Ewing tumors (ET) are highly malignant, localized in bone or soft tissue, and are molecularly defined by ews/ets translocations. DNA microarray analysis revealed a relationship of ET to both endothelium and fetal neural crest. We identified expression of histone methyltransferase enhancer of Zeste,Drosophila, Homolog 2 (EZH2) to be increased in ET. Suppressive activity of EZH2 maintains stemness in normal and malignant cells. Here, we found EWS/FLI1 bound to the EZH2 promoter in vivo, and induced EZH2 expression in ET and mesenchymal stem cells. Down-regulation of EZH2 by RNA interference in ET suppressed oncogenic transformation by inhibiting clonogenicity in vitro. Similarly, tumor development and metastasis was suppressed in immunodeficient Rag2^−/−γ_C^−/−mice. EZH2-mediated gene silencing was shown to be dependent on histone deacetylase (HDAC) activity. Subsequent microarray analysis of EZH2 knock down, HDAC-inhibitor treatment and confirmation in independent assays revealed an undifferentiated phenotype maintained by EZH2 in ET. EZH2 regulated stemness genes such as nerve growth factor receptor (NGFR), as well as genes involved in neuroectodermal and endothelial differentiation (EMP1, EPHB2, GFAP, and GAP43). These data suggest that EZH2 might have a central role in ET pathology by shaping the oncogenicity and stem cell phenotype of this tumor.

Purpose: A low mutation rate seems a general feature of pediatric cancers, in par-ticular in oncofusion gene driven tumors. Genetically, Ewing sarcoma (ES) is de-fined by balanced chromosomal EWS/ETS translocations, which give rise to onco-genic chimeric proteins (EWS-ETS). Other contributing somatic mutations involved in disease development have only been observed at low frequency. Experimental design: Tumor samples of 116 Ewing sarcoma (ES) patients were analyzed here. Whole Genome Sequencing was performed on two patients with normal, primary and relapsed tissue. Whole Exome Sequencing was performed on 50 ES and 22 matched normal tissues. A discovery data set of 14 of these tu-mor/normal pairs identified 232 somatic mutations. Recurrent non-synonymous mu-tations were validated in the 36 remaining exomes. Transcriptome analysis was per-formed in a subset of 14/50 ES and DNA copy number gain and expression of FGFR1 in 63/116 ES. Results: Relapsed tumors consistently showed a 2- to 3-fold increased number of mutations. We identified several recurrently mutated genes at low frequency (ANKRD30A, CCDC19, KIAA0319, KIAA1522, LAMB4, SLFN11, STAG2, TP53, UNC80, ZNF98). An oncogenic fibroblast growth factor receptor 1 (FGFR1) mutation (N546K) was detected, and the FGFR1 locus frequently showed copy number gain (31.7%) in primary tumors. Furthermore, high-level FGFR1 expression was noted as a characteristic feature of ES. RNA-Interference of FGFR1 expression in ES lines blocked proliferation and completely suppressed xenograft tumor growth. FGFR1 TKI inhibitor therapy in a patient with ES relapse significantly reduced 18-FDG-PET activity. Conclusions: FGFR1 may constitute a promising target for novel therapeutic ap-proaches in ES.

Ewing sarcoma, an osteolytic malignancy that mainly affects children and young adults, is characterized by early metastasis to lung and bone. In this study, we identified the pro-metastatic gene DKK2 as a highly overexpressed gene in Ewing sarcoma compared with corresponding normal tissues. Using RNA interference, we showed that DKK2 was critical for malignant cell outgrowth in vitro and in an orthotopic xenograft mouse model in vivo. Analysis of invasion potential in both settings revealed a strong correlation of DKK2 expression to Ewing sarcoma invasiveness that may be mediated by the DKK effector matrix metalloproteinase 1 (MMP1). Furthermore, gene expression analyses established the ability of DKK2 to differentially regulate genes such as CXCR4, PTHrP, RUNX2, and TGFβ1 that are associated with homing, invasion, and growth of cancer cells in bone tissue as well as genes important for osteolysis, including HIF1α, JAG1, IL6, and VEGF. DKK2 promoted bone infiltration and osteolysis in vivo and further analyses defined DKK2 as a key factor in osteotropic malignancy. Interestingly, in Ewing sarcoma cells, DKK2 suppression simultaneously increased the potential for neuronal differentiation while decreasing chondrogenic and osteogenic differentiation. Our results provide strong evidence that DKK2 is a key player in Ewing sarcoma invasion and osteolysis and also in the differential phenotype of Ewing sarcoma cells. Cancer Res; 73(2); 967–77. ©2012 AACR.

Background: Histone acetylation and deacetylation seem processes involved in the pathogenesis of Ewing sarcoma (EwS). Here histone deacetylases (HDAC) class I were investigated. Methods: Their role was determined using different inhibitors including TSA, Romidepsin, Entinostat and PCI-34051 as well as CRISPR/Cas9 class I HDAC knockouts and HDAC RNAi. To analyze resulting changes microarray analysis, qRT-PCR, western blotting, Co-IP, proliferation, apoptosis, differentiation, invasion assays and xenograft-mouse models were used. Results: Class I HDACs are constitutively expressed in EwS. Patients with high levels of individual class I HDAC expression show decreased overall survival. CRISPR/Cas9 class I HDAC knockout of individual HDACs such as HDAC1 and HDAC2 inhibited invasiveness, and blocked local tumor growth in xenograft mice. Microarray analysis demonstrated that treatment with individual HDAC inhibitors (HDACi) blocked an EWS-FLI1 specific expression profile, while Entinostat in addition suppressed metastasis relevant genes. EwS cells demonstrated increased susceptibility to treatment with chemotherapeutics including Doxorubicin in the presence of HDACi. Furthermore, HDACi treatment mimicked RNAi of EZH2 in EwS. Treated cells showed diminished growth capacity, but an increased endothelial as well as neuronal differentiation ability. HDACi synergizes with EED inhibitor (EEDi) in vitro and together inhibited tumor growth in xenograft mice. Co-IP experiments identified HDAC class I family members as part of a regulatory complex together with PRC2. Conclusions: Class I HDAC proteins seem to be important mediators of the pathognomonic EWS-ETS-mediated transcription program in EwS and in combination therapy, co-treatment with HDACi is an interesting new treatment opportunity for this malignant disease.

Ewing sarcoma (EwS) is an aggressive pediatric cancer of bone and soft tissues characterized by scant T cell infiltration and predominance of immunosuppressive myeloid cells. Given the important roles of extracellular vesicles (EVs) in cancer-host crosstalk, we hypothesized that EVs secreted by EwS tumors target myeloid cells and promote immunosuppressive phenotypes. Here, EVs were purified from EwS and fibroblast cell lines and exhibited characteristics of small EVs, including size (100–170 nm) and exosome markers CD63, CD81, and TSG101. Treatment of healthy donor-derived CD33⁺ and CD14⁺ myeloid cells with EwS EVs but not with fibroblast EVs induced pro-inflammatory cytokine release, including IL-6, IL-8, and TNF. Furthermore, EwS EVs impaired differentiation of these cells towards monocytic-derived dendritic cells (moDCs), as evidenced by reduced expression of co-stimulatory molecules CD80, CD86 and HLA-DR. Whole transcriptome analysis revealed activation of gene expression programs associated with immunosuppressive phenotypes and pro-inflammatory responses. Functionally, moDCs differentiated in the presence of EwS EVs inhibited CD4⁺ and CD8⁺ T cell proliferation as well as IFNγ release, while inducing secretion of IL-10 and IL-6. Therefore, EwS EVs may promote a local and systemic pro-inflammatory environment and weaken adaptive immunity by impairing the differentiation and function of antigen-presenting cells.