Photosensitising Activity of Phthalocyanine Dyes Screened Against Tissue Culture Cells

A series of phthalocyanine (Pc) dyes were screened for their ability to photosensitise murine embryonic fibroblasts or fibrosarcoma cells. Cells were cultured in the presence of the dyes for 24 h. following which they were irradiated with either room light or red light and cultured for a further 72‐h period. Eleven water‐insoluble Pc (including a free‐base Pc) and 6 water‐soluble sulfonated derivatives were screened in this fashion. Free base (H 2 ), copper (Cu), copper di‐. tri‐, tetra‐sulfonated (CuS 2 , CuS 3 . CuS 4 ), fiuoro chromium (FCr), iron (Fe), cobalt (Co), palladium tetra‐sulfonated (PdS 4 ). nickel (Ni) and nickel tetra‐sulfonated (NiS 4 )Pc dyes had no cytotoxic activity in these assays under conditions of either room‐light or red‐light exposure. Magnesium (Mg), zinc (Zn) and zirconium (Zr) Pc dyes were highly toxic to cells, producing 0% survival at 72 h, following exposure to both light sources. In contrast, chloro aluminum (C1AI). chloro aluminum sulfonated (C1A1S) and dichloro tin (Cl 2 Sn) Pc dyes exhibited differential phototoxicity, producing total cell death following red‐light irradiation but no or little cytotoxic effect after exposure to room light, raising the possibility that these dyes might prove useful for photo‐dynamic therapy of cancer.