Photofrin®-PDT induces covalent modification of procaspase-6 and -7: involvement of reactive oxygen species

• Main Authors: Jia-Chi Kan, 闞嘉琪
• Other Authors: Jau-Song Yu
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/06759966393201414172

碩士 === 長庚大學 === 基礎醫學研究所 === 93 === Photodynamic therapy (PDT) is a therapeutic protocol to treat solid malignancies and nonmalignant diseases. PDT works through photochemical reactions of a tumor-localized photosensitive drug and generation of reactive oxygen species (ROS), in particular singlet oxygen, to kill cells and ablate tumors by leading several cellular response including apoptosis and necrosis. Photofrin® is the first generation photosensitizer for PDT. Previous studies from our laboratory indicated that PDT with Photofrin® targeting to distinct subcellular site results in different death phenotypes of human epidermoid carcinoma A431 cells (Hsieh et al., 2003). Apoptosis is essential for cell development and tissue homeostasis in multicellular organisms. Caspases, a family of cysteine proteases, play a central role in apoptosis. Here, we report that Photofrin®-PDT can induce formation of high-molecular weight (HMW) products of caspase-6 and caspase-7 in various human cell lines. The formation of HMW products of caspase-6 and caspase-7 are Photofrin® dose- and laser dose-dependent. Photofrin®-PDT could also elicit the formation of HMW products of ectopically expressed caspase-6 or caspase-7 in cells. The Photofrin®-PDT-induced formation of HMW products did not require de novo synthesis and this modification could also be observed in an in vitro assay, where recombinant caspase-6 and caspase-7 could also form HMW products after PDT. These findings indicate that Photofrin®-PDT-induced formation of HMW products of caspase-6 and caspase-7 is mediated by a covalent cross-linking mechanism. Because ROS play a major role in PDT, several scavengers for ROS were used to investigate whether formation of the HMW products of caspase-6 and caspase-7 is mediated by ROS in Photofrin®-PDT. Results showed that Photofrin®-PDT-induced formation of HMW products could be significantly blocked by singlet oxygen scavenger L-histidine in vitro and in vivo.