EWSR1 and Ewing sarcoma: The structurally similar YK-4-279 (Table 1) was shown to bind to EWS-FL1, with a Kd value of 9 μM, and inhibit the interaction of EWS-FL1 and RNA helicase A. The YK-4-279 exhibited cytotoxicity against the Ewing sarcoma family of tumors cells (ESFT cells), with an IC50 value of 0.5–2 μM, and was inactive toward cells lacking EWS-FL1.