Blue light suppresses tumor growth and induces apoptosis

OBJECTIVE: Our lab has shown that specific doses of blue light (400-500 nm) induce apoptosis of tumor cells in culture. We hypothesized that blue light treatment of tumors in vivo induces apoptosis and suppresses cell proliferation. METHODS: Cultured A431 human epidermoid carcinoma cells were injected subcutaneously into the abdomens of female nu/nu athymic mice (n=10) and xenograft growth was monitored daily. At day 12, mice were divided into control and light-treated groups. Tumors from the light-treated animals were exposed daily to 50 J/cm² doses (90 s) of blue light delivered from a QTH dental light curing unit (VIP, Bisco, 600 mW/cm² output). Tumor volumes were assessed at days 1, 3, 5, 8, and 12 post-light treatment, then all tumors were harvested. Each tumor was divided into equal parts that were flash frozen or formalin fixed. Formalin fixed tissues were embedded in paraffin and sectioned for morphometric analysis of apoptosis via TUNEL staining. Protein lysates prepared from flash frozen tissues were used in Western blot procedures to assess cell proliferation and generalized protein oxidation. RESULTS: We found that tumor volumes were decreased by an average of 64% (p=0.05) in the light-treated group. TUNEL staining revealed a 10% increase (p=0.12) in average percent apoptosis in light-treated tumors vs. untreated controls. Western blot quantification of proliferating cell nuclear antigen (PCNA) and OxyBlot (ChemIcon, Inc.) analysis of protein oxidation showed decreases of 78% (p=0.01) and 71.5% (p=0.07), respectively, in the blue light-treated tumors vs. untreated controls. CONCLUSIONS: These data support our hypothesis that blue light treatment of tumors in vivo suppresses cell proliferation and may enhance apoptosis.