Role of reactive oxygen species (ROS) in CDDO-Me-mediated growth inhibition and apoptosis in colorectal cancer cells
Xiaohua Gao, Dorrah Deeb, Patricia Liu, Yongbo Liu, Syed Arbab-Ali, Scott A. Dulchavsky and Subhash C. Gautam
CDDO-Me, an oleanane synthetic triterpenoid has shown strong antitumorigeic activity towards diverse cancer cell types including colorectal cancer cells. In the present study, we investigated the role of free radicals in the growth inhibitory and apoptosis-inducing activity of CDDO-Me in colorectal cancer cells lines. Results demonstrated that CDDO-Me potently inhibited the growth of colorectal cancer cells and pretreatment of cancer cells with small-molecule antioxidant N-acetylcysteine (NAC) completely blocked the growth inhibitory activity of CDDO-Me. CDDO-Me caused the generation of reactive oxygen species, which was inhibited by NAC and mitochondrial chain 1 complex inhibitors DPI and rotenone. CDDO-Me induced apoptosis as demonstrated by the cleavage of PARP-1, activation of procaspases -3, -8, and -9 and mitochondrial depolarization and NAC blocked the activation of these apoptosis related processes. Furthermore, induction of apoptosis by CDDOMe was associated with the inhibition of antiapoptotic/prosurvival Akt, mTOR and NF-κB signaling proteins and the inhibition of these signaling molecules was blocked by NAC. Together these studies provided evidence that CDDO-Me is a potent anticancer agent, which imparts growth inhibition and apoptosis in colorectal cancer cells through the generation of free radicals.
Keywords: CDDO-Me, colorectal cancer, ROS, apoptosis, signaling proteins