Ewing's sarcoma precursors are highly enriched in embryonic osteochondrogenic progenitors

Activation of Wnt/β-Catenin in Ewing Sarcoma Cells Antagonizes EWS/ETS Function and Promotes Phenotypic Transition to More Metastatic Cell States

Ewing sarcomas are characterized by the presence of EWS/ETS fusion genes in the absence of other recurrent genetic alterations and mechanisms of tumor heterogeneity that contribute to disease progression remain unclear. Mutations in the Wnt/β-catenin pathway are rare in Ewing sarcoma but the Wnt pathway modulator LGR5 is often highly expressed, suggesting a potential role for the axis in tumor pathogenesis. We evaluated β-catenin and LGR5 expression in Ewing sarcoma cell lines and tumors and noted marked intra- and inter-tumor heterogeneity. Tumors with evidence of active Wnt/β-catenin signaling were associated with increased incidence of tumor relapse and worse overall survival. Paradoxically, RNA sequencing revealed a marked antagonism of EWS/ETS transcriptional activity in Wnt/β-catenin-activated tumor cells. Consistent with this, Wnt/β-catenin-activated cells displayed a phenotype that was reminiscent of Ewing sarcoma cells with partial EWS/ETS loss of function. Specifically, activation of Wnt/β-catenin induced alterations to the actin cytoskeleton, acquisition of a migratory phenotype, and upregulation of EWS/ETS-repressed genes. Notably, activation of Wnt/β-catenin signaling led to marked induction of tenascin C (TNC), an established promoter of cancer metastasis, and an EWS/ETS-repressed target gene. Loss of TNC function in Ewing sarcoma cells profoundly inhibited their migratory and metastatic potential. Our studies reveal that heterogeneous activation of Wnt/β-catenin signaling in subpopulations of tumor cells contributes to phenotypic heterogeneity and disease progression in Ewing sarcoma. Significantly, this is mediated, at least in part, by inhibition of EWS/ETS fusion protein function that results in derepression of metastasis-associated gene programs. Cancer Res; 76(17); 5040-53. ©2016 AACR.

Twenty Years on: What Do We Really Know about Ewing Sarcoma and What Is the Path Forward?

Ewing sarcoma (ES) is a highly aggressive bone and soft-tissue tumor with peak incidence among adolescents and young adults. Despite advances in local control and systemic chemotherapy, metastatic relapse after an initial clinical remission remains a significant clinical problem. In addition, metastasis at the time of presentation or at relapse continues to be the leading cause of death for patients diagnosed with ES. Since the discovery of the pathognomonic EWS-FLI1 fusion gene more than 20 years ago, much about the molecular and cellular biology of ES pathogenesis has been learned. In addition, more recent exploitation of advances in stem cell and developmental biology has provided key insights into the cellular origins of ES and the role of epigenetic deregulation in tumor initiation and maintenance. Nevertheless, the mechanisms that drive tumor relapse and metastasis remain largely unknown. These gaps in our knowledge continue to hamper the development of novel therapeutic strategies that may improve outcomes for patients with relapsed and metastatic disease. In this article we review the current status of ES biology research, highlighting areas of investigation that we consider to have the greatest potential to yield findings that will translate into clinically significant advances.

Primary pericranial Ewing's sarcoma on the temporal bone: A case report

BACKGROUND

Primary Ewing's sarcoma originating in the pericranium is an extremely rare disease entity.

CASE DESCRIPTION

A 9-year-old female patient was admitted to our department due to a left temporal subcutaneous mass. The mass was localized under the left temporal muscle and attached to the surface of the temporal bone. Head computed tomography revealed a mass with bony spicule formation on the temporal bone, however, it did not show bone destruction or intracranial invasion. F-18 fluorodeoxyglucose positron emission tomography showed no lesions other than the mass on the temporal bone. Magnetic resonance imaging showed that the mass was located between the temporal bone and the pericranium. The mass was completely resected with the underlying temporal bone and the overlying deep layer of temporal muscle, and was diagnosed as primary Ewing's sarcoma. Because the tumor was located in the subpericranium, we created a new classification, "pericranial Ewing's sarcoma," and diagnosed the present tumor as pericranial Ewing's sarcoma.

CONCLUSION

We herein present an extremely rare case of primary pericranial Ewing's sarcoma that developed on the temporal bone.

Sclerostin expression in bone tumours and tumour-like lesions

AIMS

To assess the immunophenotypic and mRNA expression of sclerostin in human skeletal tissues and in a wide range of benign and malignant bone tumours and tumour-like lesions.

METHODS AND RESULTS

Sclerostin expression was evaluated by immunohistochemistry and quantitative polymerase chain reaction (PCR). In lamellar and woven bone, there was strong sclerostin expression by osteocytes. Osteoblasts and other cell types in bone were negative. Hypertrophic chondrocytes in the growth plate and mineralized cartilage cells in zone 4 of hyaline articular cartilage strongly expressed sclerostin, but most chondrocytes in hyaline cartilage were negative. In primary bone-forming tumours, including osteosarcomas, there was patchy expression of sclerostin in mineralized osteoid and bone. Sclerostin staining was seen in woven bone in fibrous dysplasia, in osteofibrous dysplasia, and in reactive bone formed in fracture callus, in myositis ossificans, and in the wall of solitary bone cysts and aneurysmal bone cysts. Sclerostin was expressed by hypertrophic chondrocytes in osteochondroma and chondroblasts in chondroblastoma, but not by tumour cells in other bone tumours, including myeloma and metastatic carcinoma. mRNA expression of sclerostin was identified by quantitative PCR in osteosarcoma specimens and cell lines.

CONCLUSIONS

Sclerostin is an osteocyte marker that is strongly expressed in human woven and lamellar bone and mineralizing chondrocytes. This makes it a useful marker with which to identify benign and malignant osteogenic tumours and mineralizing cartilage tumours, such as chondroblastomas and other lesions in which there is bone formation.

MEIS1-mediated transactivation of synaptotagmin-like 1 promotes CXCL12/CXCR4 signaling and leukemogenesis

The TALE-class homeoprotein MEIS1 specifically collaborates with HOXA9 to drive myeloid leukemogenesis. Although MEIS1 alone has only a moderate effect on cell proliferation in vitro, it is essential for the development of HOXA9-induced leukemia in vivo. Here, using murine models of leukemogenesis, we have shown that MEIS1 promotes leukemic cell homing and engraftment in bone marrow and enhances cell-cell interactions and cytokine-mediated cell migration. We analyzed global DNA binding of MEIS1 in leukemic cells as well as gene expression alterations in MEIS1-deficent cells and identified synaptotagmin-like 1 (Sytl1, also known as Slp1) as the MEIS1 target gene that cooperates with Hoxa9 in leukemogenesis. Replacement of SYTL1 in MEIS1-deficent cells restored both cell migration and engraftment. Further analysis revealed that SYTL1 promotes cell migration via activation of the CXCL12/CXCR4 axis, as SYTL1 determines intracellular trafficking of CXCR4. Together, our results reveal that MEIS1, through induction of SYTL1, promotes leukemogenesis and supports leukemic cell homing and engraftment, facilitating interactions between leukemic cells and bone marrow stroma.

An EWS-FLI1-Induced Osteosarcoma Model Unveiled a Crucial Role of Impaired Osteogenic Differentiation on Osteosarcoma Development

EWS-FLI1, a multi-functional fusion oncogene, is exclusively detected in Ewing sarcomas. However, previous studies reported that rare varieties of osteosarcomas also harbor EWS-ETS family fusion. Here, using the doxycycline-inducible EWS-FLI1 system, we established an EWS-FLI1-dependent osteosarcoma model from murine bone marrow stromal cells. We revealed that the withdrawal of EWS-FLI1 expression enhances the osteogenic differentiation of sarcoma cells, leading to mature bone formation. Taking advantage of induced pluripotent stem cell (iPSC) technology, we also show that sarcoma-derived iPSCs with cancer-related genetic abnormalities exhibited an impaired differentiation program of osteogenic lineage irrespective of the EWS-FLI1 expression. Finally, we demonstrate that EWS-FLI1 contributed to secondary sarcoma development from the sarcoma iPSCs after osteogenic differentiation. These findings demonstrate that modulating cellular differentiation is a fundamental principle of EWS-FLI1-induced osteosarcoma development. This in vitro cancer model using sarcoma iPSCs should provide a unique platform for dissecting relationships between the cancer genome and cellular differentiation.

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EWS-FLI1 induces small-cell osteosarcoma from murine bone marrow stromal cells

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EWS-FLI1 inhibits osteogenic differentiation of sarcoma cells in vivo

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Modulating differentiation is a fundamental principle of osteosarcoma development

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Sarcoma iPSCs should provide a unique platform for dissecting cancer biology

YK-4-279 effectively antagonizes EWS-FLI1 induced leukemia in a transgenic mouse model

Ewing sarcoma is an aggressive tumor of bone and soft tissue affecting predominantly children and young adults. Tumor-specific chromosomal translocations create EWS-FLI1 and similar aberrant ETS fusion proteins that drive sarcoma development in patients. ETS family fusion proteins and over-expressed ETS proteins are also found in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) patients. Transgenic expression of EWS-FLI1 in mice promotes high penetrance erythroid leukemia with dense hepatic and splenic infiltrations. We identified a small molecule, YK-4-279, that directly binds to EWS-FLI1 and inhibits its oncogenic activity in Ewing sarcoma cell lines and xenograft mouse models. Herein, we tested in vivo therapeutic efficacy and potential side effects of YK-4-279 in the transgenic mouse model with EWS-FLI1 induced leukemia. A two-week course of treatment with YK-4-279 significantly reduced white blood cell count, nucleated erythroblasts in the peripheral blood, splenomegaly, and hepatomegaly of erythroleukemic mice. YK-4-279 inhibited EWS-FLI1 target gene expression in neoplastic cells. Treated animals showed significantly better overall survival compared to control mice that rapidly succumbed to leukemia. YK-4-279 treated mice did not show overt toxicity in liver, spleen, or bone marrow. In conclusion, this in vivo study highlights the efficacy of YK-4-279 to treat EWS-FLI1 expressing neoplasms and support its therapeutic potential for patients with Ewing sarcoma and other ETS-driven malignancies.

SLFN11: Achilles' Heel or Troublemaker

SLFN11 expression correlates with sensitivity of tumors to topoisomerase and DNA-targeting drugs and consequently with prognosis. Regulation of SLFN11 by ETS factors opens new avenues to treatment optimization, maximizing antitumor activity and minimizing adverse side effects. Interrogating drug-induced gene expression signatures for SLFN11 modulations may affect the design of therapeutic regimens.

Multipotent Mesenchymal Stromal Cells: Possible Culprits in Solid Tumors?

The clinical use of bone marrow derived multipotent mesenchymal stromal cells (BM-MSCs) in different settings ranging from tissue engineering to immunotherapies has prompted investigations on the properties of these cells in a variety of other tissues. Particularly the role of MSCs in solid tumors has been the subject of many experimental approaches. While a clear phenotypical distinction of tumor associated fibroblasts (TAFs) and MSCs within the tumor microenvironment is still missing, the homing of bone marrow MSCs in tumor sites has been extensively studied. Both, tumor-promoting and tumor-inhibiting effects of BM-MSCs have been described in this context. This ambiguity requires a reappraisal of the different studies and experimental methods employed. Here, we review the current literature on tumor-promoting and tumor-inhibiting effects of BM-MSCs with a particular emphasis on their interplay with components of the immune system and also highlight a potential role of MSCs as cell of origin for certain mesenchymal tumors.

Sequencing Overview of Ewing Sarcoma: A Journey across Genomic, Epigenomic and Transcriptomic Landscapes

Ewing sarcoma is an aggressive neoplasm occurring predominantly in adolescent Caucasians. At the genome level, a pathognomonic EWSR1-ETS translocation is present. The resulting fusion protein acts as a molecular driver in the tumor development and interferes, amongst others, with endogenous transcription and splicing. The Ewing sarcoma cell shows a poorly differentiated, stem-cell like phenotype. Consequently, the cellular origin of Ewing sarcoma is still a hot discussed topic. To further characterize Ewing sarcoma and to further elucidate the role of EWSR1-ETS fusion protein multiple genome, epigenome and transcriptome level studies were performed. In this review, the data from these studies were combined into a comprehensive overview. Presently, classical morphological predictive markers are used in the clinic and the therapy is dominantly based on systemic chemotherapy in combination with surgical interventions. Using sequencing, novel predictive markers and candidates for immuno- and targeted therapy were identified which were summarized in this review.

Deep Sequencing in Conjunction with Expression and Functional Analyses Reveals Activation of FGFR1 in Ewing Sarcoma

PURPOSE

A low mutation rate seems to be a general feature of pediatric cancers, in particular in oncofusion gene-driven tumors. Genetically, Ewing sarcoma is defined by balanced chromosomal EWS/ETS translocations, which give rise to oncogenic 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 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 Ewing sarcoma and 22 matched normal tissues. A discovery dataset of 14 of these tumor/normal pairs identified 232 somatic mutations. Recurrent nonsynonymous mutations were validated in the 36 remaining exomes. Transcriptome analysis was performed in a subset of 14 of 50 Ewing sarcomas and DNA copy number gain and expression of FGFR1 in 63 of 116 Ewing sarcomas.

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 Ewing sarcoma. RNA interference of FGFR1 expression in Ewing sarcoma lines blocked proliferation and completely suppressed xenograft tumor growth. FGFR1 tyrosine kinase inhibitor (TKI) therapy in a patient with Ewing sarcoma relapse significantly reduced 18-FDG-PET activity.

CONCLUSIONS

FGFR1 may constitute a promising target for novel therapeutic approaches in Ewing sarcoma.

EWS-FLI1 employs an E2F switch to drive target gene expression

Cell cycle progression is orchestrated by E2F factors. We previously reported that in ETS-driven cancers of the bone and prostate, activating E2F3 cooperates with ETS on target promoters. The mechanism of target co-regulation remained unknown. Using RNAi and time-resolved chromatin-immunoprecipitation in Ewing sarcoma we report replacement of E2F3/pRB by constitutively expressed repressive E2F4/p130 complexes on target genes upon EWS-FLI1 modulation. Using mathematical modeling we interrogated four alternative explanatory models for the observed EWS-FLI1/E2F3 cooperation based on longitudinal E2F target and regulating transcription factor expression analysis. Bayesian model selection revealed the formation of a synergistic complex between EWS-FLI1 and E2F3 as the by far most likely mechanism explaining the observed kinetics of E2F target induction. Consequently we propose that aberrant cell cycle activation in Ewing sarcoma is due to the de-repression of E2F targets as a consequence of transcriptional induction and physical recruitment of E2F3 by EWS-FLI1 replacing E2F4 on their target promoters.

Somatic chromosomal translocation between Ewsr1 and Fli1 loci leads to dilated cardiomyopathy in a mouse model

A mouse model that recapitulates the human Ewing's sarcoma-specific chromosomal translocation was generated utilizing the Cre/loxP-mediated recombination technique. A cross between Ewsr1-loxP and Fli1-loxP mice and expression of ubiquitous Cre recombinase induced a specific translocation between Ewsr1 and Fli1 loci in systemic organs of both adult mice and embryos. As a result Ewsr1-Fli1 fusion transcripts were expressed, suggesting a functional Ews-Fli1 protein might be synthesized in vivo. However, by two years of age, none of the Ewsr1-loxP/Fli1-loxP/CAG-Cre (EFCC) mice developed any malignancies, including Ewing-like small round cell sarcoma. Unexpectedly, all the EFCC mice suffered from dilated cardiomyopathy and died of chronic cardiac failure. Genetic recombination between Ewsr1 and Fli1 was confirmed in the myocardial tissue and apoptotic cell death of cardiac myocytes was observed at significantly higher frequency in EFCC mice. Moreover, expression of Ews-Fli1 in the cultured cardiac myocytes induced apoptosis. Collectively, these results indicated that ectopic expression of the Ews-Fli1 oncogene stimulated apoptotic signals, and suggested an important relationship between oncogenic signals and cellular context in the cell-of-origin of Ewing's sarcoma.

EWS-FLI1 utilizes divergent chromatin remodeling mechanisms to directly activate or repress enhancer elements in Ewing sarcoma

The aberrant transcription factor EWS-FLI1 drives Ewing sarcoma, but its molecular function is not completely understood. We find that EWS-FLI1 reprograms gene regulatory circuits in Ewing sarcoma by directly inducing or repressing enhancers. At GGAA repeat elements, which lack evolutionary conservation and regulatory potential in other cell types, EWS-FLI1 multimers induce chromatin opening and create de novo enhancers that physically interact with target promoters. Conversely, EWS-FLI1 inactivates conserved enhancers containing canonical ETS motifs by displacing wild-type ETS transcription factors. These divergent chromatin-remodeling patterns repress tumor suppressors and mesenchymal lineage regulators while activating oncogenes and potential therapeutic targets, such as the kinase VRK1. Our findings demonstrate how EWS-FLI1 establishes an oncogenic regulatory program governing both tumor survival and differentiation.

Gene expression response to EWS-FLI1 in mouse embryonic cartilage

Ewing's sarcoma is a rare bone tumor that affects children and adolescents. We have recently succeeded to induce Ewing's sarcoma-like small round cell tumor in mice by expression of EWS-ETS fusion genes in murine embryonic osteochondrogenic progenitors. The Ewing's sarcoma precursors are enriched in embryonic superficial zone (eSZ) cells of long bone. To get insights into the mechanisms of Ewing's sarcoma development, gene expression profiles between EWS-FLI1-sensitive eSZ cells and EWS-FLI1-resistant embryonic growth plate (eGP) cells were compared using DNA microarrays. Gene expression of eSZ and eGP cells (total, 30 samples) was evaluated with or without EWS-FLI1 expression 0, 8 or 48 h after gene transduction. Our data provide useful information for gene expression responses to fusion oncogenes in human sarcoma.

Blocking the road, stopping the engine or killing the driver? Advances in targeting EWS/FLI-1 fusion in Ewing sarcoma as novel therapy

INTRODUCTION

Ewing sarcoma (ES) represents the paradigm of an aberrant E-twenty-six (ETS) oncogene-driven cancer. It is characterized by specific rearrangements of one of five alternative ETS family member genes with EWSR1. There is experimental evidence that the resulting fusion proteins act as aberrant transcription factors driving ES pathogenesis. The transcriptional gene regulatory network driven by EWS-ETS proteins provides the oncogenic engine to the tumor. Therefore, EWS-ETS and their downstream machinery are considered ideal tumor-specific therapeutic targets.

AREAS COVERED

This review critically discusses the literature on the development of EWS-ETS-directed ES targeting strategies considering current knowledge of EWS-ETS biology and cellular context. It focuses on determinants of EWS-FLI1 function with an emphasis on interactions with chromatin structure. We speculate about the relevance of poorly investigated aspects in ES research such as chromatin remodeling and DNA damage repair for the development of targeted therapies.

EXPERT OPINION

This review questions the specificity of signature-based screening approaches to the identification of EWS-FLI1-targeted compounds. It challenges the view that targeting the downstream gene regulatory network carries potential for therapeutic breakthroughs because of resistance-inducing network rewiring. Instead, we propose to combine targeting of the fusion protein with epigenetic therapy as a future treatment strategy in ES.