Enhanced inhibitory effect of curcumin via reactive oxygen species generation in human nasopharyngeal carcinoma cells following purple-light irradiation

Curcumin, a traditional medicine, exhibits anti-carcinogenic properties in various cell lines and animals. As a phenolic compound, curcumin is light-sensitive and photoactived curcumin exhibits a greater anticancer effect compared with curcumin alone. However, the mechanisms by which curcumin inhibits tumor cell growth in human nasopharyngeal carcinoma (NPC) cells following purple light (PL) irradiation remains unclear. In the present study, CNE1 and CNE2 cells were treated with curcumin and exposed to PL at various energy densities to determine the anticancer activity of curcumin using MTT assays, staining and flow cytometry. The subsequent changes in the cell viability, morphology, cell cycle, apoptosis and reactive oxygen species (ROS) generation were measured. Curcumin inhibited cell growth in a dose-dependent manner. CNE1 and CNE2 cells tended to be arrested at the S or G2/M cell cycle stages following curcumin treatment and the levels of ROS increased in a time-dependent manner. However, after treatment with curcumin followed by PL irradiation, the levels of cytotoxicity and apoptotic cell death were significantly increased compared with the curcumin-only group. ROS generation was also enhanced in an energy-dependent manner. In summary, following PL irradiation, the anti-cancer effect of curcumin in human NPC cells was increased through apoptosis and cell cycle arrest.