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Naes SM, Ab-Rahim S, Mazlan M, Amir Hashim NA, Abdul Rahman A. Increased ENT2 expression and its association with altered purine metabolism in cell lines derived from different stages of colorectal cancer. Exp Ther Med 2023; 25:212. [PMID: 37123217 PMCID: PMC10133795 DOI: 10.3892/etm.2023.11911] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Accepted: 02/21/2023] [Indexed: 05/02/2023] Open
Abstract
Colorectal cancer (CRC) is one of the most prevalent malignant cancer types worldwide. Although the purine metabolism pathway is vital for cancer cell survival, little is known about the role of equilibrative nucleoside transporter 2 (ENT2) in CRC development and its association with purine metabolites. The aim of the present study was to evaluate the levels of hypoxanthine phosphoribosyl transferase (HPRT), hypoxanthine and uric acid (UA), as well as xanthine oxidase (XO) activity, and investigate their association with ENT2 expression levels in a normal human colon cell line and CRC cell lines derived from different stages of CRC. These analyses were performed using the normal colon CCD-841CoN cell line and a panel of human CRC cell lines comprising SW480, HCT15 and HCT116, which represent Dukes' B, C and D stages, respectively. Reverse transcription-quantitative PCR was performed to determine the level of ENT2 mRNA expression. In cells of all CRC stages, the levels of HPRT and hypoxanthine were significantly higher (P<0.05), while XO activity and UA levels were significantly decreased (P<0.05), compared with those in the CCD-841CoN cell line. ENT2 expression was found to be elevated in cells derived from all stages of CRC. The Dukes' D stage cell line had higher levels of HPRT and hypoxanthine, although its ENT2 level was not significantly lower than that of the Dukes' B and C stage cell lines. Increased levels of HPRT and hypoxanthine in various stages of CRC may indicate an increase in the activity of the salvage pathway. The increased expression of ENT2 implies the importance of the ENT2 protein in facilitating hypoxanthine transport, which is required for enhanced DNA synthesis via hypoxanthine recycling. In conclusion, ENT2 may have potential as a target in the development of CRC therapeutics.
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Affiliation(s)
- Safaa M. Naes
- Department of Biochemistry and Molecular Medicine, Faculty of Medicine, Universiti Teknologi MARA, Cawangan Selangor, Kampus Sungai Buloh, Jalan Hospital Sungai Buloh, Selangor 47000, Malaysia
- Institute of Medical and Molecular Biotechnology, Faculty of Medicine, Universiti Teknologi MARA, Cawangan Selangor, Kampus Sungai Buloh, Jalan Hospital Sungai Buloh, Selangor 47000, Malaysia
| | - Sharaniza Ab-Rahim
- Department of Biochemistry and Molecular Medicine, Faculty of Medicine, Universiti Teknologi MARA, Cawangan Selangor, Kampus Sungai Buloh, Jalan Hospital Sungai Buloh, Selangor 47000, Malaysia
| | - Musalmah Mazlan
- Department of Biochemistry and Molecular Medicine, Faculty of Medicine, Universiti Teknologi MARA, Cawangan Selangor, Kampus Sungai Buloh, Jalan Hospital Sungai Buloh, Selangor 47000, Malaysia
| | - Nurul Azmir Amir Hashim
- Department of Biochemistry and Molecular Medicine, Faculty of Medicine, Universiti Teknologi MARA, Cawangan Selangor, Kampus Sungai Buloh, Jalan Hospital Sungai Buloh, Selangor 47000, Malaysia
| | - Amirah Abdul Rahman
- Department of Biochemistry and Molecular Medicine, Faculty of Medicine, Universiti Teknologi MARA, Cawangan Selangor, Kampus Sungai Buloh, Jalan Hospital Sungai Buloh, Selangor 47000, Malaysia
- Correspondence to: Dr Amirah Abdul Rahman, Department of Biochemistry and Molecular Medicine, Faculty of Medicine, Universiti Teknologi MARA, Cawangan Selangor, Kampus Sungai Buloh, Jalan Hospital, Sungai Buloh, Selangor 47000, Malaysia
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Kim IS, Jo EK. Inosine: A bioactive metabolite with multimodal actions in human diseases. Front Pharmacol 2022; 13:1043970. [PMID: 36467085 PMCID: PMC9708727 DOI: 10.3389/fphar.2022.1043970] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Accepted: 11/02/2022] [Indexed: 08/04/2023] Open
Abstract
The nucleoside inosine is an essential metabolite for purine biosynthesis and degradation; it also acts as a bioactive molecule that regulates RNA editing, metabolic enzyme activity, and signaling pathways. As a result, inosine is emerging as a highly versatile bioactive compound and second messenger of signal transduction in cells with diverse functional abilities in different pathological states. Gut microbiota remodeling is closely associated with human disease pathogenesis and responses to dietary and medical supplementation. Recent studies have revealed a critical link between inosine and gut microbiota impacting anti-tumor, anti-inflammatory, and antimicrobial responses in a context-dependent manner. In this review, we summarize the latest progress in our understanding of the mechanistic function of inosine, to unravel its immunomodulatory actions in pathological settings such as cancer, infection, inflammation, and cardiovascular and neurological diseases. We also highlight the role of gut microbiota in connection with inosine metabolism in different pathophysiological conditions. A more thorough understanding of the mechanistic roles of inosine and how it regulates disease pathologies will pave the way for future development of therapeutic and preventive modalities for various human diseases.
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Affiliation(s)
- In Soo Kim
- Department of Medical Science, Chungnam National University College of Medicine, Daejeon, South Korea
- Department of Microbiology, Chungnam National University College of Medicine, Daejeon, South Korea
- Infection Control Convergence Research Center, Chungnam National University College of Medicine, Daejeon, South Korea
| | - Eun-Kyoung Jo
- Department of Medical Science, Chungnam National University College of Medicine, Daejeon, South Korea
- Department of Microbiology, Chungnam National University College of Medicine, Daejeon, South Korea
- Infection Control Convergence Research Center, Chungnam National University College of Medicine, Daejeon, South Korea
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Ramón J, Vila-Julià F, Molina-Granada D, Molina-Berenguer M, Melià MJ, García-Arumí E, Torres-Torronteras J, Cámara Y, Martí R. Therapy Prospects for Mitochondrial DNA Maintenance Disorders. Int J Mol Sci 2021; 22:6447. [PMID: 34208592 PMCID: PMC8234938 DOI: 10.3390/ijms22126447] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2021] [Revised: 06/10/2021] [Accepted: 06/11/2021] [Indexed: 02/07/2023] Open
Abstract
Mitochondrial DNA depletion and multiple deletions syndromes (MDDS) constitute a group of mitochondrial diseases defined by dysfunctional mitochondrial DNA (mtDNA) replication and maintenance. As is the case for many other mitochondrial diseases, the options for the treatment of these disorders are rather limited today. Some aggressive treatments such as liver transplantation or allogeneic stem cell transplantation are among the few available options for patients with some forms of MDDS. However, in recent years, significant advances in our knowledge of the biochemical pathomechanisms accounting for dysfunctional mtDNA replication have been achieved, which has opened new prospects for the treatment of these often fatal diseases. Current strategies under investigation to treat MDDS range from small molecule substrate enhancement approaches to more complex treatments, such as lentiviral or adenoassociated vector-mediated gene therapy. Some of these experimental therapies have already reached the clinical phase with very promising results, however, they are hampered by the fact that these are all rare disorders and so the patient recruitment potential for clinical trials is very limited.
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Affiliation(s)
- Javier Ramón
- Research Group on Neuromuscular and Mitochondrial Diseases, Vall d’Hebron Research Institute, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain; (J.R.); (F.V.-J.); (D.M.-G.); (M.M.-B.); (M.J.M.); (E.G.-A.); (J.T.-T.); (Y.C.)
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Ferran Vila-Julià
- Research Group on Neuromuscular and Mitochondrial Diseases, Vall d’Hebron Research Institute, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain; (J.R.); (F.V.-J.); (D.M.-G.); (M.M.-B.); (M.J.M.); (E.G.-A.); (J.T.-T.); (Y.C.)
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - David Molina-Granada
- Research Group on Neuromuscular and Mitochondrial Diseases, Vall d’Hebron Research Institute, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain; (J.R.); (F.V.-J.); (D.M.-G.); (M.M.-B.); (M.J.M.); (E.G.-A.); (J.T.-T.); (Y.C.)
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Miguel Molina-Berenguer
- Research Group on Neuromuscular and Mitochondrial Diseases, Vall d’Hebron Research Institute, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain; (J.R.); (F.V.-J.); (D.M.-G.); (M.M.-B.); (M.J.M.); (E.G.-A.); (J.T.-T.); (Y.C.)
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Maria Jesús Melià
- Research Group on Neuromuscular and Mitochondrial Diseases, Vall d’Hebron Research Institute, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain; (J.R.); (F.V.-J.); (D.M.-G.); (M.M.-B.); (M.J.M.); (E.G.-A.); (J.T.-T.); (Y.C.)
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Elena García-Arumí
- Research Group on Neuromuscular and Mitochondrial Diseases, Vall d’Hebron Research Institute, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain; (J.R.); (F.V.-J.); (D.M.-G.); (M.M.-B.); (M.J.M.); (E.G.-A.); (J.T.-T.); (Y.C.)
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Javier Torres-Torronteras
- Research Group on Neuromuscular and Mitochondrial Diseases, Vall d’Hebron Research Institute, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain; (J.R.); (F.V.-J.); (D.M.-G.); (M.M.-B.); (M.J.M.); (E.G.-A.); (J.T.-T.); (Y.C.)
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Yolanda Cámara
- Research Group on Neuromuscular and Mitochondrial Diseases, Vall d’Hebron Research Institute, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain; (J.R.); (F.V.-J.); (D.M.-G.); (M.M.-B.); (M.J.M.); (E.G.-A.); (J.T.-T.); (Y.C.)
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Ramon Martí
- Research Group on Neuromuscular and Mitochondrial Diseases, Vall d’Hebron Research Institute, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain; (J.R.); (F.V.-J.); (D.M.-G.); (M.M.-B.); (M.J.M.); (E.G.-A.); (J.T.-T.); (Y.C.)
- Biomedical Network Research Centre on Rare Diseases (CIBERER), Instituto de Salud Carlos III, 28029 Madrid, Spain
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Randazzo O, Papini F, Mantini G, Gregori A, Parrino B, Liu DSK, Cascioferro S, Carbone D, Peters GJ, Frampton AE, Garajova I, Giovannetti E. "Open Sesame?": Biomarker Status of the Human Equilibrative Nucleoside Transporter-1 and Molecular Mechanisms Influencing its Expression and Activity in the Uptake and Cytotoxicity of Gemcitabine in Pancreatic Cancer. Cancers (Basel) 2020; 12:cancers12113206. [PMID: 33142664 PMCID: PMC7692081 DOI: 10.3390/cancers12113206] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Revised: 10/25/2020] [Accepted: 10/26/2020] [Indexed: 01/14/2023] Open
Abstract
Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive tumor characterized by early invasiveness, rapid progression and resistance to treatment. For more than twenty years, gemcitabine has been the main therapy for PDAC both in the palliative and adjuvant setting. After the introduction of FOLFIRINOX as an upfront treatment for metastatic disease, gemcitabine is still commonly used in combination with nab-paclitaxel as an alternative first-line regimen, as well as a monotherapy in elderly patients unfit for combination chemotherapy. As a hydrophilic nucleoside analogue, gemcitabine requires nucleoside transporters to permeate the plasma membrane, and a major role in the uptake of this drug is played by human equilibrative nucleoside transporter 1 (hENT-1). Several studies have proposed hENT-1 as a biomarker for gemcitabine efficacy in PDAC. A recent comprehensive multimodal analysis of hENT-1 status evaluated its predictive role by both immunohistochemistry (with five different antibodies), and quantitative-PCR, supporting the use of the 10D7G2 antibody. High hENT-1 levels observed with this antibody were associated with prolonged disease-free status and overall-survival in patients receiving gemcitabine adjuvant chemotherapy. This commentary aims to critically discuss this analysis and lists molecular factors influencing hENT-1 expression. Improved knowledge on these factors should help the identification of subgroups of patients who may benefit from specific therapies and overcome the limitations of traditional biomarker studies.
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Affiliation(s)
- Ornella Randazzo
- Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam UMC, VU University Medical Center (VUmc), 1081 HV Amsterdam, The Netherlands; (O.R.); (F.P.); (G.M.); (A.G.); (G.J.P.); (I.G.)
- Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, 90123 Palermo, Italy; (B.P.); (S.C.); (D.C.)
| | - Filippo Papini
- Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam UMC, VU University Medical Center (VUmc), 1081 HV Amsterdam, The Netherlands; (O.R.); (F.P.); (G.M.); (A.G.); (G.J.P.); (I.G.)
| | - Giulia Mantini
- Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam UMC, VU University Medical Center (VUmc), 1081 HV Amsterdam, The Netherlands; (O.R.); (F.P.); (G.M.); (A.G.); (G.J.P.); (I.G.)
- Cancer Pharmacology Lab, AIRC Start Up Unit, Fondazione Pisana per la Scienza, 56017 Pisa, Italy
| | - Alessandro Gregori
- Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam UMC, VU University Medical Center (VUmc), 1081 HV Amsterdam, The Netherlands; (O.R.); (F.P.); (G.M.); (A.G.); (G.J.P.); (I.G.)
| | - Barbara Parrino
- Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, 90123 Palermo, Italy; (B.P.); (S.C.); (D.C.)
| | - Daniel S. K. Liu
- Division of Cancer, Department of Surgery & Cancer, Imperial College, Hammersmith Hospital campus, London W12 0NN, UK;
| | - Stella Cascioferro
- Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, 90123 Palermo, Italy; (B.P.); (S.C.); (D.C.)
| | - Daniela Carbone
- Dipartimento di Scienze e Tecnologie Biologiche Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, 90123 Palermo, Italy; (B.P.); (S.C.); (D.C.)
| | - Godefridus J. Peters
- Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam UMC, VU University Medical Center (VUmc), 1081 HV Amsterdam, The Netherlands; (O.R.); (F.P.); (G.M.); (A.G.); (G.J.P.); (I.G.)
- Department of Biochemistry, Medical University of Gdansk, 80-210 Gdansk, Poland
| | - Adam E. Frampton
- Division of Cancer, Department of Surgery & Cancer, Imperial College, Hammersmith Hospital campus, London W12 0NN, UK;
- Faculty of Health and Medical Sciences, The Leggett Building, University of Surrey, Guildford GU2 7XH, UK
- Correspondence: (A.E.F.); (E.G.); Tel.: +31-003-120-444-2633 (E.G.)
| | - Ingrid Garajova
- Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam UMC, VU University Medical Center (VUmc), 1081 HV Amsterdam, The Netherlands; (O.R.); (F.P.); (G.M.); (A.G.); (G.J.P.); (I.G.)
- Medical Oncology Unit, University Hospital of Parma, Via Gramsci 14, 43126 Parma, Italy
| | - Elisa Giovannetti
- Department of Medical Oncology, Cancer Center Amsterdam, Amsterdam UMC, VU University Medical Center (VUmc), 1081 HV Amsterdam, The Netherlands; (O.R.); (F.P.); (G.M.); (A.G.); (G.J.P.); (I.G.)
- Cancer Pharmacology Lab, AIRC Start Up Unit, Fondazione Pisana per la Scienza, 56017 Pisa, Italy
- Correspondence: (A.E.F.); (E.G.); Tel.: +31-003-120-444-2633 (E.G.)
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Janmale TV, Lindsay A, Gieseg SP. Nucleoside transporters are critical to the uptake and antioxidant activity of 7,8-dihydroneopterin in monocytic cells. Free Radic Res 2020; 54:341-350. [DOI: 10.1080/10715762.2020.1764948] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- Tejraj V. Janmale
- Free Radical Biochemistry Laboratory, School of Biological Sciences, University of Canterbury, Christchurch, New Zealand
| | - Angus Lindsay
- Free Radical Biochemistry Laboratory, School of Biological Sciences, University of Canterbury, Christchurch, New Zealand
- Institute for Physical Activity and Nutrition, School of Exercise and Nutrition Sciences, Deakin University, Geelong, Australia
| | - Steven P. Gieseg
- Free Radical Biochemistry Laboratory, School of Biological Sciences, University of Canterbury, Christchurch, New Zealand
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Zyma M, Pawliczak R. Characteristics and the role of purinergic receptors in pathophysiology with focus on immune response. Int Rev Immunol 2020; 39:97-117. [PMID: 32037918 DOI: 10.1080/08830185.2020.1723582] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The nucleotide adenosine-5'-triphosphate (ATP) is mostly thought to be energy carrier, but evidence presented in multiple studies proves ATP involvement into variety of processes, due to its neuromodulatory capabilities. ATP and its metabolite-adenosine, bind to the purinergic receptors, which are divided into two types: adenosine binding P1 receptor and ADP/ATP binding P2 receptor. These receptors are expressed in different tissues and organs. Recent studies report their immunomodulatory characteristics, connected with varying immunological processes, such as immunological response or antigen presentation. Besides, they seem to play an important role in medical conditions such as bronchial asthma or variety of cancers. In this article, we would like to review recent discoveries on the field of purinergic receptors research focusing on their role in immunological system, and shed a new light upon the importance of these receptors in modern medicine development.
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Affiliation(s)
- Marharyta Zyma
- Department of Immunopathology, Division of Biomedical Science, Faculty of Medicine, Medical University of Lodz, Lodz, Poland
| | - Rafał Pawliczak
- Department of Immunopathology, Division of Biomedical Science, Faculty of Medicine, Medical University of Lodz, Lodz, Poland
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Shen HY, Huang N, Reemmer J, Xiao L. Adenosine Actions on Oligodendroglia and Myelination in Autism Spectrum Disorder. Front Cell Neurosci 2018; 12:482. [PMID: 30581380 PMCID: PMC6292987 DOI: 10.3389/fncel.2018.00482] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 11/26/2018] [Indexed: 11/21/2022] Open
Abstract
Autism spectrum disorder (ASD) is the most commonly diagnosed neurodevelopmental disorder. Independent of neuronal dysfunction, ASD and its associated comorbidities have been linked to hypomyelination and oligodendroglial dysfunction. Additionally, the neuromodulator adenosine has been shown to affect certain ASD comorbidities and symptoms, such as epilepsy, impairment of cognitive function, and anxiety. Adenosine is both directly and indirectly responsible for regulating the development of oligodendroglia and myelination through its interaction with, and modulation of, several neurotransmitters, including glutamate, dopamine, and serotonin. In this review, we will focus on the recent discoveries in adenosine interaction with physiological and pathophysiological activities of oligodendroglia and myelination, as well as ASD-related aspects of adenosine actions on neuroprotection and neuroinflammation. Moreover, we will discuss the potential therapeutic value and clinical approaches of adenosine manipulation against hypomyelination in ASD.
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Affiliation(s)
- Hai-Ying Shen
- Robert Stone Dow Neurobiology Department, Legacy Research Institute, Legacy Health, Portland, OR, United States.,Department of Integrative Physiology and Neuroscience, Washington State University, Pullman, WA, United States
| | - Nanxin Huang
- Department of Histology and Embryology, Chongqing Key Laboratory of Neurobiology, Army Medical University (Third Military Medical University), Chongqing, China
| | - Jesica Reemmer
- Robert Stone Dow Neurobiology Department, Legacy Research Institute, Legacy Health, Portland, OR, United States
| | - Lan Xiao
- Department of Histology and Embryology, Chongqing Key Laboratory of Neurobiology, Army Medical University (Third Military Medical University), Chongqing, China
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El Kouni MH. Pyrimidine metabolism in schistosomes: A comparison with other parasites and the search for potential chemotherapeutic targets. Comp Biochem Physiol B Biochem Mol Biol 2017; 213:55-80. [PMID: 28735972 PMCID: PMC5593796 DOI: 10.1016/j.cbpb.2017.07.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Revised: 06/29/2017] [Accepted: 07/03/2017] [Indexed: 12/18/2022]
Abstract
Schistosomes are responsible for the parasitic disease schistosomiasis, an acute and chronic parasitic ailment that affects >240 million people in 70 countries worldwide. It is the second most devastating parasitic disease after malaria. At least 200,000 deaths per year are associated with the disease. In the absence of the availability of vaccines, chemotherapy is the main stay for combating schistosomiasis. The antischistosomal arsenal is currently limited to a single drug, Praziquantel, which is quite effective with a single-day treatment and virtually no host-toxicity. Recently, however, the question of reduced activity of Praziquantel has been raised. Therefore, the search for alternative antischistosomal drugs merits the study of new approaches of chemotherapy. The rational design of a drug is usually based on biochemical and physiological differences between pathogens and host. Pyrimidine metabolism is an excellent target for such studies. Schistosomes, unlike most of the host tissues, require a very active pyrimidine metabolism for the synthesis of DNA and RNA. This is essential for the production of the enormous numbers of eggs deposited daily by the parasite to which the granulomas response precipitates the pathogenesis of schistosomiasis. Furthermore, there are sufficient differences between corresponding enzymes of pyrimidine metabolism from the host and the parasite that can be exploited to design specific inhibitors or "subversive substrates" for the parasitic enzymes. Specificities of pyrimidine transport also diverge significantly between parasites and their mammalian host. This review deals with studies on pyrimidine metabolism in schistosomes and highlights the unique characteristic of this metabolism that could constitute excellent potential targets for the design of safe and effective antischistosomal drugs. In addition, pyrimidine metabolism in schistosomes is compared with that in other parasites where studies on pyrimidine metabolism have been more elaborate, in the hope of providing leads on how to identify likely chemotherapeutic targets which have not been looked at in schistosomes.
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Affiliation(s)
- Mahmoud H El Kouni
- Department of Pharmacology and Toxicology, Center for AIDS Research, Comprehensive Cancer Center, General Clinical Research Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
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Abstract
Microsporidia are strict obligate intracellular parasites that infect a wide range of eukaryotes including humans and economically important fish and insects. Surviving and flourishing inside another eukaryotic cell is a very specialised lifestyle that requires evolutionary innovation. Genome sequence analyses show that microsporidia have lost most of the genes needed for making primary metabolites, such as amino acids and nucleotides, and also that they have only a limited capacity for making adenosine triphosphate (ATP). Since microsporidia cannot grow and replicate without the enormous amounts of energy and nucleotide building blocks needed for protein, DNA, and RNA biosynthesis, they must have evolved ways of stealing these substrates from the infected host cell. Providing they can do this, genome analyses suggest that microsporidia have the enzyme repertoire needed to use and regenerate the imported nucleotides efficiently. Recent functional studies suggest that a critical innovation for adapting to intracellular life was the acquisition by lateral gene transfer of nucleotide transport (NTT) proteins that are now present in multiple copies in all microsporidian genomes. These proteins are expressed on the parasite surface and allow microsporidia to steal ATP and other purine nucleotides for energy and biosynthesis from their host. However, it remains unclear how other essential metabolites, such as pyrimidine nucleotides, are acquired. Transcriptomic and experimental studies suggest that microsporidia might manipulate host cell metabolism and cell biological processes to promote nucleotide synthesis and to maximise the potential for ATP and nucleotide import. In this review, we summarise recent genomic and functional data relating to how microsporidia exploit their hosts for energy and building blocks needed for growth and nucleic acid metabolism and we identify some remaining outstanding questions.
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Abstract
Adenosine, as the brain’s endogenous anticonvulsant, is considered to be responsible for seizure arrest and postictal refractoriness. On the other hand, deficiencies within the adenosine-based neuromodulatory system may contribute to epileptogenesis. Based on these natural mechanisms and on findings that adenosine and its analogs can suppress pharmacoresistant seizures, a new field of adenosine-based therapies has emerged, including the use of adenosine receptor agonists and adenosine transport inhibitors, or the inhibition of adenosine kinase, which is thought to be the key enzyme for the regulation of intra- and extracellular adenosine levels. However, most of these pharmacological approaches are limited by strong systemic side effects ranging from a decrease of heart rate, blood pressure, and body temperature to sedation. Recently, new strategies have been developed aimed at the local reconstitution of the inhibitory adenosinergic tone by intracerebral implantation of cells engineered to release adenosine. Adenosine-releasing cells or devices implanted into or near a seizure focus offer new hopes for a side effect-free therapy for pharmacoresistant epilepsy.
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Affiliation(s)
- Detlev Boison
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland.
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Cabrera-Pérez R, Torres-Torronteras J, Vila-Julià F, Ortega FJ, Cámara Y, Barquinero J, Martí R. Prospective therapeutic approaches in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). Expert Opin Orphan Drugs 2015. [DOI: 10.1517/21678707.2015.1090307] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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Lim SP, Wang QY, Noble CG, Chen YL, Dong H, Zou B, Yokokawa F, Nilar S, Smith P, Beer D, Lescar J, Shi PY. Ten years of dengue drug discovery: progress and prospects. Antiviral Res 2013; 100:500-19. [PMID: 24076358 DOI: 10.1016/j.antiviral.2013.09.013] [Citation(s) in RCA: 261] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2013] [Revised: 09/07/2013] [Accepted: 09/15/2013] [Indexed: 01/26/2023]
Abstract
To combat neglected diseases, the Novartis Institute of Tropical Diseases (NITD) was founded in 2002 through private-public funding from Novartis and the Singapore Economic Development Board. One of NITD's missions is to develop antivirals for dengue virus (DENV), the most prevalent mosquito-borne viral pathogen. Neither vaccine nor antiviral is currently available for DENV. Here we review the progress in dengue drug discovery made at NITD as well as the major discoveries made by academia and other companies. Four strategies have been pursued to identify inhibitors of DENV through targeting both viral and host proteins: (i) HTS (high-throughput screening) using virus replication assays; (ii) HTS using viral enzyme assays; (iii) structure-based in silico docking and rational design; (iv) repurposing hepatitis C virus inhibitors for DENV. Along the developmental process from hit finding to clinical candidate, many inhibitors did not advance beyond the stage of hit-to-lead optimization, due to their poor selectivity, physiochemical or pharmacokinetic properties. Only a few compounds showed efficacy in the AG129 DENV mouse model. Two nucleoside analogs, NITD-008 and Balapiravir, entered preclinical animal safety study and clinic trial, but both were terminated due to toxicity and lack of potency, respectively. Celgosivir, a host alpha-glucosidase inhibitor, is currently under clinical trial; its clinical efficacy remains to be determined. The knowledge accumulated during the past decade has provided a better rationale for ongoing dengue drug discovery. Though challenging, we are optimistic that this continuous, concerted effort will lead to an effective dengue therapy.
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Affiliation(s)
- Siew Pheng Lim
- Novartis Institute for Tropical Diseases, 10 Biopolis Road, 05-01 Chromos, Singapore 138670, Singapore
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Allard B, Turcotte M, Spring K, Pommey S, Royal I, Stagg J. Anti-CD73 therapy impairs tumor angiogenesis. Int J Cancer 2013; 134:1466-73. [DOI: 10.1002/ijc.28456] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2013] [Accepted: 08/09/2013] [Indexed: 12/12/2022]
Affiliation(s)
- Bertrand Allard
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal; Faculté de Pharmacie et Institut du Cancer de Montréal; Montréal Québec H2L 4M1 Canada
| | - Martin Turcotte
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal; Faculté de Pharmacie et Institut du Cancer de Montréal; Montréal Québec H2L 4M1 Canada
| | - Kathleen Spring
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal; Faculté de Pharmacie et Institut du Cancer de Montréal; Montréal Québec H2L 4M1 Canada
| | - Sandra Pommey
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal; Faculté de Pharmacie et Institut du Cancer de Montréal; Montréal Québec H2L 4M1 Canada
| | - Isabelle Royal
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal; Faculté de Pharmacie et Institut du Cancer de Montréal; Montréal Québec H2L 4M1 Canada
- Department of Medicine; Université de Montréal; Montréal Québec Canada
| | - John Stagg
- Centre de Recherche du Centre Hospitalier de l'Université de Montréal; Faculté de Pharmacie et Institut du Cancer de Montréal; Montréal Québec H2L 4M1 Canada
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Hussein E. Non-myeloablative bone marrow transplant and platelet infusion can transiently improve the clinical outcome of mitochondrial neurogastrointestinal encephalopathy: a case report. Transfus Apher Sci 2013; 49:208-11. [PMID: 23410918 DOI: 10.1016/j.transci.2013.01.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Revised: 08/29/2012] [Accepted: 01/10/2013] [Indexed: 11/27/2022]
Abstract
Mitochondrial neurogastrointestinal encephalopathy (MNGIE) is caused by deficiency in thymidine phosphorylase (TP), that regulates thymidine (dThd) and deoxyuridine (dUrd). Toxic levels of dThd and dUrd can lead to mitochondrial dysfunction by impairing mitochondrial DNA replication, causing GI and neurologic deterioration. We studied the impact of bone marrow transplant (BMT) and platelets, as a source of TP on the clinical outcome of MNGIE. We report a case of MNGIE, who presented with severe vomiting. Over time, he was non-ambulatory and his GI symptoms got progressively worse with severe dysphagia, abdominal pain episodes, persistent vomiting and diarrhea. Being unfit for intense conditioning regimen, he received a mini BMT, with mild conditioning regimen. Bone marrow was obtained from his HLA fully matched brother. One month after transplantation, donor chimerism in peripheral blood was 33%. Excellent clinical responses were achieved 3 months after transplantation and circulating donor cell chimerism decreased to 24% with a significant increase in platelet TP activity. Ten months post transplant the patient's symptoms recurred and fresh single donor platelets were infused, with a significant increase in platelet TP activity. Mini BMT and platelet transfusion can transiently increase circulating TP activity and might prevent progress of this fatal disease.
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Affiliation(s)
- Eiman Hussein
- Cairo University Blood Bank, Clinical Pathology Department, Cairo University, Egypt.
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Sperlágh B, Vizi ES. The role of extracellular adenosine in chemical neurotransmission in the hippocampus and Basal Ganglia: pharmacological and clinical aspects. Curr Top Med Chem 2011; 11:1034-46. [PMID: 21401497 PMCID: PMC3179034 DOI: 10.2174/156802611795347564] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2010] [Accepted: 11/25/2010] [Indexed: 12/20/2022]
Abstract
Now there is general agreement that the purine nucleoside adenosine is an important neuromodulator in the central nervous system, playing a crucial role in neuronal excitability and synaptic/non-synaptic transmission in the hippocampus and basal ganglia. Adenosine is derived from the breakdown of extra- or intracellular ATP and is released upon a variety of physiological and pathological stimuli from neuronal and non-neuronal sources, i.e. from glial cells and exerts effects diffusing far away from release sites. The resultant elevation of adenosine levels in the extracellular space reaches micromolar level, and leads to the activation A1, A2A, A2B and A3 receptors, localized to pre- and postsynaptic as well as extrasynaptic sites. Activation of presynaptic A1 receptors inhibits the release of the majority of transmitters including glutamate, acetylcholine, noradrenaline, 5-HT and dopamine, whilst the stimulation of A2A receptors facilitates the release of glutamate and acetylcholine and inhibits the release of GABA. These actions underlie modulation of neuronal excitability, synaptic plasticity and coordination of neural networks and provide intriguing target sites for pharmacological intervention in ischemia and Parkinson’s disease. However, despite that adenosine is also released during ischemia, A1 adenosine receptors do not participate in the modulation of excitotoxic glutamate release, which is nonsynaptic and is due to the reverse operation of transporters. Instead, extrasynaptic A1 receptors might be responsible for the neuroprotection afforded by A1 receptor activation.
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Affiliation(s)
- Beáta Sperlágh
- Department of Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1450 Budapest, POB 67, Hungary
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Garozzo R, Sortino MA, Vancheri C, Condorelli DF. Antiproliferative effects induced by guanine-based purines require hypoxanthine-guanine phosphoribosyltransferase activity. Biol Chem 2011; 391:1079-89. [PMID: 20536392 DOI: 10.1515/bc.2010.106] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Guanine (GUA), guanosine and GMP exert a marked growth inhibition on the U87 glioma cell line that is not seen with other tested nucleotides, nucleosides and nucleobases. This effect could be replicated in several different human tumoral cell lines. Guanine shows a higher potency than guanosine or GMP, and co-treatments with adenosine or adenine are able to antagonize or revert the antiproliferative effect of guanine. The loss of the guanine effect in a cell line bearing a mutated inactive hypoxanthine-guanine phosphoribosyltransferase (HGPRT), and the decreased potency of GUA in U87 cells silenced for HGPRT transcripts, demonstrates the central role of the intracellular metabolism of GUA for growth-inhibitory effects. Considering the potential application of growth-inhibitory substances in anticancer therapy, knowledge of the molecular mechanism underlying GUA-induced effects encourages studies aimed at defining possible tumoral targets for experimental therapies.
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Affiliation(s)
- Roberta Garozzo
- Department of Chemical Sciences, Section of Biochemistry, University of Catania, I-95125 Catania, Italy
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Plotnik DA, McLaughlin LJ, Chan J, Redmayne-Titley JN, Schwartz JL. The role of nucleoside/nucleotide transport and metabolism in the uptake and retention of 3'-fluoro-3'-deoxythymidine in human B-lymphoblast cells. Nucl Med Biol 2011; 38:979-86. [PMID: 21982569 DOI: 10.1016/j.nucmedbio.2011.03.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2011] [Revised: 03/13/2011] [Accepted: 03/26/2011] [Indexed: 10/18/2022]
Abstract
INTRODUCTION Recent studies in the human adenocarcinoma cell line A549 have identified cell growth-dependent equilibrative nucleoside transporter-1 (hENT1) as a modifier of 3'-fluoro-3'-deoxythymidine (FLT) uptake and retention. In the present study, we used the ability to isolate human lymphoblastoid clones deficient in thymidine kinase 1 (TK1) to study how metabolism and nucleoside transport influence FLT uptake and retention. METHODS Transport and metabolism of FLT were measured in the human lymphoblastoid cell line TK6 and in eight clones isolated from TK6. Four clones were TK1-proficient, while four were TK1-deficient. Both influx and efflux of FLT were measured under conditions where concentrative and equilibrative transport could be distinguished. RESULTS Sodium-dependent concentrative FLT transport dominated over equilibrative transport mechanisms and while inhibition of hENT1 reduced FLT uptake, there were no correlations between clonal variations in hENT1 levels and FLT uptake. There was an absolute requirement of TK1 for concentration of FLT in TK6 cells. FLT uptake reached a peak after 60 min of incubation with FLT after which intracellular levels of FLT and FLT metabolites declined. Efflux was rapid and was associated with reductions in FLT and each of its metabolites. Both FLT and FLT-monophosphate were found in the efflux buffer. CONCLUSIONS Initial rates of FLT uptake were a function of both concentrative and equilibrative transporters. TK1 activity was an absolute requirement for the accumulation of FLT. Retention was dependent on nucleoside/nucleotide efflux and retrograde metabolism of FLT nucleotides.
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Affiliation(s)
- David A Plotnik
- Department of Radiation Oncology, University of Washington, Box 356069, Seattle, WA 98195, USA
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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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Genistein abolishes nucleoside uptake by cardiac fibroblasts. Mol Cell Biochem 2010; 332:121-5. [PMID: 19728041 DOI: 10.1007/s11010-009-0181-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2009] [Accepted: 06/09/2009] [Indexed: 10/20/2022]
Abstract
Genistein, a soy isoflavone, is reported to exert significant beneficial action in several human disorders, which has generated immense interest in the mechanisms underlying its effects on diverse cellular processes. It has anti-proliferative action on many cell types, an effect generally attributed to tyrosine kinase inhibition. In this study, genistein was found to cause total inhibition of [3H]-thymidine incorporation into DNA and a modest reduction in [3H]-proline incorporation into protein in primary cultures of cardiac fibroblasts. The decrease in [3H]-thymidine incorporation was not associated with a decrease in cell proliferation but correlated exactly with low intracellular levels of [3H]-thymidine. Genistein dramatically reduced [3H]-thymidine but not [3H]-proline uptake by these cells in which the equilibrative nucleoside transporter may be the major route of nucleoside uptake. The effect was irreversible and was demonstrable in pulmonary fibroblasts as well. The findings suggest that nucleoside uptake mechanisms may be a novel target of genistein action in cardiac fibroblasts and point to serious limitations in using genistein to assess the role of tyrosine kinase in cell proliferation by the standard technique of [3H]-thymidine incorporation.
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Bogan KL, Brenner C. 5′-Nucleotidases and their new roles in NAD+ and phosphate metabolism. NEW J CHEM 2010. [DOI: 10.1039/b9nj00758j] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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22
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Nucleoside and nucleotide HIV reverse transcriptase inhibitors: 25 years after zidovudine. Antiviral Res 2009; 85:39-58. [PMID: 19887088 DOI: 10.1016/j.antiviral.2009.09.014] [Citation(s) in RCA: 261] [Impact Index Per Article: 17.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Revised: 09/19/2009] [Accepted: 09/23/2009] [Indexed: 12/29/2022]
Abstract
Twenty-five years ago, nucleoside analog 3'-azidothymidine (AZT) was shown to efficiently block the replication of HIV in cell culture. Subsequent studies demonstrated that AZT acts via the selective inhibition of HIV reverse transcriptase (RT) by its triphosphate metabolite. These discoveries have established the first class of antiretroviral agents: nucleoside and nucleotide reverse transcriptase inhibitors (NRTIs). Over the years that followed, NRTIs evolved into the main component of antiretroviral drug combinations that are now used for the treatment of all populations of HIV infected patients. A total of thirteen NRTI drug products are now available for clinical application: eight individual NRTIs, four fixed-dose combinations of two or three NRTIs, and one complete fixed-dose regimen containing two NRTIs and one non-nucleoside RT inhibitor. Multiple NRTIs or their prodrugs are in various stages of clinical development and new potent NRTIs are still being identified through drug discovery efforts. This article will review basic principles of the in vitro and in vivo pharmacology of NRTIs, discuss their clinical use including limitations associated with long-term NRTI therapy, and describe newly identified NRTIs with promising pharmacological profiles highlighting those in the development pipeline. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, volume 85, issue 1, 2010.
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Allen-Gipson DS, Jarrell JC, Bailey KL, Robinson JE, Kharbanda KK, Sisson JH, Wyatt TA. Ethanol blocks adenosine uptake via inhibiting the nucleoside transport system in bronchial epithelial cells. Alcohol Clin Exp Res 2009; 33:791-8. [PMID: 19298329 DOI: 10.1111/j.1530-0277.2009.00897.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND Adenosine uptake into cells by nucleoside transporters plays a significant role in governing extracellular adenosine concentration. Extracellular adenosine is an important signaling molecule that modulates many cellular functions via 4 G-protein-coupled receptor subtypes (A(1), A(2A), A(2B), and A(3)). Previously, we demonstrated that adenosine is critical in maintaining airway homeostasis and airway repair and that airway host defenses are impaired by alcohol. Taken together, we hypothesized that ethanol impairs adenosine uptake via the nucleoside transport system. METHODS To examine ethanol-induced alteration on adenosine transport, we used a human bronchial epithelial cell line (BEAS-2B). Cells were preincubated for 10 minutes in the presence and absence of varying concentrations of ethanol (EtOH). In addition, some cells were pretreated with S-(4-Nitrobenzyl)-6-thioinosine (100 microM: NBT), a potent adenosine uptake inhibitor. Uptake was then determined by addition of [(3)H]-adenosine at various time intervals. RESULTS Increasing EtOH concentrations resulted in increasing inhibition of adenosine uptake when measured at 1 minute. Cells pretreated with NBT effectively blocked adenosine uptake. In addition, short-term EtOH revealed increased extracellular adenosine concentration. Conversely, adenosine transport became desensitized in cells exposed to EtOH (100 mM) for 24 hours. To determine the mechanism of EtOH-induced desensitization of adenosine transport, cAMP activity was assessed in response to EtOH. Short-term EtOH exposure (10 minutes) had little or no effect on adenosine-mediated cAMP activation, whereas long-term EtOH exposure (24 hours) blocked adenosine-mediated cAMP activation. Western blot analysis of lysates from unstimulated BEAS-2B cells detected a single 55 kDa band indicating the presence of hENT1 and hENT2, respectively. Real-time RT-PCR of RNA from BEAS-2B revealed transcriptional expression of ENT1 and ENT2. CONCLUSIONS Collectively, these data reveal that acute exposure of cells to EtOH inhibits adenosine uptake via a nucleoside transporter, and chronic exposure of cells to EtOH desensitizes the adenosine transporter to these inhibitory effects of ethanol. Furthermore, our data suggest that inhibition of adenosine uptake by EtOH leads to an increased extracellular adenosine accumulation, influencing the effect of adenosine at the epithelial cell surface, which may alter airway homeostasis.
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Affiliation(s)
- Diane S Allen-Gipson
- Department of Internal Medicine, Pulmonary, Critical Care, Sleep and Allergy Section, 985815 Nebraska Medical Center, Omaha, NE 68198-5815, USA.
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Wu SK, Ann DK, Kim KJ, Lee VHL. Fine tuning of rabbit equilibrative nucleoside transporter activity by an alternatively spliced variant. J Drug Target 2008; 13:521-33. [PMID: 16332577 DOI: 10.1080/10611860500403099] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The full-length cDNA encoding an equilibrative nucleoside transporter (rbENT2) and its novel C-terminal variant, rbENT2A, were isolated from rabbit trachea. Rabbit ENT2 protein consists of 456 amino acid residues; rbENT2A is shorter by 41 residues. Both rbENT2 and rbENT2A transcripts are found in rabbit tissues including intestine, kidney cortex, kidney, and trachea, at varying levels of expression. When transfected in a heterologous expression system-Madin Darby canine kidney (MDCK) epithelial cell line-both rbENT2 and rbENT2A were expressed. rbENT2 had a molecular mass of 49 kDa; rbENT2A had a molecular mass of 44 kDa. Clones of both transporters yielded functional proteins that were capable of mediating uridine uptake and efflux without the needing to be coupled to a secondary ion (e.g. Na(+)). Remarkably, rbENT2A displayed a higher affinity (K(m) = 41 microM) and a lower capacity (V(max) = 0.6 nmol/mg protein/5 min) towards substrates than rbENT2 (K(m) = 272.8 microM, V(max) = 1.26 nmol/mg protein/5 min). Pharmacological profiles showed that nitro-benzyl-mercapto-purine-ribose (NBMPR) potently inhibited (3)H-uridine uptake mediated by rbENT2A, but not uptake mediated by rbENT2. The constitutive splicing, broad expression, markedly different kinetics, and distinct pharmacological characteristics of rbENT2A appear to act in conjunction with the wild type, rbENT2, to fine-tune basolateral nucleoside transport function in rabbit trachea.
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Affiliation(s)
- Sharon K Wu
- Department of Pharmaceutical Sciences, University of Southern California, Los Angeles, 90089-9121, USA
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Carter NS, Yates P, Arendt CS, Boitz JM, Ullman B. Purine and pyrimidine metabolism in Leishmania. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 625:141-54. [PMID: 18365665 DOI: 10.1007/978-0-387-77570-8_12] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Purines and pyrimidines are indispensable to all life, performing many vital functions for cells: ATP serves as the universal currency of cellular energy, cAMP and cGMP are key second messenger molecules, purine and pyrimidine nucleotides are precursors for activated forms of both carbohydrates and lipids, nucleotide derivatives of vitamins are essential cofactors in metabolic processes, and nucleoside triphosphates are the immediate precursors for DNA and RNA synthesis. Unlike their mammalian and insect hosts, Leishmania lack the metabolic machinery to make purine nucleotides de novo and must rely on their host for preformed purines. The obligatory nature of purine salvage offers, therefore, a plethora of potential targets for drug targeting, and the pathway has consequently been the focus of considerable scientific investigation. In contrast, Leishmania are prototrophic for pyrimidines and also express a small complement of pyrimidine salvage enzymes. Because the pyrimidine nucleotide biosynthetic pathways of Leishmania and humans are similar, pyrimidine metabolism in Leishmania has generally been considered less amenable to therapeutic manipulation than the purine salvage pathway. However, evidence garnered from a variety of parasitic protozoa suggests that the selective inhibition of pyrimidine biosynthetic enzymes offers a rational therapeutic paradigm. In this chapter, we present an overview of the purine and pyrimidine pathways in Leishmania, make comparisons to the equivalent pathways in their mammalian host, and explore how these pathways might be amenable to selective therapeutic targeting.
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Affiliation(s)
- Nicola S Carter
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, 3181 SW Sam Jackson Park Rd, Portland, Oregon 97239-3098, USA
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Morita K, Saida M, Morioka N, Kitayama T, Akagawa Y, Dohi T. Cyclic ADP-ribose mediates formyl methionyl leucyl phenylalanine (fMLP)-induced intracellular Ca(2+) rise and migration of human neutrophils. J Pharmacol Sci 2008; 106:492-504. [PMID: 18344610 DOI: 10.1254/jphs.fp0072083] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
Although cyclic ADP-ribose (cADPR), a novel Ca(2+)-mobilizing mediator, is suggested to be involved in the functions of neutrophils in rodents, its role in human neutrophils remains unclear. The present study examined the ability of cADPR to mobilize Ca(2+) and mediate formyl methionyl leucyl phenylalanine (fMLP)-stimulated increase in cytosolic free Ca(2+) concentration ([Ca(2+)](i)) and migration in human neutrophils. cADPR induced Ca(2+) release from digitonin-permeabilized neutrophils, and the release was blocked by 8Br-cADPR, an antagonist of cADPR. Immunophilin ligands, FK506 and rapamycin, but not cyclosporine A, inhibited cADPR-induced Ca(2+) release. 8Br-cADPR partially reduced fMLP-induced [Ca(2+)](i) rise and abolished the rise in combination with 2APB, an IP(3)-receptor antagonist. Anti-CD38Ab and NADase that interfere with cADPR formation, reduced the fMLP-induced [Ca(2+)](i) rise. When beta-NAD(+), a substrate of ADP-ribosyl cyclase, and cADPR were added to the medium, the former gradually increased [Ca(2+)](i) and the latter potentiated the fMLP-induced [Ca(2+)](i) rise. The beta-NAD(+)-induced [Ca(2+)](i) rise in Ca(2+)-free medium was inhibited by anti-CD38Ab, 8Br-cADPR, FK506, ruthenium red, and thapsigargin. mRNAs of nucleoside transporter (NT), ENT1, ENT2, CNT, and CNT3 were expressed in neutrophils; and their inhibitors, inosine, uridine, and s-(4-nitrobenzyl)-6-thioinosine, reduced the [Ca(2+)](i) rise induced by beta-NAD(+) and fMLP. fMLP-timulated migration was inhibited by the removal of Ca(2+) from the medium or by the addition of 8Br-cADPR, anti-CD38Ab, NADase, and NT inhibitors. These results suggest that cADPR was synthesized extracellularly by CD38, transported into the cells through NTs, and then Ca(2+) was mobilized by FK506-binding protein-dependent process. This process may be involved in fMLP-induced intracellular Ca(2+) signaling and migration in human neutrophils.
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Affiliation(s)
- Katsuya Morita
- Department of Dental Pharmacology, Hiroshima University Graduate School of Biomedical Sciences, Japan
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Boison D. The adenosine kinase hypothesis of epileptogenesis. Prog Neurobiol 2007; 84:249-62. [PMID: 18249058 DOI: 10.1016/j.pneurobio.2007.12.002] [Citation(s) in RCA: 132] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2007] [Revised: 11/02/2007] [Accepted: 12/05/2007] [Indexed: 02/07/2023]
Abstract
Current therapies for epilepsy are largely symptomatic and do not affect the underlying mechanisms of disease progression, i.e. epileptogenesis. Given the large percentage of pharmacoresistant chronic epilepsies, novel approaches are needed to understand and modify the underlying pathogenetic mechanisms. Although different types of brain injury (e.g. status epilepticus, traumatic brain injury, stroke) can trigger epileptogenesis, astrogliosis appears to be a homotypic response and hallmark of epilepsy. Indeed, recent findings indicate that epilepsy might be a disease of astrocyte dysfunction. This review focuses on the inhibitory neuromodulator and endogenous anticonvulsant adenosine, which is largely regulated by astrocytes and its key metabolic enzyme adenosine kinase (ADK). Recent findings support the "ADK hypothesis of epileptogenesis": (i) Mouse models of epileptogenesis suggest a sequence of events leading from initial downregulation of ADK and elevation of ambient adenosine as an acute protective response, to changes in astrocytic adenosine receptor expression, to astrocyte proliferation and hypertrophy (i.e. astrogliosis), to consequential overexpression of ADK, reduced adenosine and - finally - to spontaneous focal seizure activity restricted to regions of astrogliotic overexpression of ADK. (ii) Transgenic mice overexpressing ADK display increased sensitivity to brain injury and seizures. (iii) Inhibition of ADK prevents seizures in a mouse model of pharmacoresistant epilepsy. (iv) Intrahippocampal implants of stem cells engineered to lack ADK prevent epileptogenesis. Thus, ADK emerges both as a diagnostic marker to predict, as well as a prime therapeutic target to prevent, epileptogenesis.
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Affiliation(s)
- Detlev Boison
- R.S. Dow Neurobiology Laboratories, Legacy Research, Portland, OR 97232, USA.
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Endo Y, Obata T, Murata D, Ito M, Sakamoto K, Fukushima M, Yamasaki Y, Yamada Y, Natsume N, Sasaki T. Cellular localization and functional characterization of the equilibrative nucleoside transporters of antitumor nucleosides. Cancer Sci 2007; 98:1633-7. [PMID: 17711502 DOI: 10.1111/j.1349-7006.2007.00581.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Nucleoside transporters play an important role in the disposition of nucleosides and their analogs. To elucidate the relationship between chemosensitivity to antitumor nucleosides and the functional expression of equilibrative nucleoside transporters (ENT), we established stable cell lines of human fibrosarcoma HT-1080 and gastric carcinoma TMK-1 that constitutively overexpressed green fluorescent protein-tagged hENT1, hENT2, hENT3 and hENT4. Both hENT1 and hENT2 were predictably localized to the plasma membrane, whereas hENT3 and hENT4 were localized to the intracellular organelles. The chemosensitivity of TMK-1 cells expressing hENT1 and hENT2 to cytarabine and 1-(3-C-ethynyl-beta-D-ribopentofuranosyl) cytosine increased markedly in comparison to that of mock cells. However, no remarkable changes in sensitivity to antitumor nucleosides were observed in cell lines that expressed both hENT3 and hENT4. These data suggest that hENT3 and hENT4, which are mainly located in the intracellular organelles, are not prominent nucleoside transporters like hENT1 and hENT2, which are responsible for antitumor nucleoside uptake.
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Affiliation(s)
- Yoshio Endo
- Department of Experimental Therapeutics, Cancer Research Institute, Kanazawa University, Kanazawa 920-0934, Japan.
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Valentino ML, Martí R, Tadesse S, López LC, Manes JL, Lyzak J, Hahn A, Carelli V, Hirano M. Thymidine and deoxyuridine accumulate in tissues of patients with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). FEBS Lett 2007; 581:3410-4. [PMID: 17612528 PMCID: PMC1986782 DOI: 10.1016/j.febslet.2007.06.042] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2007] [Revised: 06/17/2007] [Accepted: 06/18/2007] [Indexed: 11/28/2022]
Abstract
Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disease due to ECGF1 gene mutations causing thymidine phosphorylase (TP) deficiency. Analysis of post-mortem samples of five MNGIE patients and two controls, revealed TP activity in all control tissues, but not in MNGIE samples. Converse to TP activity, thymidine and deoxyuridine were absent in control samples, but present in all tissues of MNGIE patients. Concentrations of both nucleosides in the tissues were generally higher than those observed in plasma of MNGIE patients. Our observations indicate that in the absence of TP activity, tissues accumulate nucleosides, which are excreted into plasma.
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Affiliation(s)
- Maria Lucia Valentino
- Department of Neurology, Columbia University Medical Center, 630 W. 168th Street, P&S 4-443, New York, NY 10032, USA
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Synergistic activity of troxacitabine (Troxatyl) and gemcitabine in pancreatic cancer. BMC Cancer 2007; 7:121. [PMID: 17608948 PMCID: PMC1948004 DOI: 10.1186/1471-2407-7-121] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2007] [Accepted: 07/03/2007] [Indexed: 11/10/2022] Open
Abstract
Background Gemcitabine, a deoxycytidine nucleoside analog, is the current standard chemotherapy used as first-line treatment for patients with locally advanced or metastatic cancer of the pancreas, and extends life survival by 5.7 months. Advanced pancreatic cancer thus remains a highly unmet medical need and new therapeutic agents are required for this patient population. Troxacitabine (Troxatyl™) is the first unnatural L-nucleoside analog to show potent preclinical antitumor activity and is currently under clinical investigation. Troxacitabine was recently evaluated as a first-line therapy in 54 patients with advanced adenocarcinoma of the pancreas and gave comparable overall results to those reported with gemcitabine in recently published randomized trials. Methods The human pancreatic adenocarcinoma cell lines, AsPC-1, Capan-2, MIA PaCa-2 and Panc-1, were exposed to troxacitabine or gemcitabine alone or in combination, for 72 h, and the effects on cell growth were determined by electronic particle counting. Synergistic efficacy was determined by the isobologram and combination-index methods of Chou and Talalay. Mechanistic studies addressed incorporation of troxacitabine into DNA and intracellular levels of troxacitabine and gemcitabine metabolites. For in vivo studies, we evaluated the effect of both drugs, alone and in combination, on the growth of established human pancreatic (AsPC-1) tumors implanted subcutaneously in nude mice. Statistical analysis was calculated by a one-way ANOVA with Dunnett as a post-test and the two-tailed unpaired t test using GraphPad prism software. Results Synergy, evaluated using the CalcuSyn Software, was observed in all four cell-lines at multiple drug concentrations resulting in combination indices under 0.7 at Fa of 0.5 (50% reduction of cell growth). The effects of drug exposures on troxacitabine and gemcitabine nucleotide pools were analyzed, and although gemcitabine reduced phosphorylation of troxacitabine when cells were exposed at equal drug concentrations, there was no effect on phosphorylated pools at drug combinations that were synergistic. The amount of troxacitabine incorporated into DNA was also not affected by the presence of gemcitabine. In vivo testing against a human pancreatic (AsPC-1) xenograft mouse tumor model indicated that both drugs were more than additive at well-tolerated doses and schedule. The biological basis for this synergy is unclear as we did not observe changes in apoptosis, DNA repair, troxacitabine incorporation into DNA or troxacitabine metabolism in the presence of gemcitabine. Conclusion These data, together with phase I clinical data showing tolerability of both agents when combined, suggest combination therapy with troxacitabine and gemcitabine warrants further evaluation in advanced pancreatic cancer patients.
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Lara MC, Valentino ML, Torres-Torronteras J, Hirano M, Martí R. Mitochondrial Neurogastrointestinal Encephalomyopathy (MNGIE): Biochemical Features and Therapeutic Approaches. Biosci Rep 2007; 27:151-63. [PMID: 17549623 DOI: 10.1007/s10540-007-9043-2] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Over the last 15 years, important research has expanded our knowledge of the clinical, molecular genetic, and biochemical features of mitochondrial neurogastrointestinal encephalomyopathy (MNGIE). The characterization of mitochondrial involvement in this disorder and the seminal determination of its genetic cause, have opened new possibilities for more detailed and deeper studies on the pathomechanisms in this progressive and fatal disease. It has been established that MNGIE is caused by mutations in the gene encoding thymidine phosphorylase (TP), which lead to absolute or nearly complete loss of its catalytic activity, producing systemic accumulations of its substrates, thymidine (dThd) and deoxyuridine (dUrd). Findings obtained from in vitro and in vivo studies indicate that the biochemical imbalances specifically impair mitochondrial DNA (mtDNA) replication, repair, or both leading to mitochondrial dysfunction. We have proposed that therapy for MNGIE should be aimed at reducing the concentrations of these toxic nucleosides to normal or nearly normal levels. The first treatment, allogeneic stem-cell transplantation (alloSCT) reported in 2006, produced a nearly full biochemical correction of the dThd and dUrd imbalances in blood. Clinical follow-up of this and other patients receiving alloSCT is necessary to determine whether this and other therapies based on a permanent restoration of TP will be effective treatment for MNGIE.
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Affiliation(s)
- M C Lara
- Centre d'Investigacions en Bioquímica i Biologia Molecular, Institut de Recerca Hospital Universitari Vall d'Hebron and Centre for Biomedical Research on Rare Diseases (CIBERER), ISCIII, P. Vall d'Hebron 119-129, 08035, Barcelona, Spain
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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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Sperlágh B, Illes P. Purinergic modulation of microglial cell activation. Purinergic Signal 2006; 3:117-27. [PMID: 18404425 PMCID: PMC2096753 DOI: 10.1007/s11302-006-9043-x] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2006] [Accepted: 01/13/2006] [Indexed: 01/10/2023] Open
Abstract
Microglial cells are resident macrophages in the brain and their activation is an important part of the brain immune response and the pathology of the major CNS diseases. Microglial activation is triggered by pathological signals and is characterized by morphological changes, proliferation, phagocytosis and the secretion of various cytokines and inflammatory mediators, which could be both destructive and protective for the nervous tissue. Purines are one of the most important mediators which regulate different aspects of microglial function. They could be released to the extracellular space from neurons, astrocytes and from the microglia itself, upon physiological neuronal activity and in response to pathological stimuli and cellular damage. Microglial activation is regulated by various subtypes of nucleotide (P2X, P2Y) and adenosine (A₁, A(₂A) and A₃) receptors, which control ionic conductances, membrane potential, gene transcription, the production of inflammatory mediators and cell survival. Among them, the role of P2X₇ receptors is especially well delineated, but P2X₄, various P2Y, A₁, A(₂A) and A₃ receptors also powerfully participate in the microglial response. The pathological role of microglial purine receptors has also been demonstrated in disease models; e.g., in ischemia, sclerosis multiplex and neuropathic pain. Due to their upregulation and selective activation under pathological conditions, they provide new avenues in the treatment of neurodegenerative and neuroinflammatory illnesses.
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Affiliation(s)
- Beáta Sperlágh
- Department of Pharmacology, Institute of Experimental Medicine, Hungarian Academy of Sciences, 1450, Budapest, Hungary
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Garattini S. Pharmacokinetics in cancer chemotherapy. Eur J Cancer 2006; 43:271-82. [PMID: 17174548 DOI: 10.1016/j.ejca.2006.10.015] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2006] [Accepted: 10/30/2006] [Indexed: 11/26/2022]
Affiliation(s)
- Silvio Garattini
- Istituto di Ricerche Farmacologiche Mario Negri, Via Eritrea 62, 20157 Milano, Italy.
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Tanaka KI, Sato T, Ohnishi Y, Nishikawa T. Hydrogen peroxide-induced thymidine incorporation into cultured rat astrocytes. J Pharmacol Sci 2006; 102:296-304. [PMID: 17072101 DOI: 10.1254/jphs.fpj06012x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
We characterized [methyl-(3)H]thymidine ([(3)H]thymidine) and [5-(3)H]uridine ([(3)H]uridine) incorporation into cultured astrocytes and neurons in the presence and absence of hydrogen peroxide (H2O2) in order to define the response to oxidative stress in the central nervous system. [(3)H]Thymidine incorporation into cultured astrocytes was remarkably decreased by N(6),2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP), a permeable analogue of cAMP, which induced a morphological change from the polygonal form (undifferentiated astrocytes) to the process-bearing one (differentiated astrocytes). H2O2 induced [(3)H]thymidine, but not [(3)H]uridine, incorporation into cultured astrocytes at only an early time from 24 h after DBcAMP treatment, although the absolute quantities of [(3)H]thymidine incorporation into astrocytes pretreated with DBcAMP were less than those into astrocytes pretreated without DBcAMP. Hydroxyurea, a replicative DNA synthesis inhibitor, suppressed dose-dependently and completely [(3)H]thymidine incorporation into astrocytes pretreated without DBcAMP, but not astrocytes pretreated with DBcAMP. H2O2 did not stimulate [(3)H]thymidine or [(3)H]uridine incorporation into astrocytes pretreated without DBcAMP and neurons. These findings indicate that only astrocytes pretreated with DBcAMP are able to increase thymidine incorporation specifically in the presence of H2O2 for a purpose other than proliferation, including the repair of H2O2-induced DNA injury, for example.
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Affiliation(s)
- Koh-ichi Tanaka
- Department of Applied Pharmacology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima City, Kagoshima, Japan.
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36
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Nagai K, Nagasawa K, Kihara Y, Okuda H, Fujimoto S. Anticancer nucleobase analogues 6-mercaptopurine and 6-thioguanine are novel substrates for equilibrative nucleoside transporter 2. Int J Pharm 2006; 333:56-61. [PMID: 17088032 DOI: 10.1016/j.ijpharm.2006.09.044] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2006] [Revised: 09/17/2006] [Accepted: 09/26/2006] [Indexed: 01/11/2023]
Abstract
Various antimetabolites of nucleobase analogues, such as 6-mercaptopurine (6-MP), 6-thioguanine (6-TG) and 5-fluorouracil (5-FU), are used for cancer treatments. The first step in nucleobase analogue drug therapy is entry of these compounds into tumor cells. Equilibrative nucleoside transporter 2 (ENT2) was previously reported to have the dual ability of transporting both nucleosides and nucleobases. In the present study, we investigated whether or not these nucleobase analogues are transported via ENT2, using mouse ENT2-overexpressing Cos-7 cells. The hypoxanthine uptake mediated by ENT2 was significantly reduced by the addition of 6-MP and 6-TG, and the inhibition of the hypoxanthine uptake by the 6-thiopurines was competitive. Transfection of ENT2 cDNA into Cos-7 cells resulted in an increase in 6-MP uptake. The 6-MP uptake via ENT2 showed clear time- and substrate concentration-dependent profiles, and was inhibited by 6-TG in an inhibitor concentration-dependent fashion. On the other hand, uracil was not a substrate for ENT2, and 5-FU had no effect on the hypoxanthine uptake via ENT2. Therefore, we concluded that 6-MP and 6-TG, but not 5-FU, are transported mediated by the same recognition site on ENT2 with hypoxanthine.
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Affiliation(s)
- Katsuhito Nagai
- Department of Environmental Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.
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Nagai K, Nagasawa K, Koma M, Hotta A, Fujimoto S. Cytidine is a novel substrate for wild-type concentrative nucleoside transporter 2. Biochem Biophys Res Commun 2006; 347:439-43. [PMID: 16828706 DOI: 10.1016/j.bbrc.2006.06.103] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Accepted: 06/19/2006] [Indexed: 12/01/2022]
Abstract
Nucleoside transporter (NT) plays key roles in the physiology of nucleosides and the pharmacology of its analogues in mammals. We previously cloned Na+/nucleoside cotransporter CNT2 from mouse M5076 ovarian sarcoma cells, the peptide encoded by it differing from that by the previously reported mouse CNT2 in five substitutions, and observed that the transporter can take up cytidine, like CNT1 and CNT3. In the present study, we examined which of the two aforementioned CNT2 is the normal one, and whether or not cytidine is transported via the previously reported CNT2. The peptide encoded by CNT2 derived from mouse intestine, liver, spleen, and ovary was identical to that previously reported. The uptake of [3H]cytidine, but not [3H]thymidine, by Cos-7 cells transfected with CNT2 cDNA obtained from mouse intestine was much greater than that by mock cells, as in the case of [3H]uridine, a typical substrate of NT. [3H]Cytidine and [3H]uridine were taken up via CNT2, in temperature-, extracellular Na+-, and substrate concentration-dependent manners. The uptake of [3H]cytidine and [3H]uridine mediated by CNT2 was significantly inhibited by the variety of nucleosides used in this study, except for thymidine, and inhibition of the [3H]uridine uptake by cytidine was competitive. The [3H]uridine uptake via CNT2 was significantly decreased by the addition of cytarabin or gemcitabine, antimetabolites of cytidine analogue. These results indicated that the previously reported mouse CNT2 is the wild-type one, and cytidine is transported mediated by the same recognition site on the CNT2 with uridine, and furthermore, cytidine analogues may be substrates for the transporter.
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Affiliation(s)
- Katsuhito Nagai
- Department of Environmental Biochemistry, Kyoto Pharmaceutical University, Misasagi, Kyoto 607-8414, Japan.
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38
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Mathias NR, Wu SK, Kim KJ, Lee VHL. Nucleoside transport in primary cultured rabbit tracheal epithelial cells. J Drug Target 2006; 13:509-19. [PMID: 16332576 DOI: 10.1080/10611860500383937] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
The present study aimed at elucidating the mechanisms of nucleoside transport in primary cultured rabbit tracheal epithelial cells (RTEC) grown on a permeable filter support. Uptake of (3)H-uridine, the model nucleoside substrate, from the apical fluid of primary cultured RTEC was examined with respect to its dependence on Na(+), substrate concentration, temperature and its sensitivity to inhibitors, other nucleosides and antiviral nucleoside analogs. Apical (3)H-uridine uptake in primary cultured RTEC was strongly dependent on an inward Na(+) gradient and temperature. Ten micromolar nitro-benzyl-mercapto-purine-ribose (NBMPR) (an inhibitor of es-type nucleoside transport in the nanomolar range) did not further inhibit this process. (3)H-uridine uptake from apical fluid was inhibited by basolateral ouabain (10 microM) and apical phloridzin (100 microM), indicating that uptake may involve a secondary active transport process. Uridine uptake was saturable with a K(m) of 3.4 +/- 1.8 microM and the V(max) of 24.3 +/- 5.2 pmoles/mg protein/30 s. Inhibition studies indicated that nucleoside analogs that have a substitution on the nucleobase competed with uridine uptake from apical fluid, but those with modifications on the ribose sugar including acyclic analogs were ineffective. The pattern of inhibition of apical (3)H-uridine, (3)H-inosine and (3)H-thymidine uptake into RTEC cells by physiological nucleosides was consistent with multiple systems: A pyrimidine-selective transport system (CNT1); a broad nucleoside substrate transport system that excludes inosine (CNT4) and an equilibrative NBMPR-insensitive nucleoside transport system (ei type). These results indicate that the presence of apically located nucleoside transporters in the epithelial cells lining the upper respiratory tract can lead to a high accumulation of nucleosides in the trachea. At least one Na(+)-dependent, secondary, active transport process may mediate the apical absorption of nucleosides or analogous molecules.
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Affiliation(s)
- Neil R Mathias
- Department of Pharmaceutical Sciences, University of Southern California, Los Angeles, 90089-9121, USA
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Bae PK, Kim JH, Kim HS, Chung IK, Paik SG, Lee CK. Intracellular uptake of thymidine and antiherpetic drugs for thymidine kinase-deficient mutants of herpes simplex virus type 1. Antiviral Res 2006; 70:93-104. [PMID: 16546268 DOI: 10.1016/j.antiviral.2006.01.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2005] [Revised: 11/30/2005] [Accepted: 01/20/2006] [Indexed: 11/21/2022]
Abstract
The influence of the thymidine (Thd) kinase (TK) of herpes simplex virus type 1 (HSV-1) on the intracellular uptake and anabolism of nucleosides has been investigated. To compare the differences between the TK-positive (TK(+)) and TK-deficient strains, acyclovir (ACV)-resistant strains were cloned from a cell culture and classified into 2 groups, viz. the TK-partial (TK(p)) and TK-negative (TK(-)). The cellular uptake of thymidine was highly dependent on the viral TK (vTK) activity. The TK(+) strain showed the highest level of intracellular thymidine uptake, the TK(p) strain a moderate level, which varied from strain to strain, and the TK(-) and mock strains showed little uptake. The inhibition of viral replication by ACV, ganciclovir (GCV) and penciclovir (PCV) did not decrease the Thd uptake at all. On the contrary, a notable increase found to be induced by ACV. The influence of the vTK on the uptake of GCV or PCV was much greater than that of ACV. The metabolism was generally less dependent on the vTK activity than the influx. The influx and phosphorylation rates of GCV and PCV were dependent on the substrate specificity of the vTK.
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Affiliation(s)
- Pan Kee Bae
- Pharmacology Research Center, Korea Research Institute of Chemical Technology, Daejon 305-600, South Korea
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40
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Affiliation(s)
- Stephen Locarnini
- Research and Molecular Development, Victorian Infectious Diseases Reference Laboratory, North Melbourne, Vic. 3051, Australia.
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41
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Alanko L, Porkka-Heiskanen T, Soinila S. Localization of equilibrative nucleoside transporters in the rat brain. J Chem Neuroanat 2006; 31:162-8. [PMID: 16448802 DOI: 10.1016/j.jchemneu.2005.12.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2005] [Revised: 12/12/2005] [Accepted: 12/14/2005] [Indexed: 11/21/2022]
Abstract
Adenosine is a recognized inhibitory neuromodulator and neuroprotective agent in the central nervous system. It is produced both intra- and extracellularly and transported across the cell membrane. Nucleoside transporters thus have a major impact on the extracellular adenosine levels, and consequently adenosine signalling. We have raised and characterized polyclonal antibodies against both the equilibrative nucleoside transporters 1 and 2, and report for the first time their distribution in rat brain at the cellular level. Double staining studies were performed to assess the localization of the transporters in neural and glial cells. Both transporters were present in practically all neurons. Some astrocytes showed equilibrative nucleoside transporter 1 staining, while equilibrative nucleoside transporter 2 staining on astrocytes was observed only sporadically.
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Affiliation(s)
- Lauri Alanko
- Department of Physiology, Institute of Biomedicine, University of Helsinki, Finland.
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Wu SK, Mathias NR, Kim KJ, Lee VHL. Functional and pharmacological mechanisms of nucleoside transport across the basolateral membrane of rabbit tracheal epithelial cells. Life Sci 2005; 78:310-20. [PMID: 16111717 DOI: 10.1016/j.lfs.2005.04.066] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2005] [Accepted: 04/22/2005] [Indexed: 10/25/2022]
Abstract
The role of basolateral membrane nucleoside transport in primary cultured rabbit tracheal epithelial cells (RTEC) was studied. Primary cultured RTEC were grown on permeable support at an air-interface. Transport studies were conducted in the uptake, efflux, and transepithelial transport configurations using (3)H-uridine as a model substrate. Time, temperature and concentration dependency of (3)H-uridine transport were evaluated in parallel to the metabolism of this substrate using scintillation counting and thin layer chromatography. Inhibition of (3)H-uridine uptake from basolateral fluid was estimated in presence of all unlabeled natural nucleosides as well as analogs and nucleobases. Functional modulation pathways of (3)H-uridine uptake were studied after treatment of RTEC with pharmacological levels of A23187, forskolin, tamoxifen, H89 and colchicine. The basolateral aspect has a low-affinity and high-capacity transport system that exhibits characteristics of bi-directionality, temperature/concentration dependency, and broad specificity towards purines and pyrimidines without requiring Na(+). Basolateral equilibrative-sensitive/insensitive (es/ei) type transport machinery manifested as a biphasic dose response to nitro-benzyl-mercapto-purine-ribose (NBMPR) inhibition. In addition, a number of therapeutically relevant nucleoside analogs appeared to compete with the uptake of uridine from basolateral fluid. Short-term pre-incubation of primary cultured RTEC with the calcium ionophore A23187 inhibited basolateral uridine uptake without affecting the J(max) and K(m). The inhibitory effect was not reversible with a protein kinase C (PKC) antagonist, tamoxifen. In contrast, basolateral uridine uptake was increased by adenylyl cyclase activator forskolin (reversible with protein kinase A (PKA) inhibitor H89), resulting in a decreased K(m), but a lower J(max). Uridine exit across the basolateral membrane of primary cultured RTEC occurs via a facilitative diffusion carrier, which can be modulated by intracellular Ca(2+) levels and PKA. Information about these carriers will help improve the transportability of antitumor and antiviral nucleoside analogs in the pulmonary setting.
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Affiliation(s)
- Sharon K Wu
- Department of Pharmaceutical Sciences, University of Southern California, Los Angeles, CA 90089-9121, USA.
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Hunsucker SA, Mitchell BS, Spychala J. The 5'-nucleotidases as regulators of nucleotide and drug metabolism. Pharmacol Ther 2005; 107:1-30. [PMID: 15963349 DOI: 10.1016/j.pharmthera.2005.01.003] [Citation(s) in RCA: 201] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/07/2005] [Indexed: 11/19/2022]
Abstract
The 5'-nucleotidases are a family of enzymes that catalyze the dephosphorylation of nucleoside monophosphates and regulate cellular nucleotide and nucleoside levels. While the nucleoside kinases responsible for the initial phosphorylation of salvaged nucleosides have been well studied, many of the catabolic nucleotidases have only recently been cloned and characterized. Aside from maintaining balanced ribo- and deoxyribonucleotide pools, substrate cycles that are formed with kinase and nucleotidase activities are also likely to regulate the activation of nucleoside analogues, a class of anticancer and antiviral agents that rely on the nucleoside kinases for phosphorylation to their active forms. Both clinical and in vitro studies suggest that an increase in nucleotidase activity can inhibit nucleoside analogue activation and result in drug resistance. The physiological role of the 5'-nucleotidases will be covered in this review, as will the evidence that these enzymes can mediate resistance to nucleoside analogues.
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Affiliation(s)
- Sally Anne Hunsucker
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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Roman J, Rivera HN, Roser-Page S, Sitaraman SV, Ritzenthaler JD. Adenosine induces fibronectin expression in lung epithelial cells: implications for airway remodeling. Am J Physiol Lung Cell Mol Physiol 2005; 290:L317-25. [PMID: 16183671 DOI: 10.1152/ajplung.00118.2005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Adenosine is an extracellular nucleoside that is elevated in tissues during hypoxia and ischemia reperfusion and has been implicated in asthma and other lung disorders. There, adenosine is considered an important modulator of physiological functions and inflammation, but its effects on matrix expression and turnover during tissue remodeling are unknown. We examined the effects of adenosine on lung epithelial cells with particular attention to the expression of fibronectin, a matrix glycoprotein highly expressed in injured tissues that has been implicated in wound healing. In A549 lung epithelial cells, we found that adenosine induced expression of fibronectin mRNA and protein in a dose- and time-dependent manner and found that the stimulatory effect of adenosine was inhibited by specific adenosine receptor antagonists. Adenosine stimulation was associated with increased levels of intracellular cAMP and with phosphorylation and DNA binding of the cAMP response element binding protein (CREB), known for its ability to stimulate fibronectin gene transcription. To confirm the latter, A549 cells were transfected with a DNA construct containing the human fibronectin promoter connected to a luciferase reporter gene. Adenosine stimulated transcription of the gene, and this effect was blocked by inhibitors of protein kinase activation. Finally, we tested primary lung fibroblasts and primary alveolar epithelial type II cells and found increased fibronectin expression in response to adenosine. Overall, our observations suggest that adenosine might modulate tissue remodeling by stimulating fibronectin expression in lung epithelial cells through induction of purinergic receptor-mediated signals that target CREB phosphorylation and stimulate fibronectin gene transcription.
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Affiliation(s)
- Jesse Roman
- Department of Medicine, Emory University School of Medicine, and Veterans Affairs Medical Center, Whitehead Biomedical Research Bldg., 615 Michael St., Ste. 205-M, Atlanta, GA 30322, USA.
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Adair TH. Growth regulation of the vascular system: an emerging role for adenosine. Am J Physiol Regul Integr Comp Physiol 2005; 289:R283-R296. [PMID: 16014444 DOI: 10.1152/ajpregu.00840.2004] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The importance of metabolic factors in the regulation of angiogenesis is well understood. An increase in metabolic activity leads to a decrease in tissue oxygenation causing tissues to become hypoxic. The hypoxia initiates a variety of signals that stimulate angiogenesis, and the increase in vascularity that follows promotes oxygen delivery to the tissues. When the tissues receive adequate amounts of oxygen, the intermediate effectors return to normal levels, and angiogenesis ceases. An emerging concept is that adenosine released from hypoxic tissues has an important role in driving the angiogenesis. The following feedback control hypothesis is proposed: AMP is dephosphorylated by ecto-5′-nucleotidase, producing adenosine under hypoxic conditions in the extracellular space adjacent to a parenchymal cell (e.g., cardiomyocyte, skeletal muscle fiber, hepatocyte, etc.). Extracellular adenosine activates A2receptors, which stimulates the release of vascular endothelial growth factor (VEGF) from the parenchymal cell. VEGF binds to its receptor (VEGF receptor 2) on endothelial cells, stimulating their proliferation and migration. Adenosine can also stimulate endothelial cell proliferation independently of VEGF, which probably involves modulation of other proangiogenic and antiangiogenic growth factors and perhaps an intracellular mechanism. In addition, hemodynamic factors associated with adenosine-induced vasodilation may have a role in the development and remodeling of the vasculature. Once a new capillary network has been established, and the diffusion/perfusion capabilities of the vasculature are sufficient to supply the parenchymal cells with adequate amounts of oxygen, adenosine and VEGF as well as other proangiogenic and antiangiogenic growth factors return to near-normal levels, thus closing the negative feedback loop. The available data indicate that adenosine might be an essential mediator for up to 50–70% of the hypoxia-induced angiogenesis in some situations; however, additional studies in intact animals will be required to fully understand the quantitative importance of adenosine.
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Affiliation(s)
- Thomas H Adair
- Dept. of Physiology and Biophysics, University of Mississippi Medical Center, 2500 N. State Street, Jackson, MS 39216-4505, USA.
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Damaraju S, Zhang J, Visser F, Tackaberry T, Dufour J, Smith KM, Slugoski M, Ritzel MWL, Baldwin SA, Young JD, Cass CE. Identification and functional characterization of variants in human concentrative nucleoside transporter 3, hCNT3 (SLC28A3), arising from single nucleotide polymorphisms in coding regions of the hCNT3 gene. Pharmacogenet Genomics 2005; 15:173-82. [PMID: 15861042 DOI: 10.1097/01213011-200503000-00006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
INTRODUCTION Human concentrative nucleoside transporter 3, hCNT3 (SLC28A3), which mediates transport of purine and pyrimidine nucleosides and a variety of antiviral and anticancer nucleoside drugs, was investigated to determine if there are single nucleotide polymorphisms in the coding regions of the hCNT3 gene. METHODS AND RESULTS Ninety-six DNA samples from Caucasians (Coriell Panel) were sequenced and sixteen variants in exons and flanking intronic regions were identified, of which five were coding variants; three of these were non-synonymous (S5N, L131F, Y513F) and were further investigated for functional alterations of the resulting recombinant proteins in Saccharomyces cerevisiae and Xenopus laevis oocytes. In yeast, immunostaining and fluorescence quantitation of the reference (wild-type) and variant CNT3 proteins showed similar levels of expression. Kinetic studies were undertaken in yeast with a high through-put semi-automated assay process; reference hCNT3 exhibited Km values of 1.7+/-0.3, 3.6+/-1.3, 2.2+/-0.7, and 2.1+/-0.6 muM and Vmax values of 1402+/-286, 1310+/-113, 1020+/-44, and 1740+/-114 pmol/mg/min, respectively, for uridine, cytidine, adenosine and inosine. Similar Km and Vmax values were obtained for the three variant proteins assayed in yeast under identical conditions. All of the characterized hCNT3 variants produced in oocytes retained sodium and proton dependence of uridine transport based on measurements of radioisotope flux and two-electrode voltage-clamp studies. CONCLUSION These results suggested a high degree of conservation of function for hCNT3 in the Caucasian population.
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Zhang J, Smith KM, Tackaberry T, Visser F, Robins MJ, Nielsen LPC, Nowak I, Karpinski E, Baldwin SA, Young JD, Cass CE. Uridine binding and transportability determinants of human concentrative nucleoside transporters. Mol Pharmacol 2005; 68:830-9. [PMID: 15955867 DOI: 10.1124/mol.105.012187] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Human concentrative nucleoside transporters 1, 2, and 3 (hCNT1, hCNT2, and hCNT3) exhibit different functional characteristics, and a better understanding of their permeant selectivities is critical for development of nucleoside analog drugs with optimal pharmacokinetic properties. In this study, the sensitivity of a high-throughput yeast expression system used previously for hCNT1 and hCNT3 was improved and used to characterize determinants for interaction of uridine (Urd) with hCNT2. The observed changes of binding energy between hCNT2 and different Urd analogs suggested that it interacts with C3'-OH, C5'-OH, and N3-H of Urd. The C2' and C5 regions of Urd played minor but significant roles for Urd-hCNT2 binding, possibly through Van der Waals interactions. Because the yeast assay only provided information about potential transportability, the permeant selectivities of recombinant hCNT1, hCNT2, and hCNT3 produced in Xenopus laevis oocytes were investigated using a two-electrode voltage clamp assay. hCNT1-mediated transport was sensitive to modifications of the N3, C3', and C5' positions of Urd. hCNT2 showed some tolerance for transporting Urd analogs with C2' or C5 modifications, little tolerance for N3 modifications, and no tolerance for any modifications at C3' or C5' of Urd. Although hCNT3 was sensitive to C3' modifications, it transported a broad range of variously substituted Urd analogs. The transportability profiles identified in this study, which reflected the binding profiles well, should prove useful in the development of anticancer and antiviral therapies with nucleoside drugs that are permeants of members of the hCNT protein family.
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Affiliation(s)
- Jing Zhang
- Department of Oncology, University of Alberta, Cross Cancer Institute, 11540 University Ave., Edmonton, Alberta, Canada T6H 1Z2
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Güttinger M, Padrun V, Pralong WF, Boison D. Seizure suppression and lack of adenosine A1 receptor desensitization after focal long-term delivery of adenosine by encapsulated myoblasts. Exp Neurol 2005; 193:53-64. [PMID: 15817264 DOI: 10.1016/j.expneurol.2004.12.012] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2004] [Revised: 11/25/2004] [Accepted: 12/10/2004] [Indexed: 12/14/2022]
Abstract
Adenosine is an important inhibitory modulator of brain activity. In a previous ex vivo gene therapy approach, local release of adenosine by encapsulated fibroblasts implanted into the vicinity of an epileptic focus, was sufficient to provide transient protection from seizures (Huber, A., Padrun, V., Deglon, N., Aebischer, P., Mohler, H., Boison, D., 2001. Grafts of adenosine-releasing cells suppress seizures in kindling epilepsy. Proc. Natl. Acad. Sci. U. S. A. 98, 7611-7616). Long-term seizure suppression beyond 2 weeks was precluded by limited life expectancy of the encapsulated fibroblasts. To study the feasibility for long-term seizure suppression by adenosine releasing brain implants, in the present contribution, mouse C2C12 myoblasts were engineered to release adenosine by genetic inactivation of adenosine kinase. After encapsulation, the myoblasts were grafted into the lateral brain ventricles of epileptic rats kindled in the hippocampus. While seizure activity in animals with wild-type implants remained unaltered, 1 week after grafting all rats with adenosine-releasing implants (n = 25) displayed complete protection from convulsive seizures and a corresponding reduction of afterdischarges in EEG-recordings. The duration of seizure suppression was maintained for a period of 3 weeks in 50% of the animals ranging to a maximum of 8 weeks in one animal. During the course of these experiments, adenosine A1 receptors remained responsive to selective agonists and antagonists indicating a lack of desensitization of A1 receptors after local long-term exposure to adenosine. Furthermore, local release of adenosine did not affect locomotor activity, whereas systemic application of the A1 agonist 2-chloro-N6-cyclopentyladenosine caused strong sedation. Thus, the local release of adenosine by cellular implants provides a feasible option for a potential side-effect free approach for the long-term treatment of focal epilepsies.
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Affiliation(s)
- Martin Güttinger
- Institute of Pharmacology and Toxicology, University of Zurich, CH-8057 Zürich, Switzerland
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Buursma AR, van Dillen IJ, van Waarde A, Vaalburg W, Hospers GAP, Mulder NH, de Vries EFJ. Monitoring HSVtk suicide gene therapy: the role of [(18)F]FHPG membrane transport. Br J Cancer 2005; 91:2079-85. [PMID: 15599382 PMCID: PMC2409793 DOI: 10.1038/sj.bjc.6602216] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Favourable pharmacokinetics of the prodrug are essential for successful HSVtk/ganciclovir (GCV) suicide gene therapy. [18F]FHPG PET might be a suitable technique to assess the pharmacokinetics of the prodrug GCV noninvasively, provided that [18F]FHPG mimics the behaviour of GCV. Since membrane transport is an important aspect of the pharmacokinetics of the prodrug, we investigated the cellular uptake mechanism of [18F]FHPG in an HSVtk expressing C6 rat glioma cell line and in tumour-bearing rats. The nucleoside transport inhibitors dipyridamol, NBMPR and 2-chloroadenosine did not significantly affect the [18F]FHPG uptake in vitro. Thymidine and uridine significantly decreased [18F]FHPG uptake by 84 and 58%, respectively, but an enzyme assay revealed that this decline was due to inhibition of the HSVtk enzyme rather than membrane transport. Nucleobase transport inhibitors, thymine and adenine, caused a 58 and 55% decline in tracer uptake, respectively. In vivo, the ratio of [18F]FHPG uptake in C6tk and C6 tumours decreased from 3.0±0.5 to 1.0±0.2 after infusion of adenine. Thus, in our tumour model, [18F]FHPG transport exclusively occurred via purine nucleobase transport. In this respect, FHPG does not resemble GCV, which is predominantly taken up via the nucleoside transporter, but rather acyclovir, which is also taken up via the purine nucleobase carrier.
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Affiliation(s)
- A R Buursma
- PET Center, Groningen University Hospital, PO Box 30.001, Hanzeplein 1, 9700 RB Groningen, The Netherlands.
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