title: Bio-distribution and subcellular localization of Hypericin and its role in PDT induced apoptosis in cancer cells.
abstract: The development of new-generation photosensitizers to improve photodynamic therapy (PDT) and photodynamic diagnosis (PDD) is an area of extensive research. One such compound that has been studied in our group is Hypericin (HY). To study the mechanism of action we have investigated uptake, intracellular localization, cell phototoxicity and morphological changes especially to ultrastructures following photodynamic treatment in poorly (CNE2) and moderately (TW0-1) differentiated human nasopharyngeal carcinoma (NPC) cells and also other tumor cells such as colon (CCL-220.1) and bladder (SD) cells in vitro. Following irradiation, phototoxicity was determined by crystal fast violet assay and apoptosis was assessed using annexin-V assay. Using spectrofluorimetry and confocal laser scanning microscopy (CLSM) we have determined cellular fluorescence localization and uptake of HY. Co-labeling with HY and fluorescent dyes specific for cell organelles revealed an intracellular localization of HY predominantly in mitochondria and lysosomes. Since many photosensitizing agents in current clinical use have mitochondrial targets, HY may be a valuable addition to current protocols. In addition, our results also indicate that leakage of lysosomal protease into cytosolic compartment might be involved in the induction of apoptosis. Electron microscopy revealed damage to plasma membrane with high drug dose (>5 microM); indicating a mechanism related to necrosis, whereas sub-lethal lower doses (<2.5 microM) resulted in induction of apoptosis indicated by typical ultrastructural signs of apoptosis. Our results based on mitochondrial and lysosomal localization support the idea that PDT can contribute to elimination of malignant cells by the induction of apoptosis, and can be of physiological significance.
authors.affiliation: Department of Medical Sciences, National Cancer Centre, 11 Hospital Drive, Singapore 169610.
authors.forename: Seyed Mohamed
authors.initials: SM
authors.lastname: Ali
authors.forename: Malini
authors.initials: M
authors.lastname: Olivo
mesh_terms: D000873:Anthracenes; D000970:Antineoplastic Agents / Q000493:pharmacokinetics* / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D003574:Cytochrome c Group / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D008247:Lysosomes / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008854:Microscopy, Electron; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D009303:Nasopharyngeal Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D009369:Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D010569:Perylene / Q000031:analogs & derivatives* / Q000493:pharmacokinetics* / Q000494:pharmacology; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000493:pharmacokinetics* / Q000494:pharmacology; D013347:Subcellular Fractions / Q000378:metabolism; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D001749:Urinary Bladder Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology
chemical_list: D000873:Anthracenes; D000970:Antineoplastic Agents; D003574:Cytochrome c Group; D017319:Photosensitizing Agents; D016159:Tumor Suppressor Protein p53; D010569:Perylene; C004965:hypericin