title: Effects of synthetic A3 adenosine receptor agonists on cell proliferation and viability are receptor independent at micromolar concentrations.
abstract: The question as to whether A3 adenosine receptor (A3AR) agonists, N (6)-(3-iodobenzyl)-adenosine-5'-N- methyluronamide (IB-MECA) and 2-chloro-N (6)-(3-iodobenzyl)-adenosine-5'-N-methyluronamide (Cl-IB-MECA), could exert cytotoxic effects at high concentrations with or without the involvement of A3AR has been a controversial issue for a long time. The initial findings suggesting that A3AR plays a crucial role in the induction of cell death upon treatment with micromolar concentrations of IB-MECA or Cl-IB-MECA were revised, however, the direct and unequivocal evidence is still missing. Therefore, the sensitivity of Chinese hamster ovary (CHO) cells transfected with human recombinant A3AR (A3-CHO) and their counter partner wild-type CHO cells, which do not express any of adenosine receptors, to micromolar concentrations of IB-MECA and Cl-IB-MECA was studied. We observed that IB-MECA and Cl-IB-MECA exhibited a strong inhibitory effect on cell proliferation due to the blockage of cell cycle progression at G1/S and G2/M transitions in both A3-CHO and CHO cells. Further analysis revealed that IB-MECA and Cl-IB-MECA attenuated the Erk1/2 signalling irrespectively to A3AR expression. In addition, Cl-IB-MECA induced massive cell death mainly with hallmarks of a necrosis in both cell lines. In contrast, IB-MECA affected cell viability only slightly independently of A3AR expression. IB-MECA induced cell death that exhibited apoptotic hallmarks. In general, the sensitivity of A3-CHO cells to micromolar concentrations of IB-MECA and Cl-IB-MECA was somewhat, but not significantly, higher than that observed in the CHO cells. These results strongly suggest that IB-MECA and Cl-IB-MECA exert cytotoxic effects at micromolar concentrations independently of A3AR expression.
authors.affiliation: Department of Biology, Faculty of Medicine and Dentistry, Palacky University Olomouc, Olomouc, Czech Republic. mlejnek_petr@volny.cz
authors.forename: Petr
authors.initials: P
authors.lastname: Mlejnek
authors.forename: Petr
authors.initials: P
authors.lastname: Dolezel
authors.forename: Ivo
authors.initials: I
authors.lastname: Frydrych
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D058909:Adenosine A3 Receptor Agonists / Q000494:pharmacology*; D000818:Animals; D016466:CHO Cells; D059447:Cell Cycle Checkpoints / Q000187:drug effects*; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003412:Cricetulus; D003603:Cytotoxins / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D043684:Receptor, Adenosine A3 / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014162:Transfection
chemical_list: D058909:Adenosine A3 Receptor Agonists; D003603:Cytotoxins; D043684:Receptor, Adenosine A3; C084956:N(6)-(3-iodobenzyl)-5'-N-methylcarboxamidoadenosine; D051057:Proto-Oncogene Proteins c-akt; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D000241:Adenosine; C090034:2-chloro-N(6)-(3-iodobenzyl)adenosine-5'-N-methyluronamide