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)

To search for possible synergy between topoisomerase (topo) II-directed chemotherapeutic agents and topo I-directed agents, IL-60 human progranulocytic leukemia cells were incubated with etoposide in the absence or presence of camptothecin (CPT). Treatment of HL-60 cells for 1 h with 15-20 microM etoposide resulted in the death of 99-99.9% of the cells as assessed by colony formation in soft agar. Unexpectedly, simultaneous incubation with 1 microM CPT increased the survival of etoposide-treated cells as much as 30-fold. Inhibition of etoposide cytotoxicity was observed at CPT concentrations as low as 0.01 microM and was one-half maximal at 0.1 microM. CPT also antagonized the cytotoxicity of 4'-(9-acridinylamino)methanesulfon-M-anisidide and daunorubicin, two structurally unrelated topo II-directed agents. Topotecan, a CPT analogue currently undergoing Phase I clinical trials, had a similar effect. Studies using an alkaline unwinding assay (to measure DNA strand breaks) and Western blotting (to assess formation of covalent adducts involving topo II) revealed that CPT did not alter the ability of etoposide to stabilize topo II-DNA adducts. CPT is a potent inhibitor of both DNA and RNA synthesis. To further assess the mechanism by which CPT diminished the cytotoxicity of topo II-directed agents, inhibitors of DNA synthesis or RNA synthesis were substituted for CPT. Aphidicolin, an inhibitor of replicative DNA polymerases, enhanced the survival of etoposide-treated HL-60 cells less than 3-fold. In contrast, inhibitors of RNA synthesis (cordycepin or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole) enhanced the survival of etoposide-treated HL-60 cells as much as 20-fold. The potential biological and therapeutic implications of these results are discussed.
Cancer Res 1991 Feb 15
PMID:Antagonism between camptothecin and topoisomerase II-directed chemotherapeutic agents in a human leukemia cell line. 170 67

A differentiation inducer butyrate and a tumor promoter teleocidin had inhibitory effects on the proliferation of PLC/PRF/5 hepatoma. Both of these reagents stimulated the production of procollagen type III peptide, enhanced the cytokeratin assembly and altered the morphological appearance. Novobiocin, a topoisomerase II inhibitor, enhanced the cytokeratin assembly induced by butyrate but antagonized that induced by teleocidin without changing the expression and the phosphorylation state of cytokeratin proteins. In addition, novobiocin acted synergistically with butyrate but not with teleocidin in stimulating the procollagen production and the acetate uptake. These results suggest that butyrate and teleocidin induce cell differentiation via distinct signaling pathway and that novobiocin and butyrate can be used as subsidiary drugs in preventing the growth of hepatoma.
Cancer Lett 1991 Oct
PMID:Novobiocin modulates cytokeratin assembly and differentiation of human hepatoma cells induced by butyrate and teleocidin. 171 36

The cyanomorpholino derivative of doxorubicin (MRA-CN) is a DNA intercalator and alkylator that is a highly potent cytotoxin, non-cross-resistant in multidrug-resistant cells, and noncardiotoxic in comparison with doxorubicin. To further examine mechanisms of action and resistance to MRA-CN, a cell line resistant to MRA-CN, ES-2R, was established by growing a human ovarian carcinoma cell line, ES-2, in increasing concentrations of the drug. The resistant subline was 4-fold resistant to MRA-CN and cross-resistant to other DNA cross-linking agents, cisplatin (7-fold) and carmustine (3-fold), as well as to the DNA strand-breaking agents etoposide (6-fold), doxorubicin (2-fold), bleomycin (5-fold), and ionizing radiation (2-fold). In contrast, ES-2R cells were not cross-resistant to vinblastine. Several months of additional growth of ES-2R cells in MRA-CN did not yield higher, stable levels of drug resistance. A low level of P-glycoprotein was detectable in the ES-2R cells. However, the extent of intracellular accumulation of [3H]MRA-CN by this resistant cell line was identical to that of the sensitive line. The number of DNA cross-links formed by cisplatin in ES-2R was only 50% of that of the ES-2 cells and was associated with a 50% increase in the rate of repair of these cross-links in the resistant cells. Ionizing radiation induced similar amounts of single- and double-strand breaks in the ES-2 line as well as in the ES-2R cells. There was no apparent difference between the two cell lines in the rate and extent of repair of these DNA breaks. Thus, enhanced DNA repair cannot explain the phenomenon of cross-resistance to radiation. Comparisons of glutathione (GSH) content and the enzymes involved in GSH homeostasis showed significant differences. Resistant cells contained 1.5-fold more GSH, a 2.2-fold increase in gamma-glutamyltranspeptidase activity, and a 2.4-fold increase in GSH reductase compared with ES-2 cells (all P less than 0.05). Total glutathione-S-transferase (GST) activity was 2.6-fold higher (P less than 0.01) in the ES-2R line. The pi-class GST subunit by Western blotting and GST activity toward ethacrynic acid were increased 2-fold in the resistant cells. Depletion of GSH levels in ES-2R cells by buthionine sulfoximine restored the sensitivity of ES-2R to MRA-CN. These findings implicate a role for GSH metabolism in the resistance phenotype of ES-2R cells. We have previously reported that these cells have an increased generation time and decreased topoisomerase II content. Thus, the ES-2R cell line exhibits a complex phenotype of broad cross-resistance, which is likely to involve multiple mechanisms, and includes enhanced DNA repair and increased GSH content and GST activity.
Cancer Res 1991 Oct 01
PMID:Multifactorial mechanisms associated with broad cross-resistance of ovarian carcinoma cells selected by cyanomorpholino doxorubicin. 171 40

Stable acquired resistance to etoposide (VP-16) or teniposide (VM-26) in HCT116 human colon carcinoma cells and A549 human lung adenocarcinoma cells, was previously obtained by weekly 1-h exposures to either drug (B. H. Long, Natl. Cancer Inst. Monogr., 4: 123-127, 1987). The purpose of this study was to identify possible mechanisms of resistance present in these cells by using human mdr1 and topoisomerase II DNA probes, antibodies to these gene products, and P4 phage unknotting assay for topoisomerase II activities. HCT116(VP)35 cells were 9-, 7-, and 6-fold resistant to VP-16, VM-26, and Adriamycin, respectively, and showed no cross-resistance to colchicine and actinomycin D. These cells had no differences in mdr1 gene, mdr1 mRNA, or P-glycoprotein levels but displayed decreased levels of topoisomerase II mRNA and enzyme activity without any alteration of drug sensitivity displayed by the enzyme. HCT116(VM)34 cells were 5-, 7-, and 21-fold resistant to VP-16, VM-26, and Adriamycin; were cross-resistant to colchicine (7-fold) and actinomycin D (18-fold); and possessed a 9-fold increase in mdr1 mRNA and increased P-glycoprotein without evidence of mdr1 gene amplification. No alterations in topoisomerase II gene or mRNA levels, enzyme activity, or drug sensitivity were observed. A549(VP)28 and A549(VM)28 cells were 8-fold resistant to VP-16 and VM-26 and 3-fold resistant to Adriamycin. Both lines were not cross-resistant to colchicine or actinomycin D but were hypersensitive to cis-platinum. No alterations in mdr1 gene, mdr1 mRNA, or P-glycoprotein levels, but lower topoisomerase II mRNA levels and decreased enzyme activities, were observed. Of the four acquired resistant cell lines, resistance is likely related to elevated mdr1 expression in one line and to decreased topoisomerase II expression in the other three lines.
Cancer Res 1991 Oct 01
PMID:Mechanisms of resistance to etoposide and teniposide in acquired resistant human colon and lung carcinoma cell lines. 171 44

The specificities of the DNA repair enzyme O6-alkylguanine-DNA alkyltransferase from brain and liver cells of the chick embryo and of DNase I were demonstrated in vitro by their response to substrate DNA pretreated with monofunctional alkylating agents of different O6-guanine alkylating ability and some antineoplastic agents. Treatment of DNA with ethidium bromide, Hoechst 33258, doxorubicin, Fe2+/bleomycin, and suramin resulted in a dose-dependent diminution of alkyltransferase activity (DE50 approximately 5 micrograms/ml, 15 micrograms/ml, 5 micrograms/ml, 5 micrograms/ml, 100 micrograms/ml, respectively). Apart from bleomycin, comparable results were obtained with DNase I. Thermal denaturation of the substrate DNA reduced both alkyltransferase and DNase I activity. No effect was seen with X-irradiation. Cisplatin decreased only DNase I activity. Some topoisomerase II and/or gyrase inhibitors remained without significant effects on the alkyltransferase reaction whereas DNA catabolism by DNase I was diminished in a dose-dependent manner (DE50 between 6.5 and 19 micrograms/ml).
J Cancer Res Clin Oncol 1991
PMID:Inhibition of O6-alkylguanine-DNA alkyltransferase and DNase I activities in vitro by some alkylating substances and antineoplastic agents. 172 Jul 84

Accumulation of gadd153 mRNA is strongly stimulated in mammalian cells by treatments which arrest growth or damage DNA (A. J. Fornace, Jr. et al., Mol. Cell. Biol., 9: 4196-4203, 1989). In previous studies, we demonstrated that the increased expression of gadd153 following treatment with several DNA-damaging agents was mediated transcriptionally (J. D. Luethy et al., J. Biol. Chem., 265: 16521-16526, 1990). To better define the specificity of this response, we have established a sensitive reporter system in which we have stably integrated a chimeric gene containing the gadd153 promoter linked to the coding region of the chloramphenicol acetyltransferase (CAT) gene into the genome of HeLa cells. Transcriptional activation from the gadd153 promoter was monitored by determining levels of CAT activity in cellular lysates prepared from gadd153CAT/HeLa cells treated with a variety of agents. The gadd153 promoter was strongly activated by a broad spectrum of genotoxic agents including UV-mimetic agents, DNA-cross-linking and alkylating agents, DNA intercalators, and topoisomerase inhibitors. Of the DNA-damaging agents tested, only X-irradiation and bleomycin treatments failed to induce gadd153 promoter activity. Agents which inhibit replication and cell division and agents which otherwise result in cytotoxicity or growth arrest also had little influence on gadd153 promoter activity. Expression of the gadd153CAT chimeric gene in xeroderma pigmentosum Group A cells, which are deficient in nucleotide excision DNA repair of pyrimidine dimers, was maximally induced at UV doses at least 6-fold lower than those required for similar induction in repair-proficient HeLa cells. However, the methyl methanesulfonate-induced gadd153 promoter activities were similar in both cell lines. Novobiocin pretreatment inhibited both UV- and methyl methanesulfonate-induced gadd153CAT expression. Collectively, these data indicate that: (a) the gadd153 promoter is activated rapidly and specifically by DNA damage; (b) the altered DNA structure is the inducing signal for the activation of the signal transduction pathway responsible for enhanced gadd153 expression; and (c) regulation of gadd153 by growth arrest is distinct from that of DNA damage. Thus, the gadd153CAT/HeLa cells are a useful model for examining the molecular mechanisms associated with the response to DNA damage and provide a reporter system for the screening of potential genotoxic agents.
Cancer Res 1992 Jan 01
PMID:Activation of the gadd153 promoter by genotoxic agents: a rapid and specific response to DNA damage. 172 86

Although various anti-cancer drugs have widely differing primary modes of action, the mechanisms of cell death appear similar but are not well understood. To investigate this problem we exposed cultured human leukemic T-lymphoblasts to 1-hr pulse doses of an alkylating agent (mafosfamide) and a topoisomerase II inhibitor (etoposide) that cause delayed cell death. The effects of these drugs on nucleotide content, poly (ADP-ribosyl)ation and DNA strand breakage were assessed. Both drugs caused DNA strand breakage, and although the pattern differed, this seemed to be the major mechanism by which cells were killed. The degree and time course of the NAD and ATP depletion that mafosfamide and etoposide caused were similar. Both drugs caused a nadir in cellular nucleotide levels 2 hr after exposure but between 2 and 6 hr there was a partial recovery. This correlates with the time course of the DNA damage they caused and appeared to result from poly (ADP-ribosyl)ation. Both drugs were shown to cause apoptotic cell death associated with endonucleolytic DNA fragmentation. We suggest that DNA damage, as a primary or secondary effect, associated with poly (ADP-ribosyl)ation and apoptotic cell death may be a common pathway of cytotoxic drug action.
 ...
PMID:DNA damage, poly (ADP-ribosyl)ation and apoptotic cell death as a potential common pathway of cytotoxic drug action. 174 64

In an effort to improve the cytotoxicity of clinically used anticancer alkylating agents, the topoisomerase II inhibitory drugs U73-975 or mitoxantrone were added to cell cultures exposed to CDDP, carboplatin, BCNU, melphalan or thiotepa. In the MCF-7 human breast cancer cell line and in the MCF-7/CP (CDDP resistant) subline, U73-975 and mitoxantrone were both potent cytotoxic agents (IC50 0.002 microM and 0.006 microM for U73-975, respectively and 0.8 microM and 0.1 microM for mitoxantrone, respectively). As evaluated by isobologram analysis, the addition of either U73-975 or mitoxantrone to 1 h exposure to CDDP resulted in greater-than-additive killing in the MCF-7 parent cells. While U73-975 was also greater-than-additive in cytotoxicity with CDDP in the MCF-7/CP line, mitoxantrone and CDDP were only additive in cytotoxicity in these cells. In the case of carboplatin, the addition of U73-975 or mitoxantrone to treatment with the drug resulted in greater-than-additive cell killing in the MCF-7 parental cell line but in the MCF-7/CP cell line these combinations were only additive in cell killing. Addition of U73-975 to treatment with BCNU resulted in only additive cytotoxicity in both cell lines; however, the combination of mitoxantrone with BCNU resulted in greater-than-additive cell killing in both the parental and CDDP resistant cell lines. When either U73-975 or mitoxantrone was added to treatment with melphalan greater-than-additive cytotoxicity resulted in both cell lines except at low melphalan concentrations in the MCF-7/CP cell line. Finally, the addition of either modulator to treatment with thiotepa in the MCF-7 cell line produced variable interactions depending on thiotepa concentration, but in the MCF-7/CP cell line either modulator in combination with thiotepa caused greater-than-additive cell killing. These results indicate that the addition of topoisomerase II inhibitory drugs may substantially increase the cytotoxicity of some alkylating agents. In vivo experiments are necessary, however, to ascertain whether a therapeutic gain is achievable.
Cancer Lett 1991 Dec 09
PMID:Combination of the minor groove-binder U73-975 or the intercalator mitoxantrone with antitumor alkylating agents in MCF-7 or MCF-7/CP cells. 176 99

Etoposide is a phase-specific, schedule-dependent derivative of podophyllotoxin that appears to act by inhibiting DNA-topoisomerase II. Early preclinical work demonstrated sharp activity in mouse leukemias and possible synergy with cisplatin. As a single agent (either orally or intravenously), it demonstrated limited benefit in non-small cell lung cancer (NSCLC), with response rates around 10%. In combination with cisplatin, it has become a mainstay of chemotherapeutic efforts, either as primary therapy or in conjunction with radiation. Response rates in advanced disease average around 30%, climbing to more than 50% in patients with Stage IIIA or IIIB disease. More recent work suggests that the issue of the true synergy of etoposide with cisplatin in NSCLC needs reassessment. The relative roles of etoposide and cisplatin in the combination are unclear, as several studies conflict. Pharmacokinetic data suggest that multiple daily fractions of etoposide are superior to prolonged infusions, warranting several future trials. The current major role for etoposide plus cisplatin would appear to be in multimodality therapy where the combination can be readily combined with radiation and/or surgery. Several other agents have been studied with etoposide or etoposide plus cisplatin (mitomycin, vindesine, doxorubicin, cyclophosphamide, ifosfamide, and carboplatin), but it is unclear whether the addition of any of them offers any response or survival advantage.
Cancer 1991 Jan 01
PMID:Etoposide in the management of non-small cell lung cancer. 184 48

Inherited susceptibility to a wide variety of neoplasias (Li-Fraumeni syndrome), has been shown in studies of one cancer-prone family, to have an intriguing association with an aberrant c-raf-1 gene and inheritance of a radioresistant phenotype in their non-cancerous skin fibroblasts. This association together with observations that DNA topoisomerases, when defective, can introduce errors into DNA and that these enzymes are perturbed in vitro by serine/threonine kinases similar to raf encoded proteins, prompted investigation of DNA topoisomerase activity of the family's fibroblasts. Since radioresistance was transferred to murine cells (NIH-3T3) when the aberrant c-raf-1 gene from this family was transfected, we also examined transformants containing this and other oncogenes. V-raf/c-myc and EJ-ras transformants were examined, the former because the family's skin fibroblasts also have 3-8-fold elevated myc expression (not apparently relevant to radioresistance) and the latter because ras, like raf, conveys radioresistance. The family members' fibroblasts and the three transfected murine lines, showed a similar perturbation of a spermidine and ATP-dependent DNA catenation activity (typical of DNA topoisomerase II). There was a significant positive correlation (r = 0.93; P = 0.0026) between the degree of activation of topoisomerase II and one measure of radioresistance (the Dq value). Relaxation of DNA supercoiling (topoisomerase I activity and other DNA nicking enzymes) was not abnormal. Cytotoxicity assays and evaluation of the influence of topoisomerase II inhibitors on DNA/protein complex formation, corroborated the existence of a qualitative topoisomerase II defect in the family's cells and transfectants. Although the contention that the qualitative topoisomerase II abnormalities observed here may be associated with malfunction is highly speculative, these findings may be relevant to the mechanism of oncogenesis, not only in this family, but with raf and ras type oncogenes.
Br J Cancer 1991 Jan
PMID:Aberrant DNA topoisomerase II activity, radioresistance and inherited susceptibility to cancer. 184 52


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