CHEK1 and Ewing sarcoma: To determine the concentration of LY2603618 required to inhibit CHK1 function we treated Ewing sarcoma cells with gemcitabine in combination with different concentrations of LY2603618 and then assessed CHK1 activation using immunoblotting for CHK1-Ser296, which is an auto-phosphorylation site in the CHK1 protein [71].