Effects of NQO1 over-expression on the susceptibility of KKU-M214 cells to chemotherapeutic agents (5-FU, Doxo, and Gem). A-B, Effect of NQO1 over-expression on mRNA and protein levels of NQO1 in KKU-M214 cells. The pCMV6-XL5-NQO1 (wild type NQO1) or pCMV6-XL5 (control vector) was transfected to KKU-M214 for 24 hr. The whole cells were collected for NQO1 enzyme activity assay (A) and Western blot analysis (B). The data represent mean ± SEM, each from three experiments. *p < 0.05 vs the control vector transfected cells. (C-E) Cytotoxicity of chemotherapeutic agents on NQO1 over-expressed KKU-M214 cells. Twenty-four hour after transfection, cells were incubated with chemotherapeutic agents for additional 24 hr (Doxo) and 48 hr (5-FU and Gem). The cytotoxicity was evaluated by SRB assay. Data represent mean ± SEM, each from three separated experiments. *p < 0.05 vs the control vector transfected cells.