Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cellular requirements for iron during DNA synthesis are related to the increased activity of the iron-containing M2 subunit of ribonucleotide reductase, the enzyme responsible for the reduction of ribonucleotides to deoxyribonucleotides. We have previously shown that transferrin-gallium (Tf-Ga) inhibits cellular iron incorporation. In the present study, Tf-Ga-induced inhibition of HL60 cell growth and upregulation of Tf receptor density was reversed with hemin. Cells exposed to 2 mumol/L Tf-Ga for six hours or longer displayed a diminution in the electron spin resonance (ESR) spectroscopy signal of the tyrosyl radical of the M2 subunit of ribonucleotide reductase. The effect of Tf-Ga on the ESR signal was reversed by hemin. Tf-Ga decreased the incorporation of 14C-adenosine into DNA and decreased intracellular deoxyribonucleotide pools, with the maximum diminution seen in deoxyadenosine triphosphate (dATP) and deoxycytidine triphosphate (dCTP) pools. Exposure of cells to combinations of Tf-Ga and hydroxyurea (a known inhibitor of ribonucleotide reductase) resulted in a marked inhibition of cell growth that was consistent with drug synergy. Our studies suggest that Tf-Ga inhibits DNA synthesis through action on the M2 subunit of ribonucleotide reductase and that combinations of Ga and hydroxyurea should be further evaluated in in vivo tumor models.
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PMID:Inhibition of leukemic HL60 cell growth by transferrin-gallium: effects on ribonucleotide reductase and demonstration of drug synergy with hydroxyurea. 275 50

In previous studies, N-hydroxy-N'-aminoguanidine (HAG) derivatives were demonstrated to suppress growth and clonogenicity of tumor cells which correlated with the inhibition of ribonucleotide reductase and DNA synthesis. The present work has focused on the properties of five HAG derivatives as inhibitors of the ribonucleotide reductase from Ehrlich ascites tumor cells. HAG derivatives acted as non-competitive inhibitors of ribonucleotide reductase with respect to the substrates CDP and ADP. The apparent Ki values for the various HAG derivatives as inhibitors of CDP reductase ranged from 3.4 to 543 microM. However, the apparent Ki values for these inhibitors with respect to ADP reductase were 2- to 10-fold lower than the respective values for CDP reductase. After a preincubation of HAG derivatives and ribonucleotide reductase in the absence of substrates, an increased inhibition was observed. The activity of the inhibited enzyme could be restored by passage over a Sephadex G-25 column and subsequent incubation with dithioerythritol. The addition of either the non-heme iron subunit or the effector-binding subunit to the intact enzyme in the assay mixture resulted in a diminished inhibition of ADP reduction. Inhibition by HAG derivatives of ribonucleotide reductase activity in the test tube was not enhanced by iron chelators. However, a combination of HAG compounds and iron chelators synergistically inhibited the growth of L1210 cells.
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PMID:Properties of N-hydroxy-N'-aminoguanidine derivatives as inhibitors of mammalian ribonucleotide reductase. 327 27

Activity increase of the cytosolic isozyme of thymidine kinase (TK) in resected specimens of lung tumor patients would be a useful marker for tumor malignancy and prognosis. In 24 resected cases of malignant lung tumors, the whole enzyme extracts of the tumorous part of the specimens showed that the activities of TK, thymidylate synthetase, and ribonucleotide reductase increased at an average of 469 (P less than 0.001), 208 (not significant), and 193% (P less than 0.02) of the corresponding enzymes in the tumor-uninvolved lung parts, respectively. Two TK isozymes, cytosolic and mitochondrial TKs, were separated better by means of p-aminophenyl 3'-TMP:CH-Sepharose gel affinity column chromatography for precise quantitation of the activity than by polyacrylamide disc gel electrophoresis. These separated isozymes from the tumorous part of the specimens were characteristically very similar to the isozymes of cytosolic and mitochondrial fractions of the xenograft (CPX-101) of human lung tumor transplanted in athymic nude mice, respectively. The cytosolic isozyme activity isolated by this method from the tumorous part was remarkably higher and more varied than that of the tumor-uninvolved part, while that of the mitochondrial isozyme was lower and less agitated. The tumor doubling time showed a good inverse correlation to the activity of the cytosolic isozyme of TK when compared logarithmically (r = -0.798, P less than 0.01). Poorly differentiated tumors exhibited significantly higher activities of the TK cytosolic isozyme than did well-to-moderately differentiated tumors (766.0 +/- 379.1 and 308.1 +/- 119.5 pmol/mg of protein/h, mean +/- SE, respectively), a phenomenon also seen in the activities of the tumors with versus without recurrences within 12 mo after resection (803.6 +/- 278.7 and 124.1 +/- 42.1 pmol/mg of protein/h, respectively). The levels of these relationships using the cytosolic TK activity provided a clearer indication of prognosis and the state of the malignancy than those using the whole extract TK activity.
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PMID:Activity of the cytosolic isozyme of thymidine kinase in human primary lung tumors with reference to malignancy. 340 30

Novel antitumor agents related to levodopa and dopamine exhibit a selective and rapid inhibition of DNA synthesis as measured by thymidine incorporation. Our investigations have attempted to determine the biochemical basis of the selective inhibition of tumor cells and in this present study we examined the effects of these agents on thymidylate synthase. The dihydroxybenzene derivatives were found to inhibit thymidylate synthase in situ at concentrations ranging between 100 and 800 microM. The quinols did not inhibit partially purified thymidylate synthase, although the oxidized quinones did cause inhibition at concentrations between 10 and 100 microM. Time course experiments suggested that the inhibition of thymidylate synthase in situ by the dihydroxybenzene derivatives occurs after the inhibition of thymidine incorporation, indicating that an earlier event was critical to the inhibition of DNA synthesis. With the use of a novel in situ assay which measured the release of [3H]water from [5-3H] uridine in intact cells, we were able to show that one of the earliest biochemical events is the inhibition of ribonucleotide reductase and that the inhibition of thymidylate synthase, which is delayed by approximately 30 min, was indirectly mediated possibly through effects on ribonucleotide reductase.
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PMID:Sequential inhibitory effects of antitumor agents related to levodopa and dopamine upon DNA synthetic enzymes. 351 Jun 22

The potentiation in the cytotoxic effect of antineoplastic agent hydroxyurea (HU) from the non-toxic concentration on P388 murine lymphocytic leukemia cells is observed with the hydrophobic iron-chelating agents, 2,2-bipyridine (bipyridyl) and 1,10-phenanthroline in a concentration and time dependent manner. However EDTA, EGTA, 2,3-dihydroxybenzoic acid (2,3-DBA), Rhodotorulic acid, 8-hydroxyquinoline (8-Hq), catechin and Desferal, and other chelators failed to show sensitization of these tumor cells towards HU. The potentiation in the cytotoxic activity of HU in combination with the bipyridyl was found to be reversible but was maintained when the drug exposed cells were washed and retreated with the non-toxic concentrations of HU or bipyridyl. The presence of Fe++ blocked completely the cytotoxic action of HU alone and a combination with iron-chelator, and partially reversed the inhibition induced by HU and bipyridyl. These findings suggest that the hydrophobic iron-chelators affect the membrane-mediated transfer, localisation and transient intracellular chelatable iron pools. As a consequence of this, the regulatory role mediated by iron on the overall activity of ribonucleotide reductase enzyme is disturbed leading to a conclusive imbalance in DNA biosynthesis.
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PMID:Sensitization of P388 murine leukemia cells to hydroxyurea cytotoxicity by hydrophobic iron-chelating agents. 351 97

The biochemical modulation of tumor cell response to increase the cytotoxicity of Hydroxyurea (HU), directed at the ribonucleotide reductase enzyme, has been studied in in vitro. Mice bearing ascites tumor models such as L1210 leukemia, Sarcoma 180 (S180) and Ehrlich ascites tumor (EAT) were employed in this study. The cytotoxicity of HU alone at various concentrations was dose dependent and showed the following order of sensitivity; L1210 greater than EAT greater than S180. The hydrophobic iron-chelating agent 2,2-bipyridyl significantly potentiated the antitumor activity of HU in all the murine tumor models studied. In contrast, hydrophilic iron-chelator, Desferal, did not show any cytotoxicity when combined with HU. The present study demonstrated the factors influencing the amelioration of HU cytotoxicity and possible therapeutic use of iron-chelating agents alone and with HU for better therapeutic results in clinics.
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PMID:Potentiation of hydroxyurea cytotoxicity by iron-chelating agent in murine tumor models in vitro. 377 2

Ribonucleotide reductase is a key enzyme in DNA replication and, as such, has been a target for antitumor agents. This enzyme is composed of two nonidentical protein subunits which can be specifically and independently inhibited. Combinations of drugs directed at the effector-binding and non-heme iron subunits of ribonucleotide reductase resulted in the synergistic inhibition of L1210 cell growth and synergistic L1210 cell kill. These combinations included dAdo/EHNA/IMPY/Desferal; dAdo/EHNA/hydroxyurea/Desferal (the EHNA was required to protect dAdo from deamination while Desferal modulated the effects of IMPY or hydroxyurea); 2-F-araA/IMPY/Desferal and 2-F-2'-dAdo/IMPY/Desferal (EHNA was not required to protect 2-F-araA or 2-F-2'-dAdo from deamination); and dGuo/8-AGuo/IMPY/Desferal (8-AGuo was required to protect dGuo from phosphorolysis). Although thymidine alone inhibited L1210 cell growth, it was not possible to potentiate the effects of thymidine with the pyrimidine nucleoside phosphorylase inhibitors, acyclothymidine, 5-chlorouracil and 2,6-dihydroxypyridine. Combinations of drugs directed at the ribonucleotide reductase and DNA polymerase sites were studied for their effects on L1210 cell growth. With these combinations, no synergistic inhibition of L1210 cell growth was observed. The combinations of aphidicolin and IMPY/Desferal and aphidicolin and dAdo/EHNA inhibited L1210 cell growth in an additive manner; the combinations of IMPY/Desferal and BuAU or IMPY/Desferal and BuPdG resulted in antagonistic inhibition of L1210 cell growth. From these results it is clear that combination chemotherapy directed at independent sites of the same key target enzyme can result in strong synergistic inhibition of cell growth and cytotoxicity offering a clear therapeutic advantage. In contrast, the combinations directed at sequential key enzymes (e.g. ribonucleotide reductase and DNA polymerase) did not result in synergistic inhibition of cell growth. The utility of combinations of drugs directed at specific but independent sites of the target enzyme (e.g. ribonucleotide reductase) has been demonstrated in tumor cell systems in culture and now must be demonstrated in vivo.
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PMID:The utility of combinations of drugs directed at specific sites of the same target enzyme--ribonucleotide reductase as the model. 390 3

It would be expected that drugs directed at the rate-limiting step in a key metabolic pathway in tumor cell proliferation would provide a useful basis for therapy of neoplasms. Ribonucleotide reductase catalyzes the rate-limiting step in the de novo synthesis of dNTP's for DNA synthesis. Further, ribonucleotide reductase is composed of two non-identical protein subunits (non-heme iron and effector-binding subunits) which can be specifically and independently inhibited. As a result, combinations of drugs specifically directed at each of the subunits of ribonucleotide reductase have been shown to cause synergistic inhibition of L1210 cell growth in culture and synergistic cell kill. This approach offers a novel basis for the design of combination chemotherapy.
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PMID:Combination chemotherapy directed at the components of nucleoside diphosphate reductase. 391 43

Ribonucleotide reductase catalyzes the rate-limiting step in DNA synthesis. It represents a key metabolic site at which specific inhibitors have been directed as potential antitumor agents. Several different classes of ribonucleotide reductase inhibitors have been generated and studied. Because of the nature of the DNA polymerase reaction in which all four dNTPs are required, the initial velocity vs dNTP concentration curve gives sigmoidal rather than hyperbolic kinetics. As a result, a 50 per cent decrease in ribonucleotide reductase activity causes a decrease in DNA polymerase activity of 75 per cent or greater depending on the ratio of [dNTP] to its Km. This has been demonstrated with theoretical calculations, actual DNA polymerase determinations and precursor studies in intact tumor cells. The structural requirements for a compound to serve as a specific inhibitor of ribonucleotide reductase, either as the non-heme iron or effector-binding subunit, are stringent. Each protein subunit comprising the active enzyme can be specifically and independently inhibited. When combinations of agents, each directed at one of the subunits of ribonucleotide reductase, are used, strong synergistic inhibition of L1210 cell growth and synergistic cytotoxicity result.
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PMID:Drug action on ribonucleotide reductase. 391 89

Mechanism of cytotoxicity of 5-fluorouracil (5-FU) in relation to impairment of RNA metabolism was studied. 5-FU depressed the levels of ribonucleotide reductase and thymidine kinase, which are two key enzymes in DNA synthesis, in solid AH-130 tumor when given intraperitoneally at a dose of 60 mg/kg, and this inhibition seemed to be very toxic against cells. But this dose of 5-FU exceeded the amount that could be degraded by the liver, which was much higher than the clinical dose. We concluded that the impairment of RNA metabolism caused by 5-FU played a minor role in its anti-tumor actions.
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PMID:[Studies on the mechanism of cytotoxicity of 5-fluorouracil--through impairment of metabolism]. 634 31


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