Intracellular fluorescence behaviour of meso-tetra(4-sulphonatophenyl)porphyrin during photodynamic treatment at various growth phases of cultured cells.

Meso-tetra(4-sulphonatophenyl)porphyrin (TPPS4) taken up by cells is mainly localized in lysosomes as previously shown by fluorescence microscopical and fluorescence spectroscopical investigations. In the present study the intracellular fluorescence behaviour and the intracellular amount of this dye at various growth periods of cells were examined. For cells irradiated in the growth phase a relocalization of TPPS4 from the lysosomes into the cytoplasm and finally into the nucleus was observed. In contrast, for cells irradiated in the stationary phase no redistribution could be detected and therefore no evidence for severe damage of the lysosomal membranes and subsequently for the release of lytical enzymes is given. In both cases lethal damage of the cells was achieved as examined using the trypan blue exclusion test. This indicates that damage of the lysosomes is less important in the photodynamic inactivation of cells sensitized by TPPS4.