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)

Although it has been shown previously that the depletion of cellular thiols increases doxorubicin cytotoxicity, the mechanism of sensitization is not clear. To study this question, the effect of D,L-buthionine-S,R-sulfoximine (BSO) on doxorubicin cytotoxicity and the stabilization of DNA-topoisomerase II complexes (cleavable complexes) was investigated in V79 cells. Incubations with BSO (10 mM) were for 5 hr beginning 4 hr prior to doxorubicin exposure since a 4 hr incubation with 10 mM BSO is known to decrease glutathione levels below 5% of control V79 cells. These BSO pre-treatment increased doxorubicin cytotoxicity. At doxorubicin concentrations of 5 micrograms/ml, BSO resulted in an 8-10 fold decrease in surviving cells, compared to cells exposed to doxorubicin alone. It was determined that BSO pre-treatments did not affect the accumulation of doxorubicin into the cell, the rate of cleavable complex stabilization by doxorubicin, or the rate of dissociation of stabilized cleavable complexes. These data suggest that BSO-induced doxorubicin sensitization occurs at a step following the stabilization of cleavable complexes or by an independent mechanism.
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PMID:Interaction of buthionine sulfoximine and the stabilization of DNA-topoisomerase II complexes by doxorubicin. 131 Apr 96

We demonstrated previously that human cytomegalovirus (CMV) infections could enhance the expression of cellular topoisomerase II and this enzyme activity is essential for CMV to replicate in vitro (Benson and Huang, 1988; Benson and Huang, 1990). In this study, we further show that in addition to m-AMSA and VM26 which we had previously reported, a widely used and clinically available drug, etoposide (VP-16 or VePesid) can irreversibly inhibit CMV replication at the drug concentration (2.5 micrograms/ml) greatly below toxic levels to stationary phase cells. Growing cells were more sensitive to etoposide than stationary phase cells and slight growth inhibition occurred at 2.5 micrograms/ml level. This inhibitor does not prevent the expression of CMV immediate-early and early genes, but can inhibit viral DNA and late viral-proteins synthesis. Because of their irreversible inhibitory effects and approval usage in clinical oncology, it is suggested that this group of compounds, particularly etoposide (VP-16), can be used to control life-threatening CMV infections, such as CMV pneumonitis and CMV retinitis, in cancer and immunocompromised patients or patients with AIDS.
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PMID:Irreversible inhibition of human cytomegalovirus replication by topoisomerase II inhibitor, etoposide: a new strategy for the treatment of human cytomegalovirus infection. 131 May 81

A carcinogen-transformed rat hepatoma cell line (Reuber H-35) was utilized as a model system for investigation of the biochemical factors which may limit the effectiveness of chemotherapy in intrinsically resistant tumors such as hepatocellular carcinoma. Northern blotting demonstrated expression of mRNA coding for the P-170 membrane-glycoprotein associated with the multi-drug resistance phenotype, while Western blotting identified the P-170 glycoprotein in the hepatoma cell membrane. Consistent with these observations, tumor cell sensitivity to the vinca alkaloids, vincristine and vinblastine, to the anthracycline antibiotics, Adriamycin and daunorubicin, and to the demethylepipodophyllotoxin derivative, VM-26, was enhanced by continuous incubation in the presence of the calcium channel antagonist, verapamil. Verapamil produced a minimal change in cell sensitivity to the demethylepipodophyllotoxin derivative, VP-16, and to the aminoacridine, m-AMSA. Relatively high detoxification potential via the glutathione metabolic pathway was also observed in the hepatoma cell. The capacity of topoisomerase II in nuclear extracts from the hepatoma cell to mediate cleavable complex formation stimulated by VM-26, VP-16 and m-AMSA appeared to be at least comparable to, if not greater than that from drug-sensitive HL-60 cells, suggesting that drug resistance may not occur at the level of this enzyme. Consistent with findings in a number of tumor cell lines resistant to antineoplastic drugs, the antiproliferative activity of the topoisomerase II inhibitors VM-26, VP-16 and m-AMSA appeared to be dissociable from the induction of DNA strand breaks, suggesting that such lesions in DNA may fail to fully account for the antiproliferative activity of these agents in the hepatoma cell.
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PMID:Components of intrinsic drug resistance in the rat hepatoma. 131 Aug 53

The cutting sites specificity of topoisomerase II from porcine spleen were determined by a modified Sanger's DNA sequencing method. The topoisomerase II prefers to cut DNA at the 3' side of A and leave 5' protruding end with two staggering bases. Through the free energy analysis for DNA duplex, we also found that the topoisomerase II seemed cut DNA preferably at energetically unstable regions. So it is concluded that the specific DNA cutting by porcine spleen topoisomerase II has two structural recognition factors: one is to localize around the energetically unstable region and another is to act at the 3' side of A base.
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PMID:The recognition of DNA cleavage sites by porcine spleen topoisomerase II. 131 Oct 75

During purification of the type I DNA topoisomerase from calf thymus mitochondria, two polypeptides, p78 and p63, cofractionate with the enzymatic activity (Lazarus et al., (1987) Biochemistry 26, 6195-6203). The two polypeptides are released from a mitochondrial inner membrane preparation by nonionic detergent lysis and both adsorb strongly to a single-stranded DNA agarose column. We have attempted to characterize the relationship between these two polypeptides and have found the following: (i) the mitochondrial topoisomerase is active in free (monomer) and associated (heterodimer) form; (ii) the catalytic activity resides solely in p78, as adjudged by both the covalent linkage of the enzyme to substrate DNA and the ability of the enzyme to relax supercoils; (iii) at low ionic strength the enzyme is active in monomer form with p78 alone being sufficient for activity; (iv) in high salt, the high molecular weight species is a 140-kDa heterodimer composed of one p78 and one p63; and (v) the two polypeptides are not structurally related as digestion with V8 protease results in distinct proteolytic fragment patterns. These results suggest that p63 may have an important role in the metabolism of the mitochondrial topoisomerase.
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PMID:DNA topoisomerase I from calf thymus mitochondria is associated with a DNA binding, inner membrane protein. 131 Nov 59

We have identified two classes of in vivo topoisomerase II cleavage sites in the Drosophila histone gene repeat. One class co-localizes with DNase I-hypersensitive regions and another novel class maps to a subset of consecutive nucleosome linker sites in the scaffold-associated region (SAR) of the histone gene loop. Prominent topoisomerase II cleavage is also observed in one of the linker regions of the two nucleosomes spanning satellite III, a centromeric SAR-like DNA sequence with a repeat length of 359 bp. At the sequence level, in vivo topoisomerase II cleavage is highly site specific. Comparison of 10 nucleosome linker sites defines an in vivo cleavage sequence whose major characteristic is a prominent GC-rich core. These GC-rich cleavage sites are flanked by extensive arrays of oligo(dA).oligo(dT) tracts characteristic of SAR sequences. Treatment of cells with distamycin selectively enhances cleavage at nucleosome linker sites of the SAR and satellite regions, suggesting that AT-rich sequences flanking cleavage sites may be involved in determining topoisomerase II activity in the cell. These observations provide evidence for the association of topoisomerase II with SARS in vivo.
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PMID:In vivo topoisomerase II cleavage of the Drosophila histone and satellite III repeats: DNA sequence and structural characteristics. 131 Dec 55

A group of chrysophanol and emodin derivatives with DNA-intercalating capability and with or without alkylating potential have been synthesized and shown to have antitumor activity in vitro. The topoisomerase II (Topo II)-mediated DNA cleavage activities induced by representative compounds 3-(2-chloroethylamino) methyl-1,8-dihydroxy-9,10-anthraquinone (SK-31690), 3-bis [(2-chloroethyl)amino]methyl-1,8-dihydroxy-9,10-anthraquinone (SK-31662), and 3-(2-hydroxyethylamino)methy-1,8-dihydroxy-9,10-anthraquinon e (SK-31694), and their cytotoxicities, have been investigated. All three compounds inhibited the kinetoplast DNA decatenation catalyzed by DNA Topo II. These compounds inhibited leukemia cell growth and stimulated, in a dose-dependent manner from 0.5 to 60 microM, the formation of Topo II-DNA cleavable complexes, when 3'-32P-labeled DNA was used. The mapping of Topo II-mediated DNA cleavage sites using HindIII-digested 3'-32P-labeled DNA showed that, at 10 microM, these compounds induced protein-linked DNA breaks that correlated with cytotoxicity, with respect to their maximal efficacy or the reciprocal concentration for the half-maximal effect. The reversibility study showed that the amounts of protein-linked DNA cleavage induced by 4'-(9-acridinylamino)methanesulfon-m-anisidide and VP-16 as well as SK-31694, which lacks alkylating potential, were markedly decreased during 30-sec exposure to 65 degrees or 0.5 M NaCl. In contrast, protein-linked DNA cleavages induced by SK-31662, which has two alkylating functionalities, and by SK-31690, which has one alkylating functionality in its structure, cannot be reversed during the 15-min exposure to 65 degrees or 0.5 M NaCl. These data suggest that Topo II is a major cellular target for cytotoxicity of these compounds. Furthermore, DNA intercalators with alkylating potential interact with Topo II-DNA cleavable complexes in an irreversible manner, with enhanced toxicity.
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PMID:Topoisomerase II-mediated DNA cleavage activity and irreversibility of cleavable complex formation induced by DNA intercalator with alkylating capability. 131 6

The ATP-independent type I topoisomerase from the crustacean Artemia franciscana was purified to near-homogeneity. Its activity was measured by an assay that uses the formation of an enzyme-cleaved DNA complex in the presence of the specific inhibitor camptothecin. The purification procedure is reported. Purified topoisomerase is a single-subunit enzyme with a molecular mass of 63 kDa. Immunoblot performed on the different steps of purification shows that the purified 63 kDa peptide is a proteolytic fragment of a protein with a molecular mass of 110 kDa. Similarly to the other purified eukaryotic topoisomerases, the crustacean enzyme does not require a bivalent cation for activity, but is stimulated in the presence of 10 mM-MgCl2; moreover, it can relax both negative and positive superhelical turns. The enzyme activity is strongly inhibited by the antitumour drug camptothecin. The enzyme inhibition is related to the stabilization of the cleavable complex between topoisomerase I and DNA.
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PMID:Purification and characterization of a proteolytic active fragment of DNA topoisomerase I from the brine shrimp Artemia franciscana (Crustacea Anostraca). 131 54

A hybrid molecule, which combines an anilinoacridine chromophore related to the antitumour drug amsacrine (m-AMSA) and a bispyrrole moiety analogous to the antiviral agent netropsin, has been examined for its ability to bind chromatin and to modulate the activity of topoisomerase II. The results show that the presence of histones does not alter the bimodal DNA binding process. Intercalation of the acridine and groove binding of the netropsin part of the drug are both observed with chromatin preparations. Moreover, the hybrid has a clear topoisomerase II-DNA cleavable complex-inducing activity close to that of m-AMSA. The role of the two parts of the hybrid ligand is discussed in relation to ternary complex formation. Two cell lines (L1210 leukemia and MCF7 mammary carcinoma) were compared in their sensitivity to the tested ligand. The drug, which appears to be an efficient growth inhibitor of leukemic cells in vitro, reveals moderate activity against P388 leukemia in vivo. The biological activity of the hybrid may derive from a mechanism that involves DNA binding and topoisomerase II inhibition. This study demonstrates that agents which intercalate and bind to the minor groove of DNA simultaneously represent a new class of drugs interfering with topoisomerase II and provide opportunities for the development of new antitumour agents.
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PMID:Biological activity and molecular interaction of a netropsin-acridine hybrid ligand with chromatin and topoisomerase II. 131 80

We have isolated a multidrug-resistant derivative of Chinese hamster ovary CHO-K1 cells by exposure to progressively increasing concentrations of Adriamycin. This cell line, designated CHO-Adrr, was 27-fold more resistant than the parental line to Adriamycin and showed similar degrees of cross-resistance to several other topoisomerase II (topo II) inhibitors, including mitoxantrone, daunomycin and etoposide. CHO-Adrr cells showed a lower (4-fold) level of cross-resistance to vincristine and colchicine, drugs associated with the multidrug-resistant phenotype. While CHO-Adrr cells showed no enhanced resistance to several mono- and bi-functional alkylating agents or to UV and ionizing radiation, they were greater than 80-fold resistant to mitomycin C (MMC). There was a 5-fold decreased level of daunomycin accumulation in CHO-Adrr cells compared to CHO-K1 cells and this was associated with increased drug efflux. The resistant cells had amplified multidrug resistance gene (mdr) sequences and overexpressed (mdr) mRNA. Verapamil was able to completely reverse Adriamycin resistance but reversal of MMC resistance was only partial, with residual 23-fold resistance. CHO-Adrr cells expressed a 4-fold reduced level of topo II protein but overexpressed an alpha class (basic) glutathione S-transferase (GST). Analysis of cell hybrids showed that while the level of resistance to Adriamycin dropped by a factor of 3 in CHO-K1/CHO-Adrr hybrids compared to CHO-Adrr/CHO-Adrr hybrids, resistance to MMC dropped 10-fold. Thus, CHO-Adrr cells appear to exhibit simultaneously several different drug resistance mechanisms including MDR and GST overexpression, and topo II reduction.
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PMID:Reduced topoisomerase II and elevated alpha class glutathione S-transferase expression in a multidrug resistant CHO cell line highly cross-resistant to mitomycin C. 131 88


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