CHEK1 and non-small cell lung carcinoma: CHK1 knockdown also substantially improved gemcitabine efficacy in four naturally gemcitabine-resistant NSCLC cell lines (H125, H650, H1648, H2122 [19]) with a shift of the dose-response curve to the left in addition to an increase in the maximally achievable cytotoxicity (IC50 ratios of 0.02 to 0.76; Figure 3; Table 1).