analogs against hCNT2-containing cells with transport-defective, drug-resistant cells. Chemosensitivity was restored partially for cladribine, completely for 5-fluorouridine and 5-fluoro-2'-deoxyuridine, whereas there was little effect on chemosensitivity for fludarabine, 7-deazaadenosine, or cytarabine. These studies, which demonstrated hCNT2 uptake of halogenated uridine analogs, suggested that hCNT2 is an important determinant of cytotoxicity of this class of compounds in vivo.
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Affiliation(s)
- T T Lang
- Canadian Institute of Health Research Membrane Protein Research Group, University of Alberta
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