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:2.7.1.21 (thymidine kinase)
7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Interferon-alpha (IFN alpha) increases the cytotoxicity of 5-fluorouracil (FUra) in vitro, and the combination has clinical efficacy against advanced colorectal cancer. IFN alpha treatment of HT-29 colon carcinoma cells induced a greater than two-fold increase in the intracellular levels of the active metabolite of FUra, FdUMP. Using cell extracts from HT-29 cells and FUra as substrate, IFN alpha produced a 1.9- and 8.7-fold increase, respectively, in the activities of uridine phosphorylase and pyrimidine nucleoside phosphorylase (PyNP). Furthermore, the effect was selective for the conversion of FUra to FdUMP, as IFN alpha did not increase the cellular levels of FUTP, nor did it change the extent of incorporation of FUra into RNA (or DNA). IFN alpha also had no effect on thymidine kinase activity, the second step in the activation of FUra. Hence the effect of IFN alpha on PyNP activity is likely a critical biochemical event that modulates the cytotoxicity of FUra.
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PMID:Stimulation of 5-fluorouracil metabolic activation by interferon-alpha in human colon carcinoma cells. 154 Jan 67

An overview was presented of our approach of inhibition of de novo and salvage pathways in pyrimidine and purine metabolism. 1. Combination of acivicin, an inhibitor of de novo biosynthesis, and dipyridamole, a transport inhibitor, provided synergistic cytotoxicity in hepatoma and colon carcinoma cells. 2. AZT, a competitive inhibitor of the salvage enzyme, thymidine kinase, and 5-FU or MTX provided synergistic cytotoxicity in hepatoma 3924A. In human colon carcinoma HT-29 cells AZT and methotrexate yielded synergistic cytotoxicity and thymidine and hypoxanthine together provided protection from the action of these drugs. 3. These observations are significant because in rat hepatoma 3924A and in human cell lines HT-29, HL-60 and K562 thymidine kinase activity was 16- to 67-fold higher than that of dTMP synthase. Therefore, inhibition of dTMP synthase activity alone may provide poor responses because the salvage pathways can circumvent this block. 4. In leukemic patients treated with tiazofurin, an inhibitor of IMP dehydrogenase, the rate-limiting enzyme of GTP biosynthesis, and with allopurinol, which inhibits GPRT activity through raising plasma hypoxanthine levels, synergistic therapeutic results were obtained. The responses in sensitive patients entailed a decrease in IMP dehydrogenase activity and GTP concentration in leukemic cells and down-regulation of the ras and myc oncogenes. The down-regulation of the ras oncogene by tiazofurin through the decrease of GTP concentration has now been shown in K562, HL-60 and hepatoma cells and in patients with chronic granulocytic leukemia in blast crisis. Tiazofurin may be useful in studies on selective depression of the expression of the ras oncogene. 5. In 27 consecutive patients 50% responded positively to tiazofurin treatment. From this group, 10 out of 12 patients (83%) with chronic granulocytic leukemia in blast crisis responded to tiazofurin treatment.
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PMID:Regulation of de novo and salvage pathways in chemotherapy. 187 99

Azidothymidine (AZT, 3'-azido-3'-deoxythymidine, zidovudine) competitively inhibited the activity of thymidine kinase (EC 2.7.1.21) in extracts of rat hepatoma and sarcoma cells; Dixon plots yielded a Ki = 1-2 microM. Azidothymidine (100 microM) exerted synergistic cytotoxicity with methotrexate (0.05 microM) in hepatoma cells in culture in clonogenic assay. Thymidine (50 microM) counteracted the effect of azidothymidine and prevented synergistic action. Azidothymidine (10 microM) was synergistically cytotoxic with 5-fluorouracil (0.3 and 0.5 microM) in HT-29 human colon carcinoma cells. Thymidine (10 microM) abolished synergism. These studies suggest a new role for azidothymidine which, as an inhibitor of thymidine salvage, should enhance synergistically the clinical anticancer impact of blockers of de novo biosynthesis of thymidylates (methotrexate, 5-fluorouracil).
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PMID:Azidothymidine inhibition of thymidine kinase and synergistic cytotoxicity with methotrexate and 5-fluorouracil in rat hepatoma and human colon cancer cells. 236 52

Biochemical differences were demonstrated between two cell lines derived from a human colon carcinoma (HCT8), one sensitive (HCT8S), and one 4.3-fold resistant to cisplatin (HCT8DDP). The cisplatin-resistant cell line overexpressed five enzymes (dihydrofolate reductase, thymidine 5'-monophosphate synthase, thymidine kinase, and DNA polymerase alpha and beta) believed to be important for DNA replicative and repair synthesis. In addition, the c-fos and c-H-ras oncogenes were also overexpressed in the HCT8DDP cells. This apparent overexpression was not associated with increases in gene copy number, it was related, however, to increased mRNA content. Expression of these key enzymes may be a significant factor in the development of clinical resistance to cisplatin. Further, these specific changes in cellular metabolism associated with cisplatin resistance may be exploited by the use of nucleoside analogues.
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PMID:Overexpression of DNA replication and repair enzymes in cisplatin-resistant human colon carcinoma HCT8 cells and circumvention by azidothymidine. 253 92

Base propenals arise from DNA by a Fe(II)-bleomycin-mediated reaction which leads to strand scission. These compounds undergo addition-elimination reactions with thiols and other nucleophilic groups under physiological conditions and form an addition product with glutathione. Thymine- and adenine-N1-propenals inhibit DNA synthesis in HeLa cells; both compounds are cytotoxic [50% inhibiting concentration (IC50) = 1 to 2 microM]. A structurally related nucleoside, thymidine-N3-propenal, designed as a metabolic pathway inhibitor, inhibits growth of HeLa, L1210 leukemia, Lewis lung carcinoma, B16 melanoma, and DLD-1 human colon carcinoma cells in culture (IC50 = 1 to 6 microM). A single injection of this compound, administered on the first day following transplant of L1210 leukemia cells, increased the mean survival time of mice by 50% (T/C = 154). Thymidine-N3-propenal selectively blocks DNA synthesis in HeLa cells and inhibits thymidine kinase (Ki = 5.1 microM) and DNA polymerase-alpha. We suggest that base propenals, rather than damaged DNA, account for some of the cytotoxic effects of bleomycin and that nucleoside propenals represent a novel class of site-directed inhibitors.
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PMID:Origin and cytotoxic properties of base propenals derived from DNA. 257 72

The transforming activity of DNA from a newly established undifferentiated human colon carcinoma cell line (MIP-101) was tested in the NIH-3T3 transfection assay. Southern blot analysis of the transfectant DNA revealed the presence of a human N-ras oncogene. Treatment of MIP-101 cells with the maturational agent sodium butyrate induced a more normal phenotype, including diminished growth rate, elimination of anchorage independent growth, and decreased tumorigenicity (R. Niles, S. Wilhelm, P. Thomas, and N. Zamcheck (1988) J. Cancer Invest. 6, 39). Here we report that there is a significant reduction in the transforming efficiency of the DNA from butyrate-treated MIP-101 cells. A nonspecific reduction in total DNA uptake as an explanation for these findings was eliminated by showing that there was similar uptake and expression of the thymidine kinase gene from the DNA of butyrate-treated and control MIP cells. Butyrate treatment had no detectable effect on the overall structure, methylation, and level of expression of the human N-ras gene from MIP-101 cells. An NIH-3T3 transformant ability after treatment with sodium butyrate. Although butyrate suppressed several transformed properties similar to MIP-101 cells, DNA from control and treated cultures had an identical level of transforming activity. The results suggest that the environment of the MIP cells may contain additional elements not present in the NIH-3T3 transformants which are required to observe the effect of butyrate on reduction of transforming activity.
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PMID:Sodium butyrate suppresses the transforming activity of an activated N-ras oncogene in human colon carcinoma cells. 267 72

Carcinoma of the colon was induced in rats by injection of a carcinogen 1,2-dimethylhydrazine (DMH), and thymidylate synthetase (TS) and thymidine kinase (TK) activities, which catalyze the biosynthesis of dTMP by the de novo pathway and the salvage pathway of pyrimidine synthesis, respectively, were measured in normal control colon, DMH-treated normal colon, and DMH-induced colon carcinoma with or without administration of two doses of an anti-cancer drug UFT (a combination of tegafur and uracil). TS and TK activities were both increased after treatment with DMH, markedly in colon carcinoma tissue, and to a lesser degree in normal-appearing colon tissue. This phenomenon is well explained by the hypothesis that biochemical alterations of DNA-synthesizing enzyme activities occur as a preliminary step prior to the development of overt cancerous transformation. A low dose of UFT inhibited TS activity but enhanced TK activity, therefore, the salvage pathway may compensate for the reduced level of the de novo synthesis. On the other hand, a large dose of UFT reduced both TS and TK activities, perhaps due to cytotoxic effects of UFT incorporation into RNA.
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PMID:Thymidylate synthetase and thymidine kinase activities in DMH-induced colon carcinomas in rats and effects of UFT. 310 3

The effects of a variety of 5-, 5'-, and 3'-substituted deoxyuridine derivatives on the cytoplasmic thymidine kinase (EC 2.7.1.21) purified from a human colon carcinoma cell line, HCT 116, were determined. Of particular interest was elucidation of the structural features important for antagonism of the feedback inhibition of thymidine kinase exerted by thymidine triphosphate. Substitutions at the 5-position altered the potency of the 5'-modified compounds. The replacement of the 5-hydrogen with a methyl group or an iodine greatly increased the affinity of compounds for the thymidine kinase. This was evident for enzyme substrates with 5'-hydroxyl groups [2'-deoxyuridine (dUrd), 2'-deoxythymidine (dThd) and 5-iodo-2'-deoxyuridine (IdUrd)], feedback inhibitors with 5'-triphosphate substitutions (dUTP, dTTP and IdUTP), and for 5'-amino derivatives [5'-amino-2',5'-dideoxyuridine (5'-AdUrd), 5'-amino-2'-5'-dideoxythymidine (5'-AdThd) and 5-iodo-5'-amino-2',5'-dideoxyuridine (5'-AIdUrd)]. Qualitatively, however, the 5-substitutions did not affect the nature of the interactions with dThd kinase. For example, in the presence of dTTP, 5'-AdUrd stimulated dThd kinase activity as much as 5'-AdThd, but approximately a 100-fold greater concentration of 5'-AdUrd was required. Similar results were obtained using intact cells in which substitutions at the 5-position affected the potency, but not the efficacy, of the 5'-amino derivatives to stimulate dThd phosphorylation. In contrast, substitutions at the 5'-position did alter the nature of the interaction with dThd kinase. Thus, the 5'-hydroxyl compounds, dUrd, dThd and IdUrd, did not reverse the enzyme inhibition produced by dTTP nor did they stimulate dThd uptake in intact cells. 5'-Deoxy-5'-(ethylthio)thymidine, 5'-deoxy-5'-[(2-hydroxyethyl)thio]thymidine, and dTMP, but not dTDP, also antagonized the inhibition of dThd kinase produced by dTTP. In comparison to 5'-AdThd, the 3'-amino derivatives, 3'-AdThd and 3'-5'-diAdThd, were much less potent, but still efficacious, antagonists of feedback inhibition. These results indicate that a wide range of dUrd derivatives can disrupt the regulation of dThd kinase and provide leads for the development of new nucleotide analogues.
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PMID:Structure-activity analysis of antagonism of the feedback inhibition of thymidine kinase. 335 1

Thymidylate synthetase (TS) and thymidine kinase (TK) are known to catalyse the methylation of dUMP for the de novo synthesis of dTMP and the phosphorylation of thymidine for the salvage synthesis of dTMP in the pyrimidine pathway, respectively. High TS and TK activities and the existence of TK isozymes have been observed in rapidly proliferating tissues. TS and TK activities in 1,2-dimethylhydrazine (DMH)-induced colon carcinomas in rats increased significantly to 331 and 207% of the activities in normal colon, respectively, and were well correlated inversely (y = -0.93x + 5.24), with a correlation coefficient of -0.787. The colonic TK isozymes were separated into two types by DEAE-cellulose column chromatography. The TK isozyme eluted from the column by the elution buffer alone without NaCl was markedly higher (23.6-fold) in activity in DMH-induced colon carcinoma than in normal control colon and was not affected by deoxycytidine triphosphate. This isozyme, whose mol. wt is 100,000 by h.p.l.c., is thought to be closely involved in rapid DNA replication. These results indicate that early biochemical changes in DMH-induced colon carcinoma in rats may serve as a useful model and provide valuable insight into the mechanisms involved in colonic carcinogenesis.
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PMID:Relative activities of thymidylate synthetase and thymidine kinase in 1,2-dimethylhydrazine-induced colon carcinomas in rats. 381 35

We have previously demonstrated that genetically modified syngeneic murine tumor cells (KBALB) expressing the herpes simplex virus thymidine kinase gene (HSV-STK) can kill nearby unmodified tumor cells in the presence of ganciclovir (GCV). The killing was mediated by a 'bystander effect' as evidenced by the prolonged animal survival when syngeneic HSV-TK gene-modified tumor cells were inoculated into mice with an intraperitoneal tumor. In this study we investigated whether irradiated xenogeneic HSV-TK gene-modified tumor cells, a human colon carcinoma cell line (HCT) transfected with the HSV-TK gene, can mediate the 'bystander effect' when used in vitro and in vivo. In vitro experiments indicate that irradiated HSV-TK gene-modified xenogeneic cells (HCT) can mediate a bystander effect on the adjacent cells when the tumor population consisted of as few as 10% of the HSV-TK expressing HCT tumor cells. In vivo, animal survival experiments demonstrate that the xenogeneic gene-modified tumor cells could generate the 'bystander effect' in mice with intraperitoneal tumors as evidenced by prolonged animal survival. In addition, histologic examination of the tumors from experimental animals showed extensive tumor necrosis 3 days post HSV-TK/GCV treatment in comparison to control animals. To evaluate the cause of necrosis in vivo, we assayed for cytokines, which may be involved in mediating this process, by performing RT-PCR and immunohistochemistry on tumor RNA and tumor cells, respectively. Production of IL-1 alpha and IL-6 mRNA within the experimental tumors was observed by RT-PCR. However, mRNA expression for other cytokines including IFN-gamma, IL-2 and IL-4 was not present. Immunohistochemical analysis for IL-1 alpha protein showed reactivity within the infiltrating mononuclear cells indicating the release of this soluble factor. These results indicate that the bystander effect can be generated using irradiated xenogeneic cells both, in vitro and in vivo. Furthermore, this process is mediated by the release of cytokines such as IL-1 alpha, IL-6 which enhances the bystander effect in vivo by immunostimulation.
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PMID:The role of cytokines in mediating the bystander effect using HSV-TK xenogeneic cells. 760 May 27


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