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)

1-(1,4-dihydro-5,8-dihydroxy-1,4-dioxonaphthalen-2-yl)-4-methylpent-3-enylfuran-2-caroxylate (SH-7), a new naphthoquinone compound, derived from shikonin, exhibited obvious inhibitory actions on topoisomerase II (Topo II) and topoisomerase I (Topo I), which were stronger than its mother compound shikonin. Notably, the SH-7's inhibitory potency on Topo II was much stronger than that on Topo I. In addition, SH-7 significantly stabilized Topo II-DNA cleavable complex and elevated the expression of phosphorylated-H2AX. The in vitro cell-based investigation demonstrated that SH-7 displayed wide cytotoxicity in diversified cancer cell lines with the mean IC(50) value of 7.75 microM. One important finding is SH-7 displayed significant cytotoxicity in the 3 MDR cell lines, with an average IC(50) value nearly equivalent to that of the corresponding parental cell lines. The average resistance factor (RF) of SH-7 was 1.74, which was much lower than those of reference drugs VP-16 (RF 145.92), ADR (RF 105.97) and VCR (RF 197.39). Further studies illustrated that SH-7 had the marked apoptosis-inducing function on leukemia HL-60 cells, which was validated to be of mitochondria-dependence. The in vivo experiments showed that SH-7 had inhibitory effects on S-180 sarcoma implanted to mice, SMMC-7721, BEL-7402 human hepatocellular carcinoma and PC-3 human prostate cancer implanted to nude mice. Taken together, these results suggest that SH-7 induces DSBs as a Topo II inhibitor, which was crucial to activate the apoptotic process, and subsequently accounts for its both in vitro and in vivo antitumor activities. The well-defined Topo II inhibitory activity, antitumor effects particularly with its obvious anti-MDR action, better solubility and less toxicity make SH-7 as a potential antitumor drug candidate for further research and development.
...
PMID:SH-7, a new synthesized shikonin derivative, exerting its potent antitumor activities as a topoisomerase inhibitor. 1657 Feb 88

Topoisomerase II is essential for cell proliferation and survival and has been a target of various anticancer drugs. ICRF-193 has long been used as a catalytic inhibitor to study the function of topoisomerase II. Here, we show that ICRF-193 treatment induces DNA damage signaling. Treatment with ICRF-193 induced G2 arrest and DNA damage signaling involving gamma-H2AX foci formation and CHK2 phosphorylation. DNA damage by ICRF-193 was further demonstrated by formation of the nuclear foci of 53BP1, NBS1, BRCA1, MDC1, and FANCD2 and increased comet tail moment. The DNA damage signaling induced by ICRF-193 was mediated by ATM and ATR and was restricted to cells in specific cell cycle stages such as S, G2, and mitosis including late and early G1 phases. Downstream signaling of ATM and ATR involved the phosphorylation of CHK2 and BRCA1. Altogether, our results demonstrate that ICRF-193 induces DNA damage signaling in a cell cycle-dependent manner and suggest that topoisomerase II might be essential for the progression of the cell cycle at several stages including DNA decondensation.
...
PMID:Cell cycle-dependent DNA damage signaling induced by ICRF-193 involves ATM, ATR, CHK2, and BRCA1. 1663 Jun 10

Spermatocytes normally sustain many meiotically induced double-strand DNA breaks (DSBs) early in meiotic prophase; in autosomal chromatin, these are repaired by initiation of meiotic homologous-recombination processes. Little is known about how spermatocytes respond to environmentally induced DNA damage after recombination-related DSBs have been repaired. The experiments described here tested the hypothesis that, even though actively completing meiotic recombination, pachytene spermatocytes cultured in the absence of testicular somatic cells initiate appropriate chromatin remodeling and cell-cycle responses to environmentally induced DNA damage. Two DNA-damaging agents were employed for in vitro treatment of pachytene spermatocytes: gamma-irradiation and etoposide, a topoisomerase II (TOP2) inhibitor that results in persistent unligated DSBs. Chromatin modifications associated with DSBs were monitored after exposure by labeling surface-spread chromatin with antibodies against RAD51 (which recognizes DSBs) and the phosphorylated variant of histone H2AFX (herein designated by its commonly used symbol, H2AX), gammaH2AX (which modifies chromatin associated with DSBs). Both gammaH2AX and RAD51 were rapidly recruited to irradiation- or etoposide-damaged chromatin. These chromatin modifications imply that spermatocytes recruit active DNA damage responses, even after recombination is substantially completed. Furthermore, irradiation-induced DNA damage inhibited okadaic acid-induced progression of spermatocytes from meiotic prophase to metaphase I (MI), implying efficacy of DNA damage checkpoint mechanisms. Apoptotic responses of spermatocytes with DNA damage differed, with an increase in frequency of early apoptotic spermatocytes after etoposide treatment, but not following irradiation. Taken together, these results demonstrate modification of pachytene spermatocyte chromatin and inhibition of meiotic progress after DNA damage by mechanisms that may ensure gametic genetic integrity.
...
PMID:Spermatocyte responses in vitro to induced DNA damage. 1670 71

Polyploidization occurs during normal development as well as during tumorigenesis. In this study, we investigated if the responses to genotoxic stress in cancer cells are influenced by the ploidy. Prolonged treatment of Hep3B cells with the spindle inhibitor nocodazole resulted in mitotic slippage, followed by re-replication of the DNA to produce polyploids. Reintroduction of p53 restored the checkpoints and suppressed polyploidization. Remarkably, a stable tetraploidy cell line could be generated from Hep3B by a transient nocodazole treatment followed by a period of recovery. Using this novel tetraploid system, we found that tetraploidization increased the cell volume without significantly affecting the cell cycle. Although tetraploidization was accompanied by an increase in centrosome number, the majority of mitoses in the tetraploid cells remained bipolar. Polyploidization sensitized cells to genotoxic stress inflicted by ionizing radiation and topoisomerase inhibitors without affecting the sensitivity to spindle inhibitors. Accordingly, more gamma-H2AX foci were induced by radiation in tetraploids than in normal Hep3B cells. Likewise, primary tetraploid human fibroblasts displayed higher gamma-H2AX foci formation than diploid human fibroblasts. An implication for chemotherapy is that some cancer cells can be sensitized to genotoxic agents by a preceding step that induces polyploidization.
...
PMID:Polyploidization increases the sensitivity to DNA-damaging agents in mammalian cells. 1688 21

Despite rapid advances in the field of DNA repair, little is known about the repair of protein-DNA adducts. Previous studies have demonstrated that topoisomerase II (TopII)-DNA adducts (TopII-DNA covalent complexes) are rapidly degraded by the proteasome. It has been hypothesized that proteasomal degradation of TopII-DNA covalent adducts exposes TopII-concealed DNA double-strand breaks (DSBs) for repair. To test this hypothesis, the anticancer drug, VP-16 (etoposide), was employed to induce TopII-DNA covalent complexes in mammalian cells, and the involvement of proteasome in processing TopII-DNA covalent complexes into DSBs was investigated. Consistent with the hypothesis, VP-16-induced DSBs as monitored by neutral comet assay, as well as DNA damage signals (e.g. gamma-H2AX) were significantly reduced in the presence of the proteasome inhibitor, MG132. Using both top2beta knock-out mouse embryonic fibroblasts and Top2beta small interfering RNA knockdown PC12 cells, as well as postmitotic neurons in which TopIIalpha was absent, we showed that VP-16-induced DNA damage signals were attenuated upon proteasome inhibition, suggesting the involvement of proteasome in the repair/processing of both TopIIalpha-DNA and TopIIbeta-DNA adducts. By contrast, hydrogen peroxide-induced gamma-H2AX was unaffected upon proteasome inhibition, suggesting a specific requirement of the proteasome pathway in the processing of TopII-DNA covalent complexes into DNA damage.
...
PMID:A protease pathway for the repair of topoisomerase II-DNA covalent complexes. 1697 21

NK314 is a novel synthetic benzo[c]phenanthridine alkaloid that has recently entered clinical trials as an antitumor compound, based on impressive activities in preclinical models. The present investigations were directed at determining the mechanism of action of this agent. NK314 induced significant G(2) cell cycle arrest in several cell lines, independent of p53 status, suggesting the existence of a common mechanism of checkpoint activation. The Chk1-Cdc25C-Cdk1 G(2) checkpoint pathway was activated in response to 100 nmol/L NK314 in ML-1 human acute myeloid leukemia cells. This was associated with the phosphorylation of the histone variant H2AX, an action that was predominant in the G(2) population, suggesting that double-strand DNA breaks caused cells to activate the checkpoint pathway. Double-strand DNA breaks were visualized as chromosomal aberrations when the G(2) checkpoint was abrogated by 7-hydroxystaurosporine. In vitro assays showed that NK314 inhibited the ability of topoisomerase IIalpha to relax supercoiled DNA and trapped topoisomerase IIalpha in its cleavage complex intermediate. CEM/VM1 cells, which are resistant to etoposide due to mutations in topoisomerase IIalpha, were cross-resistant to NK314. However, CEM/C2 cells, which are resistant to camptothecin due to mutations in topoisomerase I, retained sensitivity. These findings support the conclusion that the major mechanism of NK314 is to inhibit topoisomerase IIalpha, an action that leads to the generation of double-strand DNA breaks, which activate the G(2) DNA damage checkpoint pathway.
...
PMID:Inhibition of topoisomerase IIalpha and G2 cell cycle arrest by NK314, a novel benzo[c]phenanthridine currently in clinical trials. 1751 99

Doxorubicin is among the most effective and widely used anticancer drugs in the clinic. However, cardiotoxicity is one of the life-threatening side effects of doxorubicin-based therapy. Dexrazoxane (Zinecard, also known as ICRF-187) has been used in the clinic as a cardioprotectant against doxorubicin cardiotoxicity. The molecular basis for doxorubicin cardiotoxicity and the cardioprotective effect of dexrazoxane, however, is not fully understood. In the present study, we showed that dexrazoxane specifically abolished the DNA damage signal gamma-H2AX induced by doxorubicin, but not camptothecin or hydrogen peroxide, in H9C2 cardiomyocytes. Doxorubicin-induced DNA damage was also specifically abolished by the proteasome inhibitors bortezomib and MG132 and much reduced in top2beta(-/-) mouse embryonic fibroblasts (MEF) compared with TOP2beta(+/+) MEFs, suggesting the involvement of proteasome and DNA topoisomerase IIbeta (Top2beta). Furthermore, in addition to antagonizing Top2 cleavage complex formation, dexrazoxane also induced rapid degradation of Top2beta, which paralleled the reduction of doxorubicin-induced DNA damage. Together, our results suggest that dexrazoxane antagonizes doxorubicin-induced DNA damage through its interference with Top2beta, which could implicate Top2beta in doxorubicin cardiotoxicity. The specific involvement of proteasome and Top2beta in doxorubicin-induced DNA damage is consistent with a model in which proteasomal processing of doxorubicin-induced Top2beta-DNA covalent complexes exposes the Top2beta-concealed DNA double-strand breaks.
...
PMID:Topoisomerase IIbeta mediated DNA double-strand breaks: implications in doxorubicin cardiotoxicity and prevention by dexrazoxane. 1787 25

A precise packaging of the paternal genome during spermiogenesis is essential for fertilization and embryogenesis. Most of the nucleosomal DNA supercoiling must be eliminated in elongating spermatids (ES), and transient DNA strand breaks are observed that facilitate the process. Topoisomerases have been considered as ideal candidates for the removal of DNA supercoiling, but their catalytic activity, in the context of such a major chromatin remodeling, entails genetic risks. Using immunofluorescence, we confirmed that topoisomerase II beta (TOP2B) is the type II topoisomerase present in ES between steps 9 and 13. Interestingly, the detection of TOP2B was found coincident with detection of tyrosyl-DNA phosphodiesterase 1 (TDP1), an enzyme known to resolve topoisomerase-mediated DNA damage. The presence of gamma-H2AX (also known as H2AFX) coincident with DNA strand breakage was also confirmed at these steps and indicates that a DNA damage response is triggered. Active DNA repair in ES was demonstrated using a fluorescent in situ DNA polymerase activity assay on squash preparations of staged tubules. In the context of haploid spermatids, any unresolved double-strand breaks, resulting from a failure in the rejoining process of TOP2B, must likely rely on the error-prone nonhomologous end joining, because homologous recombination cannot proceed in the absence of a sister chromatid. Because this process is part of the normal developmental program of the spermatids, dramatic consequences for the genomic integrity of the developing male gamete may arise should any alteration in the process occur.
...
PMID:DNA damage response during chromatin remodeling in elongating spermatids of mice. 1803 20

Drugs developed for the treatment of conditions other than neoplasia can also show promise as potential antitumor agents. The fluoroquinolone antibiotic ciprofloxacin (CPFX) is known to modulate cycle cell progression and apoptosis in cancer cells, and is thought to induce DNA double-strand breaks (DSBs) via topoisomerase II (topo II) inhibition and stabilized cleavage complex (SCC) formation. DSBs trigger Ser-139 phosphorylation of histone H2AX (gammaH2AX) by PI-3-like kinases including ATM; gammaH2AX can serve as a marker of DNA damage when measured in situ using immunocytochemistry and flow cytometry. The aim of the present study was to investigate the relationship between CPFX-mediated DNA damage and induction of apoptosis in human lymphoblastoid cells and phytohaemagglutinin (PHA)-stimulated lymphocytes (Lymphs). Treatment of TK6 cells (wild-type p53) with 100 microg/ml CPFX for 2-10 h produced no increase in gammaH2AX; to the contrary, its level in S phase cells was reduced at 10 h compared to controls. Nevertheless, stabilization of topo IIalpha, ATM Ser-1981 phosphorylation and G(2) arrest was observed in TK6 cells exposed to CPFX for > or = 4 h. However, following 24 h treatment, gammaH2AX was dramatically increased in a sub-population of cells indicating the onset of apoptosis (confirmed by presence of activated caspase 3). CPFX had a similar lack of effect on induction of gammaH2AX at early time points in WTK1 and NH32 cells (devoid of functional p53) and proliferating Lymphs, however, induction of apoptosis was less pronounced than in TK6 cells. Formation of SCC and activation of ATM (but lack of gammaH2AX induction) indicates topo II-mediated chromatin or DNA changes in the absence of DSBs; ATM activation apparently triggers the G(2)M checkpoint leading to G(2) arrest. The subsequent induction of apoptosis appears to be facilitated by functional p53. CPFX may therefore have a potential use as a chemotherapeutic agent in the treatment of lymphoblast-derived cancer.
...
PMID:Ciprofloxacin-induced G2 arrest and apoptosis in TK6 lymphoblastoid cells is not dependent on DNA double-strand break formation. 1805 76

Double-strand breaks (DSBs) are highly deleterious DNA lesions as they lead to chromosome aberrations and/or apoptosis. The formation of nuclear DSBs triggers phosphorylation of histone H2AX on Ser-139 (defined as gammaH2AX), which participates in the repair of such DNA damage. Our aim was to compare the induction of gammaH2AX in relation to DSBs induced by topoisomerase II (TOPO II) poisons, etoposide (ETOP) and mitoxantrone (MXT), in V79 cells. DSBs were measured by the neutral comet assay, while gammaH2AX was quantified using immunocytochemistry and flow cytometry. Stabilized cleavage complexes (SCCs), lesions thought to be responsible for TOPO II poison-induced genotoxicity, were measured using a complex of enzyme-DNA assay. In the case of ETOP, a no observed adverse effect level (NOAEL) and lowest observed effect level (LOEL) for genotoxicity was determined; gammaH2AX levels paralleled DSBs at all concentrations but significant DNA damage was not detected below 0.5 microg/ml. Furthermore, DNA damage was dependent on the formation of SCCs. In contrast, at low MXT concentrations (0.0001-0.001 microg/ml), induction of gammaH2AX was not accompanied by increases in DSBs. Rather, DSBs were only significantly increased when SCCs were detected. These findings suggest MXT-induced genotoxicity occurred via at least two mechanisms, possibly related to DNA intercalation and/or redox cycling as well as TOPO II inhibition. Our findings also indicate that gammaH2AX can be induced by DNA lesions other than DSBs. In conclusion, gammaH2AX, when measured using immunocytochemical and flow cytometric methods, is a sensitive indicator of DNA damage and may be a useful tool in genetic toxicology screens. ETOP data are consistent with the threshold concept for TOPO II poison-induced genotoxicity and this should be considered in the safety assessment of chemicals displaying an affinity for TOPO II and genotoxic/clastogenic effects.
...
PMID:Assessment of DNA double-strand breaks and gammaH2AX induced by the topoisomerase II poisons etoposide and mitoxantrone. 1842 98


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

---