EWS/ETS-Driven Ewing Sarcoma Requires BET Bromodomain Proteins.

The EWS/ETS fusion transcription factors drive Ewing sarcoma (EWS) by orchestrating an oncogenic transcription program. Therapeutic targeting of EWS/ETS has been unsuccessful; however, identifying mediators of the EWS/ETS function could offer new therapeutic options. Here, we describe the dependency of EWS/ETS-driven transcription upon chromatin reader BET bromdomain proteins and investigate the potential of BET inhibitors in treating EWS. EWS/FLI1 and EWS/ERG were found in a transcriptional complex with BRD4, and knockdown of BRD2/3/4 significantly impaired the oncogenic phenotype of EWS cells. RNA-seq analysis following BRD4 knockdown or inhibition with JQ1 revealed an attenuated EWS/ETS transcriptional signature. In contrast to previous reports, JQ1 reduced proliferation and induced apoptosis through MYC-independent mechanisms without affecting EWS/ETS protein levels; this was confirmed by depleting BET proteins using PROTAC-BET degrader (BETd). Polycomb repressive complex 2 (PRC2)-associated factor PHF19 was downregulated by JQ1/BETd or BRD4 knockdown in multiple EWS lines. EWS/FLI1 bound a distal regulatory element of PHF19, and EWS/FLI1 knockdown resulted in downregulation of PHF19 expression. Deletion of PHF19 via CRISPR-Cas9 resulted in a decreased tumorigenic phenotype, a transcriptional signature that overlapped with JQ1 treatment, and increased sensitivity to JQ1. PHF19 expression was also associated with worse prognosis in patients with EWS. In vivo, JQ1 demonstrated antitumor efficacy in multiple mouse xenograft models of EWS. Together these results indicate that EWS/ETS requires BET epigenetic reader proteins for its transcriptional program and can be mitigated by BET inhibitors. This study provides a clear rationale for the clinical utility of BET inhibitors in treating EWS.Significance: These findings reveal the dependency of EWS/ETS transcription factors on BET epigenetic reader proteins and demonstrate the potential of BET inhibitors for the treatment of EWS. Cancer Res; 78(16); 4760-73. ©2018 AACR.

Gollavilli PN ，Pawar A ，Wilder-Romans K ，Natesan R ，Engelke CG ，Dommeti VL ，Krishnamurthy PM ，Nallasivam A ，Apel IJ ，Xu T ，Qin ZS ，Feng FY ，Asangani IA ... -  《-》

Targeting the EWS-ETS transcriptional program by BET bromodomain inhibition in Ewing sarcoma.

Hensel T ，Giorgi C ，Schmidt O ，Calzada-Wack J ，Neff F ，Buch T ，Niggli FK ，Schäfer BW ，Burdach S ，Richter GH ... -  《Oncotarget》

BET bromodomain inhibitors suppress EWS-FLI1-dependent transcription and the IGF1 autocrine mechanism in Ewing sarcoma.

Loganathan SN ，Tang N ，Fleming JT ，Ma Y ，Guo Y ，Borinstein SC ，Chiang C ，Wang J ... -  《Oncotarget》

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

Jacques C ，Lamoureux F ，Baud'huin M ，Rodriguez Calleja L ，Quillard T ，Amiaud J ，Tirode F ，Rédini F ，Bradner JE ，Heymann D ，Ory B ... -  《Oncotarget》

Reversible LSD1 inhibition interferes with global EWS/ETS transcriptional activity and impedes Ewing sarcoma tumor growth.

Ewing sarcoma is a pediatric bone tumor that absolutely relies on the transcriptional activity of the EWS/ETS family of fusion oncoproteins. While the most common fusion, EWS/FLI, utilizes lysine-specific demethylase 1 (LSD1) to repress critical tumor suppressors, small-molecule blockade of LSD1 has not yet been thoroughly explored as a therapeutic approach for Ewing sarcoma. We therefore evaluated the translational potential of potent and specific LSD1 inhibition with HCI2509 on the transcriptional program of both EWS/FLI and EWS/ERG as well as the downstream oncogenic phenotypes driven by EWS/ETS fusions in both in vitro and in vivo models of Ewing sarcoma. RNA-seq was used to compare the transcriptional profiles of EWS/FLI, EWS/ERG, and treatment with HCI2509 in both EWS/FLI- and EWS/ERG-containing cell lines. We then evaluated morphologic phenotypes of treated cells with immunofluorescence. The induction of apoptosis was evaluated using caspase-3/7 activation and TUNEL staining. Colony forming assays were used to test oncogenic transformation and xenograft studies with patient-derived cell lines were used to evaluate the effects of HCI2509 on tumorigenesis. HCI2509 caused a dramatic reversal of both the up- and downregulated transcriptional profiles of EWS/FLI and EWS/ERG accompanied by the induction of apoptosis and disruption of morphologic and oncogenic phenotypes modulated by EWS/FLI. Importantly, HCI2509 displayed single-agent efficacy in multiple xenograft models. These data support epigenetic modulation with HCI2509 as a therapeutic strategy for Ewing sarcoma, and highlight a critical dual role for LSD1 in the oncogenic transcriptional activity of EWS/ETS proteins.

Sankar S ，Theisen ER ，Bearss J ，Mulvihill T ，Hoffman LM ，Sorna V ，Beckerle MC ，Sharma S ，Lessnick SL ... -  《-》