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)

The induction of glucose-regulated proteins by a variety of specific inducers leads to an increase in resistance to Adriamycin (Shen et al., Proc. Natl., Acad. Sci. USA, 84: 3278, 1987). In this study we examine several additional agents for cross-resistance induced during a glucose-regulated response in an attempt to better define the mechanism through which this phenomenon occurs. When anoxia, calcium ionophore A23187, or 2-deoxyglucose are used, a substantial resistance is obtained against the topoisomerase II-targeted agent, etoposide. Partial resistance is induced against vincristine and actinomycin D. Glucose-regulated protein inducers do not substantially alter cellular response to either bleomycin or radiation. In the case of mitomycin C there is a cellular sensitization with anoxia and 2-deoxyglucose while calcium ionophore A23187 had no effect on survival. This study suggests that the resistance obtained during a glucose-regulated response against etoposide and Adriamycin may involve topoisomerase II.
 ...
PMID:Resistance to etoposide induced by three glucose-regulated stresses in Chinese hamster ovary cells. 250 Oct 25

The relationship between DNA topoisomerase II activity and drug resistance was studied in cloned cell lines of Adriamycin (ADR)-sensitive and -resistant P388 leukemia; drug resistant P388/ADR/3 (clone 3) and P388/ADR/7 (clone 7) cells are 5- and 10-fold more resistant to ADR than the sensitive cell line P388/4 (Cancer Res., 46: 2978, 1986). Topoisomerase II catalytic activity in crude nuclear extracts was reduced in drug-resistant cells as determined qualitatively by decatenation of kDNA. Using the centrifugal method fo quantitative analysis, topoisomerase II catalytic activity (mean +/- SE) was 81 +/- 10 units/mg total nuclear protein in sensitive cells, 29 +/- 2 units/mg total nuclear protein in resistant clone 3 cells, and 16 +/- 2 units/mg total nuclear protein in resistant clone 7 cells; these differences were highly significant (P less than 0.005). Similarly, quantitative analysis of DNA cleavage activity using 3' 32P-end-labeled pBR322 restriction fragments showed that drug-stimulated topoisomerase II cleavage activity in nuclear extracts from sensitive cells was approximately 1.7- and 2.9-fold greater than that from resistant clone 3 and 7 cells, respectively. Western blot analysis of nuclear extracts from the three cell lines using antibody against the C-terminal half of recombinant-prepared human topoisomerase II polypeptide revealed reduced immunoreactivity of topoisomerase II protein in the drug-resistant cells. These data suggest that reduced topoisomerase II activity in resistant cells, which may represent quantitative reduction of the enzyme, may be another property contributing to multifactorial drug resistance in these cells.
 ...
PMID:Direct correlation between DNA topoisomerase II activity and cytotoxicity in adriamycin-sensitive and -resistant P388 leukemia cell lines. 253 93

Resistance to etoposide (VP-16), amsacrine (mAMSA), and doxorubicin (Adriamycin) was studied in two Chinese hamster cell lines primarily selected for resistance to the epipodophyllotoxin. Both lines demonstrated profound resistance to VP-16, and mAMSA stimulated DNA breakage. However, the resistance to mAMSA cytotoxicity in both lines was less than expected from the level of resistance to the effects of topoisomerase II inhibition. Similarly, resistance to the cytotoxicity of high VP-16 concentrations in one of the lines was less than expected from the resistance to inhibition of topoisomerase II. An analysis of the relation of DNA breaks to drug cytotoxicity suggests that cross-resistance to mAMSA was mainly conferred through loss of mAMSA-stimulated, topoisomerase II-mediated DNA breaks. This mechanism also contributed towards reduced VP-16 cytotoxicity. However, our studies suggest that additional mechanisms, independent of resistance to VP-16-mediated topoisomerase II effects, greatly increased the resistance to this agent. Resistance to VP-16 cytotoxicity, not dependent on resistance to drug-mediated DNA cleavage, could be overcome at high drug concentrations in one of the resistant lines and might be responsible for the greater relative resistance to VP-16 than to mAMSA. These findings suggest the presence of two distinct mechanisms of resistance to VP-16 cytotoxicity, one presumably mediated by topoisomerase II and dependent on resistance to drug-mediated DNA scission, and a second mechanism independent of the effects of the drug on topoisomerase II.
 ...
PMID:Topoisomerase II-dependent and -independent mechanisms of etoposide resistance in Chinese hamster cell lines. 253 64

The mechanism of augmentation of tumor cell killing by immune effector cells and chemotherapeutic drugs was studied. The effect of treating tumor cells with various antineoplastic drugs on their sensitivity to murine natural cell-mediated cytotoxicity in vitro was investigated. Pretreatment with actinomycin D at nontoxic concentrations rendered L929 and WEHI-164 tumor cells more susceptible to killing by mouse spleen lymphocytes in a dose-dependent manner. Similarly, enhancement of L929 tumor cell killing by natural cell-mediated cytotoxicity was observed following treatment of the target cells with the topoisomerase II inhibitors, Adriamycin, amsacrine, bisantrene, etoposide, and teniposide, as well as with topoisomerase I inhibitor, camptothecin. In contrast, drugs which induce their cytotoxic effects by mechanisms that do not involve topoisomerase inhibition such as bleomycin, vinblastine, vincristine, and mitomycin C failed to exhibit synergism with natural cell-mediated cytotoxicity. However, moderate synergy was consistently observed with cis-platinum. The effector cells responsible for the cytotoxicity in the present system are natural cytotoxic cells since they kill WEHI-164 but not YAC cells, are resistant to treatment with anti-asialo-GM1 antibody, and their activity is abolished by anti-tumor necrosis factor antibodies. Indeed, tumor necrosis factor-mediated cytotoxicity of WEHI-164 or L929 was enhanced by treatment of the target cells with topoisomerase II inhibitors. Moreover, WEHI-164 cells selected for tumor necrosis factor resistance were resistant to natural cell-mediated cytotoxicity, and no synergy could be observed with topoisomerase inhibitors.
 ...
PMID:Synergistic antitumor effects of topoisomerase inhibitors and natural cell-mediated cytotoxicity. 253 25

We have isolated two Chinese hamster ovary cell lines, designated ADR-4 and ADR-5, which exhibit hypersensitivity to intercalating agents and epipodophyllotoxins. These drugs are thought to exert their cytotoxicity via an interaction with the enzyme topoisomerase II. However, there is no apparent change in the level or catalytic activity of topoisomerase II in the mutant cells. Drug sensitivity does not appear to be due to increased drug transport because accumulation of radiolabeled actinomycin D is similar in mutant and wild-type cells. Both mutant cell lines show enhanced resistance to hydrogen peroxide and to organic peroxides. ADR-4 cells show a degree of temperature sensitivity. ADR-5 cells show mild sensitivity to UV irradiation. Neither cell line shows significant sensitivity to mono- or bifunctional alkylating agents, ionizing radiation, or bleomycin. Cell fusion studies indicate that the phenotype of each mutant cell line is recessive and that the mutants represent two different genetic complementation groups. These studies also indicate that ADR-4 and ADR-5 Adriamycin-sensitive mutant, ADR-1. These results indicate that sensitivity to topoisomerase II inhibitors can result from abnormalities in several genes. These drug-sensitive mutants may be useful for studying the mechanisms of cell killing by topoisomerase II inhibitors, free radicals, and heat.
 ...
PMID:Isolation of two Chinese hamster ovary cell mutants hypersensitive to topoisomerase II inhibitors and cross-resistant to peroxides. 254 43

We report alkaline elution experiments that reveal the temperature dependence of DNA lesions, both single-strand breaks and DNA-protein cross-links, in L1210 cells exposed to Adriamycin. DNA damage, which at 37 degrees C is equivalent to several hundred rads of ionizing radiation exposure, diminishes as the temperature of drug exposure is lowered. At all temperatures below about 15 degrees C no DNA damage is detectable in L1210 cells exposed to Adriamycin, even at relatively high doses. The low temperature inactivity is not due to a redistribution of intracellular drug since at both 37 and 0 degrees C there is a high concentration of Adriamycin in both nuclear and cytoplasmic locations. The temperature profile for DNA damage parallels the profile for cytotoxicity, i.e., at low temperature, the drug is completely inactive as a cytotoxic agent (P. Lane, P. Vichi, D. L. Bain, and T. R. Tritton, Cancer Res., 47:4038-4042, 1987). Thus, DNA breaks and cell kill appear to be correlated with one another. However, when we examined DNA lesions in nuclei isolated from L1210 cells we found that the low temperature inability to sustain Adriamycin-induced single-strand breaks or DNA-protein cross-links was absent. In nuclei, then, the drug can provoke DNA damage at low temperature, while in whole cells it cannot. Topoisomerase II, an enzyme implicated in catalyzing DNA lesions in cells exposed to intercalating agents, retains its catalytic activity both to unknot P4 DNA at 0 degrees C, and to be induced by drug to alter the release of pBR322 supercoils, so a low temperature inactivation of this enzyme cannot explain the results. We propose that intact L1210 cells have a regulatory factor which controls DNA damage, possibly through topoisomerase II, but which is lost when nuclei are isolated.
 ...
PMID:Temperature dependence of adriamycin-induced DNA damage in L1210 cells. 255 89

Previous studies have shown that DNA topoisomerase II enzyme activity and protein levels are reduced in cloned lines of Adriamycin-resistant P388 leukemia cells relative to drug-sensitive cells (Deffie et al., Cancer Res., 49: 58-62, 1989). The molecular basis of the reduced topoisomerase II levels in these resistant cells has been investigated. Northern blot analysis of total cellular RNA from drug-sensitive and -resistant cells using a 1.8-kilobase human topoisomerase II complementary DNA revealed the presence of two mRNA species: a 6.6-kilobase transcript that was strongly expressed in drug-sensitive cells but reduced 7- to 8-fold in resistant cells; and a 5.5-kilobase transcript detected only in drug-resistant cells. Southern blot analysis of genomic DNA digested with BamHI, StuI, or PvuII and probed with the 1.8-kilobase complementary DNA for human topoisomerase II showed that, in Adriamycin-resistant cells, there were two different alleles for topoisomerase II, one identical to the native allele but with a lower gene copy number than that found in sensitive cells, and a second allele containing a mutation present only in resistant cells. These findings suggest that the reduced levels of topo II protein in drug-resistant cells may be due to reduced amounts of the native 6.6-kilobase mRNA. The unique 5.5-kilobase mRNA in resistant cells may represent a shortened transcript of the mutated topoisomerase II allele.
 ...
PMID:Evidence for a mutant allele of the gene for DNA topoisomerase II in adriamycin-resistant P388 murine leukemia cells. 255 55

The cardiac glycoside ouabain, which is a specific inhibitor of the Na+,K+-pump, confers dramatic protection from the cytotoxic effects of doxorubicin (Adriamycin). This effect was documented in cultured A549 cells (human lung adenocarcinoma). CCL210 cells (human fibroblasts), and V79 cells (hamster fibroblasts). Maximum protection from doxorubicin cytotoxicity was achieved using 1 microM ouabain for A549 and CCL210 cells and 300 microM ouabain for V79 cells. These concentrations correlated well with the concentrations of ouabain required to induce Na+,K+-pump blockade, which was assessed using the K+ analogue 86Rb+. This suggests that protection is mediated by pump blockade. Addition of ouabain at the same time as doxorubicin was just as protective as preincubation with ouabain for an hour, demonstrating that the ouabain acts rapidly. Ouabain treatment affected neither influx nor efflux of doxorubicin. Ouabain also had no effect on verapamil-induced inhibition of doxorubicin efflux. However, ouabain partially blocked the verapamil-induced potentiation of the cytotoxic effects of doxorubicin. Therefore, ouabain does not protect by affecting intracellular doxorubicin levels. Fluorescence microscopy showed that the ability of doxorubicin to reach the nucleus was not influenced by ouabain. Alkaline elution studies demonstrated that ouabain greatly decreased doxorubicin-induced DNA strand breakage. Protection from cytotoxicity correlated closely with this decrease in strand breakage. These studies suggest that the stabilization of DNA-topoisomerase II complexes is closely linked to the mechanism of doxorubicin cytotoxicity and that this stabilization is influenced by the intracellular ionic milieu.
 ...
PMID:Reduction of doxorubicin cytotoxicity by ouabain: correlation with topoisomerase-induced DNA strand breakage in human and hamster cells. 282 82

10-[3-Diethylaminopropylamino]-6-methyl-5H-pyrido[3',4':4,5] pyrrolo[2,3-g]isoquinoline (PZE) is an ellipticine derivative currently in clinical trials. PZE has been postulated to produce cellular DNA lesions by an uncommon mechanism. PZE-induced DNA damage was further investigated in L1210 cells in culture. PZE was highly cytotoxic for these cells (90% inhibitory concentration = 3.1 microM). The effects of PZE on cellular DNA were studied first by alkaline sucrose sedimentation, in comparison with those of 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA). Like m-AMSA, PZE induced DNA strand breaks which were detected without a proteolytic treatment of the cell lysate. This result rules out the existence of covalent protein bridges sealing DNA termini at the break sites. PZE was less active than m-AMSA. DNA fragmentation was maximum at 5 microM and was lower at higher concentrations. The DNA effects of PZE were also studied by alkaline elution, and compared with those of Adriamycin and m-AMSA. Like Adriamycin, PZE induced single-strand breaks (SSBs) in a bell-shaped manner with respect to drug concentration. The maximum SSB frequency [1784 +/- 370 (SEM) rad equivalents)] was obtained at 16 microM. The kinetics of SSB reversion after drug removal was slower than in the case of m-AMSA. Similar bell-shaped curves were obtained for PZE-induced double-strand breaks and DNA-protein cross-links. PZE induced more double-strand breaks per SSB than did m-AMSA. However, as in the case of m-AMSA, PZE induced equal SSB and DNA-protein cross-link frequencies. These results suggest that PZE induces DNA breaks by inhibiting topoisomerase II as do other antitumor intercalators.
 ...
PMID:Production of protein-associated DNA breaks by 10-[diethylaminopropylamino]-6-methyl-5H-pyrido[3',4':4,5]pyrrolo [2,3-g]isoquinoline in cultured L1210 cells and in isolated nuclei: comparison with other topoisomerase II inhibitors. 283 Sep 64

Pleotropic resistant human breast cancer cells (MCF-7), selected for resistance to Adriamycin, were used to study the production of DNA strand breaks by etoposide (VP-16) and its relationship to drug cytotoxicity. It was shown that the resistant MCF-7 cell line was cross-resistant to VP-16, and the degree of resistance was found to be 125-200-fold. Alkaline elution studies indicated that the parental cell line was very sensitive to VP-16 which caused extensive DNA strand breakage. In contrast, little DNA strand breakage was detected in the resistant MCF-7 cells, even at very high drug concentrations, indicating a good agreement between strand breaks and cytotoxicity. Further studies indicated that the nuclei isolated from the parental cell line were more resistant to VP-16-induced DNA strand breaks than the intact cells, while the opposite was found in the resistant cell line. In addition, the alkaline elution studies in isolated nuclei showed only a 2-fold reduction of VP-16-induced DNA breaks in nuclei from the resistant cells. In agreement with this result, it was found that nuclear extract from the resistant cells produced 2-3-fold less VP-16-induced DNA breaks than that from the sensitive cells in 32P-end-labeled SV40 DNA. VP-16 uptake and efflux studies indicated that there was a 2-3-fold decrease in net cellular accumulation of VP-16 in the resistant cells. Although the reduced uptake of VP-16 and decreased drug sensitivity of topoisomerase II appear to contribute to the mechanism of action and the development of resistance to VP-16, they do not completely explain the degree of resistance to VP-16 in this multidrug-resistant MCF-7 cell line indicating that other biochemical factors, such as activation of VP-16, are also involved in drug resistance and suggesting that the resistance is multifactorial.
 ...
PMID:DNA strand breaks produced by etoposide (VP-16,213) in sensitive and resistant human breast tumor cells: implications for the mechanism of action. 284 45


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>