The photodynamic therapy energy dose fractionation used in rat colon tumors evaluation effects

Abstract

The aim of this study is to evaluate the effects of photodynamic therapy (PDT) in colon neoplasias (adenoma and carcinoma) induced by 1,2-dimethylhydrazine (DMH - Aldrich Chemical Co., Milwaukee, USA) in rats using chloroaluminum phthalocyanine as photosensitizer incorporated into liposome and compare the methods of continuous and fractionated energy irradiation in PDT. Forty Wistar rats will receive for tumor induction weekly subcutaneous injections of 1,2-dimetilhidrazina (DMH - Aldrich Chemical Co., Milwaukee, the USA) in the dose of 65 mg/Kg during 5 weeks. Fifteen weeks later the animals will receive an intravenous (i.v.) dose of chloroaluminum phthalocyanine incorporated into liposome (5µM in 0,2ml of liposome vehicle). After 24 h the animals will be randomly divided in 2 groups (G1 and G2), anesthetized and submitted to PDT with energy irradiation fractionated (G1) or continuous (G2), using as excitement source of the photosensitizer a InGaAl (685 nm) laser through an optical fiber guided by a rigid optics (Hopkins CE7218B, Karl Storz) to the tumors. The total dose of energy (25 J/cm2) will be delivered in two fractions (5 and 20 J/cm2) separated for an interval of 150sec in the animals of group G1, while in the animals of the group G2 the energy delivered will be continuous. Each group will be randomly subdivided in 4 sub-groups (A, B, C and D) that will be sacrificed after 3 h, 24 h, 7 days and 21 days after the PDT and tissue samples will be collected for histological and imunnohistochemistry analysis and for determination of thiobarbituric acid reactant substances (TBARS) to evaluate injured tissue area, type of cell death and oxidative stress degree caused by PDT, correlating this results with the energy deliverance system: fractionated or continuous. (AU)