miRNA在HER2阳性胃癌Trastuzumab耐药中的作用及其调控机制

Trastuzumab, which is a therapeutic monoclonal antibody targeting the epidermal growth factor receptor family member HER2, has been successfully used to treat advanced breast cancers. After a large-scale phase III clinical trial on gastric cancers, Trastuzumab has been included in the National Comprehensive Cancer Network (NCCN) Clinical Practice Guideline for Gastric Cancers in 2011. Nevertheless, a majority of patients receiving Trastuzumab develop resistance soon, the underlying mechanisms of which remain elusive in gastric cancers. We found previously that the glycoprotein, Mucin-4, which competes with Trastuzumab to bind HER2, is upregulated on the surface of Trastuzumab-resistant gastric cancer cells. Mucin-4 upregulation correlates with suppressed miR-22 expression in these cells, suggesting that miRNAs play pivotal roles in mediating Transtuzumab resistance. In the present study, based on the finished screening of the differentially expressed miRNAs in Trastuzumab-resistant gastric cancer cells, the target genes of the essential candidate miRNAs and downstream regulators of Trastuzumab resistance will be established, the mechanisms involved in the regulation of these miRNAs will be defined, and ultimately the responsible upstream signaling event and network derived from HER2/Trastuzumab interaction will be dissected. This study holds out promise to systemically unravel the machinery that causes Trastuzumab resistance, thus providing theoretical basis for targeted and combined therapy of HER2-positive cancers.

曲妥珠单抗（Trastuzumab）是靶向人表皮生长因子受体家族分子HER2的治疗性单抗，已成功应用于晚期乳腺癌治疗，在完成胃癌大规模III期临床试验后，被写入2011年版"胃癌NCCN临床实践指南"。然而大多数患者接受治疗后很快出现耐药，其机制在胃癌中尚未见报道。前期研究中，我们发现Trastuzumab耐药胃癌细胞高表达能够与抗体竞争性结合HER2的黏蛋白Mucin-4，其上调与miR-22的降低密切相关，表明miRNA的表达变化在介导Trastuzumab耐药中发挥重要作用。本研究在已筛选获得耐药细胞差异表达miRNA的基础上，明确关键miRNA调控的耐药相关分子，阐明miRNA自身表达的调控机制，以及Trastuzumab/HER2相互作用对上述机制的调节作用及其分子网络，从而有助于系统认识Trastuzumab耐药的分子机制，并为HER2阳性肿瘤的靶向联合治疗提供理论依据。

针对人表皮生长因子受体2（HER2）的曲妥珠单抗（trastuzumab）是临床上应用最为成功的抗肿瘤单抗之一，但患者对这种治疗性单抗产生的耐药成为制约其疗效的瓶颈问题。本项目经过深入研究，阐明了曲妥珠单抗的耐药机制以及microRNA在其中发挥的作用。我们以耐药的肿瘤细胞系和裸鼠移植瘤为模型，发现miR-200c的下调是导致肿瘤对曲妥珠单抗耐药的重要机制。在耐药细胞中，TGF-β信号通过转录因子ZEB1抑制miR-200c的表达，而ZEB1和ZNF217均是miR-200c的靶基因，ZNF217是调控TGF-β表达的关键转录因子，从而证实肿瘤细胞中存在TGF-β/ZEB1/miR-200c/ZNF217/TGF-β的正反馈环路，导致肿瘤细胞对曲妥珠单抗产生耐药。此外，我们还发现miR-375通过靶向胰岛素样生长因子1受体（IGF1R）抑制肿瘤对曲妥珠单抗的耐药，而miR-221则通过靶向沉默抑癌基因PTEN促进耐药。相关研究在Int J Cancer等SCI收录杂志发表论文5篇，完成了既定的研究目标，为临床上克服肿瘤对HER2靶向治疗的耐药提供了新的思路。