The effect of porphyrins on normal and transformed mouse cell lines in thepresence of visible light

Photodynamic therapy consists of the uptake of a photosensitizing dye, ofte n a porphyrin, by tumor tissue and subsequent irradiation of the tumor with visible light of an appropriate wavelength matched to the absorption spect rum of the photosensitizing dye. This class of molecules produces reactive oxygen species when activated by light, resulting in a direct or indirect c ytotoxic effect on the target cells. Photodynamic therapy has been used in the treatment of cancer but the technology has a potential for the treatmen t of several disease conditions mainly because of its selectivity. However, it is not clear why the porphyrins are retained preferentially by abnormal tissue. This paper describes a study of the effect of the association of p orphyrin and visible light on two mouse fibroblast cell lines: A31, normal cells and B61, an EJ-ras transformed variant of A31. Two water-soluble porp hyrins were used, a positively charged one, tetra(N-methyl-4-pyridyl)porphy rin chloride, and a negatively charged one, tetra(4-sulfonatophenyl)porphyr in-Na salt (TPPS4) in order to assess the effect on cell survival. The resu lts suggest that the B61 cell line is more sensitive to incubation with the anionic porphyrin (TPPS4) followed by light irradiation and that the anion ic porphyrin is more efficient in killing the cells than the cationic porph yrin.