Introduction:Oncogenic activation of the K-ras gene occurs in>90%of pancreatic ductal carcinoma and plays a critical role in the pathogenesis of this malignancy. Increase of reactive oxygen species (ROS) has also been observed in a wide spectrum of cancers. This study aimed to investigate the mechanistic association between K-ras–induced transformation and increased ROS stress and its therapeutic implications in pancreatic cancer. Methods:ROS level, NADPH oxidase (NOX) activity and expression, and cel invasion were examined in human pancreatic duct epithelial E6E7 cel s transfected with K-rasG12V compared with parental E6E7 cel s. The cytotoxic effect and antitumor effect of capsaicin, a NOX inhibitor, were also tested in vitro and in vivo. Results:K-ras transfection caused activation of the membrane-associated redox enzyme NOX and elevated ROS generation through the phosphatidylinositol 3′-kinase (PI3K) pathway. Importantly, capsaicin preferential y inhibited the enzyme activity of NOX and induced severe ROS accumulation in K-ras–transformed cel s compared with parental E6E7 cel s. Furthermore, capsaicin effectively inhibited cel proliferation, prevented invasiveness of K-ras–transformed pancreatic cancer cel s, and caused minimum toxicity to parental E6E7 cel s. In vivo, capsaicin exhibited antitumor activity against pancreatic cancer and showed oxidative damage to the xenograft tumor cel s. Conclusions:K-ras oncogenic signaling causes increased ROS stress through NOX, and abnormal ROS stress can selectively kil tumor cel s by using NOX inhibitors. Our study provides a basis for developing a novel therapeutic strategy to effectively kil K-ras–transformed cel s through a redox-mediated mechanism.