Liposome-bound Zn (II)-phthalocyanine. Mechanisms for cellular uptake and photosensitization

In the present study, cellular uptake of a liposomal formulation of ZnPc (CGP 55847) has been studied in human cervix carcinoma cells of the line NHIK 3025. The cellular uptake of ZnPc is found to be completed after 4-8 h of incubation. The maximum level of ZnPc in the cells after incubation with 1 microgram/ml ZnPc in E2a medium containing 3% serum is 60 ng/mg protein. The cellular uptake is attenuated by the presence of serum and at low temperature of the incubation medium, but the activation energy (30 kJ/mol) and fluorescence microscopic analysis of cells incubated with ZnPc at 0 degree C indicate that ZnPc is taken up into cells by a diffusion-mediated pathway. Measurements of subcellular marker enzymes have been performed immediately after light exposure of ZnPc-treated cells. The mitochondrial marker enzyme (cytochrome c oxidase) and the marker enzyme for the Golgi apparatus (UDP galactosyl transferase), but not those for lysosomes (beta-N-acetyl-D-glucosaminidase) and endoplasmic reticulum (NADPH cytochrome c reductase), are inactivated upon photodynamic treatment. These results indicate that ZnPc is mainly located in the Golgi apparatus and the mitochondria of NHIK 3025 cells. In contrast, photoactivated Photofrin is found to reduce the activity of UDP galactosyl transferase, but not that of NADPH cytochrome c reductase. The tetraphenylporphine TPPS2a and light reduce the activity of NADPH cytochrome c reductase, without influencing the activity of UDP galactosyl transferase. TPPS4 and light do not attenuate the activities of UDP galactosyl transferase and NADPH cytochrome c reductase.