Meta-tetra(hydroxyphenyl)chlorin-sensitized photodynamic damage of cultured tumor and normal cells in the presence of high concentrations of α-tocopherol

α-Tocopherol at low concentrations protects biosubstrates from oxidative damage, while at high concentrations it may become toxic. Certain lines of tumor cells are reported to contain higher levels of vitamin E than normal cells. In our study α-tocopherol was successfully incorporated by cultured HT29 adenocarcinoma cells, but not by MRC-5 normal fibroblasts. At high concentrations (0.3–1 mM) α-tocopherol enhanced meta-tetra(hydroxyphenyl)chlorin (mTHPC)-sensitized photoinactivation of HT29 cells (415 nm), but not that of normal fibroblasts. At none of the concentrations used (0.001–1 mM) did α-tocopherol protect cells from photokilling, indicating that lipid peroxidation is of minor importance in mTHPC photoactivity. Our findings encourage the in vivo testing of phenolic antioxidants for selective enhancement of PDT-damage in tumors.