Motano et al. demonstrated, using a variety of non-Ewing sarcoma cell lines, that addition of a CHK1 inhibitor (MK-8776) from 18-24 hours after a 6-hour incubation with gemcitabine induced significantly greater toxicity and γH2AX than if the two drugs were incubated concurrently for 6 hours [75]. This evidence concerns the gene CHEK1 and Ewing sarcoma.