NF1介导HER2阳性胃癌对曲妥珠单抗耐药的分子机制及其靶向干预研究：走进胃癌“精准治疗”时代

Trastuzumab is currently proved to be the only effective targeted drug against HER2-positive gastric cancer. Combined with chemotherapy, trastuzumab can significantly improve the overall survival, but the response rate is only 47% and 12% of patients are resistant to trastuzumab primarily and the median progression free survival is only 6.7 months. All the patients will eventually acquire resistance to trastuzumab. Until now, the exact mechanism of resistance to trastuzumab in HER2-positive gastric cancer is still unknown. In our pilot study, the circulating tumor DNA (ctDNA) in patients with HER2-positive gastric cancer who were given trastuzumab treatment were dynamically monitored. The exons of ctDNA in 416 drug resistance-related genes were sequenced and found that the type 1 neurofibromatosis (NF1) gene mutations may mediate trastuzumab resistance. Further analysis showed that NF1 gene mutations (E217X truncation mutation in NF1 exon 6) may lead to dysfunction of NF1, elevation of RAS-GTP level, activation of RAS downstream pathways, all of which will results in tumor proliferation. Our present study are to further explore the molecular mechanisms of NF1 gene mutations mediated trastuzumab resistance in HER2-positive gastric cancer in vitro and in vivo and look for the new strategies to overcome trastuzumab resistance in HER2-positive gastric cancer.

曲妥珠单抗是目前唯一被证实对HER2阳性胃癌有效的分子靶向药物，其联合化疗能显著延长患者的生存期，但有效率仅47%，且12%的患者对曲妥珠单抗原发耐药，中位疾病控制时间仅6.7个月，患者最终都会对曲妥珠单抗产生耐药性。针对HER2阳性胃癌对曲妥珠单抗耐药的确切机制，目前尚未见报道。我们前期工作通过动态监测接受曲妥珠单抗治疗的HER2阳性胃癌患者的循环血ctDNA，对循环血ctDNA中416个耐药相关基因的外显子进行测序，结果发现1型神经纤维瘤病（NF1）基因突变可导致HER2阳性胃癌对曲妥珠单抗产生耐药性，进一步分析显示，部分NF1基因突变（第6号外显子E217X截短突变）可导致NF1抑癌功能发生缺失，导致RAS-GTP水平升高，激活RAS下游通路。本项目拟进一步在体内外探索NF1基因突变/缺失导致HER2阳性胃癌对曲妥珠单抗耐药的分子机制及寻找克服耐药的新方法，指导胃癌的精准治疗。

ToGA研究已经证实，曲妥珠单抗联合化疗可显著延长HER2+转移性胃癌（mGC）患者的总生存期，但由于胃癌具有高度的异质性，曲妥珠单抗用于胃癌治疗存在疗效有限和快速耐药的问题。因此需要明确曲妥珠单抗的原发和继发耐药机制，以筛选曲妥珠单抗响应人群和寻找克服耐药的治疗方案。. 我们的研究应用基于416基因泛实体瘤NGS检测panel，对78例胃癌患者相匹配的组织和血浆ctDNA样本进行靶向深度测序，并对24例HER2+ mGC患者曲妥珠单抗联合化疗治疗期间进行动态监测。研究发现416基因靶向深度测序HER2基因拷贝数变异（SCNA）检测结果与FISH检测结果高度一致，且HER2 SCNA动态监测比CEA能更好的预测肿瘤退缩或进展，表明基于NGS的液态活检能够预测曲妥珠单抗的治疗疗效。进一步的研究还发现大多数对曲妥珠单抗原发耐药的患者在疾病进展后展现出更高的HER2 SCNA，而获得性耐药患者HER2 SCNA相对基线明显下降。PIK3CA基因突变在曲妥珠单抗原发耐药患者中显著富集，在部分曲妥珠单抗耐药患者的基线和进展后的血浆ctDNA中可检测到ERBB2/4基因突变。基线血浆中PIK3CA/R1/C3突变和ERBB2/4基因突变与更差的PFS显著相关。此外，本研究通过in vitro和in vivo研究证实了NF1基因突变可导致曲妥珠单抗耐药，且HER2和MEK/ERK双重阻断可克服NF1突变导致的曲妥珠单抗耐药。. 本研究的一序列研究成果表明持续的ctDNA动态监测可监测曲妥珠单抗耐药的发生，揭示潜在的耐药机制，并为下一步治疗方案的调整提供有用的线索。该研究已被胃肠道肿瘤领域国际顶级期刊GUT（IF=17.94）接收。

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