Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.3 (topoisomerase)
 9,911 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Determination of the clastogenic potential of new chemical entities, particularly pharmaceuticals, is an important part of the overall safety assessment of such drugs. It is appreciated that clastogenicity can arise from perturbation of many different cellular processes distinct from direct DNA/drug interactions. One such alternative clastogenic process is inhibition of DNA topoisomerase II, during which process the topoisomerase/DNA/drug ternary complex forms stable DNA double-strand breaks (cleavable complex), which become templates for recombinational, mutagenic, and chromosomal fragmentation events. Without extensive experimentation, it is generally not possible to distinguish clastogenicity arising from direct drug/DNA interaction from that arising from inhibition of topoisomerase II. In the present investigation, we demonstrate that specific catalytic inhibitors of DNA topoisomerase II reduce the clastogenicity of topoisomerase poisons but not that arising via non-topoisomerase-dependent mechanisms. In particular, it is shown that catalytic topoisomerase II inhibitors such as chloroquine, sodium azide, and A-74932, as well as certain intercalating agents such as 9-aminoacridine and ethidium bromide, strongly antagonize the formation of micronuclei induced by the DNA gyrase inhibitor clinafloxacin and the antitumor topoisomerase II poison etoposide. These catalytic inhibitors are also shown to antagonize the clastogenicity of experimental compounds and novel pharmaceuticals presumed to be DNA intercalating agents by virtue of their response in a cell-based bleomycin amplification assay. We extend our previous hypothesis, suggesting that the clastogenicity of some nonstructurally alerting drugs may be due to an as yet unappreciated propensity for DNA intercalation. It is further proposed that intercalation-dependent inhibition of DNA topoisomerase II may be responsible for this clastogenicity and that this may be detected in intact mammalian cells with the use of catalytic topoisomerase inhibitors.
Environ Mol Mutagen 2000
PMID:Use of catalytic topoisomerase II inhibitors to probe mechanisms of chemical-induced clastogenicity in Chinese hamster V79 cells. 1069 23

The chromosome aberration assay in vitro is a useful and sensitive test for detection of genotoxins. However, aberrations can occur secondary to toxicity, with compounds that do not react with DNA and are not genotoxic in vivo. Thus, some positive results in the in vitro aberration assay are not relevant to human risk. To help evaluate the influence of toxicity, data were collected from 27 pharmaceutical and chemical companies and contract laboratories. When cytotoxicity was measured by cell counts or confluence, compounds expected to damage DNA (Category 1) generally induced aberrations without severe concomitant cytotoxicity, i.e., at cell growth 60% or more of control. The more toxic nucleoside analogues, topoisomerase inhibitors, fluoroquinolone antibiotics, antifolates, and producers of reactive oxygen were still positive with cell growth 50% or more of control. In contrast, when there was evidence that the compounds were not DNA damaging (Category 2), there was a higher proportion of toxicity-associated clastogens, with positive results at less than 50% of control cell growth. When mitotic index (MI) was used as an indicator of cytotoxicity, the pattern was less clear, although there was a tendency to more mitotic suppression with the Category 2 compounds. Overall the data indicate that a limit on toxicity, and a more accurate way of estimating it, would increase the accuracy of the assay by reducing the frequency of nonrelevant positive results with a threshold-type of dose relation. The rationale for evaluating positive results in the in vitro aberration assay, especially those associated with toxicity, is discussed, as is the need for a harmonized regulatory approach.
Environ Mol Mutagen 2000
PMID:Cytotoxicity and chromosome aberrations in vitro: experience in industry and the case for an upper limit on toxicity in the aberration assay. 1073 54

Inhibitors of topoisomerases, enzymes that produce an unusual type of DNA damage, are considered as antitumor agents. Recently it has been reported that the fernane-type triterpenoid EC-2 and its hydroxyl derivative, isolated from Euphorbia, are potent topoisomerase II inhibitors. In this study, the modifying effects of EC-2 and EC-4 on the development of putative preneoplastic lesions, glutathione S-transferase placental form (GST-P)-positive foci, in the liver of rats were investigated using a medium-term bioassay system. Fisher 344 male, 6-week-old rats were given a single intraperitoneal injection (200 mg/kg b.w.) of diethylnitrosamine or saline at the beginning of the experiment and subjected to 2/3 partial hepatectomy at the 3rd week. The test compounds were administered five times/week by i.g. gavage at a dose of 1 mg/kg b.w. from 2 to 8 weeks. Quantitation of the numbers and areas per cm(2) of induced GST-P positive foci did not demonstrated any significant differences among the groups and no variation in cell proliferation as indicated by 5-bromo- 2'-deoxyuridine (BrdU) labeling. Our results suggest that EC-2 and EC-4 have no modifying effects on rat hepatocarcinogenesis.
Teratog Carcinog Mutagen 2002
PMID:Lack of modification of rat hepatocarcinogenesis by fernane-type triterpenoids, isolated from a Euphorbia genus. 1211 13

The recently developed Tk(+/-) mouse detects in vivo somatic cell mutation in the endogenous, autosomal Tk gene. To evaluate the sensitivity of this model, we have treated Tk(+/-) mice with three agents that induce DNA damage by different mechanisms, and determined spleen lymphocyte mutant frequencies (MFs) in the autosomal Tk gene and in the X-linked Hprt gene. gamma-Radiation, which produces single- and double-strand breaks by nonspecific oxidative stress, efficiently increased Hprt MF, but not Tk MF. Mitomycin C, which produces bulky DNA monoadducts and crosslinks, was mutagenic in both the Hprt and Tk genes, but the response was greater in the Tk gene. An inhibitor of the ligase function of DNA topoisomerase II, etoposide, did not increase Hprt MF, and induced a small, but nonsignificant increase in Tk MF. Combined with previous data, the results indicate that the two genes are differentially sensitive to many agents, and that the Tk gene is more sensitive than the Hprt gene to some, but not all types of DNA damage.
Environ Mol Mutagen 2002
PMID:Mutagenicity of gamma-radiation, mitomycin C, and etoposide in the Hprt and Tk genes of Tk(+/-) mice. 1211 86

Merbarone is a catalytic inhibitor of topoisomerase II (topo II) that has been proposed to act primarily by blocking topo II-mediated DNA cleavage without stabilizing DNA-topo II-cleavable complexes. In this study merbarone was used as a model compound to investigate the genotoxic effects of catalytic inhibitors of topo II. The clastogenic properties of merbarone were evaluated using in vitro and in vivo micronucleus (MN) assays combined with CREST staining. For the in vitro MN assay, ICRF-187, a different type of catalytic inhibitor, and etoposide, a topo II poison, were used for comparison. Treatment of TK6 cells with all three of these drugs resulted in highly significant dose-related increases in kinetochore-lacking MN and, to a lesser extent, kinetochore-containing MN. In addition, a good correlation between p53 accumulation and MN formation was seen in the drug-treated cells. A mouse MN assay was performed to confirm that similar DNA-damaging effects would occur in vivo. Bone marrow smears from merbarone-treated B6C3F1 mice showed a dose-related increase in micronucleated polychromatic erythrocytes with a mean of 26 MN per 1000 cells being seen at the 60 mg/kg dose. Almost all MN lacked a kinetochore signal, indicating that merbarone was predominantly clastogenic under these conditions in vivo. The present study clearly shows that merbarone is genotoxic both in vitro and in vivo, and demonstrates the inaccuracy of earlier statements that merbarone and other catalytic inhibitors block the enzymatic activity of topo II without damaging DNA.
Environ Mol Mutagen 2002
PMID:Catalytic inhibitors of topoisomerase II are DNA-damaging agents: induction of chromosomal damage by merbarone and ICRF-187. 1211 87

Bioflavonoids are naturally occurring polyphenols with intriguing and varied therapeutic and chemoprotective activities generally ascribed to their antioxidant properties. However, many flavonoids have also been shown to be genotoxic in a variety of prokaryotic, eukaryotic, and in vivo systems. The mechanistic basis for this genotoxicity has not been fully elucidated, although structure-activity relationship studies have identified requisite flavonoid structural features. We utilized Chinese hamster V79 cells to evaluate the relationships between DNA intercalation ability, topoisomerase II interactions, reactive oxygen species (ROS) generation, and clastogenicity in a series of 14 bioflavonoids. Five of the flavonoids examined, luteolin, quercetin, genistein, apigenin, and acacetin, were strongly clastogenic. This clastogenicity was shown to require DNA intercalation (with the exception of genistein) and was substantially reduced by catalytic inhibitors of DNA topoisomerase II. The transition metals Cu(II) and Mn(II) formed chelates with and/or modified the structure and biological activity of some flavonoids but no consistent relationship could be demonstrated between metal reactivity and clastogenicity. There was no clear association between generation of ROS and clastogenicity. The data presented herein are consistent with a model in which the genotoxicity of most flavonoids arises via DNA intercalation and topo II poisoning, likely mediated through metabolism to flavonoid quinones. Interestingly, other flavonoids such as myricetin, daidzein, baicalein, fisetin, and galangin were catalytic topo II inhibitors, rather than poisons. These studies further validate the use of cell-based approaches for detecting drug/topo II interactions and raise interesting questions relating to biological and chemical mechanisms of flavonoids.
Environ Mol Mutagen 2002
PMID:Evaluation of the clastogenic, DNA intercalative, and topoisomerase II-interactive properties of bioflavonoids in Chinese hamster V79 cells. 1248 17

The topoisomerase II (topo II) inhibitors etoposide (VP-16) and merbarone (MER) were investigated with the in vivo micronucleus test (MN test) combined with fluorescence in situ hybridization (FISH) using the mouse minor satellite DNA probe to discriminate MN of clastogenic and aneugenic origin. All experiments were performed with male (102/ElxC3H/El) F1 mice bred in the mouse colony of the GSF Research Center. The sample size per experimental group was five animals and 2,000 polychromatic erythrocytes (PCE) were scored per animal from coded slides in the conventional MN test. A separate set of coded slides was used for the FISH analysis. All treatments consisted of single intraperitoneal injections. Colchicine (COL, 3 mg/kg) and mitomycin (MMC, 1 mg/kg) were used as a positive control aneugen and clastogen, respectively, and these compounds produced the expected responses. A dose of 1 mg/kg VP-16 induced 3.44% MNPCE (compared to the concurrent solvent control of 0.37%, P < 0.001) and of these 39.9% (1.4% MNPCE) showed one or more fluorescent signals. MER (7.5-60 mg/kg) increased the MNPCE frequencies in a dose-dependent manner, with 15 mg/kg being the lowest positive dose. At the highest dose of 60 mg/kg of MER, a total of 4.26% MNPCE were found (compared to 0.31% in the concurrent solvent control, P < 0.001) and of these 46.2% (2.0% MNPCE) contained one or more fluorescent signals. The data demonstrate that VP-16 and MER induced both clastogenic and aneugenic events despite their different modes of topo II inhibition.
Environ Mol Mutagen 2003
PMID:Etoposide and merbarone are clastogenic and aneugenic in the mouse bone marrow micronucleus test complemented by fluorescence in situ hybridization with the mouse minor satellite DNA probe. 1260 78

A cytogenetic study was carried out with 5-azacytidine (5-azaC) and etoposide (VP-16) in CHO-K1 and XRS-5 (mutant cells deficient for double-strand break rejoining) cell lines to verify the interaction effects of the drugs in terms of induction of chromosomal aberrations. 5-azaC is incorporated into DNA causing DNA hypomethylation, and VP-16 (inhibitor of topoisomerase II enzyme) is a potent clastogenic agent. Cells in exponential growth were treated with 5-azaC for 1 h, following incubation for 7 h, and posttreatment with VP16 for the last 3 h. In K1 cells, the combined treatments induced a significant reduction in the aberrations induced in the X and "A" (autosome) chromosomes, which are the main target for 5-azaC. However, in XRS-5 cells, the drug combination caused a significant increase in the aberrations induced in those chromosomes, but with a concomitant reduction in the randomly induced-aberrations. In addition, each cell line presented characteristic cell cycle kinetics; while the combined treatment induced an S-arrest in K1 cells, alterations in cell cycle progression were not found for XRS-5, although each drug alone caused a G2-arrest. The different cell responses presented by the cell lines may be explained on the basis of the evidence that alterations in chromatin structure caused by 5-aza-C probably occur to a different extent in K1 and XRS-5 cells, since the mutant cells present a typical hyper-condensed chromosome structure (especially the X- and "A" chromosomes), but, alternatively, 5-aza-C could induce reactivation of DNA repair genes in XRS-5 cells.
Teratog Carcinog Mutagen 2003
PMID:Chromosomal aberrations induced by 5-azacytidine combined with VP-16 (etoposide) in CHO-K1 and XRS-5 cell lines. 1261 7

Anthracyclines have been widely used as anticancer drugs against different types of human cancers. The present study evaluated the mutagenic and recombinagenic properties of two anthracycline topoisomerase II (topo II) poisons, daunorubicin (DNR) and idarubicin (IDA), as well as the related topo II catalytic inhibitor aclarubicin (ACLA), using the wing Somatic Mutation and Recombination Test (SMART) in Drosophila melanogaster. The three anthracyclines were positive in this bioassay, producing mainly mitotic homologous recombination. The results for spot-size distribution and recombinagenic activity indicate that recombinational DNA damage accounts for approximately 91, 86, and 62% of DNR, IDA, and ACLA genotoxicity, respectively. Besides being a catalytic inhibitor of topo II, ACLA is also a topoisomerase I (topo I) poison. This dual topo I and II inhibitory effect, associated with its DNA-intercalating activity, could contribute to the activity of ACLA in the SMART assay.
Environ Mol Mutagen 2004
PMID:Activity of topoisomerase inhibitors daunorubicin, idarubicin, and aclarubicin in the Drosophila Somatic Mutation and Recombination Test. 1514 64

Epidemiological studies show that benzene exposure is associated with an increased incidence of leukemia and perhaps lymphoma. Chromosomal rearrangements are common in these hematopoietic diseases. Translocation t(14;18), the long-arm deletion of chromosome 6 [del(6q)], and trisomy 12 are frequently observed in lymphoma patients. Rearrangements of the MLL gene located on chromosome 11q23, such as t(4;11) and t(6;11), are common in therapy-related leukemias resulting from treatment with topoisomerase II inhibiting drugs. To examine numerical and structural changes in these chromosomes (2, 4, 6, 11, 12, 14, and 18), fluorescence in situ hybridization (FISH) was employed on metaphase spreads from workers exposed to benzene (n = 43) and matched controls (n = 44) from Shanghai, China. Aneuploidy (both monosomy and trisomy) of all seven chromosomes was increased by benzene exposure. Benzene also induced del(6q) in a dose-dependent manner (P(trend) = 0.0002). Interestingly, translocations between chromosomes 14 and 18, t(14;18), known to be associated with follicular non-Hodgkin lymphoma, were increased in the highly exposed workers (P < 0.001). On the other hand, translocations between chromosome 11 and other partner chromosomes that are found in therapy-induced leukemias were not increased. These data add weight to the notion that benzene can induce t(14;18) and del(6q) found in lymphoma, but do not support the idea that benzene induces t(4;11) or t(6;11). However, they do not rule out the possibility that other rearrangements of the MLL gene at chromosome 11q23 may be induced by benzene.
Environ Mol Mutagen 2007 Jul
PMID:Aberrations in chromosomes associated with lymphoma and therapy-related leukemia in benzene-exposed workers. 1758 86


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