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| Author(s): |
Juliana Camilo Corrêa
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT) |
| Defense date: | 2006-10-03 |
| Examining board members: |
Janice Rodrigues Perussi;
Ester Maria Danielli Nicola;
Ana Celia Ruggiero
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| Advisor: | Janice Rodrigues Perussi |
| Abstract | |
Photodynamic Therapy (PDT) consists in a technique for cancer treatment. The treatment is based on intravenous administration of the photosensitizer (PS), which is selectively retained in tumor tissue, and when is activated with visible light it can be able to become cytotoxic, being responsible for tumor death. In this study the PS used was Photodithazine (PDZ), a derivative water-soluble of mono-L-aspartil chlorine produced in Russia. It was investigated the PDZ degradation by light (photobleaching) in several conditions and the cytotoxicity of non-irradiated and previously irradiated PDZ in the absence (dark) and presence of light in culture of normal (VERO) and tumor cells (HEp-2). These results were compared with results obtained for Photogem® (photosensitizer approved for use in PDT in Brazil, a hematoporphyrin derivative). PDZ photobleaching was induced with laser in two wavelengths (488 and 514nm) and with LED in 630nm. The degradation was monitored by the decreasing in the absorption and fluorescence intensities. It was observed the appearance of a new absorption band in 668nm (band of photoproducts) suggesting chemistry transformation. Analyses performed with the CCA method (Convex Constrain Analysis) demonstrated that two distinct species are present after the degradation of PDZ, one of then probably being the photoproducts. The photobleaching of PDZ is faster in 630nm than in 514 and 488nm. In the used concentration range of PDZ there is no predominance of aggregated species in physiologic pH, it absorbs in wavelengths higher than Photogem® and degradates in shorter time than Photogem®. However the aggregation of PDZ depends on pH. Only in low pH PDZ presented aggregated species. Studies with surfactants showed that the degradation and formation of photoproducts of PDZ is different than in PBS. Experiments with azide (the singlet oxygen scavenger) suggest that the photobleaching of PDZ occurs by the type II mechanism (singlet oxygen formation). In the cytotoxic studies of PDZ it was observed that the incubation time of the photosensitizer with cells and the presence of serum affect its cytotoxicity in non-tumor and tumor cells in absence and presence of light. When PDZ is previously irradiated occurs a decreasing in cytotoxicity in the dark in function of the irradiation time in both lines. However, the increase of IC50 is approximately 58% for HEp-2 and 25% for VERO. In the presence of light, the cytotoxicity of non-irradiated PDZ increases as a function of incubation and irradiation time. The cytotoxicity of PDZ is greater when in the presence of light in VERO and HEp-2. The increase of irradiation time of the PDZ solution enhances the cytotoxicity of photosensitizer in both cell lines. It is possible to conclude that the photoproducts of PDZ after irradiation are more cytotoxic in the dark (2,2 times) than non-irradiated PDZ and are more cytotoxic (18 folds) in non-tumor cells and 10 folds more cytotoxicity in tumor cell line in the presence of light. PDZ presents an important advantage compared to Photogem®, it is less cytotoxic in the absence of light and more citotóxicas in the presence of light than Photogem® for both cell lines. These results suggest a greater potential for clinical application for this chlorine photosensitizer. (AU) | |