Photokilling mechanisms induced by zinc(II)-phthalocyanine on cultured tumor cells

The photosensitizing effects of liposomal zinc(II)-phthalocyanine (ZnPc) on HeLa cells, with emphasis on morphological changes and mechanisms for cell death, have been studied. No dark toxicity for ZnPc alone was found. Incub ation for 1 h with ZnPc followed by red light irradiation induced a variabl e decrease in the surviving of cells, which was related to both drug concen tration and irradiation time. A lethal photodynamic effect (100% of the cel ls are killed: LD100) was induced by 5 x 10(-6) M ZnPc and 5-min irradiatio n, whereas a sublethal effect (60% of the cells are killed: LD60) was detec ted with 10(-7) M ZnPc and 3 min of red light. Toluidine blue and Hoechst 3 3258 staining showed characteristic alterations ol cell morphology. Numerou s bubbles on the plasma membrane were found immediately after an LD100 trea tment, and a necrotic morphology appeared 24 h later. On the contrary, seve re cell shrinkage with nuclear fragmentation, characteristic of apoptosis, was observed 8 and 24 h after LD60 treatments. In this case, propidium iodi de-acridine orange labeling and the TUNEL assay confirmed the occurrence of apoptosis. The highest amount of apoptotic cells appeared 24 h-after LD60 treatments, particularly in detached cells, as revealed by cell counting an d DNA electrophoresis. Both apoptotic and necrotic mechanisms for cell deat h occur in HeLa cells in dependence on the experimental protocol of ZnPc ph otodynamic treatments.