CHEK1 and Ewing sarcoma: In a dose-response assay, Ewing sarcoma were sensitive to treatment with LY2603618, a potent inhibitor of CHK1, for 6 hours (Figure 4A) and 72 hours (Supplementary Figure 6) with IC50 values of ~2 μM and ~500 nM, respectively [62, 68–70].