Defensive mechanism in cholangiocarcinoma cells against oxidative stress induced by chlorin e6-based photodynamic therapy

Abstract

Hye Myeong Lee,1,* Chung-Wook Chung,2,* Cy Hyun Kim,1,3 Do Hyung Kim,1,3 Tae Won Kwak,1 Young-Il Jeong,1 Dae Hwan Kang1,3 1National Research and Development Center for Hepatobiliary Cancer, Research Institute for Convergence of Biomedical Science and Technology, Yangsan, Republic of Korea; 2Department of Biological Sciences, Andong National University, Andong, Republic of Korea; 3School of Medicine, Pusan National University, Yangsan, Republic of Korea *Both authors contributed equally to this work Abstract: In this study, the effect of chlorin e6-based photodynamic therapy (Ce6-PDT) was investigated in human intrahepatic (HuCC-T1) and extrahepatic (SNU1196) cholangiocarcinoma (CCA) cells. The amount of intracellular Ce6 increased with increasing Ce6 concentration administered, or with incubation time, in both cell lines. The ability to take up Ce6 and generate reactive oxygen species after irradiation at 1.0 J/cm2 did not significantly differ between the two CCA cell types. However, after irradiation, marked differences were observed for photodamage and apoptotic/necrotic signals. HuCC-T1 cells are more sensitive to Ce6-PDT than SNU1196 cells. Total glutathione (GSH) levels, glutathione peroxidase and glutathione reductase activities in SNU1196 cells were significantly higher than in HuCC-T1 cells. With inhibition of enzyme activity or addition of GSH, the phototoxic effect could be controlled in CCA cells. The intracellular level of GSH is the most important determining factor in the curative action of Ce6-PDT against tumor cells. Keywords: cholangiocarcinoma, chlorin e6, photodynamic therapy, reactive oxygen species, glutathione, heme oxygenase-1