Double knockdown of NQO1 and p53 by siRNA altered KKU-100 cells to chemotherapeutic agents. (A) Effect of co-transfected NQO1 and p53 siRNA in KKU-100 cells. Cells were transfected with the pooled siRNA against NQO1 and p53 for 24 hr. The bars represent relative expression of NQO1 and p53 normalized with β-actin as internal control. (B-D) After co-transfection, cells were treated with varied concentrations of chemotherapeutic agents; 5-FU, Doxo, and Gem for another 24 hr as described in the “Methods” section. The cytotoxicity was evaluated by SRB assay. Data represent mean ± SEM, each from three separated experiments. *p < 0.05 vs the non-targeting knocked down cells and #p < 0.05 vs NQO1 knocked down cells.