5-氨基酮戊酸光動力治療誘導人類口腔癌細胞凋亡機轉之研究

Abstract

光動力治療（photodynamic therapy，PDT）是新興的癌症治療方式，5-氨基酮戊酸（5-aminolevulinic acid，ALA）為新研發的第二代光感藥物（photosensitizer）。先前我們對口腔癌病變所進行的臨床試驗結果，證實ALA的光動力治療（ 5-aminilevulinic acid-based photodynamic therapy ，ALA-PDT），可用於口腔癌病變的治療，但是其作用機轉至今尚未明瞭。本研究以人類口腔癌細胞株Ca9-22探討ALA-PDT對口腔癌細胞的影響，並進一步了解其可能的機制。我們發現，以ALA-PDT來處理Ca9-22細胞，可以造成cytochrome C的釋放及PARP的水解等，證實ALA-PDT引起人類口腔癌細胞死亡的方式為細胞凋亡。藉由流式細胞儀分析結果顯示，以4J的ALA-PDT處理Ca9-22細胞，並不能改變細胞週期。將細胞加入單重態氧的抑制劑Imidazole後，再給予ALA-PDT，對於細胞凋亡產生明顯的抑制現象，說明了在口腔癌細胞株Ca9-22中，ALA-PDT是經由產生單重態氧而造成細胞凋亡的。在Ca9-22細胞的培養液中加入caspase-8和caspase-9的抑制劑（Z-LEHD-FMK；Z-IETD-FMK），皆能減低ALA-PDT引起的細胞凋亡。西方墨點分析顯示了ALA-PDT可以同時活化caspase-8和caspase-9，也會引起細胞內phospho-JNK的上升，同時造成FLIPs、XIAP的抑制。其中，caspase-8訊息傳導路徑的引發，主要來自於其上游蛋白FADD磷酸化的增加；而caspase-9的活化，則是藉由cytochrome C的釋放所致。因此ALA-PDT可藉由粒線體及死亡接受器兩條路徑造成口腔癌細胞的凋亡。我們也發現ALA-PDT會造成phospho-JNK的增加，而JNK的抑制劑（SP600125）及NF-κB的抑制劑（Bay）可抑制ALA-PDT所引起的細胞凋亡，且當細胞經過NF-κB抑制劑處理後再進行光動力治療，phospho-JNK會被抑制，說明JNK的磷酸化會經由NF-κB。除此之外，我們更進一步證實了無論是藉由粒線體及死亡接受器兩條路徑所造成的口腔癌細胞凋亡，JNK的活化都是不可或缺的。所以ALA-PDT誘導細胞凋亡的機制，主要是經由NF-κB活化JNK所致。

Photodynamic therapy (PDT) is a kind of new developing treatment for cancer. 5-Aminolevulinic acid (ALA) is a novel photosensitizer for photodynamic therapy. We previously showed ALA-PDT can induce cytotoxicity in oral cancer cells, however, the mechanism(s) for the ALA-PDT induced cytotoxicity is still unknown. In this study, we demonstrated that ALA-PDT induces apoptosis in human oral cancer cell lines Ca9-22 as evidenced by release of cytochrome C and cleavage of PARP. Apoptosis induced by ALA-PDT was both time- and dose-dependent. Western blot analysis showed ALA-PDT treatment induced FADD, caspase-8 and -9 activations. In addition, ALA-PDT treatment induced reactive oxygen species (ROS) production as detected by DCF fluorescence. Pretreatment of cells with imidazole (singlet oxygen inhibitor) reduced the ALA-PDT-induced apoptosis. These results indicated that singlet oxygen was an important mechanism for ALA-PDT-induced apoptosis in Ca9-22 cells. ALA-PDT-induced apoptosis was also inhibited in the presence of caspase 8 or caspase 9 inhibitors (Z-LEHD-FMK, Z-IETD-FMK). We also found that ALA-PDT was able to induced JNK activation and pretreatment of cells with SP600125 (JNK inhibitor) inhibited ALA-PDT-induced FADD activation, cytochrome C release and PARP cleavage. Pretreatment of cells with Bay (NF-κB inhibitor) inhibited ALA-PDT-induced JNK activation and apoptosis.Taking together, this study showed that ALA-PDT can induce apoptosis in Ca9-22 cells via activating intrinsic- and extrinsic-apoptosis pathway, and the activating of NF-κB and subsequent JNK activation are critical for the initiation of the apoptotic processes.