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:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cells exhibiting decreased topoisomerase II (Topo II) activity are resistant to several drugs that require Topo II as an intermediate. These drugs are cytotoxic due to the formation of a cleavable complex between the drug, Topo II and DNA. Fostriecin belongs to a new class of drugs that inhibit Topo II without inducing the formation of this cleavable complex. We tested fostriecin in three human small-cell lung carcinoma cell lines. GLC4 is the parent line. GLC4/ADR is the P-glycoprotein-negative multidrug-resistant subline, which is resistant to several Topo II inhibitors due to its decreased Topo II activity. GLC4/cDDP is the cisplatin-resistant subline, which displays increased Topo II activity. Topo II activity proved to be 100% in GLC4, 35% in GLC4/ADR and 130% in GLC4/cDDP. The fostriecin concentration causing inhibition of the growth of 50% of the cells (IC50) in the microculture tetrazolium assay following continuous incubation was 11.2, 4.1 and 14.9 microM, respectively. After 1-h incubations, the IC50 was 117.8, 101.3 and 219.8 microM, respectively. Our results indicate a relationship between Topo II activity and fostriecin sensitivity in these closely related cell lines. At least in vitro, fostriecin displayed the capacity to kill cells showing resistance to drugs due to decreased Topo II activity. There was no relationship between this capacity and an increase in the activity of the reduced-folate carrier system, the proposed mechanism for cellular entry of fostriecin, since we found no correlation between the cytotoxicity of fostriecin and that of methotrexate.
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PMID:Lack of cross-resistance to fostriecin in a human small-cell lung carcinoma cell line showing topoisomerase II-related drug resistance. 165 25

DNA topoisomerase II was isolated from mouse leukemia L1210 cells and the activity was determined by using P4 phage knotted DNA and pBR 322 DNA as the substrates. Based on these results, a method for screening antitumor agents by using DNA topoisomerase II as a target was established. The experiments showed that DNA topoisomerase II catalyzed pBR 322 DNA breaking and relaxing which were reversible and dependent on ATP. The activity was increased 2-4 times in the presence of ATP 1 mmol.L-1. In contrast with type II enzyme, the activity of DNA topoisomerase I was completely inhibited in the presence of ATP 1 mmol.L-1 and had full activity in the absence of ATP. Type II enzyme also showed the unknotting activity by using p4 phage knotted DNA as a substrate. DNA cleavage and relaxing reaction induced by type II enzyme increased 5-fold in the presence of Doxorubicin (Dox) 1 microgram.ml-1 or daunorubicin (Dau). Etoposide (Eto) and aclarubicin B (Acl B) also stimulated the reaction at 100 micrograms.ml-1. The cleavage reaction resulted from topoisomerase II was inhibited by other agents, such as frankincense extracts, terpenic compounds (BC series).
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PMID:Determination of DNA topoisomerase II activity from L1210 cells--a target for screening antitumor agents. 166 90

A series of doxorubicin-resistant variants of the human LS174T colon carcinoma cell line was generated by stepwise selection. These variants also exhibited increased resistance to vinblastine, etoposide, cis-platinum, and melphalan, suggesting that resistance was multifactorial. The parental LS174T cell line and 3 resistant variants were examined for over-expression of P-glycoprotein, changes in total cellular glutathione content, and the level of topoisomerase-II expression. Changes in all of these parameters were observed in the doxorubicin-selectants, along with a marked shift in the intracellular distribution of doxorubicin. P-glycoprotein RNA and protein levels were increased 2- to 3-fold in the resistant variants, while total glutathione levels increased 1.4- to 2.1-fold. Treatment with DL-buthionine-[S,R]-sulfoximine, an inhibitor of glutathione biosynthesis, was able to reverse resistance to cis-platinum and melphalan in these variants, but had little effect on doxorubicin resistance. Immunoblot analysis of cell extracts indicated that the level of DNA topoisomerase II (EC 5.99.1.3) in the doxorubicin-resistant LS174T cells was decreased by approximately 50% compared with the parental cell line. Doxorubicin was mainly localized to the cytoplasm in resistant cells, while in the parent line it was mostly found in the nucleus. This constellation of changes suggests that selection with doxorubicin activated several mechanisms of resistance involving drug transport, metabolism, and ability to reach nuclear target sites.
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PMID:Multifactorial resistance in LS174T human colon carcinoma cells selected with doxorubicin. 168 Aug 16

Analogues of the phenylbisbenzimidazole dye pibenzimol bind tightly to the minor groove of DNA. A clonogenic assay has been used to investigate the effects of these compounds on the cytotoxicity of the topoisomerase II directed anti-cancer drugs amsacrine, CI-921 (an amsacrine analogue), acridine carboxamide, etoposide and doxorubicin. Although pibenzimol itself was inactive, several of its analogues reduced the toxicity of etoposide, amsacrine and CI-921 towards a Lewis lung mouse tumour line at concentrations between 1 and 20 mumol/l. Doxorubicin cytotoxicity was unaffected, suggesting that this drug has a distinct mechanism of action. At concentrations below 1 mumol/l, some of these dyes potentiated the cytotoxicity of etoposide and CI-921 towards Lewis lung cells. Potentiation of CI-921 activity was also found with the human tumour lines HT29 (colon), SW620 (colon) and FME (melanoma). Novel treatments may arise from the potentiation of topoisomerase II directed cytotoxicity.
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PMID:Potentiation by phenylbisbenzimidazoles of cytotoxicity of anticancer drugs directed against topoisomerase II. 169 74

In a previous study we suggested that, in addition to the reduced Adriamycin accumulation, part of the resistance in an Adriamycin-resistant human small cell lung carcinoma cell line (GLC4/ADR) could be explained by supposing a changed Adriamycin-DNA-topoisomerase II (Topo II) interaction. The present study showed that the Mr 170,000 P-glycoprotein was not overexpressed in GLC4/ADR and that verapamil did not reverse the Adriamycin resistance. GLC4/ADR expressed cross-resistance to teniposide, etoposide, 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA), and mitoxantrone. Further investigations of the drug-Topo II interaction revealed that the decatenation activity of Topo II was two- to threefold reduced in both cellular and nuclear extracts from GLC4/ADR. Topo I activities appeared similar in extracts from GLC4/ADR and the parental sensitive cell line (GLC4). The slight increase in doubling time from 15 to 18 h, while the cell cycle distribution remained unchanged, could not account for the reduced Topo II activity in GLC4/ADR. Etoposide and m-AMSA-induced DNA cleavage was 5-fold reduced in cellular extracts from GLC4/ADR. Inhibition of the decatenation activity of Topo II in the presence of VP-16 and m-AMSA was increased twofold in the cellular extracts from GLC4/ADR. Therefore, these results suggest that resistance of GLC4/ADR to Adriamycin was in part due to the reduced drug-induced formation of the cleavage complex.
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PMID:Reduced DNA topoisomerase II activity and drug-induced DNA cleavage activity in an adriamycin-resistant human small cell lung carcinoma cell line. 196 22

This study assessed the ability of major metabolites of two types of anthracycline antibiotics, doxorubicin and idarubicin (4-demethoxydaunorubicin) to damage DNA in mouse fibrosarcoma 935.1 cells. Since DNA lesions by anthracyclines may be mediated by topoisomerase II, we also characterized the ability of the drugs to inhibit this enzyme. The C-13 alcohol and aglycone metabolites of doxorubicin and idarubicin were compared to the parent drugs in terms of induction of DNA single strand breaks measured by filter elution. In whole cells, the maximal DNA strand breakage induced by the C-13 alcohol metabolites was similar to that of their respective parent drugs. In isolated nuclei, however, the alcohol metabolites were two times more potent than the parent drugs. The aglycone metabolites produced very little damage in either whole cells or nuclei. The doxorubicin compounds differed markedly from idarubicin drugs in the way their ability to induce DNA breaks was related to cytotoxic activity. Doxorubicin and doxorubicinol cytotoxic effects (50% cell growth inhibition at 0.2 and 4 microM, respectively) coincided (in terms of drug concentrations) with the induction of significant breakage of cellular DNA. In contrast, the concentrations of idarubicin and idarubicinol needed to produce 50% growth inhibition (0.005 and 0.006 microM, respectively) were about 20 times lower than drug levels that induced significant DNA damage. All six compounds inhibited the catalytic activity of isolated topoisomerase II. While the alcohol metabolites produced this inhibition at concentrations similar to those of their parent drugs (5-10 microM), the aglycones were again much less active.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:DNA damage and cytotoxicity induced by metabolites of anthracycline antibiotics, doxorubicin and idarubicin. 204 26

We have isolated, following one-step mutagenesis, a Chinese hamster ovary cell mutant hypersensitive to the intercalating agent, adriamycin (4-fold compared to parental CHO-K1 cells). This agent exerts at least part of its cytotoxic action via inhibition of the nuclear enzyme, topoisomerase II. The mutant, designated ADR-3, showed hypersensitivity to all classes of topoisomerase II inhibitors, including actinomycin D, amsacrine (m-AMSA), etoposide (VP16) and mitoxantrone. ADR-3 cells also showed cross-sensitivity to ionizing radiation, but not to UV light. Cellular accumulation of radiolabeled actinomycin D was similar in parental and mutant cells. At equimolar doses, adriamycin induced more protein-associated DNA single- and double-strand breaks in ADR-3 cells than in CHO-K1 cells. Topoisomerase II activity was elevated to a small but significant degree in ADR-3 cells, and this was reflected in a 1.5-fold higher level of topoisomerase II protein in ADR-3 than in CHO-K1 cells, as judged by Western blotting. ADR-3 cells were hypersensitive to cumene hydroperoxide but cross-resistant to hydrogen peroxide, suggesting possible abnormality in the detoxification of peroxides by glutathione peroxidase or catalase. Glutathione peroxidase activity against hydrogen peroxide was similar in CHO-K1 and ADR-3 cell extracts, but activity against cumene hydroperoxide was evaluated to a small but significant extent in mutant cells. Catalase levels were not significantly different in ADR-3 and CHO-K1 cells. ADR-3 cells were recessive in hybrids with parental CHO-K1 cells with respect to sensitivity to topoisomerase II inhibitors and X-rays, and represent a different genetic complementation group from the previously reported adriamycin-sensitive mutant, ADR-1 [Davies et al., J. Biol. Chem., 263 (1988) 17724-17729].
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PMID:Isolation and partial characterisation of a mammalian cell mutant hypersensitive to topoisomerase II inhibitors and X-rays. 215 84

Doxorubicin, a DNA-intercalator, is one of several anti-cancer drugs that have been found to stabilizes topoisomerase II cleavage complexes at drug-specific DNA sites. The distribution and DNA sequence environments of doxorubicin-stabilized sites were determined in the SV40 genome. The sites were found to be most concentrated in the major nuclear matrix-associated region and nearly absent in the vicinity of the replication origin including the enhancer sequences in the 21-bp and 72-bp tandem repeats. Among 97 doxorubicin-stabilized sites that were localized at the DNA sequence level, none coincided with any of the 90 topoisomerase II cleavage sites detected in the same regions in the absence of drug. Cleavage at the 90 enzyme-only sites was inhibited by doxorubicin and never stimulated even at low drug concentrations. All of the doxorubicin-stabilized sites had an A at the 3' terminus of at least one member of each pair of strand breaks that would constitute a topoisomerase II double-strand scission. Conversely, none of the enzyme-only sites had an A simultaneously at the corresponding positions on opposite strands. The 3'-A requirement for doxorubicin-stabilized cleavage is therefore incompatible with enzyme-only cleavage and explains the mutual exclusivity of the two classes of sites.
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PMID:Local sequence requirements for DNA cleavage by mammalian topoisomerase II in the presence of doxorubicin. 217 43

We have isolated a Chinese hamster ovary cell line, designated ADR-1, which exhibits hypersensitivity to a range of drugs which are thought to inhibit the action of the enzyme topoisomerase II. These include anthracyclines, other classes of intercalating agents, and the epipodophyllotoxin, etoposide. No significant sensitivity to radiation, or to mono- and bifunctional alkylating agents was seen, although mild cross-sensitivity to the radiomimetic agent bleomycin was observed. We have monitored the level of DNA strand breaks induced by topoisomerase II inhibitors in ADR-1 cells using alkaline elution. At equimolar Adriamycin (doxorubicin) doses, more protein-associated DNA strand breaks are induced in ADR-1 cells than in wild-type cells. This enhanced level of drug-induced strand breaks does not appear to be a function of increased drug uptake as both lines accumulate similar levels of radiolabeled daunomycin. Both the rate of repair of strand breaks and the final percentage of strand breaks rejoined was equivalent in the 2 cell lines. These results are consistent with an enhancement in the level of topoisomerase II-dependent DNA breakage in ADR-1 cells following exposure to topoisomerase II inhibitors. We have previously reported the isolation of 2 bleomycin-sensitive Chinese hamster ovary cell lines, BLM-1 and BLM-2 (C. N. Robson et al., Cancer Res. 45:5304-5309, 1985). While BLM-1 exhibited cross-sensitivity only to Adriamycin, BLM-2 was shown to be hypersensitive not only to Adriamycin out also to certain alkylating agents and to ionizing radiation. In this paper, we show that both BLM-1 and BLM-2 also exhibit mild cross-sensitivity to a range of topoisomerase II inhibitors. These results indicate that intercalating agents and epipodophyllotoxins exert their cytotoxicity via common mechanisms and suggest that the maintenance of normal levels of cellular resistance to these agents requires the products of several different genes.
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PMID:Cross-sensitivity to topoisomerase II inhibitors in cytotoxic drug-hypersensitive Chinese hamster ovary cell lines. 243 20

Ataxia telangiectasia (AT) cell lines are characterised by their hypersensitivity to ionizing radiation and bleomycin, and their failure to inhibit DNA synthesis after DNA damage. A recent report [Singh et al. (1988) Nucl. Acids Res. 16, 3919-3929] indicated that a reduction in topoisomerase II (topo II) activity was a feature of AT lymphoblast cell lines. We have studied the possible role of DNA topoisomerases in determining the phenotype of an AT fibroblast cell line. AT5BIVA cells are sensitive to the topo II inhibitors etoposide (VP16) and amsacrine (m-AMSA), compared to normal human fibroblasts (MRC5-V1 and VA13). AT5BIVA cells express a 3-fold higher level of topo II protein than MRC5-V1 cells, and 6-fold higher than VA13. This is reflected in elevated topo II activity in AT5BIVA cells. Untransformed AT5BI cells also show elevated topo II activity compared to untransformed normal cells. The extent of overproduction of topo II in AT5BIVA cells is comparable with that seen in a mutant Chinese hamster cell line, ADR-1, which is similarly hypersensitive to both bleomycin and topo II inhibitors. However, ADR-1 cells show neither hypersensitivity to ionizing radiation nor abnormal inhibition of DNA synthesis following DNA damage. Topo II overproduction per se does not appear sufficient to generate an "AT-like" phenotype. AT5BIVA cells express a reduced level of topoisomerase I (topo I) and are hypersensitive to the topo I inhibitor, camptothecin. ADR-1 cells express a normal level of topo I, indicating that a reduction in the level of topo I is not the inevitable consequence of an elevation in topo II.
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PMID:Overproduction of topoisomerase II in an ataxia telangiectasia fibroblast cell line: comparison with a topoisomerase II-overproducing hamster cell mutant. 253 56


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