title: Differential cytotoxic responses to low- and high-dose photodynamic therapy in human gastric and bladder cancer cells.
abstract: Here, we present differential cytotoxic responses to two different doses of photodynamic therapies (PDTs; low-dose PDT [LDP] and high-dose PDT [HDP]) using a chlorin-based photosensitizer, DH-II-24, in human gastric and bladder cancer cells. Fluorescence-activated cell sorting analysis using Annexin V and propidium iodide (PI) showed that LDP induced apoptotic cell death, whereas HDP predominantly caused necrotic cell death. The differential cytotoxic responses to the two PDTs were further confirmed by a DiOC(6) and PI double-staining assay via confocal microscopy. LDP, but not HDP, activated caspase-3, which was inhibited by Z-VAD, Trolox, and BAPTA-AM. LDP and HDP demonstrated opposite effects on intracellular reactive oxygen species (ROS)/Ca(2+) signals; LDP stimulated intracellular ROS production, contributing to a transient increase of intracellular Ca(2+) , whereas HDP induced a massive and prolonged elevation of intracellular Ca(2+) responsible for the transient production of intracellular ROS. In addition, the two PDTs also increased in situ transglutaminase 2 (TG2) activity, with a higher stimulation by HDP, and this increase in activity was prevented by Trolox, BAPTA-AM, and TG2-siRNA. LDP-induced apoptotic cell death was strongly inhibited by Trolox and TG2-siRNA and moderately suppressed by BAPTA-AM. However, HDP-mediated necrotic cell death was partially inhibited by BAPTA-AM but not by TG2-siRNA. Thus, these results demonstrate that LDP and HDP induced apoptotic and necrotic cell death by differential signaling mechanisms involving intracellular Ca(2+) , ROS, and TG2.
authors.affiliation: Department of Molecular and Cellular Biochemistry, School of Medicine, Kangwon National University, Chuncheon, Kangwon-do 200-701, Korea.
authors.forename: Je-Ok
authors.initials: JO
authors.lastname: Yoo
authors.forename: Young-Cheol
authors.initials: YC
authors.lastname: Lim
authors.forename: Young-Myeong
authors.initials: YM
authors.lastname: Kim
authors.forename: Kwon-Soo
authors.initials: KS
authors.lastname: Ha
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009336:Necrosis / Q000139:chemically induced; D010778:Photochemotherapy / Q000379:methods*; D011166:Porphyrins / Q000494:pharmacology; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013274:Stomach Neoplasms / Q000378:metabolism*; D011503:Transglutaminases / Q000235:genetics / Q000378:metabolism; D001749:Urinary Bladder Neoplasms / Q000378:metabolism*
chemical_list: C547071:DH-II-24 compound; D011166:Porphyrins; D017382:Reactive Oxygen Species; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D053148:Caspase 3; D019204:GTP-Binding Proteins; D002118:Calcium