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)

Over the past decade, DNA topoisomerase I and II appeared to be the targets of some antitumor agents: CPT-11 and Topotecan derived from Camptothecin which interact with topoisomerase I; Actinomycin D, Adriamycin and Daunorubicin, Elliptinium Acetate, Mitoxantrone, Etoposide and Teniposide, Amsacrine which interact with topoisomerase II. The multiple functions of these enzymes are important as they play a role during replication, transcription, recombination, repair and chromatine organisation. Particularly, they relax torsional constraints which appear when intertwined DNA strands are separated while replication fork or RNA polymerases are moving. To some extent, topoisomerase I and II are structurally and functionally different. Moreover, topoisomerase I is not indispensable for a living cell whereas topoisomerase II is. Drug-topoisomerase interaction which probably leads to antitumoral effect of the compounds studied in this review is not a trivial inhibition of the enzyme but rather a poisoning due to stabilization of cleavable complexes between the enzyme and DNA. These stabilized complexes are likely to induce apoptosis-like programmed cell death, which is characterised by DNA fragmentation. However, it appears that it is the collision of the replication fork with the drug-stabilized cleavable complex that is responsible for the cytotoxicity of the drug: poisoning of topoisomerases by antitumor agents leads to a new concept of "dynamic toxicity". Although they interact with a common target, topoisomerase II poisons have differential effects on macromolecules syntheses, cell cycle and chromosome fragmentation; a few compounds may produce free radicals. Because of these differential effects in addition to quantitative and qualitative variations of stabilized cleavable complexes, in particular DNA sequences on which topoisomerase II is stabilized, these antitumor agents do not resemble each other. Cellular resistance to topoisomerases poisons results of two principal types of alteration: target and/or drug transport modification. Decreased ability to form the cleavable complex in resistant cells may be the consequence of both decreased amount of topoisomerase or altered enzyme. On the other hand, overexpression of membrane P-glycoprotein, which pumps drugs out of the cell by an energy dependent process provokes a decreased accumulation of these drugs. Cross resistances to other drugs are mainly under control of these two different mechanisms of resistance. A complete knowledge of their individual effects and mechanisms of resistance would allow a better clinical use of topoisomerases poisons, especially when administered in combination chemotherapy.
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PMID:[Poisons of DNA topoisomerases I and II]. 808 Oct 34

Drug resistance to inhibitors of DNA topoisomerase II can result from qualitative or quantitative alterations in the target enzyme, topoisomerase II, or from perturbations in drug transport that may or may not involve P-glycoprotein. In the present study, a drug-resistant Chinese hamster ovary cell line, SMR16, was selected in the presence of an epipodophyllotoxin (VP-16) and was found to be cross-resistant to all classes of topoisomerase II inhibitors (3-35-fold). The 3-fold level of resistance of these cells to vincristine is likely due to diminished uptake of this drug, and this is not mediated by overexpression of P-glycoprotein. No alteration in transport of VP-16 was observed. Immunoblotting with several polyclonal anti-topoisomerase II antibodies demonstrated that the resistant cells contain approximately two-thirds of the parental enzyme amount. The topoisomerase II catalytic activity present in 0.35 M NaCl nuclear extracts paralleled this decrease. VP-16- and 4'-(9-acridinylamino)methanesulfon-m-anisidide-induced DNA damage, mediated by topoisomerase II, was found to be decreased 10-12-fold in both intact SMR16 cells and nuclei isolated from these cells, when measured by alkaline filter elution. However, the VP-16-induced DNA cleavage activity present in 0.35 M NaCl nuclear extracts of the resistant cells was attenuated only 2-fold, relative to wild-type cells. Homogeneous preparations of the enzyme obtained from resistant cells demonstrated the same cleavage and catalytic activity as purified wild-type topoisomerase II. Analysis by pulse-field gel electrophoresis of the DNA isolated from VM-26- and 4'-(9-acridinylamino)methanesulfon-m-anisidide-treated sensitive and resistant cells demonstrated significantly less conversion of SMR16 chromosomal DNA into 50-150-kilobase DNA fragments. Chinese hamster ovary SMR16 cells are apparently resistant to topoisomerase II poisons because the topoisomerase II that defines the DNA topological domains is either decreased in amount or insensitive to drug action.
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PMID:Topoisomerase II activity involved in cleaving DNA into topological domains is altered in a multiple drug-resistant Chinese hamster ovary cell line. 809 26

A panel of six 'wild type' and three VP-16 resistant small cell lung cancer (SCLC) cell lines is used to evaluate to what extent in vitro sensitivity testing using a clonogenic assay can contribute to combine cytotoxic drugs to regimens with improved efficacy against SCLC. The resistant lines include (a) H69/DAU4, which is classical multidrug resistant (MDR) with a P-glycoprotein efflux pump (b) NYH/VM, which exhibits an altered topoisomerase II (topo II) activity and (c) H69/VP, which is cross-resistant to vincristine, exhibits a reduced drug accumulation as H69/DAU4 but is without P-glycoprotein. 19 anticancer agents were compared in the panel. The MDR lines demonstrated, as expected, cross-resistance to all topo II drugs, but also different patterns of collateral sensitivity to BCNU, cisplatin, ara-C, hydroxyurea, and to the topo I inhibitor camptothecin. The complete panel of nine cell lines clearly demonstrated diverse sensitivity patterns to drugs with different modes of action. Correlation analysis showed high correlation coefficients (CC) among drug analogues (e.g. VP-16/VM-26 0.99, vincristine/vindesine 0.89), and between drugs with similar mechanisms of action (e.g. BCNU/Cisplatin 0.89, VP-16/Doxorubicin 0.92), whereas different drug classes demonstrated low or even negative CC (e.g. BCNU/VP-16 -0.21). When the CC of the 19 drug patterns to VP-16 were plotted against the CC to BCNU, clustering was observed between drugs acting on microtubules, on topo II, alkylating agents, and antimetabolites. In this plot, camptothecin and ara-C patterns were promising by virtue of their lack of cross-resistance to alkylating agents and topo II drugs. Thus, the differential cytotoxicity patterns on this panel of cells can (1) give information about drug mechanism of action, (2) enable the selection and combination of non-cross-resistant drugs, and (3) show where new drugs 'fit in' among established agents.
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PMID:Differential cytotoxicity of 19 anticancer agents in wild type and etoposide resistant small cell lung cancer cell lines. 809 93

In order to clarify the mechanism of drug resistance in human myeloma cells, we investigated the expressions of DNA topoisomerase I and topoisomerase II gene and the genes possibly related to drug resistance; multi-drug resistant gene 1 (MDR-1), glutathione S-transferase class pi gene (GST-pi), by Northern blotting. Myeloma cells in eight of 15 cases prior to chemotherapy expressed topoisomerase I mRNA considerably, while the expression of topoisomerase II mRNA was detected weakly in only one of 16 myeloma patients. There was not any correlation between expression of topoisomerase I mRNA and clinical drug resistance. Significant expression of MDR-1 mRNA and P-glycoprotein was not detected in 25 cases of multiple myeloma prior to chemotherapy and even after several courses of VAD (vincristine, adriamycin and dexamethasone) therapy by Northern blotting and immunostaining using monoclonal anti-P-glycoprotein antibody (MRK-16), respectively. On the other hand, 16 of 21 myeloma cases showed significant expression of GST-pi protein and GST-pi mRNA with the various strengths, but there was no apparent correlation between GST-pi mRNA expression and clinical response. Therefore these data suggest that expression of the genes we tested may not determine the level of drug resistance in multiple myeloma, but lower or no significant expression of topoisomerase II mRNA in most myeloma cells indicates the possibility that topoisomerase II inhibitors such as VP-16 and topoisomerase II-mediated cytotoxic drugs such as adriamycin, are not so effective for the treatment of multiple myeloma.
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PMID:Expressions of DNA topoisomerase I and II gene and the genes possibly related to drug resistance in human myeloma cells. 809 26

The topoisomerase II inhibitor, VP-16 (etoposide), is an important component in many chemotherapeutic regimens. To characterize resistance to this drug, the human melanoma cell line, FEM-X, was selected in multiple steps with VP-16. To prevent the development of typical multidrug resistance, an inhibitor of P-glycoprotein, the tiapamil analog, RO-11-2933, was added to the selections. The resultant clone FVP3 is 56-fold resistant to VP-16 and cross-resistant to doxorubicin (Adriamycin) (9-fold) and VM-26 (27-fold). These cells are also two- to four-fold resistant to m-AMSA, daunorubicin, and mitoxantrone. FVP3 is not resistant to the P-glycoprotein substrates vinblastine, does not express the MDR1 gene at detectable levels, and does not show reduced 3H-VP-16 accumulation. Unlike other cell lines that exhibit resistance to inhibitors of topoisomerase II, FVP3 has the same level of topoisomerase II expression and activity as FEM-X. Using live cells treated with VP-16, band depletion assays and KCI/SDS precipitation assays show that topoisomerase II from FVP3 is much less susceptible to drug-induced cleavable complex formation than is that from FEM-X. This difference in sensitivity to VP-16 is also detected using lysates from disrupted cells, but not with isolated nuclei devoid of cytoplasmic and membrane components. In addition, the topoisomerase II present in nuclear extracts from FVP3 is not resistant to the effects of VP-16 as measured by: (1) inhibition of strand passing activity during decatenation of kinetoplast DNA, (2) drug-induced linearization of plasmid DNA, and (3) immunodepletion by VP-16. These results suggest that some component of the cytoplasm or cellular membranes, or a factor depleted from nuclei during their isolation, is responsible for the resistance to VP-16 in FVP3.
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PMID:Characterization of an unusual mutant of human melanoma cells resistant to anticancer drugs that inhibit topoisomerase II. 809 46

KB-A1 and KB-A10 are 2 multi-drug-resistant cell lines which are 100- and 1,000-fold resistant to Adriamycin, respectively. We have examined the expression of P-glycoprotein at the molecular and cellular levels in these human carcinoma cells. Both MDR cell lines, when compared to the parental KB-3-1, show characteristic increases in mdr 1 gene copy number, an increase in mdr 1 mRNA expression, a corresponding increase in transcription rate and a consequent over-expression of P-glycoprotein. However, the more highly resistant KB-A10 cells have a lower gene copy number, express less mdr 1 mRNA and contain less P-glycoprotein than the A1 cell line. To determine whether higher levels of cellular resistance were attributable to enhanced efficacy of P-glycoprotein or to other cellular regulatory mechanisms, we examined other major cellular properties known to be associated with the mdr phenotype. Both the KB-A1 and KB-A10 lines exhibit similar increases in protein kinase C activity as compared to the drug-sensitive parent. In addition, neither glutathione-S-transferase nor topoisomerase II activities account for enhanced resistance of the KB-A10 cells. The above observations are contrary to the premise that the level of drug resistance is necessarily proportional to expression of P-glycoprotein or to other common factors thought to participate in drug insensitivity; consequently, new mechanisms of resistance must be in operation in these cells.
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PMID:Anomalous expression of P-glycoprotein in highly drug-resistant human KB cells. 809 16

Trifluoperazine (TFP) is effective in modulating DNA damage/repair in doxorubicin (DOX) treated cells. In the present study we have characterised the resistance phenotype of parental sensitive L1210 mouse leukaemia cells (L1210/S) adapted to grow in the presence of 0.017 microns DOX+5 microM TFP (L1210/DT). Although with prolonged exposure, 0.017 microM DOX alone produced < 35% cell kill in L1210/S cells, similar cytotoxicity was achieved at 0.43 microM DOX in L1210/S cells selected in the presence of 0.017 microM DOX+5 microM TFP. L1210/DT cells were > 30-fold resistant to DOX following a 3 h drug exposure in a soft agar colony assay. In contrast, DOX sensitivity in cells adapted to grow in 5 microM TFP alone was comparable to L1210/S cells. Resistance to other inhibitors of topoisomerase II in L1210/DT cells was > 30-fold to etoposide and > 6-fold to amsacrine. The levels of the 170 kDa and 180 kDa isoforms of topoisomerase II in an immunoblot were comparable between the L1210/S and L1210/DT cells. Cross resistance to vincristine in the L1210/DT cells was accompanied by the overexpression of plasma membrane P-glycoprotein. Although a 1.5-2-fold decrease in accumulation of etoposide and DOX was observed in the L1210/DT cells, drug levels for equivalent DNA damage in the alkaline elution assay were > 5-fold higher in the L1210/DT versus L1210/S cells. No abrogation in the modulating effects of TFP on DOX, VP-16 or amsacrine induced cytotoxicity was apparent in the L1210/DT cells. Results suggest that: (a) TFP in combination with low concentrations DOX can induce the selection of cells with the multidrug resistant phenotype; and (b) characteristics of cells selected for resistance to DOX or DOX plus TFP are comparable.
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PMID:Calmodulin inhibitor trifluoperazine in combination with doxorubicin induces the selection of tumour cells with the multidrug resistant phenotype. 809 6

Tumor cell resistance to chemotherapeutic agents of diverse structure and mechanism of action is thought to be due to efflux of drug by P-glycoprotein, which is overexpressed in tumor cells with the multidrug-resistant phenotype. Agents generally associated with the multidrug-resistant phenotype include inhibitors of topoisomerase II, e.g., doxorubicin, etoposide, and the microtubule poisons such as vinblastine, vincristine (VCR), and taxol. The antiepileptic drug phenytoin (DPH), an inhibitor of tubulin polymerization, potentiates (P < 0.05) the cytotoxicity of the chemotherapeutically useful microtubule poison VCR in tumor cells with the wild-type or multidrug-resistant phenotype. Among agents associated with the multidrug-resistant phenotype, the modulation of cytotoxicity by DPH was selectively effective with the microtubule poison VCR but not the topoisomerase II inhibitor doxorubicin. The potentiation of vincristine cytotoxicity by DPH was not due to binding to P-glycoprotein or by increasing VCR accumulation. We thus propose a novel mechanism for the modulation of resistance based on evidence that DPH at noncytotoxic concentrations can selectively enhance the cytotoxic potential of vincristine without interfering with P-glycoprotein function. Thus, studies with phenytoin could assist in characterizing other molecular determinants of multidrug resistance and the design of trials to modulate drug efficacy.
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PMID:Selective enhancement of vincristine cytotoxicity in multidrug-resistant tumor cells by dilantin (phenytoin) 810 Jul 37

Significant activity has been identified using S9788, a triazineaminopiperidine derivative, as a new modulator of multi-drug resistance against a series of drug-resistant human tumour-cell lines in vitro. Maximal non-cytotoxic concentrations (i.e., those resulting in < or = 10% cytotoxicity) of S9788 or verapamil were tested in combination with vinblastine, Adriamycin or vincristine and cytotoxicity was evaluated using a clonogenic assay, or the metabolic dye reduction MTT assay, or by monitoring growth inhibition. Under these conditions, the extent of resistance modulation by verapamil and by S9788 was comparable in the various tumour cell lines tested, although a definite concentration-dependent modulation was noted with both compounds. The highest dose-modification factors were noted in the highly vinblastine-resistant classic multi-drug-resistant subline CEM/VLB100, although resistance reversal was only partial. Resistance modulation by both verapamil and S9788 was noted in 4 drug-selected resistant sublines and 4 "intrinsically" resistant human tumour cell lines, which all exhibited significant P-glycoprotein expression. In contrast, in 2 drug-resistant human tumour sublines (GLC4/ADR and CEM/VM-1) characterized by altered topoisomerase-II activity and proving to be P-glycoprotein-negative, no resistance modulation relative to parental cells was observed. These data are consistent with the proposal that resistance modulation is mediated by interaction between S9788 and P-glycoprotein and support its clinical evaluation in patients with P-glycoprotein-positive tumours.
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PMID:Evaluation of S9788 as a potential modulator of drug resistance against human tumour sublines expressing differing resistance mechanisms in vitro. 810 61

The H209/V6 cell line was derived from the H209 small cell lung cancer cell line by selection in etoposide (VP-16). Cytogenetic analysis indicates that the sensitive and resistant cell lines share 20 marker chromosomes and thus are clearly related. However, the H209/V6 cell line has four additional structurally altered chromosomes and a 2 N-modal chromosome number, while the H209 cell line is hypotetraploid (4 N-). H209/V6 cells are cross-resistant to some drugs that interact with topoisomerase II but not mitoxantrone. H209/V6 cells are also not cross-resistant to vincristine, trimetrexate, or cisplatin. The rates of VP-16 efflux are the same in the resistant and sensitive cell lines, which is consistent with the observation that P-glycoprotein mRNA is not detectable in either cell line. Fewer VP-16-induced DNA-protein complexes are observed in H209/V6 cells, and immunoblot analysis shows that levels of topoisomerase II alpha are reduced in H209/V6 cells compared to the sensitive H209 cells. Furthermore, the topoisomerase II alpha-related protein in H209/V6 cells has an increased electrophoretic mobility, with an apparent M(r) of 160,000. The levels of the topoisomerase II alpha 6.1-kilobase mRNA in H209/V6 cells are reduced > 10-fold. In addition, a second topoisomerase II alpha-related mRNA of approximately 4.8 kilobases is observed in H209/V6 cells but not in H209 cells. The quantity and electrophoretic mobility of the M(r) 180,000 topoisomerase II beta protein and its 6.1-kilobase mRNA are the same in the sensitive and resistant cell lines. The topoisomerase II strand-passing activity in H209/V6 nuclear extracts is reduced about 2-fold, but this activity is not more resistant to inhibition by VP-16 than the activity in H209 cells. However, band depletion immunoblot experiments show that the topoisomerase II alpha-related M(r) 160,000 protein in H209/V6 cells is not bound to DNA in the presence of concentrations of VP-16 that deplete the M(r) 170,000 topoisomerase II alpha in H209 cells and the M(r) 180,000 topoisomerase II beta in both the resistant and sensitive cells. We conclude that quantitative and qualitative alterations in topoisomerase II alpha have occurred in H209/V6 cells and are likely to contribute to its resistance phenotype.
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PMID:Altered topoisomerase II alpha in a drug-resistant small cell lung cancer cell line selected in VP-16. 810 87


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