title: Nucleoside transporter subtype expression: effects on potency of adenosine kinase inhibitors.
abstract: 1. Adenosine kinase (AK) inhibitors can enhance adenosine levels and potentiate adenosine receptor activation. As the AK inhibitors 5' iodotubercidin (ITU) and 5-amino-5'-deoxyadenosine (NH(2)dAdo) are nucleoside analogues, we hypothesized that nucleoside transporter subtype expression can affect the potency of these inhibitors in intact cells. 3. Three nucleoside transporter subtypes that mediate adenosine permeation of rat cells have been characterized and cloned: equilibrative transporters rENT1 and rENT2 and concentrative transporter rCNT2. We stably transfected rat C6 glioma cells, which express rENT2 nucleoside transporters, with rENT1 (rENT1-C6 cells) or rCNT2 (rCNT2-C6 cells) nucleoside transporters. 3. We tested the effects of ITU and NH(2)dAdo on [(3)H]-adenosine uptake and conversion to [(3)H]-adenine nucleotides in the three cell types. NH(2)dAdo did not show any cell type selectivity. In contrast, ITU showed significant inhibition of [(3)H]-adenosine uptake and [(3)H]-adenine nucleotide formation at concentrations < or =100 nM in rENT1-C6 cells, while concentrations > or =3 microM were required for C6 or rCNT2-C6 cells. 4. Nitrobenzylthioinosine (NBMPR; 100 nM), a selective inhibitor of rENT1, abolished the effects of nanomolar concentrations of ITU in rENT1-C6 cells. 5. This study demonstrates that the effects of ITU, but not NH(2)dAdo, in whole cell assays are dependent upon nucleoside transporter subtype expression. Thus, cellular and tissue differences in expression of nucleoside transporter subtypes may affect the pharmacological actions of some AK inhibitors.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Manitoba, Winnipeg, Canada.
authors.forename: C J
authors.initials: CJ
authors.lastname: Sinclair
authors.forename: A E
authors.initials: AE
authors.lastname: Powell
authors.forename: W
authors.initials: W
authors.lastname: Xiong
authors.forename: C G
authors.initials: CG
authors.lastname: LaRivière
authors.forename: S A
authors.initials: SA
authors.lastname: Baldwin
authors.forename: C E
authors.initials: CE
authors.lastname: Cass
authors.forename: J D
authors.initials: JD
authors.lastname: Young
authors.forename: F E
authors.initials: FE
authors.lastname: Parkinson
mesh_terms: D000227:Adenine Nucleotides / Q000378:metabolism; D000241:Adenosine / Q000493:pharmacokinetics; D000248:Adenosine Kinase / Q000037:antagonists & inhibitors; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D003839:Deoxyadenosines / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D033705:Equilibrative Nucleoside Transport Proteins; D033721:Equilibrative Nucleoside Transporter 1; D033722:Equilibrative-Nucleoside Transporter 2; D015870:Gene Expression; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000502:physiology; D033703:Nucleoside Transport Proteins; D013868:Thioinosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014316:Tritium; D014372:Tubercidin / Q000031:analogs & derivatives* / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
chemical_list: D000227:Adenine Nucleotides; D002352:Carrier Proteins; D003839:Deoxyadenosines; D004791:Enzyme Inhibitors; D033705:Equilibrative Nucleoside Transport Proteins; D033721:Equilibrative Nucleoside Transporter 1; D033722:Equilibrative-Nucleoside Transporter 2; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D033703:Nucleoside Transport Proteins; C438652:Slc29a1 protein, rat; C438655:Slc29a2 protein, rat; C065171:cif nucleoside transporter; D014316:Tritium; C034214:5-iodotubercidin; D013868:Thioinosine; D000248:Adenosine Kinase; C001789:4-nitrobenzylthioinosine; D000241:Adenosine; D014372:Tubercidin