Polyphyllin I Promotes Autophagic Cell Death and Apoptosis of Colon Cancer Cells via the ROS-Inhibited AKT/mTOR Pathway

Colon cancer is a common malignant tumor of the digestive tract, and it is considered among the biggest killers. Scientific and reasonable treatments can effectively improve the survival rate of patients if performed in the early stages. Polyphyllin I (PPI), a pennogenyl saponin isolated from Paris polyphylla var. yunnanensis, has exhibited strong anti-cancer activities in previous studies. Here, we report that PPI exhibits a cytotoxic effect on colon cancer cells. PPI suppressed cell viability and induced autophagic cell death in SW480 cells after 12 and 24 h, with the IC50 values 4.9 ± 0.1 μmol/L and 3.5 ± 0.2 μmol/L, respectively. Furthermore, we found PPI induced time-concentration-dependent autophagy and apoptosis in SW480 cells. In addition, down-regulated AKT/mTOR activity was found in PPI-treated SW480 cells. Increased levels of ROS might link to autophagy and apoptosis because reducing the level of ROS by antioxidant N-acetylcysteine (NAC) treatment mitigated PPI-induced autophagy and apoptosis. Although we did not know the molecular mechanism of how PPI induced ROS production, this is the first study to show that PPI induces ROS production and down-regulates the AKT/mTOR pathway, which subsequently promotes the autophagic cell death and apoptosis of colon cancer cells. This present study reports PPI as a potential therapeutic agent for colon cancer and reveals its underlying mechanisms of action.