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

alpha-Tocopherol at low concentrations protects biosubstrates from oxidativ e damage, while at high concentrations it may become toxic. Certain lines o f tumor cells are reported to contain higher levels of vitamin E than norma l cells. In our study alpha-tocopherol was successfully incorporated by cul tured HT29 adenocarcinoma cells, but not by MRC-5 normal fibroblasts. At hi gh concentrations (0.3-1 mM) alpha-tocopherol enhanced meta-tetra(hydroxyph enyl)chlorin (mTHPC)-sensitized photoinactivation of HT29 cells (415 nm), b ut not that of normal fibroblasts. At none of the concentrations used (0.00 1-1 mM) did alpha-tocopherol protect cells from photokilling, indicating th at lipid peroxidation is of minor importance in mTHPC photoactivity. Our fi ndings encourage the in vivo testing of phenolic antioxidants for selective enhancement of PDT-damage in tumors. (C) 1999 Elsevier Science Ireland Ltd . All rights reserved.