Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.7 (DNA polymerase)
 17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Synergistic killing of L1210 cells occurs when methotrexate (MTX) is administered just before 1-beta-D-arabinofuranosylcytosine (Ara-C). This pehnomenon is dependent upon both the dose and time of exposure to MTX. Such increased killing of cells can be explained by the enhanced intracellular accumulation of Ara-C in cells exposed to MTX. This enhancement of Ara-C entry into cells was only observed when the dose of MTX was high enough (1, 10, and 100 muM) to result in free intracellular nondihydrofolate reductase-bound MTX. At the highest doses of MTX (10 and 100 muM) Ara-C triphosphate was increased eightfold and deoxycytidine triphosphate was decreased by 50%. Therefore, the maximum synergistic cell kill when MTX precedes Ara-C may be the consequence of greater inhibition of DNA polymerase by th;e increased Ara-C triphosphate in the presence of the decreasing natural substrate of this enzyme, deoxycytidine triphosphate. Enhanced Ara-C accumulation after administration of MTX was also observed in human acute myelogenous leukemia cells.
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PMID:Mechanism of synergistic cell killing when methotrexate precedes cytosine arabinoside: study of L1210 and human leukemic cells. 28 43

Enzymes of deoxyribonucleotide and DNA biosynthesis, which are little known in plants, were studied in root tips of germinating broad beans (Vicia faba) and in fast-growing cultures of soybean cells (Glycine max). The plant cells contain a ribonucleoside 5'-diphosphate reductase which is detected in vitro only during a limited period of growth, viz. 30--32 h after inhibition of Vicia seeds, and between the second and third day after inoculation of soybean cultures. In both species ribonucleotide reductase activity precedes maximum DNA synthesis. The reductases could be precipitated with ammonium sulfate but were not purified further due to the extremely low enzyme content of the plant extracts. Therefore the reductive pathway of deoxyribotide formation was also established in Vicia root tips by efficient labeling of the plant DNA with a ribonucleoside, [5-3H]cytidine, which reaches a maximum at the same time as the reductase activity measured in vitro. Cycloheximide inhibits this process, indicating the need for de novo enzyme induction. In contrast, DNA polymerase is present in the tissue throughout the entire development and rises only 2-fold in activity during the S phase. The soluble polymerases were partially characterized in both legume species and were found very similar to the DNA polymerase of pea seedlings. Ribonucleotide reductase is more likely a limiting component of DNA formation during the plant cell cycle than DNA polymerase.
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PMID:Deoxyribonucleotide synthesis and DNA polymerase activity in plant cells (Vicia faba and Glycine max). 42 Aug 54

Regenerating rat liver was used as a semisynchronous system in which to investigate the effects of 6-thioguanine on biochemical processes occurring in discrete phases of the cell cycle. 6-Thioguanine inhibited the first wave of DNA biosynthesis in regenerating rat liver. This effect appeared to be the result of a decrease, caused by 6-thioguanine, in the induction of several enzyme activities (i.e., thymidine kinase, deoxycytidylate deaminase, cytidine diphosphate reductase, and DNA polymerase) necessary for the initiation of DNA replication in regenerating liver. There was a fairly short period during which 6-thioguanine could be given to rats to accomplish the inhibition of the appearance of the induced activities of these enzymes; this period corresponded to the time just before enzyme induction. The inhibition of the induced synthesis of this group of enzymes occurred in the presence of an intact translational apparatus and intact polysomes and in the absence of interference with the incorporation of radioactive leucine and tyrosine into total protein of liver. Synthesis of polyadenylate-containing RNA was depressed in 6-thioguanine-treated rats, whereas the synthesis of polyadenylate-lacking RNA was unaffected. It is suggested that the inhibition of the synthesis of polyadenylate-containing RNA by 6-thioguanine is at least in part responsible for the observed decrease in induced enzyme activities and the resulting interference with DNA replication.
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PMID:Effects of 6-thioguanine on macromolecular events in regenerating rat liver. 87 Jan 91

Ribonucleotide reductase which catalyzes the rate-limiting step in the de novo synthesis of dNTPs is composed of two non-identical protein subunits which are not under coordinate control in terms of synthesis and degradation. The mRNAs for the effector-binding (EB) and non-heme iron (NHI) subunits are likewise not under coordinate control during cell cycle traverse. Inhibitors directed at the specific subunits of ribonucleotide reductase block DNA synthesis. These current studies show that drugs such as IMPY or hydroxyurea which specifically inhibit the NHI subunit cause a marked increase in the steady-state level of the mRNA for the NHI subunit while resulting in a decrease in the level of mRNA for the EB subunit. In cells treated with deoxyadenosine, the patterns of the mRNAs for the NHI and EB subunits were different from those seen in the IMPY- or hydroxyurea-treated cells. Control experiments utilizing inhibitors (aphidicolin or araC) directed at DNA polymerase showed that the pattern of changes in the mRNA levels for the NHI and EB subunits were specific for the reductase inhibitors. These changes in the mRNAs for the NHI and EB subunits may be due to drug-induced alterations in transcription rates and/or degradation rates for the specific mRNAs.
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PMID:Factors affecting the mRNA levels for the non-heme iron and effector-binding subunits of ribonucleotide reductase. 149 19

The sugar boronated thymidine nucleoside, 5' -0-[(triphenylphosphine-boryl) carbonyl]-3'-0-acetyl thymidine 1, and the boron-modified nucleoside phosphotriester, 5'-(diethylphosphite- cyanoborane)-3'-acetylthymidine 2, were successfully synthesized. Both compounds demonstrated differential activity when tested against eight cell lines, with significant cytotoxic activity against the growth of human Tmolt3 leukemia, colon adenocarcinoma, HeLa S3 uterine carcinoma, and osteosarcoma cells. In in vivo studies these agents were found to be active against the growth of Ehrlich ascites carcinoma at 8 mg/kg/day I.P. and to be marginally active against the growth of L1210 and Lewis lung cancers in mice. The mode of action of these thymidine derivatives in Tmolt3 cells was the inhibition of DNA and protein synthesis. Compound 2 was highly effective in inhibiting DNA polymerase alpha and m-RNA, r-RNA and t-RNA polymerase activities. Both compounds inhibited ribonucleoside reductase activity. The de novo purine pathway appeared to be the major site of inhibition of the agents, with IMP dehydrogenase, PRPP amido transferase, and dihydrofolate reductase activities being significantly inhibited. In the pyrimidine pathway, carbamyl phosphate synthetase and aspartate transcarbamylase activities were inhibited by 1. As expected, d[NTP] levels were significantly reduced by treatment with the agents. DNA strand scission was evident after incubating Tmolt3 cells for 24 hr with the agents.
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PMID:Antineoplastic activity of boron-containing thymidine nucleosides in Tmolt3 leukemic cells. 150 1

Naturally occurring sesquiterpene lactones and their semisynthetic derivatives, such as the O = C-C = CH-bearing helenalin and its esters, have been shown to demonstrate potent cytotoxicity against the growth of murine L1210 lymphoid leukemia and human Tmolt3 leukemia, colon adenocarcinoma, HeLaS3, lung bronchogenic, KB, osteosarcoma, and glioma cells. The modes of action of helenalin in L1210 cells are the inhibition of DNA, RNA, and protein syntheses. This study confirms that thiol bearing enzymes of nucleic acid metabolism were significantly inhibited, e.g. DNA polymerase alpha, IMP hydrogenase, and ribonucleoside reductase. The addition of GSH to the reaction medium demonstrated total recovery of L1210 ribonucleoside reductase activity. Helenalin reduced cellular GSH levels in L1210 cells. Helenalin also reduced all four pool levels of d(NTP)s which would account for part of the observed inhibition of DNA synthesis. Reductions in the ribonucleotide pool levels were also generally evident after drug treatment. Thus, the sesquiterpene lactones appear to have more than one mode of action in L1210 cells. All of the modes of actions of helenalin are feasible mechanisms to lower nucleic acid synthesis and cause cell death of the L1210 leukemia cells.
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PMID:The cytotoxicity of helenalin, its mono and difunctional esters, and related sesquiterpene lactones in murine and human tumor cells. 152 2

Purine and pyrimidine adducts of alpha-methylene-gamma-lactone demonstrated potent cytotoxicity against murine L1210 lymphoid leukemia growth as well as a variety of human tissue cultured tumors. The most potent compound, 9-[(2-methyl-4-methylene-5-oxotetrahydrofuran-2-yl)-methyl 1] adenine 1 demonstrated significant inhibition of DNA synthesis in L1210 leukemic cells with moderate inhibition of protein synthesis. The major enzyme activities inhibited by 1 were DNA polymerase alpha, ribonucleoside reductase and t-RNA polymerase with marginal inhibition of thymidine kinase, TMP kinase, PRPP amidotransferase and IMP dehydrogenase. The inhibition of DNA polymerase alpha activity by 1 was evident at the lowest concentration 25 microM and was evident within 15 min incubation at 100 microM. The magnitude of enzyme inhibition was consistent with the observed DNA synthesis inhibition by 1. The only deoxyribonucleotide level reduced by 1 was the dATP pool level. U.V. absorption of DNA after interacting with 1 demonstrated a hyperchromic effect and L1210 DNA strand scission was observed after 24 hr incubation with 1 suggesting some type of interference with the DNA template by the drug.
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PMID:The effects of alpha-methylene-gamma-lactone purines and pyrimidines on L1210 lymphoid leukemia nucleic acid metabolism. 201 69

Helenalin and bis (helenalinyl) malonate, sesquiterpene lactones, were shown to be cytotoxic against the growth of P-388 lymphocytic leukemia cells in culture. DNA and protein synthesis were reduced by these agents preferentially, with RNA synthesis being affected only marginally. This study focused on the identification of the enzyme target(s) responsible for the inhibition of DNA synthesis by the sesquiterpene lactones. Purine synthesis was strongly inhibited at the IMP dehydrogenase step. Suppression of IMP dehydrogenase activity and purine synthesis paralleled the DNA synthesis inhibition with respect to both dose dependence and time of incubation with drug. Deoxyribonucleoside triphosphate pools in the P-388 cells were significantly reduced by both drugs and the DNA polymerase alpha activity was only moderately inhibited by both drugs in cytoplasmic preparation. However, inhibition of a partially purified DNA polymerase alpha was of a much greater magnitude. Activity of the ribonucleotide reductase complex was reduced by more than 50% at 100 microM concentration of either drug. The drugs appeared to affect the hydrogen donor system of the reductase complex, since the activity of the ribonucleotide reductase enzyme itself was not affected but both thioredoxin and glutaredoxin were markedly inactivated by the sesquiterpene lactones. Thymidylate synthetase activity was not affected by the sesquiterpene lactones in P-388 cells. These data suggest that the inhibition of IMP dehydrogenase and the ribonucleotide reductase complex activities by helenalin and bis (helenalinyl) melonate was the primary reason for the observed inhibition of DNA synthesis, but that inhibition of DNA polymerase alpha may also play a role. The inhibition of the sensitive enzymes is likely to be related to drug alkylation of thiol active groups of the enzymes in a manner similar to the action of N-ethylmaleimide. The mode of action of helenalin and bis (helenalinyl) malonate does not appear to be similar to that of the parthenolide-type sesquiterpene lactones which contain an epoxide moiety.
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PMID:Inhibition of nucleic acid synthesis in P-388 lymphocytic leukemia cells in culture by sesquiterpene lactones. 289 92

Microinjection is shown to be a useful tool for studies of chemical inhibition of DNA synthesis: inhibitor-treated cells were injected with combinations of radioactive precursors and their uptake into DNA was monitored by autoradiography. The results obtained from inhibition by cytosinearabinoside, aphidicolin, trifluorothymidine, and fluorodeoxyuridine agreed well with the common knowledge about these drugs. Short-term (but not long-term) treatments with methotrexate were compensated by injections of thymidine-nucleotides. The effect of hydroxyurea was in part, but not fully, reversed by injection of all four deoxytriphosphates; this implies a second mechanism besides inhibition of ribonucleotide reductase. Regulation of reductase was responsible for the effect of thymidine: the enhanced dTTP caused a depletion of dCTP and dATP. Novobiocin was different from all other drugs tested, DNA polymerase or enzymes of the precursor metabolism are obviously not targets of this drug.
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PMID:Microinjected deoxynucleotides for the study of chemical inhibition of DNA synthesis. 296 41

Mechanism-based enzyme inactivator, alanine racemase, S-adenosylhomocysteine hydrolase, D-amino acid aminotransferase, gamma-aminobutyric acid aminotransferase, arginine decarboxylase, aromatase, L-aromatic amino acid decarboxylase, dihydrofolate reductase, dihydroorotate dehydrogenase DNA polymerase I, dopamine beta-hydroxylase, histidine decarboxylase, beta-lactamase, monoamine oxidase, ornithine decarboxylase, serine proteases, testosterone 5 alpha-reductase, thymidylate synthetase, xanthine oxidase.
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PMID:The potential use of mechanism-based enzyme inactivators in medicine. 306 67


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