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)

To study the involvement of DNA topoisomerases in recombination in mammalian cells, we used gene transfer assays to examine the effects of DNA topoisomerase inhibitors on nonhomologous (illegitimate) and homologous recombination. The assays were performed by transfecting adenine phosphoribosyltransferase-deficient (APRT-) CHO cells with plasmids carrying the wild-type or mutant aprt genes and by treating the cells with the inhibitors, followed by subsequent cultivation to select for APRT-positive (APRT+) colonies. Treatments with DNA topoisomerase II inhibitors such as VP-16, VM-26, ICRF-193 resulted in a 3- to 5-fold stimulation of integration of both closed-circular and linearized plasmids carrying the wild-type aprt gene into the recipient genome through nonhomologous recombination. The same treatments also increased 6- to 9-fold and 3-fold the number of APRT+ recombinant colonies that were generated by cotransfecting two closed-circular plasmids with nonoverlapping defective aprt genes and their linearized equivalents, respectively. However, this cotransfection assay involved intrinsically nonhomologous recombination processes; normalization of the frequencies by dividing them with those of the above nonhomologous recombination revealed 2-fold enhancement of homologous recombination events between the circular mutant genes but not between the linear ones. In contrast, DNA topoisomerase I inhibitor, camptothecin, showed no such effect on either recombination. From these results, we discuss the function of DNA topoisomerases on recombination in mammalian cells.
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PMID:Effects of DNA topoisomerase inhibitors on nonhomologous and homologous recombination in mammalian cells. 859 37

Specific inhibitors of topoisomerase II (e.g., ICRF-193, an inhibitor of the catalytic activity of topoisomerase II and etoposide that stabilizes enzyme/DNA cleavable complexes) have been used to probe the role of topoisomerase II in the fragmentation of DNA during drug-induced apoptosis of human HL-60 leukemia cells. Topoisomerase II plays a role in the attachment of 50-kilobase domains of DNA to the nuclear matrix; fragments of this size are cleaved during apoptosis. Apoptosis was induced by 50 microM etoposide or 300 mM N-methylformamide (NMF), a nongenotoxic agent. Treatment with etoposide or NMF induced the morphology of apoptosis within 4 hr. Analysis of DNA integrity by electrophoresis showed coincident fragmentation from 50 kb and to integers of 200 bp. Transient protein-associated DNA strand breaks, characteristic of etoposide-induced damage, were visualized as DNA fragments of > 600 kb. Preincubation with ICRF-193 (100 microM) reduced the number of etoposide-induced DNA strand breaks by 50% and delayed the appearance of DNA fragmentation by approximately 18 hr. However, ICRF-193 had no effect on either NMF- or camptothecin-induced DNA fragmentation. The induction of apoptosis by both etoposide and NMF was associated with a reduction in the cellular levels of topoisomerases II alpha and II beta. ICRF-193 inhibited proteolytic cleavage of topoisomerase II induced by etoposide but not by NMF. The data suggest that the activity of topoisomerase II is not required for the cleavage of DNA to 50-kb fragments but that proteolysis of topoisomerase II represents a conserved event of apoptosis.
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PMID:Selective inhibition of topoisomerase II by ICRF-193 does not support a role for topoisomerase II activity in the fragmentation of chromatin during apoptosis of human leukemia cells. 862 34

Cellular topoisomerase II is specifically inactivated by the drug ICRF-193. This compound turns topoisomerase II into a closed clamp that is unable to cleave DNA. We have investigated the effects of this inhibitor on the replication of herpes simplex virus type 1. We show that ICRF-193 at low multiplicities of infection dramatically inhibits viral DNA synthesis and the production of infectious virus. The inhibition is less efficient at high multiplicities of infection. In addition, inhibition of viral DNA synthesis was observed only when ICRF-193 was present during the first 4 h of the infectious cycle. The transient replication of plasmids containing a herpes simplex virus type 1 origin of DNA replication, oriS, was affected by ICRF-193 in the same way. In contrast, neither cellular DNA synthesis nor replication of plasmids containing a simian virus 40 origin of DNA replication was inhibited. The observed effect on herpes simplex virus DNA replication was not caused by a decreased transcription of replication genes inasmuch as the levels of UL8, UL9, UL29, and UL30 rmRNAs were unaffected by the drug. These results suggest that topoisomerase II plays a vital role during the replication of herpes simplex virus type 1 DNA. We speculate that topoisomerase II is involved in the decatenation of newly synthesized daughter molecules.
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PMID:Inhibition of topoisomerase II by ICRF-193 prevents efficient replication of herpes simplex virus type 1. 867 78

Anthracenyl-amino acid conjugates represent a novel chemical class of topoisomerase (topo) inhibitor. NU/ICRF 505 is a lead compound that stabilises topo I cleavable complexes and is actively cytotoxic at low microM concentrations. In this study, endonucleolytic DNA cleavage was used as a marker of apoptosis to investigate mechanisms of cell death produced by this compound. NU/ICRF 505 (5 microM) induced a substantial increase in the level of DNA fragmentation in HL60 cells (up to 30% of total extracted DNA) but only after a 48 and 72 h drug exposure (compared with 6 h after treatment with camptothecin), as determined qualitatively by conventional gel electrophoresis and quantitatively by spectrofluorimetry. This effect was substantially reversed by co-treatment with zinc (1 mM). Subsequent studies with the human lung (NX002), ovarian (A2780) and colon (HT29) cancer cell lines yielded evidence of formation of higher molecular weight DNA fragments in NX002 and A2780 cells in response to NU/ICRF 505 (5 microM). Co-treatment with zinc (1 mM) caused a small decrease in DNA fragmentation. These data suggest that the induction of apoptosis may play an important role in the mechanism of cytotoxicity of NU/ICRF 505 in HL60 cells and that other pathways of cell death may also be operative in NX002 and A2780 in conjunction with apoptosis.
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PMID:Induction of apoptosis in human cancer cell lines by the novel anthracenyl-amino acid topoisomerase I inhibitor NU/ICRF 505. 869 51

The bis(2,6-dioxopiperazine)s are a structurally and mechanistically unique class of topoisomerase II inhibitors that do not bind DNA and that do not stabilize topoisomerase II-DNA strand passing intermediates ("cleavable complexes"). The most effective topoisomerase II inhibitor in the bis(2,6-dioxopiperazine) series is ICRF-193 (meso or S*, R* isomer), with a meso 2,3-butanediyl linker connecting the dioxopiperazine rings. The two enantiomeric diastereomers, (R,R) and (S,S), of ICRF-193 possessing the two optically active 2,3-butanediyl linkers have been prepared from their respective optically pure 2,4-diaminobutanes via 2,3-diaminobutane-N,N,N',N'-tetraacetic acid, esterification, and imide formation. Both in vivo and in vitro assays for catalytic inhibition of topoisomerase II were employed to show that the (S,S)- and (R,R)-isomers are almost inactive as topoisomerase II inhibitors. The data indicate that the meso stereochemistry of the alkanediyl linker is crucial for activity and provides additional evidence that the cytotoxicity of the bis(2,6-dioxopiperazine)s is due to their ability to inhibit topoisomerase II.
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PMID:Inhibition of topoisomerase II by ICRF-193, the meso isomer of 2,3-bis(2,6-dioxopiperazin-4-yl)butane. Critical dependence on 2,3-butanediyl linker absolute configuration. 875 26

Etoposide (VP-16), one of the topoisomerase II (TopoII) inhibitors, interferes with TopoII by inducing the formation of and stabilizing a cleavable enzyme-DNA complex. VP-16 has been demonstrated to induce apoptosis in murine thymocytes. To clarify the mechanism of action of VP-16, we examined the in vitro effect of a non-cleavable-complex-forming type TopoII inhibitor, ICRF-193 which inhibits the DNA strand breakage induced by VP-16, on murine thymocytes in which apoptosis had been induced with VP-16. DNA fragmentation is characteristic of apoptosis. In the early stages, ICRF-193 decreased DNA fragmentation induced by VP-16, although this inhibitory effect decreased in the later. These data suggest that TopoII inhibitors induce apoptosis in murine thymocytes in two ways: with DNA-strand breaks in the early stage or without them. ICRF-193 itself induced apoptosis in murine thymocytes. The time course of DNA fragmentation caused by ICRF-193 was different from that of VP-16.
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PMID:ICRF-193 modifies etoposide-induced apoptosis in thymocytes. 877 Feb 36

Anthracenyl-amino acid conjugates (AAC) represent a novel class of topoisomerase (topo) inhibitor. The relationship between mechanism of enzyme inhibition and in vitro cytotoxicity has been investigated in a panel of 5 Chinese hamster ovary (CHO) and 2 human ovarian cancer cell lines (A2780) shown to possess different drug resistance phenotypes associated with altered expression of topo I and topo II. From a total of 13 compounds, 4 displayed broad-spectrum activity (IC50 ranging from 3.5-29.7 microM). NU/ICRF 500 (topo II catalytic inhibitor) was 1.4-fold more active against CHO ADR-1, which overexpresses topo II and was essentially noncross-resistant in CHO ADR-r (13.9-fold resistant to doxorubicin (DOX)) and 2780AD (1,460-fold resistant to DOX). NU/ICRF 505, which stabilises topo I cleavable complexes, was noncross-resistant in CHO ADR-3 (3,4-fold resistant to camptothecin) and only 1.8-fold cross-resistant in 2780AD. Hypersensitivity was recorded in ADR-r that overexpresses topo I. The most active compound was NU/ICRF 506, a dual catalytic inhibitor of topo I and II. Hypersensitivity was observed in ADR-r (1.4-fold) but not ADR-1, indicating that topo I is the likely nuclear target, and a low level of resistance was seen in the CHO ADR-6 drug transport mutant and 2780AD. The topo II catalytic inhibitor NU/ICRF 513 only produced hypersensitivity in ADR-r. These data suggest that NU/ICRF 500, 505, and 506 induce cell death, at least partly, through topo inhibition. NU/ICRF 513 appears to be cytotoxic via a nontopo mechanism of action. In addition, NU/ICRF 505 significantly inhibited the growth of two human xenografts (HT-29 colon cancer and NX002 nonsmall-cell lung cancer) in nude mice after i.p. administration at a dose of 25 mg/kg. The important properties of noncross-resistance and in vivo antitumour activity merit further development of AAC as potential new anticancer drugs.
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PMID:Development of anthracenyl-amino acid conjugates as topoisomerase I and II inhibitors that circumvent drug resistance. 883 16

Etoposide is a topoisomerase II inhibitor that induces DNA cleavable complex and has been used as an antitumor drug. We isolated two genes that were transcriptionally suppressed at an early stage of incubation in etoposide-treated RVC lymphoma cells, using modified PCR-based subtractive hybridization. Sequencing revealed that one of these genes, which was approximately 1.7 kb and which encoded a protein of 320 amino acids, was identical to hnRNP A1. The other was a novel gene of about 2.2 kb encoding a protein of 469 amino acids. These genes were also down-regulated in the cells incubated with camptothecin, a topoisomerase I inhibitor that induces DNA single strand breaks, but not in those exposed to ICRF-154, a topoisomerase II inhibitor that does not induce DNA cleavable complex formation. These results suggest that the early down-regulation of these genes contributes to the cytotoxicity of the topoisomerase inhibitors that induce DNA cleavage.
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PMID:Molecular cloning of the genes suppressed in RVC lymphoma cells by topoisomerase inhibitors. 891 29

Anthracenyl-amino acid and dipeptide conjugates represent new classes of topoisomerase (topo) inhibitors. To investigate the structural basis for their different selectivity against topo I and II and varying potency, the binding of six compounds to d(CGTACG) was studied by molecular modeling. Modeling data were in good agreement with physical data showing that five compounds intercalated DNA with the anthraquinone chromophore orientated in parallel to the long dimension of the d(CpG) base pairs and the amino acid placed in the minor groove. Differences in binding modes emerged which correlated to different biological properties. The amino acid chain of the topo I inhibitor (NU/ICRF 600, gly-phe) extended significantly out from the helical axis horizontal. The amino acid side chains of two topo II inhibitors (NU/ICRF 510, arginine and NU/ ICRF 512, methionine) were inserted into the minor groove, whereas the C-terminal groups (hydrazide) of two potent topo II inhibitors (NU/ICRF 500 and 506, serine) were placed into the minor groove while the amino acid side chains pointed away from the minor groove. These data provide structural information which may prove valuable in rational design of second generation analogs.
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PMID:Molecular modeling of the interaction of anthracenyl-amino acid topoisomerase inhibitors with the DNA sequence d(CGTACG). 891 31

VP-16 and ICRF-193 are different types of antitumor topoisomerase II inhibitors, being cleavable and non-cleavable complex-stabilizing types, respectively. To examine the possibility of enhancing the efficacy of combination chemotherapy, we carried out simultaneous and sequencial treatment of cells with the two drugs. When KB cells were exposed continually to low concentrations (0.05 - 0.2 microM) of the drugs, the effects were synergistic. In contrast, when the cells were treated with high concentrations of ICRF-193 and VP-16 for 1 hour, the VP-16-induced cytotoxicity was prevented by ICRF-193 and the degree of prevention was increased by the pretreatment of cells with ICRF-193, while post-treatment with ICRF-193 had little effect on the cytotoxicity of VP-16. ICRF-193 at 1 microM was found to interact with about half molecules of topisomerase IIa and II beta in cells, as judged by increased amounts of a salt-stable complex. ICRF-193 inhibited in vitro VP-16-induced cleavable complex formation, but a much higher concentration was needed to reverse the cleavage already generated by VP-16. Thus, the antagonistic or synergistic effects of ICRF-193 and VP-16 depend on the concentration of the drug, as it may be critical as to how many molecules of cellular topoisomerase II interact with the drugs.
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PMID:The combination of different types of antitumor topoisomerase II inhibitors, ICRF-193 and VP-16, has synergistic and antagonistic effects on cell survival, depending on treatment schedule. 891 80


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