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8 April 2005 Phototocytotoxicity of Photogem submitted to photobleaching
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Photodynamic therapy (PDT) is a technique for inducing tissue damage with light irradiation of a drug selectively retained in malignant tissue in presence of oxygen. The same mechanisms responsible for PDT efficacy can destroy the sensitizer, a process called photobleaching. In this work, the photobleaching of Photogem (a hematoporphyrin derivative used in Brazil made in Russia) was induced to study phototoxicity of the photoproducts upon a tumor (HEp-2) and non-tumor (VERO) cell line. Photogem was previously irradiated at 514nm and 630 nm (50mW/cm2) for 120 min. The sensitizer photobleaching was monitored by fluorescence and absorption properties changes and photoproducts formation evidenced by the appearance of a new absorption band around 640nm. Irradiated and non-irradiated Photogem were incubated for 18h with the cells. After drug removal, cells were irradiated with LED at 630 nm with intensities of 13, 20 and 25mW/cm2 for different times. Then, the cells were incubated for 48 hours to determine the cells viability by the MTT method. The cells in the dark were used as control. The IC50 decreases as light intensity increases, being more pronounced for tumor cells. Previously irradiated Photogem needs one-hour irradiation for both cell lines to have the same IC50 value of non-irradiated Photogem, which are irradiated for 14 min in tumor cells and 25 min in non-tumor cells. The results suggest that the photoproducts of Photogem are less cytotoxic either in the dark or in the light, decreasing with increase of intensity. These results underline the importance of dosimetry in PDT.
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Priscila F.C. Menezes, Vanderlei Salvador Bagnato, Claudio H. Sibata, Hidetake Imasato, and Janice R. Perussi "Phototocytotoxicity of Photogem submitted to photobleaching", Proc. SPIE 5689, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XIV, (8 April 2005);

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