Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Streptonigrin (SN, CAS no. 3930-19-6) is an aminoquinone antitumor antibiotic isolated from cultures of Streptomyces flocculus. This compound is a member of a group of antitumor agents which possess the aminoquinone moiety and that includes also mitomycin C, porfiromycin, actinomycin, rifamycin and geldanamycin. Because of the potential use of SN in clinical chemotherapy, the study of its genotoxicity has considerable practical significance.SN inhibits the synthesis of DNA and RNA, causes DNA strand breaks after reduction with NADH, induces unscheduled DNA synthesis and DNA adducts and inhibits topoisomerase II. At the chromosome level, this antibiotic causes chromosome damage and increases the frequency of sister-chromatid exchanges.SN cleaves DNA in cell-free systems by a mechanism that involves complexing with metal ions and autoxidation of the quinone moiety to semiquinone in the presence of NADH with production of oxygen-derived reactive species. Recent evidence strongly suggests that the clastogenic action of this compound is partially mediated by free radicals. The present review aims at summarizing past and current knowledge concerning the genotoxic effects of SN.
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PMID:Genotoxicity of streptonigrin: a review. 1122 3

The aporphine alkaloids (+)-dicentrine and (+)-bulbocapnine are non-planar molecules lacking features normally associated with DNA binding by intercalation or minor groove binding. Surprisingly, dicentrine showed significant activity as a topoisomerase II (EC 5.99.1.3) inhibitor and also was active in a DNA unwinding assay. The DNA unwinding suggests DNA intercalation, which could explain the inhibition of topoisomerase II. Bulbocapnine, which differs from dicentrine only by the presence of a hydroxyl group at position 11 and the absence of a methoxyl group at position 9, was inactive in all assays. Molecular modeling showed that dicentrine can attain a relatively planar conformation, whereas bulbocapnine cannot, due to steric interaction between the 11-hydroxyl group and an oxygen of the methylenedioxy ring. These observations suggest that dicentrine is an "adaptive" DNA intercalator, which can bind DNA only by adopting a somewhat strained planar conformation. The requirement of a suboptimal conformation to achieve DNA binding appears to make dicentrine a weaker topoisomerase II inhibitor than the very planar oxoaporphine alkaloid liriodenine. These results suggest that it may be possible to modulate DNA binding and biologic activity of drugs by modifications affecting their ability to adopt planar conformations.
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PMID:Topoisomerase II inhibition by aporphine alkaloids. 1123 Aug 1

The structure of the complex formed between d(CGTACG)2 and 9-amino-N-[2-(4-morpholinyl)ethyl]-4-acridinecarboxamide, an inactive derivative of the antitumour agents N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) and 9-amino-DACA, has been solved to a resolution of 1.8 A using X-ray crystallography. The complex crystallises in the space group P6(4 )and the final structure has an overall R factor of 21.9%. A drug molecule intercalates between each of the CpG dinucleotide steps with its side chain lying in the major groove, and its protonated morpholino nitrogen partially occupying positions close to the N7 and O6 atoms of guanine G2. The morpholino group is disordered, the major conformer adopting a twisted boat conformation that makes van der Waals contact with the O4 oxygen of thymine T3. A water molecule forms bridging hydrogen bonds between the 4-carboxamide NH and the phosphate group of guanine G2. Sugar rings are found in alternating C3'-exo/C2'-endo conformations except for cytosine C1 which is C3'-endo. Intercalation perturbs helix winding throughout the hexanucleotide compared with B-DNA, steps 1 and 2 being unwound by 10 and 8 degrees, respectively, while the central TpA step is overwound by 11 degrees. An additional drug molecule lies at the end of each DNA helix linking it to the next duplex to form a continuously stacked structure. The protonated morpholino nitrogen of this 'end-stacked' drug hydrogen bonds to the N7 atom of guanine G6, and its conformationally disordered morpholino ring forms a C-H...O hydrogen bond with the guanine O6 oxygen. In both drug molecules the 4-carboxamide group is internally hydrogen bonded to the protonated N10 atom of the acridine ring. We discuss our findings with respect to the potential role played by the interaction of the drug side chain and the topoisomerase II protein in the poisoning of topoisomerase activity by the acridinecarboxamides.
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PMID:Crystal structure of 9-amino-N-[2-(4-morpholinyl)ethyl]-4-acridinecarboxamide bound to d(CGTACG)2: implications for structure-activity relationships of acridinecarboxamide topoisomerase poisons. 1180 84

We have used stopped-flow spectrophotometry and the sodium dodecyl sulfate sequestration technique to study the kinetics of dissociation of DNA complexes of the mixed topoisomerase I/II poison N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (termed DACA) and a range of related linear tricyclic carboxamides with neutral chromophores. Complexes of DACA and related acridine and phenazinecarboxamides bearing an N,N-dimethylaminoethyl side chain dissociate from calf thymus DNA by a kinetic pathway involving four discernible steps in a manner similar to complexes of N-[(2-dimethylamino)ethyl]-9-aminoacridine-4-carboxamide (termed 9-amino-DACA). We infer from these findings that the side chains of DACA, its phenazine homologue, and 9-amino-DACA make comparable interactions with the DNA base pairs. In the case of 9-amino-DACA, a selective topoisomerase II poison, these are known, by crystallographic analysis, to involve hydrogen-bonding interactions between the protonated dimethylammonium group of the side chain and the O6/N7 atoms of guanine and to include a bridging water molecule hydrogen bonded to the carboxamide group and a phosphate oxygen. By contrast, we find that other linear tricyclic carboxamides with neutral chromophores which lack a peri nitrogen atom and are biologically inactive dissociate from DNA by a different mechanism in which it appears their side chains fail to interact with guanine. We conclude that the ability of the carboxamide group to lie preferentially in the plane of the chromophore, so facilitating the dimethylammonium-guanine hydrogen bond and ensuring maintenance of the water-bridged carboxamide-phosphate interaction, is a critical requirement for antitumor activity among ligands of the linear tricyclic carboxamide class. However, unlike the situation for 9-amino-DACA, for ligands with uncharged chromophores containing peri nitrogen atoms such as DACA, this outcome is possible with the 4-carboxamide group rotated cis or trans with respect to the ring nitrogen. This difference may have relevance to the ability of DACA to be a dual poison of both topoisomerases I and II.
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PMID:Kinetic studies of the binding of acridinecarboxamide topoisomerase poisons to DNA: implications for mode of binding of ligands with uncharged chromophores. 1183 1

Polychlorinated biphenyls (PCBs) are highly persistent contaminants in our environment. Their persistence is due to a general resistance to metabolic attack. Lower halogenated PCBs, however, are metabolized to mono- and dihydroxy compounds, and the latter may be further oxidized to quinones with the formation of reactive oxygen species (ROS). We have shown that PCB metabolism generates ROS in vitro and in cells in culture and this leads to oxidative DNA damage, like DNA strand breaks and 8-oxo-dG formation. In the present study, we have evaluated the reactivity of PCB metabolites with other nucleophiles, like glutathione (GSH), by assessing (1) quantitative GSH binding in vitro, (2) GSH and thiol (sulfhydryl) depletion in HL-60 cells, (3) the associated cytotoxicity, and (4) the inhibition of topoisomerase II activity in vitro. PCB quinones were found to bind GSH in vitro at a ratio of 1:1.5 and to deplete GSH in HL-60 cells as measured by both spectrophotometric and spectrofluorometric methods. By flow cytometry analysis, we confirmed that there was intracellular GSH depletion in HL-60 cells by PCB quinones and this is associated with cytotoxicity. On the other hand, the PCB hydroquinone metabolites did not bind GSH or other thiols within 1 h of exposure. However, by spectral analyses we found that the PCB hydroquinones could be oxidized enzymatically to the quinones, which could then bind GSH. The resulting hydroquinone-glutathione addition product(s) could undergo a second and third cycle of oxidation and GSH addition with the formation of di- and tri-GSH-PCB adducts. The effect of the PCB metabolites was also tested on a sulfhydryl-containing enzyme, topoisomerase II. PCB quinones inhibited topoisomerase II activity while the PCB hydroquinone metabolites did not. Hence, the oxidation of PCB hydroquinone metabolites to quinones in cells followed by the binding of quinones to GSH and to protein sulfhydryl groups and the resulting oxidative stress may be important aspects of the toxicity of these compounds.
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PMID:Sulfhydryl binding and topoisomerase inhibition by PCB metabolites. 1195 35

Traditional semen analysis is essential for the diagnosis of male infertility. A number of studies over the past decade have reported that a significant contributing factor to male fertility that is not revealed as part of semen analysis is sperm DNA, specifically its composition and organization. Exogenous and endogenous factors can cause damage to sperm DNA. For example, topoisomerase II activity, which is necessary for sperm DNA packaging, can adversely influence the competence of sperm DNA if the activity of the enzyme is abnormal. Germ cell apoptosis can be induced by oxygen radicals produced from environmental (for example cigarette smoke) or testicular (for example localized ischaemia) sources. Several assays have been developed that are useful for assessing sperm DNA composition and organization. To date, each of these assays has revealed that when sperm DNA has been damaged or packaged improperly there is a concomitant and often significant decline in male fertility.
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PMID:The clinical value of sperm nuclear DNA assessment. 1208 7

Hypoxia-inducible factor 1 (HIF-1) is a master regulator of the transcriptional response to oxygen deprivation. HIF-1 has been implicated in the regulation of genes involved in angiogenesis [e.g., vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase] and anaerobic metabolism (e.g., glycolytic enzymes). HIF-1 is essential for angiogenesis and is associated with tumor progression. In addition, overexpression of HIF-1 alpha has been demonstrated in many common human cancers. Therefore, HIF-1 is an attractive molecular target for development of novel cancer therapeutics. We have developed a cell-based high-throughput screen for the identification of small molecule inhibitors of the HIF-1 pathway. We have genetically engineered U251 human glioma cells to stably express a recombinant vector in which the luciferase reporter gene is under control of three copies of a canonical hypoxia-responsive element (U251-HRE). U251-HRE cells consistently expressed luciferase in a hypoxia- and HIF-1-dependent fashion. We now report the results of a pilot screen of the National Cancer Institute "Diversity Set," a collection of approximately 2000 compounds selected to represent the greater chemical diversity of the National Cancer Institute chemical repository. We found four compounds that specifically inhibited HIF-1-dependent induction of luciferase but not luciferase expression driven by a constitutive promoter. In addition, these compounds inhibited hypoxic induction of VEGF mRNA and protein expression in U251 cells. Interestingly, three compounds are closely related camptothecin analogues and topoisomerase (Topo)-I inhibitors. We show that concomitant with HIF-1 and VEGF inhibition, the activity of the Topo-I inhibitors tested is associated with induction of cyclooxygenase 2 mRNA expression. The luciferase-based high-throughput screen is a feasible tool for the identification of small molecule inhibitors of HIF-1 transcriptional activation. In addition, our results suggest that altered Topo-I function may be associated with repression of HIF-1-dependent induction of gene expression.
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PMID:Identification of small molecule inhibitors of hypoxia-inducible factor 1 transcriptional activation pathway. 1215 35

Aliphatic amine N-oxides have long been identified as non-toxic metabolites of a large number of tertiary amines drugs. Bioreduction of such N-oxides will generate the active parent amine. This principle has been adopted to develop AQ4N, a di-N-oxide anticancer prodrug with little intrinsic cytotoxicity. However, AQ4N is bioreduced in hypoxic regions of solid tumors and micrometastatic deposits to generate a cytotoxic alkylaminoanthraquinone metabolite. The 4-electron reduction metabolite of AQ4N has high affinity for DNA and is a potent inhibitor of topoisomerase II, a DNA processing enzyme crucial to cell division. The development of AQ4N has proceeded on many fronts in order to establish this unique anticancer prodrug opportunity. Preclinical studies in vivo have demonstrated that although AQ4N has little or no intrinsic cytotoxic activity per se it (i) enhances the antitumor effects of radiation and conventional chemotherapeutic agents, (ii) is pharmacokinetically stable, and (iii) is a substrate for cytochrome P450 (CYP). A study of AQ4N metabolism in vitro and ex vivo using purified CYP enzymes, phenotyped human livers and CYP transfected cell lines shows that CYP3A, 1A and 1B1 family members contribute to AQ4N bioreduction in the absence of oxygen. Importantly AQ4N is shown to be metabolized by tumors known to express CYP isoforms. AQ4N is currently in Phase I clinical trials.
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PMID:Bioreductively activated antitumor N-oxides: the case of AQ4N, a unique approach to hypoxia-activated cancer chemotherapy. 1221 68

Some fluoroquinolone antibiotics (FQs) become toxic and mutagenic upon exposure to ultraviolet radiation (UV). Topoisomerase inhibition has been proposed as one possible mechanism involved in this photochemical genotoxicity. To study this reaction, inhibition of the human topoisomerase IIalpha enzyme by four FQs varying in photochemical genotoxic potency (Bay y3118 [y3118] > Lomefloxacin [Lmx] > Ciprofloxacin [Cpx] > Moxifloxacin [Mox]) was measured in vitro in the presence of UVA irradiation. None of the FQs inhibited topoisomerase IIalpha in the absence of irradiation. In contrast, with irradiation at 365 nm, the potent photochemically genotoxic y3118 produced strong inhibition of the enzyme by 15% and Cpx caused a weak 5% inhibition, but the more photochemically genotoxic Lmx only showed a transient inhibitory effect at one concentration and one irradiation dose. The photostable Mox had no effect with irradiation. Topoisomerase IIalpha inhibition by y3118 only occurred when the FQ, DNA, and enzyme were simultaneously present in the UVA-irradiated reaction mixture and was abolished in the absence of ATP, indicating the possible formation of a ternary structure. The y3118 photochemical topoisomerase inhibition correlated with the increased irradiation-mediated binding of radiolabeled FQ to DNA:topoisomerase complexes and was irreversible, like that of the topoisomerase poison, etoposide, without irradiation. The inhibitory effect of photoactivated y3118 on topoisomerase IIalpha was also observed in the presence of the antioxidant TEMPO, indicating that reactive oxygen species were not involved in the inhibition. These observations demonstrate that some but not all photochemically genotoxic FQs inhibit human topoisomerase IIalpha, possibly by UV-induced affinity of FQs to DNA:topoisomerase complexes.
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PMID:Inhibition of human topoisomerase IIalpha by fluoroquinolones and ultraviolet A irradiation. 1221 56

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.
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PMID:Evaluation of the clastogenic, DNA intercalative, and topoisomerase II-interactive properties of bioflavonoids in Chinese hamster V79 cells. 1248 17


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