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

---

Query: EC:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Very low concentrations of paclitaxel, a clinically active anticancer agent isolated from the bark of the Pacific yew tree, were found to produce micronuclei in human colon carcinoma cells, suggesting inhibition of mitotic spindle assembly or function. The possibility that paclitaxel acts at the level of the mitotic spindle was investigated by evaluating its ability to inhibit the progression of mitotic cells to G1 phase. Paclitaxel inhibited mitotic progression with a median inhibitory concentration of 4 nM, a concentration equivalent to the median cytotoxic concentration, without arresting cells in mitosis. A direct correlation was shown to exist between the cytotoxic potency and ability to inhibit mitotic progression for analogues of paclitaxel and antimicrotubule agents but not for the topoisomerase II-active agents etoposide and teniposide. After release from the nocodazole block, cells synchronized in mitosis remained sensitive to very low concentrations of paclitaxel for < 30 min, the time required for spindle formation, yet remained sensitive to vinblastine for > 90 min. This result indicates that very low concentrations of paclitaxel inhibit formation of mitotic spindles in cells without affecting function of preformed spindles and without arresting cells in mitosis. Continuous exposure to low nanomolar concentrations of paclitaxel for more than one cell cycle resulted in cells with DNA contents > 4C and as much as 8C. These results support a hypothesis, that, by not being capable of segregating sister chromatids, paclitaxel-treated cells eventually reform nuclear membranes around individual or clusters of chromosomes, revert to G1 phase cells containing 4C DNA, and enter S phase, resulting in cells with as much as 8C DNA content. It is proposed that this is the primary cytotoxic mechanism of paclitaxel.
...
PMID:Paclitaxel inhibits progression of mitotic cells to G1 phase by interference with spindle formation without affecting other microtubule functions during anaphase and telephase. 791 75

Studies were done to determine (a) the subcellular distribution of the alpha (170 kDa) and beta (180 kDa) isozymes of topoisomerase II, and (b) the extent to which each isozyme forms complexes with DNA in tumor cells incubated with and without VM-26. Western blotting revealed that topoisomerase II beta was highly unstable during cell fractionation. However, preincubation of human CEM leukemia cells with 5-100 microM VM-26 for 30 min protected the beta isozyme from degradation by progressively increasing the amount of this isoform bound to DNA. The amount of topoisomerase II beta detected in nuclei of CEM cells incubated for 30 min with 25 microM VM-26 was 7-fold greater than in nuclei from untreated control cells. VM-26 also had a protective effect on topoisomerase II beta in HL-60 leukemia and WiDR colon carcinoma cells. In contrast, the intercalating agents mitoxantrone and m-AMSA did not protect topoisomerase II beta from degradation during cell fractionation. The stabilization of topoisomerase II beta by VM-26 allowed subsequent studies of the subcellular distribution of the topoisomerase II isozymes. Both isozymes were detected in the nonmatrix (high salt-soluble) fraction of nuclei from CEM cells, but only topoisomerase II alpha was present in the nuclear matrix. VM-26 stabilized binding of the alpha and beta topoisomerase II isoenzymes to nonmatrix DNA and topoisomerase II alpha to matrix DNA. The differences observed in the subnuclear distribution and DNA binding pattern of the topoisomerase II isozymes support the hypotheses that each isozyme has a distinct cellular function, and that both the alpha and beta isozymes are potential targets for VM-26 in intact cells. In addition, the results demonstrated that pretreatment of various cell lines with VM-26 is a useful way to stabilize topoisomerase II beta during cell fractionation.
...
PMID:Subcellular distribution of the alpha and beta topoisomerase II-DNA complexes stabilized by VM-26. 798 Jun 48

Previous reports from this laboratory have demonstrated that novobiocin produces supraadditive cytotoxicity and increases the formation of drug-stabilized topoisomerase II-DNA covalent complexes in WEHI-3B myelomonocytic leukemia and A549 lung carcinoma cells when combined with etoposide (VP-16). Inhibition of the efflux of VP-16 by novobiocin is responsible for the increase in VP-16 accumulation, which in turn leads to increased formation of VP-16-stabilized topoisomerase II-DNA covalent complexes and increased cytotoxicity. We now report that novobiocin synergistically enhanced the sensitivity of the multidrug resistant variants, WEHI-3B/NOVO and A549(VP)28, to VP-16, causing almost complete reversal of the resistance to the epipodophyllotoxin. These two tumor cell variants are resistant to several topoisomerase II-targeted drugs, particularly VP-16, but not to Vinca alkaloids; this finding corresponds to the fact that they do not overexpress the P-glycoprotein. The effects of novobiocin in these resistant sublines are mediated through the intracellular accumulation of VP-16, resulting in an increase in the formation of lethal VP-16-induced topoisomerase II-DNA covalent complexes. In the P-glycoprotein expressing multidrug resistant HCT116(VM)34 colon carcinoma and L1210/VMDRC0.06 leukemia cell lines, the latter being transfected with the human mdr-1 gene, novobiocin did not potentiate the cytotoxic activity of VP-16 nor increase the intracellular accumulation of VP-16 and the formation of covalent complexes, whereas their normal counterparts were sensitive to the potentiating activity of novobiocin when used in combination with VP-16. These results indicate that the action of novobiocin on the intracellular transport of VP-16 is not directed at the level of the P-glycoprotein, but that the action of novobiocin is antagonized by the presence of the P-glycoprotein. Since novobiocin is a clinically available antibiotic, has numerous structural analogues available for comparative studies, and has a relatively low toxicity profile, this drug, as well as structurally related agents, would appear to have significant clinical potential in combination with an epipodophyllotoxin for the treatment of non-P-glycoprotein expressing multidrug resistant tumors.
...
PMID:Reversal of etoposide resistance in non-P-glycoprotein expressing multidrug resistant tumor cell lines by novobiocin. 810 48

The cytotoxicity of a class of compounds related to the topoisomerase-II poison amsacrine was investigated against plateau-phase murine Lewis lung carcinoma cells (LLTC), HCT-8 human colon carcinoma cells and other cell lines. Methyl N-[4-(9-acridinylamino)-2-methoxy-phenyl]carbamate hydrochloride and the corresponding demethoxy compound, which contain a methylcarbamate instead of the methylsulphonylamino group, manifested relatively high cytotoxic activity against plateau-phase cells as measured by clonogenic survival. The concentration of drug required for a given cytotoxic effect on plateau-phase cells was about 2 times higher than that required for an equitoxic effect on actively proliferating cells. In contrast, at least 5 times more amsacrine, doxorubicin or etoposide was needed for an equitoxic effect on plateau-phase cells. Cells taken directly from subcutaneous LLTC tumours and exposed to drugs displayed the same differential drug sensitivity to the carbamate compounds, suggesting that the plateau-phase cells provide an appropriate model for cells growing in vivo. The greater cytotoxicity of the carbamate drugs was shown to depend critically on the provision of an energy source such as glucose, suggesting that nutrient starvation both in plateau-phase cells and in tumours induced a glucose-sensitive resistance mechanism. It is suggested that the carbamate analogues of amsacrine recognize a form of topoisomerase II, possibly topoisomerase II beta, the activity of which increases relative to that of topoisomerase II alpha in non-cycling cells, and might be used to devise new strategies for the treatment of solid tumours.
...
PMID:Novel carbamate analogues of amsacrine with activity against non-cycling murine and human tumour cells. 819 67

The makaluvamines were isolated from a sponge of the genus Zyzzya by following bioactivity against the human colon carcinoma cell line, HCT 116. These compounds have considerable cytotoxic activity. The makaluvamines appear to be acting through inhibition of DNA topoisomerase II. The compounds show enhanced toxicity toward a topoisomerase II-cleavable complex-sensitive cell line, they inhibit topoisomerase II decatenation of kinetoplast DNA in vitro. Makaluvamine C was shown to produce protein-linked DNA double-strand breaks, and makaluvamine A produced DNA double-strand breaks by neutral filter elution in a dose-dependent fashion similar to 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA). The makaluvamines also increased the life span of nude mice bearing solid tumors of human ovarian cancer cells.
...
PMID:Makaluvamines, marine natural products, are active anti-cancer agents and DNA topo II inhibitors. 825 Oct 41

We used human tumor cell lines from the National Cancer Institute's In Vitro Antineoplastic Drug Screen to assess whether sensitivity to any of the approximately 45,000 compounds tested previously correlated with the presence of a ras oncogene. Among these cell lines, the mutations in Ki-ras2 clustered in non-small cell lung and colon carcinoma subpanels, and five of the six leukemia lines contained mutations in either N-ras or Ki-ras2. These analyses revealed a striking correlation with 1-beta-D-arabinofuranosylcytosine (Ara-C) and 2,2'-O-cyclocytidine sensitivity in the cell lines harboring ras mutations compared to the tumor lines with wild-type ras alleles. Strong correlations were also found with topoisomerase (topo) II inhibitors, especially 3'-hydroxydaunorubicin and an olivacine derivative. These differential sensitivities persisted in an additional 22 non-small cell lung carcinoma lines (ras mutations, n = 12 and wild-type ras, n = 10). Thus, the association with Ara-C sensitivity was greatest while topo II inhibitors showed a lower, but significant, correlation. These results suggest that the ras oncogene may play a determinant role in rendering tumor cells sensitive to deoxycytidine analogues and topo II inhibitors.
...
PMID:Enhanced sensitivity to 1-beta-D-arabinofuranosylcytosine and topoisomerase II inhibitors in tumor cell lines harboring activated ras oncogenes. 891 59

Irinotecan, a DNA-topoisomerase-I inhibitor, is active against metastatic colon carcinoma. We investigated the effects of irinotecan and 5FU combinations in human colon-carcinoma cell line HT-29, both in vitro and in vivo. Cytotoxicity of 24-hr exposure was evaluated by SRB technique and the nature of interactions were determined by median-effect analysis. Strong synergism between irinotecan and 5FU was observed after sequential exposure, and only additivity after simultaneous exposure. At 50% level of kill, the mean sums of fractional effects were 0.13 +/- 0.05 and 0.18 +/- 0.02 respectively for the 2 sequential schedules, indicating that the combined amount of the 2 drugs necessary to kill 50% cells was only 0.18 and 0.13 times respectively, as much as would be required if they demonstrated purely additive behavior. In nude-mice xenografts, schedule-dependent toxicity was observed: the schedule in which irinotecan was administered i.v. 6 hours before 5FU was the most toxic. Higher anti-tumoral activity was noted when 20 mg/kg/day of each drug was administered sequentially (a delay of 6 hr between the 2 drugs) to mice over 5 days, in comparison with simultaneous administration. In vivo data confirmed those obtained in vitro in the same human colon-cancer model. These results suggest that irinotecan and 5FU combinations are of clinical interest and that the schedule of administration is a critical parameter for chemotherapeutic efficacy.
...
PMID:Sequence-dependent activity of the irinotecan-5FU combination in human colon-cancer model HT-29 in vitro and in vivo. 939 54

Caspases are aspartate-specific cysteine proteases that play a pivotal role in drug-induced cell death. We designed RT-PCR assays to analyse the expression of CASP-3, CASP-4, CASP-6 and the long and short isoforms of CASP-2 genes in human cells. These genes heterogeneously coexpress in leukemic cell lines and bone marrow samples from patients with de novo acute myelogenous leukemia at diagnosis. Treatment of U937 and HL60 leukemic cells and HT29 colon carcinoma cells with the topoisomerase II inhibitor etoposide upregulates CASP-2 and CASP-3 genes in these cells before inducing their apoptosis. This effect of etoposide is not observed in K562 cells and bcl-2-transfected U937 cells which are less sensitive to drug-induced apoptosis. Nuclear run-on experiments demonstrate that etoposide increases CASP gene transcription in U937 cells, an effect that is prevented by Bcl-2 overexpression. Upregulation of CASP genes is associated with an enhanced synthesis of related procaspases that precedes the appearance of apoptosis markers including caspase-3 activation, poly(ADP-ribose) polymerase cleavage and internucleosomal DNA fragmentation. These results suggest that the ability of tumor cells to upregulate CASP-2 and CASP-3 genes in response to cytotoxic drugs could be predictive of their sensitivity to drug-induced apoptosis.
...
PMID:Upregulation of CASP genes in human tumor cells undergoing etoposide-induced apoptosis. 967 9

In this study, simultaneous administration of certain inhibitors of topoisomerase I and topoisomerase II produced synergistic cytotoxicity in a series of human glioma cell lines. Camptothecin (CPT) and etoposide (VP-16) produced combination indices (CI) <1.0 in all glioma cell lines tested, including those that were relatively resistant to the two topoisomerase inhibitors individually. In contrast, CPT and VP-16 produced additive cytotoxicity in HT-29 and SW-620 colon carcinoma cell lines. To explore the molecular basis for synergy in glioma cells, we focused on one glioma cell line (U87) in which even sub-cytotoxic doses of CPT potentiated the action of VP-16. Except for genistein (a topo II agent with tyrosine kinase inhibitory function), all topo II inhibitors tested (doxorubicin, ellipticine, and m-AMSA) were synergistic with CPT. While CPT and VP-16 produced cytotoxicity and protein-linked DNA breaks (PLDB) that were supra-additive in U87 glioma cells, CPT and genistein produced additive results. Pretreatment of U87 cells with the tyrosine kinase inhibitor tyrphostin-A23 or the tyrosine phosphatase activator O-phospho-L-tyrosine (OPLT) reduced combination PLDB from synergistic to additive levels, but had no effect on the formation of PLDB induced by either CPT or VP-16 alone. CPT and VP-16 also produced a synergistic accumulation of sub-G0 (apoptotic) cells which was blocked by tyrphostin-A23. No significant increase in topoisomerase protein levels could be detected in response to combination treatment. Thus, synergistic effects between topoisomerase I and topoisomerase II inhibitors in U87 glioma cells may depend upon phosphorylation of cellular proteins other than the topoisomerases themselves.
...
PMID:Synergistic cytotoxicity, apoptosis and protein-linked DNA breakage by etoposide and camptothecin in human U87 glioma cells: dependence on tyrosine phosphorylation. 1035 42

C1311 is a novel therapeutic agent with potent activity against experimental colorectal cancer that has been selected for entry into clinical trial. The compound has previously been shown to have DNA-binding properties and to inhibit the catalytic activity of topoisomerase II. In this study, cellular uptake and mechanisms by which C1311 interacts with DNA and exerts cytotoxic effects in intact colon carcinoma cells were investigated. The HT29 colon cancer cell line was chosen to follow cellular distribution of C1311 over a time course of 24 h at drug concentrations that just inhibited cell proliferation by 50% or 100%. Nuclear uptake of C1311 and co-localization with lysosomal or mitochondrial dyes was examined by fluorescence microscopy and effects on these cellular compartments were determined by measurement of acid phosphatase levels, rhodamine 123 release or DNA-binding behaviour. The strength and mode of DNA binding was established by thermal melting stabilization, direct titration and viscometric studies of host duplex length. The onset of apoptosis was followed using a TUNEL assay and DNA-fragmentation to determine a causal relationship of cell death. Growth inhibition of HT29 cells by C1311 was concomitant with rapid drug accumulation in nuclei and in this context we showed that the compound binds to duplex DNA by intercalation, with likely A/T sequence-preferential binding. Drug uptake was also seen in lysosomes, leading to lysosomal rupture and a marked increase of acid phosphatase activity 8 h after exposure to C1311 concentrations that effect total growth inhibition. Moreover, at these concentrations lysosomal swelling and breakdown preceded apoptosis, which was not evident up to 24 h after exposure to drug. Thus, the lysosomotropic effect of C1311 appears to be a novel feature of this anticancer agent. As it is unlikely that C1311-induced DNA damage alone would be sufficient for cytotoxic activity, lysosomal rupture may be a critical component for therapeutic efficacy.
...
PMID:Cellular uptake, cytotoxicity and DNA-binding studies of the novel imidazoacridinone antineoplastic agent C1311. 1049 67


<< Previous 1 2 3 4 5 6 Next >>

---