The Long Noncoding RNA RP11-728F11.4 Promotes Atherosclerosis.

OBJECTIVE: Noncoding RNAs are emerging as important players in gene regulation and cardiovascular diseases. Their roles in the pathogenesis of atherosclerosis are not fully understood. The purpose of this study was to determine the role played by a previously uncharacterized long noncoding RNA, RP11-728F11.4, in the development of atherosclerosis and the mechanisms by which it acts. Approach and Results: Expression microarray analysis revealed that atherosclerotic plaques had increased expression of RP11-728F11.4 as well as the cognate gene FXYD6 (FXYD domain containing ion transport regulator 6), which encodes a modulator of Na+/K+-ATPase. In vitro experiments showed that RP11-728F11.4 interacted with the RNA-binding protein EWSR1 (Ewings sarcoma RNA binding protein-1) and upregulated FXYD6 expression. Lentivirus-induced overexpression of RP11-728F11.4 in cultured monocytes-derived macrophages resulted in higher Na+/K+-ATPase activity, intracellular cholesterol accumulation, and increased proinflammatory cytokine production. The effects of RP11-728F11.4 were enhanced by siRNA-mediated knockdown of EWSR1 and reduced by downregulation of FXYD domain containing ion transport regulator 6. In vivo experiments in apoE knockout mice fed a Western diet demonstrated that RP11-728F11.4 increased proinflammatory cytokine production and augmented atherosclerotic lesions. CONCLUSIONS: RP11-728F11.4 promotes atherosclerosis, with an influence on cholesterol homeostasis and proinflammatory molecule production, thus representing a potential therapeutic target. Graphic Abstract: A graphic abstract is available for this article.

The Ewing sarcoma protein regulates DNA damage-induced alternative splicing.

The Ewing sarcoma (EWS) protein is a member of the TET (TLS/EWS/TAF15) family of RNA- and DNA-binding proteins whose expression is altered in cancer. We report that EWS depletion results in alternative splicing changes of genes involved in DNA repair and genotoxic stress signaling, including ABL1, CHEK2, and MAP4K2. Chromatin and RNA crosslinking immunoprecipitation results indicate that EWS cotranscriptionally binds to its target RNAs. This association is reduced upon irradiation of cells with ultraviolet light, concomitant with transient enrichment of EWS in nucleoli and with alternative splicing changes that parallel those induced by EWS depletion and that lead to reduced c-ABL protein expression. Consistent with the functional relevance of EWS-mediated alternative splicing regulation in DNA damage response, EWS depletion reduces cell viability and proliferation upon UV irradiation, effects that are attenuated by restoring c-ABL expression. These results provide insights into posttranscriptional mechanisms of DNA damage response by a TET protein.

New Insights about the Wnt/ß-Catenin Signaling Pathway in Primary Bone Tumors and Their Microenvironment: A Promising Target to Develop Therapeutic Strategies?

Osteosarcoma and Ewing sarcoma are the most common malignant primary bone tumors mainly occurring in children, adolescents and young adults. Current standard therapy includes multidrug chemotherapy and/or radiation specifically for Ewing sarcoma, associated with tumor resection. However, patient survival has not evolved for the past decade and remains closely related to the response of tumor cells to chemotherapy, reaching around 75% at 5 years for patients with localized forms of osteosarcoma or Ewing sarcoma but less than 30% in metastatic diseases and patients resistant to initial chemotherapy. Despite Ewing sarcoma being characterized by specific EWSR1-ETS gene fusions resulting in oncogenic transcription factors, currently, no targeted therapy could be implemented. It seems even more difficult to develop a targeted therapeutic strategy in osteosarcoma which is characterized by high complexity and heterogeneity in genomic alterations. Nevertheless, the common point between these different bone tumors is their ability to deregulate bone homeostasis and remodeling and divert them to their benefit. Therefore, targeting different actors of the bone tumor microenvironment has been hypothesized to develop new therapeutic strategies. In this context, it is well known that the Wnt/ß-catenin signaling pathway plays a key role in cancer development, including osteosarcoma and Ewing sarcoma as well as in bone remodeling. Moreover, recent studies highlight the implication of the Wnt/ß-catenin pathway in angiogenesis and immuno-surveillance, two key mechanisms involved in metastatic dissemination. This review focuses on the role played by this signaling pathway in the development of primary bone tumors and the modulation of their specific microenvironment.

Inactivation of EWS reduces PGC-1α protein stability and mitochondrial homeostasis.

EWS (Ewing sarcoma) encodes an RNA/ssDNA binding protein that is frequently rearranged in a number of different cancers by chromosomal translocations. Physiologically, EWS has diverse and essential roles in various organ development and cellular processes. In this study, we uncovered a new role of EWS in mitochondrial homeostasis and energy metabolism. Loss of EWS leads to a significant decrease in mitochondria abundance and activity, which is caused by a rapid degradation of Peroxisome proliferator-activated receptor γ Coactivator (PGC-1α), a central regulator of mitochondria biogenesis, function, and cellular energy metabolism. EWS inactivation leads to increased ubiquitination and proteolysis of PGC-1α via proteasome pathway. Complementation of EWS in Ews-deficient cells restores PGC-1α and mitochondrial abundance. We found that expression of E3 ubiquitin ligase, FBXW7 (F-box/WD40 domain protein 7), is increased in the absence of Ews and depletion of Fbxw7 in Ews-null cells restores PGC-1α expression and mitochondrial density. Consistent with these findings, mitochondrial abundance and activity are significantly reduced in brown fat and skeletal muscles of Ews-deficient mice. Furthermore, expression of mitochondrial biogenesis, respiration and fatty acid ß-oxidation genes is significantly reduced in the liver of Ews-null mice. These results demonstrate a novel role of EWS in mitochondrial and cellular energy homeostasis by controlling PGC-1α protein stability, and further implicate altered mitochondrial and energy metabolism in cancers harboring the EWS translocation.

Systems biology of Ewing sarcoma: a network model of EWS-FLI1 effect on proliferation and apoptosis.

Ewing sarcoma is the second most frequent pediatric bone tumor. In most of the patients, a chromosomal translocation leads to the expression of the EWS-FLI1 chimeric transcription factor that is the major oncogene in this pathology. Relative genetic simplicity of Ewing sarcoma makes it particularly attractive for studying cancer in a systemic manner. Silencing EWS-FLI1 induces cell cycle alteration and ultimately leads to apoptosis, but the exact molecular mechanisms underlying this phenotype are unclear. In this study, a network linking EWS-FLI1 to cell cycle and apoptosis phenotypes was constructed through an original method of network reconstruction. Transcriptome time-series after EWS-FLI1 silencing were used to identify core modulated genes by an original scoring method based on fitting expression profile dynamics curves. Literature data mining was then used to connect these modulated genes into a network. The validity of a subpart of this network was assessed by siRNA/RT-QPCR experiments on four additional Ewing cell lines and confirmed most of the links. Based on the network and the transcriptome data, CUL1 was identified as a new potential target of EWS-FLI1. Altogether, using an original methodology of data integration, we provide the first version of EWS-FLI1 network model of cell cycle and apoptosis regulation.

Therapeutic Potential of NTRK3 Inhibition in Desmoplastic Small Round Cell Tumor.

PURPOSE: Desmoplastic small round cell tumor (DSRCT) is a highly lethal intra-abdominal sarcoma of adolescents and young adults. DSRCT harbors a t(11;22)(p13:q12) that generates the EWSR1-WT1 chimeric transcription factor, the key oncogenic driver of DSRCT. EWSR1-WT1 rewires global gene expression networks and activates aberrant expression of targets that together mediate oncogenesis. EWSR1-WT1 also activates a neural gene expression program. EXPERIMENTAL DESIGN: Among these neural markers, we found prominent expression of neurotrophic tyrosine kinase receptor 3 (NTRK3), a druggable receptor tyrosine kinase. We investigated the regulation of NTRK3 by EWSR1-WT1 and its potential as a therapeutic target in vitro and in vivo, the latter using novel patient-derived models of DSRCT. RESULTS: We found that EWSR1-WT1 binds upstream of NTRK3 and activates its transcription. NTRK3 mRNA is highly expressed in DSRCT compared with other major chimeric transcription factor-driven sarcomas and most DSRCTs are strongly immunoreactive for NTRK3 protein. Remarkably, expression of NTRK3 kinase domain mRNA in DSRCT is also higher than in cancers with NTRK3 fusions. Abrogation of NTRK3 expression by RNAi silencing reduces growth of DSRCT cells and pharmacologic targeting of NTRK3 with entrectinib is effective in both in vitro and in vivo models of DSRCT. CONCLUSIONS: Our results indicate that EWSR1-WT1 directly activates NTRK3 expression in DSRCT cells, which are dependent on its expression and activity for growth. Pharmacologic inhibition of NTRK3 by entrectinib significantly reduces growth of DSRCT cells both in vitro and in vivo, providing a rationale for clinical evaluation of NTRK3 as a therapeutic target in DSRCT.

Pharmaceutical Interference of the EWS-FLI1-driven Transcriptome By Cotargeting H3K27ac and RNA Polymerase Activity in Ewing Sarcoma.

The EWSR1-FLI1 t(11;22)(q24;q12) translocation is the hallmark genomic alteration of Ewing sarcoma, a malignancy of the bone and surrounding tissue, predominantly affecting children and adolescents. Although significant progress has been made for the treatment of localized disease, patients with metastasis or who relapse after chemotherapy have less than a 30% five-year survival rate. EWS-FLI1 is currently not clinically druggable, driving the need for more effective targeted therapies. Treatment with the H3K27 demethylase inhibitor, GSK-J4, leads to an increase in H3K27me and a decrease in H3K27ac, a significant event in Ewing sarcoma because H3K27ac associates strongly with EWS-FLI1 binding at enhancers and promoters and subsequent activity of EWS-FLI1 target genes. We were able to identify targets of EWS-FLI1 tumorigenesis directly inhibited by GSK-J4. GSK-J4 disruption of EWS-FLI1-driven transcription was toxic to Ewing sarcoma cells and slowed tumor growth in patient-derived xenografts (PDX) of Ewing sarcoma. Responses were markedly exacerbated by cotreatment with a disruptor of RNA polymerase II activity, the CDK7 inhibitor THZ1. This combination together suppressed EWS-FLI1 target genes and viability of ex vivo PDX Ewing sarcoma cells in a synergistic manner. In PDX models of Ewing Sarcoma, the combination shrank tumors. We present a new therapeutic strategy to treat Ewing sarcoma by decreasing H3K27ac at EWS-FLI1-driven transcripts, exacerbated by blocking phosphorylation of the C-terminal domain of RNA polymerase II to further hinder the EWS-FLI1-driven transcriptome.

Targeting Pan-ETS Factors Inhibits Melanoma Progression.

The failure of once promising target-specific therapeutic strategies often arises from redundancies in gene expression pathways. Even with new melanoma treatments, many patients are not responsive or develop resistance, leading to disease progression in terms of growth and metastasis. We previously discovered that the transcription factors ETS1 and PAX3 drive melanoma growth and metastasis by promoting the expression of the MET receptor. Here, we find that there are multiple ETS family members expressed in melanoma and that these factors have redundant functions. The small molecule YK-4-279, initially developed to target the ETS gene-containing translocation product EWS-FLI1, significantly inhibited cellular growth, invasion, and ETS factor function in melanoma cell lines and a clinically relevant transgenic mouse model, BrafCA;Tyr-CreERT2;Ptenf/f. One of the antitumor effects of YK-4-279 in melanoma is achieved via interference of multiple ETS family members with PAX3 and the expression of the PAX3-ETS downstream gene MET. Expression of exogenous MET provided partial rescue of the effects of YK-4-279, further supporting that MET loss is a significant contributor to the antitumor effects of the drug. This is the first study identifying multiple overlapping functions of the ETS family promoting melanoma. In addition, targeting all factors, rather than individual members, demonstrated impactful deleterious consequences in melanoma progression. Given that multiple ETS factors are known to have oncogenic functions in other malignancies, these findings have a high therapeutic impact. SIGNIFICANCE: These findings identify YK-4-279 as a promising therapeutic agent against melanoma by targeting multiple ETS family members and blocking their ability to act as transcription factors.

Development of an Ewing sarcoma cell line with resistance to EWS­FLI1 inhibitor YK­4­279.

Despite Ewing sarcoma (ES) being the second most common pediatric malignancy of bone and soft tissue, few novel therapeutic approaches have been introduced over the past few decades. ES contains a pathognomonic chromosomal translocation that leads to a fusion protein between EWSR1 and an ets family member, most often FLI1. EWS­FLI1 is the most common type of fusion protein and is a well­vetted therapeutic target. A small molecule inhibitor of EWS­FLI1, YK­4­279 (YK) was developed with the intention to serve as a targeted therapy option for patients with ES. The present study investigated resistance mechanisms by developing an ES cell line specifically resistant to YK. The ES cell line A4573 was treated with YK to create resistant cells by long term continuous exposure. The results revealed that resistance in A4573 was robust and sustainable, with a >27­fold increase in IC50 lasting up to 16 weeks in the absence of the compound. Resistant ES cells were still sensitive to standard of care drugs, including doxorubicin, vincristine and etoposide, which may be valuable in future combination treatments in the clinic. Resistant ES cells revealed an increased expression of CD99. RNA sequencing and qPCR validation of resistant ES cells confirmed an increased expression of ANO1, BRSK2 and IGSF21, and a reduced expression of COL24A1, PRSS23 and RAB38 genes. A functional association between these genes and mechanism of resistance remains to be investigated. The present study created a cell line to investigate YK resistance.

--A high-throughput screen identifies inhibitors of the interaction between the oncogenic transcription factor ERG and the cofactor EWS.

Aberrant expression of the transcription factor ERG is a key driving event in approximately one-half of all of prostate cancers. Lacking an enzymatic pocket and mainly disordered, the structure of ERG is difficult to exploit for therapeutic design. We recently identified EWS as a specific interacting partner of ERG that is required for oncogenic function. In this study, we aimed to target this specific protein-protein interaction with small molecules. A high-throughput screening (HTS) strategy was implemented to identify potential protein-protein interaction inhibitors. Secondary assays verified the function of several hit compounds, and one lead compound inhibited ERG-mediated phenotypes in prostate cells. This is the first study aimed at targeting the ERG-EWS protein-protein interaction for the development of a small molecule-based prostate cancer therapy.

Trabectedin Inhibits EWS-FLI1 and Evicts SWI/SNF from Chromatin in a Schedule-dependent Manner.

PURPOSE: The successful clinical translation of compounds that target specific oncogenic transcription factors will require an understanding of the mechanism of target suppression to optimize the dose and schedule of administration. We have previously shown trabectedin reverses the gene signature of the EWS-FLI1 transcription factor. In this report, we establish the mechanism of suppression and use it to justify the reevaluation of this drug in the clinic in patients with Ewing sarcoma.Experimental Design: We demonstrate a novel epigenetic mechanism of trabectedin using biochemical fractionation and chromatin immunoprecipitation sequencing. We link the effect to drug schedule and EWS-FLI1 downstream target expression using confocal microscopy, qPCR, Western blot analysis, and cell viability assays. Finally, we quantitate target suppression within the three-dimensional architecture of the tumor in vivo using 18F-FLT imaging. RESULTS: Trabectedin evicts the SWI/SNF chromatin-remodeling complex from chromatin and redistributes EWS-FLI1 in the nucleus leading to a marked increase in H3K27me3 and H3K9me3 at EWS-FLI1 target genes. These effects only occur at high concentrations of trabectedin leading to suppression of EWS-FLI1 target genes and a loss of cell viability. In vivo, low-dose irinotecan is required to improve the magnitude, penetrance, and duration of target suppression in the three-dimensional architecture of the tumor leading to differentiation of the Ewing sarcoma xenograft into benign mesenchymal tissue. CONCLUSIONS: These data provide the justification to evaluate trabectedin in the clinic on a short infusion schedule in combination with low-dose irinotecan with 18F-FLT PET imaging in patients with Ewing sarcoma.

Oncogenic serine-threonine kinase receptor-associated protein modulates the function of Ewing sarcoma protein through a novel mechanism.

Although much is known about the oncogenic functions of chimeric Ewing sarcoma (EWS) fusion proteins that result from chromosomal translocations, the cellular role of the normal EWS protein is not well characterized. We have previously identified a WD domain-containing protein, serine-threonine kinase receptor-associated protein (STRAP), which inhibits transforming growth factor beta (TGF-beta) signaling through interaction with receptors and Smad7 and promotes growth and enhances tumorigenicity. Here, we report the interaction between STRAP and EWS using matrix-assisted laser desorption/ionization, time-of-flight and tandem mass spectrometry. Although STRAP is localized in both cytoplasm and nucleus, nuclear STRAP colocalizes and associates specifically with EWS in the nucleus through its NH(2) and COOH termini. We have found that normal EWS protein is up-regulated in human cancers, which correlates with the up-regulation of STRAP in 71% of colorectal cancers and 54% of lung cancers, suggesting a cooperative role of these two proteins in human cancers. TGF-beta has no effect on STRAP and EWS interaction. However, EWS, like STRAP, attenuates TGF-beta-dependent transcription. STRAP inhibits EWS-dependent p300-mediated transactivation of EWS target genes, such as ApoCIII and c-fos, in a TGF-beta-independent manner. Interestingly, we have shown that STRAP blocks the interaction between EWS and p300, whereas the complex formation between STRAP and EWS is not affected by p300. These results suggest that STRAP inhibits the transactivation function of EWS by displacing p300 from the functional transcriptional complex. Thus, this study provides a novel TGF-beta-independent function of STRAP and describes a mechanism by which STRAP regulates the function of oncogenic EWS protein.

Combined analysis of gene expression and genome binding profiles identified potential therapeutic targets of ciclopirox in Ewing sarcoma.

Ciclopirox (CPX) is a synthetic antifungal drug that is mainly used to treat dermatomycoses. The aim of the present study was to determine whether CPX could influence Ewing sarcoma progression. The present study suggested that CPX treatment may inhibit Ewing sarcoma (ES) progression through Ewing sarcoma breakpoint region 1­Friend leukemia integration 1 (EWS­FLI1), a common fusion transcript structure in patients with ES. To determine the underlying mechanisms of ES progression, cross analysis was conducted on three high­throughput genome or transcript me datasets from the Gene Expression Omnibus. The results indicated that CPX may inhibit ES growth by affecting vasculature development and DNA replication. A combination of genome­wide expression and binding profiles revealed several potential targets for CPX in ES, including collagen type I α2 chain, N­myc proto­oncogene and transforming growth factor ß1, which contained significantly enriched binding peaks of FLI1. In addition, network analysis, including a protein­protein interaction network and a transcription regulatory network, provided further detailed information about the roles of CPX in ES. This study may provide a novel solution for ES treatment and may also aid in improving its prognosis.

Development of Mithramycin Analogues with Increased Selectivity toward ETS Transcription Factor Expressing Cancers.

Mithramycin A (1) was identified as the top potential inhibitor of the aberrant ETS transcription factor EWS-FLI1, which causes Ewing sarcoma. Unfortunately, 1 has a narrow therapeutic window, compelling us to seek less toxic and more selective analogues. Here, we used MTMSA (2) to generate analogues via peptide coupling and fragment-based drug development strategies. Cytotoxicity assays in ETS and non-ETS dependent cell lines identified two dipeptide analogues, 60 and 61, with 19.1- and 15.6-fold selectivity, respectively, compared to 1.5-fold for 1. Importantly, the cytotoxicity of 60 and 61 is <100 nM in ETS cells. Molecular assays demonstrated the inhibitory capacity of these analogues against EWS-FLI1 mediated transcription in Ewing sarcoma. Structural analysis shows that positioning the tryptophan residue in a distal position improves selectivity, presumably via interaction with the ETS transcription factor. Thus, these analogues may present new ways to target transcription factors for clinical use.

Combinatorial Drug Screening Identifies Ewing Sarcoma-specific Sensitivities.

Improvements in survival for Ewing sarcoma pediatric and adolescent patients have been modest over the past 20 years. Combinations of anticancer agents endure as an option to overcome resistance to single treatments caused by compensatory pathways. Moreover, combinations are thought to lessen any associated adverse side effects through reduced dosing, which is particularly important in childhood tumors. Using a parallel phenotypic combinatorial screening approach of cells derived from three pediatric tumor types, we identified Ewing sarcoma-specific interactions of a diverse set of targeted agents including approved drugs. We were able to retrieve highly synergistic drug combinations specific for Ewing sarcoma and identified signaling processes important for Ewing sarcoma cell proliferation determined by EWS-FLI1 We generated a molecular target profile of PKC412, a multikinase inhibitor with strong synergistic propensity in Ewing sarcoma, revealing its targets in critical Ewing sarcoma signaling routes. Using a multilevel experimental approach including quantitative phosphoproteomics, we analyzed the molecular rationale behind the disease-specific synergistic effect of simultaneous application of PKC412 and IGF1R inhibitors. The mechanism of the drug synergy between these inhibitors is different from the sum of the mechanisms of the single agents. The combination effectively inhibited pathway crosstalk and averted feedback loop repression, in EWS-FLI1-dependent manner. Mol Cancer Ther; 16(1); 88-101. ©2016 AACR.

Inhibition of the oncogenic fusion protein EWS-FLI1 causes G2-M cell cycle arrest and enhanced vincristine sensitivity in Ewing's sarcoma.

Ewing's sarcoma (ES) is a rare and highly malignant cancer that grows in the bones or surrounding tissues mostly affecting adolescents and young adults. A chimeric fusion between the RNA binding protein EWS and the ETS family transcription factor FLI1 (EWS-FLI1), which is generated from a chromosomal translocation, is implicated in driving most ES cases by modulation of transcription and alternative splicing. The small-molecule YK-4-279 inhibits EWS-FLI1 function and induces apoptosis in ES cells. We aimed to identify both the underlying mechanism of the drug and potential combination therapies that might enhance its antitumor activity. We tested 69 anticancer drugs in combination with YK-4-279 and found that vinca alkaloids exhibited synergy with YK-4-279 in five ES cell lines. The combination of YK-4-279 and vincristine reduced tumor burden and increased survival in mice bearing ES xenografts. We determined that independent drug-induced events converged to cause this synergistic therapeutic effect. YK-4-279 rapidly induced G2-M arrest, increased the abundance of cyclin B1, and decreased EWS-FLI1-mediated generation of microtubule-associated proteins, which rendered cells more susceptible to microtubule depolymerization by vincristine. YK-4-279 reduced the expression of the EWS-FLI1 target gene encoding the ubiquitin ligase UBE2C, which, in part, contributed to the increase in cyclin B1. YK-4-279 also increased the abundance of proapoptotic isoforms of MCL1 and BCL2, presumably through inhibition of alternative splicing by EWS-FLI1, thus promoting cell death in response to vincristine. Thus, a combination of vincristine and YK-4-279 might be therapeutically effective in ES patients.

Identification of Mithramycin Analogues with Improved Targeting of the EWS-FLI1 Transcription Factor.

PURPOSE: The goal of this study was to identify second-generation mithramycin analogues that better target the EWS-FLI1 transcription factor for Ewing sarcoma. We previously established mithramycin as an EWS-FLI1 inhibitor, but the compound's toxicity prevented its use at effective concentrations in patients. EXPERIMENTAL DESIGN: We screened a panel of mithralogs to establish their ability to inhibit EWS-FLI1 in Ewing sarcoma. We compared the IC50 with the MTD established in mice to determine the relationship between efficacy and toxicity. We confirmed the suppression of EWS-FLI1 at the promoter, mRNA, gene signature, and protein levels. We established an improved therapeutic window by using time-lapse microscopy to model the effects on cellular proliferation in Ewing sarcoma cells relative to HepG2 control cells. Finally, we established an improved therapeutic window using a xenograft model of Ewing sarcoma. RESULTS: EC-8105 was found to be the most potent analogue and was able to suppress EWS-FLI1 activity at concentrations nontoxic to other cell types. EC-8042 was substantially less toxic than mithramycin in multiple species but maintained suppression of EWS-FLI1 at similar concentrations. Both compounds markedly suppressed Ewing sarcoma xenograft growth and inhibited EWS-FLI1 in vivo CONCLUSIONS: These results provide a basis for the continued development of EC-8042 and EC-8105 as EWS-FLI1 inhibitors for the clinic. Clin Cancer Res; 22(16); 4105-18. ©2016 AACR.

Therapeutic opportunities in Ewing sarcoma: EWS-FLI inhibition via LSD1 targeting.

Ewing sarcoma is an aggressive primary pediatric bone tumor, often diagnosed in adolescents and young adults. A pathognomonic reciprocal chromosomal translocation results in a fusion gene coding for a protein which derives its N-terminus from a FUS/EWS/TAF15 (FET) protein family member, commonly EWS, and C-terminus containing the DNA-binding domain of an ETS transcription factor, commonly FLI1. Nearly 85% of cases express the EWS-FLI protein which functions as a transcription factor and drives oncogenesis. As the primary genomic lesion and a protein which is not expressed in normal cells, disrupting EWS-FLI function is an attractive therapeutic strategy for Ewing sarcoma. However, transcription factors are notoriously difficult targets for the development of small molecules. Improved understanding of the oncogenic mechanisms employed by EWS-FLI to hijack normal cellular programming has uncovered potential novel approaches to pharmacologically block EWS-FLI function. In this review we examine targeting the chromatin regulatory enzymes recruited to conspire in oncogenesis with a focus on the histone lysine specific demethylase 1 (LSD1). LSD1 inhibitors are being aggressively investigated in acute myeloid leukemia and the results of early clinical trials will help inform the future use of LSD1 inhibitors in sarcoma. High LSD1 expression is observed in Ewing sarcoma patient samples and mechanistic and preclinical data suggest LSD1 inhibition globally disrupts the function of EWS-ETS proteins.

Targeting the epigenetic readers in Ewing sarcoma inhibits the oncogenic transcription factor EWS/Fli1.

Ewing Sarcoma is a rare bone and soft tissue malignancy affecting children and young adults. Chromosomal translocations in this cancer produce fusion oncogenes as characteristic molecular signatures of the disease. The most common case is the translocation t (11; 22) (q24;q12) which yields the EWS-Fli1 chimeric transcription factor. Finding a way to directly target EWS-Fli1 remains a central therapeutic approach to eradicate this aggressive cancer. Here we demonstrate that treating Ewing Sarcoma cells with JQ1(+), a BET bromodomain inhibitor, represses directly EWS-Fli1 transcription as well as its transcriptional program. Moreover, the Chromatin Immuno Precipitation experiments demonstrate for the first time that these results are a consequence of the depletion of BRD4, one of the BET bromodomains protein from the EWS-Fli1 promoter. In vitro, JQ1(+) treatment reduces the cell viability, impairs the cell clonogenic and the migratory abilities, and induces a G1-phase blockage as well as a time- and a dose-dependent apoptosis. Furthermore, in our in vivo model, we observed a tumor burden delay, an inhibition of the global vascularization and an increase of the mice overall survival. Taken together, our data indicate that inhibiting the BET bromodomains interferes with EWS-FLi1 transcription and could be a promising strategy in the Ewing tumors context.