組蛋白甲基轉移脢抑制劑之發展---(總計畫與子計畫二)合成與設計組蛋白甲基轉移脢抑制劑調控腫瘤幹細胞的生長(I)

Abstract

近幾年來癌症有效療法的研究已經開始探討腫瘤幹細胞，目前提出的腫瘤幹細胞(tumor stem cells，TSCs)概念認為，某些癌症起源於一小部份自我更新能力很強的細胞，這一小部分細胞即是腫瘤幹細胞。對抗腫瘤幹細胞的癌症治療已經在一些原位腫瘤和血癌的動物實驗中得到驗證；這些腫瘤幹細胞能不斷補充生成新的腫瘤細胞，癌症病人要徹底治療腫瘤避免增生和轉移，必須清除這些腫瘤幹細胞。 G9a為一組蛋白甲基轉移酶，負責催化組蛋白H3K9的甲基化。郭教授最近的研究報告顯示，在不同類型癌症病人的腫瘤組織中，G9a與腫瘤的分化呈現高度相關性，顯示G9a可能參與、調控癌症轉移的過程，同時G9a的表現與肺癌細胞株的轉移浸襲能力呈正相關。Ep-CAM技術阻斷了G9a的組蛋白甲基轉移活性，可以抑制肺癌細胞之轉移侵襲能力，顯示G9a的酵素活性參與在G9a調控癌細胞轉移的機轉中。但是至目前為止還沒有針對G9a的有效藥物上市，只有一個小分子抑制劑（BIX-01294）已公佈，但其副作用並不足以令其成為可上市之藥品。這是一個新的生物標靶的目標和一項重大的挑戰，但也是新型藥物開發很好的機會。本計畫最主要是運用本實驗室專長的微波組合式化學(見下圖)，利用Fragment-based drug discovery的策略，以低分子量之官能基片段組合出最有可能作為標靶治療癌症幹細胞進行篩選所需的小分子化合物，以便進行多樣化快速合成具有可能抑制G9a生物活性的雜環分子庫，從中發掘出新型、可專利的小分子先導藥物，並以電腦模擬4D-QSAR的方式設計出更有效的結構，藉著改變化學骨架及官能基來找出更有效的化合物，因為有效的分子庫設計可減少分子合成的數量和生物測試，同時運用先進的配方技術以達到最佳化之效果。現在已經發現NCTU-SUN-727以及NCTU-SUN-771等化合物，其有效抑制率最佳結果已達50%以上，我們團隊正在轉換分子構形，以發揮其最大功效。孫仲銘教授與郭明良教授、曾宇鳳教授組成堅強的團隊，以多樣性的快速合成、高通量的篩選平台、先進的電腦模擬機制來找尋對抗腫瘤幹細胞的全新藥物。

G9a is a mammalian histone methyltransferase and catalyzes the histone 3 lyine 9 dimethylation, which was known to involve in the epigenetic silencing of tumor suppressor genes. Our previous studies have demonstrated the G9a mediated lung cancer metastasis as well as G9a played a key role in two malignant cancers, ovarian and colon, in Taiwan. Only one selective small molecule G9a inhibitor, BIX-01294, has been reported so far. BIX-01294 was developed under Structural Genomics Consortium as a G9a-like protein and G9a histone lysine methyltransferase (HMTase) inhibitor (IC50 values are 0.7 and 1.7 μM respectively) that displays no activity at other HTMases up to 37 μM. G9a as a good biological target for cancer stem cell therapy since our team has proven that G9a promotes lung cancer invasion and metastasis by silencing the cell adhesion molecule Ep-CAM. Despite the tremendous progress made in exploring G9a mechanism, the generating its small molecule inhibitor is still rather unexplored on the market. This gap between knowing a novel target for therapy and needing small molecule inhibitors presents a major challenge but also is good opportunity for drug discovery and development. The chemical development of potential compounds as the G9a inhibitors makes progress slowly. There is no doubt that modern technologies, such as combinatorial synthesis (see Figure below) integrated high-throughput microwave-assisted synthesis and in vitro biological screening have accelerated many aspects of the discovery research process. Within the pharmaceutical research, diversity-oriented synthesis focuses on obtaining maximum benefit from the small molecules created in the drug discovery process. Part of this research is the application of small molecule inhibitors to assist in the characterization of the biological function of targets. The lack of well-characterized small molecules as tools has hampered the wider use of chemical genomics approaches. We will focus on these strategies applied to the fast access larger and focused libraries with properties amenable to target validation (G9a) and on the challenges in annotating their biological function in cancer stem cell. The overall goal of this integrated project is to identify, synthesize, and optimize G9a inhibitors with good safety and pharmacokinetics profiles ready for clinical testing in cancer treatment. To achieve this goal, each research units will responsible to carry out their respective research and constant feedback to each other to optimize the potent compounds and push for IND final goal.