Non-thermal gas plasma-induced endoplasmic reticulum stress mediates apoptosis in human colon cancer cells

Colorectal cancer is a common type of tumor among both men and women worldwide. Conventional remedies such as chemotherapies pose the risk of side-effects, and in many cases cancer cells develop chemoresistance to these treatments. Non-thermal gas plasma (NTGP) was recently identified as a potential tool for cancer treatment. In this study, we investigated the potential use of NTGP to control SNUC5 human colon carcinoma cells. We hypothesized that NTGP would generate reactive oxygen species (ROS) in these cells, resulting in induction of endoplasmic reticulum (ER) stress. ROS generation, expression of ER stress-related proteins and mitochondrial calcium levels were analyzed. Our results confirmed that plasma-generated ROS induce apoptosis in SNUC5 cells. Furthermore, we found that plasma exposure resulted in mitochondrial calcium accumulation and expression of unfolded protein response (UPR) proteins such as glucose-related protein 78 (GRP78), protein kinase R (PKR)-like ER kinase (PERK), and inositol-requiring enzyme 1 (IRE1). Elevated expression of spliced X-box binding protein 1 (XBP1) and CCAAT/enhancer-binding protein homologous protein (CHOP) further confirmed that ROS generated by NTGP induces apoptosis through the ER stress signaling pathway.