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)

The antineoplastic quinobenoxazines A-62176 and A-74932 were shown to be potent inhibitors of mammalian DNA topoisomerase II in vivo. This was demonstrated by their selective inhibition of the SV40 DNA replication stages that require topoisomerase II. Neither drug stabilized a covalent complex of the enzyme with SV40 DNA, which suggests that they are not poisons of DNA topoisomerase II. A-77601, an analog having little antitumor activity, barely inhibited DNA topoisomerase II in vivo, even at high concentrations. These findings were supported by in vitro studies which showed that A-62176 and A-74932, but not A-77601, strongly inhibited the catalytic activity of mammalian DNA topoisomerase II. A-62176 did not cause topoisomerase II-mediated DNA strand breaks in vitro under conditions in which adriamycin produced extensive DNA breakage. The antineoplastic and topoisomerase inhibitory activities of the quinobenoxazines correlate with their ability to unwind DNA. A-62176 antagonized the poisoning of topoisomerase II by VM-26 in vivo and in vitro, but had no effect on DNA breakage induced by camptothecin, a DNA topoisomerase I poison. A-62176 and A-74932 thus inhibit DNA topoisomerase II reactions at a step prior to the formation of the "cleavable complex" intermediate. These findings indicate that stabilization of the DNA topoisomerase II-DNA cleavable complex is not necessary for the antitumor activity of this class of quinolones and that the catalytic inhibition of DNA topoisomerase II may contribute significantly to the anticancer activity of other DNA topoisomerase II inhibitors.
Biochemistry 1994 Sep 20
PMID:Quinobenoxazines: a class of novel antitumor quinolones and potent mammalian DNA topoisomerase II catalytic inhibitors. 772 84

Type I and II topoisomerase activities were partially purified from Pneumocystis carinii. The catalytic (strand-passing) activities of both enzymes were selectively inhibited by members of a series of dicationic-substituted bis-benzimidazoles compared with those of topoisomerases of mammalian (calf thymus) origin. The most active inhibitors of the parasite enzymes were also highly effective in an in vivo animal model of P. carinii pneumonia. Selected dicationic-substituted bis-benzimidazoles also strongly inhibited the induction of the topoisomerase I- and II-mediated cleavable complex, suggesting that the biologically active DNA minor groove-binding molecules inhibit the enzyme-DNA binding step of the topoisomerase reaction sequence. The apparent selectivities for the parasite enzymes and the low levels of toxicity to mammalian cells for the biologically active bis-benzimidazoles suggest that these compounds hold promise as effective therapeutic agents in the treatment of a life-threatening AIDS-related disease, P. carinii pneumonia.
Antimicrob Agents Chemother 1994 Sep
PMID:Selective inhibition of topoisomerases from Pneumocystis carinii compared with that of topoisomerases from mammalian cells. 781 Sep 95

In Streptomyces ambofaciens NSA2002, pigmented wild-type colonies spontaneously give rise to pigment-negative (Pig-) mutants at a frequency of about 0.5%. This genetic instability is related to large deletions which can be associated with amplifications of DNA sequences. The influence of three fluoroquinolones (ciprofloxacin, enoxacin, and norfloxacin) on this property was investigated. At a survival rate higher than 60%, most colonies showed a patchwork phenotype consisting of phenotypically heterogeneous colonies harboring numerous mutant sectors. Moreover, the frequency of Pig- mutants rose to more than 90% at survival rates equal to or higher than 10%. Induced Pig- mutants showed the same phenotypical features as did spontaneous mutants. Most of them also harbored deletions, associated in some cases with DNA amplifications, in two loci of the large unstable region, AUD6 and AUD90 (derived from amplifiable unit of DNA). The size of deletions in induced mutants could rise to 1.5 Mb. These results show that ciprofloxacin, enoxacin, and norfloxacin greatly stimulate genetic instability and the occurrence of DNA rearrangements in S. ambofaciens. Moreover, these three fluoroquinolones had the same rank order for both toxic (i.e., antibacterial) and genotoxic activities. If the antibacterial effect of fluoroquinolones in S. ambofaciens is due to their interference with DNA gyrase, as shown for some other organisms, the genotoxic effect observed could be due to their interaction with this type II topoisomerase. This suggests that DNA gyrase is involved in the process of genetic instability in S. ambofaciens.
Antimicrob Agents Chemother 1994 Sep
PMID:Stimulation of genetic instability and associated large genomic rearrangements in Streptomyces ambofaciens by three fluoroquinolones. 781 Oct 7

Human epidermoid KB cell lines resistant to high levels of adriamycin, C-A90, C-A120, C-A500, and C-A1000, were isolated in selection medium containing increasing concentrations of adriamycin, 1 microgram/ml of cepharanthine, a multidrug-resistance (MDR) reversing agent, and 100 nM of mezerein, a protein kinase C activating agent. One of the adriamycin-resistant KB cell lines, C-A500, was cross-resistant to drugs that typify the classical multidrug resistance phenotype, such as vincristine, actinomycin D, VP-16, and colchicine. The accumulation of adriamycin and vincristine was decreased in C-A500 cells and the efflux of adriamycin from C-A500 was enhanced compared with parental KB-3-1 cells. These adriamycin-resistant KB cells did not contain detectable levels of P-glycoprotein or overexpress MDR1. Multidrug-resistance-associated protein (MRP) and MRP mRNA were expressed in the adriamycin-resistant KB cells, C-A120, C-A500, and C-A1000, but not in parental KB-3-1 and revertant C-AR cells. The MRP gene was amplified in all the MDR cells that overexpressed MRP mRNA. DNA topoisomerase II levels were markedly decreased in C-A500 and C-A1000 cells but only slightly decreased in C-A120 cells. These results indicate that MRP overexpressed in the resistant cells may be responsible for the reduced accumulation of adriamycin and vincristine and that both the increased expression of MRP and decreased levels of topoisomerase II underlie the drug resistance in C-A120, C-A500, and C-A1000 cell lines.
Somat Cell Mol Genet 1994 Sep
PMID:Non-P-glycoprotein-mediated multidrug-resistant human KB cells selected in medium containing adriamycin, cepharanthine, and mezerein. 782 64

Inhibitors of macromolecular synthesis and topoisomerases induce apoptosis in the human leukaemic cell line, U937. In this study, U937 cells were treated with the RNA synthesis inhibitor, actinomycin D (1 microM), the protein synthesis inhibitors, emetine (1 microM) and cycloheximide (100 microM), the topoisomerase II inhibitor, teniposide (5 microM), or the topoisomerase I inhibitor, camptothecin (1 microM). Apoptotic cell death was assessed both by flow cytometry and agarose gel electrophoresis, and was correlated to the appearance of large (20 to > or = 580 kilobase pairs) DNA fragments, as assessed by field inversion gel electrophoresis. In all cases, the appearance of DNA fragments of 20-50 kilobase pairs accompanied the appearance of an apoptotic population and of internucleosomal cleavage. However, teniposide additionally induced a marked increase in fragmentation to > or = 580 kilobase pairs. The cotreatment of cells with zinc (1 mM) inhibited the formation of all large DNA fragments, internucleosomal cleavage and the appearance of an apoptotic population. We conclude that the generation of large DNA fragments is characteristic of apoptosis induced by various stimuli in U937, as has been found previously in rat thymocytes. However, unlike what occurs in rat thymocytes, zinc treatment does not dissociate the formation of large fragments from conventional markers of apoptosis.
J Cell Sci 1994 Sep
PMID:Formation of high molecular mass DNA fragments is a marker of apoptosis in the human leukaemic cell line, U937. 784 65

The induction of apoptosis following topoisomerase inhibitors proceeds in at least three distinct steps: (1) induction of cleavable complexes (potentially lethal damage), (2) topoisomerase-induced DNA damage, and (3) a presently unknown sequence of events that must either lead to cell cycle arrest (G2-block, differentiation) or apoptosis. DNA degradation provides a convenient way to quantify apoptosis in HL-60 cells. Extensive apoptosis can be induced rapidly in undifferentiated HL-60 cells without prevention by cycloheximide or actinomycin D. Therefore, HL-60 cells appear to express constitutively the apoptotic machinery that may be kept under control of a yet unknown repressor. The absence of the tumor suppressor p53 and the presence of bcl-2 are in contrast with the sensitivity of these cells to apoptosis. Agents that modify chromatin structure (zinc, poly[ADPribose] inhibitors, spermine) can block DNA fragmentation without affecting cell survival. By contrast macrophage-like differentiation by phorbol esters suppresses apoptosis without affecting topoisomerase-induced DNA damage. Better understanding of the apoptotic regulation in the widely used and characterized HL-60 cell line should allow the identification of new mechanisms and parameters of cellular sensitivity and resistance to the cytotoxic activity of anticancer agents.
Leuk Lymphoma 1994 Sep
PMID:Apoptosis induced by DNA topoisomerase I and II inhibitors in human leukemic HL-60 cells. 785

Ofloxacin, a specific inhibitor of bacterial topoisomerase II, is known to inhibit the growth of yeast cells and to induce rho- mutants in the yeast S. cerevisiae. The frequency of ofloxacin-induced petite mutants under non-growth conditions was found to be strongly diminished when the cells were depleted in intramitochondrial ATP. Under optimal conditions of mitochondrial mutagenesis the drug induced mitotic recombination and reverse mutation in diploid strains but failed to cure either killer plasmids or the 2 microns DNA of dividing cells. The sensitivity to ofloxacin of the strains deficient in the DNA strand-break repair pathway (rad52) was significantly higher then that of the wild-type strains and of the mutants deficient in excision or mutagenic DNA repair. The results are compatible with the idea that the cytotoxic and genetic activity of ofloxacin in yeast probably results from the inhibited DNA ligation function of topoisomerase II creating DNA breaks that are reparable through the recombination repair pathway.
Curr Genet 1994 Sep
PMID:Energy-dependent mitochondrial mutagenicity of antibacterial ofloxacin and its recombinogenic activity in yeast. 785 13

The sequence specificity of topoisomerase-II-mediated DNA cleavage, stimulated by 2-methyl-9-hydroxy ellipticinium and 4',5,7-trihydroxyflavone (genistein) was investigated by sequencing analysis of DNA cleavage sites and molecular modeling techniques. The former drug exhibits a marked preference for a T base at the position immediately preceding the cleavage site (-1). The latter shares the preference for the same base, with an additional preference for a thymine at position +1. The cleavage intensity patterns in the presence of the two drugs differ considerably. From a conformational point of view, ellipticinium and genistein exhibit similar overall shape and dimensions. However, the fused ring system in the former generates a planar structure whereas the single bond, connecting the two aromatic portions in the latter, allows internal rotation. The most stable conformation of genistein corresponds to a deviation of about 40 degrees from planarity. A computer-assisted analysis was carried out to compare the steric and electrostatic properties of the two compounds. Two types of preferred (energetically almost degenerate) alignment for the two molecules were found. One corresponds to overlapping of the 9-hydroxyl containing ring of ellipticinium with the 4'-hydroxyphenyl moiety of genistein, the other envisages the same moiety of ellipticine superimposed to the hydroxyl-benzopyrone portion of genistein. The structural similarities of the test drugs might account for the common preference for stimulation of DNA cleavage at position +1, whereas the different possible arrangements of genistein in the cleavable complex could explain both the additional +1 specificity exhibited by this compound and the differences in cleavage intensity patterns observed in comparison to ellipticinium.
J Mol Recognit 1994 Sep
PMID:Conformational properties of topoisomerase II inhibitors and sequence specificity of DNA cleavage. 788 May 48

African trypanosomiasis continues to pose a challenge for the development of new chemotherapy. Type II topoisomerases, essential enzymes in nucleic acid metabolism, have proven highly suitable as targets for antibacterial and antitumor therapy. Well-characterized topoisomerase II inhibitors affect the cognate nuclear and mitochondrial enzymes in Trypanosoma equiperdum. Inhibition is accompanied by extensive fragmentation and structural alteration in nuclear and mitochondrial DNA. Some clinically important antitrypanosomal drugs bind to DNA (i.e., pentamidine, isometamidium, diminazene). These agents inhibit the mitochondrial, but not nuclear, topoisomerase II of trypanosomes. These studies suggest that type II topoisomerase inhibitors may prove to be effective and safe new antitrypanosomal drugs.
Acta Trop 1993 Sep
PMID:Inhibition of topoisomerases in African trypanosomes. 790 62

Two Chinese hamster ovary cell clones resistant to okadaic acid (OA) were isolated. The OA-resistance was associated with resistance to colchicine, Vinca alkaloids and inhibitors of DNA topoisomerase (topo) II. Drug accumulation assays showed that the intracellular levels of OA, vinblastine and vincristine, but not the topo II inhibitor etoposide, were significantly lowered in the OA-resistant mutants than in the parental cells. These results, together with the finding of an increased level of P-glycoprotein (P-gp) in the mutant cells, indicate that the resistances to OA, Vinca alkaloids and colchicine are due to a P-gp-mediated mechanism. Resistance to topo II inhibitors, however, was associated with reduced activity of topo II. Thus, at least two events, overexpression of P-gp and reduction of topo II activity, occurred in a single OA-resistant cell line, contributing to expression of the MDR phenotype.
Biochem Biophys Res Commun 1994 Sep 15
PMID:Chinese hamster ovary cells resistant to okadaic acid express a multidrug resistant phenotype. 791 70


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