Phototoxic action of a lipophilic Zn(II) phthalocyanine in tumor spheroids and a murine colon carcinoma in vivo model.

NICOLÁS A. CHIARANTE; GARCÍA VIOR M. CECILIA; ELSA ZOTTA; JULIETA MARINO; LEONOR P. ROGUIN

Buenos Aires

Congreso; Reunión Conjunta de Sociedades Biomédicas.; 2017

Sociedades biomédicas (SAIC)

Phthalocyanines have been found to be optimal photosensitizers for photodynamic therapy. In a previous work, we demonstrated the cytotoxic action of a lipophilic Zn(II) phthalocyanine (Pc9) encapsulated into poloxamine polymeric micelles (T1107) in two-dimensional cultures of CT26 cells (murine colon carcinoma, IC50 = 10 ± 2 nM). After localizing mainly in lysosomes and endoplasmic reticulum, Pc9-T1107 formulation induced an apoptotic cell death mediated by the generation of reactive oxygen species. In this study, in order to explore the in vivo efficacy of Pc9-T1017, we tested two experimental models: three-dimensional CT26 cell cultures and a syngeneic model of Balb/c mice bearing CT26 tumors. When different concentrations of Pc9-T1107 were incubated with CT26 spheroids, no effect on cell survival was evident in the dark, while a significant decrease was shown after irradiation, being the IC50 value of 370 ± 11 nM. Thus, after incubating spheroids for different time periods, the volume of Pc9-treated spheroids was smaller than non-treated spheroids. Furthermore, spheroid growth kinetics was dependent on Pc9 concentration. An apoptotic mechanism of cell death was also confirmed in Pc9-exposed spheroids by the observation of highly condensed nuclei stained with Höechst 33258 and by detecting a significant decrease in procaspase-3 expression levels. In vivo assays revealed that the administration of 0,074 mg/kg of Pc9-T1107 reduced 46% tumor volume, without affecting body weight of treated- mice. Histological analyses of control and treated tumor slices showed an 11% and 51% of necrotic areas, respectively, after hematoxylin?eosin staining. Furthermore, an increase in the expression levels of Bax and a decrease in Bcl-2/Bcl-XL/Bid levels were determined after WB of tumor lysates. In conclusion, our results indicated that Pc9 behaves as an efficient photosensitizer inducing an apoptotic cell death both in 3D cultures as well as in a colon carcinoma in vivo model.