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)

The cellular metabolism of 3'-amino-2',3'-dideoxycytidine (3'-NH2-dCyd), a cytotoxic agent previously reported to be a poor substrate for purified Cyd/dCyd deaminase (dCydD), was compared with that of cytosine arabinoside (ara-C) in cells that displayed dCydD activity (HeLa) and in cells that did not (L1210). Growth inhibition induced by 3'-NH2-dCyd was dependent on the levels of anabolic enzymes, particularly dCyd kinase (dCydK), whereas cytotoxicity induced by ara-C was dependent on the expression of both anabolic and catabolic enzyme activities. Competition kinetics using purified enzyme revealed that the binding affinity of ara-C to dCydK was 5-fold that of the amino analog. However, this binding advantage is apparently offset in cells that contain high levels of dCydD, since the Ki values for this enzyme were 0.2 and 23 mM for ara-C and 3'-NH2-dCyd, respectively. This was reflected in the decrease in analog sensitivity observed between the two cell lines, whereby the concentrations of ara-C and 3'-NH2-dCyd required to inhibit growth by 50% were 200 and 7 times higher, respectively, in the dCydD-containing HeLa cells as compared with the dCydD-deficient L1210 cells. The metabolic stability and cytotoxicity of 3'-NH2-dCyd was independent of cell number. An unexpected finding was the extent to which the effectiveness of ara-C could be mitigated by the number of dCydD-containing cells. A completely cytotoxic concentration of ara-C was rendered nontoxic by a 10-fold increase in cell number. This observation was supported by an increase in I-beta-D-arabinofuranosyluracil (ara-U) formation, a decrease in ara-C 5'-triphosphate (ara-CTP) accumulation, and a rise in cell viability with increasing cell number. These findings indicate that unlike ara-C, the effectiveness of 3'-NH2-dCyd is independent of the level of deaminase, which suggests its possible utility in situations in which high levels of deaminase are manifest.
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PMID:The role of deoxycytidine-metabolizing enzymes in the cytotoxicity induced by 3'-amino-2',3'-dideoxycytidine and cytosine arabinoside. 131 70

Gravid Angiostrongylus cantonensis can utilize radiolabelled bicarbonate, orotate, uracil, uridine and cytidine but not cytosine, thymine and thymidine for the synthesis of RNA and DNA. In cell-free extracts of the worm, a phosphoribosyltransferase was shown to convert orotate to OMP and uracil to UMP. A similar reaction was not observed with cytosine and thymine. Uridine was readily phosphorylated by a kinase but a similar reaction for thymidine and deoxyuridine was not found. Cytidine could be phosphorylated by a kinase or be deaminated by a deaminase to uridine. No deaminase for cytosine was detected. There was also no phosphotransferase activity for pyrimidine nucleosides in the cytosolic or membrane fractions. Pyrimidine nucleosides were, in general, converted to the bases by a phosphorylase reaction but only uracil and thymine could form nucleosides in the reverse reaction. The activity of thymidylate synthetase was also measured. These results indicate that the nematode synthesizes pyrimidine nucleotides by de novo synthesis and by utilization of uridine and uracil and that cytosine and thymine nucleotides are formed mainly through UMP. The thymidylate synthetase reaction appears to be vital for the growth of the parasite.
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PMID:Precursors of pyrimidine nucleotide biosynthesis for gravid Angiostrongylus cantonensis (Nematoda: Metastrongyloidea). 137 74

In summary, there are compelling laboratory and clinical data indicating that higher doses of ara-C than are currently used in SDaC protocols constitute optimal therapy. The cellular pharmacokinetics of ara-C are optimized at extracellular drug concentrations in the 10 to 15 mumol/L range. At these concentrations, transport rates are no longer rate-limiting, and ara-C phosphorylation capacity is saturated. The prime determinants of ara-C effect then shift to multiple intracellular events including anabolism to nucleotides, catabolism via deamination by Cyd-dCyd deaminase and dCMP deaminase, half-life of ara-CTP, the extent of incorporation into DNA, and the half-life of ara-CMP residues in DNA. It is postulated that at these high doses an additional effect of ara-C occurs on the cell membrane through affects on membrane phospholipid synthesis. This effect may contribute to the brisk cell lysis associated with HiDaC treatment. When administered as repetitive doses of 3 g/m2 over a 1- to 3-hour period, systemic deamination of ara-C gives rise to high plasma concentrations of ara-U. This metabolite has a long plasma half-life and, at least in the mouse, is concentrated in the liver and kidneys. High concentrations in these organs retard the further catabolism of ara-C and thus increase the systemic AUC providing a longer exposure period to the drug. A similar mechanism may obtain in patients treated with HiDaC. The observed decreased clearance of ara-C when administered in gram versus milligram doses and the long-terminal gamma-phase in plasma clearance of the drug associated with HiDaC usage quite probably reflects this effect of ara-U in patients. Additionally, by some as yet unknown mechanism, high concentrations of ara-U cause accumulation of leukemia cells in S-phase, the phase of the cell cycle wherein ara-C is maximally effective. This effect of ara-U may add to the cytokinetic effects initiated by rapid cytoreduction, which summate in the observed enhancement of the proliferative fraction of residual leukemia cells on day 8. The effect of a second course of therapy at this time is thereby enhanced. These dose-related and metabolite-drug interactions that occur when ara-C is given at high doses constitute a means for "self-potentiation" and may thus contribute to its overall therapeutic efficacy.
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PMID:Effect of dose on the pharmacokinetic and pharmacodynamic effects of cytarabine. 178 Jul 54

1-beta-D-Arabinofuranosyl-5-azacytosine (ara-5-aza-Cyd) had potent cytotoxicity against human T-type lymphoblastic cells in culture. When Molt-4 cells were exposed to ara-5-aza-Cyd for 24 h, clonogenic survival was reduced by 50 and 98% at initial concentrations of 10(-7) and 10(-6) M, respectively, compared to 3 X 10(-8) and 10(-6) M, respectively, for the same effect with 1-beta-D-arabinofuranosylcytosine (ara-C). The analogue is chemically unstable, with a t1/2 of 12 h at 37 degrees C in phosphate-buffered saline. ara-5-aza-Cyd is not significantly deaminated by human Cyd-deoxycytidine (dCyd) deaminase, in contrast to ara-C. It is phosphorylated by human cytoplasmic dCyd kinase, with a Km of 55 microM and a relative Vmax of 310% compared to dCyd. The primary metabolite (70%) in Molt-4 cells was identified as ara-5-aza-Cyd triphosphate. Thymidine but not uridine or amino acid incorporation was inhibited by ara-5-aza-Cyd. ara-5-aza-Cyd was incorporated in a dose-dependent manner into DNA, but not RNA, primarily in internucleotide linkage as the original compound. Incorporation into the cellular methanol-insoluble fraction was 3- to 5-fold higher at 8 h than was ara-C incorporation. ara-5-aza-Cyd may have a unique activity against tumor cells resistant to ara-C, particularly where high Cyd-dCyd deaminase activity is a factor. The mode of action, like that of ara-C, is probably mediated through its incorporation into DNA and inhibition of DNA synthesis.
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PMID:Metabolism of 1-beta-D-arabinofuranosyl-5-azacytosine and incorporation into DNA of human T-lymphoblastic cells (Molt-4). 241 96

The nucleoside analog 2',3'-dideoxycytidine (ddCyd) has been shown to inhibit the infectivity and cytopathic effect of human immunodeficiency virus on human OKT4+ lymphocytes in vitro. Metabolism of ddCyd by human T-lymphoblastic cells (Molt 4) negative for human immunodeficiency virus and OKT4 was examined. Molt 4 cells accumulated ddCyd and its phosphorylated derivatives into acid-soluble and acid-insoluble material in a dose-dependent manner. For each concentration tested, 2',3'-dideoxycytidine triphosphate represented 40% of the total acid-soluble pool of ddCyd metabolites. Uptake of 5 microM ddCyd was linear for 4 h after addition of drug. Efflux of ddCyd metabolites from cells followed a biphasic course with an initial retention half-life of 2.6 h for 2',3'-dideoxycytidine triphosphate. DNA, but not RNA, of cells incubated with [3H]ddCyd became radiolabeled. Nuclease and phosphatase treatment of DNA followed by reverse-phase high pressure liquid chromatography showed that the nucleoside was incorporated into DNA in its original form. ddCyd was not susceptible to deamination by human Cyd-dCyd deaminase. It was a poor substrate for human cytoplasmic and mitochondrial dCyd kinases, with Km values of 180 +/- 30 and 120 +/- 20 microM, respectively. DNA polymerases alpha, beta, and gamma varied in their sensitivity to inhibition by ddCTP with Ki values of 110 +/- 40, 2.6 +/- 0.3, and 0.016 +/- 0.008 microM, respectively; however, inhibition was competitive with dCTP in each case.
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PMID:Cellular metabolism of 2',3'-dideoxycytidine, a compound active against human immunodeficiency virus in vitro. 243 80

2',3'-Didehydro-2',3'-dideoxy-5-chlorocytidine (D4CC) is, in contrast with 2',3'-dideoxy-5-chlorocytidine (ddClCyd) and 2',3'-didehydro-2',3'-dideoxy-5-chlorouridine (D4CU), a potent and selective inhibitor of the replication of human immunodeficiency virus (HIV) types 1 and 2, simian immunodeficiency virus (SIV) and simian AIDS related virus (SRV). D4CC is a poor inhibitor of the phosphorylation of [5-3H]2'-deoxycytidine (dCyd) by partially purified MT-4 cell dCyd kinase (Ki: 612 microM). The findings that (i) D4CC has little, if any, affinity for MT-4 cell Cyd/dCyd deaminase, (ii) D4CU is not antivirally active and (iii) the antiretroviral action of D4CC can be reversed by dCyd, but not dThd, indicate that D4CC is antivirally active as its Cyd metabolite (D4CC 5'-triphosphate) and does not need to be deaminated (to the corresponding Urd metabolite) to exert its antiretroviral action.
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PMID:2',3'-didehydro-2',3'-dideoxy-5-chlorocytidine is a selective anti-retrovirus agent. 259 Jan 97

Various 5-substituted 2'-deoxyuridine (dUrd), 2'-deoxycytidine (dCyd), 1-beta-D-arabinofuranosyluracil (araU) and 1-beta-D-arabinofuranosylcytosine (araC) analogues have been investigated for their stimulatory effect on the growth of a thymidylate (dTMP) synthetase-deficient murine mammary carcinoma cell line (FM3A/TS-) that is auxotrophic for thymidine (dThd). Such stimulatory effect may be considered as indicative for the incorporation of the nucleoside analogue into host cell DNA. Based on this premise, several dUrd analogues were found to be incorporated into FM3A/TS- cell DNA (in decreasing order of incorporation): 5-bromo-dUrd greater than 5-chloro-dUrd greater than 5-(3-hydroxy-1-propynyl)-dUrd greater greater than 5-(1-pentynyl)-dUrd approximately 5-(1-propynyl)-dUrd approximately 5-iodo-dUrd greater than 5-(5-carboxy-1-hexenyl)-dUrd greater than 5-(3,3-dimethyl-1-butynyl)-dUrd greater than 5-ethyl-dUrd greater than 5-(5-chloro-1-pentynyl)-dUrd greater than 5-ethynyl-dUrd approximately 5 vinyl-dUrd greater than 5-phenylethynyl-dUrd greater than 5-(5-cyano-1-pentenyl)-dUrd greater than 5-(1-propenyl)-dUrd greater than 5-(1-hexynyl)-dUrd greater than 5-(5-hexyn-1-enyl)-dUrd. Among the 5-substituted dCyd analogues, 5-methyl-dCyd, 5-chloro-dCyd, 5-bromo-dCyd and 5-iodo-dCyd were also found to stimulate cell growth, and are therefore assumed to be incorporated into FM3A/TS- cell DNA. Since the stimulatory effects of these compounds on FM3A/TS- cell proliferation were suppressed in the presence of a Cyd deaminase inhibitor (tetrahydrouridine) or dCMP deaminase inhibitor (2'-deoxytetrahydrouridine), it is surmised that the dCyd analogues are first deaminated to the corresponding dUrd analogues before they are incorporated into DNA. None of the 5-substituted araU or araC analogues tested were able to sustain the growth of FM3A/TS- cells. It is postulated, therefore, that these araU or araC analogues are not incorporated to any appreciable extent into the DNA of FM3A/TS- cells, or, if they are incorporated, prevent cell growth. Thus, the dTMP synthetase-deficient FM3A/TS- cell line represents a unique system to distinguish those pyrimidine nucleoside analogues that are able to sustain cell growth and, therefore, assumed to be incorporated into the host cell DNA from those pyrimidine nucleoside analogues that are not.
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PMID:Incorporation of 5-substituted pyrimidine nucleoside analogues into DNA of a thymidylate synthetase-deficient murine FM3A carcinoma cell line. 399 Apr 43

Few reports have dealt with the kinetics and metabolism of AraC and analogs by rat intestine. Using everted rat jejunum with continuous perfusion, it was possible to demonstrate that AraC and Cyd cross the intestinal barrier(s) by a carrier mediated process which was saturable and exhibited fairly good fitting of the flux rate by Michaelis-Menten equation. The transport rate of different analogs was not consistent with the pH-partition theory of membrane transport of drugs being rather dependent on the chemical structure of the nucleoside. A free amino group of cytosine increased the rate of transport within the present series of AraC analogs. There was a detectable deaminase as well as esterase activity towards AraC and its analogs in rat jejunum.
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PMID:Kinetics of transport and metabolism of 1-beta-D-arabinofuranosylcytosine and structural analogs by everted perfused rat jejunum. 670 82

Cytidine (CR) deaminase was purified 47,000-fold to homogeneity from human placenta. The molecular mass of CR deaminase was estimated to be 48.7 kDa by gel filtration and 16.1 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis, suggesting that it contains three or four identical subunits. We determined the amino acid sequence of several peptide fragments and designed 5'-primers to amplify, by the polymerase chain reaction, a specific 364-base pair DNA fragment using human liver complementary DNA (cDNA) as the template. This DNA fragment, which contains the codons of one peptide, was used as a probe to screen a cDNA library from human liver. We isolated and sequenced a cDNA clone of 910 base pairs that contained a 5' nontranslated region, a 438-base pair coding region, and a 3' nontranslated region with a polyadenylated tail. The translated region of the clone contained a deduced sequence of 146 amino acids, with a predicted molecular mass of 16.2 kDa and the sequences of our peptides. The cDNA was ligated in pGEX vector and expressed in Escherichia coli. The expressed protein had a high CR deaminase activity and molecular mass of 16.3 kDa. These data demonstrate clearly that the open reading frame of our cDNA clone codes for a functional human CR deaminase. Polymerase chain reaction amplifications of gene-specific DNA fragments from human/rodent hybrid cells indicate the localization of CR deaminase gene to human chromosome 1. The cDNA for CR deaminase will be a useful molecular probe to investigate the importance of this enzyme in chemotherapy.
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PMID:Human cytidine deaminase: purification of enzyme, cloning, and expression of its complementary DNA. 792 72

Capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) is a novel oral fluoropyrimidine carbamate, which is converted to 5-fluorouracil (5-FU) selectively in tumours through a cascade of three enzymes. The present study investigated tissue localisation of the three enzymes in humans, which was helpful for us to design the compound. Carboxylesterase was almost exclusively located in the liver and hepatoma, but not in other tumours and normal tissue adjacent to the tumours. Cytidine (Cyd) deaminase was located in high concentrations in the liver and various types of solid tumours. Finally, thymidine phosphorylase (dThdPase) was also more concentrated in various types of tumour tissues than in normal tissues. These unique tissue localisation patterns enabled us to design capecitabine. Oral capecitabine would pass intact through the intestinal tract, but would be converted first by carboxylesterase to 5'-deoxy-5-fluorocytidine (5'-dFCyd) in the liver, then by Cyd deaminase to 5'-deoxy-5-fluorouridine (5'-dFUrd) in the liver and tumour tissues and finally by dThdPase to 5-FU in tumours. In cultures of human cancer cell lines, the highest level of cytotoxicity was shown by 5-FU itself, followed by 5'-dFUrd. Capecitabine and 5'-dFCyd had weak cytotoxic activity only at high concentrations. The cytotoxicity of the intermediate metabolites 5'-dFCyd and 5'-dFCyd was suppressed by inhibitors of Cyd deaminase and dThdPase, respectively, indicating that these metabolites become effective only after their conversion to 5-FU. Capecitabine, which is finally converted to 5-FU by dThdPase in tumours, should be much safer and more effective than 5-FU, and this was indeed the case in the HCT116 human colon cancer and the MX-1 breast cancer xenograft models.
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PMID:Design of a novel oral fluoropyrimidine carbamate, capecitabine, which generates 5-fluorouracil selectively in tumours by enzymes concentrated in human liver and cancer tissue. 984 91


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