Targeted Therapy for EWS-FLI1 in Ewing Sarcoma

SIMPLE SUMMARY: Ewing sarcoma (EwS) is a highly aggressive and metastatic cancer in children and adolescents. Canonical therapy mainly comprises the combination of intensive chemotherapy, radiation, and local surgery, which give rise to acute and chronic adverse effects. Drugs targeting EwS without side effects are in urgent demand. Genetically, EwS is characterized by chromosomal translocations with a low mutation burden. As a result, the chimeric protein EWS-ETS, mainly EWS-FLI1(85%), is critical for the malignancy of EwS. EWS-FLI1 directly binds to GGAA microsatellites in enhancers and promotors of the target genes and recruits multiple transcription factors or epigenetic regulators to reprogramme the epigenome. Direct targeting EWS-FLI1 is difficult due to the disordered structure, we mainly review the current knowledge of EWS-FLI1 property, the EWS-FLI1 protein complex, and the downstream pathways, we also summarize the targeted therapy of EwS by taking advantage of the EWS-FLI1 protein complex and the immunotherapy of the genes activated by EWS-FLI1. ABSTRACT: Ewing sarcoma (EwS) is a rare and predominantly pediatric malignancy of bone and soft tissue in children and adolescents. Although international collaborations have greatly improved the prognosis of most EwS, the occurrence of macrometastases or relapse remains challenging. The prototypic oncogene EWS-FLI1 acts as an aberrant transcription factor that drives the cellular transformation of EwS. In addition to its involvement in RNA splicing and the DNA damage response, this chimeric protein directly binds to GGAA repeats, thereby modifying the transcriptional profile of EwS. Direct pharmacological targeting of EWS-FLI1 is difficult because of its intrinsically disordered structure. However, targeting the EWS-FLI1 protein complex or downstream pathways provides additional therapeutic options. This review describes the EWS-FLI1 protein partners and downstream pathways, as well as the related target therapies for the treatment of EwS.