Tetrandrine Induces Apoptosis of Human Nasopharyngeal Carcinoma NPC-TW 076 Cells through Reactive Oxygen Species Accompanied by an Endoplasmic Reticulum Stress Signaling Pathway

Nasopharyngeal carcinoma (NPC) is an epithelial malignancy of the head and neck and the incidence is higher in Southeast Asia. Tetrandrine (TET) is a bisbenzylisoquinoline alkaloid, a natural product, and exhibits biological activities including action against many human cancer cell lines. However, the molecular mechanism of TET-induced cell apoptosis in human NPC cells is still unclear. In the present study, we investigated TET-induced apoptotic cell death and associated possible signal pathways on human nasopharyngeal carcinoma NPC-TW 076 cells in vitro. Phase contrast microscopy was used to examine cell morphology and DAPI staining was used to examine chromatin condensation. Flow cytometry assay was used to measure total viable cells, cell cycle and sub-G1 phase distribution, reactive oxygen species (ROS), Ca2+, and mitochondria membrane potential (Delta Psi m) in NPC-TW 076 cells. Results indicate that TET induced cell death through the cell morphological changes, caused G(0)/G(1) phase arrest, increased ROS and Ca2+ production, and finally caused apoptotic cell death in NPC-TW 076 cells. There was no influence on the level of Delta Psi m after TET treatment. Western blotting indicated that TET increased endoplasmic reticulum (ER) stress associated protein expression such as GADD153, GRP78, ATF-6 alpha and ATF-6 beta which indicated that TET induced cell death through ER stress. ER stress is a potential target in cancer treatment, so the ability of TET to induce ER stress response and to activate programming cell death in NPC-TW 076 cells make this molecule become a promising anticancer agent.