title: Photodynamic therapy induced Fas-mediated apoptosis in human carcinoma cells.
abstract: Photodynamic therapy (PDT) is a clinical approach that utilizes light-activated drugs for the treatment of a variety of pathologic conditions. Human poorly (CNE2) and moderately differentiated (TW0-1) human nasopharyngeal carcinoma (NPC) cells undergo rapid apoptosis when treated with PDT sensitized with Hypocrellin A (HA) and Hypocrellin B (HB). It has been shown that these compounds have a strong photodynamic effect on tumors and viruses. The initiating events of PDT sensitized HA and HB-induced apoptosis are poorly defined. In the current study, we sought to determine whether Fas/FasL upregulation and involvement of mitochondrial events are an early event in HA and HB-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. Photoactivation of HA and HB 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 activation and appeared to be a primary event in PDT induced apoptosis. Furthermore, these results indicate that release of mitochondrial cytochrome c into the cytoplasm is a secondary event following the activation of initiator caspase-8 preceding caspase-3 activation, cleavage of PARP and DNA fragmentation. Cytochrome c appeared in the cytosol within 2-3 h post PDT. Cleavage of PARP was observed at 3-4 h following PDT and caspase-3 specific inhibitor DEVD-CHO and broad-spectrum caspases inhibitor z-VAD-fmk blocked caspase-3 activation and PARP cleavage suggesting that caspase-3 plays an important role in HA and HB-induced apoptosis.
authors.affiliation: Department of Medical Sciences, National Cancer Centre, Singapore.
authors.forename: Seyed Mohamed
authors.initials: SM
authors.lastname: Ali
authors.forename: Soo Khee
authors.initials: SK
authors.lastname: Chee
authors.forename: Gan Yik
authors.initials: GY
authors.lastname: Yuen
authors.forename: Malini
authors.initials: M
authors.lastname: Olivo
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D002277:Carcinoma / Q000378:metabolism / Q000473:pathology* / Q000628:therapy*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D053222:Fas Ligand Protein; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009303:Nasopharyngeal Neoplasms / Q000378:metabolism / Q000473:pathology* / Q000628:therapy*; D010569:Perylene / Q000008:administration & dosage* / Q000031:analogs & derivatives*; D019800:Phenol; D010778:Photochemotherapy; D017319:Photosensitizing Agents / Q000008:administration & dosage*; D011809:Quinones / Q000008:administration & dosage*; D014407:Tumor Cells, Cultured; D019014:fas Receptor / Q000378:metabolism*
chemical_list: D003574:Cytochrome c Group; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D008562:Membrane Glycoproteins; D017319:Photosensitizing Agents; D011809:Quinones; D019014:fas Receptor; D019800:Phenol; D010569:Perylene; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; C048388:hypocrellin A