RESUMEN
Homozygous 5'-methylthioadenosine phosphorylase (MTAP) deletions occur in approximately 15% of human cancers. Co-deletion of MTAP and methionine adenosyltransferase 2 alpha (MAT2a) induces a synthetic lethal phenotype involving protein arginine methyltransferase 5 (PRMT5) inhibition. MAT2a inhibitors are now in clinical trials for genotypic MTAP-/- cancers, however the MTAP-/- genotype represents fewer than 2% of human colorectal cancers (CRCs), limiting the utility of MAT2a inhibitors in these and other MTAP+/+ cancers. Methylthio-DADMe-immucillin-A (MTDIA) is a picomolar transition state analog inhibitor of MTAP that renders cells enzymatically MTAP-deficient to induce the MTAP-/- phenotype. Here, we demonstrate that MTDIA and MAT2a inhibitor AG-270 combination therapy mimics synthetic lethality in MTAP+/+ CRC cell lines with similar effects in mouse xenografts and without adverse histology on normal tissues. Combination treatment is synergistic with a 104-fold increase in drug potency for inhibition of CRC cell growth in culture. Combined MTDIA and AG-270 decreases S-adenosyl-L-methionine and increases 5'-methylthioadenosine in cells. The increased intracellular methylthioadenosine:S-adenosyl-L-methionine ratio inhibits PRMT5 activity, leading to cellular arrest and apoptotic cell death by causing MDM4 alternative splicing and p53 activation. Combination MTDIA and AG-270 treatment differs from direct inhibition of PRMT5 by GSK3326595 by avoiding toxicity caused by cell death in the normal gut epithelium induced by the PRMT5 inhibitor. The combination of MTAP and MAT2a inhibitors expands this synthetic lethal approach to include MTAP+/+ cancers, especially the remaining 98% of CRCs without the MTAP-/- genotype.
Asunto(s)
Desoxiadenosinas , Metionina Adenosiltransferasa , Neoplasias , Proteína-Arginina N-Metiltransferasas , Purina-Nucleósido Fosforilasa , S-Adenosilmetionina , Animales , Humanos , Ratones , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Desoxiadenosinas/antagonistas & inhibidores , Desoxiadenosinas/genética , Desoxiadenosinas/metabolismo , Sinergismo Farmacológico , Inhibidores Enzimáticos/farmacología , Inhibidores Enzimáticos/uso terapéutico , Metionina Adenosiltransferasa/antagonistas & inhibidores , Metionina Adenosiltransferasa/genética , Metionina Adenosiltransferasa/metabolismo , Neoplasias/genética , Neoplasias/fisiopatología , Neoplasias/terapia , Proteína-Arginina N-Metiltransferasas/antagonistas & inhibidores , Proteína-Arginina N-Metiltransferasas/metabolismo , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas/metabolismo , Purina-Nucleósido Fosforilasa/genética , Purina-Nucleósido Fosforilasa/metabolismo , Pirrolidinas/farmacología , Pirrolidinas/uso terapéutico , S-Adenosilmetionina/metabolismoRESUMEN
Cordycepin, a nucleoside-derivative-isolated form Cordyceps militaris, has been reported to suppress tumor cell proliferation and cause apoptosis. This study investigates the effect of cordycepin on the migration of human glioblastoma cells. Cordycepin suppressed the migration of the human glioblastoma cell lines U87MG and LN229 in transwell and wound healing assays. Cordycepin decreased protein expression of integrin α1, focal adhesion kinase (FAK), p-FAK, paxillin and p-paxillin. The lysosomal inhibitor NH4Cl blocked the ability of cordycepin to inhibit focal adhesion protein expression and glioma cell migration. In addition, the protein phosphatase inhibitors calyculin A and okadaic acid blocked the cordycepin-mediated reduction in p-Akt, p-FAK and migration. Hematoxylin and eosin staining of mouse xenografts demonstrated that cordycepin reduced brain tumor size in vivo. In conclusion, cordycepin inhibited migration of human glioblastoma cells by affecting lysosomal degradation and protein phosphatase activation. This pathway may be a useful target for clinical therapy in the future.
Asunto(s)
Antineoplásicos/uso terapéutico , Apoptosis/efectos de los fármacos , Neoplasias Encefálicas/tratamiento farmacológico , Desoxiadenosinas/uso terapéutico , Glioblastoma/tratamiento farmacológico , Lisosomas/efectos de los fármacos , Fosfoproteínas Fosfatasas/metabolismo , Cloruro de Amonio/farmacología , Animales , Antineoplásicos/química , Antineoplásicos/farmacología , Neoplasias Encefálicas/metabolismo , Neoplasias Encefálicas/patología , Línea Celular Tumoral , Movimiento Celular/efectos de los fármacos , Desoxiadenosinas/antagonistas & inhibidores , Desoxiadenosinas/farmacología , Activación Enzimática/efectos de los fármacos , Inhibidores Enzimáticos/farmacología , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Glioblastoma/metabolismo , Glioblastoma/patología , Humanos , Lisosomas/metabolismo , Lisosomas/patología , Toxinas Marinas , Ratones Desnudos , Proteínas de Neoplasias/antagonistas & inhibidores , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Ácido Ocadaico/farmacología , Oxazoles/farmacología , Fosfoproteínas Fosfatasas/química , Proteolisis/efectos de los fármacos , Carga Tumoral/efectos de los fármacos , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Cordyceps sinensis, a fungus that parasitizes on the larva of Lepidoptera, has been used as a valued traditional Chinese medicine. We investigated the effects of water extracts of Cordyceps sinensis (WECS), and particularly focused on its anticancer and antimetastatic actions. Based on in vitro studies, we report that WECS showed an anticancer action, and this action was antagonized by an adenosine A3 receptor antagonist. Moreover, this anticancer action of WECS was promoted by an adenosine deaminase inhibitor. These results suggest that one of the components of WECS with an anticancer action might be an adenosine or its derivatives. Therefore, we focused on cordycepin (3'-deoxyadenosine) as one of the active ingredients of WECS. According to our experiments, cordycepin showed an anticancer effect through the stimulation of adenosine A3 receptor, followed by glycogen synthase kinase (GSK)-3ß activation and cyclin D1 suppression. Cordycepin also showed an antimetastatic action through inhibiting platelet aggregation induced by cancer cells and suppressing the invasiveness of cancer cells via inhibiting the activity of matrix metalloproteinase (MMP)-2 and MMP-9, and accelerating the secretion of tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 from cancer cells. In conclusion, cordycepin, an active component of WECS, might be a candidate anticancer and antimetastatic agent.
Asunto(s)
Cordyceps/química , Desoxiadenosinas/uso terapéutico , Metástasis de la Neoplasia/tratamiento farmacológico , Pentostatina/farmacología , Fitoterapia , Extractos Vegetales/farmacología , Agonistas del Receptor de Adenosina A3/farmacología , Agonistas del Receptor de Adenosina A3/uso terapéutico , Antagonistas del Receptor de Adenosina A3/farmacología , Animales , Antineoplásicos/administración & dosificación , Antineoplásicos/farmacología , Antineoplásicos/uso terapéutico , Aterosclerosis/tratamiento farmacológico , Línea Celular Tumoral , Desoxiadenosinas/administración & dosificación , Desoxiadenosinas/antagonistas & inhibidores , Desoxiadenosinas/farmacología , Quimioterapia Combinada , Humanos , Macrófagos del Hígado/efectos de los fármacos , Medicina Tradicional China , Metotrexato/uso terapéutico , Modelos Biológicos , Pentostatina/administración & dosificación , Extractos Vegetales/química , Extractos Vegetales/uso terapéutico , Receptor de Adenosina A3 , Transducción de Señal/efectos de los fármacosRESUMEN
This study aimed to verify the effect of 3'-deoxyadenosine and deoxycoformycin on hematologic parameters and adenosine deaminase (ADA) activity in plasma and brain of mice infected with Trypanosoma evansi. Seventy animals were divided into seven groups, which were divided into two subgroups each for sampling on days 4 and 8 post-infection (PI). The groups were composed of three uninfected groups (A-C), namely, not-treated (A), treated with 3'-deoxyadenosine (B), and treated with deoxycoformycin (C) and four infected groups, mice with T. evansi (D-G), namely, not-treated (D), treated with 3'-deoxyadenosine (E), treated with deoxycoformycin (F), and treated with a combination 3'-deoxyadenosine and deoxycoformycin (G). Hematological parameters and ADA activity were evaluated in plasma and brain. Animals in groups B and C exhibited a reduction in the levels of plasma total protein compared group A. Animals in groups D and F showed changes in the hematological parameters. The ADA activity significantly reduced in the animals of groups C, D, F and G. Mice in the group E presented increased ADA activity in plasma. Therefore, we conclude that the treatment interferes significantly in the hematologic parameters in mice infected with T. evansi. On the other hand, when the ADA inhibitor was used we observed a significant decrease in the values of hematocrit, total erythrocytes, and hemoglobin concentration. The deoxycoformycin was able to inhibit the ADA activity of parasite thus it may be one of the mechanisms of efficacy of this treatment.
Asunto(s)
Inhibidores de la Adenosina Desaminasa/uso terapéutico , Adenosina Desaminasa/metabolismo , Encéfalo/enzimología , Pentostatina/uso terapéutico , Tripanosomiasis/tratamiento farmacológico , Adenosina Desaminasa/sangre , Inhibidores de la Adenosina Desaminasa/farmacología , Animales , Proteínas Sanguíneas/efectos de los fármacos , Proteínas Sanguíneas/metabolismo , Encéfalo/efectos de los fármacos , Desoxiadenosinas/antagonistas & inhibidores , Desoxiadenosinas/farmacología , Desoxiadenosinas/uso terapéutico , Relación Dosis-Respuesta a Droga , Recuento de Eritrocitos , Femenino , Hematócrito , Hemoglobinas/análisis , Recuento de Leucocitos , Ratones , Parasitemia/tratamiento farmacológico , Pentostatina/farmacología , Trypanosoma/efectos de los fármacos , Trypanosoma/enzimología , Tripanosomiasis/sangre , Tripanosomiasis/enzimologíaRESUMEN
MTAN has been known to occur in a variety of bacterial cell types. Due to the evolution of bacterial strains which are resistant to some of the most powerful antibiotics there has been a renewed interest in the development of novel anti-microbial agents. Presented herein is a synthesis of a potent MTAN inhibitor, namely 2-amino-4-[5-(4-amino-5H-pyrrolo[3,2-d]pyrimidin-7-yl)-3,4-dihydroxypyrrolidin-2-ylmethylsulfanyl]-butyric acid (1).
Asunto(s)
Butiratos/síntesis química , Butiratos/farmacología , Desoxiadenosinas/antagonistas & inhibidores , S-Adenosilhomocisteína/antagonistas & inhibidores , Tionucleósidos/antagonistas & inhibidores , Espectrofotometría UltravioletaRESUMEN
To identify the cellular gene target for Tat, we performed gene expression profile analysis and found that Tat up-regulates the expression of the OGG1 (8-oxoguanine-DNA glycosylase-1) gene, which encodes an enzyme responsible for repairing the oxidatively damaged guanosine, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG). We observed that Tat induced OGG1 gene expression by enhancing its promoter activity without changing its mRNA stability. We found that the upstream AP-4 site within the OGG1 promoter is responsible and that Tat interacted with AP-4 and removed AP-4 from the OGG1 promoter by in vivo chromatin immunoprecipitation assay. Thus, Tat appears to activate OGG1 expression by sequestrating AP-4. Interestingly, although Tat induces oxidative stress known to generate 8-oxo-dG, which causes the G:C to T:A transversion, we observed that the amount of 8-oxo-dG was reduced by Tat. When OGG1 was knocked down by small interfering RNA, Tat increased the amount of 8-oxo-dG, thus confirming the role of OGG1 in preventing the formation of 8-oxo-dG. These findings collectively indicate the possibility that Tat may play a role in maintenance of the genetic integrity of the proviral and host cellular genomes by up-regulating OGG1 as a feed-forward mechanism.
Asunto(s)
ADN Glicosilasas/genética , Productos del Gen tat/farmacología , Regulación hacia Arriba/efectos de los fármacos , Sitios de Unión , Línea Celular , ADN Glicosilasas/fisiología , Proteínas de Unión al ADN , Desoxiadenosinas/antagonistas & inhibidores , Desoxiadenosinas/biosíntesis , Perfilación de la Expresión Génica , Regulación de la Expresión Génica/efectos de los fármacos , Humanos , Regiones Promotoras Genéticas/efectos de los fármacos , Estabilidad del ARN , Factores de Transcripción , Regulación hacia Arriba/genéticaRESUMEN
Our past work on nucleoside toxicity in sympathetic neurons has clearly revealed that adenosine and 2'-deoxyadenosine (dAdo) have different mechanisms of action in inducing apoptotic death. For example, adenosine is toxic to neurons only during early phase of growth whereas dAdo kills even mature neurons. In this study, we hypothesize that dAdo-induced apoptosis is initiated when ATP concentration of sympathetic neurons decreases below a critical level. To prove our hypothesis we used adenosine as a tool to replenish ATP levels of sympathetic neurons. We demonstrate that dAdo toxicity in mature sympathetic neurons was fully prevented by adenosine treatment. Furthermore, we demonstrate that depletion of ATP caused by dAdo was prevented by pretreatment with adenosine. These data suggest that intracellular accumulation of adenosine could play a neuroprotective role in preventing death associated with reduction in neuronal ATP concentration.
Asunto(s)
Adenosina/farmacología , Apoptosis/efectos de los fármacos , Desoxiadenosinas/toxicidad , Neuronas/efectos de los fármacos , Sistema Nervioso Simpático/efectos de los fármacos , Animales , Embrión de Pollo , Desoxiadenosinas/antagonistas & inhibidores , Evaluación Preclínica de Medicamentos , Ganglios Espinales/efectos de los fármacos , Ganglios Espinales/patología , Neuronas/patología , Sistema Nervioso Simpático/citologíaRESUMEN
As neutropenia is a common side effect of treatment with 2-chlorodeoxyadenosine (2-CdA), we investigated the myelosuppressive action of 2-CdA in Dexter-type human long-term bone marrow cultures (LTBMCs). LTBMCs were incubated with varying doses of 2-CdA (5 to 20 nM/L) during the first week. At 20 and 10 nM/L 2-CdA, we found a marked reduction in colony-forming unit-granulocyte/macrophage (CFU-GM) production throughout the culture period of 7 weeks (maximum reduction to 3.5% of untreated control cultures with 20 nM/L and to 27.2% with 10 nM/L, respectively). Even the lowest 2-CdA dose tested (5 nM/L) strongly reduced the number of CFU-GM progenitors during the first 3 weeks (maximum reduction to 52.4% of untreated controls), but this effect was transient, and values had recovered to normal within in 5 weeks. 2-CdA was also shown to cause a dose-dependent decrease in long-term culture-initiating cell (LTCIC) detections after 5 weeks in culture (49.6% of control cultures with 10 nM/L 2-CdA and 14% with 20 nM/L 2-CdA, respectively). When 2-CdA was added to LTBMCs initiated on preformed irradiated stromal feeder layers, similar results on CFU-GM production were obtained, indicating that the effects observed were not secondary to effects on the formation of a supportive layer. In addition, IL-6-concentrations in the supernatant of LTBMCs measured at various intervals after the addition of fresh medium with or without 2-CdA showed no significant decrease in cultures treated with 2-CdA. As neutropenia has been shown to be associated with a small but significant risk of fatal infection, we subsequently investigated the reversal potential of the 2-CdA effect by addition of recombinant human granulocyte colony-stimulating factor (rhG-CSF) or rh interleukin-3 (rhIL-3). The weekly addition of 100 ng/mL rhG-CSF counteracted the 2-CdA-mediated decrease in CFU-GM numbers during the entire period of 7 weeks, reaching statistical significance from weeks 3 to 7 (p < 0.05). Addition of rhIL-3 (100 ng/mL) showed an enhancement of CFU-GM output in 2-CdA-treated cultures that resulted in their numbers exceeding those in control cultures (without 2-CdA) from weeks 1 to 5 (p < 0.05) with a maximum increase of 5.1-fold over the parallel control value at week 3.(ABSTRACT TRUNCATED AT 400 WORDS)
Asunto(s)
2-Cloroadenosina/análogos & derivados , Desoxiadenosinas/farmacología , Factor Estimulante de Colonias de Granulocitos/farmacología , Células Madre Hematopoyéticas/efectos de los fármacos , Interleucina-3/farmacología , 2-Cloroadenosina/antagonistas & inhibidores , 2-Cloroadenosina/farmacología , Médula Ósea/metabolismo , División Celular/efectos de los fármacos , Células Cultivadas , Ensayo de Unidades Formadoras de Colonias , Desoxiadenosinas/antagonistas & inhibidores , Antagonismo de Drogas , Humanos , Interleucina-6/biosíntesisRESUMEN
Carcinogenesis is a complex process characterized by the cumulative activation of various oncogenes and the inactivation of suppressor genes. Epigenetic mechanisms are also involved. Mutational activation of ras family genes occurs in most spontaneous or carcinogen-induced liver tumors, in susceptible mice, and less frequently in preneoplastic lesions. This suggests a pathogenetic role of these changes in hepatic carcinogenesis, in the mouse. Overexpression of various growth-related genes occurs in preneoplastic tissue during rat liver carcinogenesis, but mutational activation of protooncogenes, notably of ras family genes, seems to be a late and rare event, while c-myc amplification is a late but frequent event in both rodent and human carcinogenesis. However, mutation of the suppressor p53 gene has been found in relatively early preneoplastic lesions in rat liver, and it may be frequently seen in human hepatocellular carcinomas. The possibility that this mutation is involved in the initiation stage of liver carcinogenesis is an attractive hypothesis which needs further evaluation. DNA hypomethylation is involved in carcinogenesis, but the mechanisms underlying this effect are still elusive. Hypomethylation of growth-related genes is associated with their overexpression and this could favor overgrowth of preneoplastic liver tissue. Decrease in S-adenosyl methionine/S-adenosylhomocysteine (SAM/SAH) ratio occurs in the liver of rats fed a methyl deficient diet, which is a carcinogenic treatment, and in preneoplastic liver tissue, developing in initiated/promoted rats fed an adequate diet. The role of low SAM/SAH ratio in carcinogenesis is substantiated by the tumor chemopreventive effect of lipotropic compounds. Treatment with exogenous SAM prevents the development of preneoplastic and neoplastic lesions in rat liver. This is associated with recovery of SAM/SAH ratio, DNA methylation and inhibition of growth-related gene expression. SAM effect on prenoplastic cell growth is abolished by 5-azacytidine, a hypomethylating agent, indicating the involvement of DNA methylation. The possibility that in SAM-treated rats, methylation and inhibition of the expression of growth-related genes is implicated in growth restraint is attractive and should be further evaluated. Modulation of rat liver carcinogenesis by influencing gene expression through DNA methylation or other epigenetic mechanisms could be a new approach to chemoprevention of these tumors.
Asunto(s)
Adenoma/genética , Carcinoma Hepatocelular/genética , ADN de Neoplasias/metabolismo , Desoxiadenosinas/antagonistas & inhibidores , Genes ras/genética , Neoplasias Hepáticas/genética , Mutación Puntual/genética , Lesiones Precancerosas/genética , S-Adenosilmetionina/farmacología , Tionucleósidos/antagonistas & inhibidores , Adenoma/prevención & control , Animales , Carcinoma Hepatocelular/prevención & control , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Genes myc/genética , Genes p53/genética , Neoplasias Hepáticas/prevención & control , Metilación , Ratones , Ratones Endogámicos , Lesiones Precancerosas/prevención & control , RatasRESUMEN
We compared deoxyadenosine (AdR)- and cyclic AMP (cAMP)-induced cell cycle arrest and cytotoxicity in wild type and mutant S49 cells to determine whether they resulted from the same or different mechanisms. Cyclic AMP and deoxyadenosine are synergistic rather than additive in cytotoxicity assays, suggesting different mechanisms of toxicity. Although cyclic AMP causes cell death after 72 h, in concentrations sufficient to result in cell cycle arrest it is reversible with virtually no cytotoxicity for at least 24 h, whereas AdR-induced cell cycle arrest is lethal and irreversible. AdR-induced G1 cell cycle arrest results in diminished ribonucleotide reductase activity but the kinetics of this inhibition differ from cyclic AMP-induced cell cycle arrest. Cyclic AMP arrest and cytotoxicity depend on cyclic AMP-dependent protein kinase (PKA) activity, whereas AdR toxicity does not differ between cell lines with or without PKA activity. Furthermore, deoxycytidine prevents AdR cell cycle arrest and cytotoxicity but has no effect on cyclic AMP G1 arrest. Finally, comparison of cytofluorographic patterns of G1-arrested cells suggests that the AdR block is later in G1 than cyclic AMP-induced cell cycle arrest. In summary, these data show that while the mechanisms of cell cycle arrest and cytotoxicity of cyclic AMP and deoxyadenosine are uncertain, they do appear to involve different pathways.
Asunto(s)
Ciclo Celular/efectos de los fármacos , AMP Cíclico/toxicidad , Desoxiadenosinas/toxicidad , Muerte Celular , División Celular , Desoxiadenosinas/antagonistas & inhibidores , Desoxicitidina/farmacología , Sinergismo Farmacológico , Cinética , ARN Mensajero/metabolismo , Ribonucleótido Reductasas/efectos de los fármacos , Ribonucleótido Reductasas/metabolismo , Células Tumorales CultivadasRESUMEN
Antitumor agents which block the de novo synthesis of nucleotides can be circumvented by the presence of salvage pathways for the reutilization of nucleobases and nucleosides. Studies have been carried out which show that 5-hexyl-2'-deoxyuridine (HdUrd) effectively blocks the cytotoxic effects of deoxyadenosine and fluorodeoxyuridine in L1210 cells. Although HdUrd (500 microM) had essentially no effect on the growth of L1210 cells in culture, the total uptake of [14C]cytidine into these cells was inhibited 99% by this concentration of HdUrd. The inhibitory effects of fluorodeoxyuridine (FdUrd) and deoxyadenosine could be completely prevented by the presence of HdUrd (200 microM). The growth inhibitory effects of fluorouracil were not prevented by HdUrd. Dipyridamole prevented the inhibition of L1210 cell growth by FdUrd but not by deoxyadenosine or fluorouracil. 5-Isopropyl-, 5-pentyl-, and 5-octyldeoxyuridine were not effective in preventing the cytotoxic effects of deoxyadenosine. The data suggest that HdUrd might be useful in blocking the salvage of nucleosides, thereby potentiating the effects of inhibitors of de novo nucleotide synthesis.
Asunto(s)
Antimetabolitos Antineoplásicos/farmacología , Desoxiadenosinas/farmacología , Desoxiuridina/análogos & derivados , Floxuridina/farmacología , Células Tumorales Cultivadas/citología , Animales , División Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Desoxiadenosinas/antagonistas & inhibidores , Desoxiuridina/farmacología , Relación Dosis-Respuesta a Droga , Floxuridina/antagonistas & inhibidores , Cinética , Leucemia L1210 , Ratones , Células Tumorales Cultivadas/efectos de los fármacosAsunto(s)
Hígado/efectos de los fármacos , Biosíntesis de Proteínas , Triptófano/farmacología , Amanitinas/antagonistas & inhibidores , Animales , Tetracloruro de Carbono/antagonistas & inhibidores , Dactinomicina/antagonistas & inhibidores , Desoxiadenosinas/antagonistas & inhibidores , Etionina/antagonistas & inhibidores , Femenino , Técnicas In Vitro , Hígado/metabolismo , Microsomas Hepáticos/metabolismo , Puromicina/antagonistas & inhibidores , ARN/metabolismo , ARN Mensajero/biosíntesis , Ratas , Ratas Endogámicas , Esparsomicina/antagonistas & inhibidoresRESUMEN
The rate of deamination of 5'-deoxy-5'-S-isobutylthioadenosine [(iBuS5'Ado] in chick embryo fibroblasts was substantially reduced after their infection and morphological transformation by Rous sarcoma virus. Concomitant with the reduction in rate of (iBuS)5'Ado deamination there was a decrease in adenosine deaminase and 5'-adenylic acid deaminase activities. The drop of these activities was related to infection and not to the expression of the src gene. (iBuS)5'Ado was deaminated by at least three enzymes or isoenzymes whose apparent molecular weights have been estimated to be 295000, 121000 and 37000 respectively. Two of these enzymes have been characterized as 5'-adenylic acid deaminase and the heavy form of adenosine deaminase, respectively.