Regulation of tumor angiogenesis by EZH2

Vasohibin-1 is identified as a master-regulator of endothelial cell apoptosis using gene network analysis

BACKGROUND

Apoptosis is a critical process in endothelial cell (EC) biology and pathology, which has been extensively studied at protein level. Numerous gene expression studies of EC apoptosis have also been performed, however few attempts have been made to use gene expression data to identify the molecular relationships and master regulators that underlie EC apoptosis. Therefore, we sought to understand these relationships by generating a Bayesian gene regulatory network (GRN) model.

RESULTS

ECs were induced to undergo apoptosis using serum withdrawal and followed over a time course in triplicate, using microarrays. When generating the GRN, this EC time course data was supplemented by a library of microarray data from EC treated with siRNAs targeting over 350 signalling molecules.The GRN model proposed Vasohibin-1 (VASH1) as one of the candidate master-regulators of EC apoptosis with numerous downstream mRNAs. To evaluate the role played by VASH1 in EC, we used siRNA to reduce the expression of VASH1. Of 10 mRNAs downstream of VASH1 in the GRN that were examined, 7 were significantly up- or down-regulated in the direction predicted by the GRN.Further supporting an important biological role of VASH1 in EC, targeted reduction of VASH1 mRNA abundance conferred resistance to serum withdrawal-induced EC death.

CONCLUSION

We have utilised Bayesian GRN modelling to identify a novel candidate master regulator of EC apoptosis. This study demonstrates how GRN technology can complement traditional methods to hypothesise the regulatory relationships that underlie important biological processes.

Selective inhibition of Ezh2 by a small molecule inhibitor blocks tumor cells proliferation

Ezh2 (Enhancer of zeste homolog 2) protein is the enzymatic component of the Polycomb repressive complex 2 (PRC2), which represses gene expression by methylating lysine 27 of histone H3 (H3K27) and regulates cell proliferation and differentiation during embryonic development. Recently, hot-spot mutations of Ezh2 were identified in diffused large B-cell lymphomas and follicular lymphomas. To investigate if tumor growth is dependent on the enzymatic activity of Ezh2, we developed a potent and selective small molecule inhibitor, EI1, which inhibits the enzymatic activity of Ezh2 through direct binding to the enzyme and competing with the methyl group donor S-Adenosyl methionine. EI1-treated cells exhibit genome-wide loss of H3K27 methylation and activation of PRC2 target genes. Furthermore, inhibition of Ezh2 by EI1 in diffused large B-cell lymphomas cells carrying the Y641 mutations results in decreased proliferation, cell cycle arrest, and apoptosis. These results provide strong validation of Ezh2 as a potential therapeutic target for the treatment of cancer.

Characterization of the EZH2-MMSET histone methyltransferase regulatory axis in cancer

Histone methyltransferases (HMTases), as chromatin modifiers, regulate the transcriptomic landscape in normal development as well in diseases such as cancer. Here, we molecularly order two HMTases, EZH2 and MMSET, that have established genetic links to oncogenesis. EZH2, which mediates histone H3K27 trimethylation and is associated with gene silencing, was shown to be coordinately expressed and function upstream of MMSET, which mediates H3K36 dimethylation and is associated with active transcription. We found that the EZH2-MMSET HMTase axis is coordinated by a microRNA network and that the oncogenic functions of EZH2 require MMSET activity. Together, these results suggest that the EZH2-MMSET HMTase axis coordinately functions as a master regulator of transcriptional repression, activation, and oncogenesis and may represent an attractive therapeutic target in cancer.

Tumor angiogenesis and anti-angiogenic therapy

Anti-angiogenic therapy is an anti-cancer strategy that targets the new vessels that grow to provide oxygen and nutrients to actively proliferating tumor cells. Most of the current anti-cancer reagents used in the clinical setting indiscriminately target all rapidly dividing cells, resulting in severe adverse effects such as immunosuppression, intestinal problems and hair loss. In comparison, anti-angiogenic reagents theoretically have fewer side effects because, except in the uterine endometrium, neoangiogenesis rarely occurs in healthy adults. Currently, the most established approach for limiting tumor angiogenesis is blockade of the vascular endothelial growth factor (VEGF) pathway. In line with the results of preclinical studies, significant therapeutic effects of VEGF blockers have been reported in various types of human cancers, even in patients with progressive/recurrent cancer who could not otherwise be treated. However, some patients are refractory to this treatment or acquire resistance to VEGF inhibitors. Moreover, several studies have shown that VEGF blockade damages healthy vessels and results in adverse effects such as hemorrhagic and thrombotic events. In recent research that indicated possible ways to overcome these problems, several VEGF-independent and tumor-selective pro-angiogenic mechanisms were discovered that could be targeted in combination with or without conventional VEGF blockade. These findings offer opportunities to greatly improve current anti-angiogenic treatment for cancer.

Endoglin (CD105) contributes to platinum resistance and is a target for tumor-specific therapy in epithelial ovarian cancer

PURPOSE

Endoglin (CD105) is a membranous protein overexpressed in tumor-associated endothelial cells, chemoresistant populations of ovarian cancer cells, and potentially stem cells. Our objective was to evaluate the effects and mechanisms of targeting endoglin in ovarian cancer.

EXPERIMENTAL DESIGN

Global and membranous endoglin expression was evaluated in multiple ovarian cancer lines. In vitro, the effects of siRNA-mediated endoglin knockdown with and without chemotherapy were evaluated by MTT assay, cell-cycle analysis, alkaline comet assay, γ-H2AX foci formation, and quantitative PCR. In an orthotopic mouse model, endoglin was targeted with chitosan-encapsulated siRNA with and without carboplatin.

RESULTS

Endoglin expression was surprisingly predominantly cytoplasmic, with a small population of surface-positive cells. Endoglin inhibition decreased cell viability, increased apoptosis, induced double-stranded DNA damage, and increased cisplatin sensitivity. Targeting endoglin downregulates expression of numerous DNA repair genes, including BARD1, H2AFX, NBN, NTHL1, and SIRT1. BARD1 was also associated with platinum resistance, and was induced by platinum exposure. In vivo, antiendoglin treatment decreased tumor weight in both ES2 and HeyA8MDR models when compared with control (35%-41% reduction, P < 0.05). Endoglin inhibition with carboplatin was associated with even greater inhibitory effect when compared with control (58%-62% reduction, P < 0.001).

CONCLUSIONS

Endoglin downregulation promotes apoptosis, induces significant DNA damage through modulation of numerous DNA repair genes, and improves platinum sensitivity both in vivo and in vitro. Antiendoglin therapy would allow dual treatment of both tumor angiogenesis and a subset of aggressive tumor cells expressing endoglin and is being actively pursued as therapy in ovarian cancer.

Chromatin H3K27me3/H3K4me3 histone marks define gene sets in high-grade serous ovarian cancer that distinguish malignant, tumour-sustaining and chemo-resistant ovarian tumour cells

In embryonic stem (ES) cells, bivalent chromatin domains containing H3K4me3 and H3K27me3 marks silence developmental genes, while keeping them poised for activation following differentiation. We have identified gene sets associated with H3K27me3 and H3K4me3 marks at transcription start sites in a high-grade ovarian serous tumour and examined their association with epigenetic silencing and malignant progression. This revealed novel silenced bivalent marked genes, not described previously for ES cells, which are significantly enriched for the PI3K (P<10(-7)) and TGF-β signalling pathways (P<10(-5)). We matched histone marked gene sets to gene expression sets of eight normal fallopian tubes and 499 high-grade serous malignant ovarian samples. This revealed a significant decrease in gene expression for the H3K27me3 and bivalent gene sets in malignant tissue. We then correlated H3K27me3 and bivalent gene sets to gene expression data of ovarian tumour 'stem cell-like' sustaining cells versus non-sustaining cells. This showed a significantly lower expression for the H3K27me3 and bivalent gene sets in the tumour-sustaining cells. Similarly, comparison of matched chemo-sensitive and chemo-resistant ovarian cell lines showed a significantly lower expression of H3K27me3/bivalent marked genes in the chemo-resistant compared with the chemo-sensitive cell line. Our analysis supports the hypothesis that bivalent marks are associated with epigenetic silencing in ovarian cancer. However it also suggests that additional tumour specific bivalent marks, to those known in ES cells, are present in tumours and may potentially influence the subsequent development of drug resistance and tumour progression.

The vasohibin family: a novel family for angiogenesis regulation

Angiogenesis, a formation of neovessels, is regulated by the local balance between angiogenesis stimulators and inhibitors. A number of such endogenous regulators of angiogenesis have been found in the body. Recently, vasohibin-1 (VASH1) was isolated as a negative feedback regulator of angiogenesis produced by endothelial cells (ECs) and subsequently vasohibin-2 (VASH2) as a homologue of VASH1. It was then explored that VASH1 is expressed in ECs to terminate angiogenesis, whereas VASH2 is expressed in cells other than ECs to promote angiogenesis in the mouse model of angiogenesis. This review will focus on the vasohibin family members, which are novel regulators of angiogenesis.

Nanog signaling in cancer promotes stem-like phenotype and immune evasion

Adaptation of tumor cells to the host is a major cause of cancer progression, failure of therapy, and ultimately death. Immune selection drives this adaptation in human cancer by enriching tumor cells with a cancer stem cell-like (CSC-like) phenotype that makes them resistant to CTL-mediated apoptosis; however, the mechanisms that mediate CSC maintenance and proliferation are largely unknown. Here, we report that CTL-mediated immune selection drives the evolution of tumor cells toward a CSC-like phenotype and that the CSC-like phenotype arises through the Akt signaling pathway via transcriptional induction of Tcl1a by Nanog. Furthermore, we found that hyperactivation of the Nanog/Tcl1a/Akt signaling axis was conserved across multiple types of human cancer. Inhibition of Nanog in a murine model of colon cancer rendered tumor cells susceptible to immune-mediated clearance and led to successful, long-term control of the disease. Our findings establish a firm link among immune selection, disease progression, and the development of a stem-like tumor phenotype in human cancer and implicate the Nanog/Tcl1a/Akt pathway as a central molecular target in this process.

Promotion of glioblastoma cell motility by enhancer of zeste homolog 2 (EZH2) is mediated by AXL receptor kinase

Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of the Polycomb-repressive complex 2 (PRC2) that epigenetically silences gene transcription through histone H3 lysine trimethylation (H3K27me3). EZH2 has been implicated in stem cell maintenance and is overexpressed in hematological and solid malignancie`s including malignant glioma. EZH2 is thought to promote tumor progression by silencing tumor suppressor genes. Hence pharmacological disruption of the PRC2 is an attractive therapeutic strategy for cancer treatment. Here we show that EZH2 is expressed in human glioma and correlates with malignancy. Silencing of EZH2 reduced glioma cell proliferation and invasiveness. While we did not observe induction of cell cycle-associated tumor suppressor genes by silencing or pharmacological inhibition of EZH2, microarray analyses demonstrated a strong transcriptional reduction of the AXL receptor kinase. Neither histone nor DNA methylation appeared to be involved in the positive regulation of AXL by EZH2. Silencing AXL mimicked the antiinvasive effects of EZH2 knockdown. Finally, AXL expression is found in human gliomas with high EZH2 expression. Collectively these data suggest that EZH2 drives glioma invasiveness via transcriptional control of AXL independent of histone or DNA methylation.

Resistance and escape from antiangiogenesis therapy: clinical implications and future strategies

Angiogenesis has long been considered an important target for cancer therapy. Initial efforts have primarily focused on targeting of endothelial and tumor-derived vascular endothelial growth factor signaling. As evidence emerges that angiogenesis has significant mechanistic complexity, therapeutic resistance and escape have become practical limitations to drug development. Here, we review the mechanisms by which dynamic changes occur in the tumor microenvironment in response to antiangiogenic therapy, leading to drug resistance. These mechanisms include direct selection of clonal cell populations with the capacity to rapidly upregulate alternative proangiogenic pathways, increased invasive capacity, and intrinsic resistance to hypoxia. The implications of normalization of vasculature with subsequently improved vascular function as a result of antiangiogenic therapy are explored, as are the implications of the ability to incorporate and co-opt otherwise normal vasculature. Finally, we consider the extent to which a better understanding of the biology of hypoxia and reoxygenation, as well as the depth and breadth of systems invested in angiogenesis, may offer putative biomarkers and novel therapeutic targets. Insights gained through this work may offer solutions for personalizing antiangiogenesis approaches and improving the outcome of patients with cancer.

Mechanisms of ovarian cancer metastasis: biochemical pathways

Ovarian cancer is the most lethal gynecologic malignancy. Despite advances in chemotherapy, the five-year survival rate of advanced ovarian cancer patients with peritoneal metastasis remains around 30%. The most significant prognostic factor is stage, and most patients present at an advanced stage with peritoneal dissemination. There is often no clearly identifiable precursor lesion; therefore, the events leading to metastatic disease are poorly understood. This article reviews metastatic suppressor genes, the epithelial-mesenchymal transition (EMT), and the tumor microenvironment as they relate to ovarian cancer metastasis. Additionally, novel chemotherapeutic agents targeting the metastasis-related biochemical pathways are discussed.

SUZ12 promotes human epithelial ovarian cancer by suppressing apoptosis via silencing HRK

Epithelial ovarian cancer (EOC) ranks first as the cause of death for gynecological cancers in the United States. SUZ12 is a component of the polycomb repressive complex 2 (PRC2) and is essential for PRC2-mediated gene silencing by generating trimethylation on lysine 27 residue of histone H3 (H3K27Me3). The role of SUZ12 in EOC has never been investigated. Here, we show that SUZ12 is expressed at significantly higher levels in human EOC (n = 117) compared with either normal human ovarian surface epithelium (n = 35, P < 0.001) or fallopian tube epithelium (n = 15, P < 0.001). There is a positive correlation between expression of SUZ12 and EZH2 in human EOC (P < 0.001). In addition, expression of SUZ12 positively correlates with Ki67, a marker of cell proliferation (P < 0.001), and predicts shorter overall survival (P = 0.0078). Notably, knockdown of SUZ12 suppresses the growth of human EOC cells in vitro and in vivo in both orthotopic and subcutaneous xenograft EOC models. In addition, SUZ12 knockdown decreases the levels of H3K27Me3 and triggers apoptosis of human EOC cells. Mechanistically, we identified Harakiri (HRK), a proapoptotic gene, as a novel SUZ12 target gene, and showed that HRK upregulation mediates apoptosis induced by SUZ12 knockdown in human EOC cells. In summary, we show that SUZ12 promotes the proliferation of human EOC cells by inhibiting apoptosis and HRK is a novel SUZ12 target gene whose upregulation contributes to apoptosis induced by SUZ12 knockdown.

Epigenetic regulation of cell adhesion and communication by enhancer of zeste homolog 2 in human endothelial cells

The histone methyltransferase enhancer of zeste homolog 2 (Ezh2) mediates trimethylation of lysine 27 in histone 3, which acts as a repressive epigenetic mark. Ezh2 is essential for maintaining pluripotency of stem cells, but information on its role in differentiated cells is sparse. Whole-genome mRNA expression arrays identified 964 genes that were regulated by >2-fold 72 hours after small interfering RNA-mediated silencing of Ezh2 in human umbilical vein endothelial cells. Among them, genes associated with the gene ontology terms cell communication and cell adhesion were significantly overrepresented, suggesting a functional role for Ezh2 in the regulation of angiogenesis. Indeed, adhesion, migration, and tube formation assays revealed significantly altered angiogenic properties of human umbilical vein endothelial cells after silencing of Ezh2. To identify direct target genes of Ezh2, we performed chromatin immunoprecipitation experiments followed by whole-genome promoter arrays (chromatin immunoprecipitation-on-chip) and identified 5585 genes associated with trimethylation of lysine 27 in histone 3. Comparative analysis with our mRNA expression data identified 276 genes that met our criteria for putative Ezh2 target genes, upregulation by >2-fold after Ezh2 silencing and association with trimethylation of lysine 27 in histone 3. Notably, we observed a striking overrepresentation of genes involved in wingless-type mouse mammary tumor virus integration site (WNT) signaling pathways. Epigenetic regulation of several of these genes by Ezh2 was specifically confirmed by polymerase chain reaction analysis of DNA enrichment after chromatin immunoprecipitation using an antibody specific for trimethylation of lysine 27 in histone 3. Combining mRNA expression arrays and chromatin immunoprecipitation-on-chip analysis, we identified 276 Ezh2 target genes in endothelial cells. Ezh2-dependent repression of genes involved in cell adhesion and communication contributes to the regulation of angiogenesis.

Development and validation of a prognostic gene-expression signature for lung adenocarcinoma

Although several prognostic signatures have been developed in lung cancer, their application in clinical practice has been limited because they have not been validated in multiple independent data sets. Moreover, the lack of common genes between the signatures makes it difficult to know what biological process may be reflected or measured by the signature. By using classical data exploration approach with gene expression data from patients with lung adenocarcinoma (n = 186), we uncovered two distinct subgroups of lung adenocarcinoma and identified prognostic 193-gene gene expression signature associated with two subgroups. The signature was validated in 4 independent lung adenocarcinoma cohorts, including 556 patients. In multivariate analysis, the signature was an independent predictor of overall survival (hazard ratio, 2.4; 95% confidence interval, 1.2 to 4.8; p = 0.01). An integrated analysis of the signature revealed that E2F1 plays key roles in regulating genes in the signature. Subset analysis demonstrated that the gene signature could identify high-risk patients in early stage (stage I disease), and patients who would have benefit of adjuvant chemotherapy. Thus, our study provided evidence for molecular basis of clinically relevant two distinct two subtypes of lung adenocarcinoma.

Moving beyond VEGF for anti-angiogenesis strategies in gynecologic cancer

Gynecologic cancer is a major burden in both developed and developing countries. Almost a half million deaths from gynecologic cancer are reported each year. Understanding the molecular biology of cancer is a principle resource leading to the identification of new potential therapeutic targets, which may be parlayed into novel therapeutic options in gynecologic cancer. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase, which plays a pivotal role in many aspects of malignant growth including cancer cell survival, migration, invasion, angiogenesis and metastasis. Various human cancer tissues have demonstrated high expression of FAK or activated FAK, which has been correlated with survival of cancer patients. Among gynecologic cancers, reports have emerged demonstrating that FAK is involved in the pathogenesis of ovarian, endometrial, and cervical cancers. In addition, the polycomb group protein enhancer of Zeste homologue 2 (EZH2), Dll4/notch and EphA2 has also emerged as important regulators of endothelial cell biology and angiogenesis. Herein, we review the role of these new targets in tumor angiogenesis and the rationale for further clinical development.

Interleukin-6 induces S100A9 expression in colonic epithelial cells through STAT3 activation in experimental ulcerative colitis

Background

Intestinal epithelium is essential for maintaining normal intestinal homeostasis; its breakdown leads to chronic inflammatory pathologies, such as inflammatory bowel diseases (IBDs). Although high concentrations of S100A9 protein and interleukin-6 (IL-6) are found in patients with IBD, the expression mechanism of S100A9 in colonic epithelial cells (CECs) remains elusive. We investigated the role of IL-6 in S100A9 expression in CECs using a colitis model.

Methods

IL-6 and S100A9 expression, signal transducer and activator of transcription 3 (STAT3) phosphorylation, and infiltration of immune cells were analyzed in mice with dextran sulfate sodium (DSS)-induced colitis. The effects of soluble gp130-Fc protein (sgp130Fc) and S100A9 small interfering (si) RNA (si-S100A9) on DSS-induced colitis were evaluated. The molecular mechanism of S100A9 expression was investigated in an IL-6-treated Caco-2 cell line using chromatin immunoprecipitation assays.

Results

IL-6 concentrations increased significantly in the colon tissues of DSS-treated mice. sgp130Fc or si-S100A9 administration to DSS-treated mice reduced granulocyte infiltration in CECs and induced the down-regulation of S100A9 and colitis disease activity. Treatment with STAT3 inhibitors upon IL-6 stimulation in the Caco-2 cell line demonstrated that IL-6 mediated S100A9 expression through STAT3 activation. Moreover, we found that phospho-STAT3 binds directly to the S100A9 promoter. S100A9 may recruit immune cells into inflamed colon tissues.

Conclusions

Elevated S100A9 expression in CECs mediated by an IL-6/STAT3 signaling cascade may play an important role in the development of colitis.

Prognostic biomarkers in ovarian cancer

Epithelial ovarian cancer (EOC) remains the most lethal gynecological malignancy despite several decades of progress in diagnosis and treatment. Taking advantage of the robust development of discovery and utility of prognostic biomarkers, clinicians and researchers are developing personalized and targeted treatment strategies. This review encompasses recently discovered biomarkers of ovarian cancer, the utility of published prognostic biomarkers for EOC (especially biomarkers related to angiogenesis and key signaling pathways), and their integration into clinical practice.

Metronomic activity of CD44-targeted hyaluronic acid-paclitaxel in ovarian carcinoma

PURPOSE

Most primary human ovarian tumors and peritoneal implants, as well as tumor vascular endothelial cells, express the CD44 family of cell surface proteoglycans, the natural ligand for which is hyaluronic acid. Metronomic dosing, the frequent administration of chemotherapeutics at substantially lower than maximum tolerated doses (MTD), has been shown to result in reduced normal tissue toxicity and to minimize "off-treatment" exposure resulting in an improved therapeutic ratio.

EXPERIMENTAL DESIGN

We tested the hypothesis that hyaluronic acid (HA) conjugates of paclitaxel (TXL; HA-TXL) would exert strong antitumor effects with metronomic (MET) dosing and induce antiangiogenic effects superior to those achieved with MTD administration or with free TXL. Female nude mice bearing SKOV3ip1 or HeyA8 ovarian cancer cells were treated intraperitoneally (i.p.) with MET HA-TXL regimens (or MTD administration) to determine therapeutic and biologic effects.

RESULTS

All MET HA-TXL-treated mice and the MTD group revealed significantly reduced tumor weights and nodules compared with controls (all P values < 0.05) in the chemotherapy-sensitive models. However, the MTD HA-TXL-treated mice showed significant weight loss compared with control mice, whereas body weights were not affected in the metronomic groups in HeyA8-MDR model, reflecting reduced toxicity. In the taxane-resistant HeyA8-MDR model, significant reduction in tumor weight and nodule counts was noted in the metronomic groups whereas the response of the MTD group did not achieve significance. While both MTD and metronomic regimens reduced proliferation (Ki-67) and increased apoptosis (TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling), only metronomic treatment resulted in significant reductions in angiogenesis (CD31, microvessel density). Moreover, metronomic treatment resulted in substantial increases in thrombospondin-1 (Tsp-1), an inhibitor of angiogenesis.

CONCLUSIONS

This study showed that MET HA-TXL regimens have substantial antitumor activity in ovarian carcinoma, likely via a predominant antiangiogenic mechanism.

Targeting angiogenesis in gynecologic cancers

Gynecologic malignancies carry an estimated incidence of 83,750 cases per year and estimated mortality rate of more than 27,000 women per year. New therapies and therapeutic approaches are needed to improve the outlook for women with gynecologic cancers. Recent insights at the molecular and cellular levels are paving the way for a more directed approach to target mechanisms driving tumorigenesis. This article reviews the roles of new and emerging antiangiogenesis drugs, summarizes the data obtained from clinical trials of antiangiogenic agents, and discusses trials under way to address the role of such strategies in gynecologic cancers.

Cancer angiogenesis induced by Kaposi sarcoma-associated herpesvirus is mediated by EZH2

EZH2 is a component of the epigenetic regulator PRC2 that suppresses gene expression. Elevated expression of EZH2 is common in human cancers and is associated with tumor progression and poor prognosis. In this study, we show that EZH2 elevation is associated with epigenetic modifications of Kaposi sarcoma-associated herpesvirus (KSHV), an oncogenic virus that promotes the development of Kaposi sarcoma and other malignancies that occur in patients with chronic HIV infections. KSHV induction of EZH2 expression was essential for KSHV-induced angiogenesis. High expression of EZH2 was observed in Kaposi sarcoma tumors. In cell culture, latent KSHV infection upregulated the expression of EZH2 in human endothelial cells through the expression of vFLIP and LANA, two KSHV-latent genes that activate the NF-κB pathway. KSHV-mediated upregulation of EZH2 was required for the induction of Ephrin-B2, an essential proangiogenic factor that drives endothelial cell tubule formation. Taken together, our findings indicate that KSHV regulates the host epigenetic modifier EZH2 to promote angiogenesis.

Clinical and biological relevance of enhancer of zeste homolog 2 in triple-negative breast cancer

The polycomb group protein, enhancer of zeste homolog 2, is a transcriptional repressor involved in cell cycle regulation and has been linked to aggressive breast cancer. We examined the clinical and biological significance of enhancer of zeste homolog 2 expression in triple-negative breast cancers. Tissue microarrays were constructed with invasive breast cancer cases and stained with the enhancer of zeste homolog 2, cytokeratin 5/6, epidermal growth factor receptor 1, and p53. The expression of these markers was correlated with clinicopathologic variables and patients' outcome. Furthermore, in vivo enhancer of zeste homolog 2 gene silencing was achieved using small interfering RNA incorporated into chitosan nanoparticles. Of 261 cases of invasive breast cancer, high expression of the enhancer of zeste homolog 2 was detected in 87 (33%) cases, and it was strongly associated with a triple-negative breast cancer phenotype (P < .001) compared with all other non-triple-negative breast cancers. Furthermore, high enhancer of zeste homolog 2 was significantly associated with high histologic grade (P = .01), estrogen receptor negativity (P < .001), progesterone receptor negativity (P < .001), epidermal growth factor receptor positivity (P = .04), and high p53 expression (P < .001). Survival analysis demonstrated that patients with high enhancer of zeste homolog 2 had a poorer overall survival compared with those with low enhancer of zeste homolog 2 (P = .03), and it retained its significance as an independent prognostic factor (P = .02). In addition, enhancer of zeste homolog 2 gene silencing resulted in a significant reduction in tumor growth (P < .01) in the orthotopic MB-231 mouse model of breast carcinoma. Our results show that high enhancer of zeste homolog 2 expression is significantly associated with triple-negative breast cancer and decreased survival. Enhancer of zeste homolog 2 may represent a potential therapeutic target for this aggressive disease, which warrants further investigation.

Epigenetic regulation of vascular endothelial growth factor a dynamic expression in transitional cell carcinoma

Vascular endothelial growth factor A (VEGF-A) is a key mediator in the neovascularization of cancers. We have found that VEGF-A was expressed at significantly higher levels in high-grade transitional cell carcinoma (TCC) cells than low-grade TCC cells in our previous study. In the present study, promoter methylation pattern was assessed and quantified by bisulfite genomic sequencing (BGS) and specific VEGF-A CpG sites in low-grade, but not in high-grade, TCC cells were observed. Reporter assays indicated that hypermethylation of nine CpG sites can inhibit the transcriptional activity of the VEGF-A gene. Subsequent chromatin immunoprecipitation (ChIP) assay revealed down-regulation of transcription activity of VEGF-A with increasing binding of methyl-CpG-binding protein 2 (MBD2) and trimethyl-histone H3 (Lys9) proteins to these CpG sites in low-grade TCC cells during hypermethylation. Furthermore, treatment of low-grade TCC cells with DNA methyltransferase inhibitor and histone deacetylase inhibitor can restore the expression of VEGF-A and promote the invasive ability of low-grade TCC cells. Hypermethylation with lower expression levels of VEGF-A in low-grade TCC tumors than high-grade TCC tumors was also confirmed in clinical specimens by reverse transcriptase-PCR and pyrosequencing analyses. Our findings are the first results indicating that VEGF-A expression is suppressed in low-grade TCC tumors by promoter hypermethylation. This offers a new perspective on the role of VEGF-A in TCC tumor behavior.

Bevacizumab and ovarian cancer

PURPOSE OF REVIEW

Vascular endothelial growth factor (VEGF), one of the major pathways involved in tumor angiogenesis, is often overexpressed in epithelial ovarian cancer (EOC), and therefore an attractive target for therapy. This review aims to evaluate the rationale for targeting angiogenic pathways by the usage of the anti-VEGF agent bevacizumab in EOC.

RECENT FINDINGS

Bevacizumab monotherapy has been shown to be effective in the treatment of EOC with response rate of 16-21% in phase II trials. In phase III trials, patients with advanced EOC who received combination chemotherapy (paclitaxel + carboplatin) plus bevacizumab with maintenance bevacizumab had significantly longer progression-free survival than those who received chemotherapy alone, but did not prolong overall survival. The most common grade 3/4 adverse events of bevacizumab monotherapy include hypertension and proteinuria, while heavily pretreated patients were at increased risk of bowel perforation. The addition of bevacizumab to the standard chemotherapy in patients with advanced EOC may not be cost-effective.

SUMMARY

Bevacizumab has significant activity and is the most promising drug in EOC. However, understanding of its unique adverse events and identification of predictive biomarkers of bevacizumab response are necessary in order to select patients most likely to benefit from this therapy.

FOXP3 orchestrates H4K16 acetylation and H3K4 trimethylation for activation of multiple genes by recruiting MOF and causing displacement of PLU-1

Both H4K16 acetylation and H3K4 trimethylation are required for gene activation. However, it is still largely unclear how these modifications are orchestrated by transcriptional factors. Here, we analyzed the mechanism of the transcriptional activation by FOXP3, an X-linked suppressor of autoimmune diseases and cancers. FOXP3 binds near transcriptional start sites of its target genes. By recruiting MOF and displacing histone H3K4 demethylase PLU-1, FOXP3 increases both H4K16 acetylation and H3K4 trimethylation at the FOXP3-associated chromatins of multiple FOXP3-activated genes. RNAi-mediated silencing of MOF reduced both gene activation and tumor suppression by FOXP3, while both somatic mutations in clinical cancer samples and targeted mutation of FOXP3 in mouse prostate epithelial cells disrupted nuclear localization of MOF. Our data demonstrate a pull-push model in which a single transcription factor orchestrates two epigenetic alterations necessary for gene activation and provide a mechanism for somatic inactivation of the FOXP3 protein function in cancer cells.

MicroRNA-181a - a tale of discrepancies

MicroRNAs (miRNAs) are short noncoding RNAs that act as post-transcriptional regulators. The low complementarity required between the sequences of a miRNA and its target mRNA enables a single miRNA to act on a large range of targets. Thus miRNAs have an intersecting complex effect that spans a multiplicity of pathways and processes. In this review, the different roles of a vital miRNA, miR-181a, in physiological and pathological developments are collated in an attempt to highlight the intersections of such processes and to show how the deregulation of miR-181a could in one context drive malignancy, whereas in another it can lead to autoimmunity. Such deregulation could be related to the faulty levels of one of its own targets, p53, which was recently reported to control an array of miRNAs, one of which is miR-181a. This sheds light on a hidden loop of chaos behind chronic diseases such as autoimmunity and cancer.

Paraneoplastic thrombocytosis in ovarian cancer

BACKGROUND

The mechanisms of paraneoplastic thrombocytosis in ovarian cancer and the role that platelets play in abetting cancer growth are unclear.

METHODS

We analyzed clinical data on 619 patients with epithelial ovarian cancer to test associations between platelet counts and disease outcome. Human samples and mouse models of epithelial ovarian cancer were used to explore the underlying mechanisms of paraneoplastic thrombocytosis. The effects of platelets on tumor growth and angiogenesis were ascertained.

RESULTS

Thrombocytosis was significantly associated with advanced disease and shortened survival. Plasma levels of thrombopoietin and interleukin-6 were significantly elevated in patients who had thrombocytosis as compared with those who did not. In mouse models, increased hepatic thrombopoietin synthesis in response to tumor-derived interleukin-6 was an underlying mechanism of paraneoplastic thrombocytosis. Tumor-derived interleukin-6 and hepatic thrombopoietin were also linked to thrombocytosis in patients. Silencing thrombopoietin and interleukin-6 abrogated thrombocytosis in tumor-bearing mice. Anti-interleukin-6 antibody treatment significantly reduced platelet counts in tumor-bearing mice and in patients with epithelial ovarian cancer. In addition, neutralizing interleukin-6 significantly enhanced the therapeutic efficacy of paclitaxel in mouse models of epithelial ovarian cancer. The use of an antiplatelet antibody to halve platelet counts in tumor-bearing mice significantly reduced tumor growth and angiogenesis.

CONCLUSIONS

These findings support the existence of a paracrine circuit wherein increased production of thrombopoietic cytokines in tumor and host tissue leads to paraneoplastic thrombocytosis, which fuels tumor growth. We speculate that countering paraneoplastic thrombocytosis either directly or indirectly by targeting these cytokines may have therapeutic potential. (Funded by the National Cancer Institute and others.).

FGF-2 regulates cell proliferation, migration, and angiogenesis through an NDY1/KDM2B-miR-101-EZH2 pathway

The histone H3K27 methyltransferase EZH2 plays an important role in oncogenesis, by mechanisms that are incompletely understood. Here, we show that the JmjC domain histone H3 demethylase NDY1 synergizes with EZH2 to silence the EZH2 inhibitor miR-101. NDY1 and EZH2 repress miR-101 by binding its promoter in concert, via a process triggered by upregulation of NDY1. Whereas EZH2 binding depends on NDY1, the latter binds independently of EZH2. However, both are required to repress transcription. NDY1 and EZH2 acting in concert upregulate EZH2 and stabilize the repression of miR-101 and its outcome. NDY1 is induced by FGF-2 via CREB phosphorylation and activation, downstream of DYRK1A, and mediates the FGF-2 and EZH2 effects on cell proliferation, migration, and angiogenesis. The FGF-2-NDY1/EZH2-miR-101-EZH2 axis described here was found to be active in bladder cancer. These data delineate an oncogenic pathway that functionally links FGF-2 with EZH2 via NDY1 and miR-101.

The dynamic interplay in chromatin remodeling factors polycomb and trithorax proteins in response to DNA damage

The dynamic interplay in polycomb group (PcG) and trithorax group (TrxG) proteins in response to DNA damage directly involves in the DNA double strand breaks (DSBs) sites and potentially function in both homologous recombination (HR) and nonhomologous end joining (NHEJ) pathways. The process includes chromatin remodeling that is a major mechanism used by cells to relax chromatin in DNA damage response (DDR) and repair. PcGs show resistance ability to the process while, some tumor suppressor genes involves in the DDR and repair by interacting with TrxGs. Understanding how the dynamic interplay in PcGs and TrxGs impacts on DDR will shed light on the mechanisms of carcinogenesis and develop a new target from anti-DDR related drugs.

The role of EZH2 in tumour progression

Accumulated evidence shows that EZH2 is deregulated in a wide range of cancer types, and it has a crucial role in stem cell maintenance and tumour development. Therefore, blocking EZH2 expression or activity may represent a promising strategy for anticancer treatment. In this review, we address the current understanding of the mechanisms underlying EZH2 regulation alongside the function of EZH2 gene targets that are involved in cancer progression. Finally, we will describe cancer therapies that target EZH2 or its downstream cascades, which could potentially reverse the oncogenic and stemness properties of the tumour cells to suppress cancer progression and recurrence.

ALDH1A1 is a novel EZH2 target gene in epithelial ovarian cancer identified by genome-wide approaches

Epithelial ovarian cancer (EOC) remains the most lethal gynecologic malignancy in the United States. EZH2 silences gene expression through trimethylating lysine 27 on histone H3 (H3K27Me3). EZH2 is often overexpressed in EOC and has been suggested as a target for EOC intervention. However, EZH2 target genes in EOC remain poorly understood. Here, we mapped the genomic loci occupied by EZH2/H3K27Me3 using chromatin immunoprecipitation followed by next-generation sequencing (ChIP-seq) and globally profiled gene expression in EZH2-knockdown EOC cells. Cross-examination of gene expression and ChIP-seq revealed a list of 60 EZH2 direct target genes whose expression was upregulated more than 1.5-fold upon EZH2 knockdown. For three selected genes (ALDH1A1, SSTR1, and DACT3), we validated their upregulation upon EZH2 knockdown and confirmed the binding of EZH2/H3K27Me3 to their genomic loci. Furthermore, the presence of H3K27Me3 at the genomic loci of these EZH2 target genes was dependent upon EZH2. Interestingly, expression of ALDH1A1, a putative marker for EOC stem cells, was significantly downregulated in high-grade serous EOC (n = 53) compared with ovarian surface epithelial cells (n = 10, P < 0.001). Notably, expression of ALDH1A1 negatively correlated with expression of EZH2 (n = 63, Spearman r = -0.41, P < 0.001). Thus, we identified a list of 60 EZH2 target genes and established that ALDH1A1 is a novel EZH2 target gene in EOC cells. Our results suggest a role for EZH2 in regulating EOC stem cell equilibrium via regulation of ALDH1A1 expression.

Curcumin analogue CDF inhibits pancreatic tumor growth by switching on suppressor microRNAs and attenuating EZH2 expression

The histone methyltransferase EZH2 is a central epigenetic regulator of cell survival, proliferation, and cancer stem cell (CSC) function. EZH2 expression is increased in various human cancers, including highly aggressive pancreatic cancers, but the mechanisms underlying for its biologic effects are not yet well understood. In this study, we probed EZH2 function in pancreatic cancer using diflourinated-curcumin (CDF), a novel analogue of the turmeric spice component curcumin that has antioxidant properties. CDF decreased pancreatic cancer cell survival, clonogenicity, formation of pancreatospheres, invasive cell migration, and CSC function in human pancreatic cancer cells. These effects were associated with decreased expression of EZH2 and increased expression of a panel of tumor-suppressive microRNAs (miRNA), including let-7a, b, c, d, miR-26a, miR-101, miR-146a, andmiR-200b, c that are typically lost in pancreatic cancer. Mechanistic investigations revealed that reexpression of miR-101 was sufficient to limit the expression of EZH2 and the proinvasive cell surface adhesion molecule EpCAM. In an orthotopic xenograft model of human pancreatic cancer, administration of CDF inhibited tumor growth in a manner associated with reduced expression of EZH2, Notch-1, CD44, EpCAM, and Nanog and increased expression of let-7, miR-26a, and miR-101. Taken together, our results indicated that CDF inhibited pancreatic cancer tumor growth and aggressiveness by targeting an EZH2-miRNA regulatory circuit for epigenetically controlled gene expression.

SET8 promotes epithelial-mesenchymal transition and confers TWIST dual transcriptional activities

SET8 is implicated in transcriptional regulation, heterochromatin formation, genomic stability, cell-cycle progression, and development. As such, it is predicted that SET8 might be involved in the development and progression of tumour. However, whether and how SET8 might be implicated in tumourigenesis is currently unknown. Here, we report that SET8 is physically associated with TWIST, a master regulator of epithelial-mesenchymal transition (EMT). We demonstrated that SET8 and TWIST are functionally interdependent in promoting EMT and enhancing the invasive potential of breast cancer cells in vitro and in vivo. We showed that SET8 acts as a dual epigenetic modifier on the promoters of the TWIST target genes E-cadherin and N-cadherin via its H4K20 monomethylation activity. Significantly, in breast carcinoma samples, SET8 expression is positively correlated with metastasis and the expression of TWIST and N-cadherin and negatively correlated with E-cadherin. Together, our experiments revealed a novel role for SET8 in tumour invasion and metastasis and provide a molecular mechanism underlying TWIST-promoted EMT, suggesting SET8 as a potential target for intervention of the metastasis of breast cancer.

Epigenetics, nervous system tumors, and cancer stem cells

Recent advances have begun to elucidate how epigenetic regulatory mechanisms are responsible for establishing and maintaining cell identity during development and adult life and how the disruption of these processes is, not surprisingly, one of the hallmarks of cancer. In this review, we describe the major epigenetic mechanisms (i.e., DNA methylation, histone and chromatin modification, non-coding RNA deployment, RNA editing, and nuclear reorganization) and discuss the broad spectrum of epigenetic alterations that have been uncovered in pediatric and adult nervous system tumors. We also highlight emerging evidence that suggests epigenetic deregulation is a characteristic feature of so-called cancer stem cells (CSCs), which are thought to be present in a range of nervous system tumors and responsible for tumor maintenance, progression, treatment resistance, and recurrence. We believe that better understanding how epigenetic mechanisms operate in neural cells and identifying the etiologies and consequences of epigenetic deregulation in tumor cells and CSCs, in particular, are likely to promote the development of enhanced molecular diagnostics and more targeted and effective therapeutic agents for treating recalcitrant nervous system tumors.

Polycomb and the emerging epigenetics of pancreatic cancer

INTRODUCTION

The revolution of epigenetics has revitalized cancer research, shifting focus away from somatic mutation toward a more holistic perspective involving the dynamic states of chromatin. Disruption of chromatin organization can directly and indirectly precipitate genomic instability and transformation.

DISCUSSION

One group of epigenetic mediators, the Polycomb group (PcG) proteins, establishes heritable gene repression through methylation of histone tails. Although classically considered regulators of development and cellular differentiation, PcG proteins engage in a variety of neoplastic processes, including cellular proliferation and invasion. Due to their multifaceted potential, PcG proteins rest at the intersection of transcriptional memory and malignancy. Expression levels of PcG proteins hold enormous diagnostic and prognostic value in breast, prostate, and more recently, gastrointestinal cancers.

CONCLUSION

In this review, we briefly summarize the function of PcG proteins and report the latest developments in understanding their role in pancreatic cancer.

Targeting the notch ligand JAGGED1 in both tumor cells and stroma in ovarian cancer

PURPOSE

Jagged1, a Notch ligand, is expressed on both tumor epithelial and endothelial cells and therefore may be amenable to dual targeting of the tumor stroma and malignant cell compartments of the tumor microenvironment.

EXPERIMENTAL DESIGN

We describe in vitro effects of targeting of Jagged1 on ovarian cancer cells and in vivo effects of independent targeting of stromal and malignant cell Jagged1 using species-specific human or murine siRNA constructs incorporated into chitosan nanoparticles and delivered intravenously in an orthotopic mouse model.

RESULTS

Jagged1 expression was prominent in SKOV3ip1 and IGROV-AF1, and significantly overexpressed in SKOV3TRip2, a taxane-resistant SKOV3 subclone. Jagged1 silencing with siRNA decreased cell viability and reversed taxane chemoresistance. In two different orthotopic ovarian cancer models, treatment with anti-human Jagged1 siRNA-CH reduced growth by 54.4% to 58.3% and with anti-murine Jagged1 siRNA-CH reduced growth by 41.7% to 48.8%. The combination of both species-specific constructs reduced tumor weight by 87.5% to 93.1% and sensitized SKOV3TRip2 tumors to docetaxel in vivo. Tumors showed reduced microvessel density with anti-murine Jagged1 constructs and decreased proliferation with anti-human Jagged1 siRNAs-CH. In addition, we show that Jagged1 downregulation does not sensitize cells to taxanes through a reduction in MDR1 expression, but at least in part by cross-talk with the GLI2 mediator of the Hedgehog pathway.

CONCLUSIONS

Jagged1 plays dual roles in cancer progression through an angiogenic function in tumor endothelial cells and through proliferation and chemoresistance in tumor cells. Dual inhibition represents an attractive therapeutic strategy for ovarian and potentially other malignancies.

The Y641C mutation of EZH2 alters substrate specificity for histone H3 lysine 27 methylation states

Mutations at tyrosine 641 (Y641F, Y641N, Y641S and Y641H) in the SET domain of EZH2 have been identified in patients with certain subtypes of non-Hodgkin lymphoma (NHL). These mutations were shown to change the substrate specificity of EZH2 for various methylation states of lysine 27 on histone H3 (H3K27). An additional mutation at EZH2 Y641 to cysteine (Y641C) was also found in one patient with NHL and in SKM-1 cells derived from a patient with myelodisplastic syndrome (MDS). The Y641C mutation has been reported to dramatically reduce enzymatic activity. Here, we demonstrate that while the Y641C mutation ablates enzymatic activity against unmethylated and monomethylated H3K27, it is superior to wild-type in catalyzing the formation of trimethylated H3K27 from the dimethylated precursor.

Genome-wide profiling of DNA methylation in human cancer cells

Global changes in DNA methylation correlate with altered gene expression and genomic instability in cancer. We have developed a methylation-specific digital sequencing (MSDS) method that can assess DNA methylation on a genomic scale. MSDS is a simple, low-cost method that combines the use of methylation-sensitive restriction enzymes with second generation sequencing technology. DNA methylation in two colon cancer cell lines, HT29 and HCT116, was measured using MSDS. When methylation levels were compared between the two cell lines, many differentially methylated regions (DMRs) were identified in CpG island shore regions (located within 2kb of a CpG island), gene body regions and intergenic regions. The number of DMRs in the vicinity of gene transcription start sites correlated with the level of expression of TACC1, CLDN1, and PLEKHC1 (FERMT2) genes, which have been linked to carcinogenesis. The MSDS method has the potential to provide novel insight into the functional complexity of the human genome.

Biological roles of the Delta family Notch ligand Dll4 in tumor and endothelial cells in ovarian cancer

Emerging evidence suggests that the Notch/Delta-like ligand 4 (Dll4) pathway may offer important new targets for antiangiogenesis approaches. In this study, we investigated the clinical and biological significance of Dll4 in ovarian cancer. Dll4 was overexpressed in 72% of tumors examined in which it was an independent predictor of poor survival. Patients with tumors responding to anti-VEGF therapy had lower levels of Dll4 than patients with stable or progressive disease. Under hypoxic conditions, VEGF increased Dll4 expression in the tumor vasculature. Immobilized Dll4 also downregulated VEGFR2 expression in endothelial cells directly through methylation of the VEGFR2 promoter. RNAi-mediated silencing of Dll4 in ovarian tumor cells and tumor-associated endothelial cells inhibited cell growth and angiogenesis, accompanied by induction of hypoxia in the tumor microenvironment. Combining Dll4-targeted siRNA with bevacizumab resulted in greater inhibition of tumor growth, compared with control or treatment with bevacizumab alone. Together, our findings establish that Dll4 plays a functionally important role in both the tumor and endothelial compartments of ovarian cancer and that targeting Dll4 in combination with anti-VEGF treatment might improve outcomes of ovarian cancer treatment.

EZH2 depletion blocks the proliferation of colon cancer cells

The Enhancer of Zeste 2 (EZH2) protein has been reported to stimulate cell growth in some cancers and is therefore considered to represent an interesting new target for therapeutic intervention. Here, we investigated a possible role of EZH2 for the growth control of colon cancer cells. RNA interference (RNAi)-mediated intracellular EZH2 depletion led to cell cycle arrest of colon carcinoma cells at the G1/S transition. This was associated with a reduction of cell numbers upon transient transfection of synthetic EZH2-targeting siRNAs and with inhibition of their colony formation capacity upon stable expression of vector-borne siRNAs. We furthermore tested whether EZH2 may repress the growth-inhibitory p27 gene, as reported for pancreatic cancer. However, expression analyses of colon cancer cell lines and colon cancer biopsies did not reveal a consistent correlation between EZH2 and p27 levels. Moreover, EZH2 depletion did not re-induce p27 expression in colon cancer cells, indicating that p27 repression by EZH2 may be cell- or tissue-specific. Whole genome transcriptome analyses identified cellular genes affected by EZH2 depletion in colon cancer cell lines. They included several cancer-associated genes linked to cellular proliferation or invasion, such as Dag1, MageD1, SDC1, Timp2, and Tob1. In conclusion, our results demonstrate that EZH2 depletion blocks the growth of colon cancer cells. These findings might provide benefits for the treatment of colon cancer.

SWI/SNF nucleosome remodellers and cancer

SWI/SNF chromatin remodelling complexes use the energy of ATP hydrolysis to remodel nucleosomes and to modulate transcription. Growing evidence indicates that these complexes have a widespread role in tumour suppression, as inactivating mutations in several SWI/SNF subunits have recently been identified at a high frequency in a variety of cancers. However, the mechanisms by which mutations in these complexes drive tumorigenesis are unclear. In this Review we discuss the contributions of SWI/SNF mutations to cancer formation, examine their normal functions and discuss opportunities for novel therapeutic interventions for SWI/SNF-mutant cancers.

MicroRNA therapeutics: principles, expectations, and challenges

MicroRNAs (miRNAs) are a class of highly abundant non-coding RNA molecules that are involved in several biological processes. Many miRNAs are often deregulated in several diseases including cancer. There is substantial interest in exploiting miRNAs for therapeutic applications. In this editorial, we briefly review current advances in the use of miRNAs or antisense oligonucleotides (antagomirs) for such therapies. One of the key issues related to therapy using miRNAs is degradation of naked particles in vivo. To overcome this limitation, delivery systems for miRNA-based therapeutic agents have been developed, which hold tremendous potential for improving therapeutic outcome of cancer patients.

Histone onco-modifications

Post-translational modification of histones provides an important regulatory platform for processes such as gene expression, DNA replication and repair, chromosome condensation and segregation and apoptosis. Disruption of these processes has been linked to the multistep process of carcinogenesis. We review the aberrant covalent histone modifications observed in cancer, and discuss how these epigenetic changes, caused by alterations in histone-modifying enzymes, can contribute to the development of a variety of human cancers. As a conclusion, a new terminology 'histone onco-modifications' is proposed to describe post-translational modifications of histones, which have been linked to cancer. This new term would take into account the active contribution and importance of these histone modifications in the development and progression of cancer.

Epigenetic regulation of key vascular genes and growth factors

The role of small RNAs in epigenetic regulation is an emerging field. This research may also open novel treatment strategies based on manipulation of the epigenetic status of the target tissues. Our objective is to review epigenetic regulation of key vascular genes and growth factors. Vascular endothelial growth factor A (VEGF-A) is one of the key players in regulating and maintaining cardiovascular functions and pathology. Although its epigenetic regulation is still not completely understood, expression of the VEGF gene can be manipulated by epigenetic mechanisms using small RNAs that are targeted to the gene promoter which results in the alteration of histone code. VEGF exerts its effects mostly through two receptors, VEGFR1 and VEGFR2, and their expression is also regulated by promoter DNA methylation in various cancer cells. These findings suggest the importance of epigenetic mechanisms in the regulation of vascular functions.

Functional roles of Src and Fgr in ovarian carcinoma

PURPOSE

Src is an attractive target because it is overexpressed in a number of malignancies, including ovarian cancer. However, the effect of Src silencing on other Src family kinases (SFKs) is not known. We hypothesized that other SFK members could compensate for the lack of Src activity.

EXPERIMENTAL DESIGN

Cell viability after either Src or Fgr silencing was examined in ovarian cancer cell lines by MTT assay. Expression of SFKs after Src silencing in ovarian cancer cells was examined by real-time reverse transcriptase (RT)-PCR. Therapeutic effect of in vivo Src and/or Fgr silencing was examined using siRNA incorporated into chitosan nanoparticles (siRNA/CH-NP). Microvessel density, cell proliferation, and apoptosis markers were determined by immunohistochemical staining in ovarian tumor tissues.

RESULTS

Src silencing enhanced cytotoxicity of docetaxel in both SKOV3ip1 and HeyA8 cells. In addition, Src silencing using siRNA/CH-NP in combination with docetaxel resulted in significant inhibition of tumor growth compared with control siRNA/CH-NP (81.8% reduction in SKOV3ip1, P = 0.017; 84.3% reduction in HeyA8, P < 0.005). These effects were mediated by decreased tumor cell proliferation and angiogenesis, and increased tumor cell apoptosis. Next, we assessed the effects of Src silencing on other SFK members in ovarian cancer cell lines. Src silencing resulted in significantly increased Fgr levels. Dual Src and Fgr silencing in vitro resulted in increased apoptosis that was mediated by increased caspase and AKT activity. In addition, dual silencing of Src and Fgr in vivo using siRNA/CH-NP resulted in the greatest reduction in tumor growth compared with silencing of either Src or Fgr alone in the HeyA8 model (68.8%, P < 0.05).

CONCLUSIONS

This study demonstrates that, in addition to Src, Fgr plays a biologically significant role in ovarian cancer growth and might represent an important target.

Targeted delivery of small interfering RNA using reconstituted high-density lipoprotein nanoparticles

RNA interference holds tremendous potential as a therapeutic approach, especially in the treatment of malignant tumors. However, efficient and biocompatible delivery methods are needed for systemic delivery of small interfering RNA (siRNA). To maintain a high level of growth, tumor cells scavenge high-density lipoprotein (HDL) particles by overexpressing its receptor: scavenger receptor type B1 (SR-B1). In this study, we exploited this cellular characteristic to achieve efficient siRNA delivery and established a novel formulation of siRNA by incorporating it into reconstituted HDL (rHDL) nanoparticles. Here, we demonstrate that rHDL nanoparticles facilitate highly efficient systemic delivery of siRNA in vivo, mediated by the SR-B1. Moreover, in therapeutic proof-of-concept studies, these nanoparticles were effective in silencing the expression of two proteins that are key to cancer growth and metastasis (signal transducer and activator of transcription 3 and focal adhesion kinase) in orthotopic mouse models of ovarian and colorectal cancer. These data indicate that an rHDL nanoparticle is a novel and highly efficient siRNA carrier, and therefore, this novel technology could serve as the foundation for new cancer therapeutic approaches.