Topoisomerase IIα Expression Research Articles

Predictive value of MRP2, p53, bcl2 and topoisomerase II immunostainings for the efficacy of anthracyclines-based adjuvant chemotherapy in breast cancer: Results from two randomized trials

616 Background: The identification of predictive biomarkers for the efficacy of adjuvant treatments could allow to better tailor adjuvant treatments. We evaluated the predictive value of MRP2, bcl2, topoisomerase IIα (Topo IIα) expression and p53 status for the efficacy of adjuvant anthracyclines (A)-based chemotherapy. Methods: Tumor samples from 823 patients included at Institut Gustave Roussy (IGR) in two randomized trials comparing an A-based chemotherapy with no treatment were used to perform a tissue-array. Chemotherapy consisted of 5FU (500mg/m2), farmorubicine (90% of patients) or doxorubicin (50 mg/m2) and cyclophosphamide (500 mg/m2) (D1=D28) for 6 cycles. Immunostainings (cut-off: >10% stained cells) were performed for MRP2 (M2III-6; 1:300; Alexis), p53 ( DO-7; 1:50; Dako), bcl2 (124; 1:50; Dako), and Topo IIα (KI-S1; 1:5000; Chemicon). We previously reported predictive values of ER, HER2 expression and molecular subclassification using the same tissue-array (Conforti, Annals of Oncology, 2007). Results: After a median follow-up of 10 years, 174 patients (22%) have presented a relapse and 186 patients (24%) died. Chemotherapy improved DFS (HR = 0.77, 95% CI: 0.63- 0.9), but not OS (HR = 0.88, 95% CI: 0.66–1.1). A positive staining for MRP2, p53, Topo IIα and bcl2 was observed in 122 (16%), 157 (20%), 267 (35%) and 251 (34%) assessable samples respectively. P53 and Topo IIα were more frequently expressed in patients with basal-like (51% and 53%) or HER2-overexpressing tumors (44% and 57%), as compared to other groups (HER2- and nonbasal BC) (11% and 28%). Bcl2 was more frequently positive in patients with luminal-like breast cancer (47% versus 16%, p<0.01). No significant interaction was observed between the four biomarkers expression and treatment efficacy for both DFS and OS (adjusted p values for interaction ranged between 0.30 and 0.85). Conclusions: In this study, we did not detect significant interaction between MRP2, p53, bcl2 and Topo Iia expressions and treatment efficacy. Nevertheless, such study cannot exclude a possible interaction with a higher number of events or different methods (DNA sequencing for p53 mutations and lower dilution [1:200] for S1 Ab). No significant financial relationships to disclose.

BRCA1-Mediated Ubiquitination Inhibits Topoisomerase IIαActivity in Response to Oxidative Stress

Topoisomerase IIalpha is known to be critically involved in both cell proliferation and cell death. The mechanisms responsible for stress-dependent topoisomerase IIalpha alterations, however, remain unclear. This study focused on the behavior of topoisomerase IIalpha in response to oxidative stress induced by hydrogen peroxide (H(2)O(2)). The catalytic activity of topoisomerase IIalpha in MOLT-4 cells treated with H(2)O(2) decreased in parallel with the alteration of topoisomerase IIalpha expression. The ubiquitination of topoisomerase IIalpha was dependent on oxidative stress. BRCA1, a tumor-suppressor gene, appeared to be involved in these alterations in topoisomerase IIalpha. Furthermore, the retinoblastoma protein (pRb) was required for the ubiquitination of topoisomerase IIalpha by BRCA1. We conclude that the functions of topoisomerase IIalpha are regulated by ubiquitination on exposure to oxidative stress.

Topoisomerase IIα Expression as an Independent Prognostic Factor in Hodgkin's Lymphoma

To correlate the immunohistochemical expression of topoisomerase IIalpha (topoIIalpha) in Hodgkin's lymphoma (HL) with clinicopathological parameters, the expression of Ki-67 and the outcome of patients, who had been homogenously treated with ABVD or equivalent regimens. Immunohistochemistry using the monoclonal antibody Ki-S1 (topoIIalpha) was performed in 238 HL patients. MiB1 (Ki-67) expression was evaluated in 211/238. The mean +/- SD percentage of topoIIalpha- and Ki-67-positive Hodgkin-Reed-Sternberg (HRS) cells was 63 +/- 19% (5%-98%) and 73 +/- 19% (8%-99%), respectively. The median percentage of topoIIalpha-positive HRS cells was 64% (interquartile range, 51-78%). There was no correlation between topoIIalpha expression and patient characteristics. TopoIIalpha and Ki-67 expression were correlated (Spearman's Rho 0.255, P < 0.001). TopoIlalpha expression within the highest quartile of this patient population was predictive of failure free survival (FFS) (10-year rates 82 +/- 3% vs 68 +/- 7%, P = 0.02 for patients falling into the quartiles 1-3 and 4 respectively). In multivariate analysis topoIIalpha expression was independently predictive of FFS. TopoIIalpha was expressed in all cases of HL showing a correlation with Ki-67 expression. Under current standard therapy including drugs inhibiting its activity, topoIIalpha was an independent adverse predictor of FFS with no statistically significant correlation with other established prognostic factors.

Upregulation of topoisomerase IIα expression in advanced gallbladder carcinoma: a potential chemotherapeutic target

The lack of treatment options other than surgical resection results in unfavourable prognosis of advanced gallbladder carcinoma. The aim of this study was to identify cancer-specific cellular targets that would form the basis for some therapeutic approaches for this disease. Twelve advanced gallbladder carcinoma tissue samples and three samples of normal gallbladder epithelium were screened to identify differentially expressed genes by DNA microarray analysis. The results obtained were validated in an independent sample set by quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR). Among the genes picked-up, one molecule, topoisomerase IIalpha (TOPO IIalpha), was further assessed immunohistochemically as a potential chemotherapeutic target, and the growth inhibitory effects of etoposide, doxorubicin and idarubicin, representative TOPO IIalpha inhibitors, on two different gallbladder carcinoma cell lines were compared with that of gemcitabine and 5-fulorouracil. Five upregulated genes were identified: four cell cycle-related genes (TOPO IIalpha, cyclin B2, CDC28 protein kinase regulatory subunit 2, ubiquitin-conjugating enzyme E2C) and a metabolism-related gene (gamma-glutamyl hydrolase). Immunohistochemically, TOPO IIalpha was expressed in gallbladder cancer cells, and 16 of 35 cases (46%) had strong TOPO IIalpha expression defined as having a labeling index of >50%. In in vitro growth inhibition assay, etoposide, as well as doxorubicin and idarubicin, was the most effective for OCUG-1 cells that had strong TOPO IIalpha expression, while gemicitabine was the most effective for NOZ cells with weak TOPO IIalpha expression. Etoposide induced apoptosis of OCUG-1 cells. TOPO IIalpha might be an effective chemotherapeutic target in advanced gallbladder carcinoma, especially when it is expressed strongly.

Does Polysomy of Chromosome 17 Have a Role in ERBB2 and Topoisomerase IIα Expression?

Objectives: ERBB2 is an oncogene with prognostic and predictive value. Topoisomerase IIα is an enzyme encoding close to the ERBB2 oncogene, that represents a molecular target for anthracyclines. An indirect mechanism of increasing ERBB2 and topoisomerase IIα gene copy number is chromosome 17 polysomy. The aim of the present study was to clarify the implication of polysomy 17 in ERBB2 and topoisomerase IIα expression. In addition, we assessed the relation of ERBB2 and topoisomerase IIα gene dosage to mRNA and protein levels. Methods: We selected 83 cases diagnosed as invasive breast cancer. We analysed ERBB2 and topoisomerase IIα genes, mRNA and protein by fluorescence in situ hybridisation, real-time reverse-transcription polymerase chain reaction and immunohistochemistry. Results: We observed a progressive increase in mRNA expression from 0+ to 3+ and also a significant difference in the ERBB2 RNA levels between normal and amplified cases. We found that polysomy of chromosome 17 does not affect the ERBB2 expression and that topoisomerase IIα mRNA expression is not related to gene status. Conclusions: Our results demonstrate that polysomy of chromosome 17 is not related to ERBB2 expression. Thereby, it is important to use centromeric probes to clearly discriminate between true ERBB2 gene amplification and polysomy of chromosome 17.

Down-regulation of human topoisomerase IIα expression correlates with relative amounts of specificity factors Sp1 and Sp3 bound at proximal and distal promoter regions

BackgroundTopoisomerase IIα has been shown to be down-regulated in doxorubicin-resistant cell lines. The specificity proteins Sp1 and Sp3 have been implicated in regulation of topoisomerase IIα transcription, although the mechanism by which they regulate expression is not fully understood. Sp1 has been shown to bind specifically to both proximal and distal GC elements of the human topoisomerase IIα promoter in vitro, while Sp3 binds only to the distal GC element unless additional flanking sequences are included. While Sp1 is thought to be an activator of human topoisomerase IIα, the functional significance of Sp3 binding is not known. Therefore, we sought to determine the functional relationship between Sp1 and Sp3 binding to the topoisomerase IIα promoter in vivo. We investigated endogenous levels of Sp1, Sp3 and topoisomerase IIα as well as binding of both Sp1 and Sp3 to the GC boxes of the topoisomerase IIα promoter in breast cancer cell lines in vivo after short term doxorubicin exposure.ResultsFunctional effects of Sp1 and Sp3 were studied using transient cotransfection assays using a topoisomerase IIα promoter reporter construct. The in vivo interactions of Sp1 and Sp3 with the GC elements of the topoisomerase IIα promoter were studied in doxorubicin-treated breast cancer cell lines using chromatin immunoprecipitation assays. Relative amounts of endogenous proteins were measured using immunoblotting. In vivo DNA looping mediated by proteins bound at the GC1 and GC2 elements was studied using the chromatin conformation capture assay. Both Sp1 and Sp3 bound to the GC1 and GC2 regions. Sp1 and Sp3 were transcriptional activators and repressors respectively, with Sp3 repression being dominant over Sp1-mediated activation. The GC1 and GC2 elements are linked in vivo to form a loop, thus bringing distal regulatory elements and their cognate transcription factors into close proximity with the transcription start site.ConclusionThese observations provide a mechanistic explanation for the modulation of topoisomerase IIα and concomitant down-regulation that can be mediated by topoisomerase II poisons. Competition between Sp1 and Sp3 for the same cognate DNA would result in activation or repression depending on absolute amounts of each transcription factor in cells treated with doxorubicin.

Evaluation of Topoisomerase IIa Expression in Pancreatic Ductal Adenocarcinoma: A Pilot Study Using Chromogenic in situ Hybridization and Immunohistochemistry on Tissue Microarrays

Background/Aims: To co-evaluate topoisomerase Ila (Topo Ila) protein expression and gene status in pancreatic ductal adenocarcinoma, determining the potential prognostic impact of its alterations. Methods: Using tissue microarrays, 50 sporadic, primary pancreatic ductal adenocarcinomas were cored twice and re-embedded into one paraffin block with a core diameter of 1 mm. Immunohistochemistry and chromogenic in situ hybridization were performed in serial tissue sections for the detection of protein expression levels, chromosome 17 and Topo Ila gene status, respectively. Finally using a semi-automated image analysis system we evaluated the levels of protein expression. Results: A significant proportion of the tumors showed Topo Ila overexpression (32/50 or 64%). Gene amplification and deletion were detected in 9 and 4 cases, respectively, associated with protein overexpression. Aneuploidy regarding chromosome 17 was observed in 19/50 tumors and correlated with poor survival rate (Cox regression test: p = 0.001). Topo Ila protein expression was strongly correlated with stage (p = 0.021) and grade (p = 0.034). Conclusions: Topo Ila gene amplification correlates with protein overexpression, but not vice versa. This is a crucial observation for the application of targeted chemotherapies, such as anthracyclines, only in subgroups of patients, according to molecular deregulation criteria and not only to immunohistochemical results. Also, chromosome 17 and not Topo Ila gene instability can be used as a potential independent prognostic factor.

Prognostic significance of cyclooxygenase‐2 and DNA topoisomerase IIα expression in oral carcinoma

Despite recent advances in the diagnosis and treatment of oral carcinoma, outcomes remain disappointing. The identification of new prognostic factors is necessary to improve survival. To determine the prognostic significance of cyclooxygenase (COX)-2 and DNA topoisomerase (DNA-Topo) IIalpha expression in patients with oral carcinoma, we immunohistochemically examined these enzymes and studied their relation to overall 5-year survival. Surgical specimens were obtained from 160 patients with oral carcinoma, 80 with and 80 without regional lymph node metastasis. The specimens were immunostained for COX-2 and DNA-Topo IIalpha as an index of cell proliferative activity. COX-2 immunoreactivity and clinicopathological data were analyzed, and 5-year survival was calculated by the Kaplan-Meier method. COX-2 expression in primary lesions was higher in cases with lymph node metastasis than in those without lymph node metastasis. An increase in tumor size was associated with increased COX-2 expression. In most cases with lymph node metastasis, COX-2 expression was higher in metastatic lesions than in primary lesions. As COX-2 expression increased, the DNA-Topo IIalpha labeling index significantly increased and the overall 5-year survival rate decreased. Expression of COX-2 and DNA-Topo IIalpha were related to lymph node metastasis, cell proliferative activity, and overall 5-year survival rate in oral carcinoma. These enzymes may therefore be valuable diagnostic and prognostic indices in oral carcinoma.

Modulation of topoisomerase IIα expression by a DNA sequence-specific polyamide

Topoisomerase IIalpha (topo IIalpha) is an important target for several chemotherapeutic agents, including etoposide and doxorubicin. Confluent cells express low levels of topo IIalpha and are resistant to etoposide treatment. Repression of transcription in confluent cells is mediated by binding of the transcription factor NF-Y to inverted CCAAT motifs within the topo IIalpha promoter. To block the repressive binding of NF-Y, a polyamide (JH-37) was designed to bind to the flanking regions of selected CCAAT sites within the topo IIalpha promoter. Electrophoretic mobility shift assays and DNase I footprinting assays showed occupancy of the inverted CCAAT sites by JH-37. Chromatin immunoprecipitation assays confirmed in vivo inhibition of NF-Y binding to the topo IIalpha promoter. Following incubation of confluent NIH3T3 cells with JH-37, increased expression of topo IIalpha mRNA and protein was detectable. This correlated both with increased DNA double-strand breaks as shown by comet assay and decreased cell viability following exposure to etoposide. Polyamides can modulate gene expression and chemosensitivity of cancer cells.

Topoisomerase IIα expression correlates with diminished disease-free survival in invasive breast cancer

Topoisomerase II alpha (Topo II alpha) plays a role in DNA replication and is the molecular target for anthracyline-based chemotherapy. The purpose of this study was to evaluate the relationship between Topo II alpha expression and survival in patients with invasive breast cancer. Formalin-fixed, paraffin-embedded tumor specimens from 24 women with invasive breast cancer were stained for Topo II alpha expression. All women underwent mastectomy. Radiotherapy was given at the University of Utah Department of Radiation Oncology. Of the patients, 23 (96%) received chemotherapy. The level of Topo II alpha expression within tumor cells was compared with clinical factors and overall survival. The median percentage of tumor cells expressing Topo II alpha was 70%. Increased Topo II alpha tumor expression significantly correlated with diminished disease-free survival. Five-year disease-free survival was 100% for patients with <70% of breast cancer cells expressing Topo II alpha compared with 42% for patients with > or =70% Topo II alpha expression (p = 0.008). The level of Topo II alpha expression within tumor cells correlated with T stage (p = 0.008) but not with other pathologic factors. Increased Topo II alpha expression significantly correlated with diminished disease-free survival in patients with invasive breast cancer. These findings may indicate a role for Topo II alpha expression as a prognostic factor in breast cancer.

Protein Kinase C δ Activates Topoisomerase IIα To Induce Apoptotic Cell Death in Response to DNA Damage

ABSTRACT DNA topoisomerase II is an essential nuclear enzyme that modulates DNA processes by altering the topological state of double-stranded DNA. This enzyme is required for chromosome condensation and segregation; however, the regulatory mechanism of its activation is largely unknown. Here we demonstrate that topoisomerase IIα is activated in response to genotoxic stress. Concomitant with the activation, the expression of topoisomerase IIα is increased following DNA damage. The results also demonstrate that the proapoptotic kinase protein kinase C δ (PKCδ) interacts with topoisomerase IIα. This association is in an S-phase-specific manner and is required for stabilization and catalytic activation of topoisomerase IIα in response to DNA damage. Conversely, inhibition of PKCδ activity attenuates DNA damage-induced activation of topoisomerase IIα. Finally, aberrant activation of topoisomerase IIα by PKCδ is associated with induction of apoptosis upon exposure to genotoxic agents. These findings indicate that PKCδ regulates topoisomerase IIα and thereby cell fate in the genotoxic stress response.

Association between Immunohistochemical Expression of Topoisomerase IIα, Her2 and Hormone Receptors and Response to Primary Chemotherapy in Breast Cancer

The aim of this study was to evaluate the association between immunohistochemical expression of topoisomerase IIalpha, HER2 and hormone receptors and response to primary anthracycline-based chemotherapy in locally advanced breast cancer. We analyzed 109 medical charts of patients treated with primary anthracycline-based chemotherapy in the Women's Integral Health Care Center from 1996 to 2004. The clinical and pathological response to primary chemotherapy was associated with topoisomerase Ilalpha and HER2 expression and hormone receptor negativity. Statistical analysis was performed using chi-squared, Fisher's exact test and Mann-Whitney test. No statistical association between clinical response and expression of topoisomerase Ilalpha, HER2 and hormone receptor negativity was found. However, there was an association between complete pathological response and hormone receptor negativity (P = 0.0289). The present study suggested that these markers should not be considered predictors of response to primary anthracycline-based chemotherapy, and prospective studies must be designed for this purpose.

Targeting topoisomerase IIa in endometrial adenocarcinoma: a combined chromogenic in situ hybridization and immunohistochemistry study based on tissue microarrays

Topoisomerase IIa is a nucleic enzyme that affects the topological structure of DNA and also is a target for chemotherapy (ie, anthracyclines). In this study, we coevaluated its protein expression with chromosome 17 and gene status. Using tissue microarrays, 40 cases of sporadic, primary endometrial adenocarcinomas, 5 cases of atypical hyperplasia, and 5 cases of benign hyperplasia were obtained and reembedded into two paraffin blocks with a core diameter of 1 mm. Immunohistochemistry combined with chromogenic in situ hybridization was performed in 2 and 5 microm sections, respectively. Finally using a semiautomated Image Analysis System, we evaluated the levels of Nuclear labeling index of topoisomerase IIa expression. Statistical analysis was performed by SPSS version 11.0 software. The results indicate that chromosome 17 instability (aneuploidy in 7/40 cases) and Topo IIa gene deregulation (amplification in 3/40 and deletion in 1/40 cases) are significant genetic events correlated with biologic behavior in endometrial adenocarcinoma. Because protein overexpression was observed in a significant proportion of the tumors (18/40), detection of the specific gene deregulation mechanism is a crucial process for application of targeted chemotherapies, which are characterized by different levels of cardiotoxicity and other serious effects.

Topoisomerase II-α expression increases with increasing Gleason score and with hormone insensitivity in prostate carcinoma

Aim: To investigate and compare topoisomerase II-α expression in benign prostatic hyperplasia (BPH), prostate cancer of varying Gleason scores and hormone-insensitive prostate cancer. Methods: The immunohistochemical expression of topoisomerase II-α...

Changes of Topoisomerase IIα Expression in Breast Tumors after Neoadjuvant Chemotherapy Predicts Relapse-Free Survival

To assess the value of changes in the expression of topoisomerase IIalpha (TopoII) and the proto-oncogene erbB-2 (HER-2) as predictors of relapse-free survival in women with operable breast cancer treated with anthracycline-based neoadjuvant chemotherapy. Seventy-seven patients with primary breast cancer who had undergone neoadjuvant anthracycline-based chemotherapy were included in the present study. TopoII and HER-2 were measured by immunohistochemistry in prechemotherapy and postchemotherapy (at the time of surgery) tumor specimens, and the value of their changes as predictors of relapse-free survival were evaluated by Kaplan-Meier and Cox proportional hazard regression analyses. Neoadjuvant chemotherapy resulted in a significant reduction in the percentage of cells expressing TopoII (P < 0.0001). No significant change was observed for HER-2. TopoII and HER-2 expression before chemotherapy predicted tumor response to treatment. Changes in TopoII expression after chemotherapy were strongly associated with a poor relapse-free survival (P < 0.0001) in a Cox multivariate analysis adjusted for other clinicopathologic prognostic factors. Changes in TopoII expression after anthracycline-based neoadjuvant chemotherapy is an independent predictor of a poor relapse-free survival in patients with breast cancer. Tumor cells displaying an increased TopoII expression after treatment may be responsible for relapses, and may, therefore, define a group of patients with anthracycline-resistant breast cancer.

The expression of topoisomerase II alpha mRNA is increased by the minor groove DNA‐binding drug Hoechst 33258 in African green monkey kidney (Vero) cells

Topoisomerase IIα is a gene that plays a critical role in the replication of DNA. Several anti-tumor chemotherapeutic agents selectively target the topoisomerase IIαprotein and promote the death of rapidly dividing tumor cells. In many drug resistant tumors, topoisomerase IIαhas been shown to be transcriptionally down regulated. This lowered level of topoisomerase IIαexpression has an adverse effect on the chemosensitivity of tumors to anti-tumor chemotherapeutic agents. In this study, we examined the effect of the DNA minor groove-binding agent Hoechst 33258 on the expression of topoisomerase IIα mRNA in subconfluent Vero and MCF-7 cell lines. While we did not detect endogenous expression of topoisomerase IIα mRNA in the MCF-7 cells, the addition of hoechst 33258 to Vero cells resulted in increased expression of topoisomerase IIα mRNA. In order to further investigate these results, we have amplified and cloned the promoter regions of topoisomerase IIα from both Vero and human genomic DNA into the luciferase reporter vector pGL3. Transient transfection analysis and sequence comparisons of the promoter regions from both human and monkey genomic DNA will provide additional information as to the role conserved promoter elements have in promoting the up regulation of topoisomerase IIα in response to Hoechst 33258. Results from these studies will help to identify sequence specific promoter elements that can be targeted for modifying the expression of genes known to be influential in the chemosensitivity of cancer cells. This research was supported through funding from NIH Grant 1R15CA096723-01

Altered Expression Pattern of Topoisomerase IIα, in Ovarian Tumor Epithelial and Stromal Cells after Platinum-Based Chemotherapy

OBJECTIVE: The aim of this study was to evaluate the expression of topoisomerase IIα (TOP2A) in epithelial and stromal cells of ovarian cancer. METHODS: TOP2A expression was analyzed in normal ovarian tissue and in laser-microdissected ovarian tumor epithelial and adjacent stromal cells using quantitative real time RT-PCR (n = 38), RNA in situ hybridization (n =13), and immunhistochemistry (n = 69). Results: TOP2A mRNA was detected by RNA in situ hybridization in all ovarian cancer samples, with stronger hybridization signals in tumor epithelial cells compared to adjacent stromal cells. The same expression pattern was found by immunohistochemistry (P = .0001). Very interestingly, specific changes of TOP2A were found in recurrent ovarian cancer after platinum-based chemotherapy: TOP2A expression decreased in tumor epithelial cells (P = .056) of recurrent ovarian cancer, whereas it increased in tumor adjacent stromal cells (P = .023) compared to primary ovarian cancer. CONCLUSION: TOP2A mRNA and protein expressions in ovarian cancer exhibit specific patterns in tumor epithelial and adjacent stromal cells, which are differentially modulated after platinum-based chemotherapy. These data support the possible importance of the stromal compartment in tumor progression and suggest that tumor stromal cells might be relevant to the development of chemotherapy resistance in ovarian cancer.

Targeting topoisomerase IIa in endometrial adenocarcinoma

Topoisomerase IIa is a nucleic enzyme that affects the topological structure of DNA and also is a target for chemotherapy (ie, anthracyclines). In this study, we coevaluated its protein expression with chromosome 17 and gene status. Using tissue microarrays, 40 cases of sporadic, primary endometrial adenocarcinomas, 5 cases of atypical hyperplasia, and 5 cases of benign hyperplasia were obtained and reembedded into two paraffin blocks with a core diameter of 1 mm. Immunohistochemistry combined with chromogenic in situ hybridization was performed in 2 and 5 μm sections, respectively. Finally using a semiautomated Image Analysis System, we evaluated the levels of Nuclear labeling index of topoisomerase IIa expression. Statistical analysis was performed by SPSS version 11.0 software. The results indicate that chromosome 17 instability (aneuploidy in 7/40 cases) and Topo IIa gene deregulation (amplification in 3/40 and deletion in 1/40 cases) are significant genetic events correlated with biologic behavior in endometrial adenocarcinoma. Because protein overexpression was observed in a significant proportion of the tumors (18/40), detection of the specific gene deregulation mechanism is a crucial process for application of targeted chemotherapies, which are characterized by different levels of cardiotoxicity and other serious effects.

Synergistic Interaction between Histone Deacetylase and Topoisomerase II Inhibitors Is Mediated through Topoisomerase IIβ

DNA topoisomerase II inhibitors and poisons are among the most efficacious drugs for the treatment of cancer. Sensitivity of cancer cells to the cytotoxic effects of topoisomerase II targeting agents is thought to depend on the expression of the topoisomerase IIalpha isoform, and drug resistance is often associated with loss or mutation of topoisomerase IIalpha. Histone deacetylase inhibitors (HDACi) are a novel class of compounds that potentiate the antitumor effects of topoisomerase II-targeting agents. The interaction between HDACi and topoisomerase II-targeting agents in cancer cells was evaluated as a function of topoisomerase IIalpha and topoisomerase IIbeta expression. Topoisomerase II isoforms were selectively depleted using small interfering RNA and antisense. Drug-induced formation of cleavable complexes involving topoisomerase IIalpha and topoisomerase IIbeta was evaluated by trapped-in-agarose DNA immunostaining and band depletion assays in the presence and absence of HDACi. Preexposure to HDACi increased the cytotoxicity of topoisomerase II poisons. This was associated with a down-regulation of topoisomerase IIalpha expression but had no effects on topoisomerase IIbeta. In the setting of HDACi-induced chromatin decondensation and topoisomerase IIalpha depletion, topoisomerase II poison cytotoxicity was mediated through topoisomerase IIbeta cleavable complex formation. The HDACi-induced sensitization was also observed in cells with target-specific resistance to topoisomerase II poisons. The recruitment of topoisomerase IIbeta as a target may overcome primary or emergent drug resistance to topoisomerase II-targeting agents and hence may broaden the applicability of this important class of anticancer agents.

Overexpression of Cyclooxygenase-2 Is Associated with a Favorable Prognostic Phenotype in Breast Carcinoma

Objectives: Cyclooxygenase (COX) is the rate-limiting enzyme that catalyzes the conversion of arachidonic acid to prostaglandins. The purpose of the present study was to investigate the involvement of COX-2 protein in breast cancer biological behavior through its correlation with the well-known clinicopathological parameters and the expression of p53, c-erbB-2, topoisomerase IIα (topoIIα) and peroxisome proliferator-activated receptor (PPARγ) proteins, as well as its effect on patients’ survival. Methods: We performed immunohistochemistry to detect COX-2, estrogen receptor (ER), progesterone receptor (PR), p53, c-erbB-2, topoIIα and PPARγ proteins in 175 cases of invasive breast carcinomas. The results were elaborated by statistic analysis. Results: Cytoplasmic expression of COX-2 was detected in 66.9% of breast carcinoma samples and was inversely correlated with both nuclear and histological grade (p < 0.0001 and p = 0.039, respectively), whereas its association with PR was found to be positive (p = 0.016). COX-2 expression was inversely correlated with topoIIα and p53 (p = 0.033 and p = 0.002, respectively), whereas its association with PPARγ was parallel (p < 0.0001). In addition, c-erbB-2 of tumor cells was inversely correlated with COX-2 in stromal cells of the tumor (p = 0.011). Neither univariate nor multivariate analysis demonstrated any association between COX-2 expression and patient overall or disease-free survival. Conclusions: The current data suggest that increased expression of COX-2 may be related to breast carcinomas with less aggressive phenotype. This suggestion is further supported by the positive correlation between COX-2 and PPARγ, since the latter is considered to be indicative of a less malignant phenotype of tumor cells.