Lysosomal and mitochondrial permeabilization mediates zinc(II)cationic phthalocyanine phototoxicity

JULIETA MARINO; MARÍA C. GARCÍA VIOR; VERÓNICA A. FURMENTO; VIVIANA C. BLANK; JOSEFINA AWRUCH; LEONOR P. ROGUIN

INTERNATIONAL JOURNAL OF BIOCHEMISTRY AND CELLULAR BIOLOGY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2013 vol. 45 p. 2553 - 2562

1357-2725

In order to find a novel photosensitizer to be used in photodynamic therapy for cancer treatment, wehave previously showed that the cationic zinc(II) phthalocyanine named Pc13, the sulfur-linked dye2,9(10),16(17),23(24)-tetrakis[(2-trimethylammonium) ethylsulfanyl]phthalocyaninatozinc(II) tetraio-dide, exerts a selective phototoxic effect on human nasopharynx KB carcinoma cells and induces anapoptotic response characterized by an increase in the activity of caspase-3. Since the activation of anapoptotic pathway by chemotherapeutic agents contributes to the elimination of malignant cells, in thisstudy we investigated the molecular mechanisms underlying the antitumor action of Pc13. We found thatafter light exposure, Pc13 induced the production of reactive oxygen species (ROS), which are mediatingthe resultant cytotoxic action on KB cells. ROS led to an early permeabilization of lysosomal membranes asdemonstrated by the reduction of lysosome fluorescence with acridine orange and the release of lysoso-mal proteases to cytosol. Treatment with antioxidants inhibited ROS generation, preserved the integrityof lysosomal membrane and increased cell proliferation in a concentration-dependent manner. Lysosomedisruption was followed by mitochondrial depolarization, cytosolic release of cytochrome C and caspasesactivation. Although no change in the total amount of Bax was observed, the translocation of Bax fromcytosol to mitochondria, the cleavage of the pro-apoptotic protein Bid, together with the decrease ofthe anti-apoptotic proteins Bcl-XLand Bcl-2 indicated the involvement of Bcl-2 family proteins in theinduction of the mitochondrial pathway. It was also demonstrated that cathepsin D, but not caspase-8,contributed to Bid cleavage. In conclusion, Pc13-induced cell photodamage is triggered by ROS genera-tion and activation of the mitochondrial apoptotic pathway through the release of lysosomal proteases.In addition, our results also indicated that Pc13 induced a caspase-dependent apoptotic response, beingactivation of caspase-8, -9 and -3 the result of a post-mitochondrial event.