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

BAZ2A-RNA mediated association with TOP2A and KDM1A represses genes implicated in prostate cancer

BAZ2A represses rRNA genes (rDNA) that are transcribed by RNA polymerase I. In prostate cancer (PCa), BAZ2A function goes beyond this role because it represses genes frequently silenced in metastatic disease. However, the mechanisms of this BAZ2A-mediated repression remain elusive. Here, we show that BAZ2A represses genes through its RNA-binding TAM domain using mechanisms differing from rDNA silencing. Although the TAM domain mediates BAZ2A recruitment to rDNA, in PCa, this is not required for BAZ2A association with target genes. Instead, the BAZ2A-TAM domain in association with RNA mediates the interaction with topoisomerase 2A (TOP2A) and histone demethylase KDM1A, whose expression positively correlates with BAZ2A levels in localized and metastatic PCa. TOP2A and KDM1A pharmacological inhibition up-regulate BAZ2A-repressed genes that are regulated by inactive enhancers bound by BAZ2A, whereas rRNA genes are not affected. Our findings showed a novel RNA-based mechanism of gene regulation in PCa. Furthermore, we determined that RNA-mediated interactions between BAZ2A and TOP2A and KDM1A repress genes critical to PCa and may prove to be useful to stratify prostate cancer risk and treatment in patients.

Synthesis and evaluation of 7-(3-aminopropyloxy)-substituted flavone analogue as a topoisomerase IIα catalytic inhibitor and its sensitizing effect to enzalutamide in castration-resistant prostate cancer cells

Prostate cancer patients primarily receive androgen receptor (AR)-targeted drugs as a primary treatment option because prostate cancer is associated with highly activated AR signaling. AR amplification made prostate cancer cells viable under treatment of AR-targeted therapy, leading to castration resistance. AR amplification was more common in enzalutamide-resistant patients. As a strategy to overcome castration resistance and to improve the efficacy of enzalutamide, second-generation nonsteroidal antiandrogen drugs for castration-resistant prostate cancer (CRPC) including topoisomerase II (topo II) poisons such as etoposide and mitoxantrone, have been administered in combination with enzalutamide. In the present study, it was confirmed that amplification of topo IIα, but not I and IIβ, was directly and proportionally associated with poor clinical outcome of Prostate cancer. Among a novel series of newly designed and synthesized 7-(3-aminopropyloxy)-substituted flavone analogues, compound 6, the most potent derivative, was further characterized and identified as a topo IIα catalytic inhibitor that intercalates into DNA and binds to the DNA minor groove with better efficacy and less genotoxicity than etoposide, a topo II poison. Compound 6 showed remarkable efficacy in inhibiting AR-negative CRPC cell growth and sensitizing activity to enzalutamide in AR-positive CRPC cells, thus confirming the potential of topo IIα catalytic inhibitor to overcome resistance to androgen deprivation therapy.

AK-I-190, a New Catalytic Inhibitor of Topoisomerase II with Anti-Proliferative and Pro-Apoptotic Activity on Androgen-Negative Prostate Cancer Cells

Castration-resistant prostate cancer (CRPC) is a clinical challenge in treatment because of its aggressive nature and resistance to androgen deprivation therapy. Topoisomerase II catalytic inhibitors have been suggested as a strategy to overcome these issues. We previously reported AK-I-190 as a novel topoisomerase II inhibitor. In this study, the mechanism of AK-I-190 was clarified using various types of spectroscopic and biological evaluations. AK-I-190 showed potent topoisomerase II inhibitory activity through intercalating into DNA without stabilizing the DNA-enzyme cleavage complex, resulting in significantly less DNA toxicity than etoposide, a clinically used topoisomerase II poison. AK-I-190 induced G1 arrest and effectively inhibited cell proliferation and colony formation in combination with paclitaxel in an androgen receptor–negative CRPC cell line. Our results confirmed that topoisomerase II catalytic inhibition inhibited proliferation and induced apoptosis of AR-independently growing prostate cancer cells. These findings indicate the clinical relevance of topoisomerase II catalytic inhibitors in androgen receptor-negative prostate cancer.

Etoposide and topoisomerase II inhibition for aggressive prostate cancer: Data from a translational study

BACKGROUND

Etoposide phosphate (VP-16) is a topoisomerase 2 (TOP2) inhibitor that demonstrated activity in patients with metastatic castration-resistant prostate cancer (mCRPC). We investigated the sensitivity of prostate cancer (PCa) cells (LNCaP, 22Rv1, PC3, DU145, PDB and MDB) to VP-16 and the possible relationship between VP-16 activity and TOP2 expression. The activity of VP-16 was compared with that of docetaxel, enzalutamide and olaparib. The prevalence and clinical significance of TOP2 genetic and transcriptomic alterations was also explored in mCRPC.

METHODS

Cell cultures and crystal violet cell proliferation assays were performed. Specific antibodies were used in western blots analyses of cell protein extracts. Datasets were analyzed in cBioportal.

RESULTS

VP-16 was active in all PCa cell lines analyzed and demonstrated increased activity in PC3 and DU145 cells. VP-16 was more cytotoxic compared to the other treatments, except for LNCaP and 22Rv1, which were more sensitive to docetaxel. Maintenance of antiandrogen treatment in MDB and PDB increased sensitivity to VP-16, docetaxel and enzalutamide. TOP2A was found overexpressed in 22Rv1, DU145 and PC3, whereas TOP2B was overexpressed in 22Rv1 and PDB. In the mCRPC datasets analysis, TOP2A mRNA overexpression was associated with worse patients' prognosis, with the molecular features of neuroendocrine prostate cancer (NEPC) and with lower androgen receptor (AR) score. Patients overexpressing TOP2A mRNA were more likely to harbor RB1 loss.

CONCLUSIONS

Specific subpopulations of patients with aggressive variant prostate cancer (AVPC) could benefit from VP-16 treatment. TOP2A overexpression, rather than TOP2B, might be a good biomarker to predict response to VP-16.

SPOP is essential for DNA-protein cross-link repair in prostate cancer cells: SPOP-dependent removal of topoisomerase 2A from the topoisomerase 2A-DNA cleavage complex

SPOP, speckle-type POZ protein is a substrate adaptor protein of the Cullin-3/RING ubiquitin E3 complex. The spop gene is the most commonly point mutated in human primary prostate cancers, but the pathological contribution of the SPOP mutations remains unclear. In this study, we investigated several known factors that are critical in the DNA–­protein cross-link repair process. The depletion of SPOP or overexpression of a prostate cancer–associated SPOP mutant, F133V, in androgen receptor-positive prostate cancer cells increased the amount of topoisomerase 2A (TOP2A) in the nuclei together with the increased amount of γH2AX, an indication of DNA breaks. Tyrosyl–DNA phosphodiesterases (TDPs) and an endo/exonuclease MRE11 are enzymes that liberate TOP2A from the TOP2A–DNA cleavage complex, and thus is essential for the completion of the DNA repair process. We found that the amount of TDP1 and TDP2 was decreased in SPOP-depleted cells, and that of TDP2 and MRE11 was decreased in F133V-overexpressing cells. These results suggest that the F133V mutant exerts dominant-negative and gain-of-function effects in down-regulation of TDP2 and MRE11, respectively. We conclude that SPOP is involved in the DNA–protein cross-link repair process through the elimination of TOP2A from the TOP2A cleavage complex, which may contribute to the genome stability.

Expression of Topoisomerase II-α protein in salivary gland tumors

Salivary glands give rise to approximately 30 histological distinct tumor types, which results in a diagnostic challenge for the pathologist. The present retrospective, immunohistochemical study aimed to evaluate the expression of Topoisomerase II-α, a nuclear enzyme, as a diagnostic and prognostic marker in benign and malignant salivary gland tumors, including leomorphic adenoma, mucoepidermoid carcinoma, acinic cell carcinoma and carcinoma ex-pleomorphic adenoma. A total of 59 cases of benign and malignant salivary gland tumors were included in the present study. Representative paraffin-embedded sections were immunostained for Topoisomerase II-α (Topo II-α). The expression level was semi-quantified for each case and then correlated with the histological diagnosis using hematoxylin and eosin-stained slides, grade of tumor and total survival. Significant differences were revealed between the expression level of Topo II-α in pleomorphic adenoma and mucoepidermoid carcinoma (P<0.001), carcinoma ex-pleomorphic adenoma (P<0.001), acinic cell carcinoma (P=0.005) and a group composed of all the malignant tumors (P<0.001). Cancer-specific survival rates were insignificantly increased in tumors expressing low levels of Topo II-α (P=0.464). Thus, the present study demonstrated different expression levels of Topo II-α in benign and malignant salivary gland tumors. These differing expression levels may act as valuable biomarkers for the correct histological diagnosis. Further studies conducted on a larger scale may lead to even more conclusive results.

Topoisomerase 2 Alpha Cooperates with Androgen Receptor to Contribute to Prostate Cancer Progression

Overexpression of TOP2A is associated with risk of systemic progression in prostate cancer patients, and higher levels of TOP2A were found in hormone-resistant cases. To elucidate the mechanism by which high levels of TOP2A contribute to tumor progression we generated TOP2A overexpressing prostate cancer cell lines. We show that TOP2A promotes tumor aggressiveness by inducing chromosomal rearrangements of genes that contribute to a more invasive phenotype. Anti-androgen treatment alone was ineffective in killing TOP2A overexpressing cells due to activation of an androgen receptor network. TOP2A poisons killed tumor cells more efficiently early in the progression course, while at later stages they provided greater benefit when combined with anti-androgen therapy. Mechanistically, we find that TOP2A enhances androgen signaling by facilitating transcription of androgen responsive genes, thereby promoting tumor cell growth. These studies revealed a relationship between TOP2A and androgen receptor signaling pathway that contributes to prostate cancer progression and confers sensitivity to treatments.

Catalytic inhibitors of DNA topoisomerase II suppress the androgen receptor signaling and prostate cancer progression

Although the new generation of androgen receptor (AR) antagonists like enzalutamide (ENZ) prolong survival of metastatic castration-resistant prostate cancer (CRPC), AR-driven tumors eventually recur indicating that additional therapies are required to fully block AR function. Since DNA topoisomerase II (Topo II) was demonstrated to be essential for AR to initiate gene transcription, this study tested whether catalytic inhibitors of Topo II can block AR signaling and suppress ENZ-resistant CRPC growth. Using multiple prostate cancer cell lines, we showed that catalytic Topo II inhibitors, ICRF187 and ICRF193 inhibited transcription activities of the wild-type AR, mutant ARs (F876L and W741C) and the AR-V7 splice variant. ICRF187 and ICRF193 decreased AR recruitment to target promoters and reduced AR nuclear localization. Both ICRF187 and ICRF193 also inhibited cell proliferation and delayed cell cycling at the G2/M phase. ICRF187 inhibited tumor growth of castration-resistant LNCaP and 22RV1 xenografts as well as ENZ-resistant MR49F xenografts. We conclude that catalytic Topo II inhibitors can block AR signaling and inhibit tumor growth of CRPC xenografts, identifying a potential co-targeting approach using these inhibitors in combination with AR pathway inhibitors in CRPC.

Antiproliferative activities of Fagara xanthoxyloides and Pseudocedrela kotschyi against prostate cancer cell lines

BACKGROUND/AIM

Roots of Fagara zanthoxyloides and Pseudocedrela kotchyii are used as chewing sticks and as medicinal remedies for diarrhea, cough and fever in West Africa. Extracts of the two plants also possess anti-bacterial, anti-fungal and anti-malarial activities. The aim of the present study was to determine the effects of such extracts on the growth, proliferation and induction of apoptosis in four prostate cancer cell lines. Materials and Methods. Androgen-independent PC3 and DU-145 and androgen-dependent LNCaP and CWR-22 prostate cancer cell lines were cultured for five days with different concentrations of the extracts and examined for growth inhibition and evidence of apoptosis.

RESULTS

Irrespective of their androgen dependence, all four cancer cell lines exhibited a dose-dependent decrease in cell proliferation and viability by the 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium bromide (MTT) assay and in induction of apoptosis. The results also show that LNCap cells were the most sensitive to the two extracts, with highest inhibition at day 3 and exhibiting the highest rate of apoptosis. Conclusion. These observations suggest that F. zanthoxyloides and P. kotchyii could serve as potential chemopreventive agents in the treatment of prostate cancer.

Prognostication of prostate cancer based on TOP2A protein and gene assessment: TOP2A in prostate cancer

Background

TOP2A encodes for topoisomerase IIα, a nuclear enzyme that controls DNA topological structure and cell cycle progression. This enzyme is a marker of cell proliferation in normal and neoplastic tissues; however, little information is available about its expression in prostate cancer (PCa).

Methods

Immunohistochemistry (IHC) was automated using mouse monoclonal antibody against TOP2A (clone SWT3D1; DAKO, Carpenteria, CA, USA) at dilution 1:800 and Flex Plus detection system in autostainer 48Ultra (DAKO). FISH was performed using TOP2A (17q21)/ CEP17 probe kit (Kreateck Biotechnology, San Diego, CA, USA). Biochemical and pathological data from 193 patients with PCa were retrieved for the analysis, whose significance was considered when p < 0.05. Also, fractal analysis was performed in a subset of 20 randomly selected cases.

Results

TOP2A protein expression correlated with higher Gleason scores and higher levels of preoperative PSA (p = 0.018 and p = 0.011). Patients with higher levels of TOP2A presented shorter biochemical recurrence-free survival (BRFS) (p = 0.001). In multivariate analysis, we found that TOP2A remained an independent prognostic factor of BRFS, with a relative risk of 1.98 (p = 0.001; 95% CI, 1.338–2.93); thus, cases that expressed high levels of this enzyme had a shorter BRFS compared with TOP2A-negative or TOP2A-low cases. No alterations in TOP2A gene status nor correlation between FISH and IHC results were observed. Concerning fractal analysis, patients who expressed higher levels of TOP2A have angiolymphatic invasion and presented higher Gleason scores (p = 0.033 and p = 0.025, respectively). Also, patients with higher expression of TOP2A presented shorter BRFS (p = 0.001).

Conclusions

This is the first study to perform TOP2A protein and gene digital assessment and fractal analysis in association with BRFS in a large series of PCa. Also, we show that TOP2A gene copy number alterations are not observed in this type of tumor. So, higher protein expression of TOP2A is not related to gene amplification in PCa. Furthermore, TOP2A protein assessment has prognostic importance and, due to its relation with poor outcome, TOP2A IHC evaluation in the biopsy can represent an important tool for selecting the most suitable surgical and clinical approach for patients with PCa.

MicroRNA profiles of prostate carcinoma detected by multiplatform microRNA screening

MicroRNAs (miRNAs) are small RNA molecules that regulate gene expression via posttranscriptional inhibition of protein synthesis. They play a vital role in tumorigenesis. To characterize the diagnostic potential of miRNAs in prostate cancer, a leading cause of cancer mortality, we performed screening of miRNA expression profiles. We used commercially available microarrays to establish miRNA expression profiles from a cohort of 20 cancer samples. The expression of selected miRNAs was analyzed by quantitative real-time PCR and the identity of miRNA expressing cells was determined by miRNA in situ hybridization. We identified 25 miRNAs that showed a significant differential expression in cancer samples. The comparison with previously published data generated by deep sequencing of cDNA libraries of small RNA molecules revealed a concordance rate of 47% among miRNAs identified with both techniques. The differential expression of miRNAs miR-375, miR-143 and miR-145 was validated by quantitative PCR. MiRNA in situ hybridization revealed that the differential expression is cancer-cell associated. A combination of three miRNAs correctly classified tissue samples with an accuracy of 77.6% with an area under the receiver-operator characteristic curve of 0.810. Our data extend the knowledge about the deregulation of miRNAs in prostate cancer. The differential expression of several miRNAs is highly consistent using independent cohorts of tumor samples, different tissue preservation methods and different experimental methods. Our results indicate that combinations of miRNAs are promising biomarkers for the diagnosis of prostate cancer.

Antiproliferative mechanisms of the flavonoids 2,2'-dihydroxychalcone and fisetin in human prostate cancer cells

We have previously demonstrated the antiproliferative effect of two flavonoids-2,2'-dihydroxychalcone (DHC), a novel synthetic flavonoid, and fisetin, a naturally occurring flavonol-in prostate cancer cells. In this study, we further examine the mechanisms of these compounds on survival and proliferation pathways. DHC and fisetin (1-50 microM) caused a dose-dependent reduction in viability, a concomitant increase in apoptosis in PC3 cells at 72 h, and a decrease in clonogenic survival at 24 h treatment. DHC was considerably more potent than fisetin in these cytotoxicity assays. The mechanism of accelerated cellular senescence was not activated by either compound in PC3 or lymph node carcinoma of the prostate (LNCaP) cells. Gene expression alterations in PC3 and LNCaP cells treated with 15 muM DHC and 25 microM fisetin for 6 to 24 h were determined by oligonucleotide array. Amongst the most highly represented functional categories of genes altered by both compounds was the cell cycle category. In total, 100 cell cycle genes were altered by DHC and fisetin including 27 genes with key functions in G2/M phase that were downregulated by both compounds. Other functional categories altered included chromosome organization, apoptosis, and stress response. These results demonstrate the multiple mechanisms of antitumor activity of DHC and fisetin in prostate cancer cells in vitro.

Gene expression changes are age-dependent and lobe-specific in the brown Norway rat model of prostatic hyperplasia

BACKGROUND

Benign prostatic hyperplasia (BPH) is an age-related enlargement of the prostate, characterized by increased proliferation of stromal and epithelial cells. Despite its prevalence, the etiology of BPH is unknown.

METHODS

The Brown Norway rat is a model for age-dependent, lobe-specific hyperplasia of the prostate. Histological analyses of the dorsal and lateral lobes from aged rats reveal focal areas characterized by increased numbers of luminal epithelial cells, whereas the ventral lobe is unaffected. This study examined differential gene expression by lobe and age in the Brown Norway rat prostate. The objective was to identify genes with different levels of expression in the prostate lobes from 4-month (young) and 24-month (old) animals, and to subsequently link changes in gene expression to mechanisms of prostate aging.

RESULTS

The number of age-dependent differentially expressed genes was greatest in the dorsal compared to the ventral and lateral lobes. Minimal redundancy was observed among the differentially expressed genes in the three lobes. Age-related changes in the expression levels of 14 candidate genes in the dorsal, lateral and ventral lobes were confirmed by quantitative RT-PCR. Genes that exhibited age-related differences in their expression were associated with proliferation, oxidative stress, and prostate cancer progression, including topoisomerase II alpha (Topo2a), aurora kinase B (Aurkb), stathmin 1 (Stmn1), and glutathione S-transferase pi. Immunohistochemistry for Topo2a, Aurkb, and Stmn1 confirmed age-related changes in protein localization in the lateral lobe of young and aged prostates.

CONCLUSION

These findings provide clues to the molecular events associated with aging in the prostate.

Topoisomerase IIalpha mRNA and protein expression in ovarian carcinoma: correlation with clinicopathological factors and prognosis

Topoisomerase IIalpha (Top IIalpha) is a nuclear enzyme that plays a central role in DNA metabolism, and is a molecular target for a variety of chemotherapeutic agents. Top IIalpha has recently gained attention as a biomarker for therapy response and patient survival. In this study, we attempted to assess the feasibility of measuring Top IIalpha gene expression in RNA, isolated from archival formalin-fixed paraffin-embedded tissue specimens, which are used routinely in pathology laboratories. We have employed a new technique on the basis of magnetic particles' separation and purification of nucleic acids, and evaluated both protein and mRNA expressions from the same routinely processed tissue blocks. We investigated the expression of Top IIalpha mRNA and protein by real-time reverse transcription polymerase chain reaction and immunohistochemistry, in a cohort of 133 primary ovarian carcinomas, and evaluated the association between Top IIalpha expression and clincopathological variables as well as patient outcome. Elevated Top IIalpha mRNA expression was observed in high-grade tumors (P=0.003) and advanced stage disease (P=0.011). In univariate Kaplan-Meier analysis, patients with higher expression of Top IIalpha nuclear protein had a significantly decreased overall survival (P=0.045). Interestingly, we detected cytoplasmic protein expression of Top IIalpha in a subset of samples. Cytoplasmic expression of Top IIalpha was associated with the expression of chromosomal region maintenance/exportin 1 (CRM1)-a nuclear export protein (P=0.008). Our study suggests that Top IIalpha overexpression is involved in the progression of ovarian cancer in a subset of the patients. Our results encourage the further evaluation of the prognostic and predictive values of Top IIalpha expression in ovarian carcinoma, which might help to assess the patients' risk profile, and the planning of an individualized therapy.

Gene panel model predictive of outcome in men at high-risk of systemic progression and death from prostate cancer after radical retropubic prostatectomy

PURPOSE

In men who are at high-risk of prostate cancer, progression and death from cancer after radical retropubic prostatectomy (RRP), limited prognostic information is provided by established prognostic features. The objective of this study was to develop a model predictive of outcome in this group of patients.

METHODS

Candidate genes were identified from microarray expression data from 102 laser capture microdissected prostate tissue samples. Candidates were overexpressed in tumor compared with normal prostate and more frequently in Gleason patterns 4 and 5 than in 3. A case control study of 157 high-risk patients, matched on Gleason score and stage with systemic progression or death of prostate cancer as the end point, was used to evaluate the expression of candidate genes and build a multivariate model. Tumor was collected from the highest Gleason score in paraffin-embedded blocks and the gene expression was quantified by real-time reverse transcription polymerase chain reaction. Validation of the final model was performed on a separate case-control study of 57 high-risk patients who underwent RRP.

RESULTS

A model incorporating gene expression of topoisomerase-2a, cadherin-10, the fusion status based on ERG, ETV1, and ETV4 expression, and the aneuploidy status resulted in a 0.81 area under the curve (AUC) in receiver operating characteristic statistical analysis for the identification of men with systemic progression and death from high grade prostate cancer. The AUC was 0.79 in the independent validation study.

CONCLUSION

The model can identify men with high-risk prostate cancer who may benefit from more intensive postoperative follow-up and adjuvant therapies.

Identification of prognostic biomarkers for prostate cancer

PURPOSE

This paper describes a process for the identification of genes that can report on the aggressiveness of prostate tumors and thereby add to the information provided by current pathologic analysis.

MATERIALS AND METHODS

Expression profiling data from over 100 laser capture microdissection derived samples from nonneoplastic epithelium; Gleason patterns 3, 4, and 5 and node metastasis prostate cancer were used to identify genes at abnormally high levels in only some tumors. These variably overexpressed genes were stratified by their association with aggressive phenotypes and were subsequently filtered to exclude genes with redundant expression patterns. Selected genes were validated in a case-control study in which cases (systemic progression within 5 years) and controls (no systemic progression at 7 years of follow-up) were matched for all clinical and pathologic criteria from time of prostatectomy (n = 175). Both cases and controls, therefore, could have nodal invasion or seminal vesicle involvement at the time of initial treatment.

RESULTS

A number of candidate variably overexpressed genes selected for their association with aggressive prostate cancer phenotype were evaluated in the case control study. The most prominent candidates were SSTR1 and genes related to proliferation, including TOP2A.

CONCLUSIONS

The process described here identified genes that add information not available from current clinical measures and can improve the prognosis of prostate cancer.

Low-level TOP2A amplification in prostate cancer is associated with HER2 duplication, androgen resistance, and decreased survival

HER2 and TOP2A genes, located on 17q, can be coamplified in cancer. Overexpression of both genes has been reported in high-grade, androgen-resistant prostate cancer. Both genes have not been compared in a single prostate cancer study and the frequency of TOP2A amplifications in prostate cancer is unknown. Using tissue microarrays, we did immunohistochemistry and fluorescence in situ hybridization for HER2 and TOP2A in 100 prostate cancers (41 localized and 59 advanced) and 42 cases of benign prostatic hyperplasia (BPH). Amplification was defined as a target/centromere signal ratio of > or =1.5. HER2 immunohistochemistry was scored from 0 to 3+. Percentage nuclei staining for topoisomerase IIalpha (topoIIalpha) was recorded; overexpression was defined as > or =5% cells staining. Eighteen (31%) advanced prostate cancers showed topoIIalpha overexpression; 12 (26%) showed TOP2A low-level amplification; 9 (16%) expressed HER2; and 6 (13%) showed HER2 low-level amplification. No high-level amplification of either gene (target/centromere signal ratio of > or =3.0) was detected. TOP2A coexpression and coamplification were seen in 75% and 66% of HER2-positive cases, respectively. Localized prostate cancer or BPH showed no gene amplification or topoIIalpha overexpression. Gene amplification or overexpression correlated with high stage and Gleason score. The presence of TOP2A amplification in advanced cancer was associated with androgen resistance and decreased survival by multivariate analysis. This is the first study to document low-level TOP2A amplification in prostate cancer and an association with reduced survival. TOP2A amplification may occur with or without HER2 duplication and is often associated with topoIIalpha expression. Therapies directed against topoIIalpha (and HER2) in such patients may improve survival.

Ethonafide-Induced Cytotoxicity Is Mediated by Topoisomerase II Inhibition in Prostate Cancer Cells

Ethonafide is an anthracene-containing derivative of amonafide that belongs to the azonafide series of anticancer agents. The lack of cross-resistance in multidrug-resistant cancer cell lines and the absence of a quinone and hydroquinone moiety make ethonafide a potentially less cardiotoxic replacement for existing anthracene-containing anticancer agents. For this study, we investigated the anticancer activity and mechanism of ethonafide in human prostate cancer cell lines. Ethonafide was cytotoxic against three human prostate cancer cell lines at nanomolar concentrations. Ethonafide was found to be better tolerated and more effective at inhibiting tumor growth compared with mitoxantrone in a human xenograft tumor regression mouse model. Mechanistically, we found that ethonafide inhibited topoisomerase II activity by stabilizing the enzyme-DNA complex, involving both topoisomerase IIalpha and -beta. In addition, ethonafide induced a potent G(2) cell cycle arrest in the DU 145 human prostate cancer cell line. By creating stable cell lines with decreased expression of topoisomerase IIalpha or -beta, we found that a decrease in topoisomerase IIalpha protein expression renders the cell line resistant to ethonafide. The decrease in sensitivity to ethonafide was associated with a decrease in DNA damage and an increase in DNA repair as measured by the neutral comet assay. These data demonstrate that ethonafide is a topoisomerase II poison and that it is topoisomerase IIalpha-specific in the DU 145 human prostate cancer cell line.