Combination treatment with photodynamic therapy and curcumin induces mitochondria-dependent apoptosis in AMC-HN3 cells

Photodynamic therapy (PDT) is a treatment for the selective destruction of cancerous and non-neoplastic cells that involves the simultaneous presence of light, oxygen and a light-activatable chemical known as a photosensitizer. Curcumin is one of the most extensively investigated phytochemicals with chemopreventive potential and antitumor effects. In this study, the effect of a combination of PDT and curcumin on apoptotic cell death in AMC-HN3 cells and the molecular mechanism underlying apoptosis was examined to confirm the interaction between photofrin-induced PDT and curcumin during combined mortality. The combination treatment with curcumin and PDT inhibited approximately 70% of the cell viability after PDT, whereas the PDT and curcumin only groups showed a 50 and 10% decrease in cell viability, respectively. In addition, the combination treatment increased the apoptotic events, such as nuclear fragmentation and nuclear condensation. This combination group showed an increase in ROS generation that was higher than that observed after each single treatment. Compared to the single agent treatments, the combination therapy induced the enhanced loss of Delta psi(m). Furthermore, the cytosolic levels of cytochrome c were significantly elevated in the combination group. Caspases-9, -3 and PARP, which are apoptosis-related proteins induced by mitochondrial activation, were upregulated remarkably by the combination treatment. When co-treated with glutathione, a singlet oxygen quencher, the combination treatment-induced synergistic cytotoxic and apoptotic effects, enhanced the generation of ROS and suppressed the upregulation of caspase-3 and PARP. These results suggest that the combination modality with PDT and curcumin have a better treatment effect in vitro. The induction of mitochondrial-dependent apoptosis due to the increased generation of ROS may be involved in this combination treatment.