Retention and phototoxicity of tetra(4-sulfonatophenyl)porphine in cultivated human cells. The effect of fractionation of light.

Human cervix carcinoma cells of the line NHIK 3025 were incubated for 18 h with tetra(4-sulfonatophenyl)porphine (TPPS4) and further incubated for 1-29 h in sensitizer free medium before exposure to light. After 1 h in sensitizer free medium only a 20% further loss of TPPS4 was observed within the next 28 h. During the time in sensitizer free medium, each TPPS4 molecule became more efficient in sensitizing single cells to photoinactivation. This enhanced photosensitizing efficiency of TPPS4 correlated well with the enhanced fluorescence yield of TPPS4. In some experiments the cells were exposed to a light dose inactivating 10% of the cells after incubation for 1 h in sensitizer free medium and a second graded light dose given 4-28 h later. Exposure of the cells to the first light dose led to loss of 60% of TPPS4 from the cells. Despite the significant loss of sensitizer from the cells the fluorescence yield of TPPS4 from each cell was found to increase (e.g. by 100% 4 h after light exposure). The enhanced fluorescence yield of cell bound TPPS4 was followed by a 1.6-2.5-fold increase in sensitivity of each cell to second light dose. Thus, a small light dose increased the photosensitivity of TPPS4-loaded NHIK 3025 cells for several hours after the first light exposure. The advantageous effect of light fractionation was reduced by a significantly enhanced loss of sensitizer induced by the first light exposure. The optimal time between the two fractions of light seems to be 30-90 min.