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      Hypericin induced death receptor-mediated apoptosis in photoactivated tumor cells.

      International Journal of Molecular Medicine

      Tumor Cells, Cultured, Antigens, CD95, biosynthesis, Antineoplastic Agents, pharmacology, Arabidopsis Proteins, Blotting, Western, Caspase 8, Caspase 9, Caspases, metabolism, Cell Differentiation, Cells, Cultured, Cytochrome c Group, Cytosol, DNA Fragmentation, Enzyme Activation, Enzyme Inhibitors, Fas Ligand Protein, Fatty Acid Desaturases, Flow Cytometry, Humans, Membrane Glycoproteins, Membrane Potentials, Mitochondria, Perylene, analogs & derivatives, Photochemotherapy, Time Factors

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          Nasopharyngeal carcinoma (NPC) is a malignant disease of the head/neck region with a 5-year survival level of approximately 65%. To explore the novel therapeutic strategies in the management of this disease, the potential effects of photodynamic therapy (PDT) in NPC cells were investigated. PDT, a new mode of treatment, is based on the combined use of light-absorbing compounds and light irradiation. Two human NPC cells such as, poorly differentiated (NPC/CNE2) and moderately differentiated (NPC/TW0-1) and other types of tumor cells like colon (CCL-220.1) and bladder (SD) undergo rapid apoptosis when treated with PDT sensitized with hypericin (HY). It has been shown that this compound has a strong photodynamic effect on tumors and viruses. However, the initiating events of PDT sensitized HY-induced apoptosis are not identified completely. In this study, we sought to determine whether Fas/FasL upregulation and involvement of mitochondrial events are an early event in HY-treated PDT induced apoptosis. Loss of mitochondrial transmembrane potential, release of cytochrome c, involvement of caspases 8 and 3 and the status caspase-3 specific substrate PARP, were evaluated in PDT treated tumor cells. Photosensitization of HY enhanced both CD95/CD95L expression and induced CD95-signaling dependent cell death in all tumor cell lines studied. CD95/CD95L expression appeared within 2 h following light irradiation and appeared to be a principal event in PDT induced apoptosis. Furthermore, these results indicate that release of mitochondrial cytochrome c into the cytoplasm within 2-3 h post PDT is a secondary event following the activation of initiator caspase-8 preceding Apaf-1, caspase-9 and caspase-3 activation, cleavage of PARP and DNA fragmentation.

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