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)

VP-16 resistant cells, FvprB350 (50B-3), were isolated from mouse breast cancer cell line FM3A. 50B-3 cells showed 84-fold higher resistance than their parent cells. Reduced drug uptake was not found in resistant cells. Quantitative analysis of drug-stimulated DNA cleavage activity using 3'32P end-labeled pBR322 restriction fragments showed that VP-16 stimulated DNA-topoisomerase II cleavable complex forming activity in crude nuclear extract from 50B-3 cells was approximately one-fifth as compared with that of FM3A wild-type cells. Dot-blot analysis of RNA extracted from the two cell lines showed that mRNA levels of topoisomerase II in 50B-3 cells drastically decreased and catalytic activity was also 1/2-1/3 as compared with that of parent cells. 50B-3 cells showed cross resistance to VM-26, m-AMSA, adriamycin. These findings suggest that reduced topoisomerase II activity (cellular levels) and cleavable complex forming activity may be significant factors in the marked drug resistance.
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PMID:Reduced DNA topoisomerase II in VP-16 resistant mouse breast cancer cell line. 136 91

Various compounds were evaluated for their ability to induce prophage lambda in the Escherichia coli WP2s(lambda) microscreen assay. The inability of a DNA gyrase subunit B inhibitor (novobiocin) to induce prophage indicated that inhibition of the gyrase's ATPase was insufficient to elicit the SOS response. In contrast, poisons of DNA gyrase subunit A (nalidixic acid and oxolinic acid) were the most potent inducers of prophage among the agents examined here. This suggested that inhibition of the ligation function of subunit A, which also has a DNA nicking activity, likely resulted in DNA breaks that were available (as single-stranded DNA) to act as strong SOS-inducing signals, leading to prophage induction. Agents that both intercalated and produced reactive-oxygen species (the mammalian DNA topoisomerase II poisons, adriamycin, ellipticine, and m-AMSA) were the next most potent inducers of prophage. Agents that produced reactive-oxygen species only (hydrogen peroxide and paraquat) were less potent than adriamycin and ellipticine but more potent than m-AMSA. Agents that intercalated but did not generate reactive-oxygen species (actinomycin D) or that did neither (teniposide) were unable to induce prophage, suggesting that intercalation alone may be insufficient to induce prophage. These results illustrate the variety of mechanisms (and the relative effectiveness of these mechanisms) by which agents can induce prophage. Nonetheless, these agents may induce prophage by producing essentially the same type of DNA damage, i.e., DNA strand breaks. The potent genotoxicity of the DNA gyrase subunit A poisons illustrates the genotoxic consequences of perturbing an important DNA-protein complex such as that formed by DNA and DNA topoisomerase.
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PMID:Prophage induction by DNA topoisomerase II poisons and reactive-oxygen species: role of DNA breaks. 137 45

By contrast with other DNA minor groove binders, Hoechst 33258 inhibited topoisomerase-mediated activity in intact cells. To determine whether specific structural alterations could modify the topoisomerase reactivity of this drug, a series of analogs of Hoechst 33258 (compound 1) was examined. When the relative DNA binding affinities (Ka) of these agents were determined, compound 1 had the highest Ka while agents with substitutions in either of the benzimidazole moieties showed reduced affinity. Whether these changes in DNA binding correlated with topoisomerase inhibitory potency was next examined. In isolated nuclei, 25 microM of agents 1, 5 and 7 reduced VM-26 induced cross-links by 64, 65 and 83%, compared with 15 to 25% reductions by agents 2, 3, 4 and 6, respectively. The structural modification common to the less active compounds was the substitution of an oxygen for nitrogen at either position 1 or 2. On the basis of these results, agents 1, 2, 3 and 7, representing a range of inhibitory potency, were chosen for further analyses. Cross-link induction by m-AMSA and camptothecin in isolated nuclei, as well as by VM-26 in intact cells, was inhibited to a greater extent by agents 1 and 7 than 2 or 3. Additionally, all four drugs inhibited relaxation of pBR 322 DNA induced by both topoisomerases, although topoisomerase I was 2 to 5-fold more sensitive than topoisomerase II. A linear correlation was observed between the logarithms of the Ka value of compounds 1, 2 and 3 and their IC25 values for both topoisomerases, suggesting a strong dependence on DNA binding affinity for enzyme inhibition. Nevertheless, agent 7, despite having less affinity for calf thymus DNA than 1, was the most potent topoisomerase inhibitor tested in intact cells and in isolated enzyme systems. Thus, retention of nitrogen at positions 1 and 2 as well as the addition of nitrogen at position 16 was associated with increased topoisomerase inhibitory potency.
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PMID:Effects of analogs of the DNA minor groove binder Hoechst 33258 on topoisomerase II and I mediated activities. 137 46

The coumermycin antibiotic novobiocin, which interacts with the nuclear enzyme topoisomerase II, produced supra-additive toxicity to WEHI-3B D+ leukemia cells at clinically achievable concentrations, when combined with teniposide (VM-26) or etoposide (VP-16). Simultaneous exposure of cells to both agents was required for maximum efficacy of the combination. Novobiocin also produced supra-additive toxicity to A549 human lung carcinoma cells when combined with VM-26 or VP-16. At concentrations above the peak plasma levels achievable in patients, novobiocin lost its potentiating activity. Exposure of WEHI-3B D+ cells to novobiocin did not modify the cytotoxicity produced by the topoisomerase II inhibitor m-AMSA, whereas, in contrast, novobiocin antagonized the cytotoxicity of m-AMSA in A549 cells. Although it has been suggested that inhibitors of the syntheses of DNA and RNA interfere with the cytotoxic activity of the epipodophyllotoxins, maximum potentiation of the cytotoxicities of VP-16 and VM-26 occurred at novobiocin concentrations that decreased the rates of synthesis of both DNA and RNA in WEHI-3B D+ cells by about 50%. The number of DNA-topoisomerase-II covalent complexes stabilized by VM-26 in WEHI-3B D+ cells was greatly increased when cells were exposed simultaneously to VM-26 and novobiocin for 1 hr, but not when cells were treated with m-AMSA and novobiocin for the same period of time. Novobiocin did not affect the amount of covalent complexes produced by VM-26 in isolated nuclei, suggesting that the potentiating activity of novobiocin was not due to its direct interaction with the nuclear topoisomerase II enzyme. Our findings suggest that therapeutic levels of novobiocin may be capable of enhancing the clinical activities of VP-16 and VM-26.
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PMID:Potentiation by novobiocin of the cytotoxic activity of etoposide (VP-16) and teniposide (VM-26). 137 86

Exposure of exponentially growing human promyelocytic of lymphocytic leukemic cells to the putative DNA topoisomerase II inhibitor fostriecin (FST), at a concentration of 1 microM, results in the suppression of their rate of progression through the S and G2 phases of the cell cycle. At concentrations between 5 microM and 0.5 mM, FST triggers endonucleolytic DNA degradation in human promyelocytic leukemia cells, resulting in apoptotic cell death; this effect is not selective for any particular phase of the cell cycle. Little or no apoptotic cell death is observed in lymphocytic leukemic cells at any FST concentration. Because FST, unlike other inhibitors of topoisomerase II, such as teniposide (TN) or amsacrine (m-AMSA), does not stabilize cleavable DNA-topoisomerase complexes, the observed differences between the effects of FST versus TN or m-AMSA on the cell cycle may provide clues regarding the role of such complexes in the kinetic effects of these inhibitors. The present results, therefore, are compared with our earlier data on the effects of TN and m-AMSA on the same cells. The only observed difference is the loss of cell cycle phase-specific triggering of DNA degradation by FST in human promyelocytic leukemia cells, compared to the S phase-specific effects of TN and m-AMSA. Therefore, stabilization of the DNA-topoisomerase cleavable complexes may be essential in the selectivity of cell kill during S phase. However, it appears that the presence of stabilized complexes is not essential to the suppression of cell progression through S or G2 or the induction of apoptotis or necrosis, in general, by topoisomerase II inhibitors.
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PMID:Cytostatic and cytotoxic effects of fostriecin on human promyelocytic HL-60 and lymphocytic MOLT-4 leukemic cells. 154 Sep 62

Resistance to 0.8 microM 4'-(9-acridinylamino)methanesulphon-m-anisidide (m-AMSA) was induced by stepwise increases of drug concentration in the human tumor cell line CALc18 originating from a breast adenocarcinoma. The resistant cell line CALc18/AMSA exhibited a resistance index of 10 and a cross-resistance to other topoisomerase II inhibitors. A 3-fold decrease in the levels of topoisomerase II decatenating activity was found in CALc18/AMSA cells. By contrast, topoisomerase I activity was increased by about 3-fold in resistant cells. Interestingly this line was hypersensitive to camptothecin, a specific inhibitor of topoisomerase I. Restriction endonuclease patterns of the topoisomerase I and topoisomerase II loci were found to be identical in CALc18/AMSA and CALc18 with no evidence of gene amplification and rearrangements. Alkaline elution of m-AMSA-treated cells showed that DNA single strand breaks and DNA-protein crosslinks were decreased in CALc18/AMSA. The DNA lesions also obtained in m-AMSA-treated nuclei indicated that no drug uptake modification occurred in both cells. Moreover, the in vitro m-AMSA-induced DNA cleavage per unit of decatenating activity and the inhibitory effects of antitumoral drugs on decatenation were not found to be different with topoisomerase II from sensitive or resistant cells. However the specific cleavage induced by m-AMSA/per mg of crude protein from resistant cells was 2 to 3 times decreased. Multidrug resistance gene transcripts were not detected while levels of acidic glutathione S transferase mRNA were found to be 8 to 10-fold greater in resistant than in sensitive cell line with no amplification of the gene. In conclusion, the diminution of topoisomerase II activity and the increase of both topoisomerase I and acidic glutathione S transferase transcripts could contribute to the resistant phenotype of these breast cancer cells.
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PMID:Study of molecular markers of resistance to m-AMSA in a human breast cancer cell line. Decrease of topoisomerase II and increase of both topoisomerase I and acidic glutathione S transferase. 164 55

Saintopin is an antitumor antibiotic recently discovered in mechanistically oriented screening using purified calf thymus DNA topoisomerases. Saintopin induced topoisomerase I mediated DNA cleavage comparable to that of camptothecin, and topoisomerase II mediated DNA cleavage equipotent to those of 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) or 4'-demethylepipodophyllotoxin 9-(4,6-O-ethylidene-beta-D-glucopyranoside) (VP-16). Treatment of a reaction mixture containing saintopin and topoisomerase I or II with either elevated temperature (65 degrees C) or higher salt concentration (0.5 M NaCl) resulted in a substantial reduction in DNA cleavage, suggesting that the topoisomerase I and II mediated DNA cleavage induced by saintopin is through the mechanism of stabilizing the reversible enzyme-DNA "cleavable complex". Consistent with the cleavable complex formation with both topoisomerases, saintopin inhibited catalytic activities of both topoisomerase I and topoisomerase II. The DNA cleavage intensity pattern induced by saintopin with topoisomerase I was different from that by camptothecin. A difference in cleavage pattern was also detected between saintopin and m-AMSA or VP-16 in topoisomerase II mediated DNA cleavage. DNA unwinding assay using T4 DNA ligase showed that saintopin is a weak DNA intercalator like m-AMSA. Thus, saintopin represents a new class of antitumor agent that can induce both mammalian DNA topoisomerase I and mammalian DNA topisomerase II mediated DNA cleavage.
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PMID:Induction of mammalian DNA topoisomerase I and II mediated DNA cleavage by saintopin, a new antitumor agent from fungus. 164 1

Exposure of promyelocytic leukemic HL-60 cells to 3-60 nM of the DNA topoisomerase I inhibitor camptothecin (CAM) or to 30-450 nM and 0.12-1.5 microM of DNA topoisomerase II inhibitors teniposide (TN) and 4-(9-acridynylamino)-3-methanesulfon-m-anisidide (m-AMSA), respectively, resulted in two distinct kinetic effects: (1) the cells entered S phase but the rate of DNA replication was reduced in proportion to the inhibitor concentration; (2) the transition from G2 to M was impaired, approximately 1 h after addition of the inhibitor. As a consequence, the cells accumulated in the S (preferentially in early S) and in G2 phases of the cell cycle. Whereas CAM was more efficient in suppressing cell progression through S phase, TN and m-AMSA were more potent G2 blockers. At these low inhibitor concentrations no signs of immediate cytotoxicity or DNA degradation were apparent. However, above 145 nM of CAM, 900 nM of TN, or 2 microM of m-AMSA extensive DNA degradation in nuclei of S phase cells was evident within 6 h of addition of the inhibitor, resulting in the loss of S and G2 + M cells from these cultures. The data indicate that depending on concentration, mechanisms mediating the cytostatic/cytotoxic activity of both DNA topoisomerase I and II inhibitors may be quite different. Suppression of the DNA replication and the G2 to M transition, seen at low inhibitor concentrations, is compatible with the assumption that the inhibitor-induced stabilization of the topoisomerase-DNA cleavable complexes interferes with DNA replication and chromosome condensation/segregation, respectively. Above the threshold concentration for each inhibitor, an endonucleolytic activity is triggered, resulting in rapid DNA degradation in nuclei of S and G2 phase cells. The endonucleolytic effect is not only cell cycle phase-specific but is also modulated by tissue-specific factors because it cannot be observed, e.g., in the lymphocytic leukemic cell lines.
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PMID:The concentration-dependent diversity of effects of DNA topoisomerase I and II inhibitors on the cell cycle of HL-60 cells. 164 59

Topoisomerase II is now viewed as an important cellular target of antitumor drugs including both DNA intercalators (m-AMSA, ellipticine and Adriamycin) and the nonintercalator epipodophyllotoxin derivatives (VP-16 and VM-26). Topoisomerase I is also shown to be the cellular target of camptotecin. These drugs targeting topoisomerase have been used to establish a relationship between drug-induced cleavable complex formation and cytotoxicity. Mechanistically oriented screening based on the identification of these chemotherapeutic targets have identified a number of antitumor agents that induce topoisomerases mediated DNA cleavage. The new antitumor drugs targeting topoisomerases are reviewed.
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PMID:[Antitumor agents targeting mammalian topoisomerases]. 165 81

The nuclear matrix of eukaryotic cells comprises a dynamic framework on which DNA is organized into discrete functional units of replication and transcription. There is growing evidence that matrix-associated DNA and proteins are direct targets of a wide range of clinically active anticancer agents. DNA associated with matrix-bound replication and transcription sites has a relatively open conformation and is preferentially damaged by ionizing radiation and certain alkylating agents. Fludarabine phosphate, a purine antimetabolite, inhibits DNA replication by blocking the synthesis of matrix-associated primer RNA and RNA-primed Okazaki fragments. VM-26 and m-AMSA appear to interact specifically with nuclear matrix topoisomerase II, and one mechanism of cellular resistance to these agents is associated with depletion of the matrix enzyme. Studies of the interactions of anticancer agents with targets in the nuclear matrix should provide further insight into the mechanisms by which these agents exert their therapeutic effects.
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PMID:Nuclear matrix targets for anticancer agents. 165 99


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