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

CIC-DUX4 Induces Small Round Cell Sarcomas Distinct from Ewing Sarcoma

CIC-DUX4 sarcoma (CDS) or CIC-rearranged sarcoma is a subcategory of small round cell sarcoma resembling the morphological phenotypes of Ewing sarcoma (ES). However, recent clinicopathologic and molecular genetic analyses indicate that CDS is an independent disease entity from ES. Few ancillary markers have been used in the differential diagnosis of CDS, and additional CDS-specific biomarkers are needed for more definitive classification. Here, we report the generation of an ex vivo mouse model for CDS by transducing embryonic mesenchymal cells (eMC) with human CIC-DUX4 cDNA. Recipient mice transplanted with eMC-expressing CIC-DUX4 rapidly developed an aggressive, undifferentiated sarcoma composed of small round to short spindle cells. Gene-expression profiles of CDS and eMC revealed upregulation of CIC-DUX4 downstream genes such as PEA3 family genes, Ccnd2, Crh, and Zic1 IHC analyses for both mouse and human tumors showed that CCND2 and MUC5AC are reliable biomarkers to distinguish CDS from ES. Gene silencing of CIC-DUX4 as well as Ccnd2, Ret, and Bcl2 effectively inhibited CDS tumor growth in vitro The CDK4/6 inhibitor palbociclib and the soft tissue sarcoma drug trabectedin also blocked the growth of mouse CDS. In summary, our mouse model provides important biological information about CDS and provides a useful platform to explore biomarkers and therapeutic agents for CDS. Cancer Res; 77(11); 2927-37. ©2017 AACR.

Tissue-Engineered Model of Human Osteolytic Bone Tumor

Ewing's sarcoma (ES) is a poorly differentiated pediatric tumor of aggressive behavior characterized by propensity to metastasize to bone. Interactions between the tumor and bone cells orchestrate a vicious cycle in which tumor cells induce osteoclast differentiation and activation to cause osteolytic lesions, broken bones, pain, and hypercalcemia. The lack of controllable models that can recapitulate osteolysis in ES impedes the development of new therapies and limits our understanding of how tumor cells invade bone. In response to this need, tissue-engineered models are now being developed to enable quantitative, predictive studies of human tumors. In this study, we report a novel bioengineered model of ES that incorporates the osteolytic process. Our strategy is based on engineering human bone containing both osteoclasts and osteoblasts within three-dimensional mineralized bone matrix. We show that the bone matrix is resorbed by mature osteoclasts while the new bone matrix is formed by osteoblasts, leading to calcium release and bone remodeling. Introduction of ES cell aggregates into the bone niche induced decreases in bone density, connectivity, and matrix deposition. Additionally, therapeutic reagents, such as zoledronic acid, which have demonstrated efficacy in ES treatment, inhibited bone resorption mediated by osteoclasts in the tumor model.

Loss of Ewing sarcoma EWS allele promotes tumorigenesis by inducing chromosomal instability in zebrafish

The Ewing sarcoma family of tumors expresses aberrant EWSR1- (EWS) fusion genes that are derived from chromosomal translocation. Although these fusion genes are well characterized as transcription factors, their formation leaves a single EWS allele in the sarcoma cells, and the contribution that the loss of EWS makes towards disease pathogenesis is unknown. To address this question, we utilized zebrafish mutants for ewsa and tp53. The zebrafish tp53(M214K)^w/m line and the ewsa^w/m, zygotic ewsa^m/m, and Maternal-Zygotic (MZ) ewsa^m/m lines all displayed zero to low incidence of tumorigenesis. However, when the ewsa and tp53 mutant lines were crossed with each other, the incidence of tumorigenesis drastically increased. Furthermore, 27 hour post fertilization (hpf) MZ ewsa^m/m mutant embryos displayed a higher incidence of aberrant chromosome numbers and mitotic dysfunction compared to wildtype zebrafish embryos. Consistent with this finding, tumor samples obtained from ewsa^m/m;tp53^w/m zebrafish displayed loss of heterozygosity (LOH) for the wildtype tp53 locus. These results suggest that wildtype Ewsa inhibits LOH induction, possibly by maintaining chromosomal stability. We propose that the loss of ewsa promotes tumorigenesis, and EWS deficiency may contribute to the pathogenesis of EWS-fusion-expressing sarcomas.

Palliative Care in Musculoskeletal Oncology

Patients in advanced stages of illness trajectories with local and widespread musculoskeletal incurable malignancies, either treatment naive or having recurrence are referred to the palliative care clinic to relieve various disease-related symptoms and to improve the quality of life. Palliative care is a specialized medicine that offers treatment to the disease-specific symptoms, places emphasis on the psychosocial and spiritual aspects of life and help the patients and their family to cope with advance stage cancer in a stronger and reasonable way. The overall outcome of musculoskeletal malignancies has improved with the advent of multidisciplinary management. Even then these tumors do relapse and leads to organ failures and disease-specific deaths in children and young adults in productive age group thus requiring an integrated approach to improve the supportive/palliative care needs in end-stage disease. In this article, we would like to discuss the spectrum of presentation of advanced musculoskeletal malignancies, skeletal metastasis, and their management.

Micro-Environmental Stress Induces Src-Dependent Activation of Invadopodia and Cell Migration in Ewing Sarcoma

Metastatic Ewing sarcoma has a very poor prognosis and therefore new investigations into the biologic drivers of metastatic progression are key to finding new therapeutic approaches. The tumor microenvironment is highly dynamic, leading to exposure of different regions of a growing solid tumor to changes in oxygen and nutrient availability. Tumor cells must adapt to such stress in order to survive and propagate. In the current study, we investigate how Ewing sarcoma cells respond to the stress of growth factor deprivation and hypoxia. Our findings reveal that serum deprivation leads to a reversible change in Ewing cell cytoskeletal phenotypes. Using an array of migration and invasion techniques, including gelatin matrix degradation invadopodia assays, we show that exposure of Ewing sarcoma cells to serum deprivation and hypoxia triggers enhanced migration, invadopodia formation, matrix degradation and invasion. Further, these functional changes are accompanied by and dependent on activation of Src kinase. Activation of Src, and the associated invasive cell phenotype, were blocked by exposing hypoxia and serum-deprived cells to the Src inhibitor dasatinib. These results indicate that Ewing sarcoma cells demonstrate significant plasticity in response to rapidly changing micro-environmental stresses that can result from rapid tumor growth and from necrosis-causing therapies. In response to these stresses, Ewing cells transition to a more migratory and invasive state and our data show that Src is an important mediator of this stress response. Our data support exploration of clinically available Src inhibitors as adjuvant agents for metastasis prevention in Ewing sarcoma.

Regulatory mechanisms, expression levels and proliferation effects of the FUS-DDIT3 fusion oncogene in liposarcoma

Fusion oncogenes are among the most common types of oncogene in human cancers. The gene rearrangements result in new combinations of regulatory elements and functional protein domains. Here we studied a subgroup of sarcomas and leukaemias characterized by the FET (FUS, EWSR1, TAF15) family of fusion oncogenes, including FUS-DDIT3 in myxoid liposarcoma (MLS). We investigated the regulatory mechanisms, expression levels and effects of FUS-DDIT3 in detail. FUS-DDIT3 showed a lower expression than normal FUS at both the mRNA and protein levels, and single-cell analysis revealed a lack of correlation between FUS-DDIT3 and FUS expression. FUS-DDIT3 transcription was regulated by the FUS promotor, while its mRNA stability depended on the DDIT3 sequence. FUS-DDIT3 protein stability was regulated by protein interactions through the FUS part, rather than the leucine zipper containing DDIT3 part. In addition, in vitro as well as in vivo FUS-DDIT3 protein expression data displayed highly variable expression levels between individual MLS cells. Combined mRNA and protein analyses at the single-cell level showed that FUS-DDIT3 protein expression was inversely correlated to the expression of cell proliferation-associated genes. We concluded that FUS-DDIT3 is uniquely regulated at the transcriptional as well as the post-translational level and that its expression level is important for MLS tumour development. The FET fusion oncogenes are potentially powerful drug targets and detailed knowledge about their regulation and functions may help in the development of novel treatments.

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.

EWS-FLI1 impairs aryl hydrocarbon receptor activation by blocking tryptophan breakdown via the kynurenine pathway

Ewing sarcoma (ES) is an aggressive pediatric tumor driven by the fusion protein EWS-FLI1. We report that EWS-FLI1 suppresses TDO2-mediated tryptophan (TRP) breakdown in ES cells. Gene expression and metabolite analyses reveal an EWS-FLI1-dependent regulation of TRP metabolism. TRP consumption increased in the absence of EWS-FLI1, resulting in kynurenine and kynurenic acid accumulation, both aryl hydrocarbon receptor (AHR) ligands. Activated AHR binds to the promoter region of target genes. We demonstrate that EWS-FLI1 knockdown results in AHR nuclear translocation and activation. Our data suggest that EWS-FLI1 suppresses autocrine AHR signaling by inhibiting TDO2-catalyzed TRP breakdown.

Chest wall Ewing sarcoma: a population-based analysis

BACKGROUND

The globally low incidence of pediatric chest wall Ewing sarcoma (CWES) has limited prior studies of this disease to mostly small, single-institution reviews. Our objective was to assess incidence, demographics, treatment patterns, and long-term survival of this disease through a population-based analysis.

MATERIALS AND METHODS

The Surveillance, Epidemiology, and End Results database was used to identify patients aged 0-21 y diagnosed with CWES from 1973 to 2011. Patients were grouped by decade to assess changes in treatment patterns and outcomes. The effects of clinical, demographic, and treatment variables on overall survival (OS) were assessed by the computation of Kaplan-Meier curves and the log-rank test, with Cox proportional hazard regression used for multivariable analysis.

RESULTS

A total of 193 pediatric patients with histologically confirmed CWES were identified. The disease was more common in men (61%), whites (92%), and 11- to 17-y olds (49%). It was metastatic at presentation in 37% of patients. When grouped approximately by decade, 10-y OS improved progressively from 38% in 1973-1979 to 65% in 2000-2011 (P = 0.033). The use of radiation decreased from 84% in the earliest period to 40% in the most recent, whereas the proportion of patients receiving surgery increased from 75% to 85%. When controlling for covariates in multivariable analysis, male patients were found to have a higher mortality than female patients (hazard ratio: 2.4; confidence interval: 1.4, 4.4; P = 0.0028).

CONCLUSIONS

This population-based analysis of CWES demonstrated an impressive trend of improving OS, with increasing use of surgery and decreasing use of radiation therapy. Our study demonstrated a gender difference in survival of CWES, with females having a better prognosis. The presence of metastatic disease is a very important prognostic factor for this illness.