HMME combined with green light-emitting diode irradiation results in efficient apoptosis on human tongue squamous cell carcinoma.

Hematoporphyrin monomethyl ether (HMME) is a novel and promising porphyrin-related photosensitizer for photodynamic therapy (PDT). This study aimed to investigate the efficacy and potential mechanism of HMME-PDT under irradiation of green light-emitting diode (LED) with wavelength of 530 ± 20 nm in treating human tongue squamous cell carcinoma Tca8113 cells in vitro. The HMME concentrations were 1.25, 2.5, and 5 μg/ml while the energy densities were 0.6, 1.2, 1.8, 2.4, and 3.0 J/cm(2). MTT assay demonstrated that HMME-PDT significantly inhibited the proliferation of Tca8113 cells, and the cytotoxicity was improved with increased HMME concentration and light intensity. The amount of cells decreased significantly and the morphology of cells changed drastically after HMME-PDT. Flow cytometry analysis revealed that HMME-PDT induced both apoptosis and necrosis, but apoptosis was the main form of cell death. Apoptotic morphology was confirmed by Hoechst 33342 staining. Laser scanning confocal microscopy observation showed that HMME was mainly localized in mitochondria. The production of intracellular reactive oxygen species increased remarkably after PDT treatment, and both sodium azide (the singlet oxygen quencher) and D-mannitol (the hydroxyl radical scavenger) could protect Tca8113 cells from death induced by HMME-PDT. Additionally, the activity of caspase-3 also increased markedly in treated groups, and the cell death could be rescued by a reversible inhibitor (Ac-DEVD-CHO) of caspase-3. These results demonstrated that HMME combined with green LED significantly induced apoptosis of Tca8113 cells, suggesting that HMME-PDT using green LED might be a potential therapeutic strategy for human tongue squamous cell carcinoma.