應用基因轉殖的小鼠模式研究肺癌形成與其對標靶藥物反應的分子機制

Abstract

肺癌是臺灣地區、同時也是全世界十大癌症死因的首位。高比例的國人肺腺癌患者中，其上皮生長因子受體(EGFR)，經常有過度表現或突變的情形。而針對這個特定目標設計的標靶藥物，如erlotinib 和gefitinib，也已經使用於臨床治療。然而，部分帶有EGFR 基因突變的肺腺癌患者，並無法以標靶藥物有效治療與控制病情。推測其原因，有可能是這些患者除了EGFR基因異常外，另外還帶有其他的基因突變。這些被列入考慮的突變基因中，包括著名的抗細胞凋亡基因BCL-2。BCL-2 蛋白質的表現，已在包括肺癌等多種癌症檢體與癌症細胞株中被檢測到。然而BCL-2在肺癌中所扮演的角色，目前還有許多待解與不明瞭的地方。為了進一步了解在in vivo 狀態下，BCL-2 對肺癌形成分子機制的影響，本計畫已成功創造出同時帶有人類BCL-2 與人類突變上皮生長因子受體EGFR T790M-L858R 的基因轉殖小鼠。並誘導轉殖基因在小鼠肺部過度表現，用以研究BCL-2在EGFR突變型肺癌生成時，所扮演的角色。初步成果顯示，此新穎基因轉殖小鼠在以藥物(doxycycline)誘導約五周後，可由肉眼與組織切片觀察到肺部腫瘤的形成。而肺部細胞也可偵側到EGFR 與BCL-2蛋白質的高度表現。同時在EGFR下游，與細胞的增生、存活、與生長等相關的訊息傳導分子如Akt、ErK1/2與mTOR等也有被活化的現象。本研究的成果，有助於我們對於肺癌形成分子機制的進一步了解，進而設計出更有效的標靶藥物與組合，以造福患者。

Expression of the anti-apoptotic protein BCL-2 has been identified in approximately 35% of non-small cell lung cancer (NSCLC) in a meta-analysis. The molecular mechanisms by which BCL-2 may contribute to oncogenic EGFR-driven tumor development and targeted therapeutics remain to be elucidated in vivo. To investigate the impact of BCL-2 overexpression in oncogenic EGFR-driven lung tumors, we have created a novel transgenic mouse model harboring both the pre-survival hBCL-2 and the kinase domain mutation hEGFR T790M-L858R. The preliminary data showed that the mouse lung cancer model develops lung tumor features approximately 5 weeks after doxycycline induction of the lung-specific transgenic gene expression. Consistent with the development of lung tumor nodules upon doxycycline induction, isolated mouse lung tissues had high levels of EGFR and BCL-2 proteins as judged by immunoblotting analysis. Elevated levels of selected EGFR downstream mediators critical for cell proliferation (Erk1/2), survival (Akt), and growth (mTOR) were also found in the lung tissue of the double mutant mice. In the future, more studies will need to be done to determine whether BCL-2 may synergize with oncogenic EGFR in lung tumorigenesis.