HER3在曲妥珠单抗治疗HER2阳性胃癌中的作用及其机制研究

ToGA trial has proved that Trastuzumab can improve disease-free survival and total survival of HER2-positive gastric cancer. Our previous study found that the co-overexpression of HER2 and HER3 in gastric cancer predicted the poor prognosis and the expression of HER2 was strongly correlated with the expression of HER3 in gastric cancer. We speculate that HER3 over-expression may be associated with proliferation, apotosis, migration of HER2-positive gastric cancer, and play an important role in HER2-positive gastric cancer treated with Trastuzumab. Using gene silencing technology to down-regulate the expression of HER3, we observe the changes of proliferation, apotosis, migration of HER2-positive gastric cancer. Using proximity ligation assay (PLA) to detect the HER2-HER3 heterodimer in gastric cancer tissue and cell, we observe the effect of Trastuzumab in the heterodimeration of HER2-HER3。In mice in situ xenograft model, using pWPT-GFP transfected gastric cancer cell, we oberseve the antitumor effect of Trastuzumab plus HER3 monoantibody in vivo. The results of our study will prove that the overexpression of HER3 is related with the maligency phentye of HER2-positive gastric cancer, and Trastuzumab may disrupt the heterodimerization of HER2 and HER3 in a ligand dependent or independent way and inbihit the phosphorylation of HER2 and HER3 to show its antitumor activity, which may be related with PI3K/AKT and Ras/MAPK pathway. The finding will offer a new therapeutic targets in personal treatment of gastric cancer, which may improve the survival of gastric cancer patients.

HER2单克隆抗体（曲妥珠单抗，Trastuzumab）能够延长HER2阳性胃癌患者无疾病生存期和总生存期。前期研究发现胃癌患者HER2/HER3协调高表达预后不良，且HER2、HER3在胃癌中表达呈强相关。我们推测HER3与HER2阳性胃癌恶性表型有关，在曲妥珠治疗HER2阳性胃癌中起重要作用。体外实验应用基因沉默技术下调HER3后，观察其与胃癌细胞恶性表型的关系，应用PLA技术检测胃癌组织、细胞中HER2-HER3异二聚体表达情况，及其在曲妥珠单抗治疗前后表达变化；并且在原位种植瘤动物模型上，在体动态观察曲妥珠单抗联合HER3单抗的抗肿瘤作用。预期结果：HER3与HER2阳性胃癌细胞恶性表型密切相关，曲妥珠单抗可能通过配体依赖或者配体非依赖途径阻断HER2-HER3异二聚体形成，抑制胃癌增殖等恶性表型，并阐明相关分子机制。为胃癌个体化治疗提供新预靶点，以期提高疗效，改善预后。

背景：HER2、HER3同属HER/erbB家族成员，可与其他RTK形成异二聚体激活下游通路。前期研究表明HER3高表达是胃癌预后不良的指标之一，但相关机制尚不明了。我们拟先分析HER3的高表达与胃癌临床指标的关系，及其相关分子机制，然后探讨其与其他RTK之间的相互作用，及其不同表达模式与胃癌表型关系及其相关机制。方法：我们应用免疫组化及实时PCR防范检测161例胃癌标本HER2，HER3及c-MET的表达。分析其与胃癌表型及下游通路的关系。在体外及体内实验同时观察上述现象，并且沉默HER3，观察其与这些指标的关系。结果：HER3在胃癌中表达明显高于正常组织，HER3的高表达与AKT活化，肿瘤大仙，转移相关，胃癌中HER3表达提示预后不良，在体内和体外试验均证实下调HER3，能够抑制胃癌细胞增殖、迁移下降，凋亡增加，细胞周期阻滞，其过程可能与AKT的去活化有关。且不影响HER2的表达及活化。沉默HER3后，CyclinB1 及p27kip1 的T157活性下降，实现肿瘤细胞G2/M期阻滞，通过PI3K/AKT通路下调MMPs调控肿瘤细胞迁移及转移。不同RTKs的表达模式同样可以判断预后。使用HER2特异性抑制剂Lapatinib和c-MET特异性抑制剂PHA665752进一步能够显示组成型活化RTKs通路对胃癌细胞生存的重要性，HER3/HER2及HER3/MET两种不同的表达模式能够通过AKT和MAPK通路转到生长信号入肿瘤细胞，体内体外实验皆证实，沉默HER3后发现，与HER3形成的两种异二聚体对胃癌细胞的生长促进作用减缓。结论：HER3是一个新型的判断预后的指标，其通过PI3K/AKT通路调控胃癌的增殖与转移。HER3在诸多RTKs激酶形成异二聚体实现细胞功能的过程中起关键作用。HER3可作为胃癌治疗的新靶点。