肺癌是台灣癌症死亡的首要原因，而肺癌病人絕大部分都在晚期才被發現，並不適合以手術的方式進行治療。化學治療雖然已被證實對肺癌的治療有一定程度的助益，但是整體而言並不能有效控制疾病的進展。而且，化學治療抗藥性往往在化學治療處理後不久就發生。接著，由於失控的癌症轉移，病人多半在短期內就死亡。因此新的肺癌治療法極為需要。近年來，癌症幹細胞(CSCs)已經被證實存在於不同種類的腫瘤中，並且具有促使癌症的轉移以及化學治療抗藥性的功能，因此它是一個癌症治療的可能標的。此外，在不同型態的人類癌症中，發現了一群擁有腫瘤幹細胞特性的細胞，“Side-population”(SP)細胞。雖然SP細胞在肺癌已經被鑑定出來，然而對於人類肺癌幹細胞的特性仍然不清楚。惡性肋膜積水(MPE)常見於肺癌的病患。由於它的轉移性質且在臨床上較易於獲得，使它成為一個研究肺癌幹細胞的良好平台。
在當前的研究中，我們首先嘗試從肺癌病人的MPE中鑑定SP細胞的存在，然後分離出SP細胞，找尋肺癌幹細胞的標記。在人類肺癌細胞株(A549、H1650、AS2、CL1-0)中，我們發現SP細胞的比例皆有所不同。同時，我們也證明了SP細胞在肺癌病人的MPE中所佔的百分比，約為0.41~0.14%。然而，從結果顯示，SP細胞與非SP細胞在肺癌幹細胞之候選標記(CD44、CD133、CD166及ABCG2)的表現量上並無顯著差異。此外，在比較腫瘤形成球狀的能力與在生物體內形成腫瘤的能力，SP細胞與非SP細胞的結果也無差異。再者，我們利用Aldefluor assay的方法，在肺癌細胞株(A549、H1650、AS2、CL1-0)中，發現一群具有腫瘤幹細胞的潛力的細胞，稱為ALDHbr細胞。但細胞株中ALDHbr細胞與SP細胞的百分比，並無良好的相關性。有趣的是，我們發現干擾素(IFN)的處理能調控幹細胞的產生。當A549、H1650、及AS2細胞在干擾素γ長期地處理下，其SP細胞與ALDHbr細胞的比例會減少，但是在CL1-0細胞中，反而比例增加。此外，我們發現Sox2蛋白在CL1-0細胞的表現量遠高於其他細胞株。因此，我們推測Sox2蛋白可能依據干擾素的刺激來調控幹細胞的命運。然而，目前還只是初步的結果，需要更多的研究來確認。雖然在本研究中，我們沒有成功地發現肺癌幹細胞的標記，但是我們有完善的方法可以鑑定潛在的肺癌幹細胞的存在。我們還發現，干擾素的處理可能會影響幹細胞的命運，並且這種現象可能是藉由Sox2蛋白的表現而有所更改。

Lung cancer is the leading cause of cancer death in Taiwan. The majority of patients present with their illness in the advanced stages that preclude curative surgical resections. Though chemotherapy has clearly shown a clinically significant benefit, the improvement of survival is modest and chemoresistance often occurs. Finally, patients with metastatic disease ultimately died of their disease. Thus, novel therapy is needful. Recently, cancer stem cell (CSC) has been proved to exist in a variety of tumors, which contribute to tumor metastasis and drug resistance. In many types of human cancers, a group of side-population (SP) cells were found to possess CSC properties. Though the SP cells have also been identified in lung cancer, the characteristics of human lung cancer stem cell are still obscure. Malignant plural effusion (MPE) is a common complication of lung cancer. The metastatic properties and the clinical availability make cancer cells in MPE a reasonable source to study lung cancer stem cell. In the current study, we firstly tried to identify SP cells in MPEs from patients with lung cancer and then isolate the SP cells for finding markers of lung cancer stem cells. The SP cells exist in lung cancer cell lines-A549, H1650, AS2 and CL1-0 with various percentages. We also demonstrated the presence of SP population (0.41~14%) in MPEs from patients with lung cancer. However, we showed no difference in the expression of potential stem cell markers (CD44、CD166、CD133、ABCG2) between the SP and non-SP cells. There is no difference in the tumor spheroid formation and xenograft formation in SCID mice between SP and non-SP cells either. By Aldefluor assay, we found potential CSCs (ALDHbr cells) in lung cancer cell lines (A549, H1650, AS2 and CL1-0). The percentages of ALDHbr and SP cells in the cell lines, however, are not correlated well. Interestingly, we found interferon (IFN) treatment is able to modulate stem cell generation. The ratio of SP and ALDHbr cell decreased after long-term IFN-γ treatment in A549, H1650, and AS2 cell lines, but increased in CL1-0 cells. Furthermore, we founded the expression of Sox2 protein in CL1-0 is much higher than that of other cell lines. Therefore, Sox2 protein may modulate stem cell fate upon IFN stimulation. However, the results are preliminary, which require more studies to confirm. We did not successfully discover markers for lung cancer stem cells in the study, but we have developed methods to identify potential lung cancer stem cells. We also found that IFN treatment may influence stem cell fate and the phenomenon might be modified by the expression of Sox2 protein.

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