支架蛋白Aki1作为K-Ras突变大肠癌治疗新靶向的研究

Epidermal growth factor receptor (EGFR) has been proved to play a important role in tumorigenesis, growth, and suvival. Anti-EGFR using EGFR inhibitor (gefitinib) and/or EGFR antibody (cetuximab) have been widely utilized in clinical therapy of non-small cell lung cancer, colon cancer, head-and-neck cancer, etc. However, acquired resistance to EGFR inhibitors and K-ras mutation related resistance to cetuximab are serious problems for these reagents. Therefore, it is urgent to understand the resistant mechanism, thereby develop new reagents to overcome the drug resistance. We have reported that hepatocyte growth factor (HGF) induces gefitinib resistance in lung cancer with EGFR activating mutations. More recently, we showed that EGFR downstream scaffold protein, Aki1 could be a novel target for lung cancer, even if the lung cancer cells have developed T790M second mutation and became resistance to EGFR inhibitors. In the present study, we further explored the role of Aki1 in colon cancer. Our primary experiments showed that Aki1 was expressed in most of colon cancer cell lines. In contrast to EGFR, deletion of Aki1 by siRNA successfully induced apoptosis of colonl cancer cells even in the presence of K-ras mutation. These results suggested that Aki1 is a novel therapeutic target for colon cancer. In our project, we will furthur investigate the mechanism of how Aki1 works in the survival signal pathway and clarify the relationship between EGFR, Aki1 and K-ras. Our results will provide important evidences for developing novel therapeutic strategy for K-ras mutant colon cancer.

EGFR在肿瘤发生发展中起到重要作用。EGFR抑制剂（易瑞沙等）和抗体（爱必妥等）已在肺癌、大肠癌、头颈部肿瘤等的临床治疗中显示了良好的效果，然而易瑞沙的获得性耐药和K-ras突变导致的爱必妥耐药阻碍了此类药物的应用和效果。申请人已经报道了肝细胞生长因子导致肺癌对易瑞沙耐药，并报道了EGFR下游支架蛋白Aki1作为肺癌治疗的新靶点的可能性。本项目旨在探讨Aki1在大肠癌治疗中的作用。初步实验表明沉默Aki1基因可导致大肠癌细胞凋亡，不同于EGFR的是，这一作用不受K-ras突变的影响。上述发现提示Aki1或许是K-ras突变大肠癌治疗的新靶点。本项目拟采用基因转染、沉默、小鼠肿瘤模型以及组织标本染色等技术，旨在获得Aki1作为大肠癌新靶向的可靠证据，进一步揭示Aki1与EGFR以及k-ras间的关系，为开发新的靶向药物提供科学依据。

申请人已经报道了肝细胞生长因子导致肺癌对易瑞沙耐药，并报道了EGFR下游支架蛋白Aki1作为肺癌治疗的新靶点的可能性。本项目预实验表明沉默Aki1基因可导致K-ras突变的大肠癌细胞凋亡，提示Aki1或许是K-ras突变大肠癌治疗的新靶点。因此本项目主要研究Aki1与K-ras突变以及EGFR三者间的关系以及Aki1作为新治疗靶点的可能性。项目进行过程中，我们进一步发现：沉默Aki1可抑制包括大肠癌、肺癌和胰腺癌在内的多种K-ras突变肿瘤，而EGFR的突变以及表达与否并不影响这一抑制作用。同时、Aki1与c-Raf、K-ras分子相互作用，抑制了MAPK信号途径。我们过去的研究已经表明Aki1在PI3K/Akt信号途径中扮演重要角色，而本项目中发现Aki1在Ras/Raf/MAPK途径中同样有重要作用。众所周知，同时抑制PI3K/Akt和MAPK途径下游分子可以抑制K-ras突变肿瘤，但严重的副作用限制了这种疗法的应用。因此，Aki1有望成为多种K-ras突变肿瘤的更好的治疗靶点。上述发现超过了项目申请时的设想，项目过程中已构建了K-ras突变原发肺癌与大肠癌小鼠，目前继续深入研究，以获得Aki1作为多种K-ras突变肿瘤治疗新靶点的可靠证据，阐明其作用机制。.除上述研究进展外，我们还发现了HGF对于EGFR野型的肺癌细胞，可降低其对EGFR-TKI的敏感性。同时 ,我们发现对于EGFR野型肺癌细胞,PI3K抑制剂或MEK抑制剂均可降低细胞增殖,而只有 PI3K抑制剂可降低EGFR突变肺癌细胞的增殖。证明对于野型细胞的增殖,PI3K/Akt和MAPK通路均有重要作用。上述内容发表于Oncotarget(已接收,待发表)。 除上述发现外,我们在靶向治疗联合放疗的机制上也进行了探讨,发现PTEN/PI3K/Akt通 路直接影响肿瘤的放疗敏感性,证实了PI3K/mTOR以及MET抑制剂的放疗增敏作用。发表于Mol Canc Ther,和BBRC。