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)

Gene amplification is one of the most important mechanisms leading to deregulated gene expression in cancer. The exact quantitative detection of this frequent genomic alteration in solid tumors is often hampered by an admixture of nonneoplastic bystander and stroma cells. To overcome this obstacle and to develop an objective quantitative method we have combined laser-assisted microdissection of tumor cells with the novel 5'-exonuclease-based real-time polymerase chain reaction (PCR) assay. The latter method enables the highly reproducible exact quantification of minute amounts of nucleic acids. As a model system amplification of c-erbB2/Her-2/neu gene and the adjacent topoisomerase IIalpha gene was determined in paraffin-embedded breast cancer specimens (n = 23) after immunohistochemical labeling and laser-based microdissection of tumor cells. The high sensitivity of real-time PCR enabled the reliable and objective detection of low-level amplifications in as few as 50 cells from archival tissue sections. Low-level amplifications were shown to escape from detection unless tumor cells were isolated by microdissection. In selected cases intratumor heterogeneity was demonstrated using areas of approximately 50 to 100 cells. This novel approach combining immunohistochemistry, laser microdissection, and quantitative kinetic PCR allows morphology-guided studies in archival tissue specimens and will enable the exact quantification of gene copy numbers in even small and precancerous lesions.
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PMID:Detection of gene amplification in archival breast cancer specimens by laser-assisted microdissection and quantitative real-time polymerase chain reaction. 1085 9

Overexpression of the HER2/neu oncogene is associated with tumorigenicity and drug resistance in many types of cancer. Three different human Ewing's sarcoma cell lines (TC71, RD, and A4573) were found to express high levels of the HER2/neu protein. Transduction of TC71 cells with the E1A gene using an adenoviral vector (Ad-E1A) down-regulated HER2/neu overexpression in those cells and increased cytostasis. E1A-induced apoptosis was demonstrated by both flow cytometric analysis and Western blot analysis using a poly(ADP-ribose) polymerase antibody. After transduction of the E1A gene into these cells, the sensitivity of these cells to VP-16 (etoposide) was enhanced 18-fold and to Adriamycin 5-fold. However, no change was seen in cisplatin sensitivity. E1A also significantly increased topoisomerase IIalpha protein expression, indicating that the up-regulation of topoisomerase IIalpha may be one of the mechanisms by which E1A enhanced the sensitivity to topoisomerase II-targeting anticancer drugs, such as VP-16 and Adriamycin, but not cisplatin. In summary, these studies demonstrated that Ad-E1A can down-regulate HER2/neu overexpression and up-regulate topoisomerase IIalpha expression in human Ewing's sarcoma cells, increasing their apoptosis rate and enhancing their sensitivity to VP-16 and ADRIAMYCIN:
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PMID:E1A sensitizes HER2/neu-overexpressing Ewing's sarcoma cells to topoisomerase II-targeting anticancer drugs. 1130 98

Amplification of the HER-2/neu oncogene and amplification of the topoisomerase IIalpha gene are important determinators of the response to chemotherapy in advanced breast cancer. Assays of these genes are usually carried out using primary tumor samples, because biopsies from metastatic lesions are not usually taken. We studied the concordance of Her-2/neu and topoisomerase IIalpha amplification in primary breast tumors and their metastases by immunostaining and DNA in situ hybridization. HER-2/neu amplification, present in 28% of the primary tumors (n = 46), was always associated with amplification in its metastasis. Conversely, no metastases with HER-2/neu amplification were seen without amplification in the primary tumor. Topoisomerase IIalpha gene copy status (amplification/deletion/unaltered) remained generally unchanged in HER-2/neu-positive tumors, but in three cases, the predominant cell population in metastatic tissue was present only as a subpopulation in the primary tumor. We conclude that amplification of HER-2/neu measured in primary tumor reflects the status of metastases. Minor discrepancies between primary and metastatic tumors in topoisomerase IIalpha gene copy status may reflect evolvement of the amplicon structure in successive cell divisions.
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PMID:Amplification of HER-2/neu and topoisomerase IIalpha in primary and metastatic breast cancer. 1145 72

Fewer than 20% of patients with pancreatic cancer present with disease macroscopically confined to the pancreas, and approximately 40% already have locally advanced disease. Based on data from the Gastrointestinal Tumor Study Group, adjuvant therapy with radiation and 5-fluorouracil has become standard practice in the United States; however, in other countries, adjuvant treatment has not been as widely accepted. Other issues include the potential of neoadjuvant therapy and optimal systemic management. The issue of second-line therapy has also been raised in the treatment of pancreatic carcinoma, after the establishment of gemcitabine as a first-line standard treatment approach, in which it achieves a significant clinical benefit response. Other combination partners with gemcitabine under investigation include the antimetabolite 5-fluorouracil, the topoisomerase-I inhibitor irinotecan, the taxane docetaxel, the platinum oxaliplatin, the multitargeted antifolate pemetrexed, the farnesyl transferase inhibitor R-115777, the anti-HER2/neu antibody trastuzumab, and the epidermal growth factor inhibitor cetuximab. Combined-modality approaches with gemcitabine and radiation are also under active investigation.
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PMID:Future directions in the treatment of pancreatic cancer. 1257 31

We have shown previously that the Epstein-Barr virus nuclear antigen-1 (EBNA1) can act as a transforming suppressor in the HER2/neu-overexpressing ovarian cancer cells. In the present study, by using flow cytometric analysis, we demonstrate that EBNA1 could prolong G(2)/M phase and sensitize to Taxol-induced apoptosis in the EBNA1-expressing ovarian cancer cell stable transfectants. In addition, EBNA1 could also significantly increase topoisomerase IIalpha protein expression, indicating that the up-regulation of topoisomerase IIalpha may be one of the mechanisms by which EBNA1 enhances the sensitivity of ovarian cancer cells to topoisomerase II-targeting anticancer drugs, such as VP-16 and Adriamycin. These data suggest that EBNA1 not only prolongs cell cycle at G(2)/M phase and up-regulates topoisomerase IIalpha expression in HER2/neu-overexpressing ovarian cancer cells, but also increases cellular apoptosis through sensitization of cancer cells to topoisomerase II-directing anticancer drugs.
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PMID:EBNA1 may prolong G(2)/M phase and sensitize HER2/neu-overexpressing ovarian cancer cells to both topoisomerase II-targeting and paclitaxel drugs. 1289 73

This article attempts to provide the reader with a complete overview of topoisomerase (topo) II alpha as a marker for predicting the efficacy of anthracyclines in patients with breast cancer. In the first section of this article, in vitro data supporting the predictive value of topo II alpha are reviewed. Interestingly, these data suggest that the interaction between HER2 and anthracycline efficacy, which has been hypothesized in several clinical studies performed in the past decade, might depend on the concomitant topo II alpha status. Molecular pathology studies further reinforce the concept that HER2 might not be directly involved in the prediction of response to anthracyclines. They report that topo II alpha gene amplification can be found in 25%-40% of HER2/neu-amplified tumors, while no topo II gene amplification is detected in the absence of HER2/neu gene amplification. In the second part of this article, a series of clinical studies are reviewed and interpreted. These studies have attempted to correlate topo II alpha status with anthracycline efficacy in the adjuvant, neoadjuvant, and metastatic settings. All of the studies evaluating the topo II alpha gene suggest that gene amplification might be associated with an increased efficacy of anthracyclines, and some of the studies evaluating topo II alpha protein find that protein overexpression might correlate with an increased sensitivity to these compounds. Despite these findings, however, the reported studies do not provide the proof of principle needed to authorize the use of topo II alpha as a predictive marker for standard practice. A new generation of research is currently testing the predictive value of topo II alpha. It is hoped that these projects, which are described in the last section of the article, will clarify the role of topo IIa in the prediction of response to anthracyclines.
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PMID:Topoisomerase II alpha as a marker predicting the efficacy of anthracyclines in breast cancer: are we at the end of the beginning? 1449 10

We sought to identify the frequency of amplification of the topoisomerase IIalpha gene (TOP2A) in pancreatic cancer and determine the usefulness of TOP2A immunolabeling in screening for TOP2A and human epidermal growth factor receptor (HER)2/neu amplification. We examined 55 pancreatic adenocarcinoma specimens for TOP2A immunolabeling and identified TOP2A protein expression in all specimens with a nuclear labeling index (NLI; positive nuclei/total nuclei x 100) of 5% to 80%. Normal pancreatic ductal epithelium, proposed to give rise to pancreatic adenocarcinoma, did not demonstrate detectable TOP2A expression. In a subset of specimens selected for fluorescence in situ hybridization analysis of TOP2A and HER2/neu amplification using a recently developed multicolor probe, 7 of 8 lesions with an NLI of 25% or more demonstrated TOP2A amplification, in contrast with 2 of 14 lesions with a TOP2A NLI of less than 25%. In 8 of 9 TOP2A-amplified cases, coamplification of HER2/neu was present, suggesting a potential relationship between TOP2A and HER2/neu in pancreatic adenocarcinoma. We propose that TOP2A immunolabeling be used in conjunction with a newly developed multicolor probe to screen patients with pancreatic adenocarcinoma to determine the best potential therapeutic modalities, such as TOP2A inhibitors, trastuzumab, or both.
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PMID:A subset of pancreatic adenocarcinomas demonstrates coamplification of topoisomerase IIalpha and HER2/neu: use of immunolabeling and multicolor FISH for potential patient screening andtreatment. 1576 77

Pediatric malignant non-brainstem glioma (PMNBG) is a rare tumor that accounts for only about five percent of childhood intracranial neoplasms. DNA topoisomerase IIalpha (TIIalpha) is a novel marker of cell-cycle turnover and a target of high-risk chemotherapy in PMNBG. We have shown that TIIalpha protein expression strongly correlates with event-free and overall survival in these malignancies. The molecular mechanism causing the varying TIIalpha protein expression in PMNBG remains unknown. Utilizing a combined approach of immunocytochemistry-based morphology guidance, laser-assisted microdissection and quantitative real-time PCR, we report a low-level co-amplification of the neighboring TIIalpha and Her-2/neu gene loci on chromosome 17q11-q22 in one of seventeen examined PMNBGs. Analysis of both genes by real-time PCR in the crude tumor samples without prior tissue heterogeneity reduction via laser microdissection, resulted in loss of detection of amplification of the syngeneic Her-2/neu locus. Gene dosage assessment in a microscopically distant tumor area revealed no amplification of either gene. Our results suggest that low-level amplification of the TIIalpha gene locus may be a sporadic mechanism of increased TIIalpha protein expression in PMNBG, which can coincide with low-level amplification of Her-2/neu. The observed intratumor genetic heterogeneity for TIIalpha in PMNBGs may have an impact on the relevance of TIIalpha as a biological constituent of outcome in these neoplasms.
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PMID:DNA topoisomerase IIalpha and Her-2/neu gene dosages in pediatric malignant gliomas. 1580 8

The aim of this study was to evaluate the role of several biological and histological markers (topoisomerase IIalpha, MIB-1, E2F, apoptotic index, APE/ref-1, p53, Her-2/neu, estrogen and porgesterone receptors, and histological grading) as predictors of pathologic response after anthracycline-based chemotherapy for breast cancer. A series of 50 consecutive breast cancer patients receiving anthracycline-based primary chemotherapy were retrospectively studied. Biological markers were assessed by immunohistochemistry (and by TUNEL assay for apoptotic index) in pre-treatment core biopsies and post-treatment surgical samples. The expression of topoisomerase IIalpha, E2F, MIB-1, estrogen and progesterone receptors decreased, while APE/ref-1 staining increased after treatment. Higher topoisomerase IIalpha (P=0.007) and lower APE/ref-1 (P=0.04) expression were associated with better pathologic response.
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PMID:Topoisomerase IIalpha and APE/ref-1 are associated with pathologic response to primary anthracycline-based chemotherapy for breast cancer. 1591 Nov 9

Fatty acid synthase (FAS), the key metabolic multi-enzyme that is responsible for the terminal catalytic step in the de novo fatty acid biosynthesis, plays an active role in the development, maintenance, and enhancement of the malignant phenotype in a subset of breast carcinomas. We recently described that a molecular bi-directional cross-talk between FAS and the Her-2/neu (erbB-2) oncogene is taking place at the level of transcription, translation, and activity in breast cancer cells. Because Her-2/neu has been linked with altered sensitivity to cytotoxic drugs, we envisioned that FAS gene expression may represent a novel predictive molecular factor for breast cancer response to chemotherapy in a Her-2/neu-related manner. We herein evaluated whether chemotherapy-induced cell damage acts in an epigenetic fashion by inducing changes in the transcriptional activation of FAS gene in breast cancer cells. To evaluate this option, FAS- and Her-2/neu-overexpressing SK-Br3 breast cancer cells were transiently transfected with a FAS promoter-reporter construct (FAS-Luciferase) harboring all the elements necessary for high level expression in cancer cells. SK-Br3 cells cultured in the presence of topoisomerase IIalpha (TOP2A) inhibitors doxorubicin and etopoxide (VP-16) demonstrated a 2- to 3-fold increase in FAS promoter activity when compared with control cells growing in drug-free culture conditions. We failed to observe any significant activation of FAS promoter following exposure to the anti-metabolite 5-fluorouracil, the alkylating drug cisplatin, or the microtubule interfering-agents paclitaxel and vincristine. Moreover, the up-regulatory effects of TOP2A inhibitors on the transcriptional activation of FAS gene expression were not significantly decreased when the FAS promoter was damaged at the sterol regulatory element binding protein (SREBP)-binding site. Considering that FAS inhibition produces profound inhibition of DNA replication and S-phase progression in cancer cells, we finally asked whether a cross-talk between TOP2A and FAS could exhibit a Her-2/neu-related bi-directional nature. TOP2A protein levels were decreased during treatment with the anti-Her-2/neu antibody trastuzumab while, concomitantly, FAS promoter activity and FAS protein expression were significantly reduced. Of note, when the expression levels of TOP2A protein were analyzed following exposure of SK-Br3 cells to increasing concentrations of the novel slow-binding FAS inhibitor C75, a dose-dependent reduction in TOP2A expression was observed. Although FAS gene is not physically located in the Her-2/neu-TOP2A amplicon, our present findings strongly suggest that a tight functional association between FAS, Her-2/neu and TOP2A genes is taking place in a subset of breast carcinoma cells.
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PMID:DNA topoisomerase IIalpha (TOP2A) inhibitors up-regulate fatty acid synthase gene expression in SK-Br3 breast cancer cells: in vitro evidence for a 'functional amplicon' involving FAS, Her-2/neu and TOP2A genes. 1708 11


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