Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Deoxycytidine kinase, which phosphorylates deoxycytidine (CdR) and its analog, cytosine arabinoside (ara-C), has been purified 71-fold from human leukemic cells. Biochemical properties of the partially purified enzyme included a molecular weight of 68,000, Kms of 7.8 muM for CdR and 25.6 muM for ara-C, and optimal activity with ATP and GTP as phosphate donors. Ara-C phosphorylation was strongly inhibited by CdR (Ki = 0.17 muM) and dCTP (Ki = 7.3 muM) and was weakly inhibited by ara-CTP (Ki = 0.13 mM). Purification by calcium phosphate gel elution and DEAE chromatography effectively separated this enzyme from cytidine deaminase, which deaminates both CdR and ara-C, and from uridine-cytidine kinase, the enzyme which phosphorylates 5-azacytidine. CdR kinase activity was found to decrease and cytidine deaminase to increase with maturation of normal and leukemic granulocytes. Myeloblasts purified by Ficoll sedimentation revealed an average kinase activity of 15.4 U/mg protein in acute myelocytic leukemia and 12.3 U/mg protein in blastic crisis of chronic myelocytic leukemia (CML). The average ratio of CdR kinase to deaminase activity in crude cell extracts varied from 0.197 in AML and 0.089 in blastic crisis to 0.0004 in normal granulocytes, reflecting the changes which take place with cellular maturation. The absolute levels of kinase and deaminase and the ratio of these two enzymes varied considerably among patients with AML, indicating that quantitative differences may be found in the metabolism of CdR and its analogs in leukemic cells.
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PMID:Deoxycytidine kinase: properties of the enzyme from human leukemic granulocytes. 5 55

In this study we investigated the Ara-CTP-forming capacity of leukemic cells in different phases of the cell cycle. Cells from two leukemic cell lines and leukemic bone marrow cells from patients and rats (BNML model) with acute myelocytic leukemia were separated according to cell cycle phase by means of an albumin density gradient in a specially designed sedimentation chamber. We found that the activity of CdR kinase and Cyt deaminase is much less influenced by cell-cycle phase progression than TdR kinase activity. For the leukemic cell lines HL-60 and BNML-CL/O CdR kinase activity is even independent of cell-cycle phase. In addition, Ara-CTP formation is not restricted to cells in S-phase. Cell cycle phase-independent Ara-CTP formation creates a situation in which cells which are not in S-phase during exposure to Ara-C might undergo the cytotoxic effects of Ara-C as soon as they enter S-phase.
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PMID:Deoxycytidine kinase, thymidine kinase and cytidine deaminase and the formation of Ara-CTP in leukemic cells in different phases of the cell cycle. 215 90

In this study, it has been shown that in 21 patients with AML the dCyd kinase and dCyd deaminase activities correspond closely to the clinical response to ara-C remission induction therapy. Patients with primary disease were treated with a conventional-dose ara-C regimen whereas nonresponders and relapsed patients followed an ID ara-C regimen (1 g/m2 X 12). Of these 21 patients (11 with primary disease and ten relapsed), seven had ara-C resistant disease (three primary and four relapsed patients). Five of the seven patients had a very low dCyd kinase and normal dCyd deaminase activity, whereas the other two had a normal dCyd kinase and an increased dCyd deaminase activity.
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PMID:Deoxycytidine kinase and deoxycytidine deaminase values correspond closely to clinical response to cytosine arabinoside remission induction therapy in patients with acute myelogenous leukemia. 303 20

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

Cytidine deaminase, an enzyme that catalyses the deamination of both cytidine and its nucleoside analogues including the antineoplastic agents cytosine arabinoside (ara-C) and 5-azacytidine (5-azaC), has been partially purified from normal and leukemic human granulocytes. The purification procedure included heat precipitation at 70 degrees C, ammonium sulfate precipitation, calcium phosphate gel ion exchange, and Sephadex G-150 gel filtration. The enzyme has mol wt 51,000, isoelectric pH of 4.8, and maximum activity over a broad pH range of 5-9.5. The enzyme is stabilized by the presence of the sulfhydryl reagent, dithiothreitol. Cytidine deaminase from normal human granulocytes has a greater affinity for its physiologic substrate cytidine (K(m) = 1.1 x 10(-5) M) than for ara-C (8.8 x 10(-5) M) or 5-azaC (4.3 x 10(-4) M). Halogenated analogues such as 5-fluorocytidine and 5-bromo-2'-deoxycytidine also exhibited substrate activity, with maximum velocities greater than that of the physiologic substrates cytidine and deoxycytidine. No activity was observed with nucleotides or deoxynucleotides. The relative maximum velocity of the enzyme for cytidine and its nucleoside analogues remained constant during purification, indicating that a single enzyme was responsible for deamination of these substrates. Tetrahydrouridine (THU) was found to be a strong competitive inhibitor of partially purified deaminase with a K(i) of 5.4 x 10(-8) M. The biochemical properties of partially purified preparations of cytidine deaminase from normal and leukemic cells were compared with respect to isoelectric pH, molecular weight, and substrate and inhibitor kinetic parameters, and no differences were observed. However, normal circulating granulocytes contained a significantly greater concentration of cytidine deaminase (3.52+/-1.86 x 10(3)/mg protein) than chronic myelocytic leukemia (CML) cells (1.40+/-0.70 x 10(3) U/mg protein) or acute myelocytic leukemia (AML) cells (0.19+/-0.17 x 10(3) U/mg protein). To explain these differences in enzyme levels in leukemic versus normal cells, the changes in cytidine deaminase levels associated with maturation of normal granulocytes were studied in normal human bone marrow. Myeloid precursors obtained from bone marrow aspirates were separated into mature and immature fractions by Ficoll density centrifugation. Deaminase activity in lysates of mature granulocytes was 3.55-14.2 times greater than the activity found in the lysates of immature cells. Decreased enzyme activity was also found in immature myeloid cells from a patient with CML as compared to mature granulocytes from the same patient. These observations support the conclusion that the greater specific activity of cytidine deaminase in normal mature granulocytes as compared to leukemic cells is related to the process of granulocyte maturation rather than a specific enzymatic defect in leukemic cells.
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PMID:Purification and properties of cytidine deaminase from normal and leukemic granulocytes. 452 17

1. The conversion of cytosine arabinoside into its active metabolite cytosine arabinoside triphosphate, and catabolism by deamination to uracil arabinoside, was measured in intact marrow myeloblasts from patients with acute myeloid leukaemia. The ratio of uracil arabinoside/cytosine arabinoside triphosphate ranged from 0.32 to 19.11. 2. The effect of tetrahydrouridine, and inhibitor of cytosine arabinoside deamination, on cytosine arabinoside triphosphate production was studied. The greatest increase of cytosine arabinoside triphosphate production caused by addition of tetrahydrouridine was 27%. 3. The increase in cytosine arabinoside triphosphate production wad not related to the ratio of uracil arabinoside/cytosine arabinoside triphosphate or to the deaminase activity per 10(6) cells. It wa proportional to the percentage change of cytosine arabinoside in the incubation medium. 4. The sensitivity of DNA synthesis to inhibition by cytosine arabinoside was measured in myeloblasts from 11 patients. Addition of tetrahydrouridine did not increase the sensitivity of the marrow to cytosine arabinoside. 5. Cytosine arabinoside deamination is unlikely to be an important mechanism of resistance in myeloblasts in vivo, although it may produce apparent resistance in vitro.
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PMID:Cytosine arabinoside deamination in human leukaemic myeloblasts and resistance to cytosine arabinoside therapy. 694 Jun 87

Ara-C phosphorylation and Ara-C deamination was measured in vitro, using intact marrow myeloblasts from 25 patients with previously untreated acute myeloid leukaemia. At Ara-C concentrations above 10 microM there was no longer a linear relationship of phosphorylation to Ara-C concentration. Ara-U production was measured by sampling the incubation medium. This method showed greater Ara-U production than previous methods sampling the cell pellet alone. However, Ara-CTP/Ara-U ratios from intact myeloblasts were much higher than those recorded in studies using lysed myeloblasts. Using 1 microM Ara-C, a concentration representative of in vivo concentrations, deamination and phosphorylation were related to therapeutic response to Ara-C-containing drug regimens. There was no significant correlation of these variables with response, although 5/16 non-responders had low Ara-C phosphorylation (less than 1.5 pmol/10(6) cells/45 min/l pm Ara-C) compared with 0/9 responders. Measuring deaminase activity did not help in selecting non-responders. Even in patients with low phosphorylation increasing Ara-C concentration increased Ara-CTP levels proportionally, but up to 10 times conventional doses may be necessary to exceed endogenous dCTP levels.
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PMID:The relationship of Ara-C metabolism in vitro to therapeutic response in acute myeloid leukaemia. 695 91

Various 2'-azido- and 2'-aminoarabinofuranosyl purine and pyrimidine nucleosides have been synthesized. Among these, the derivatives of cytosine and of adenine inhibit the growth of some tumor cell lines in vitro and in vivo. 2'-Azidoarabinofuranosyl cytosine also interferes with the replication of herpes simplex virus types I and II. Whereas 2'-azidoara-C is resistant to deamination by a partially purified CdR deaminase from KB cells, the adenine derivatives are substrates for aminohydrolases partially purified from calf and mouse intestines. Both azido- and aminoara-C are phosphorylated by partially purified CdR kinases from leukemia L1210 and from human AML blast cells. The accumulated data encourage exploration of the clinical utility of the more potent of these analogues.
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PMID:Synthesis, biologic effects, and biochemical properties of some 2'-azido- and 2'-amino-2'-deoxyarabinofuranosyl pyrimidines and purines. 744 52

While on therapy for acute myeloid leukemia, a 15-year-old girl developed extensive punctate keratitis of both eyes following high-dose cytarabine therapy (HD-Ara-C). Pharmacokinetic monitoring showed an increase of the Ara-C plasma levels up to twice the steady-state level within 10 minutes after discontinuation of the Ara-C infusion. Calculations of Ara-C plasma half-life, plasma clearance and volume of distribution were within the expected range. Owing to the short half-life of Ara-C in blood due to rapid deamination, varying infusion velocities will result in markedly varying plasma levels. Higher peak plasma levels lead to proportionally higher diffusion into compartments like tears, aqueous humor and cerebrospinal fluid. In compartments which lack noteworthy deaminase activity, dose intensity will be much more enhanced than in plasma. Peak plasma levels, therefore, may be associated with multifold local toxicity without concurrent increase of hematological toxicity. Especially when the drug is given in small volumes of infusion, these considerations should be taken into account. Precise control of infusion parameters and application of artificial tears for dilution of the Ara-C concentration on the corneal surface should be part of keratitis prophylaxis.
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PMID:Is there a relationship between cytarabine pharmacokinetics and keratitis?--A case report. 831 60

A new human myeloid leukemia cell line, designated KF-19, and its drug resistant sublines have been established. The KF-19 cell line was established from the pericardial effusion of a patient with acute myeloid leukemia clinically resistant to chemotherapy and KF-19 cells were characterized by expression of myeloid markers and differentiation into neutrophil- and macrophage-like cells upon optimal stimulations. KF-19AraC, KF-19ADR and KF-19VCR were established as sublines resistant to cytosine arabinoside (AraC), adriamycin (ADR) and vincristine (VCR), respectively. Efflux of the corresponding drugs was documented in each cell line. Expression of the MDR1 gene and the P-glycoprotein was found only in KF-19ADR, which showed a cross resistance to anthracyclines and vinca alkaloids; this resistance was reversed by verapamil or cyclosporin A. KF-19VCR lacking MDR1 gene and P-glycoprotein expression showed only resistance to vinca alkaloids, which was partially reversed by verapamil and cyclosporin A. Unexpectedly, KF-19ADR and KF-19VCR displayed cross resistance to AraC, despite lack of alterations of deoxycytidine kinase (dCK) and deaminase (dA) activities. KF-19AraC showed an efflux of AraC as well as a decreased level of dCK, but not of dA. In addition, KF-19AraC showed cross resistance to VCR in the efflux assay. The cell lines reported herein will provide new aspects on the mechanisms of drug resistance in leukemic cells.
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PMID:Characterization of newly established human myeloid leukemia cell line (KF-19) and its drug resistant sublines. 900 51


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