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Photodynamic Therapy (PDT) using a sensitizing drug is recognized as a promising medical technique for cancer
treatment. It is a two step process that requires the administration of a photosensitizer followed by light exposure to treat
a disease. Following light exposure the photosensitizer is excited to a higher energy state which generates free radicals
and singlet oxygen. The present study was carried out to assess the oxidative damage induced by bis (3, 5-diiodo-2, 4, 6-
trihydroxyphenyl) squaraine in skin tumor tissues of mice with/ without light treatment. Skin tumor was induced using 7,
12-Dimethyl Benz(a)anthracene and croton oil. The tumor bearing mice were given an intraperitoneal injection with the
squaraine dye. After 24h, the tumor area of a few animals injected with the dye, were exposed to visible light from a
1000 W halogen lamp and others kept away from light. All the mice were sacrificed one week after the PDT treatment
and the oxidative profile was analyzed (TBARS, SOD, catalase, GSH, GPx and GR) in tumor/ skin tissues. The dye
induces oxidative stress in the tumor site only on illumination and the oxidative status of the tumor tissue was found to
be unaltered in the absence of light. The results of the study clearly shows that the tumor destruction mediated by PDT
using bis (3, 5-diiodo-2, 4, 6-trihydroxyphenyl) squaraine as a photosensitizer is due to the generation of reactive oxygen
species, produced by the light induced changes in the dye.
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