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Paroha S, Verma J, Dubey RD, Dewangan RP, Molugulu N, Bapat RA, Sahoo PK, Kesharwani P. Recent advances and prospects in gemcitabine drug delivery systems. Int J Pharm 2021; 592:120043. [DOI: 10.1016/j.ijpharm.2020.120043] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Revised: 10/17/2020] [Accepted: 10/29/2020] [Indexed: 12/13/2022]
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Gote V, Ansong M, Pal D. Prodrugs and nanomicelles to overcome ocular barriers for drug penetration. Expert Opin Drug Metab Toxicol 2020; 16:885-906. [PMID: 32729364 DOI: 10.1080/17425255.2020.1803278] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
INTRODUCTION Ocular barriers hinder drug delivery and reduce drug bioavailability. This article focuses on enhancing drug absorption across the corneal and conjunctival epithelium. Both, transporter targeted prodrug formulations and nanomicellar strategy is proven to enhance the drug permeation of therapeutic agents across various ocular barriers. These strategies can increase aqueous drug solubility and stability of many hydrophobic drugs for topical ophthalmic formulations. AREAS COVERED The article discusses various ocular barriers, ocular influx, and efflux transporters. It elaborates various prodrug strategies used for enhancing drug absorption. Along with this, the article also describes nanomicellar formulation, its characteristic and advantages, and applications in for anterior and posterior segment drug delivery. EXPERT OPINION Prodrugs and nanomicellar formulations provide an effective strategy for improving drug absorption and drug bioavailability across various ocular barriers. It will be exciting to see the efficacy of nanomicelles for treating back of the eye disorders after their topical application. This is considered as a holy grail of ocular drug delivery due to the dynamic and static ocular barriers, restricting posterior entry of topically applied drug formulations.
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Affiliation(s)
- Vrinda Gote
- Division of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City , Kansas City, MO, USA
| | - Michael Ansong
- Division of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City , Kansas City, MO, USA
| | - Dhananjay Pal
- Division of Pharmacology and Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City , Kansas City, MO, USA
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Fattahi N, Shahbazi MA, Maleki A, Hamidi M, Ramazani A, Santos HA. Emerging insights on drug delivery by fatty acid mediated synthesis of lipophilic prodrugs as novel nanomedicines. J Control Release 2020; 326:556-598. [PMID: 32726650 DOI: 10.1016/j.jconrel.2020.07.012] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2020] [Revised: 07/09/2020] [Accepted: 07/10/2020] [Indexed: 12/25/2022]
Abstract
Many drug molecules that are currently in the market suffer from short half-life, poor absorption, low specificity, rapid degradation, and resistance development. The design and development of lipophilic prodrugs can provide numerous benefits to overcome these challenges. Fatty acids (FAs), which are lipophilic biomolecules constituted of essential components of the living cells, carry out many necessary functions required for the development of efficient prodrugs. Chemical conjugation of FAs to drug molecules may change their pharmacodynamics/pharmacokinetics in vivo and even their toxicity profile. Well-designed FA-based prodrugs can also present other benefits, such as improved oral bioavailability, promoted tumor targeting efficiency, controlled drug release, and enhanced cellular penetration, leading to improved therapeutic efficacy. In this review, we discuss diverse drug molecules conjugated to various unsaturated FAs. Furthermore, various drug-FA conjugates loaded into various nanostructure delivery systems, including liposomes, solid lipid nanoparticles, emulsions, nano-assemblies, micelles, and polymeric nanoparticles, are reviewed. The present review aims to inspire readers to explore new avenues in prodrug design based on the various FAs with or without nanostructured delivery systems.
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Affiliation(s)
- Nadia Fattahi
- Department of Chemistry, Faculty of Science, University of Zanjan, P.O. Box 45195-313, Zanjan, Iran; Trita Nanomedicine Research Center (TNRC), Trita Third Millennium Pharmaceuticals, 45331-55681 Zanjan, Iran
| | - Mohammad-Ali Shahbazi
- Drug Research Program, Division of Pharmaceutical Chemistry and Technology, Faculty of Pharmacy, University of Helsinki, Helsinki FI-00014, Finland; Department of Pharmaceutical Nanotechnology, School of Pharmacy, Zanjan University of Medical Sciences, Zanjan, Iran; Zanjan Pharmaceutical Nanotechnology Research Center (ZPNRC), Zanjan University of Medical Sciences, Zanjan, Iran.
| | - Aziz Maleki
- Department of Pharmaceutical Nanotechnology, School of Pharmacy, Zanjan University of Medical Sciences, Zanjan, Iran; Zanjan Pharmaceutical Nanotechnology Research Center (ZPNRC), Zanjan University of Medical Sciences, Zanjan, Iran
| | - Mehrdad Hamidi
- Trita Nanomedicine Research Center (TNRC), Trita Third Millennium Pharmaceuticals, 45331-55681 Zanjan, Iran; Department of Pharmaceutical Nanotechnology, School of Pharmacy, Zanjan University of Medical Sciences, Zanjan, Iran; Zanjan Pharmaceutical Nanotechnology Research Center (ZPNRC), Zanjan University of Medical Sciences, Zanjan, Iran.
| | - Ali Ramazani
- Department of Chemistry, Faculty of Science, University of Zanjan, P.O. Box 45195-313, Zanjan, Iran; Research Institute of Modern Biological Techniques (RIMBT), University of Zanjan, P.O. Box 45195-313, Zanjan, Iran
| | - Hélder A Santos
- Drug Research Program, Division of Pharmaceutical Chemistry and Technology, Faculty of Pharmacy, University of Helsinki, Helsinki FI-00014, Finland; Helsinki Institute of Life Science (HiLIFE), Faculty of Pharmacy, University of Helsinki, Helsinki FI-00014, Finland.
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Correia C, Xavier CPR, Duarte D, Ferreira A, Moreira S, Vasconcelos MH, Vale N. Development of potent CPP6-gemcitabine conjugates against human prostate cancer cell line (PC-3). RSC Med Chem 2020; 11:268-273. [PMID: 33479633 DOI: 10.1039/c9md00489k] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2019] [Accepted: 12/31/2019] [Indexed: 01/19/2023] Open
Abstract
Gemcitabine (dFdC) is a nucleoside analogue used in the treatment of various cancers, being a standard treatment for advanced pancreatic cancer. The effect of gemcitabine is severely compromised due to its rapid plasma degradation, systemic toxicity and drug resistance, which restricts its therapeutic efficacy. Our main goal was to develop new active conjugates of dFdC with novel cell-penetrating hexapeptides (CPP6) to facilitate intracellular delivery of this drug. All new peptides were prepared by solid phase peptide synthesis (SPPS), purified and characterized by HPLC and LC-MS. Cell-penetrating peptides (CPP) contain a considerably high ratio of positively charged amino acids, imparting them with cationic character. Tumor cells are characterized by an increased anionic nature of their membrane surface, a property that could be used by CPP to target these cells. The BxPC-3, MCF-7 and PC-3 cancer cell lines were used to evaluate the in vitro cytotoxicity of conjugates and the results showed that conjugating dFdC with CPP6 significantly enhanced cell growth inhibitory activity on PC-3 cells, with IC50 between 14 and 15 nM. These new conjugates have potential to become new therapeutic tools for cancer therapy.
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Affiliation(s)
- Cristiana Correia
- Laboratory of Pharmacology , Department of Drug Sciences , Faculty of Pharmacy , University of Porto , Rua de Jorge Viterbo Ferreira 228 , 4050-313 Porto , Portugal . .,Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP) , Rua Júlio Amaral de Carvalho , 45 , 4200-135 Porto , Portugal.,Instituto de Investigação e Inovação em Saúde (i3S) , University of Porto , Rua Alfredo Allen, 208 , 4200-135 Porto , Portugal
| | - Cristina P R Xavier
- Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP) , Rua Júlio Amaral de Carvalho , 45 , 4200-135 Porto , Portugal.,Instituto de Investigação e Inovação em Saúde (i3S) , University of Porto , Rua Alfredo Allen, 208 , 4200-135 Porto , Portugal
| | - Diana Duarte
- Laboratory of Pharmacology , Department of Drug Sciences , Faculty of Pharmacy , University of Porto , Rua de Jorge Viterbo Ferreira 228 , 4050-313 Porto , Portugal . .,Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP) , Rua Júlio Amaral de Carvalho , 45 , 4200-135 Porto , Portugal.,Instituto de Investigação e Inovação em Saúde (i3S) , University of Porto , Rua Alfredo Allen, 208 , 4200-135 Porto , Portugal
| | - Abigail Ferreira
- Laboratory of Pharmacology , Department of Drug Sciences , Faculty of Pharmacy , University of Porto , Rua de Jorge Viterbo Ferreira 228 , 4050-313 Porto , Portugal . .,LAQV/REQUIMTE , Department of Chemical Sciences , Faculty of Pharmacy , University of Porto , Rua de Jorge Viterbo Ferreira 228 , 4050-313 Porto , Portugal
| | - Sara Moreira
- Laboratory of Pharmacology , Department of Drug Sciences , Faculty of Pharmacy , University of Porto , Rua de Jorge Viterbo Ferreira 228 , 4050-313 Porto , Portugal . .,Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP) , Rua Júlio Amaral de Carvalho , 45 , 4200-135 Porto , Portugal.,Instituto de Investigação e Inovação em Saúde (i3S) , University of Porto , Rua Alfredo Allen, 208 , 4200-135 Porto , Portugal
| | - M Helena Vasconcelos
- Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP) , Rua Júlio Amaral de Carvalho , 45 , 4200-135 Porto , Portugal.,Instituto de Investigação e Inovação em Saúde (i3S) , University of Porto , Rua Alfredo Allen, 208 , 4200-135 Porto , Portugal.,Laboratory of Microbiology , Department of Biological Sciences , Faculty of Pharmacy , University of Porto , Rua de Jorge Viterbo Ferreira, 228 , 4050-313 Porto , Portugal
| | - Nuno Vale
- Laboratory of Pharmacology , Department of Drug Sciences , Faculty of Pharmacy , University of Porto , Rua de Jorge Viterbo Ferreira 228 , 4050-313 Porto , Portugal . .,Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP) , Rua Júlio Amaral de Carvalho , 45 , 4200-135 Porto , Portugal.,Instituto de Investigação e Inovação em Saúde (i3S) , University of Porto , Rua Alfredo Allen, 208 , 4200-135 Porto , Portugal.,Department of Molecular Pathology and Immunology , Abel Salazar Biomedical Sciences Institute (ICBAS) , University of Porto , Rua de Jorge Viterbo Ferreira 228 , 4050-313 Porto , Portugal
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Dubey RD, Saneja A, Gupta PK, Gupta PN. Recent advances in drug delivery strategies for improved therapeutic efficacy of gemcitabine. Eur J Pharm Sci 2016; 93:147-62. [PMID: 27531553 DOI: 10.1016/j.ejps.2016.08.021] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2016] [Revised: 08/09/2016] [Accepted: 08/10/2016] [Indexed: 02/07/2023]
Abstract
Gemcitabine (2',2'-difluoro-2'-deoxycytidine; dFdC) is an efficacious anticancer agent acting against a wide range of solid tumors, including pancreatic, non-small cell lung, bladder, breast, ovarian, thyroid and multiple myelomas. However, short plasma half-life due to metabolism by cytidine deaminase necessitates administration of high dose, which limits its medical applicability. Further, due to its hydrophilic nature, it cannot traverse cell membranes by passive diffusion and, therefore, enters via nucleoside transporters that may lead to drug resistance. To circumvent these limitations, macromolecular prodrugs and nanocarrier-based formulations of Gemcitabine are gaining wide recognition. The nanoformulations based approaches by virtue of their controlled release and targeted delivery have proved to improve bioavailability, increase therapeutic efficacy and reduce adverse effects of the drug. Furthermore, the combination of Gemcitabine with other anticancer agents as well as siRNAs using nanocarriers has also been investigated in order to enhance its therapeutic potential. This review deals with challenges and recent advances in the delivery of Gemcitabine with particular emphasis on macromolecular prodrugs and nanomedicines.
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Affiliation(s)
- Ravindra Dhar Dubey
- Formulation & Drug Delivery Division, CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu-Tawi 180001, India
| | - Ankit Saneja
- Formulation & Drug Delivery Division, CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu-Tawi 180001, India
| | - Prasoon K Gupta
- Natural Product Chemistry Division, CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu-Tawi 180001, India.
| | - Prem N Gupta
- Formulation & Drug Delivery Division, CSIR-Indian Institute of Integrative Medicine, Canal Road, Jammu-Tawi 180001, India.
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6
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Klaassen CD, Aleksunes LM. Xenobiotic, bile acid, and cholesterol transporters: function and regulation. Pharmacol Rev 2010; 62:1-96. [PMID: 20103563 PMCID: PMC2835398 DOI: 10.1124/pr.109.002014] [Citation(s) in RCA: 548] [Impact Index Per Article: 39.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Transporters influence the disposition of chemicals within the body by participating in absorption, distribution, and elimination. Transporters of the solute carrier family (SLC) comprise a variety of proteins, including organic cation transporters (OCT) 1 to 3, organic cation/carnitine transporters (OCTN) 1 to 3, organic anion transporters (OAT) 1 to 7, various organic anion transporting polypeptide isoforms, sodium taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter, peptide transporters (PEPT) 1 and 2, concentrative nucleoside transporters (CNT) 1 to 3, equilibrative nucleoside transporter (ENT) 1 to 3, and multidrug and toxin extrusion transporters (MATE) 1 and 2, which mediate the uptake (except MATEs) of organic anions and cations as well as peptides and nucleosides. Efflux transporters of the ATP-binding cassette superfamily, such as ATP-binding cassette transporter A1 (ABCA1), multidrug resistance proteins (MDR) 1 and 2, bile salt export pump, multidrug resistance-associated proteins (MRP) 1 to 9, breast cancer resistance protein, and ATP-binding cassette subfamily G members 5 and 8, are responsible for the unidirectional export of endogenous and exogenous substances. Other efflux transporters [ATPase copper-transporting beta polypeptide (ATP7B) and ATPase class I type 8B member 1 (ATP8B1) as well as organic solute transporters (OST) alpha and beta] also play major roles in the transport of some endogenous chemicals across biological membranes. This review article provides a comprehensive overview of these transporters (both rodent and human) with regard to tissue distribution, subcellular localization, and substrate preferences. Because uptake and efflux transporters are expressed in multiple cell types, the roles of transporters in a variety of tissues, including the liver, kidneys, intestine, brain, heart, placenta, mammary glands, immune cells, and testes are discussed. Attention is also placed upon a variety of regulatory factors that influence transporter expression and function, including transcriptional activation and post-translational modifications as well as subcellular trafficking. Sex differences, ontogeny, and pharmacological and toxicological regulation of transporters are also addressed. Transporters are important transmembrane proteins that mediate the cellular entry and exit of a wide range of substrates throughout the body and thereby play important roles in human physiology, pharmacology, pathology, and toxicology.
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Affiliation(s)
- Curtis D Klaassen
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, 3901 Rainbow Blvd., Kansas City, KS 66160-7417, USA.
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7
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Vickers MF, Young JD, Baldwin SA, Ellison MJ, Cass CE. Functional production of mammalian concentrative nucleoside transporters inSaccharomyces cerevisiae. Mol Membr Biol 2009. [DOI: 10.1080/09687680010033306] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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Smith KM, Slugoski MD, Cass CE, Baldwin SA, Karpinski E, Young JD. Cation coupling properties of human concentrative nucleoside transporters hCNT1, hCNT2 and hCNT3. Mol Membr Biol 2009; 24:53-64. [PMID: 17453413 DOI: 10.1080/09687860600942534] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The SLC28 family of concentrative nucleoside transporter (CNT) proteins in mammalian cells contains members of two distinct phylogenic subfamilies. In humans, hCNT1 and hCNT2 belong to one subfamily, and hCNT3 to the other. All three CNTs mediate inwardly-directed Na(+)/nucleoside cotransport, and are either pyrimidine nucleoside-selective (hCNT1), purine nucleoside-selective (hCNT2), or broadly selective for both pyrimidine and purine nucleosides (hCNT3). While previous studies have characterized cation interactions with both hCNT1 and hCNT3, little is known about the corresponding properties of hCNT2. In the present study, heterologous expression in Xenopus oocytes in combination with radioisotope flux and electrophysiological techniques has allowed us to undertake a side-by-side comparison of hCNT2 with other hCNT family members. Apparent K (50) values for Na(+) activation were voltage-dependent, and similar in magnitude for all three transporters. Only hCNT3 was also able to couple transport of uridine to uptake of H(+). The Na(+)/nucleoside stoichiometry of hCNT2, as determined from both Hill coefficients and direct charge/flux measurements, was 1:1. This result was the same as for hCNT1, but different from that of hCNT3 (2:1). The charge-to-(22)Na(+) uptake stoichiometry was 1:1 for all three hCNTs. In parallel with their division into two separate CNT subfamilies, hCNT2 shares common cation specificity and coupling characteristics with hCNT1, which differ markedly from those of hCNT3.
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Affiliation(s)
- Kyla M Smith
- The Membrane Protein Research Group, Department of Physiology, University of Alberta, Alberta, Canada
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Mabel W. L. Ritzel, Amy M. L. Ng, S. Recent molecular advances in studies of the concentrative Na+-dependent nucleoside transporter (CNT) family: identification and characterization of novel human and mouse proteins (hCNT3 and mCNT3) broadly selective for purine and pyrimidine nucleosides (systemcib). Mol Membr Biol 2009. [DOI: 10.1080/09687680118530] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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10
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Redzic ZB, Hasan FA, Al-Sarraf H. Effects of omeprazole treatment on nucleoside transporter expression and adenosine uptake in rat gastric mucosa. Can J Physiol Pharmacol 2009; 87:402-10. [PMID: 19448739 DOI: 10.1139/y09-016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Increased adenosine concentration inhibits gastric acid secretion in rat via adenosine A1 and A2A receptors, whereas achlorhydria suppresses A1 and A2A receptor gene expression. This study aimed to examine the effects of omeprazole-induced achlorhydria on the expression and functional activity of nucleoside transporters in rat gastric mucosa. Wistar rats were treated for either 1 or 3 days with 0.4 mmol/kg omeprazole via gavage; controls were treated with vehicle. The expression of nucleoside transporters at the transcript level was explored by quantitative real-time polymerase chain reaction assays; the functional activity of nucleoside transporters in gastric mucosa was explored by observing [3H]adenosine uptake in vitro. Gastric mucosa expressed rat equilibrative nucleoside transporter (rENT) 1 and 2, and rat concentrative nucleoside transporter (rCNT) 1, 2, and 3 at the transcript level, and the estimated values for the threshold cycles for target amplification (Ct) were 31.5 +/- 2, 28.5 +/- 2.1, 32.9 +/- 2.2, 29.1 +/- 2, and 28.9 +/- 2.5, respectively (n = 3 or 4). The Ct value for rat beta-actin was 21.9 +/- 1.8 (n = 4). In vitro uptake of [3H]adenosine by gastric mucosa samples consisted of Na+-dependent and Na+-independent components. One-day omeprazole treatment caused no change in nucleoside transporter mRNA levels or in [3H]adenosine uptake. Three-day omeprazole treatments, however, led to a 12-fold and 17-fold increase in rENT2 and rCNT1 mRNA levels, respectively. Samples taken after 3 days of treatment also took up significantly more [3H]adenosine than did samples from the corresponding control. In conclusion, the possible modification of nucleoside transport activities by changes in intraluminal acidity may have significance as part of a purinergic regulatory feedback mechanism in the control of gastric acid secretion.
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Affiliation(s)
- Zoran B Redzic
- Department of Physiology, Faculty of Medicine, Kuwait University, P.O. Box 24923, Safat 13110 Kuwait.
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11
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Mannermaa E, Vellonen KS, Urtti A. Drug transport in corneal epithelium and blood-retina barrier: emerging role of transporters in ocular pharmacokinetics. Adv Drug Deliv Rev 2006; 58:1136-63. [PMID: 17081648 DOI: 10.1016/j.addr.2006.07.024] [Citation(s) in RCA: 217] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2006] [Accepted: 07/31/2006] [Indexed: 12/12/2022]
Abstract
Corneal epithelium and blood-retina barrier (i.e. retinal capillaries and retinal pigment epithelium (RPE)) are the key membranes that regulate the access of xenobiotics into the ocular tissues. Corneal epithelium limits drug absorption from the lacrimal fluid into the anterior chamber after eyedrop administration, whereas blood-retina barrier restricts the entry of drugs from systemic circulation to the posterior eye segment. Like in general pharmacokinetics, the role of transporters has been considered to be quite limited as compared to the passive diffusion of drugs across the membranes. As the functional role of transporters is being revealed it has become evident that the transporters are widely important in pharmacokinetics. This review updates the current knowledge about the transporters in the corneal epithelium and blood-retina barrier and demonstrates that the information is far from complete. We also show that quite many ocular drugs are known to interact with transporters, but the studies about the expression and function of those transporters in the eye are still sparse. Therefore, the transporters probably have greater role in ocular pharmacokinetics than we currently realise.
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Affiliation(s)
- Eliisa Mannermaa
- Department of Pharmaceutics, University of Kuopio, FIN-70211 Kuopio, Finland
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12
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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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Vickers MF, Young JD, Baldwin SA, Mackey JR, Cass CE. Nucleoside transporter proteins: emerging targets for drug discovery. ACTA ACUST UNITED AC 2005. [DOI: 10.1517/14728222.4.4.515] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Sakowicz M, Szutowicz A, Pawelczyk T. Insulin and glucose induced changes in expression level of nucleoside transporters and adenosine transport in rat T lymphocytes. Biochem Pharmacol 2004; 68:1309-20. [PMID: 15345320 DOI: 10.1016/j.bcp.2004.06.020] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2004] [Accepted: 06/14/2004] [Indexed: 11/24/2022]
Abstract
Adenosine is an endogenous agent exerting potent action on the immune system including regulation of lymphocyte functioning. Impaired T lymphocyte functioning is a common feature of diabetes. The aims of this study were to examine the effects of glucose and insulin on nucleoside transporters (NT) expression level and adenosine (Ado) transport in rat T lymphocytes cultured under the defined concentrations of glucose and insulin. Performed experiments revealed that rat T lymphocytes expressed the equilibrative nucleoside transporter type 1 and 2 (rENT1, rENT2) and concentrative nucleoside transporter type 2 (rCNT2). The mRNA levels of rENT2 and rCNT2 were highly dependent on insulin but were not affected by changes in extracellular glucose concentration. Exposition of T cells to 10nM insulin resulted in 73% increase in rENT2 mRNA and 50% decrease in the rCNT2 mRNA level. The level of rENT1 mRNA was sensitive to extracellular glucose concentration but not to insulin. The highest differences among cells cultured in high (20mM) and low (5mM) glucose were observed in equilibrative nitrobenzylthioinosine sensitive adenosine transport, which was lowered by 65% in cells cultured at high glucose. Alterations in adenosine transport were accompanied by changes in adenosine accumulation in the cell. These results indicate that adenosine transport in rat T lymphocytes is independently and differentially regulated by glucose and insulin by means of changes in the nucleoside transporters expression level. Altered adenosine transport has a great impact on its intracellular level. This suggests that under diabetic conditions adenosine action on T lymphocytes might be altered.
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Affiliation(s)
- Monika Sakowicz
- Department of Molecular Medicine, Medical University of Gdansk, Poland
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15
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Vickers MF, Zhang J, Visser F, Tackaberry T, Robins MJ, Nielsen LPC, Nowak I, Baldwin SA, Young JD, Cass CE. Uridine recognition motifs of human equilibrative nucleoside transporters 1 and 2 produced in Saccharomyces cerevisiae. NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 2004; 23:361-73. [PMID: 15043160 DOI: 10.1081/ncn-120028333] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The sugar moiety of nucleosides has been shown to play a major role in permeant-transporter interaction with human equilibrative nucleoside transporters 1 and 2 (hENT1 and hENT2). To better understand the structural requirements for interactions with hENT1 and hENT2, a series of uridine analogs with sugar modifications were subjected to an assay that tested their abilities to inhibit [3H]uridine transport mediated by recombinant hENT1 and hENT2 produced in Saccharomyces cerevisiae. hENT1 displayed higher affinity for uridine than hENT2. Both transporters barely tolerated modifications or inversion of configuration at C(3'). The C(2')-OH at uridine was a structural determinant for uridine-hENT1, but not for uridine-hENT2, interactions. Both transporters were sensitive to modifications at C(5') and hENT2 displayed more tolerance to removal of C(5')-OH than hENT1; addition of an O-methyl group at C(5') greatly reduced interaction with either hENT1 or hENT2. The changes in binding energies between transporter proteins and the different uridine analogs suggested that hENT1 formed strong interactions with C(3')-OH and moderate interactions with C(2')-OH and C(5')-OH of uridine, whereas hENT2 formed strong interactions with C(3')-OH, weak interactions with C(5')-OH, and no interaction with C(2')-OH.
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Affiliation(s)
- Mark F Vickers
- Membrane Protein Research Group, University of Alberta, Edmonton, Alberta, Canada
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16
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Smith KM, Ng AML, Yao SYM, Labedz KA, Knaus EE, Wiebe LI, Cass CE, Baldwin SA, Chen XZ, Karpinski E, Young JD. Electrophysiological characterization of a recombinant human Na+-coupled nucleoside transporter (hCNT1) produced in Xenopus oocytes. J Physiol 2004; 558:807-23. [PMID: 15194733 PMCID: PMC1665023 DOI: 10.1113/jphysiol.2004.068189] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Human concentrative nucleoside transporter 1 (hCNT1) mediates active transport of nucleosides and anticancer and antiviral nucleoside drugs across cell membranes by coupling influx to the movement of Na(+) down its electrochemical gradient. The two-microelectrode voltage-clamp technique was used to measure steady-state and presteady-state currents of recombinant hCNT1 produced in Xenopus oocytes. Transport was electrogenic, phloridzin sensitive and specific for pyrimidine nucleosides and adenosine. Nucleoside analogues that induced inwardly directed Na(+) currents included the anticancer drugs 5-fluorouridine, 5-fluoro-2'-deoxyuridine, cladribine and cytarabine, the antiviral drugs zidovudine and zalcitabine, and the novel thymidine mimics 1-(2-deoxy-beta-d-ribofuranosyl)-2,4-difluoro-5-methylbenzene and 1-(2-deoxy-beta-d-ribofuranosyl)-2,4-difluoro-5-iodobenzene. Apparent K(m) values for 5-fluorouridine, 5-fluoro-2'-deoxyuridine and zidovudine were 18, 15 and 450 microm, respectively. hCNT1 was Na(+) specific, and the kinetics of steady-state uridine-evoked Na(+) currents were consistent with an ordered simultaneous transport model in which Na(+) binds first followed by uridine. Membrane potential influenced both ion binding and carrier translocation. The Na(+)-nucleoside coupling stoichiometry, determined directly by comparing the uridine-induced inward charge movement to [(14)C]uridine uptake was 1: 1. hCNT1 presteady-state currents were used to determine the fraction of the membrane field sensed by Na(+) (61%), the valency of the movable charge (-0.81) and the average number of transporters present in the oocyte plasma membrane (6.8 x 10(10) per cell). The hCNT1 turnover rate at -50 mV was 9.6 molecules of uridine transported per second.
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Affiliation(s)
- Kyla M Smith
- Membrane Protein Research Group, Department of Physiology, Faculty of Pharmacy, 7-55 Medical Sciences Building, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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17
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Larráyoz IM, Casado FJ, Pastor-Anglada M, Lostao MP. Electrophysiological Characterization of the Human Na+/Nucleoside Cotransporter 1 (hCNT1) and Role of Adenosine on hCNT1 Function. J Biol Chem 2004; 279:8999-9007. [PMID: 14701834 DOI: 10.1074/jbc.m311940200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We previously reported that the human Na(+)/nucleoside transporter pyrimidine-preferring 1 (hCNT1) is electrogenic and transports gemcitabine and 5'-deoxy-5-fluorouridine, a precursor of the active drug 5-fluorouracil. Nevertheless, a complete electrophysiological characterization of the basic properties of hCNT1-mediated translocation has not been performed yet, and the exact role of adenosine in hCNT1 function has not been addressed either. In the present work we have used the two-electrode voltage clamp technique to investigate hCNT1 transport mechanism and study the kinetic properties of adenosine as an inhibitor of hCNT1. We show that hCNT1 exhibits presteady-state currents that disappear upon the addition of adenosine or uridine. Adenosine, a purine nucleoside described as a substrate of the pyrimidine-preferring transporters, is not a substrate of hCNT1 but a high affinity blocker able to inhibit uridine-induced inward currents, the Na(+)-leak currents, and the presteady-state currents, with a K(i) of 6.5 microM. The kinetic parameters for uridine, gemcitabine, and 5'-deoxy-5-fluorouridine were studied as a function of membrane potential; at -50 mV, K(0.5) was 37, 18, and 245 microM, respectively, and remained voltage-independent. I(max) for gemcitabine was voltage-independent and accounts for approximately 40% that for uridine at -50 mV. Maximal current for 5'-DFUR was voltage-dependent and was approximately 150% that for uridine at all membrane potentials. K(0.5)(Na(+)) for Na(+) was voltage-independent at hyperpolarized membrane potentials (1.2 mM at -50 mV), whereas I(max)(Na(+)) was voltage-dependent, increasing 2-fold from -50 to -150 mV. Direct measurements of (3)H-nucleoside or (22)Na fluxes with the charge-associated revealed a ratio of two positive inward charges per nucleoside and one Na(+) per positive inward charge, suggesting a stoichiometry of two Na(+)/nucleoside.
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Affiliation(s)
- Ignacio M Larráyoz
- Departamento de Fisiología y Nutrición, Universidad de Navarra, Pamplona 31080, Spain
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18
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Bergman AM, Kuiper CM, Voorn DA, Comijn EM, Myhren F, Sandvold ML, Hendriks HR, Peters GJ. Antiproliferative activity and mechanism of action of fatty acid derivatives of arabinofuranosylcytosine in leukemia and solid tumor cell lines. Biochem Pharmacol 2004; 67:503-11. [PMID: 15037202 DOI: 10.1016/j.bcp.2003.09.028] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2003] [Accepted: 09/12/2003] [Indexed: 12/01/2022]
Abstract
1-beta-D-arabinofuranosylcytosine (ara-C) is a deoxycytidine analog with activity in leukemia, which requires phosphorylation by deoxycytidine kinase (dCK) to allow formation of its active phosphate 1-beta-D-arabinofuranosylcytosine triphosphate, but can be deaminated by deoxycytidine deaminase. Altered membrane transport is also a mechanism of drug resistance. In order to facilitate ara-C uptake and prolong retention in the cell, lipophilic prodrugs were synthesized. Fatty acid groups with a varying acyl chain length and number of double bonds were esterified at the 5' position on the sugar moiety of ara-C. The compounds were tested in two pairs of ara-C resistant leukemic cell lines (murine L1210 and rat BCLO and their resistant variants L4A6 and Bara-C, respectively) and two pairs of cell lines with a resistance to gemcitabine, another deoxycytidine analog (human ovarian cancer A2780 and murine colon cancer C26-A and their resistant variants AG6000 and C26-G, respectively). L4A6, Bara-C and AG6000 have varying degrees of decreased dCK activity, while the mechanism for C26-G is not yet clear. In the parent cell lines, ara-C was more active, but in the resistant variants several of the analogs were more active, while the degree of cross-resistance varied. In AG6000 with a total dCK deficiency, all compounds were inactive. Structure-activity relation analysis showed that ara-C derivatives with shorter acyl chains and more double bonds were more active in the parental and drug resistant cells. Further mechanistic studies were performed with the elaidic acid derivative of ara-C (CP-4055). CP-4055 inhibited deamination of dCyd partly and induced DNA synthesis inhibition effectively in C26-A and C26-G cells, but the retention of inhibition was much longer for CP-4055 than for ara-C. In contrast to ara-C, CP-4055 inhibited RNA synthesis for 60% after drug exposure. In conclusion, CP-4055 seems to be a promising prodrug, whose effects were different and longer lasting than for the parent drug.
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Affiliation(s)
- A M Bergman
- Department of Medical Oncology, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, The Netherlands
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19
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Mangravite LM, Badagnani I, Giacomini KM. Nucleoside transporters in the disposition and targeting of nucleoside analogs in the kidney. Eur J Pharmacol 2003; 479:269-81. [PMID: 14612157 DOI: 10.1016/j.ejphar.2003.08.076] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Systemic disposition of nucleosides and nucleoside analogs is dependent on renal handling of these compounds. There are five known, functionally characterized nucleoside transporters with varying substrate specificities for nucleosides: concentrative nucleoside transporters (CNT1-CNT3; Solute Carrier (SLC) 28A1-28A3), which mediate the intracellular flux of nucleosides, and equilibrative nucleoside transporters (ENT1-ENT2; SLC29A1-SLC29A2), which mediate bi-directional facilitated diffusion of nucleosides. All five of these transporters are expressed in the kidney. Concentrative nucleoside transporters primarily localize to the apical membrane of renal epithelial cells while equilibrative nucleoside transporters primarily localize to the basolateral membrane. These transporters work in concert to mediate reabsorptive flux of naturally occurring nucleosides and nucleoside analogs. In addition, equilibrative transporters also participate in secretory flux of some nucleoside analogs. Nucleoside transporters also serve in the targeting of nucleoside analog therapies to renal tumors. This review examines the role that these transporters play in renal disposition of nucleosides and nucleoside analogs in both systemic and kidney-specific therapies.
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Affiliation(s)
- Lara M Mangravite
- Department of Biopharmaceutical Sciences, University of California, San Francisco, 513 Parnassus Avenue, San Francisco, CA 94143-0446, USA
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20
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Buchmann I, Vogg ATJ, Glatting G, Schultheiss S, Möller P, Leithäuser F, Schulte M, Gfrörer W, Kotzerke J, Reske SN. [18F]5-fluoro-2-deoxyuridine-PET for imaging of malignant tumors and for measuring tissue proliferation. Cancer Biother Radiopharm 2003; 18:327-37. [PMID: 12954120 DOI: 10.1089/108497803322285080] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
The nucleoside 5-fluoro-2-deoxyuridine is a pyrimidine analogue accumulating in proliferative cells. We prospectively evaluated biodistribution of the PET tracer [(18)F]5-fluoro-2-deoxyuridine (FdUrd), its value for imaging malignant tumors, and its correlation to both [(18)F]2-fluoro-2-deoxyglucose (FDG)-PET findings and histological proliferation indices. In 11 previously untreated patients (5 lung carcinoma; 3 soft tissue sarcoma; 2 gastrointestinal carcinoma; 1 non-Hodgkin lymphoma [NHL]), mean doses of 290 MBq FdUrd and 390 MBq FDG were administered intravenously on subsequent days. Static PET scans were initiated 50-70 min after administration and the mean standardized uptake values (SUV) were calculated. Dynamic emission FdUrd scans were performed in 8/11 patients. Time-activity curves of blood and tumors as well as SUV of tumor lesions and organs were calculated. Proliferative activity was evaluated by Ki-67 immunohistostaining of biopsies. Tracer accumulated physiologically in liver, kidney, and bladder. SUVs were: kidney, 4.8 +/- 0.66; liver, 4.1 +/- 0.36; vertebrae, 0.70 +/- 0.17; spleen, 0.37 +/- 0.06; lungs, 0.19 +/- 0.05; femora/humeri, 0.14 +/- 0.03. Five patients exhibited significant intratumoral FdUrd-uptake (2 sarcomas; 1 NHL; 2 lung carcinomas) with mean SUVs ranging from 0.7 to 10.5. Metastases were not detected. Time-activity curves showed a rapid initial increase of intratumoral activity followed by activity retention. FDG-PET was positive in 10/11 patients. Correlation between the SUV of FdUrd-PET and FDG-PET or the tissue proliferation index, respectively, was not significant. FdUrd was a suitable tracer for imaging malignant tumors only in exceptional cases: Sarcoma, NHL, and some lung carcinomas were detected. FdUrd-PET was less effective than FDG-PET. In this group of patients, it was not useful in measuring tissue proliferation.
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Affiliation(s)
- Inga Buchmann
- Abteilung für Nuklearmedizin, Universittskliniken Ulm, Germany.
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21
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Clarke ML, Mackey JR, Baldwin SA, Young JD, Cass CE. The role of membrane transporters in cellular resistance to anticancer nucleoside drugs. Cancer Treat Res 2003; 112:27-47. [PMID: 12481710 DOI: 10.1007/978-1-4615-1173-1_2] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
Affiliation(s)
- Marilyn L Clarke
- Department of Experimental Oncology, Cross Cancer Institute, Edmonton, Alberta, Canada
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22
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Pawelczyk T, Podgorska M, Sakowicz M. The effect of insulin on expression level of nucleoside transporters in diabetic rats. Mol Pharmacol 2003; 63:81-8. [PMID: 12488539 DOI: 10.1124/mol.63.1.81] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Evidence that the time course of insulin-induced changes in adenosine level in diabetic rats is different from that observed for expression of adenosine kinase prompted us to study the insulin effect on expression of nucleoside transporters in tissues of diabetic rats. RNase protection assay demonstrated that mRNA levels of equilibrative (rENT) and Na+-dependent nucleoside transporters (rCNT) were altered in diabetic tissues. The rENT1 mRNA level with respect to values obtained in age- and sex-matched nondiabetic rats was decreased by 45, 32, and 10% in diabetic heart, liver, and kidney, respectively. The level of rENT2 mRNA was lowered by 40% in diabetic kidney and heart, and by 24% in diabetic liver. Changes in the expression pattern of rCNT1 and rCNT2 in diabetic tissues differed significantly from that observed for rENT. The levels of rCNT1 and rCNT2 mRNA did not change significantly in diabetic kidney. In diabetic heart, the mRNA levels of rCNT1 and rCNT2 increased 1.7- and 2-fold, respectively. Changes in expression of nucleoside transporters were accompanied by alterations in adenosine content. Administration of insulin to diabetic rats resulted in a drop in adenosine concentration in examined tissues and return of the rCNT1, rCNT2, and rENT2 but not rENT1 mRNA levels to values observed in nondiabetic rats. In summary, these data demonstrate that insulin affects expression of nucleoside transporters in a cell-specific manner. We conclude that change in the expression level of the nucleoside transporters occurring in tissues of diabetic rat is an important factor influencing adenosine levels in the cell.
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Affiliation(s)
- Tadeusz Pawelczyk
- Department of Molecular Medicine, Medical University of Gdansk, Gdansk, Poland.
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23
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Huang M, Wang Y, Collins M, Gu JJ, Mitchell BS, Graves LM. Inhibition of nucleoside transport by p38 MAPK inhibitors. J Biol Chem 2002; 277:28364-7. [PMID: 12077112 DOI: 10.1074/jbc.c200321200] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
While investigating the ability of p38 MAPK to regulate cytarabine (Ara C)-dependent differentiation of erythroleukemia K562 cells, we observed effects that indicated that the imidazoline class of p38 MAPK inhibitors prevented nucleoside transport. Incubation of K562 cells with SB203580, SB203580-iodo, or SB202474, an analogue of SB203580 that does not inhibit p38 MAPK activity, inhibited the uptake of [3H]Ara C or [3H]uridine and the differentiation of K562 cells. Consistent with the effects of these compounds on the nitrobenzylthioinosine (NBMPR)-sensitive equilibrative nucleoside transporter (ENT1), incubation with SB203580 or SB203580-iodo eliminated the binding of [3H]NBMPR to K562 cells or membranes isolated from human erythrocytes. Furthermore, using a uridine-dependent cell type (G9c), we observed that SB203580 or SB203580-iodo efficiently inhibited the salvage synthesis of pyrimidine nucleotides in vivo. Thus these studies demonstrate that the NBMPR-sensitive equilibrative nucleoside transporters are novel and unexpected targets for the p38 MAPK inhibitors at concentrations typically used to inhibit protein kinases.
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Affiliation(s)
- Min Huang
- Department of Pharmacology and the Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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24
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Shimamoto Y, Koizumi K, Okabe H, Kazuno H, Murakami Y, Nakagawa F, Matsuda A, Sasaki T, Fukushima M. Sensitivity of human cancer cells to the new anticancer ribo-nucleoside TAS-106 is correlated with expression of uridine-cytidine kinase 2. Jpn J Cancer Res 2002; 93:825-33. [PMID: 12149149 PMCID: PMC5927072 DOI: 10.1111/j.1349-7006.2002.tb01325.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
TAS-106 [1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine] is a new anticancer ribo-nucleoside with promising antitumor activity. We have previously presented evidence suggesting that the TAS-106 sensitivity of cells is correlated with intracellular accumulation of the triphosphate of TAS-106, which may be affected both by cellular membrane transport mechanisms and uridine-cytidine kinase (UCK) activity. Since the presence of a UCK family consisting of two members, UCK1 and UCK2, has recently been reported in human cells, we investigated the relation between expression of UCK1 and UCK2 at both the mRNA and protein levels and UCK activity (TAS-106 phosphorylation activity) in a panel of 10 human cancer cell lines. Measurement of UCK activity in these cell lines revealed that it was well correlated with the cells' sensitivity to TAS-106. In addition, the mRNA or protein expression level of UCK2 was closely correlated with UCK activity in these cell lines, but neither the level of expression of UCK1 mRNA nor that of protein was correlated with enzyme activity. We therefore compared the protein expression level of UCK2 in several human tumor tissues and the corresponding normal tissues. Expression of UCK2 protein was barely detectable in 4 of the 5 human tumor tissues, but tended to be high in the pancreatic tumor tissue. It could not be detected at all in any of the normal tissues. Thus, expression of UCK2 appeared to be correlated with cellular sensitivity to TAS-106, and it may contribute to the tumor-selective cytotoxicity of TAS-106.
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Affiliation(s)
- Yuji Shimamoto
- Hanno Research Center, Taiho Pharmaceutical Co., Ltd., Hanno, Saitama 357-8527, Japan.
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25
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Bergman AM, Pinedo HM, Peters GJ. Determinants of resistance to 2',2'-difluorodeoxycytidine (gemcitabine). Drug Resist Updat 2002; 5:19-33. [PMID: 12127861 DOI: 10.1016/s1368-7646(02)00002-x] [Citation(s) in RCA: 260] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The inherent or induced resistance of tumors to cytostatic agents is a major clinical problem. In this review, we summarize the pre-clinical mechanisms of acquired and inherent resistance to the fluorinated deoxycytidine analog gemcitabine (2',2'-difluorodeoxycytidine, dFdC, Gemzar((R))), which has proven activity in non-small cell lung carcinoma, pancreatic and bladder cancer. Extensive research has been performed to elucidate the complex mechanism of action of this relatively new drug. Gemcitabine requires phosphorylation to mono-, di- and triphosphates to be active. Similar to the structurally and functionally related deoxycytidine analog ara-C, the first, crucial step in phosphorylation is catalyzed by deoxycytidine kinase (dCK). However, in contrast to ara-C, gemcitabine has multiple intracellular targets; up- or down-regulation of these targets may confer resistance to this drug. Resistance is associated with altered activities of enzymes involved in the metabolism of the drug, of target enzymes, and of enzymes involved in programmed cell death. However, the only strong correlations with gemcitabine sensitivity are dCK activity and dFdCTP pools, with a potential important role for ribonucleotide reductase.
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Affiliation(s)
- Andries M Bergman
- Department of Medical Oncology, VU University Medical Center, Amsterdam, The Netherlands
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26
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Abstract
The body defends itself against potentially harmful compounds like drugs, toxic compounds, and their metabolites by elimination, in which the kidney plays an important role. Renal clearance is used to determine renal elimination mechanisms of a drug, which is the result of glomerular filtration, active tubular secretion and reabsorption. The renal proximal tubule is the primary site of carrier-mediated transport from blood to urine. Renal secretory mechanisms exists for, anionic compounds and organic cations. Both systems comprises several transport proteins, and knowledge of the molecular identity of these transporters and their substrate specificity has increased considerably in the past decade. Due to overlapping specificities of the transport proteins, drug interactions at the level of tubular secretion is an event that may occur in clinical situation. This review describes the different processes that determine renal drug handling, the techniques that have been developed to attain more insight in the various aspects of drug excretion, the functional characteristics of the individual transport proteins, and finally the implications of drug interactions in a clinical perspective.
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Affiliation(s)
- R Masereeuw
- Department of Pharmacology and Toxicology, University Medical Centre Nijmegen, The Netherlands
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27
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Ritzel MW, Ng AM, Yao SY, Graham K, Loewen SK, Smith KM, Ritzel RG, Mowles DA, Carpenter P, Chen XZ, Karpinski E, Hyde RJ, Baldwin SA, Cass CE, Young JD. Molecular identification and characterization of novel human and mouse concentrative Na+-nucleoside cotransporter proteins (hCNT3 and mCNT3) broadly selective for purine and pyrimidine nucleosides (system cib). J Biol Chem 2001; 276:2914-27. [PMID: 11032837 DOI: 10.1074/jbc.m007746200] [Citation(s) in RCA: 263] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The human concentrative (Na(+)-linked) plasma membrane transport proteins hCNT1 and hCNT2 are selective for pyrimidine nucleosides (system cit) and purine nucleosides (system cif), respectively. Both have homologs in other mammalian species and belong to a gene family (CNT) that also includes hfCNT, a newly identified broad specificity pyrimidine and purine Na(+)-nucleoside symporter (system cib) from the ancient marine vertebrate, the Pacific hagfish (Eptatretus stouti). We now report the cDNA cloning and characterization of cib homologs of hfCNT from human mammary gland, differentiated human myeloid HL-60 cells, and mouse liver. The 691- and 703-residue human and mouse proteins, designated hCNT3 and mCNT3, respectively, were 79% identical in amino acid sequence and contained 13 putative transmembrane helices. hCNT3 was 48, 47, and 57% identical to hCNT1, hCNT2, and hfCNT, respectively. When produced in Xenopus oocytes, both proteins exhibited Na(+)-dependent cib-type functional activities. hCNT3 was electrogenic, and a sigmoidal dependence of uridine influx on Na(+) concentration indicated a Na(+):uridine coupling ratio of at least 2:1 for both hCNT3 and mCNT3 (cf 1:1 for hCNT1/2). Phorbol myristate acetate-induced differentiation of HL-60 cells led to the parallel appearance of cib-type activity and hCNT3 mRNA. Tissues containing hCNT3 transcripts included pancreas, bone marrow, trachea, mammary gland, liver, prostate, and regions of intestine, brain, and heart. The hCNT3 gene mapped to chromosome 9q22.2 and included an upstream phorbol myristate acetate response element.
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Affiliation(s)
- M W Ritzel
- Membrane Transport Research Group, Departments of Physiology, Oncology, and Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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28
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Lostao MP, Mata JF, Larrayoz IM, Inzillo SM, Casado FJ, Pastor-Anglada M. Electrogenic uptake of nucleosides and nucleoside-derived drugs by the human nucleoside transporter 1 (hCNT1) expressed in Xenopus laevis oocytes. FEBS Lett 2000; 481:137-40. [PMID: 10996312 DOI: 10.1016/s0014-5793(00)01983-9] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The concentrative pyrimidine-preferring nucleoside transporter 1 (hCNT1), cloned from human fetal liver, was expressed in Xenopus laevis oocytes. Using the two-electrode voltage-clamp technique, it is shown that translocation of nucleosides by this transporter generates sodium inward currents. Membrane hyperpolarization (from -50 to -150 mV) did not affect the K(0.5) for uridine, although it increased the transport current approximately 3-fold. Gemcitabine (a pyrimidine nucleoside-derived drug) but not fludarabine (a purine nucleoside-derived drug) induced currents in oocytes expressing the hCNT1 transporter. The K(0.5) value for gemcitabine at -50 mV membrane potential was lower than that for natural substrates, although this drug induced a lower current than uridine and cytidine, thus suggesting that the affinity binding of the drug transporter is high but that translocation occurs more slowly. The analysis of the currents generated by the hCNT1-mediated transport of nucleoside-derived drugs used in anticancer and antiviral therapies will be useful in the characterization of the pharmacological profile of this family of drug transporters and will allow rapid screening for uptake of newly developed nucleoside-derived drugs.
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Affiliation(s)
- M P Lostao
- Departamento de Fisiologia y Nutrición, Universidad de Navarra, Pamplona, Spain
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29
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Dragan Y, Valdés R, Gomez-Angelats M, Felipe A, Javier Casado F, Pitot H, Pastor-Anglada M. Selective loss of nucleoside carrier expression in rat hepatocarcinomas. Hepatology 2000; 32:239-46. [PMID: 10915730 DOI: 10.1053/jhep.2000.9546] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
Evidence that hepatoma cell lines show differential expression of concentrative nucleoside transporters (CNT1 and CNT2) prompted us to study the transporter proteins in 2 models of hepatocarcinogenesis, the chemically induced Solt and Farber model and the albumin-SV40 large T antigen (Alb-SV40) transgenic rat. CNT1 expression was lower in tumor biopsy specimens from Alb-SV40 rat livers than in normal tissue. Immunocytochemistry revealed that the CNT1 protein was indeed absent in the tumor lesions. CNT1 was also absent in a cell line, L25, derived from the Alb-SV40 transgenic rat liver tumors, whereas another cell line, L37, derived from the normal-appearing parenchyma, retained the expression of both carrier isoforms. The protein expression correlated with the nucleoside transport properties of these cell lines. Moreover, although CNT2 expression was highly dependent on the growth characteristics of the 2 cell lines, as was CNT1 (albeit to a lower extent) in L37 cells, it was not expressed in L25 cells at any stage of cell growth. In contrast to the transgenic model of hepatocarcinogenesis, in the chemically induced tumors the expression of CNT2 was lower, although still detectable. In summary, these data indicate that hepatocarcinogenesis leads to a selective loss or diminished expression of nucleoside carrier isoforms, a feature that may be relevant to our understanding of the molecular basis of the bioavailability of those drugs that are nucleoside derivatives and may be substrates of these carriers. The transport properties and isoform-expression profile of the L25 and L37 cell lines make them suitable hepatocyte culture models with which to study nucleoside transport processes and drug sensitivity.
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Affiliation(s)
- Y Dragan
- McArdle Laboratory for Cancer Research, Department of Oncology, School of Medicine, University of Wisconsin, Madison, WI, USA
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30
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Van Aubel RA, Masereeuw R, Russel FG. Molecular pharmacology of renal organic anion transporters. Am J Physiol Renal Physiol 2000; 279:F216-32. [PMID: 10919840 DOI: 10.1152/ajprenal.2000.279.2.f216] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Renal organic anion transport systems play an important role in the elimination of drugs, toxic compounds, and their metabolites, many of which are potentially harmful to the body. The renal proximal tubule is the primary site of carrier-mediated transport from blood to urine of a wide variety of anionic substrates. Recent studies have shown that organic anion secretion in renal proximal tubule is mediated by distinct sodium-dependent and sodium-independent transport systems. Knowledge of the molecular identity of these transporters and their substrate specificity has increased considerably in the past few years by cloning of various carrier proteins. However, a number of fundamental questions still have to be answered to elucidate the participation of the cloned transporters in the overall tubular secretion of anionic xenobiotics. This review summarizes the latest knowledge on molecular and pharmacological properties of renal organic anion transporters and homologs, with special reference to their nephron and plasma membrane localization, transport characteristics, and substrate and inhibitor specificity. A number of the recently cloned transporters, such as the p-aminohippurate/dicarboxylate exchanger OAT1, the anion/sulfate exchanger SAT1, the peptide transporters PEPT1 and PEPT2, and the nucleoside transporters CNT1 and CNT2, are key proteins in organic anion handling that possess the same characteristics as has been predicted from previous physiological studies. The role of other cloned transporters, such as MRP1, MRP2, OATP1, OAT-K1, and OAT-K2, is still poorly characterized, whereas the only information that is available on the homologs OAT2, OAT3, OATP3, and MRP3-6 is that they are expressed in the kidney, but their localization, not to mention their function, remains to be elucidated.
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Affiliation(s)
- R A Van Aubel
- Department of Pharmacology and Toxicology, Institute of Cellular Signaling, University of Nijmegen, The Netherlands
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Abstract
Pharmaceutical scientists increasingly utilize transporters for drug delivery and targeting. The biological barriers to drug delivery can basically be divided into epithelial, endothelial, elimination, and target cell barriers. Membrane transporters play an important role in drug entrance and exit from the body. In addition, it is possible to utilize transporters for drug delivery, e.g., improving oral absorption via the peptide transporter. Identification, a better understanding of their transport characteristics, and the regulation of the membrane transporters will allow the development of better drug delivery strategies.
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Affiliation(s)
- D M Oh
- Department of Pharmacokinetics, Dynamics, and Metabolism, Parke-Davis Pharmaceutical Research Division, Warner-Lambert Company, Ann Arbor, Michigan 48105, USA
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Patel DH, Crawford CR, Naeve CW, Belt JA. Cloning, genomic organization and chromosomal localization of the gene encoding the murine sodium-dependent, purine-selective, concentrative nucleoside transporter (CNT2). Gene 2000; 242:51-8. [PMID: 10721696 DOI: 10.1016/s0378-1119(99)00521-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A PCR-based strategy was used to isolate a 2653 bp cDNA encoding the mouse sodium-dependent, purine nucleoside selective, concentrative nucleoside transporter (designated mCNT2). The deduced protein sequence exhibits 93 and 80% identity to the previously cloned rat and human sodium-dependent, purine nucleoside selective, nucleoside transporters, respectively. Characterization of 3H-nucleoside uptake by COS-1 cells transiently transfected with the cDNA demonstrated that it encoded a functional nucleoside transport activity with selectivity for purine nucleosides. The cDNA was used to screen a murine (strain 129SvJ/6) genomic library in pBeloBAC11 to identify a clone containing the mCNT2 gene. A PCR strategy was used to identify and sequence the intron-exon boundaries and to determine the approximate sizes of the introns. The mCNT2 gene spans approximately 13.7 kb and is encoded by 15 exons. The gene was mapped to mouse chromosome 2e3 by fluorescence in situ hybridization.
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Affiliation(s)
- D H Patel
- Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
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Graham KA, Leithoff J, Coe IR, Mowles D, Mackey JR, Young JD, Cass CE. Differential transport of cytosine-containing nucleosides by recombinant human concentrative nucleoside transporter protein hCNT1. NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS 2000; 19:415-34. [PMID: 10772724 DOI: 10.1080/15257770008033018] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The transportability of cytosine-containing nucleosides by recombinant hCNT1 was investigated in transfected mammalian cells. Apparent K(m) values for hCNT1-mediated transport of uridine, cytidine and deoxycytidine were, respectively, 59, 140 and 150 microM. Uridine transport was inhibited 89, 32 and 11%, respectively, by 500 microM gemcitabine, cytarabine and lamivudine, demonstrating that, unlike gemcitabine (a high-affinity hCNT1 permeant), cytarabine and lamivudine are poor hCNT1 permeants.
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Affiliation(s)
- K A Graham
- Department of Oncology, University of Alberta, Cross Cancer Institute, Edmonton, Canada
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Chapter 9 Molecular mechanisms of nucleoside and nucleoside drug transport. CURRENT TOPICS IN MEMBRANES 2000. [DOI: 10.1016/s1063-5823(00)50011-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
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35
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Balimane PV, Sinko PJ. Involvement of multiple transporters in the oral absorption of nucleoside analogues. Adv Drug Deliv Rev 1999; 39:183-209. [PMID: 10837774 DOI: 10.1016/s0169-409x(99)00026-5] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Many nucleoside analogues such as azt, ddI, ddC, d4T, 3TC, acv and vacv are currently being used in the treatment of patients infected with HIV, suffering from AIDS, or AIDS-related opportunistic infections. The transport of nucleoside analogues across the gastrointestinal tract is mediated by a number of transporters that fall into three broad categories, i.e., Na(+)-dependent concentrative transporters, Na(+)-independent equilibrative transporters and H(+)/peptide transporters. The first two transporter classes contain a large number of subtypes that are based on the substrate specificity. Recent studies have shown that most of the anti-HIV nucleoside analogues are transported by one or more of the nucleoside transporters. Furthermore, certain analogues, such as acv, appear to be absorbed by non-carrier-mediated diffusion, whereas vacv is apparently transported by non-nucleoside transporters (e.g., the oligopeptide transporter, PepT1 and possibly others). Thus, it is desirable to understand the precise nature of the absorption mechanism of these drugs to improve bioavailability and reduce the variability that is commonly observed in vivo in human patients. A complete understanding of the complex interactions of nucleoside analogues with the various transporters will help in designing better delivery systems and strategies to improve efficacy. In the current report, the mechanisms of nucleoside and nucleoside-analogue transport are reviewed. Also, methods of exploiting prodrugs to improve the bioavailability characteristics of drugs are highlighted.
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Affiliation(s)
- PV Balimane
- College of Pharmacy, Rutgers-The State University of New Jersey, 160 Frelinghuysen Road, Piscataway, NJ, USA
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36
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Baldwin SA, Mackey JR, Cass CE, Young JD. Nucleoside transporters: molecular biology and implications for therapeutic development. MOLECULAR MEDICINE TODAY 1999; 5:216-24. [PMID: 10322314 DOI: 10.1016/s1357-4310(99)01459-8] [Citation(s) in RCA: 263] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The uptake of nucleosides (or nucleobases) is essential for nucleic acid synthesis in many human cell types and in parasitic organisms that cannot synthesize nucleotides de novo. The transporters responsible are also the route of entry for many cytotoxic nucleoside analogues used in cancer and viral chemotherapy. Moreover, by regulating adenosine concentrations in the vicinity of its cell-surface receptors, nucleoside transporters profoundly affect neurotransmission, vascular tone and other processes. The recent molecular characterization of two families of human nucleoside transporters has provided new insights into the mechanisms of natural nucleoside and drug uptake and into future developments of improved therapies.
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Affiliation(s)
- S A Baldwin
- School of Biochemistry and Molecular Biology, University of Leeds, Leeds, UK LS2 9JT.
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Roman RM, Fitz JG. Emerging roles of purinergic signaling in gastrointestinal epithelial secretion and hepatobiliary function. Gastroenterology 1999; 116:964-79. [PMID: 10092320 DOI: 10.1016/s0016-5085(99)70081-8] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- R M Roman
- Division of Gastroenterology, Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
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Cass CE, Young JD, Baldwin SA, Cabrita MA, Graham KA, Griffiths M, Jennings LL, Mackey JR, Ng AM, Ritzel MW, Vickers MF, Yao SY. Nucleoside transporters of mammalian cells. PHARMACEUTICAL BIOTECHNOLOGY 1999; 12:313-52. [PMID: 10742981 DOI: 10.1007/0-306-46812-3_12] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/14/2023]
Abstract
In this review, we have summarized recent advances in our understanding of the biology of nucleoside transport arising from new insights provided by the isolation and functional expression of cDNAs encoding the major nucleoside transporters of mammalian cells. Nucleoside transporters are required for permeation of nucleosides across biological membranes and are present in the plasma membranes of most cell types. There is growing evidence that functional nucleoside transporters are required for translocation of nucleosides between intracellular compartments and thus are also present in organellar membranes. Functional studies during the 1980s established that nucleoside transport in mammalian cells occurs by two mechanistically distinct processes, facilitated diffusion and Na(+)-nucleoside cotransport. The determination of the primary amino acid sequences of the equilibrative and concentrative transporters of human and rat cells has provided a structural basis for the functional differences among the different transporter subtypes. Although nucleoside transporter proteins were first purified from human erythrocytes a decade ago, the low abundance of nucleoside transporter proteins in membranes of mammalian cells has hindered analysis of relationships between transporter structure and function. The molecular cloning of cDNAs encoding nucleoside transporters and the development of heterologous expression systems for production of recombinant nucleoside transporters, when combined with recombinant DNA technologies, provide powerful tools for characterization of functional domains within transporter proteins that are involved in nucleoside recognition and translocation. As relationships between molecular structure and function are determined, it should be possible to develop new approaches for optimizing the transportability of nucleoside drugs into diseased tissues, for development of new transport inhibitors, including reagents that are targeted to the concentrative transporters, and, eventually, for manipulation of transporter function through an understanding of the regulation of transport activity.
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Affiliation(s)
- C E Cass
- Molecular Biology of Membranes Group, University of Alberta, Edmonton, Canada
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39
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Pajor AM. Sequence of a pyrimidine-selective Na+/nucleoside cotransporter from pig kidney, pkCNT1. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1415:266-9. [PMID: 9858747 DOI: 10.1016/s0005-2736(98)00192-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A 3 kb cDNA called pkCNT1, a new member of the Na+/nucleoside cotransporter family, was cloned from pig kidney and sequenced. The sequence of pkCNT1 encodes a 647 amino acid protein that is 84% identical to the sequence of the rat pyrimidine-selective Na+/nucleoside cotransporter, rCNT1. pkCNT1 transports pyrimidines, such as thymidine and uridine, and has a Km for uridine of 9 microM.
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Affiliation(s)
- A M Pajor
- University of Arizona, Department of Physiology, College of Medicine, Tucson, AZ 85724-5051,
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40
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del Santo B, Valdés R, Mata J, Felipe A, Casado FJ, Pastor-Anglada M. Differential expression and regulation of nucleoside transport systems in rat liver parenchymal and hepatoma cells. Hepatology 1998; 28:1504-11. [PMID: 9828213 DOI: 10.1002/hep.510280609] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Primary cultures of rat-liver parenchymal cells show carrier-mediated nucleoside uptake by a mechanism that mainly involves concentrative, Na+-dependent transport activity. In contrast, the hepatoma cell line FAO shows high nucleoside transport activity, although it is mostly accounted for by Na+-independent transport processes. This is associated with a low amount of sodium purine nucleoside transporter (SPNT) mRNA. SPNT encodes a purine-preferring transporter expressed in liver parenchymal cells. To analyze whether SPNT expression is modulated during cell proliferation, SPNT mRNA levels were determined in the early phase of liver growth after partial hepatectomy and in synchronized FAO cells that had been induced to proliferate. SPNT mRNA amounts increased as early as 2 hours after partial hepatectomy. FAO cells induced to proliferate after serum refeeding show an increase in SPNT mRNA levels, which is followed by an increase in Na+-dependent nucleoside uptake and occurs before the peak of 3H-thymidine incorporation into DNA. FAO cells also express significant equilibrative nucleoside transport activity, which may be accounted for by the expression of the nitrobenzylthioinosine (NBTI)-sensitive and -insensitive isoforms, rat equilibrative nucleoside transporter 1 (rENT1) and rENT2, respectively. Interestingly, rENT2 mRNA levels follow a similar pattern to that described for SPNT when FAO cells are induced to proliferate, whereas rENT1 appears to be constitutively expressed. Liver parenchymal cells show low and negligible mRNA levels for rENT1 and rENT2 transporters, respectively, although most of the equilibrative transport activity found in hepatocytes is NBTI-resistant. It is concluded that: 1) SPNT expression is regulated both in vivo and in vitro in a way that appears to be dependent on cell cycle progression; 2) SPNT expression may be a feature of differentiated hepatocytes; and 3) equilibrative transporters are differentially regulated, rENT2 expression being cell cycle-dependent. This is consistent with its putative role as a growth factor-induced delayed early response gene.
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Affiliation(s)
- B del Santo
- Departament de Bioquímica i Biologia Molecular Universitat de Barcelona, Spain
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41
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Jennings LL, Cass CE, Ritzel MW, Yao SY, Young JD, Griffiths M, Baldwin SA. Adenosine transport: Recent advances in the molecular biology of nucleoside transporter proteins. Drug Dev Res 1998. [DOI: 10.1002/(sici)1098-2299(199811/12)45:3/4<277::aid-ddr26>3.0.co;2-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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42
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Ritzel MW, Yao SY, Ng AM, Mackey JR, Cass CE, Young JD. Molecular cloning, functional expression and chromosomal localization of a cDNA encoding a human Na+/nucleoside cotransporter (hCNT2) selective for purine nucleosides and uridine. Mol Membr Biol 1998; 15:203-11. [PMID: 10087507 DOI: 10.3109/09687689709044322] [Citation(s) in RCA: 150] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Two Na(+)-dependent nucleoside transporters implicated in adenosine and uridine transport in mammalian cells are distinguished functionally on the basis of substrate specificity: CNT1 is selective for pyrimidine nucleosides but also transports adenosine; CNT2 (also termed SPNT) is selective for purine nucleosides but also transports uridine. Both proteins belong to a gene family that includes the NupC proton/nucleoside symporter of E. coli. cDNAs encoding members of the CNT family have been isolated from rat tissues (jejunum, brain, liver; rCNT1 and rCNT2/SPNT) and, most recently, human kidney (hCNT1 and hSPNT1). Here, the molecular cloning and functional characterization of a CNT2/SPNT-type transporter from human small intestine are described. The encoded 658-residue protein (hCNT2 in the nomenclature) had the same predicted amino acid sequence as human kidney hSPNT1, except for a polymorphism at residue 75 (Arg substituted by Ser), and was 83 and 72% identical to rCNT2 and hCNT1, respectively. Sequence differences between hCNT2 and rCNT2 were greatest at the N-terminus. In Xenopus oocytes, recombinant hCNT2 exhibited the functional characteristics of a Na(+)-dependent nucleoside transporter with selectivity for adenosine, other purine nucleosides and uridine (adenosine and uridine K(m) app values 8 and 40 microM, respectively). hCNT2 transcripts were found in kidney and small intestine but, unlike rCNT2, were not detected in liver. Deoxyadenosine, which undergoes net renal secretion in humans, was less readily transported than adenosine. hCNT2 also mediated small, but significant, fluxes of the antiviral purine nucleoside analogue 2',3'-dideoxyinosine. hCNT2 is, therefore potentially involved in both the intestinal absorption and renal handling of purine nucleosides (including adenosine), uridine and purine nucleoside drugs. The gene encoding hCNT2 was mapped to chromosome 15q15.
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Affiliation(s)
- M W Ritzel
- Department of Physiology, University of Alberta, Edmonton, Canada
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43
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Sundaram M, Yao SY, Ng AM, Griffiths M, Cass CE, Baldwin SA, Young JD. Chimeric constructs between human and rat equilibrative nucleoside transporters (hENT1 and rENT1) reveal hENT1 structural domains interacting with coronary vasoactive drugs. J Biol Chem 1998; 273:21519-25. [PMID: 9705281 DOI: 10.1074/jbc.273.34.21519] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have recently isolated cDNAs from human placenta and rat jejunum encoding the prototypic human and rat equilibrative nitrobenzylthioinosine (NBMPR)-sensitive nucleoside transporters hENT1 and rENT1. The two proteins (456 and 457 residues, Mr 50,000) are 78% identical in amino acid sequence and contain 11 potential transmembrane segments (TMs) with a large putative extracellular loop between TMs 1 and 2 and a large cytoplasmic loop between TMs 6 and 7. When expressed in Xenopus oocytes, recombinant hENT1 and rENT1 transport both purine and pyrimidine nucleosides, including adenosine, and are inhibited by nanomolar concentrations of NBMPR. hENT1 is also potently inhibited by coronary vasodilator drugs (dipyridamole, dilazep, and draflazine), whereas rENT1 is insensitive to inhibition by these compounds (dipyridamole IC50 values 190 nM (hENT1) and >/=10 microM (rENT1) at 10 microM uridine). In the present study, we have generated reciprocal chimeras between hENT1 and rENT1, using splice sites at residues 99 (end of TM 2) and 231 (end of TM 6), to identify structural domains of hENT1 responsible for transport inhibition by vasoactive compounds. Transplanting the amino-terminal half of hENT1 into rENT1 converted rENT1 into a dipyridamole/dilazep-sensitive transporter, whereas the amino-terminal half of rENT1 rendered hENT1 dipyridamole/dilazep-insensitive. Domain swaps within the amino-terminal halves of hENT1 and rENT1 identified residues 100-231 (incorporating TMs 3-6) of hENT1 as the major site of vasodilator interaction. Since these drugs function as competitive inhibitors of nucleoside transport and NBMPR binding, TMs 3-6 are likely to form part of the substrate-binding site.
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Affiliation(s)
- M Sundaram
- Membrane Transport Research Group, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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Crawford CR, Patel DH, Naeve C, Belt JA. Cloning of the human equilibrative, nitrobenzylmercaptopurine riboside (NBMPR)-insensitive nucleoside transporter ei by functional expression in a transport-deficient cell line. J Biol Chem 1998; 273:5288-93. [PMID: 9478986 DOI: 10.1074/jbc.273.9.5288] [Citation(s) in RCA: 169] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mammalian cells obtain nucleic acid precursors through the de novo synthesis of nucleotides and the salvage of exogenous nucleobases and nucleosides. The first step in the salvage pathway is transport across the plasma membrane. Several transport activities, including equilibrative and concentrative mechanisms, have been identified by their functional properties. We report here the functional cloning of a 2.6-kilobase pair human cDNA encoding the nitrobenzylmercaptopurine riboside (NBMPR)-insensitive, equilibrative nucleoside transporter ei by functional complementation of the transport deficiency in a subline of CEM human leukemia cells. Expression of this cDNA conferred an NBMPR-insensitive, sodium-independent nucleoside transport activity to the cells that exhibited substrate specificity and inhibitor sensitivity characteristic of the ei transporter. The cDNA contained a single open reading frame that encoded a 456-residue protein with 11 potential membrane-spanning regions and two consensus sites for N-glycosylation in the first predicted extracellular loop. The predicted protein was 50% identical to the recently cloned human NBMPR-sensitive, equilibrative nucleoside transporter ENT1 and thus was designated ENT2. Surprisingly, the carboxyl-terminal portion of the ENT2 protein was nearly identical to a smaller protein in the GenBankTM data base (human HNP36, 326 residues) that has been identified as a growth factor-induced delayed early response gene of unknown function. Comparison of the ENT2 and HNP36 nucleotide sequences suggested that HNP36 was translated from a second start codon within the ENT2 open reading frame. Transient expression studies with the full-length ENT2 and a 5'-truncated construct that lacks the first start codon (predicted protein 99% identical to HNP36) demonstrated that only the full-length construct conferred uridine transport activity to the cells. These data suggest that the delayed early response gene HNP36 is a truncated form of ENT2 and that the full-length open reading frame of ENT2 is required for production of a functional plasma membrane ei transporter.
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Affiliation(s)
- C R Crawford
- Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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45
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Yao SY, Ng AM, Muzyka WR, Griffiths M, Cass CE, Baldwin SA, Young JD. Molecular cloning and functional characterization of nitrobenzylthioinosine (NBMPR)-sensitive (es) and NBMPR-insensitive (ei) equilibrative nucleoside transporter proteins (rENT1 and rENT2) from rat tissues. J Biol Chem 1997; 272:28423-30. [PMID: 9353301 DOI: 10.1074/jbc.272.45.28423] [Citation(s) in RCA: 180] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Equilibrative nucleoside transport processes in mammalian cells are either nitrobenzylthioinosine (NBMPR)-sensitive (es) or NBMPR-insensitive (ei). Previously, we isolated a cDNA from human placenta encoding the 456-residue glycoprotein hENT1. When expressed in Xenopus oocytes, hENT1 mediated es-type transport activity and was inhibited by coronary vasoactive drugs (dipyridamole and dilazep) that may compete with nucleosides and NBMPR for binding to the substrate binding site. We now report the molecular cloning and functional expression of es and ei homologs of hENT1 from rat tissues; rENT1 (457 residues) was 78% identical to hENT1 in amino acid sequence, and rENT2 (456 residues) was 49-50% identical to rENT1/hENT1 and corresponded to a full-length form of the delayed-early proliferative response gene product HNP36, a protein of unknown function previously cloned in truncated form. rENT1 was inhibited by NBMPR (IC50 = 4.6 nM at 10 microM uridine), whereas rENT2 was NBMPR-insensitive (IC50 > 1 microM). Both proteins mediated saturable uridine influx (Km = 0.15 and 0.30 mM, respectively), were broadly selective for purine and pyrimidine nucleosides, including adenosine, and were relatively insensitive to inhibition by dipyridamole and dilazep (IC50 > 1 microM). These observations demonstrate that es and ei nucleoside transport activities are mediated by separate, but homologous, proteins and establish a function for the HNP36 gene product.
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Affiliation(s)
- S Y Yao
- Membrane Transport Research Group, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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46
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Wang J, Schaner ME, Thomassen S, Su SF, Piquette-Miller M, Giacomini KM. Functional and molecular characteristics of Na(+)-dependent nucleoside transporters. Pharm Res 1997; 14:1524-32. [PMID: 9434270 DOI: 10.1023/a:1012113931332] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Nucleoside transporters play a critical role in the absorption, disposition, and targeting of therapeutically used nucleosides and nucleoside analogs. This review is focused on the Na(+)-dependent, concentrative nucleoside transporters which are found in a variety of cells including renal, intestinal and hepatic epithelia. Five major Na(+)-dependent nucleoside transporter subtypes have been characterized in isolated tissue preparations: N1 is purine selective; N2 is pyrimidine selective and N3-N5 exhibit variable selectively for both purine and pyrimidine nucleosides. The recent cloning of N1 and N2 nucleoside transporters has provided the first information on the molecular function and structure of concentrative nucleoside transporters. In this manuscript we review the characteristics of the various subtypes of nucleoside transporters and the molecular structure, functional properties, and tissue distribution of the cloned Na(+)-dependent nucleoside transporters. In addition, the interactions of nucleosides and nucleoside analogs with the cloned transporters in mammalian and amphibian expression systems are presented. Mammalian expression systems may be particularly useful during drug development in screening potential compounds for improved bioavailability and tissue specific targeting. Finally, we present our view of future ares of study in the field of nucleoside transporters.
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Affiliation(s)
- J Wang
- Department of Biopharmaceutical Sciences, University of California, San Francisco 94143, USA
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Schaner ME, Wang J, Zevin S, Gerstin KM, Giacomini KM. Transient expression of a purine-selective nucleoside transporter (SPNTint) in a human cell line (HeLa). Pharm Res 1997; 14:1316-21. [PMID: 9358542 DOI: 10.1023/a:1012148016794] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
PURPOSE The goal of this study was to develop a mammalian expression system for the cloned rat intestinal, Na(+)-dependent, purine-selective nucleoside transporter (SPNTint) and to study the interactions of nucleosides and nucleoside analogs with this transporter. METHODS Lipofection was used to transfect HeLa cells with a mammalian expression vector (pcDNA3) containing the cDNA insert encoding SPNTint. Nucleoside transport activity was measured using [3H]inosine, [3H]uridine, [3H]-dideoxyinosine (ddI), and [3H]-2-chloro-2'-deoxyadenosine (2CdA) as model substrates. RESULTS Expression of SPNTint was observed between 36 and 90 h post-transfection, with maximal expression at 66 h. At 66 h, Na(+)-stimulated uptake of [3H]inosine in cells transiently transfected with SPNTint was approximately threefold greater than that in cells transfected with empty vector (p < 0.05). The Na(+)-stimulated uptake of both inosine and uridine was saturable (K(m) = 28.1 +/- 7.1 microM and 20.6 +/- 5.6 microM, respectively) in the transfected cells and was significantly inhibited by the naturally occurring nucleosides (1 mM) inosine and uridine and to a lesser extent by thymidine. The nucleoside analogs ddI (IC50 = 46 microM) and 2CdA (IC50 = 13 microM) also significantly inhibited the Na(+)-stimulated uptake of [3H]inosine. A Na(+)-stimulated uptake of [3H]2CdA was observed suggesting that 2CdA is also a permeant of SPNTint. CONCLUSIONS HeLa cells transiently transfected with SPNTint represent a useful tool to study the kinetics and interactions of drugs with SPNTint.
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Affiliation(s)
- M E Schaner
- Department of Biopharmaceutical Sciences, University of California San Francisco 94143, USA
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Chandrasena G, Giltay R, Patil SD, Bakken A, Unadkat JD. Functional expression of human intestinal Na+-dependent and Na+-independent nucleoside transporters in Xenopus laevis oocytes. Biochem Pharmacol 1997; 53:1909-18. [PMID: 9256166 DOI: 10.1016/s0006-2952(97)00170-6] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We have shown previously that the human jejunal brush border membrane expresses both the N1 (cif) and the N2 (cit) Na+-dependent (concentrative) nucleoside transporters but not the Na+-independent (facilitative) nitrobenzylmercaptopurineriboside (NBMPR)-sensitive (es) transporter (Patil SD and Unadkat JD, Am J Physiol, 272: 1314-1320, 1997). In the present study, we have demonstrated that when Xenopus laevis oocytes are microinjected with human jejunal mRNA, four nucleoside transporters are expressed simultaneously, namely the N1 and N2 Na+-dependent nucleoside transporters and the es and the NBMPR-insensitive (ei) Na+-independent transporters. The expressed Na+-dependent nucleoside transporters showed substrate specificity identical to that previously described by us using jejunal brush border membrane vesicles (Patil SD and Unadkat JD, Am J Physiol, 272: 1314-1320, 1997). The expressed es and ei Na+-independent transporters demonstrated broad substrate selectivity with both purines and pyrimidines capable of inhibiting the uptake of guanosine and thymidine mediated by this transporter. The expressed Na+-dependent nucleoside transporters mediated the transport of their respective nucleoside substrates with a high affinity and a low capacity, whereas the es and the ei transporters mediated the transport of nucleosides with a low affinity and a high capacity. Collectively, these observations suggest that the Na+-independent nucleoside transporters are expressed in the basolateral membrane of the human jejunal epithelium. Based on these data, we hypothesize that the concentrative transporters in the brush border membrane and equilibrative transporters in the basolateral membrane are arranged in series in the human jejunal epithelium to allow efficient vectorial transport of nucleosides from the lumen to the blood. The simultaneous expression of four nucleoside transporters in X. laevis oocytes establishes a basis for molecular cloning of these four human nucleoside transporters.
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Affiliation(s)
- G Chandrasena
- Department of Pharmaceutics, University of Washington, Seattle 98195, USA
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