Enhanced cytotoxicity and apoptosis through inhibiting autophagy in metastatic potential colon cancer SW620 cells treated with Chlorin e6 photodynamic therapy.

Photodynamic therapy (PDT) is a novel and non-invasive treatment that induces apoptosis and autophagy. Autophagy could play a pro-survival role, thus inhibiting autophagic activity might be a promising method to enhance the effectiveness of PDT for tumors. In the present study, photosensitizer Chlorin e6 (Ce6) was found to mainly locate in endoplasmic reticulum, and to a lesser extent in mitochondria and lysosome. Chlorin e6 photodynamic therapy (Ce6-PDT) could kill human colon cancer SW620 cells by inducing apoptotic cell death, and autophagy also induced by Ce6-PDT in colon cancer cells. More importantly, autophagy played a pro-survival role. Its inhibition enhanced Ce6-PDT-associated apoptotic cell death because cells pretreated with the typical autophagy inhibitor 3-methyladenine exhibited higher cytotoxicity and apoptotic cell death.