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)

Etoposide remains an integral component of therapy for non-small cell lung cancer. Its single-agent activity, and, hence, its activity in combination therapy, need to be reassessed in light of several reports of increased activity at higher doses. Although no effective means of overcoming resistance to etoposide appear to exist, topoisomerase II levels may predict sensitivity to treatment. Biologic response modifiers appear to add little or nothing to standard etoposide chemotherapy for non-small cell lung cancer. Continuous low-dose etoposide infusions do not appear to exhibit the same degree of activity as has been observed with prolonged oral dosing. The availability of effective means of reducing hematologic and emetic side effects of chemotherapy may permit rational trials of more intensive therapy.
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PMID:The role of standard-dose etoposide in the management of non-small cell lung cancer. 133 19

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

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

Etoposide, a podophyllotoxin derivative, has demonstrated antitumor efficacy in a number of human malignancies, including lymphomas, germinal tumors, and lung cancer (especially small cell). Etoposide's antineoplastic activity is achieved through DNA strand breakage, which likely results from the formation of a complex involving drug, DNA, and the DNA unwinding enzyme, topoisomerase II. The drug's steady state volume of distribution ranges from 5 to 17 L/m2, and it is highly bound to plasma protein with an average free plasma fraction of 6%. A number of etoposide metabolites have been confirmed or postulated. Several cell lines have been shown to acquire resistance to etoposide through membrane transport changes. Considerable intrapatient variability exists in pharmacokinetic parameters following intravenous (IV) and oral dosing. Approximately 30% to 40% of unchanged IV drug is excreted in the urine, whereas biliary excretion appears a minor route of drug elimination. The bioavailability of oral etoposide averages 50%, although wide variability exists both among and within different patients. Bioavailability decreases as the dose of oral etoposide is increased. Several recent studies have attempted to correlate etoposide plasma concentrations with toxicity (primarily myelosuppression) in hopes of using this information to optimize drug dosing.
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PMID:Etoposide pharmacology. 149 25

Etoposide (VP16-213), a topoisomerase II inhibitor, has produced complete responses in 17% of previously treated patients with acute nonlymphocytic leukemia (ANLL) but has little activity in acute lymphoblastic leukemia. As salvage therapy for relapsed ANLL etoposide produces 28% complete responses in combination with amsacrine, 49% with 5-azacytidine, and 51% with anthracycline. It has been successfully combined with high-dose cytarabine as a salvage treatment. In a randomized trial in previously untreated patients with ANLL, etoposide significantly prolonged remission duration. Etoposide has been used to intensify postinduction therapy with or without bone marrow rescue, but its exact role in that setting has not been clarified. Because of its schedule dependency in other tumors, etoposide should be investigated using different schedules in ANLL.
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PMID:Etoposide in the treatment of leukemias. 149 26

The antibacterial activities of the fluorinated 4-quinolones (e.g., ciprofloxacin) have been ascribed to a marked inhibition of bacterial DNA gyrase. In contrast, the influence on purified mammalian DNA enzymes, including topoisomerases, has been reported to be several orders of magnitude weaker, occurring at concentrations higher than 100 micrograms of ciprofloxacin per ml. In this study, using a nondenaturing filter elution method, a marked induction of double-strand DNA breaks in human lymphoblastoid cells exposed to 80 micrograms of ciprofloxacin per ml was seen. The proportion of single-strand versus double-strand DNA breaks was similar to that seen with the topoisomerase II inhibitory antitumor agent VP-16. The cellular recovery was more rapid after treatment with ciprofloxacin than after treatment with VP-16, displaying a normal elution profile within 15 min at 37 degrees C (60 min for VP-16). These data indicate that ciprofloxacin has an effect on intracellularly located topoisomerase II in humans.
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PMID:Ciprofloxacin-induced inhibition of topoisomerase II in human lymphoblastoid cells. 164 8

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

Although the stabilization of topoisomerase II cleavable complexes by etoposide (VP-16) has been recognized to be important for cell killing, the lethal events following the formation of cleavable complexes remain to be elucidated. In an attempt to characterize the biochemical requirements for VP-16-induced cytotoxicity, we examined the effects of calcium depletion in Chinese hamster DC3F cells. Four-hour preincubation in calcium-free medium or in complete medium containing 5 mM [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) protected against the cytotoxicity of VP-16. Under these same conditions, the VP-16-induced DNA single-strand break frequency in calcium-depleted cells remained similar to that of control cells. Cell-cycle analysis and thymidine pulse incorporation indicated that calcium depletion did not alter DNA synthesis and cell cycle distribution. Drug-induced cytotoxicity was restored progressively within 4-8 hr after calcium-depleted cells were refed with calcium-containing medium. Calcium depletion also protected against the cytotoxicity of camptothecin, hyperthermia and, to a lesser extent, nitrogen mustard and gamma radiation in DC3F cells. Similar results were obtained in human colon carcinoma HT-29 cells. Our results suggest that topoisomerase II-mediated DNA breaks are only potentially lethal and that calcium-dependent cellular processes are required for the cytotoxicity of topoisomerase inhibitors.
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PMID:Cell death induced by topoisomerase inhibitors. Role of calcium in mammalian cells. 164 24

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

In the accompanying paper (K. Tanabe, Y. Ikegami, R. Ishida, and T. Andoh, Cancer Res., 51: 4903-4908, 1991), we showed that ICRF-154 and -193, dioxopiperazine derivatives, inhibited the activity of purified topoisomerase II, without formation of a cleavable DNA-protein complex. In order to see whether ICRF-154 and ICRF-193 affect cellular topoisomerase II in situ or not, we examined the effect of these drugs on etoposide (VP-16)-induced, topoisomerase II-mediated DNA breaks in RPMI 8402 cells by alkaline sedimentation analysis. When RPMI 8402 cells were exposed to VP-16 in the presence of ICRF-154 or ICRF-193 for 1 h, VP-16-induced DNA strand breaks were greatly inhibited by both ICRF compounds. In parallel with this observation, VP-16-induced growth inhibition was also reversed by ICRF-193. Exposure of cells to ICRF-154 resulted in a progressive accumulation of cells with 4C DNA content. Although mitotic index did not significantly increase, mitotic abnormalities were seen in cells exposed to ICRF-193 or ICRF-154: all mitotic cells exhibited early mitotic figures with fewer condensed and entangled chromosomes. The most sensitive phase of the cell cycle to ICRF-154 was the G2-M. ICRF-154 did not affect the spindle formation. However, abnormally oriented spindles were observed in drug-treated cells in parallel with the appearance of multinucleated cells. The results suggest that ICRF-154 and -193 inhibit topoisomerase II activity in RPMI 8402 cells, and this effect resulted in the appearance of cells in G2 and early M phase with fewer condensed and entangled chromosomes and of cells with multilobed nuclei.
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PMID:Inhibition of intracellular topoisomerase II by antitumor bis(2,6-dioxopiperazine) derivatives: mode of cell growth inhibition distinct from that of cleavable complex-forming type inhibitors. 165 5


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