胸腺嘧啶核苷酸合成酶的抑制合併標靶藥物在小細胞肺癌的細胞毒殺效果之研究

Abstract

肺癌 (lung cancer) 居全世界癌症死因之首，而其中侵略性很強的小細胞肺癌約占所有肺癌種類的百分之十五至二十。雖然小細胞肺癌對最初的化療有極佳的敏感性，大部分的病人最後還是會復發，五年存活率僅約百分之五。因此，小細胞肺癌急需新穎的治療策略。胸腺嘧啶核苷酸合成酶 (thymidylate synthase; TS) 為前體DNA生合成的關鍵酵素，是癌症化療的重要標的。而愛寧達 (alimta; pemetrexed) 是目前用於臨床治療非小細胞肺癌及間皮瘤 (mesothelioma) 的胸腺嘧啶核苷酸合成酶抑制劑。儘管有研究指出在小細胞肺癌中具高表現量的胸腺嘧啶核苷酸合成酶，單獨使用愛寧達在小細胞肺癌病人上的效果有限。因此，我們將胸腺嘧啶核苷酸合成酶抑制劑合併使用mTOR 抑制劑癌伏妥 (afinitor; everolimus; RAD001) 用於小細胞肺癌細胞研究。結果顯示，這兩種藥物的合併使用會造成H209小細胞肺癌細胞的胸腺嘧啶核苷酸合成酶的表現量上升且無法有效的抑制其細胞生長。我們因而推論胸腺嘧啶核苷酸合成酶表現量的上升，在小細胞肺癌細胞抵抗這組組合的治療上扮演重要的角色。因此，我們利用小干擾RNA (siRNA) 的技術將胸腺嘧啶核苷酸合成酶的基因剔除 (knockdown)，並合併使用mTOR 抑制劑癌伏妥或組織蛋白去乙醯酶 (histone deacetylase; HDAC) 抑制劑伏瑞斯特 (vorinostat; SAHA)於小細胞肺癌細胞上。結果顯示胸腺嘧啶核苷酸合成酶的抑制會增強癌伏妥或伏瑞斯特所導致的抗增生及細胞凋亡並促使細胞週期停滯於S期。本研究的結果有助於提供未來在治療小細胞肺癌上以胸腺嘧啶核苷酸合成酶為標靶的新穎組合藥物設計。

Lung cancer is the leading cause of cancer related death worldwide. Small cell lung cancer (SCLC) is an aggressive form of lung cancer, which accounts for about 15%-20% of all cases. Although SCLC has an initial relatively high sensitivity to chemotherapy, tumor relapse or disease progression may occur quickly, and the overall 5-year survival rate is less than < 5%. Therefore, novel treatment strategies are urgently needed. Thymidylate synthase (TS), an enzyme that is critical in the de novo synthesis of DNA, is an important target in cancer chemotherapy. The TS inhibitor pemetrexed is approved to be used alone or with other drugs to treat non-small cell lung cancer (NSCLC) and mesothelioma. Despite the fact that TS expression in SCLC is high, single agent pemetrexed has minimal effect on SCLC patients. Consequently, we use TS inhibitor pemetrexed in combination with the mTOR inhibitor everolimus for the treatment of SCLC cells. Our data showed that combination of these two agents up-regulated expression of TS and did not effectively inhibit cell growth in the H209 SCLC cells. We suspected that up-regulation of TS expression may play an important role in the acquired resistance to the combination treatment. Thus, we replaced TS inhibitor pemetrexed with TS siRNA and combined with mTOR inhibitor everolimus or HDAC inhibitor vorinostat in treatment of SCLC cells. Our results demonstrated that inhibition of TS enhanced everolimus or vorinostat-induced anti-proliferative effect and apoptosis that were accompanied with cell cycle arrest in S phase of SCLC cell lines. Results from this study may provide a new TS-targeted combination therapeutic method in the treatment of SCLC.