GLUTATHIONE及去氧核糖核酸甲機化對癌細胞氧化砷抗藥性之影響

Abstract

砷元素廣泛的散佈在自然界中。長期的 暴露在過量的砷會增加得到皮膚癌、肺 癌、膀胱癌等癌症的機會。但自古以來， 砷就被西方醫學及傳統中醫用來治療多種 疾病，最近發現，氧化砷能治療對化學治 療、全反式維生素甲酸完全沒有效用的急 性前骨髓型白血病病人。砷也被應用在其 他癌症的臨床試驗中。 細胞排除砷的能力似乎和glutathione 系統有關，此外砷對細胞的毒性似乎和去 氧核糖核酸甲機化的程度有關。我們初期 研究顯示對氧化砷有抗藥性的癌細胞， glutathione 的量較高，使用抗藥逆轉劑 buthionine sulfoximine (BSO) 降低 glutathione 可增加氧化砷的敏感度。 本計畫的目的在探討癌細胞抗氧化砷 和glutathione，及去氧核糖核酸甲機化的 關係。我們發現在一系列癌細胞中 glutathione 的量和氧化砷的毒性很有相 關。對氧化砷敏感的NTU-B1 細胞(低 glutathione)去氧核糖核酸甲機化的程度， 比對氧化砷有抗藥性的NTU-B1/P14(高 glutathione)為低。用BSO 處理NTUB1/ P14 細胞可增強氧化砷對癌細胞的毒 殺能力，但去氧核糖核酸甲機化的程度並 無改變。全細胞去氧核糖核酸甲機化的程 度應和氧化砷有抗藥性無關，也許只有和 特定基因的去氧核糖核酸甲機化有關。細 胞內glutathione 的改變也無法改變全細胞 去氧核糖核酸甲機化的程度。

Arsenic is a ubiquitous element that presents in environment. Chronic exposure of arsenic compound is associated with increased risk of skin cancer, lung cancer, bladder cancer, etc. Arsenic is an ancient medication and was used widely in both western and Chinese medicine. It has been used to treat acute promyelocytic leukemia in the past few years. Arsenic has been used in clinical trials involving other cancer types. Cellular glutathione system and DNA hypomethylation has been linked to arsenic toxicity to normal cells. Our preliminary study on a panel of cancer cell lines suggested that high cellular glutathione was associated with arsenic resistance in cancer cells. The objective of this project is to correlate cellular glutathione level, DNA methylation level with arsenic resistance in cancer cells. In a panel of cell lines, cytotoxicity to arsenic correlate well to glutathione content in cancer cells. NTU-B1 cells that contain low level of glutathione has lower level of global DNA methylation than high glutathione containing arsenic resistant NTU-B1/P14 cells. However, there was no further DNA hypomethylation when BSO were added to either NTU-B1 or NTU2 B1/P14 cells. There is no correlation between arsenic sensitivity to global DNA methylation. Arsenic sensitivity may be related to only some specific gene methylation. Depletion of glutathione by BSO was not able to change global DNA methylation in cancer cells.