Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have measured reverse transcriptase enzyme activity per virus particle for samples of avian myeloblastosis virus (BAI strain) and murine leukemia virus (RAUSCHER) USing the synthetic template poly(rC)-oligo(dG). Absolute virus concentrations were determined directly by laser beat frequency spectroscopy. Enzyme activity per virion was determined from the slope of the activity plotted as a function of virus concentration. With this reverse transcriptase assay, the minimum activity (expressed as picomoles of dGTP incorporated/virion per hour) is estimated at (28.1 +/- 4.2) X 10(-7) for avian myeloblastosis virus and (1.1 +/- 0.2) X 10(-7) for murine leukemia virus. The sensitivity of this assay, which is determined by the level of incorporated radioactivity measurable above background, is 2.5 X 10(-4) virions for avian myeloblastosis virus (with dGTP specific activity of 8.9 Ci/mmol) and 88 X 10(-4) virions for murine leukemia virus (with dGTP specific activity of 6.52 CI/mmol). These results show that although reverse transcriptase assays can obviously be used to measure relative virus concentrations of equally purified samples of the same virus, they can be very misleading when used to compare the concentrations of different virus species.
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PMID:Reverse transcriptase activity per virion for avian myeloblastosis virus and Rauscher murine leukemia virus. 5 65

Commercial-grade aurintricarboxylic acid (ATA) inhibits poly(A), poly(C) and viral RNA-directed DNA synthesis by detergent-disrupted virions of Moloney murine leukemia virus. Paper chromatography of crude ATA yields two active components, which appear to behave identically, and at least two inactive components. The concentration of ATA needed to inhibit polymerase activity is proportional to the concentration of viral protein. The inhibition is neither attributable to contaminating heavy metal ions in the ATA preparation nor to chelation by ATA of Mn2+ or Zn2+, the necessary co-factors. Inhibition of the polymerase reaction by ATA greatly increases the Km for the primer [oligo(T)/oligo(dG)], while it only slightly lowers the Vmax and does not affect the Km's for the template [poly(A)/poly(C)] or the substrate (TTP/dGTP). Thus, ATA seems to reduce specifically the affinity of the polymerase for the DNA primer molecule.
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PMID:Inhibition of RNA-directed DNA polymerase by aurintricarboxylic acid. 5 43

High activity of terminal deoxynucleotidyl transferase (terminal transferase) was found in a new "thymus-dependent" cell line (RPMI 8402) which is of acute lymphoblastic leukemia origin. This enzyme resembled the terminal transferase from other human cells in all its properties including Km (0.7 x 10(-6) m for dGTP). The high activity of this enzyme in RPMI 8402 and fresh acute leukemia lymphoblasts, in contrast to the low activity of this enzyme reported for "thymus-independent' cells, suggested that this cell line may have originated from leukemia cells. Moreover, the high activity of terminal transferase in RPMI 8402 cells should make feasible large-scale purification of this enzyme for detailed studies.
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PMID:High terminal deoxynucleotidyl transferase activity in a new T-cell line (RPMI 8402) of acute lymphoblastic leukemia origin. 80 34

Tiazofurin (TR), an inhibitor of IMP dehydrogenase, causes remissions and induced differentiation in human leukemia through lowering the concentrations of GTP and dGTP. A deoxycytidine analog, difluorodeoxycytidine (DFDC), is an anti-tumor agent phosphorylated by deoxycytidine kinase, resulting in decreased concentration of dCTP, leading to inhibition of DNA synthesis. In HL-60 cells DFDC induced differentiation and inhibited proliferation in a dose-dependent manner (IC50 = 4 nM); TR provided synergism with DFDC. DFDC inhibited proliferation in OVCAR-5 human ovarian carcinoma cells (IC50 = 25 nM) and colony formation in PANC-1 human pancreatic carcinoma cells (IC50 = 2 nM) and rat hepatoma 3924A cells (IC50 = 22 nM). TR and DFDC are synergistically cytotoxic in hepatoma cells and additive in PANC-1 cells. The two drugs together should be helpful in treating leukemias and solid tumors in humans.
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PMID:Synergistic action of tiazofurin and difluorodeoxycytidine on differentiation and cytotoxicity. 134 74

Metabolic effects and mode of cytotoxicity of 5-deazaacyclotetrahydrofolate (5-DACTHF, BW543U76), a glycineamide ribonucleotide transformylase inhibitor, were studied in MOLT-4 cells, a human T-cell leukemia line. 5-DACTHF inhibits purine synthesis with 50% inhibitory concentration values of 0.5 microM and 0.08 microM following 6- or 24-h exposure to drug, respectively. At 6 h, adenine nucleotide synthesis is preferentially inhibited over guanine nucleotide synthesis. A similar effect was observed with another glycineamide ribonucleotide transformylase inhibitor, 5,10-dideazatetrahydrofolate. GTP was depleted to 40% of control and ATP to 10% of control by 5 microM 5-DACTHF. After a transitory increase, UTP and CTP were depleted to 30% of control. Deoxynucleotides were also depleted by the drug; dCTP was depleted to the greatest extent, followed by dATP, dTTP, and dGTP, respectively. MOLT-4 cell growth was inhibited by 5-DACTHF with a 50% inhibitory concentration of 0.066 microM. Complete reversal was effected by hypoxanthine, and there was no reversal by thymidine. The drug was cytotoxic to MOLT-4 cells in the range 0.25 to 5.0 microM, but a minimum of 48 h was required for trypan blue-staining dead cells to appear. The rate and extent of kill with the thymidylate synthase inhibitor 2-methyl-10-propargyl-5,8-dideazafolate was greater than with 5-DACTHF, which indicates that kill by inhibition of thymidylate synthase is more effective than that by inhibition of purine synthesis. Electron microscopy of MOLT-4 cells exposed to 5-DACTHF showed electron-dense mitochondria and nuclear changes reminiscent of apoptosis. These morphological changes were accompanied by the appearance of DNA strand breaks at approximately 180-base pair intervals (internucleosomal breaks). Concomitant proteolysis of nuclear proteins poly(ADP-ribose) polymerase and lamin B was observed.
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PMID:Metabolic effects and kill of human T-cell leukemia by 5-deazaacyclotetrahydrofolate, a specific inhibitor of glycineamide ribonucleotide transformylase. 151 46

2'-Deoxy-6-thioguanosine 5'-triphosphate (S6dGTP), a metabolite of the antileukemia agent 6-thioguanine, was evaluated as a substrate for purified human DNA polymerases. Using bacteriophage M13 single-strand DNA as a template, S6dGTP substituted efficiently for dGTP and stimulated DNA synthesis in reactions without dGTP, with DNA polymerases alpha, delta, and gamma from the human leukemia cell line K562. The apparent Km values for dGTP and S6dGTP were very similar, i.e., 1.2 microM each for polymerase alpha, 2.8 and 3.6 microM, respectively, for polymerase delta, and 0.8 microM each for polymerase gamma; however, the relative Vmax values for the modified nucleotide were 25-50% lower than those of the corresponding natural substrate. Using a highly sensitive electrophoretic assay of chain elongation across M13mp9 (+)-strand DNA by the aforementioned human DNA polymerases, S6dGTP was shown to be incorporated at the 3' end of the nascent growing DNA chain, and the patterns of chain extension with S6dGTP as substrate were identical to those obtained in the presence of dGTP. There were no major differences using S6dGTP in place of dGTP with these DNA polymerases; however, at higher concentrations (1-10 microM) the analog stimulated primer elongation in reactions without dATP, indicating some misincorporation at sites of S6G.T base pairs during DNA synthesis. Using p(dA)12-18 as the initiator for calf thymus terminal deoxynucleotidyltransferase, S6dGTP inhibited the incorporation of all four natural deoxyribonucleoside 5'-triphosphates into the primer, in a competitive manner. The apparent Ki values for the analog were 6-20 times lower than the Km values for the four endogenous substrates. As a substrate, S6dGTP was added to the 3'-hydroxyl termini of primer, although tailing efficiency with the analog was lower than that in the presence of the natural substrate. These findings indicate that S6dGTP is a relatively good substrate for several mammalian DNA polymerases, including terminal deoxynucleotidyltransferase.
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PMID:2'-Deoxy-6-thioguanosine 5'-triphosphate as a substrate for purified human DNA polymerases and calf thymus terminal deoxynucleotidyltransferase in vitro. 192 85

This investigation analyzed the metabolism of 2',2'-difluorodeoxycytidine (dFdC) in K562 human leukemia cells and evaluated it as a biochemical modulator for the phosphorylation of several arabinosyl nucleosides. The rate of accumulation of dFdC triphosphate was linear up to 3 h and maximal during incubation with 10 microM dFdC (92 microM/h). Deoxynucleotides analyzed at this time showed a decrease in dCTP, dATP, and dGTP levels, indicating an inhibitory role of dFdC nucleotides in ribonucleotide reduction. We evaluated the hypothesis that dFdC-mediated deoxyribonucleoside triphosphate perturbation enhances the phosphorylation of substrates that use deoxycytidine kinase or deoxyguanosine kinase, because these enzymes are inhibited by dCTP or dGTP, respectively. When the activity of these nucleoside kinases was rate limiting to triphosphate formation, the accumulation of triphosphates of deoxycytidine, 1-beta-D-arabinofuranosylcytosine, and 1-beta-D-arabinofuranosylguanine was potentiated in cells pretreated with dFdC. In contrast, the phosphorylation of 9-beta-D-arabinofuranosyladenine was not affected, since it is mainly phosphorylated by adenosine kinase, which is not influenced by deoxyribonucleoside triphosphates. Treatment of cells with dFdC followed by 1-beta-D-arabinofuranosylcytosine resulted in greater cytotoxicity than sum effects of each drug alone. The data indicate that an enhanced cytotoxicity could be obtained by administering dFdC as a modulator followed by 1-beta-D-arabinofuranosylcytosine or 1-beta-D-arabinofuranosylguanine in optimal sequence, suggesting that these results should be considered in the design of combination clinical protocols.
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PMID:Modulatory activity of 2',2'-difluorodeoxycytidine on the phosphorylation and cytotoxicity of arabinosyl nucleosides. 234 May 17

Experimental evidence has indicated that T lymphoblasts are more sensitive to deoxynucleoside toxicity than are B lymphoblasts. These data have led to the use of purine enzyme inhibitors as selective chemotherapeutic drugs in the treatment of T cell malignancies ranging from T cell acute lymphoblastic leukaemia to cutaneous T cell lymphomas. We have compared the toxicities of 2'-deoxyadenosine, 2'-deoxyguanosine, and thymidine for T cell lines derived from patients with T cell acute lymphoblastic leukaemia with those for mature T cell lines derived from patients with cutaneous T cell leukaemia/lymphoma. We have found that both deoxynucleosides are far less toxic to the mature T cell lies than to T lymphoblasts and that the mature cells accumulate much lower amounts of dATP and dGTP when exposed to deoxyadenosine and deoxyguanosine, respectively. Similar studies performed on peripheral blood cells from patients with T cell leukaemias of mature phenotype and on peripheral blood T cells demonstrate similar low amounts of deoxynucleotide accumulation. Measurements of the activities of several purine metabolizing enzymes that participate in deoxynucleoside phosphorylation or degradation do not reveal differences which would explain the toxicity of deoxynucleosides for immature, as compared to mature, T cells. We conclude that deoxynucleoside metabolism in leukaemic T cells varies with their degree of differentiation. These observations may be relevant to the design of chemotherapeutic regimes for T cell malignancies.
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PMID:Differential metabolism of deoxyribonucleosides by leukaemic T cells of immature and mature phenotype. 299 81

A cell line with immature blast cell morphology was isolated from HL-60 promyelocytic leukemia cell cultures and designated HL-T. This new cell type is biphenotypic, expressing terminal transferase (TdT) together with myelomonocytoid immunologic features. TdT enzymatic activity, undetectable in HL-60, was determined to be 140 to 180 units/10(8) HL-T cells by the dGTP-assay, approximately 20% of the activity found in lymphoblastoid cell lines. HL-T predominantly synthesize the known 58-kDa TdT-protein plus a minor 54/56-kDa doublet. The 58-kDa steady state form is nonglycosylated and is phosphorylated. Precursor antigens S3.13 and MY-10, absent on HL-60, are expressed by HL-T; however, the cells are negative for HLA-Dr. Southern blot analysis by hybridization with immunoglobulin heavy chain (JH) and T cell-receptor chain gene (T beta) probes shows JH to be in the germ-line configuration in both cell lines and the T beta gene to be in germ-line in HL-60 but to be rearranged in HL-T. Truncation of the gene encoding the granulocyte-macrophage-colony-stimulating factor (GM-CSF), as found in HL-60, is not observed in HL-T. HL-T are resistant to differentiation-induction by retinoic acid and 1,25-dihydroxyvitamin D3. Cytogenetically HL-T share with HL-60 a deletion of the short arm of chromosome 9 at breakpoint p13, an aberration frequently found in patients with T cell leukemia. In addition, HL-T display t(8;9)(p11;p24) and trisomy 20. Tetraploidy is observed in 80% of HL-T metaphases with aberrations identical to those in the diploid karyotype. Like HL-60, the new line shows some surface-antigenic-T cell characteristics. Despite an antigenic pattern most consistent with that of helper-inducer T cells (T4+, D44+/-, 4B4+, 2H4-, TQ1+/-), HL-T cells and their conditioned culture medium suppress antigen, mitogen, and mixed-leukocyte-culture-mediated lymphocyte proliferation.
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PMID:HL-T, a new cell line derived from HL-60 promyelocytic leukemia cell cultures expressing terminal transferase and secreting suppressor activity. 330 49

Trimetrexate is a novel lipophilic folate antagonist that causes growth inhibition, inhibition of nucleic acid biosynthesis, and cytotoxicity at nanomolar concentrations in tissue cultures. The potency of trimetrexate cytotoxicity against most cell lines is greater than that of methotrexate. Trimetrexate has antitumor activity in vivo in several murine leukemia and solid tumor systems, including tumors in which methotrexate is inactive. Antitumor activity was seen following oral, intravenous, or intraperitoneal administration. Trimetrexate causes a pronounced and early depression in incorporation of deoxyuridine into DNA. In tumor cell lines resistant to methotrexate because of a drug transport defect, trimetrexate retains activity. In many such cases the methotrexate-resistant tumors show collateral sensitivity to trimetrexate. In methotrexate-resistant cells with impaired drug transport, trimetrexate sensitivity was even more pronounced when cells were grown in folate-free medium supplemented with physiological levels of tetrahydrofolate cofactor. In the human tumor stem cell colony assay, trimetrexate, at concentrations achievable in vivo, gave activity against many human tumors, including samples that were unresponsive to methotrexate. Trimetrexate crosses the blood-brain barrier, and at very high doses may cause neurotoxicity. At conventional doses the primary toxic effects in mice are gastrointestinal. This toxicity is reversible at therapeutic doses. Unlike earlier lipophilic antifolates, trimetrexate has rapid plasma clearance (t1/2 in mice of 45 minutes). Trimetrexate is a tight-binding competitive inhibitor of dihydrofolate reductase. The Ki,slope for inhibition of the human enzyme was 4 X 10(-11) M. A dose-dependent decrease in cellular purine ribonucleotide pools is given by trimetrexate. Pyrimidine ribonucleotide pools tend to increase in treated cells. Trimetrexate caused a marked depression of cellular pools of dTTP and dGTP, and a lesser depression in dATP. Cytotoxicity of trimetrexate in vitro was prevented by leucovorin. Leucovorin also protected mice from trimetrexate toxicity. Thymidine protected cells from lethal effects of low concentrations of trimetrexate, but not from high concentrations. The combination of thymidine and hypoxanthine completely protected cells from low and high concentrations of trimetrexate. A new, stable and highly water-soluble formulation of trimetrexate has been developed. Because of the interesting biochemical and pharmacological properties of trimetrexate, and its experimental antitumor activity, clinical trials are planned.
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PMID:Biochemical pharmacology of the lipophilic antifolate, trimetrexate. 623 75


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