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)

Ascididemin (ASC) is a pentacyclic DNA-intercalating agent isolated from the Mediterranean ascidian Cystodytes dellechiajei. This marine alkaloid exhibits marked cytotoxic activities against a range of tumor cells, but its mechanism of action remains poorly understood. We investigated the effects of ASC on DNA cleavage by human topoisomerases I and II. Relaxation assays using supercoiled DNA showed that ASC stimulated double-stranded cleavage of DNA by topoisomerase II, but exerted only a very weak effect on topoisomerase I. ASC is a conventional topoisomerase II poison that significantly promoted DNA cleavage, essentially at sites having a C on the 3' side of the cleaved bond (-1 position), as observed with etoposide. The stimulation of DNA cleavage by topoisomerase I in the presence of ASC was considerably weaker than that observed with camptothecin. Cytotoxicity measurements showed that ASC was even less toxic to P388 leukemia cells than to P388CPT5 cells resistant to camptothecin. In addition, the marine alkaloid was found to be equally toxic to HL-60 leukemia cells sensitive or resistant to mitoxantrone. It is therefore unlikely that topoisomerases are the main cellular targets for ASC. This alkaloid was found to strongly induce apoptosis in HL-60 and P388 leukemia cells. Cell cycle analysis showed that ASC treatment was associated with a loss of cells in the G1 phase accompanied with a large increase in the sub-G1 region. Cleavage experiments with poly(ADP-ribose) polymerase (PARP) revealed that caspase-3 was a mediator of the apoptotic pathway induced by ASC. The DNA of ASC-treated cells was severely fragmented. Collectively, these findings indicate that ASC is a potent inducer of apoptosis in leukemia cells.
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PMID:Inhibition of topoisomerase II by the marine alkaloid ascididemin and induction of apoptosis in leukemia cells. 1087 27

The potent novel poly(ADP-ribose) polymerase (PARP) inhibitor, NU1025, enhances the cytotoxicity of DNA-methylating agents and ionizing radiation by inhibiting DNA repair. We report here an investigation of the role of PARP in the cellular responses to inhibitors of topoisomerase I and II using NU1025. The cytotoxicity of the topoisomerase I inhibitor, camptothecin, was increased 2.6-fold in L1210 cells by co-incubation with NU1025. Camptothecin-induced DNA strand breaks were also increased 2.5-fold by NU1025 and exposure to camptothecin-activated PARP. In contrast, NU1025 did not increase the DNA strand breakage or cytotoxicity caused by the topoisomerase II inhibitor etoposide. Exposure to etoposide did not activate PARP even at concentrations that caused significant levels of apoptosis. Taken together, these data suggest that potentiation of camptothecin cytotoxicity by NU1025 is a direct result of increased DNA strand breakage, and that activation of PARP by camptothecin-induced DNA damage contributes to its repair and consequently cell survival. However, in L1210 cells at least, it would appear that PARP is not involved in the cellular response to etoposide-mediated DNA damage. On the basis of these data, PARP inhibitors may be potentially useful in combination with topoisomerase I inhibitor anticancer chemotherapy.
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PMID:Differential effects of the poly (ADP-ribose) polymerase (PARP) inhibitor NU1025 on topoisomerase I and II inhibitor cytotoxicity in L1210 cells in vitro. 1113 22

Staurosporine, a protein kinase and etoposide, a topoisomerase II inhibitor, are known to enhance apoptosis. The differential effects of these agents on T98G glioblastoma and SK-N-SH neuroblastoma, cell lines both derived from human tumors, have not been determined. We assessed cellular viability, DNA fragmentation and laddering, chromatin condensation, and Poly(ADP-ribose) polymerase (PARP) cleavage induced by these agents at a series of concentrations and times. In addition, to gain an understanding of the mechanism by which these agents work, we measured Protein Kinase C (PKC) activity. Staurosporine induced significant alterations in all apoptotic parameters tested in both cell lines. Etoposide induced apoptotic alterations similar to those caused by staurosporine in neuroblastoma but produced no detectable apoptotic changes in glioblastoma cells. Etoposide induced membrane but not cytosolic PKC activity in neuroblastoma but had no effect on PKC activity in glioblastoma. Our results show that the induction of apoptosis is cell type dependent. PKC activity appears to be crucial in the initiation of apoptosis.
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PMID:Differential responses of human neuroblastoma and glioblastoma to apoptosis. 1145 93

The cytokine hepatocyte growth factor/scatter factor (HGF/SF) has been found to protect a variety of epithelial and cancer cell types against cytotoxicity and apoptosis induced by DNA damage, but the specific apoptotic signaling events and the levels at which they are blocked by HGF/SF have not been identified. We found that treatment of MDA-MB-453 human breast cancer cells with adriamycin (also known as doxorubicin, a DNA topoisomerase IIalpha inhibitor) induced a series of time-dependent events, including the mitochondrial release of cytochrome c and apoptosis-inducing factor, mitochondrial membrane depolarization, activation of a set of caspases (caspase-9, -3, -7, -2, and -8), cleavage of poly(ADP-ribose) polymerase (PARP), and up-regulation of expression of the Fas ligand. All of these events were blocked by preincubation of the cells with HGF/SF. In contrast, the pan-caspase inhibitor benzyloxycarbonyl-VAD-fluoromethylketone blocked some of these events (e.g. caspase-3 activation and PARP cleavage) but did not block cytochrome c release or mitochondrial depolarization. These findings suggest that HGF/SF functions, in part, upstream of the mitochondria to block mitochondrial apoptosis signaling, prevent activation of multiple caspases, and protect breast cancer cells against apoptosis.
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PMID:Hepatocyte growth factor/scatter factor blocks the mitochondrial pathway of apoptosis signaling in breast cancer cells. 1157 Dec 97

The human monoclonal antibody SC-1 was isolated from a patient with a diffuse-type adenocarcinoma of the stomach using somatic cell hybridization. The immunoglobulin (Ig)M antibody reacts specifically with diffuse- (70%) and intestinal-type (25%) gastric adenocarcinoma and induces apoptosis in vitro and in vivo. When used in clinical trials with stomach carcinoma patients, significant apoptotic and regressive effects in primary tumors have been observed with the antibody SC-1. The SC-1 receptor is a new 82 kd membrane-bound isoform of glycosylphosphatidylinositol (GPI)-linked CD55 (decay-accelerating factor, DAF). CD55 is known to protect cells from lysis through autologous complement and is coexpressed with the ubiquitously distributed 70 kd isoform. The SC-1-specific CD55 isoform is up-regulated shortly after antibody binding, followed by an internalization of the antibody/receptor-complex, whereas the membranous expression of wild-type CD55 remains unchanged. The apoptotic process is marked by cleavage of cytokeratin 18, indicating the involvement of caspase-6 in the apoptotic process. In contrast to other apoptotic pathways, a cleavage of poly(ADP-ribose)polymerase (PARP) is not observed. The expression of the cell-cycle regulator c-myc becomes up-regulated, whereas expression of topoisomerase IIalpha is down-regulated. Induction of apoptosis leads to an increase in the internal Ca(2+) concentration, which is not necessary for the apoptotic process but for the transport of newly synthesized SC-1-specific CD55 isoform to the membrane.
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PMID:Regulation of the new coexpressed CD55 (decay-accelerating factor) receptor on stomach carcinoma cells involved in antibody SC-1-induced apoptosis. 1170 63

XK469, a synthetic quinoxaline phenoxypropionic acid derivative, has been found to have selective activity against a broad panel of solid tumors including several drug-resistant cell lines and has been approved for phase I clinical evaluation. Recent studies suggested that XK469 is a selective topoisomerase IIbeta inhibitor, but the mechanism of XK469-induced cell death remains unknown. Here we investigate the ability of XK469 to induce apoptosis of human cancer cells. In the human ovarian cancer cell line PA1, XK469 caused the release of cytochrome c, activation of caspases including caspases 9, 7 and 3, cleavage of PARP, and subsequently cell death. Moreover, Bcl2 and Bax were cleaved in XK469 treated cells. PA1 cells expressing the dominant negative-caspase 9 were less sensitive to XK469. Importantly, in these PA1 cells expressing DN-casp 9, the activation of caspases including caspases 3, 7 and 9, and cleavage of Bax and Bcl2 were inhibited, suggesting that the activation of the mitochondrial pathway is required for XK469-induced anticancer activity. These results indicate that the induction of apoptosis by XK469 may account for its anti-tumor activity and such activity is required for the activation of the mitochondrial pathway. Thus, our study defines a possible mechanism, at least in part, underlying XK469-induced anti-cancer activity.
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PMID:Induction of apoptosis by the new anticancer drug XK469 in human ovarian cancer cell lines. 1208 31

The role of DNA topoisomerase (Topo) IIbeta in cancer chemotherapy remains unclear, although this particular isoform has been implicated in drug resistance. In this study, we investigated Topo IIbeta as a target for 2-[4-(7-chloro-2-quinoxalinyloxy)phenoxy]-propionic acid (XK469), a novel synthetic quinoxaline phenoxypropionic acid derivative, in a Waldenstrom's macroglobulinemia (WM) model. In vitro, the WSU-WM cell line was exposed to 1.0, 2.0, 5.0, 8.0, and 10 microM XK469. Our results demonstrate a concentration-dependent cell growth inhibition with a concentration-independent inhibition of Topo IIbeta, as determined by band depletion assay. The cell growth inhibition of cells correlated well with increase in Bax:Bcl-2 ratio and poly(ADP-ribose) polymerase (PARP) cleavage. We used our established WSU-WM severe combined immunodeficient mouse xenograft model to test the efficacy and effect of XK469 on Topo IIbeta in vivo. Topo IIbeta was inhibited equally using two different dose schedules (20 and 40 mg/kg, i.v., for a total of 120 and 240 mg/kg, respectively); however, there was no significant decrease in tumor weight. Western blot analysis of cells isolated from s.c. tumors showed no induction of the Bax protein and a very low Bax:Bcl-2 ratio of approximately 0.3 in correlation with minimum PARP cleavage. Our study shows that XK469 inhibits Topo IIbeta in WSU-WM cells both in vitro and in vivo at or below the maximum tolerated dose in severe combined immunodeficient mice. However, there was no change of apoptosis-related molecules such as PARP, Bax, and Bcl-2 or reduction in tumor weight in association with Topo IIbeta inhibition. We conclude that Topo IIbeta inhibition by XK469 as a target is not sufficient for therapeutic effects in WSU-WM.
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PMID:2-[4-(7-chloro-2-quinoxalinyloxy)phenoxy]-propionic acid (XK469) inhibition of topoisomerase IIbeta is not sufficient for therapeutic response in human Waldenstrom's macroglobulinemia xenograft model. 1251 64

We have previously reported that XK469 inhibited topoisomerase (topo) IIbeta, in Waldenstrom's macroglobulinemia cell line (WSU-WM) however the inhibition alone is not sufficient to induce apoptosis. In this study, the apoptotic potential of XK469 and its mechanism in WSU-WM cell line was investigated. Exposure of WSU-WM cells to XK469 caused a decrease in viable cell number in a dose-dependent manner. In addition, XK469 caused the activation of caspase 3 resulting in subsequent cleavage of PARP. These events were preceded by the release of cytochrome c from the mitochondria to the cytosol. Simultaneous exposure of cells to cyclosporin A prevented the release of cytochrome c to cytosol and reduced the loss of viability. XK469 caused the activation of p53 with up-regulation of p53-dependent proteins such as Bax, p21, Gadd 45 and cyclin B1 in association with G2M arrest. The addition of ubiquitin carboxyl terminal hydrolase (UCH-L1) inhibitor (NaBH4) inhibited up-regulation of p53 and p53 related molecules by XK469 and reduced the loss of viability. Pre-incubation with NOK-1, a monoclonal antibody that prevents Fas-Fas ligand interaction and is inhibitory to Fas signaling interfered with XK469 induced activation of caspase 8 and also reduced the loss of viability. Simultaneous exposure of all three inhibitors (cyclosporin A, NaBH4 and NOK-1) abrogated the toxicity of XK469 by 95%. These data define multiple sequences of biochemical events that mediate cell death induced by XK469. Our study suggests a complex mechanistic cascade of XK469-mediated apoptosis that involves Fas signaling pathway, ubiquitination, p53 activation and cytochrome c release.
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PMID:XK469, a topo IIbeta inhibitor, induces apoptosis in Waldenstrom's macroglobulinemia through multiple pathways. 1461 35

The response of different tumours to radiation varies. This variation has been attributed to, among others, varying DNA repair capabilities The response of three tumour lines, differing in their sensitivities to radiation, namely, murine fibrosarcoma, lymphosarcoma and ascites, was studied by following the activities of enzymes known to be involved in DNA repair. The activities of poly (ADP-ribose) polymerase (PARP), DNA polymerase b and DNA ligase in fibrosarcoma, lymphosarcoma and ascites recorded varying degrees of increase following gamma irradiation (2 Gy). The increase was more pronounced in fibrosarcoma, which recorded a maximum 2 h after irradiation for b polymerase, and at 4 h for ligase and PARP, thereafter declining to near normal levels after 24 h. In contrast, the activity of DNA Topoisomerase I declined, corresponding to an increase in the PARP activity. The maximum increase in the activity of beta polymerase, ligase and PARP from lymphosarcoma and ascites was observed 2 h after irradiation with a corresponding decrease in Topoisomerase I activity. Search for the target enzymes and proteins for modification by PARP in gamma -irradiated fibrosarcoma tumour cells revealed that nuclei, and not chromatin, were preferentially modified by PARP. Among the nuclear proteins, histones were found to be ribosylated. The enzyme topoisomerase was ribosylated by PARP in vitro, and this modification was found to inhibit topoisomerase activity. We speculate that a possible role of PARP is to coordinate the activities of other enzymes in DNA repair by selectively inhibiting certain enzymes by the ribosylation process.
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PMID:Response of DNA repair enzymes in murine fibrosarcoma, lymphosarcoma and ascites cells following gamma irradiation. 1464 26

The main anticancer action of doxorubicin (DOX) is believed to be due to topoisomerase II inhibition and free radical generation. Our previous study has demonstrated that TAS-103, a topoisomerase inhibitor, induces apoptosis through DNA cleavage and subsequent H(2)O(2) generation mediated by NAD(P)H oxidase activation [H. Mizutani et al. J. Biol. Chem. 277 (2002) 30684-30689]. Therefore, to clarify whether DOX functions as an anticancer drug through the same mechanism or not, we investigated the mechanism of apoptosis induced by DOX in the human leukemia cell line HL-60 and the H(2)O(2)-resistant sub-clone, HP100. DOX-induced DNA ladder formation could be detected in HL-60 cells after a 7 h incubation, whereas it could not be detected under the same condition in HP100 cells, suggesting the involvement of H(2)O(2)-mediated pathways in apoptosis. Flow cytometry revealed that H(2)O(2) formation preceded the increase in Delta Psi m and caspase-3 activation. Poly(ADP-ribose) polymerase (PARP) and NAD(P)H oxidase inhibitors prevented DOX-induced DNA ladder formation in HL-60 cells. Moreover, DOX significantly induced formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine, an indicator of oxidative DNA damage, in HL-60 cells at 1 h, but not in HP100 cells. DOX-induced apoptosis was mainly initiated by oxidative DNA damage in comparison with the ability of other topoisomerase inhibitors (TAS-103, amrubicin and amrubicinol) to cause DNA cleavage and apoptosis. These results suggest that the critical apoptotic trigger of DOX is considered to be oxidative DNA damage by the DOX-induced direct H(2)O(2) generation, although DOX-induced apoptosis may involve topoisomerase II inhibition. This oxidative DNA damage causes indirect H(2)O(2) generation through PARP and NAD(P)H oxidase activation, leading to the Delta Psi m increase and subsequent caspase-3 activation in DOX-induced apoptosis.
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PMID:Mechanism of apoptosis induced by doxorubicin through the generation of hydrogen peroxide. 1568 Mar 9


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