Phototoxic action of a lypophilic Zn(II) phthalocyanine in colon carcinoma cells

CHIARANTE N.A; MARINO V.J.; GARCIA VIOR M.C.; SOSNIK A; AWRUCH J; ROGUIN, L.P.

Córdoba

Congreso; 16th International Congress on Photobiology; 2014

Facultad de Ciencias Químicas, Universidad Nacional de córdoba

Phthalocyanines (Pcs) have been found to be useful photosensitizers for photodynamic therapy (PDT) [1-2]. The tendency of Pcs to form aggregates has encouraged the use of nanocarriers that improve their solubility [3]. The aim of this work was to study the photodynamic performance of 2,9(10),16(17),23(24)-tetrakis[(2?dimethylamino)ethylsulfanyl] phthalocyaninatozinc(II) (Pc9) encapsulated into a poloxamine polymeric micelle (T1107) in a murine colon carcinoma cell line (CT26). Pc9-T1107 was found to be cytotoxic after irradiation at 2.8 J.cm-2, being the concentration that inhibited 50% of cell growth (IC50 value) of 11 ± 1 nM. It was also demonstrated that after light exposure of Pc9-loaded cells, the production of reactive oxygen species (ROS) increased in a concentration-dependent manner. In addition, a lower cytotoxic effect was obtained when cells were pretreated with the antioxidant TROLOX. By confocal microscopy, a mainly lysosomal localization of Pc9-T1107 was observed. Furthermore, after cell irradiation, the reduction of the fluorescence emission of a lysosomal probe was evident, suggesting the permeabilization of the lysosomal membrane. In accordance with this result, we also showed a significant increase in the cytosolic amount of the lysosomal enzyme cathepsin D in a time-dependent manner after PDT. The inhibitory activity induced by Pc9-T1107 in cell growth was partially reverted in the presence of pepstatin A, a cathepsin D inhibitor. In conclusion, our results showed that Pc9 is a potent cytotoxic agent for PDT, being cell death probably mediated by the generation of ROS and the release of lysosomal proteases.