基于c-Met的靶向抑制联合放、化疗在结直肠癌治疗中的药效学评价和机制研究

Significant progress has been made in developing target-based cancer therapies. Among many targets, the c-Met receptor tyrosine kinase gained considerable attention. HGF/c-Met pathway is dysregulated in various human malignancies, and plays a vital role in tumor formation and progression. Recent data suggested that c-Met expression level is correlated with metastasis of colorectal carcinoma cells, indicating c-Met is an attractive target in colorectal cancer treatment. Although several c-Met tyrosine kinase inhibitors (c-Met-TKIs) are under clinical trials and yield impressive responses, rapidly acquired resistance seems an important limitation as experienced with other TKIs. Our particularly interest will be focused on exploring the combination effects of c-Met targeted therapy and irradiation/anticancer agents. For one reason, because of the heterogeneity nature of tumor cells, combining of anticancer agents with c-Met targeted therapy could enhance clinical benefit of current therapy for colon carcinoma. Our preliminary data also demonstrated that combination of irradiation/cisplatin with c-Met knockdown synergistically inhibited proliferation and migration of colon cancer cells. Furthermore, combination with irradiation or anticancer agents is a strategy to overcome or prevent the acquired resistance of c-Met targeted therapy. The c-Met receptor relies on its multitude of signaling adaptors and cell surface co-receptors to mediate biological responses; combination with irradiation/anticancer agents underlying multiple mechanisms could block activation of other signaling events that bypass the continued requirement for c-Met target. In order to efficiently assess the combination treatment, a tetracycline-inducible c-Met conditional knockdown will be constructed in colon cancer cells, providing a suitable platform to evaluate combination efficacy of c-Met-targeting therapy and irradiation/anticancer agents, including active compounds from herbal medicine, traditional chemotherapy agents and inhibitors that target other RTKs. Moreover, the mechanisms of action will be further explored by investigating the regulation of genes that related to proliferation and metastasis. Additionally, the mechanisms leading to resistance of c-Met-targeting therapy will be explored. This study will provide further evidence for the clinical use of c-Met-targeting therapy in colon cancer either alone or combination treatment with irradiation or anticancer agents.

c-Met通路的异常活化与结直肠癌的发生发展密切相关，基于该激酶的靶向干预代表了结直肠癌治疗的新方向。临床实验表明分子靶向治疗与单独放、化疗一样会导致肿瘤耐药，因此建立一种研究模式探讨c-Met靶向干预联合放、化疗协同药效，及该协同作用降低肿瘤耐药的可能性尤为重要。基于前期的可调控RNAi技术，我们建立了c-Met表达可人为调控的稳定细胞系，发现c-Met沉默可程度依赖地抑制结肠癌细胞的增殖；c-Met沉默与放射线或DNA交联剂顺铂的联合使用可显著抑制细胞增殖，而与拓扑异构酶抑制剂伊立替康却无协同效应。本课题将系统研究c-Met靶向干预联合放疗和作用机制不同的化疗药等对结肠癌生长和转移的影响，探讨具有协同作用的联合用药组合对相关信号网络的影响，并利用c-Met可不同程度被调控的特色，探讨c-Met靶向干预联合放、化疗对抗肿瘤耐药的分子机制，为基于c-Met靶向治疗的临床应用提供思路。

尽管基于EGFR的靶向治疗在结直肠癌的临床应用中取得良好疗效，但仍存在原发性耐药和继发耐药产生的严重问题。c-Met通路的异常活化与结直肠癌的发生发展密切相关，基于该激酶的靶向干预代表了结直肠癌治疗的新方向。临床实验表明，分子靶向治疗与单独放、化疗一样会导致肿瘤耐药，因此建立一种研究模式探讨c-Met靶向干预联合放、化疗协同药效，及该协同作用降低肿瘤耐药的可能性尤为重要。. 本课题主要完成了三部分工作：（1）在含KRAS突变的结直肠癌细胞株上，构建了基于四环素的c-Met可调控稳定细胞系，发现c-Met靶向抑制可显著降低含KRAS突变的结肠癌细胞的增殖、迁移和侵袭能力，并抑制Akt和ERK通路的活化；（2）评价了c-Met靶向抑制与50余种抗肿瘤药物／小分子的联合作用，体内外实验结果均显示，c-Met靶向抑制可增加含KRAS突变的结直肠癌细胞株对5-FU和紫杉醇的敏感性，其作用机制主要是通过激活caspase介导的细胞凋亡发挥的；（3）发现c-Met靶向抑制通过激活Chk1/Chk2, 增加放疗引起的DNA损伤，阻滞细胞生长于G2/M期，显著增加放疗敏感性。. 本课题的研究结果首次发现c-Met的靶向抑制在含有KRAS突变的结直肠癌治疗中具有重要意义，提示其可能是克服针对EGFR靶向治疗产生原发性耐药的手段。此外，发现c-Met靶向抑制能够增加放／化疗的抗肿瘤活性，该协同作用降低肿瘤继发耐药的可能。