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PubMed2003

A role of topoisomerase II in linking DNA replication to chromosome condensation.

The condensin complex and topoisomerase II (topo II) have different biochemical activities in vitro, and both are required for mitotic chromosome condensation. We have used Xenopus egg extracts to investigate the functional interplay between condensin and topo II in chromosome condensation. When unreplicated chromatin is directly converted into chromosomes with single chromatids, the two proteins must function together, although they are independently targeted to chromosomes. In contrast, the requirement for topo II is temporarily separable from that of condensin when chromosome assembly is induced after DNA replication. This experimental setting allows us to find that, in the absence of condensin, topo II becomes enriched in an axial structure within uncondensed chromatin. Subsequent addition of condensin converts this structure into mitotic chromosomes in an ATP hydrolysis-dependent manner. Strikingly, preventing DNA replication by the addition of geminin or aphidicolin disturbs the formation of topo II-containing axes and alters the binding property of topo II with chromatin. Our results suggest that topo II plays an important role in an early stage of chromosome condensation, and that this function of topo II is tightly coupled with prior DNA replication.

Adenosine Triphosphatases↗
PubMed1992

Inhibition of cytotoxic T lymphocyte-induced target cell DNA fragmentation, but not lysis, by inhibitors of DNA topoisomerases I and II.

Cytotoxic T lymphocytes (CTL) kill their target cells via a contact-dependent mechanism that results in the perturbation of the target cell's plasma membrane and the fragmentation of the target cell's DNA into nucleosomal particles. The membrane disruption is presumed to be due to the action of perforin, while the DNA fragmentation is thought to be by the activation of an endogenous nuclease(s). DNA topoisomerases I and II are nuclear enzymes with inherent endonuclease activities. We have investigated their role in the CTL-induced DNA fragmentation process. We report that in CTL killing assays, the treatment of target cells with topoisomerase I and II inhibitors blocks the CTL-induced DNA fragmentation process, but not the lysis of the target cell.

Amsacrine↗
PubMed1994

Cost-benefit of granulocyte colony-stimulating factor administration in older patients with non-Hodgkin's lymphoma treated with combination chemotherapy.

BACKGROUND: Older patients with non-Hodgkin's lymphoma (NHL) display a poorer response to chemotherapy and a significantly higher treatment-associated toxicity than do younger individuals. We investigated the potential clinical benefits and the cost-effectiveness of accelerated granulocyte recovery induced by recombinant granulocyte colony-stimulating factor (G-CSF) in patients with aggressive NHLs, aged 60-70 years, during treatment with a second-generation combination chemotherapy. PATIENTS AND METHODS: 12 consecutive patients (median age 66 years) treated with six to eight courses of CHVmP/VB plus subcutaneous G-CSF (5 micrograms/kg/day) were compared with 11 consecutive subjects (median age 65 years) who received the same chemotherapy regimen without growth factor support. The two groups of patients were fully comparable as to the clinicopathologic features. A comparative analysis of treatment costs (including hospitalization, antimicrobial prophylaxis and therapy, supportive and diagnostic procedures, and G-CSF) was also performed. RESULTS: Both the overall response rate and the percentage of complete remissions were comparable in the two treatment groups. In the control group, 32.5% of chemotherapy courses were delayed, as opposed to 19% in the G-CSF group (p = 0.05). The mean duration of delay for patients receiving or not receiving G-CSF was 10.1 and 25.9 days, respectively (p = 0.02). Grade 3 and 4 granulocytopenia complicated 27.7% of chemotherapy courses in control patients and only 4.8% in subjects receiving G-CSF (p < 0.001). Similarly, severe infections and mucositis were significantly higher in patients receiving chemotherapy alone (15.6% and 3.6%, respectively) compared to the G-CSF group (4.8%, p = 0.01; p = 0.04, respectively). A mean of 1.1 days/course of hospitalization was required in the control group, as opposed to 0.2 days/course in patients receiving G-CSF (p = 0.05). Although overall treatment costs were higher in the control group, single cost of the recombinant growth factor exceeded by far all the other expenses in the G-CSF group, reaching a statistical relevance (p = 0.01). CONCLUSIONS: The inclusion of prophylactic G-CSF in the treatment plan for aggressive NHL in older patients appears safe and cost-effective in view of the peculiar clinical features of aged subjects and the possibility of delivering effective doses of antineoplastic drugs on an outpatient setting.

Age Factors↗
PubMed1994

EORTC study of non-Hodgkin's lymphoma: phase III study comparing CHVmP-VB and ProMACE-MOPP in patients with stage II, III, and IV intermediate- and high-grade lymphoma.

In the EORTC lymphoma cooperative group, a randomized phase III study was done for patients with stage II, III, IV intermediate- and high-grade lymphoma. Eight courses of CHVmP-VB were compared to eight courses of ProMACE-MOPP. Response was evaluated after 8 courses. Of 430 patients entered, 346 were eligible for this first analysis. Additional radiotherapy was given at initial large masses or residual disease after three courses. Response rate was higher in the CHVmP-VB arm in comparison to the ProMACE-MOPP arm, 82% vs. 65% (p < 0.0005). In the ProMACE-MOPP arm, treatment had to be interrupted because of patient refusal in 7% of the patients. So far there has been no significant difference in freedom from progression at 5 years (49% vs. 47%), relapse-free survival (59% vs. 59%), or overall survival (55% vs. 49%). Patients with early response at 4 courses showed no better RFS in comparison with late responders between 4 and 8 courses. The International Index, based on age, stage, SLDH, performance status, and number of extranodal localizations showed a good prognostic significance in this series of patients.

Adult↗
PubMed1992

Effect of topoisomerase poisoning by antitumor drugs VM 26, fostriecin and camptothecin on DNA repair replication by mammalian cell extracts.

A recently developed in vitro excision-repair system was used to investigate the effect of the topoisomerase poisons VM 26, fostriecin and camptothecin on DNA repair replication carried out by Chinese hamster ovary cell extracts. VM 26 and camptothecin partially inhibit topoisomerases II and I respectively, which are present in the repair-competent extracts, but have only slight effects on the repair efficiency. On the contrary, the antitumor drug fostriecin markedly affects repair replication but, in contrast to a previous report, does not seem to have, under the experimental conditions used, any inhibitory effect on topoisomerase II. This lack of correlation between the ability to inhibit DNA topoisomerases and the effect on DNA repair replication suggests that topoisomerases should not play a primary role in mammalian excision repair. The use of cleavable-complex stabilizing poisons to investigate the role of eukaryotic topoisomerases in DNA excision repair is discussed.

Alkenes↗
PubMed1976

The cause of G2-arrest in Chinese hamster ovary cells treated with anticancer drugs.

The nature of G2-arrest was studied in Chinese hamster ovary cells after exposure to 4'-demethyl-epipodophyllotoxin 9-)4,6-0-2-thenylidene-beta-D-glycopyranoside (VM26), 1,3-bis(2-chloroethyl)-1-nitrosourea, 1,3-cis(2-chloroethyl)-1-nitrosourea, cis-4[[[(2-chloroethyl)-nitrosoamino] carbonyl] amino]- cyclohexane carboxylic acid, or neocarzinostatin. To determine whether this G2-arrest was due to a metabolic block or to damage to the genetic material, we employed the phenomenon of premature chromosome condensation to visualize the chromosomes of the G2-blocked cells by fusing them with mitotic cells. The prematurely condensed chromosomes (PCC) of the treated cells were scored for their position in the cell cycle and the extent of chromosomal damage in the G2-PCC. The data revealed a significant enrichment of the G2-fraction in all the treatments. Most of the G2- PCC from the treated cells were extensively damaged, showing 10 or more breaks and exchanges per cell. These studies clearly indicated that the treated cells accumulated in G2-phase because of their failure to progress into mitosis as a direct or indirect result of the extensive damage to the chromosomes.

Animals↗
PubMed1991

Activation of programmed cell death by recombinant human tumor necrosis factor plus topoisomerase II-targeted drugs in L929 tumor cells.

The mechanism of death induced by recombinant human tumor necrosis factor (rHuTNF) in L929 tumor cells of C3H mice was investigated. Treatment with rHuTNF led to fragmentation of DNA into nucleosomal oligomers and to induction of the expression of TRPM-2, a programmed cell death-associated gene. Both events preceded cell death by several hours. Treatment with DNA topoisomerase II inhibitors accelerated both the rHuTNF-mediated DNA fragmentation and the elevation in TRPM-2 messenger RNA levels. These results suggest that rHuTNF exerts its cytotoxicity on L929 cells by activating programmed cell death, leading to apoptosis, and that topoisomerase II inhibitors enhance rHuTNF-mediated cytotoxicity by accelerating this process.

Animals↗
PubMed1986

Novobiocin inhibits RNA polymerase III transcription in vitro by a mechanism distinct from DNA topoisomerase II.

The role of DNA topoisomerases in eucaryotic class III gene transcription in vitro has been studied through the use of inhibitory drugs and antisera to DNA topoisomerases I and II. The DNA topoisomerase II inhibitors, novobiocin and coumermycin AI, were found to inhibit transcription of cloned 5S and tRNA genes. Novobiocin acts by interfering with an ATP-requiring step in the pathway to stable preinitiation complex formation. However, it is unlikely that this step reflects the enzymatic action of DNA topoisomerase II since a specific inhibitor of this enzyme (VM-26) and anti-DNA topoisomerase II antibodies fail to inhibit transcription under conditions where topoisomerase II enzymatic activity is inhibited. Similarly, a specific inhibitor of DNA topoisomerase I (camptothecin) and anti-DNA topoisomerase I antibodies fail to inhibit class III gene transcription. These results argue against a role for either DNA topoisomerase in 5S or tRNA gene transcription in vitro.

Aminocoumarins↗
PubMed1990

Transcription of adenovirus and HeLa cell genes in the presence of drugs that inhibit topoisomerase I and II function.

The requirements for topoisomerases in transcription of adenovirus and HeLa cell genes were analyzed using drugs that specifically inhibit either topoisomerases I or II. Cleavage of viral DNA by topoisomerases in the presence of either camptothecin or VM26 was used to determine drug concentrations that led to maximal inhibition of ligation in the cleavage and ligation step of topoisomerase I or II respectively. Inhibition of topoisomerase II with VM26 did not cause a direct reduction in transcription of adenoviral genes or HeLa cell heat shock genes. VM26 did, however, interfere with other cellular processes. It reduced nucleoside uptake into HeLa cells from the medium, and it altered the normal nuclear to cytoplasmic ratio of specific RNAs. Treatment of cells with camptothecin to inhibit topoisomerase I reduced but did not abolish transcription of viral and HeLa cell genes. Transcription mediated by both RNA polymerases I and II was reduced. Topoisomerase II did not appear to substitute for topoisomerase I in transcription since treatment of cells with VM26 and camptothecin did not reduce transcript accumulation relative to cells treated with camptothecin alone.

Adenovirus Early Proteins↗
PubMed1991

Interactions of Drosophila DNA topoisomerase II with left-handed Z-DNA in supercoiled minicircles.

The native form of Drosophila melanogaster DNA topoisomerase II was purified from Schneider's S3 tissue culture cells and studied with two supercoiled minicircle preparations, mini and mini-CG, 354 bp and 370 bp in length, respectively. Mini-CG contains a d(CG)7 insert which assumes a left-handed Z-DNA conformation in negative supercoiled topoisomers with a negative linking number difference - delta Lk greater than or equal to 2. The interactions of topoisomerase II with topoisomer families of mini and mini-CG were studied by band-shift gel electrophoresis in which the individual topoisomers and their discrete or aggregated protein complexes were resolved. A monoclonal anti-Z-DNA IgG antibody (23B6) bound and aggregated only mini-CG, thereby confirming the presence of Z-DNA. Topoisomerase II bound and relaxed mini-CG more readily than mini. In both cases, there was a preference for more highly negatively supercoiled topoisomers. The topoisomerase II inhibitor VM-26 induced the formation of stable covalent DNA-protein intermediates. In addition, the non-hydrolyzable GTP analogue GTP gamma S inhibited the binding and relaxation activities. Experiments to detect topoisomerase cleavage sites failed to elicit specific loci on either minicircle preparation. We conclude that Drosophila topoisomerase II is able to bind and process small minicircles with lengths as short as 360 bp and negative superhelix densities, - sigma, which can exceed 0.1. Furthermore, the enzyme has a preferential affinity for topoisomers containing Z-DNA segments and relaxes these molecules, presumably by cleavage external to the inserts. Thus, a potentially functional relationship between topoisomerase II, an enzyme regulating the topological state of DNA-chromatin in vivo, and left-handed Z-DNA, a conformation stabilized by negative supercoiling, has been established.

Animals↗
PubMed1992

Incomplete reversion of double stranded DNA cleavage mediated by Drosophila topoisomerase II: formation of single stranded DNA cleavage complex in the presence of an anti-tumor drug VM26.

Anti-tumor drug VM26 greatly stimulates topoisomerase II mediated DNA cleavage by stabilizing the cleavable complex. Addition of a strong detergent such as SDS to the cleavable complex induces the double stranded DNA cleavage. We demonstrate here that heat treatment can reverse the double stranded DNA cleavage; however, topoisomerase II remains bound to DNA even in the presence of SDS. This reversed complex has been shown to contain single strand DNA breaks with topoisomerase II covalently linked to the nicked DNA. Chelation of Mg++ by EDTA and the addition of salt to a high concentration also reverse the double strand DNA cleavage, and like heat reversion, topoisomerase II remains bound to DNA through single strand DNA break. The reversion complex can be analyzed and isolated by CsCl density gradient centrifugation. We have detected multiple discrete bands from such a gradient, corresponding to protein/DNA complexes with 1, 2, 3, ..... topoisomerase II molecules bound per DNA molecule. Analysis of topoisomerase II/DNA complexes isolated from the CsCl gradient indicates that there are single stranded DNA breaks associated with the CsCl stable complexes. Therefore, topoisomerase II/DNA complex formed in the presence of VM26 cannot be completely reversed to yield free DNA and enzyme. We discuss the possible significance of this finding to the mechanism of action of VM26 in the topoisomerase II reactions.

Animals↗
PubMed1998

Meiotic double-strand breaks in yeast artificial chromosomes containing human DNA.

Meiotic recombination in the yeast Saccharomyces cerevisiae is initiated by double-strand breaks (DSB) in chromosomal DNA. These DSB, which can be mapped in the rad 50S mutant yeast strain, are caused by a topoisomerase II-like enzyme, the protein Spo11. Evidence suggests that this protein is located in the axial element of the meiotic chromosome which implies that the DSB are located in these chromosomes in the vicinity of the bases of the DNA loops. We have found that in the yeast artificial chromosomes carrying human DNA, at the level of resolution obtained by pulsed field gel electrophoresis (PFGE), the meiotic DSB in the diploid yeast are co-localized with the DNase I hypersensitive sites (HS) in a haploid strain of yeast. These HS are located close to sequences which, under stress, have the potential to form secondary structures containing unpaired nucleotides. Clusters of such sequences could be a hallmark of the bases of the chromatin loops.

Chromatin↗
PubMed1991

Concentrations of VP16 and VM26 in human brain tumors.

VP16 and VM26 were determined by high pressure liquid chromatography in intracerebral tumors, adjacent normal brain tissue, plasma and CSF samples from 24 patients given the two drugs before surgical resection of the tumor. The drugs were administered at doses of 100-150 mg/m2 as a 1-hour i.v. infusion, between 1.5 and 12 hours before surgery. Concentrations of VP16 ranged between 1.05 and 3.28 micrograms/g in tumors in the series of patients who received the drug 1.5-3 hours before surgery and between less than 0.05 and 1.12 micrograms/g in four patients who received the drug 9-13 hours before surgery. Tumor concentrations of VM26 also varied, ranging from less than 0.05 to 1.68 micrograms/g between 1.5 and 12 hours before surgery. VP16 and VM26 in the apparently normal brain tissue surrounding the tumor were low or undetectable except in one patient who had received radiotherapy, in whom we found 3.1 micrograms/g.

Adult↗
PubMed1991

Superiority of second over first generation chemotherapy in a randomized trial for stage III-IV intermediate and high-grade non-Hodgkin's lymphoma (NHL): the 1980-1985 EORTC trial. The EORTC Lymphoma Group.

A first-generation CHOP-like cyclic combination chemotherapy (CT) regimen using cyclophosphamide 600 mg/m2 IV d1, hydroxorubicin (doxorubicin) 50 mg/m2 IV d1, VM26 60 mg/m2 IV d1, and prednisone 40 mg/m2 PO d1-5 (CHVmP) was compared to a second-generation combination wherein vincristine 1.4 mg/m2 IV and bleomycin 6 mg/m2 IM/IV were added at mid-interval (d15) to the former drugs (CHVmP + VB) in the treatment of intermediate- and high-grade malignant NHL. From April 1980 to January 1986, 141 eligible patients with stage III-IV unfavorable histologies (except T lymphoblastic NHL) entered this EORTC randomized trial. In both arms adjuvant radiotherapy (30 Gy) was given in instances of bulky or residual disease. In all patient subsets the outcome favored the second-generation regimen. The difference was even greater in patients with Diffuse Large Cell Lymphoma (DLCL). At 5 years, overall survival was 53% with CHVmP + VB versus 29% (p = 0.002). The advantage was due to a higher complete remission (CR) rate (80% versus 50%, p = 0.01). Indeed, once CR was achieved the relapse-free survival (RFS) was not significantly influenced (59% versus 49%). No significant additional toxicity could be attributed to vincristine and bleomycin. This study demonstrates a clear benefit for intermediate- and high-risk malignant NHL and particularly DLCL from intercalating non-myelotoxic drugs at mid-cycle intervals, without adverse effects.

Adolescent↗
PubMed1986

A case of small cell lung cancer successfully treated with VM26.

A 79-year-old man was admitted to our hospital for a close examination of an abnormal shadow on a routine chest roentgenogram. A large tumorous shadow in the right S1 segment, and hilar and mediastinal node swelling were observed. Transbronchial biopsy revealed that the histologic type of the tumor was oat cell carcinoma. The clinical stage was considered to be limited disease. Because of his age, 79 years, he was treated with VM26 as a single agent. VM26 was administered by intravenous drip infusion of 60 mg/m2 daily for five consecutive days every three to four weeks. After the third course of treatment with VM26, he achieved partial response, and then radiation therapy to the primary site and the hilar and mediastinal nodes was given at a total dose of 6,000 rad. There have been few phase II studies of VM26 in patients with small cell lung cancer (SCLC). Further phase II studies should be conducted for confirmation of the reproducibility of the phase II study of VM26 in SCLC, and the efficacy of combination chemotherapy including VM26 against SCLC should also be tested.

Aged↗
PubMed1984

Phase II study of VM 26 in extensively pretreated breast cancer.

A significant activity of VM 26 in solid tumors has been established in brain tumors, bladder cancer, and neuroblastoma. Preliminary favorable results in breast cancer stimulated a phase II study at our institution to define the activity of VM 26 in patients with advanced, homogeneously pretreated breast cancer.

Adult↗