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)

We demonstrated previously that human cytomegalovirus (CMV) infections could enhance the expression of cellular topoisomerase II and this enzyme activity is essential for CMV to replicate in vitro (Benson and Huang, 1988; Benson and Huang, 1990). In this study, we further show that in addition to m-AMSA and VM26 which we had previously reported, a widely used and clinically available drug, etoposide (VP-16 or VePesid) can irreversibly inhibit CMV replication at the drug concentration (2.5 micrograms/ml) greatly below toxic levels to stationary phase cells. Growing cells were more sensitive to etoposide than stationary phase cells and slight growth inhibition occurred at 2.5 micrograms/ml level. This inhibitor does not prevent the expression of CMV immediate-early and early genes, but can inhibit viral DNA and late viral-proteins synthesis. Because of their irreversible inhibitory effects and approval usage in clinical oncology, it is suggested that this group of compounds, particularly etoposide (VP-16), can be used to control life-threatening CMV infections, such as CMV pneumonitis and CMV retinitis, in cancer and immunocompromised patients or patients with AIDS.
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PMID:Irreversible inhibition of human cytomegalovirus replication by topoisomerase II inhibitor, etoposide: a new strategy for the treatment of human cytomegalovirus infection. 131 May 81

A carcinogen-transformed rat hepatoma cell line (Reuber H-35) was utilized as a model system for investigation of the biochemical factors which may limit the effectiveness of chemotherapy in intrinsically resistant tumors such as hepatocellular carcinoma. Northern blotting demonstrated expression of mRNA coding for the P-170 membrane-glycoprotein associated with the multi-drug resistance phenotype, while Western blotting identified the P-170 glycoprotein in the hepatoma cell membrane. Consistent with these observations, tumor cell sensitivity to the vinca alkaloids, vincristine and vinblastine, to the anthracycline antibiotics, Adriamycin and daunorubicin, and to the demethylepipodophyllotoxin derivative, VM-26, was enhanced by continuous incubation in the presence of the calcium channel antagonist, verapamil. Verapamil produced a minimal change in cell sensitivity to the demethylepipodophyllotoxin derivative, VP-16, and to the aminoacridine, m-AMSA. Relatively high detoxification potential via the glutathione metabolic pathway was also observed in the hepatoma cell. The capacity of topoisomerase II in nuclear extracts from the hepatoma cell to mediate cleavable complex formation stimulated by VM-26, VP-16 and m-AMSA appeared to be at least comparable to, if not greater than that from drug-sensitive HL-60 cells, suggesting that drug resistance may not occur at the level of this enzyme. Consistent with findings in a number of tumor cell lines resistant to antineoplastic drugs, the antiproliferative activity of the topoisomerase II inhibitors VM-26, VP-16 and m-AMSA appeared to be dissociable from the induction of DNA strand breaks, suggesting that such lesions in DNA may fail to fully account for the antiproliferative activity of these agents in the hepatoma cell.
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PMID:Components of intrinsic drug resistance in the rat hepatoma. 131 Aug 53

Amsacrine and demethylepipodophyllotoxins (etoposide and teniposide) are potent topoisomerase II inhibitors which have optimum activity in different cancers. To investigate whether these differences are due to different activity on cellular oncogenes, drug-induced topoisomerase II cleavage sites were mapped and sequenced in the human c-myc protooncogene. In the presence of purified murine L1210 topoisomerase II, amsacrine induces prominent cleavage in the P2 promoter (site 2499/2502). Footprinting experiments indicate that topoisomerase II binds to the entire promoter region (approximately 20 base pairs on the sides of the P2 site). In the case of teniposide or etoposide, cleavage is more diffuse and markedly less at the P2 site. Mapping of cleavage sites in human small cell lung carcinoma cells (NCI N417) also shows that cleavage in the P2 promoter region is induced preferentially by amsacrine but not by demethylepipodophyllotoxins. Thus, selective gene damage among topoisomerase II inhibitors may contribute to differential anticancer activity.
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PMID:Differential effects of amsacrine and epipodophyllotoxins on topoisomerase II cleavage in the human c-myc protooncogene. 131 59

Treatment of human K-562-J leukemia cells for 1 h with the topoisomerase II-reactive drugs VP-16, VM-26, or mAMSA resulted in a dose-dependent inhibition of proliferation and in an increase in the percentage of cells staining positive for hemoglobin, a marker of erythroid differentiation. Staining for hemoglobin of up to about 60% of the cells was observed at 20 microM VP-16, 1 microM VM-26, and 8 microM mAMSA. Such treatment also caused a G2/M arrest in the cell cycle. Incubation of the cells with radiolabeled VP-16 indicated that the induced erythroid differentiation was not due to continuous cell exposure to a residual amount of the drug. VP-16-induced erythroid differentiation was also not affected by DNA, RNA, or protein synthesis inhibitors. Differentiation induction and the G2/M arrest evoked by VP-16, VM-26, and mAMSA were, however, reduced in the presence of novobiocin. Our results indicate that topo-reactive drugs that cause G2/M arrest in the K-562-J cell cycle can induce in these cells erythroid differentiation after a short and irreversible interaction with their target molecule(s).
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PMID:The effect of topoisomerase inhibitors on the expression of differentiation markers and cell cycle progression in human K-562 leukemia cells. 133 Jun 53

Previous studies using the mutant Chinese hamster ovary cell line VpmR-5 indicate that its resistance to epipodophyllotoxins and intercalating agents is likely to be mediated through a qualitative change in type II topoisomerase that confers resistance to drug-stimulated DNA cleavage activity. In a further investigation of the genetic basis of drug resistance in VpmR-5 cells, we fused a hypoxanthine-guanine phosphoribosyl transferase-deficient subline of VpmR-5 (Vtgm-6) with normal human lymphocytes and analyzed the resultant hybrid lines (HL) for altered drug sensitivity. In all, 3 of 16 hybrid clones exhibited partial reconstitution of sensitivity to etoposide, mitoxantrone, doxorubicin, and 5-iminodaunorubicin while retaining complete resistance to m-AMSA. However, enhanced sensitivity to drug-induced DNA cleavage activity was observed only for etoposide. Biochemical and molecular-marker analysis of the hybrids failed to identify human chromosome 17 (the provisional location of TOP2) or any other human chromosome that is consistently and uniquely associated with drug sensitivity. We therefore sought to verify the chromosomal assignment of TOP2 by Southern blot hybridization of TOP2 cDNA on a human hybrid mapping panel and confirmed its location on chromosome 17. However, no hybridizing sequence to the TOP2 cDNA was found in any of the 16 Vtgm-6 hybrid lines. Efforts to select more directly for human chromosome 17 VpmR-5 hybrids using microcell fusion of mouse A9 cells carrying human 17 linked to pSV2neo were unsuccessful. None of the five hybrid clones thus obtained had 17q markers, including the gene for TOP2. Although the mechanism underlying partial reversion to a drug-sensitive phenotype in the original Vtgm-6 hybrid lines has yet to be defined, the data obtained in these lines indicate that anthracycline- and anthracenedione-induced cytotoxic effects can be dissociated from DNA cleavage activity. This suggests that pathways distal to cleavable-complex formation or, alternatively, independent of interactions with topoisomerase II that involve other intracellular targets are important in mediating the cytotoxicity produced by these drugs.
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PMID:Dissociation of cytotoxicity and DNA cleavage activity induced by topoisomerase II-reactive intercalating agents in hamster-human somatic cell hybrids. 133 69

We have previously observed that the DNA topoisomerase I inhibitor camptothecin (CAM), or DNA topoisomerase II inhibitors teniposide (TEN) and amsacrine (m-AMSA) trigger endonucleolytic activity in myelogenous (HL-60 or KG1), but not lymphocytic (MOLT-4) leukaemic cell lines. DNA degradation and other signs of apoptotic death were seen as early as 2-4 h after cell exposure to these inhibitors. Cells replicating DNA (S phase) were selectively sensitive whereas cells in G1 were resistant; the sensitivity of G2 or M cells could not be assessed in these studies. The present studies were aimed at revealing whether DNA repair replication induced by ionizing radiation can sensitize the cells, and to probe the sensitivity of cells arrested in G2 or M, to these inhibitors. The data show that gamma-irradiation (0.5-15 Gy) of HL-60 cells does not alter their pattern of sensitivity, i.e. G1 cells, although engaged in DNA repair replication, still remain resistant to CAM compared with the S phase cells. Likewise, irradiation of MOLT-4 cells also does not render them sensitive to either CAM or TEN, regardless of their position in the cell cycle. Irradiation, however, by slowing the rate of cell progression through S, increased the proportion of S phase cells, and thus made the whole cell population more sensitive to CAM. HL-60 cells arrested in G2 either by irradiation or treatments with Hoechst 33342 or doxorubicin appear to be more resistant to CAM relative to S phase cells. Also resistant are cells arrested in M by vinblastine. The data suggest that some factor(s) exist exclusively in S phase cells, which precondition them to respond to the inhibitors of DNA topoisomerases by rapid activation of endogenous nuclease(s) and subsequent death by apoptosis. HL-60 cells in G1, G2 or M, or MOLT-4 cells, regardless of the phase of the cycle, appear to be protected from such a mechanism, and even induction of DNA repair replication cannot initiate DNA degradation in response to DNA topoisomerase inhibitors. These data, together with the evidence in the literature that topoisomerase I may be involved in DNA repair, suggest that a combination of these inhibitors with treatments that synchronize cells in the S phase and/or recruit quiescent cells to proliferation, including radiation, may be of value in the clinic.
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PMID:Apoptotic cell death triggered by camptothecin or teniposide. The cell cycle specificity and effects of ionizing radiation. 133 22

Methods of uncoupling the DNA binding, cleavage and religation reactions of topoisomerase II were employed to investigate the influence of topoisomerase II-directed drugs on the individual steps in the enzyme's catalytic cycle. A special DNA substrate containing a major topoisomerase II interaction site, which can be cleaved by the enzyme in the absence of any concomitant religation, was used to examine the effect of topoisomerase II-directed agents upon the DNA cleavage reaction. The experiment demonstrated that the topoisomerase II targeting agent Ro 15-0216 stimulates the DNA cleavage reaction extensively, whereas the traditional topoisomerase II inhibitor, mAMSA, has only a minor effect on this reaction. Topoisomerase II trapped in the cleavage complexes can religate to the 3' hydroxyl end of another DNA strand. Using this religation assay, it was demonstrated that the major effect of mAMSA is an inhibition of the enzyme's religation reaction, whereas Ro 15-0216 has no effect on this reaction. Recently, considerable attention has been given to drugs preventing topoisomerase II from introducing DNA cleavages. In the present paper the initial non-covalent DNA binding reaction of topoisomerase II was investigated under conditions excluding enzyme-mediated DNA cleavage. This demonstrated that the anthracycline, aclarubicin, prevents topoisomerase II from performing its initial non-covalent DNA binding reaction and thereby abolishes the DNA cleavage reaction of the enzyme. The results presented here demonstrate that profound differences exist in the mode of action of different agents targeting topoisomerase II, and that the enzyme can be affected by such agents at both its DNA binding, cleavage and religation subreactions.
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PMID:Mode of action of topoisomerase II-targeting agents at a specific DNA sequence. Uncoupling the DNA binding, cleavage and religation events. 133 85

Fifteen specific inhibitors of DNA topoisomerases I and II were used to elucidate whether these enzymes participate in the excision repair of UV-induced DNA damage, monitoring DNA repair synthesis in confluent saponin-permeabilized human fibroblasts. To achieve a sufficient degree of accuracy dose--response experiments were performed, analysed by linear regression, and the concentrations at which repair activity was reduced to 50% were calculated and designated K50. Camptothecin, a specific inhibitor of topoisomerase I did not markedly diminish DNA repair synthesis. Similarly, when combined with topoisomerase II inhibitors [nalidixic acid, oxolinic acid, 4'-demethylepipodophyllotoxin-9-(4,6-O-ethylidene-beta-D-glucop yra noside) (etoposide), 4'-demethylepipodophyllotoxin-thenylidene-beta-D-glucoside (teniposide), 1,4-dihydroxy-5,8-bis ((2-[(2-hydroxyethyl)amino]ethyl)amino)-9,10-anthracenedione (mitoxantrone), 5-(N-phenyl-carboxamido)-2-thiobarbituric acid (merbarone) or 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA)], it did not lower K50 values determined for topoisomerase II-specific drugs in separate experiments. The effects observed can be classified according to the mechanism of action the inhibitors exhibit. (i) Novobiocin and coumermycin, inhibitors of the ATPase subunit of topoisomerase II, completely reduced DNA repair synthesis. (ii) Inhibition of repair was also found for ethidium bromide, quinacrine and distamycin, drugs known to modify the DNA substrate by intercalation or binding to the DNA minor groove. (iii) Inhibitors acting through intercalation and, simultaneously, binding to the cleavable DNA-topoisomerase complex (m-AMSA, mitoxantrone, doxorubicin and daunorubicin) also suppressed reparative DNA synthesis. (iv) Only small effects were observed for etoposide, nalidixic acid and oxolinic acid, whereas teniposide caused marked inhibition of DNA repair synthesis. (v) Merbarone, a novel type of topoisomerase II inhibitor, blocked UV-induced DNA repair drastically. The results are best explained by assuming that in UV-irradiated human fibroblasts the 180 kDa form of topoisomerase II is the main target enzyme for inhibitors which suppressed DNA excision repair and that this isozyme is involved in steps preceding repair-specific DNA incision.
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PMID:The function of DNA topoisomerases in UV-induced DNA excision repair: studies with specific inhibitors in permeabilized human fibroblasts. 133 77

A non-P-glycoprotein-mediated mechanism of multidrug resistance (non-Pgp MDR) has been identified in doxorubicin-selected sublines of the human non-small cell lung carcinoma cell line SW-1573. These sublines are cross-resistant to daunorubicin, VP16-213, Vinca alkaloids, colchicine, gramicidin D, and 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA). They accumulate less drug than the parental cells and their resistance is not due to the MDR1-encoded P-glycoprotein, as the resistant cell lines have lost the low amount of MDR1 mRNA detectable in parental cells. Here we show that the resistant cell lines also contain less topoisomerase II mRNA and enzyme activity than the parental cells. This might contribute to the resistance of these lines to drugs interacting with topoisomerase II, such as doxorubicin, daunorubicin, and VP16-213, but cannot account for the resistance to the other drugs. We have tested whether all properties of the non-Pgp MDR cell lines cosegregate in somatic cell fusions between lethally gamma-irradiated, resistant donor cells and drug-sensitive acceptor cells. Whereas a MDR phenotype with reduced drug accumulation and the loss of MDR1 P-glycoprotein mRNA were cotransferred to the acceptor cells, the decrease in topoisomerase II gene expression was not. We conclude that the MDR phenotype, the reduced drug accumulation, and the loss of MDR1 P-glycoprotein mRNA are genetically linked. They might be due to a single dominant mutation, which does not cause the alteration in topoisomerase II.
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PMID:Genetic transfer of non-P-glycoprotein-mediated multidrug resistance (MDR) in somatic cell fusion: dissection of a compound MDR phenotype. 134 62

In an attempt to characterize and overcome tumor cell resistance to amsacrine (m-AMSA), we studied the structure-activity relationships for amsacrine and seven of its analogs. Using the human leukemic cell line, CCRF-CEM, and its derivatives that express either P-glycoprotein (Pgp)-associated multidrug resistance (MDR) (CEM/VLB100) or altered topoisomerase II-associated MDR (at-MDR) (CEM/VM-1), we assessed antitumor effects of these drugs in a 48-hr growth inhibition assay. We also measured drug-topoisomerase II interactions in an intact cell assay that permits quantitation of drug-stabilized DNA-topoisomerase II complexes. We found that among the tested compounds, amsacrine has an intermediate effect on cell growth in all three cell lines. The CEM/VM-1 cells were 8.6-fold cross-resistant to m-AMSA, and the cross-resistance to the analogs was from 3.0- to 10.5-fold. In the CEM/VLB100 cells, the resistance pattern was different: several analogs, including amsacrine, showed little or no cross-resistance (0.5- to 2.8-fold), whereas for those compounds with substituents at position 3 on the acridine ring, resistance was relatively higher (9.9- or 16.2-fold). Substituents at this position substantially decrease the lipophilicity of the two compounds examined, probably because they both contain amino groups that would be charged at physiologic pH. Compound 12489, having a 1'-NHSO2C6H4NH2 substituent, was very potent in the three cell lines, showing only a slightly higher IC50 value in the CEM/VM-1 line and a lower IC50 value in the CEM/VLB100 and in the CEM cells.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Structure-activity studies of amsacrine analogs in drug resistant human leukemia cell lines expressing either altered DNA topoisomerase II or P-glycoprotein. 136 24


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