CONICET | Buscador de Institutos y Recursos Humanos

Abstract We have previously showed that the cationic zinc(II) phthalocyanine named Pc 13, the sulphur-linked dye 2,9(10),16(17),23(24)-tetrakis[(2-trimethylammonium) ethylsulfanyl]phthalocyaninatozinc(II) tetraioidide, exerts a selective phototoxic effect on human nasopharynx KB carcinoma cells and induces an apoptotic response characterized by an increase in the activity of caspase-3. In this study, we investigated the molecular mechanisms underlying the antitumor action of Pc 13. We found that after light exposure, Pc 13 induced the production of reactive oxygen species (ROS), which are mediating the resultant cytotoxic action on KB cells. ROS led to an early permeabilization of lysosomal membranes as demonstrated by the reduction of lysosome fluorescence with acridine orange and the release of lysosomal protease cathepsin D to cytosol. Treatment with antioxidants inhibited ROS generation and preserved the integrity of lysosomal membrane diminishing the expression levels of cytosolic cathepsin D and increasing cell proliferation in a concentration-dependent manner. Lysosome disruption was followed by mitochondrial depolarization, cytosolic release of cytochrome C and caspases activation. Although no change in the total amount of Bax was observed, the translocation of Bax from cytosol to mitochondria, the cleavage of the pro-apoptotic protein Bid, together with the decrease of the anti-apoptotic proteins Bcl-XL and Bcl-2 indicated the involvement of Bcl-2 family proteins in the induction of the mitochondrial pathway. It was also demonstrated that cathepsin D, but not caspase-8, contributed to Bid cleavage. In conclusion, Pc 13 induced-cell photodamage is triggered by ROS generation and activation of the mitochondrial apoptotic pathway through the release of lysosomal proteases. In addition, our results also indicated that Pc 13 induced a caspase-dependent apoptotic response, being activation of caspase-8, -9 and -3 the result of a post-mitochondrial event.