砷是一種常見的環境毒物，在流行病學的研究當中指出，長期暴露之下，砷會造 成人體的神經毒性及周邊血管疾病等。不過近來也有學者發現，三氧化二砷 （As2O3）對於急性前骨髓性白血病（Acute promyelocytic leukemia; APL）的患者具有療效，被認為可以作為癌症的治療藥物。口腔癌長年排名在台灣十大癌症之中，且好發率有逐年攀升的趨勢，其中大約有75%是因為個人習慣造成的，包括抽菸、酗酒等。在某些特定區域，尤其是東南亞的國家，嚼食檳榔也是對於導致口腔癌發展的危險因子之一。為了尋找治療口腔癌更有效的方法，並針對砷具有抗癌作用的特性，進一步探討是否能將砷化合物的療效擴展到口腔癌的治療。本篇研究利用三株來自口腔不同部位的鱗狀癌細胞株（Fadu、OEC-M1和OC3）加以處理不同濃度的亞砷酸鈉（Sodium arsenite, NaAsO2）及二甲基砷酸（(CH3)2AsO2H, DMA），結果顯示在OEC-M1及OC3分別處理1 μM 亞砷酸 和1 mM二甲基砷酸，以及Fadu細胞株處理10 μM 亞砷酸鈉和1 mM二甲基砷酸24小時後，細胞會呈現鼓起（cell rounded-up）且細胞膜有發泡（membrane blebbing）的現象，顯現細胞凋亡（apoptosis）的特徵。利用細胞存活率實驗的測定，這三株口腔癌細胞隨著處理的砷化合物濃度增加，活細胞比例都有明顯的降低。而經由流式細胞儀探測，亞硝酸鈉和二甲基砷酸會造成細胞週期的分布改變，不僅增加subG1期的細胞數量，也會促使細胞進停滯在G2/M。再根據annexin V/PI雙染細胞凋亡分析，也證實亞砷酸鈉以及二甲基砷酸會造成口腔癌細胞凋亡。另外，在砷化合物處理之後會活化半胱氨酸蛋白酶（caspase-8, 9及3）並造成聚（腺苷二磷酸-核糖）多聚酶（PARP）的剪切，伴隨著有絲分裂原活化蛋白激酶（JNK、ERK1/2及p38 MAPK）的磷酸化。由此得知，不論是亞砷酸鈉還是二甲基砷酸都會經由半胱氨酸蛋白酶路徑的活化使Fadu、OEC-M1和OC3細胞凋亡，而絲裂原活化蛋白激酶的表現也參與其中的調控機制。

Arsenic is a well-documented environmental toxicant. Epidemiological survey implicates that exposure to arsenic will induce neurotoxicity and peripheral vascular disease. In fact, arsenic trioxide (ATO) has also been used for medicinal purposes, originally to treat acute promyelocytic leukemia (APL), showing ability for anticancer treatment. Oral cancer has been in top 10 common cancers for decades in Taiwan, and the incidence rate still increases year after year. Around 75 percent of oral cancers are linked to modifiable behaviors, such as tobacco use and excessive alcohol consumption. Also, betel chewing in some certain areas, especially in Southeast Asia, is known to be a strong risk factor for developing oral cancers. In the present study, we investigated three oral squamous carcinoma cells (Fadu, OEC-M1, and OC3) treated by sodium arsenite (NaAsO2) and dimethylarsenic acid (DMA) to determine whether the arsenic compounds could be the anti-cancer agents. Results showed that cells appeared rounded up and became membrane blebbing after treatments with NaAsO2 (1 μM) and DMA (1 mM) for 24 hr in OEC-M1 and OC3 cell lines, and NaAsO2 (10 μM) and DMA (1 mM) for 24 hr in Fadu cell line, respectively. These morphological changes revealed characteristics of apoptosis. In cell viability test, the surviving percentage of all three cell lines significantly decreased as the dosage of arsenic compounds increased (10 to 100 μM NaAsO2 and 1 to 100 mM DMA). The impact of arsenic compounds on cell cycle regulation was detected by flow cytometry, and data showed that the percentage of subG1 and G2/M phase cells among three cell lines increased in both NaAsO2 and DMA treatments. We further confirmed that cells underwent apoptosis under both arsenic compound treatments through annexinV/PI double staining. In addition, examined by western blot, activation of caspase-8, -9 and -3; cleavage of poly ADP-ribose polymerase (PARP); and phosphorylation of JNK, ERK1/2, and p38 could all be observed by NaAsO2 and DMA treatments among three cell lines. Taken together, NaAsO2 and DMA could induce cell apoptosis through extrinsic and intrinsic apoptotic pathways and cause the activation of MAPK pathways in Fadu, OEC-M1 and OC3 oral cancer cell lines.

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