Inhibitory Effect of Gallotannin on Lung Metastasis of Metastatic Colorectal Cancer Cells by Inducing Apoptosis, Cell Cycle Arrest and Autophagy

Colorectal cancer (CRC) is the second most common cause of cancer death in the world, and metastatic CRC is a major cause of cancer death. Gallotannin (GT), a polyphenolic compound, has shown various biological effects such as anti-oxidant, anti-inflammatory, antimicrobial, and antitumor effects. However, the effects of GT on metastatic CRC cells are not completely understood. This study aimed to investigate the anti-metastatic effect of GT and the underlying mechanisms on metastatic CRC cells. Oral administration of GT suppressed the lung metastasis of metastatic CRC cells in the experimental mouse model. GT decreased the viability of metastatic CRC cell lines, including CT26, HCT116, and SW620, by inducing apoptosis through the activation of extrinsic and intrinsic pathways, cell cycle arrest through inactivation of CDK2/cyclin A complex, and autophagic cell death through up-regulation of LC3B and p62 levels. GT regulated PI3K/AKT/mTOR and AMPK signaling pathways, which are critical for the development and maintenance of cancer. Additionally, non-cytotoxic concentrations of GT can suppress migration and invasion of CRC cells by inhibiting the expression and activity of matrix metalloproteinase (MMP)-2 and MMP-9 and epithelial-mesenchymal transition by downregulating the expression of mesenchymal markers including snail, twist, and vimentin. In conclusion, GT prevented colorectal lung metastasis by reducing survival and inhibiting the metastatic phenotypes of CRC cells.