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)

The antracyclines induce multiple intracellular effects; however, inhibition of the nuclear enzyme topoisomerase II (TOPO II) is the main mechanism of action. Resistance to anthracyclines in tumor cells is multifactorial. The main mechanisms are: (1) the classic multidrug resistance (MDR) phenotype, which is due to the presence of P-glycoprotein (PGP) in plasma membrane, that is, a "pump" that can extrude a wide range of anticancer drugs. Membrane-active drugs (e.g., verapamil) have been found in vitro to reverse this phenotype. Most clinical studies including chemosensitizers have, however, been disappointing. (2) Non-PGP-mediated MDR: this phenotype is characterized by expression of other proteins in the plasma membrane which are also able to extrude anticancer drugs. (3) Changes in the intracellular distribution of drug: this mechanism has been demonstrated in several cell lines, most often in combination with PGP or non-PGP-mediated resistance. (4) Glutathione transferases (GST) and detoxification mechanisms: these represent a multigene family of enzymes that conjugate glutathione to chemically reactive groups. Direct evidence for a causative role of GST in anthracycline resistance is missing. (5) Alterations in TOPO II (at-MDR): DNA topoisomerases are involved in several aspects of DNA metabolism, in particular genetic recombination, DNA transcription, and chromosome segregation. Low levels of expression or alterations in TOPO II are associated in vitro with resistance. (6) Increased DNA repair: in several cell lines, an increase in the efficacy of DNA repair has been associated with resistance to doxorubicin (DOX). So far, only classic MDR has been shown to contribute to resistance in clinical conditions, whereas evidence for the other mechanisms of resistance is still missing.
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PMID:Cellular resistance to anthracyclines. 891 38

Peripheral blood samples from 18 patients with chronic lymphocytic leukemias (CLL) who were either untreated but who were later sensitive to chlorambucil (CLL S) or resistant to a combination containing doxorubicin, vincristine, cyclophosphamide and prednisone (CLL R) were studied for glutathione system, P-glycoprotein, PCNA and topoisomerase II expression. P-glycoprotein expression detected by an immunocytochemical technique using MRK 16 antibody was present at the same level in CLL S and CLL R. The percentage of cells positive for P-gp was below 5% in all samples tested. Topoisomerase IIalpha level was quantified by Western blot analysis. None of the 18 CLL samples had detectable topoisomerase IIalpha protein. In addition, 12 CLL were tested for PCNA staining and no samples had more than 1% of positive cells at immunocytochemical detection indicating that CLL cells were not engaged in the cell cycle. Some differences were found between CLL S and CLL R in the glutathione system. Glutathione concentration (GSH) and GST activity was the same in CLL S and CLL R. The glutathione-S-transferase (GST) isoenzyme profile was different in the two CLL groups. The mean GST-pi and GST-alpha quantitation were twice as high as in CLL R compared to CLL S, but this difference did not reach statistical significance because of large variations between CLL samples. A significant correlation was observed between GST-pi expression and GST activity using CDNB as the substrate. GST-mu was detected in only one of seven CLL before therapy and in six of 11 resistant to chemotherapy. No correlation was found between P-glycoprotein expression, GST activity and the different GST isoenzymes studied. These results suggest that the glutathione system could play a role in the resistance of anticancer agents in chronic lymphocytic leukemia. The role of the other drug resistance mechanisms (P-glycoprotein and topoisomerase IIalpha) seems to be of limited importance.
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PMID:Drug resistance mechanisms in chronic lymphocytic leukemia. 894 35

Drug resistance often results in failure of anticancer chemotherapy in leukemias. Several mechanisms of drug resistance are known with multidrug resistance (MDR) being the best characterized one. MDR can be due to enhanced expression of certain genes (MDR1, MRP or LRP), alterations in glutathione-S-transferase activity or GSH levels and to reduction of the amount or the activity of topoisomerase II. Here we review the current status of the clinical significance of the various mechanisms of MDR in leukemias and also discuss possibilities for the reversal of MDR. MDR1 gene expression has been seen in many leukemias, notably in acute myeloid leukemia (AML) and blast crisis of chronic myeloid leukemia. Both MDR1 RNA and P-glycoprotein expression of the leukemic cells have been shown to correlate with poor clinical outcome in AML. However, preliminary results indicate that the MRP gene as well as the LRP gene can be expressed in AML. Thus, drug resistance in leukemias appears to be multifactorial. P-glycoprotein-mediated MDR can be reversed by several drugs. These resistance modifiers are currently evaluated with regard to their clinical efficacy. Despite some encouraging results, reversal of drug resistance and subsequent improvement in clinical outcome remains to be shown.
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PMID:Multidrug resistance in leukemias and its reversal. 903 Oct 75

This study was designed to elucidate the mechanisms of cisplatin (CDDP) resistance using two human ovarian cancer cell lines, KF and TYK, and two CDDP-resistant lines, KFr and TYK/R, derived from the former lines. KFr and TYK/R showed about 3-fold higher resistance to the cytotoxic effects of CDDP than their parental lines. They also showed a significant increase in sensitivity to not only etoposide, but also (+)-(4S)-4, 11-diethyl-4-hydroxy-9-[(4-piperidino -piperidino)carbonyloxy]-1H -pyrano[3',4':6,7]inodolizino[1,2-b]quinoline-3,14(4H, 12H)-dione hydrochloride trihydrate (CPT-11). Cellular CDDP accumulation levels in KFr and TYK/R were decreased from those of the parental cells. By contrast, the cellular glutathione (GSH) content in KFr cells was 1.7-fold higher than that in KF, whereas TYK/R cells had a 40% lower content than TYK cells. Cellular mRNA levels of drug-resistance-related genes, such as DNA topoisomerase (topo) I and topo II, glutathione S-transferase-pi (GST-pi), gamma-glutamylcysteine synthetase (gamma-GCS), and metallothionein (hMT) genes, were compared between drug-sensitive KF or TYK and KFr or TYK/R. KFr cells had 8.5- and 24.7-fold higher mRNA levels of gamma-GCS and topo II genes than KF cells while KFr had only a slight increase in GST-pi mRNA level as compared with KF. By contrast, TYK/R cells had 2.9- and 1.7-fold higher hMT and topo I mRNA levels than TYK cells. Acquisition of CDDP resistance in human ovarian cancer cells thus appeared to be related mainly to expression of gamma-GCS, topo II and hMT genes, and partly to that of topo I and GST-pi genes, in addition to a decrease in CDDP accumulation.
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PMID:Altered expression of gamma-glutamylcysteine synthetase, metallothionein and topoisomerase I or II during acquisition of drug resistance to cisplatin in human ovarian cancer cells. 911 51

We examined the genetic and biochemical bases for drug resistance and the order of appearance of different mechanisms underlying the increasingly more resistant murine erythroleukemia cell lines established in Adriamycin (ADR). In the first-step low-level resistant cell line PC4-A5 (able to grow in 5 ng/mL ADR), there was a 2-fold reduction in topoisomerase IIalpha and topoisomerase IIbeta mRNA levels, as well as topoisomerase IIalpha protein and activity levels as compared with the parental cell line. The topoisomerase IIalpha activity levels remained reduced as the cells became increasingly more resistant. In contrast, the topoisomerase II mRNA and protein levels returned to approximately the parental levels in resistant cells growing in higher drug concentrations (40-160 ng/mL). Parental cells expressed the multidrug resistance protein (MRP), but beginning with PC4-A5 MRP expression decreased and remained reduced in increasingly resistant cell lines. At high levels of ADR resistance, the cells expressed the mdr3 gene concomitant with the appearance of vincristine resistance and energy-dependent daunomycin and vincristine efflux. Glutathione levels, internal pH, and expression of the major vault protein (MVP) remained unchanged in all cell lines. Fluorescence microscopy revealed no alterations in daunomycin distribution or vesicle numbers between the parental and resistant cell lines. Different resistance mechanisms emerge sequentially as cells become more resistant to ADR; the mechanisms are retained during the development of multidrug resistance (MDR). In intermediate-level MDR cell lines (PC4-A10 and PC4-A20), resistance involves an as yet undetermined mechanism(s).
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PMID:Emergence of different mechanisms of resistance in the evolution of multidrug resistance in murine erythroleukemia cell lines. 939 72

In order to better understand acquired resistance to antitumor agents in acute myelogenous leukemia (AML), we investigated various drug resistance mechanisms; namely, topoisomerase II (topo II), glutathione system and P-glycoprotein (P-gp). Blast cells of 31 patients with AML, 21 before treatment (BT) and 10 at relapse (AR) were studied. Topo II was evaluated by Western blot analysis. Glutathione-S-transferase activity (GST) and glutathione content (GSH) were investigated by spectrophotometric assays. GST isoenzymes (-alpha, -mu and -pi) were tested by Western blot and by immunocytochemical staining. P-gp was evaluated by an immunocytochemical method using MRK 16 antibody. Our results showed that GST, GSH and GST-pi were similar in patients BT and AR GST-mu was detected in 13/21 AML BT and in 5/10 AML AR. GST-alpha expression was higher (p < 0.05) in AML AR (60 +/- 105 AU/mg) compared to AML BT (10 +/- 10 AU/mg). A relationship was found between GST-pi quantitation evaluated by Western blot and immunocytochemical staining, whereas no correlation was observed for the other isoenzymes. Topo II was detected in only 4 AML BT and 3 AML AR. Eleven out of 21 AML BT and 3/10 AML AR expressed P-gp with immunohistochemical study. These results indicate that only the "glutathione system", especially the GST-alpha could be involved in drug resistance in AML.
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PMID:Glutathione system, topoisomerase II level and multidrug resistance phenotype in acute myelogenous leukemia before treatment and at relapse. 949 83

Beta-Lapachone a novel topoisomerase inhibitor, has been found to induce apoptosis in various human cancer cells. In this study we report that a dramatic elevation of hydrogen peroxide (H2O2) in human leukemia HL-60 cells following 1 microM beta-lapachone treatment and that this increase was effectively inhibited by treatment with antioxidant N-acetyl-L-cysteine (NAC), ascorbic acid, alpha-tocopherol. NAC strongly prevented beta-lapachone-induced apoptotic characteristics such as DNA fragmentation and apoptotic morphology. However, treatment of HL-60 cells with another topoisomerase inhibitor camptothecin (CPT) did not induce H2O2 production as compared to untreated cells. NAC also failed to block CPT-induced apoptosis. Correlated with these findings, we found that cancer cell lines K562, MCF-7, and SW620, contained high level of intracellular glutathione (GSH), were not elevated in H2O2 and were resistant to apoptosis after treatment with beta-lapachone. In contrast, cancer cell lines such as, HL-60, U937, and Molt-4 which have lower level of GSH, were readily increased of H2O2 and were sensitive to this drug. Furthermore, ectopic overexpression of Bcl-2 in HL-60 cells also attenuated beta-lapachone-induced H2O2 and conferred resistance to beta-lapachone-induced cell death. Beta-Lapachone at the concentration as low as 0.25 microM effectively induced HL-60 cells to undergo monocytic differentiation, as evidenced by CD14 antigenicity and alpha-naphthyl acetate esterase activity. Again, the beta-lapachone-induced monocytic differentiation was suppressed by NAC. These results suggest that intracellular H2O2 generation plays a crucial role in beta-lapachone-induced cell death and differentiation.
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PMID:Involvement of hydrogen peroxide in topoisomerase inhibitor beta-lapachone-induced apoptosis and differentiation in human leukemia cells. 955 79

We have established ten transplantable human soft-tissue sarcoma (STS) xenografts grown as subcutaneous tumours in the nude mouse. Nine xenografts originated from patients that needed chemotherapy in the course of their disease. The xenografts were tested for their sensitivity to maximum tolerated doses of five anti-cancer agents. Growth of treated tumours was expressed as a percentage of control tumour growth and a growth inhibition > 75% was measured for doxorubicin in 20% of the STS xenografts, for cyclophosphamide in 30%, for ifosfamide in 20%, for vincristine in 20%, whereas etoposide was not effective in the STS xenografts. In three out of ten STS xenografts MDR1 mRNA was detectable, but this was not related to the resistance against doxorubicin, vincristine or etoposide. Topoisomerase IIalpha mRNA expression levels did not reflect sensitivity to doxorubicin or etoposide. In all STS tissues, however, these levels were lower than topoisomerase IIalpha mRNA in a drug-sensitive human ovarian cancer xenograft. Glutathione concentrations and the activities of glutathione S-transferase, glutathione peroxidase and glutathione reductase were not related to resistance against the alkylating agents or doxorubicin. Of interest, in all STS tissues, glutathione S-transferase pi was the predominant isoenzyme present. In conclusion, chemosensitivity of the STS xenografts reflects clinical response rates in phase II trials on the same compounds in adult STS patients. Relatively low levels of topoisomerase IIalpha mRNA may partly account for intrinsic resistance against, for example, doxorubicin. Additional factors must contribute to moderate responsiveness to alkylating agents.
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PMID:Characterization of human soft-tissue sarcoma xenografts for use in secondary drug screening. 986 68

The rate of the GSH conjugate formation, the inhibition of DNA topoisomerase-I and the cytotoxic activity against L1210 cells of the naphthoquinones showed the same order; 5,8-dimethoxy-1,4-naphthoquinone (DMNQ) > 6-(1-hydroxyethyl)-DMNQ > 2-(1-hydroxyethyl)-DMNQ; the steric hindrance of the substituents, particularly 2-substutuent, in reacting with cellular nucleophiles must be the main cause for lowering the bioactivities. Acetylation of 2-(1-hydroxyethyl)-DMNQ producing 2-(acetyloxyethyl)-DMNQ potentiated the bioactivities; 2-(1-hydroxyethyl)-DMNQ did not react with GSH and the enzyme, and showed ED50 of 0.680 microgram/ml, whereas the values of 2-(1-acetyloxyethyl)-DMNQ were the conjugate formation of 0.14 microM, IC50 value of 81 microM for the enzyme inhibition and ED50 of 0.146 microgram/ml for the cytotoxcity. Furthermore, the acetylation 2-(1-hydroxyethyl)-DMNQ (T/C, 119%) enhanced the T/C values for the mice bearing S-180 tumor [T/C of 2-(1-acetyloxyethyl)-DMNQ, 276%]. It was assumed that the difference in bioactivities ensued by acetylation was based on the mechanism of the so-called bioreductive alkylation.
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PMID:Naphthazarin derivatives: synthesis, cytotoxic mechanism and evaluation of antitumor activity. 987 1

In spite of extensive investigation, the mechanism for cell cytotoxicity of the anthracycline antitumor drug adriamycin (ADR) has not yet been completely understood but the nature of the cytotoxic effects of this drug is generally related to its interaction with nuclear components, such as DNA and topoisomerase II. In a previous paper, we studied, using Confocal Laser Scanning Microscopy (CLSM), the localization of ADR and its glutathione (GSH)-conjugate (ADRIGLU), obtained by the anaerobic reaction of the parent anthracycline with reduced GSH, in drug-sensitive and in multidrug resistant (MDR) cells. In all drug-sensitive lines used, ADR was mostly located in the nuclei, while its GSH-conjugate was found only in the cytoplasm, predominantly in the Golgi region. In this study we examined the morphological changes induced by ADR or its GSH-conjugated adduct (ADRIGLU) treatments in TVM-A12 (clone 2) melanoma and K562 erythroleukemia human cell lines, correlated to programmed cell death (apoptosis). We observed that ADR-induced apoptosis in both cell lines tested after 5 h treatment: CLSM and Scanning Electron Microscopy (SEM) showed cell shrinkage, fragmentation and condensation of nuclear chromatin, cell surface blebbing and cytoplasmic vacuolization. On the contrary, ADRIGLU-induced fragmentation and condensation of nuclear chromatin, typical of apoptosis, only after 48-72 h treatment. Cytoflourimetric assay by propidium iodide staining confirmed the data obtained by CLSM and SEM. Our data suggest that apoptosis activation by anthracycline antitumor drugs is induced not only by direct interaction with nuclear components but also with cytoplasmic compartments.
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PMID:Induction of apoptosis in neoplastic cells by anthracycline antitumor drugs: nuclear and cytoplasmic triggering? 1047 Jan 35


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