Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.4 (deaminase)
 5,113 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The distribution of arabinosylcytosine (ara-C) and its metabolites has been measured in the liver, small intestine, spleen, and kidney of mice inoculated ip 5-6 days earlier with L1210 leukemia cells. Two major metabolites were found in the tissues--the nucleotides and the deaminated inactive product, arabinosyluracil (ara-U). The decay curve of ara-C in most of these tissues was curvilinear; the ara-C half-lives estimated from the terminal phases were 8. 11, 12, and 12 hr for spleen, kidney, intestine, and liver tissues, respectively. The ara-C half-life was not correlated with the deoxycytidine deaminase activity in the tissues. However, the deaminase activity in vitro correlated well with the amount of ara-U present in vivo. Similar analyses were made for L1210 leukemic cells and ascites fluid. A high nucleotide level was found in the cells and a significant amount of nucleotides was also identifiable in the ascites fluid. The activities of deoxycytidine kinase, but not of deoxycytidine deaminase, in host tissues of mice inoculated with L1210 leukemic cells sensitive to ara-C were greater than in those of normal mice. The phosphorylating activities in vitro correlated with the amount of nucleotide present in vivo in mice bearing L1210 leukemic cells. However, the infiltration of leukemic cells containing high kinase activities into the host tissues accounted for most, if not all, of the nucleotide level in these tissues. This is further evidenced by the fact that inoculating mice with L1210 leukemic cells resistant to ara-C did not alter the kinase activity or nucleotide levels of the host tissues; these resistant cells contain negligible amounts of ara-C phosphorylating activities.
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PMID:Correlation of mouse tissue distribution of arabinosylcytosine in vivo with enzymatic activities in vitro. 0 36

Extracts of solid mouse tumors were examined for deoxycytidine kinase and deaminase activities. 1beta-D-Arabinofuranosylcytosine nucleotide was formed at a rate of 45 nmoles/hr by Glioma 26/57 and only 14 nmoles/hr by Ridgway osteogenic sarcoma. Deaminase activity was highest in Lewis lung (114 nmoles of 1-Beta-D-arabinofurano-syluridine formed per hr) and in CaD2 (104 nmoles of u-beta-D-arabinofuranosyluridine formed per hr). Deaminase activity in tumor extracts is sensitive to freezing, while deaminase activity in monkey serum is not. It was observed that kinase activity varies by as much as 50% in different cell lines of the same tumor. In the presence of tetrahydrouridine, kinase activity was significantly increased in most of the tumors studied.
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PMID:Kinase and deaminase activity in a variety of subcutaneous mouse tumors. 16 84

An integrated mathematic computer-based model of the pharmacokinetics, intracellular enzyme kinetics, and cell kinetics of the treatment of L1210 leukemia by cytosine arabinoside (ara-C) is described. The compartment model of Bischoff and Dedrick is extended to the intracellular level by inclusion of equations describing the phosphorylation, dephosphorylation, and deamination of ara-C with enzymatic feedback control. The activities of kinase, deaminase, and phosphatase are explicitly included in the models and are estimated from relevant data. Cell proliferation is described by a continuous-flow mathematic model in which cellular maturation and cell-to-cell variability in maturation rates are key variables. Cell proliferation is related to intracellular biochemistry through mathematic expressions which relate cell lethality and progression delay to the time course of intracellular ara-CTP. In vitro and in vivo experiments performed in a number of laboratories are compared by simulation. The most sensitive parameters in dose-response and cell-survival simulations are deoxycytidine kinase activity, ara-CTP half-life, renal clearance of ara-C, and cell-kinetic parameters for proliferation and cell killing. Progression delay is vital to the realistic simulation of divided-dose schedules. By comparative simulation we have identified areas of uncertainty which can be classified by a few additional measurements. The applications of simulations combining pharmacokinetic, biochemical, and cell-kinetic data in vitro and in vivo are discussed, exploring consistency among different measurements, and relating experimental protocols to clinical treatment.
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PMID:Computer simulation of leukemia therapy: combined pharmacokinetics, intracellular enzyme kinetics, and cell kinetics of the treatment of L1210 leukemia by cytosine arabinoside. 102 30

Though data from cell lines are abundant, the reason for the development of resistance to 1-beta-D arabinofuranosylcytosine (ara-C) in vivo remains unresolved. A broad interpatient variation of metabolic parameters has further complicated interpretation of the results. The present study compares ara-C metabolism in leukemic blasts of two patients with newly diagnosed disease, before and after repeated treatment with ara-C containing chemotherapy regimens in vivo. Membrane transport of ara-C was unchanged after treatment. In addition, cell-free extracts of blasts obtained after treatment failure showed an unchanged cytidine deaminase activity. Though deoxycytidine kinase activity in cell extracts was unaltered or increased after treatment failure, the activity in situ, measured as the rate of 1-beta-D-arabinofuranosylcytosine triphosphate (ara-CTP) formation, was decreased. This could be shown to be due to an expansion of the deoxycytidine triphosphate (dCTP) pool. The severalfold increase in dCTP pool was accompanied by a decrease in thymidine triphosphate (dTTP) pool and correlated with a decrease in deoxycytidylate deaminase (dCMP-deaminase) activity in cell free extracts. Low dCMP-deaminase activity had been shown to confer an ara-C resistant phenotype to cell lines in vitro. Data presented in this paper show that a selection for leukemic blasts with low dCMP-deaminase activity can also be favored by ara-C containing treatment regimens in vivo. Our data suggest that this mechanism might contribute to treatment failure.
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PMID:Concordant changes of pyrimidine metabolism in blasts of two cases of acute myeloid leukemia after repeated treatment with ara-C in vivo. 223 89

The activities of aspartate transcarbamylase (de novo pyrimidine biosynthesis pathway) and of deoxycytidine kinase as well as deoxycytidine deaminase (salvage pyrimidine biosynthesis pathway) were determined in extracts prepared from 40 brain tumors of different types in comparison with extracts from normal nervous tissues. Aspartate transcarbamylase, which is undetectable in normal brain tissue, is present in all tumor samples and in some cases rises to very high activities. Deoxycytidine kinase activity is present in all tissues but its level is generally higher in tumors. Deoxycytidine deaminase is present in all the tissues which were analyzed, although its activity is lower in some of the tumor samples. 1-beta-D-Arabinofuranosylcytosine is a substrate for both deoxycytidine kinase and deaminase in all the samples used except one. These results suggest some potential for the utilization of 1-beta-D-arabinofuranosylcytosine and N-(phosphonacetyl)-L-aspartate in the treatment of brain tumors.
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PMID:Pyrimidine pathways enzymes in human tumors of brain and associated tissues: potentialities for the therapeutic use of N-(phosphonacetyl-L-aspartate and 1-beta-D-arabinofuranosylcytosine. 282 6

The in vivo development of an ara-C-resistant leukemic cell line is reported in a rat leukemia model (BNML) that is generally accepted as a relevant model for human acute myelocytic leukemia. It took 32 continuous leukemia transplant generations, performed over 20 months, and a total dose of 28.5 g ara-C/kg to induce complete resistance. Preliminary data indicate that the development of ara-C resistance is related with decreased intracellular levels of deoxycytidine kinase. Deoxycytidine deaminase levels were not increased. Thus this enzyme does not seem to be involved with induction of resistance. This preclinical rat model for human AML provides a solid basis for studies in depth on the mechanism(s) and possible prevention and effective treatment of resistance to ara-C.
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PMID:In vivo development of cytosine arabinoside resistance in the BN acute myelocytic leukemia. 347 77

Purine and pyrimidine enzyme profiles of human cell lines have been investigated. A novel observation was the finding that most of the cell lines showed very low or undetectable levels of cytidine (deoxycytidine) deaminase, while they possessed pyrimidine 5'-nucleotidase, cytidine and deoxycytidine kinase activities. Most cell lines showed high levels of adenosine deaminase and purine nucleoside phosphorylase activities and low levels of purine 5'-nucleotidase. We propose that high adenosine deaminase and purine nucleoside phosphorylase activities and low cytidine deaminase activity may be of importance for immature hematopoietic cells in order to ensure a balanced synthesis of the DNA precursors.
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PMID:Low cytidine deaminase levels in human hematopoietic cell lines. 362 11

2-Chlorodeoxyadenosine (CdA), an adenosine-deaminase-resistant purine deoxynucleoside, is markedly toxic toward human T-lymphoblastoid cell lines in vitro and is an effective agent against L1210 leukemia in vivo. The present studies have examined the toxicity, and in some cases, metabolism, of CdA in (1) multiple established human cell lines of varying phenotype, (2) leukemia and lymphoma cells taken directly from patients, (3) normal bone marrow cells, and (4) normal peripheral blood lymphocytes. Nanomolar concentrations of CdA blocked the proliferation of lymphoblastoid cell lines with a high ratio of deoxycytidine kinase to deoxynucleotidase. The drug had virtually no effect on the growth of cell lines derived from solid tissues. The CdA inhibited the spontaneous uptake of tritiated thymidine by many T and non-T, non-B acute lymphoblastic leukemia cell specimens at concentrations less than or equal to 5 nM. The same concentrations did not impair either thymidine uptake or granulocyte-monocyte colony formation by normal bone marrow cells. In common with deoxyadenosine, but unlike several other agents affecting purine and purine metabolism, CdA was lethal to resting normal T lymphocytes and to slowly dividing malignant T cells. In both resting and proliferating lymphocytes, the CdA was phosphorylated by deoxycytidine kinase and entered a rapidly turning over nucleotide pool. Dividing lymphocytes also incorporated abundant CdA into DNA. The selective toxicity of CdA toward both dividing and resting lymphocytes may render the drug useful as an immunosuppressive or antileukemic agent.
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PMID:Specific toxicity of 2-chlorodeoxyadenosine toward resting and proliferating human lymphocytes. 613 5

The measurements of deoxyadenosine kinase, adenosine kinase, and deoxycytidine kinase were examined in human placental cytosol to achieve a valid and reliable assay linear with time and protein. Our studies confirm the need to inhibit deaminase enzymes, since deoxyadenosine and deoxycytidine undergo extensive deamination and phosphorolysis. The use of a uniformly labeled nucleoside substrate introduced an artifact because the chromatographic behavior of the deoxyribose-1-phosphate, formed during the assay, was difficult to distinguish from the deoxynucleoside phosphate product. Accurate product identification was also essential. Finally, the substitution of GTP in place of ATP as the phosphate donor, the addition of a sulfhydryl reducing agent and a monovalent cation need to be considered when an assay is optimized. The use of these methods have lead to valid assays in placental cytosol that are linear with time and protein. Consideration of these important principles are necessary when establishing a valid and reliable nucleoside kinase assay in a crude tissue preparation.
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PMID:Measurement of nucleoside kinases in crude tissue extracts. 631 76

A subline of human KB cells that was resistant to 1-beta-D-arabinofuranosylcytosine (ara-C) was established by continuous exposure of the cells to increasing concentrations of ara-C. Thirteen resistant clones were isolated from the resistant subline (KB/ara-C). KB/ara-C showed 1,300-fold higher resistance than the parent KB cells to ara-C; the most resistant clones, clones 7 and 10, showed 1,330-fold higher resistance. In the absence of ara-C, the resistance of the parent KB/ara-C cells was stable for at least 14 weeks, whereas that of clone 7 was stable for 10 weeks, but was slightly less after 14 weeks. The ara-C kinase and ara-C deaminase activities of the 13 clones and the cellular uptake of ara-C by several clones were measured. In general the clones showed decreased deoxycytidine kinase activity and decreased cellular uptake of ara-C. Most clones had higher cytidine deaminase activity than KB cells, but some had activity similar to that of the KB cells. A clear inverse relationship was found between the ara-C sensitivity of the clones and their kinase activity, but not their deaminase activity or their ara-C uptake. These results clearly demonstrate that a major mechanism of ara-C resistance of these human KB cells was a decrease in the activity of the ara-C activating enzyme deoxycytidine kinase. The parent KB/ara-C cells showed no clear cross-resistance to various antitumor agents other than an ara-C derivative, including metabolic inhibitors, alkylating agents, DNA binders and mitotic spindle poisons.
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PMID:Establishment of human KB cells resistant to 1-beta-D-arabinofuranosylcytosine, and mechanisms of cellular resistance in isolated clones. 648 76


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