thioinosine and purine

The thiopurines, 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG), are used in the treatment of leukemia. Incorporation of deoxythioguanosine nucleotides (dG(s)) into the DNA of thiopurine-treated cells causes cell death, but there is also evidence that thiopurine metabolites, particularly the 6-MP metabolite methylthioinosine monophosphate (MeTIMP), inhibit de novo purine synthesis (DNPS). The toxicity of DNPS inhibitors is influenced by methylthioadenosine phosphorylase (MTAP), a gene frequently deleted in cancers. Because the growth of MTAP-deleted tumor cells is dependent on DNPS or hypoxanthine salvage, we would predict such cells to show differential sensitivity to 6-MP and 6-TG. To test this hypothesis, sensitivity to 6-MP and 6-TG was compared in relation to MTAP status using cytotoxicity assays in two MTAP-deficient cell lines transfected to express MTAP: the T-cell acute lymphoblastic leukemic cell line, Jurkat, transfected with MTAP cDNA under the control of a tetracycline-inducible promoter, and a lung cancer cell line (A549-MTAP(-)) transfected to express MTAP constitutively (A549-MTAP(+)). Sensitivity to 6-MP or methyl mercaptopurine riboside, which is converted intracellularly to MeTIMP, was markedly higher in both cell lines under MTAP(-) conditions. Measurement of thiopurine metabolites support the hypothesis that DNPS inhibition is a major cause of cell death with 6-MP, whereas dG(s) incorporation is the main cause of cytotoxicity with 6-TG. These data suggest that thiopurines, particularly 6-MP, may be more effective in patients with deleted MTAP.

Topics: Antimetabolites, Antineoplastic; Cell Line, Tumor; Drug Resistance, Neoplasm; Gene Deletion; Humans; Immunoblotting; Mercaptopurine; Neoplasms; Purine-Nucleoside Phosphorylase; Purines; Thioguanine; Thioinosine; Thionucleotides

Previously, we have shown that hydrogen peroxide (H2O2) and glucose deprivation (GD) induced ATP loss and cell death in astrocytes. Here, we reported that adenosine and related purine nucleos(t)ides recovered cellular ATP level and completely prevented the cell death in rat primary astrocytes co-treated with H2O2 and glucose deprivation. Time- and concentration-dependently, H2O2 induced cell death and ATP loss in glucose-deprived astrocytes. Adenosine or ATP prevented both astrocytic death and ATP loss caused by H2O2/GD in dose-dependent manner. Further, inhibition of adenosine deamination or transport with erythro-9-(-hydroxy-3-nonyl)adenosine or S-(4-nitrobenzyl)-6-thioinosine largely attenuated the protective effect of adenosine. Other purine nucleos(t)ides such as inosine, guanosine, ADP, AMP, ITP and GTP also showed similar protective effects. Adenosine or ATP also blocked the mitochondrial dysfunction and glutathione (GSH) depletion in H2O2-treated glucose-deprived astrocytes. The present results suggest that adenosine and related purine nucleos(t)ides may protect astrocytes from H2O2 and glucose deprivation induced the potentiated death by restoration of cellular ATP level.

Topics: Adenine; Adenosine; Analysis of Variance; Animals; Animals, Newborn; Astrocytes; Benzimidazoles; Carbocyanines; Cell Death; Cells, Cultured; Dose-Response Relationship, Drug; Drug Interactions; Glucose; Hydrogen Peroxide; In Vitro Techniques; L-Lactate Dehydrogenase; Membrane Potentials; Mitochondria; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Purines; Rats; Rats, Sprague-Dawley; Theobromine; Thioinosine; Time Factors; Xanthines

Adenosine is an endogenous nucleoside that signals through G-protein coupled receptors. Extracellular adenosine is required for receptor activation and two pathways have been identified for formation and cellular release of adenosine. The CLASSICAL pathway relies on intracellular formation of adenosine from adenine nucleotides and cellular efflux of adenosine via equilibrative nucleoside transporters (ENTs). The ALTERNATE pathway involves cellular release of adenine nucleotides, hydrolysis via ecto-5'-nucleotidases and extracellular formation of adenosine.. A rat model of cerebral ischemia and primary cultures of rat forebrain astrocytes and neurons were used.. Using a rat model of cerebral ischemia, the ENT1 inhibitor nitrobenzylmercaptopurine ribonucleoside (NBMPR) significantly increased post-ischemic forebrain adenosine levels and significantly decreased hippocampal neuron injury relative to saline-treatment. NBMPR-induced increases in adenosine receptor activation were not detected, suggesting that altering the intracellular:extracellular distribution of adenosine can affect ischemic outcome. Using primary cultures of rat forebrain astrocytes and neurons, adenosine release was evoked by ischemic-like conditions. Dipyridamole, an inhibitor of ENTs, was more effective at inhibiting adenosine release from neurons than from astrocytes. In contrast, alpha , beta-methylene ADP, an inhibitor of ecto-5'-nucleotidase, was effective at inhibiting adenosine release from astrocytes, but not from neurons. Thus, during ischemic-like conditions, neurons released adenosine via the CLASSICAL pathway, while astrocytes released adenosine via the ALTERNATE pathway.. These cell type differences in pathways for adenosine formation during ischemia may allow transport inhibitors to block simultaneously adenosine release from neurons and adenosine uptake into astrocytes. In principle, this could improve neuronal ATP levels without decreasing adenosine receptor activation.

Topics: Adenosine; Affinity Labels; Animals; Astrocytes; Brain Ischemia; Cells, Cultured; Deoxyglucose; Dipyridamole; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Interactions; Glucose; Hypoxia; Inosine; Models, Biological; Neurons; Oligomycins; Phosphodiesterase Inhibitors; Prosencephalon; Purines; Rats; Thioinosine; Tritium

Methotrexate pretreatment of L1210 cells had been shown previously by us to cause an enhancement of the intracellular accumulation of 5-fluorouracil and of the formation of 5-fluorouracil nucleotides which was correlated with synergistic cytotoxicity. This effect of methotrexate was associated with increases in 5-phosphoribosyl-1-pyrophosphate, the cofactor required for the conversion of 5-fluorouracil to 5-fluorouridine-5'-monophosphate (FUMP). Because these influences on 5-fluorouracil metabolism were most likely mediated by the activity of methotrexate as an inhibitor of purine synthesis, the effects of other agents that inhibit purine synthesis were examined. An inhibitor of amidophosphoribosyltransferase, 6-methylmercaptopurine ribonucleoside, the glutamine antagonists, azaserine and 6-diazo-5-oxo-L-norleucine (DON), and the L-aspartate analogue inhibitor of adenylsuccinate synthetase, L-alanosine, all reduced the incorporation of [1-14C]glycine into adenine and guanine bases isolated from nucleic acids. Each drug also resulted in intracellular elevations of 5-phosphoribosyl-1-pyrophosphate that were 15- to 25-fold greater than control levels. These alterations in de novo purine nucleotide synthesis were associated with enhanced intracellular 5-fluorouracil accumulation and synergistic cytotoxicity.

Topics: Alanine; Animals; Azaserine; Cell Line, Tumor; Cell Survival; Diazooxonorleucine; Dose-Response Relationship, Drug; Fluorouracil; Methotrexate; Nucleic Acid Synthesis Inhibitors; Purines; Thioinosine; Thionucleotides; Uracil Nucleotides

Topics: Bone Marrow; Injections, Intravenous; Leukopenia; Mercaptopurine; Mice; Neoplasms; Nucleosides; Pharmacology; Purines; Pyrimidines; Research; Thioinosine; Thrombocytopenia; Toxicology

Topics: Antimetabolites; Child; Humans; Infant; Leukemia; Mercaptopurine; Purines; Thioinosine