Cytotoxicity of TPT was increased in the presence of CHEK1 inhibitor. A. IC50 values of CHEK1 inhibitor (PF477736) were determined by XTT assay done in 3 days upon treatment in 3 replicates. (*) indicates the concentrations used in Figure 3C. B. Western blot analysis of total CHEK1 was done using total protein lysates. GAPDH was used as a loading control. The band intensity was quantified by ImageJ and CHEK1 level was normalized by GAPDH. The CHEK1 levels in different cell lines were calculated relative to that of Ovcar5. IC50 values and relative CHEK1 levels were plotted to examine their relationships by Microsoft Excel. C-E. XTT assays were done in the absence and presence of CHEK1 inhibitor in 3 replicates and Fa (fraction affected), fraction of dead cells, was calculated from XTT assay. TPT IC50 values were calculated by CompuSyn software.