EGFR tyrosine kinase inhibitors (TKIs) are standard therapy for EGFR-mutant non-small cell lung cancer (NSCLC); however, these tumours eventually acquire chemoresistance. U3-1402 is an anti-HER3 antibody-drug conjugate with a novel topoisomerase I inhibitor, DXd. In the current study, we evaluated the anticancer efficacy of U3-1402 in EGFR-mutant NSCLC cells with acquired resistance to EGFR-TKIs. HCC827GR5 and PC9AZDR7 are EGFR-TKI-resistant clones for gefitinib and osimertinib, respectively. U3-1402 alone or in combination with the EGFR-TKI erlotinib demonstrated potent anticancer efficacy in HCC827GR5 cells using an in vitro growth inhibition assay and in vivo xenograft mouse model. U3-1402 induced apoptosis in HCC827GR5 cells accompanying phosphorylation of histone H2A.X, a marker of DNA damage, but did not block HER3/PI3K/AKT signalling. Further, we found using flow cytometry that the cell surface HER3 expression level in HCC827GR5 cells was twice that found in HCC827 cells, indicating internalization of U3-1402 was increased in resistant cells. In addition, administration of U3-1402 notably repressed growth of EGFR-TKI osimertinib-resistant PC9AZDR7 xenograft tumours, and that PC9AZDR7 cells expressed five times greater cell surface HER3 than PC9 cells. Furthermore, using immunofluorescent microscopy, HER3 was observed predominantly in the nucleus of PC9 cells, but was localized in the cytoplasm of PC9AZDR7 cells. This finding indicates that altered trafficking of the HER3-U3-1402 complex may accelerate linker payload cleavage by cytoplasmic lysosomal enzymes, resulting in DNA damage. Our results indicate that administration of U3-1402 alone or in combination with an EGFR-TKI may have potential as a novel therapy for EGFR-TKI-resistant EGFR-mutant NSCLC.

中文翻译：

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掺入DNA拓扑异构酶I抑制剂U3-1402的靶向HER3的抗体-药物偶联物征服了EGFR酪氨酸激酶抑制剂耐药的NSCLC。

EGFR酪氨酸激酶抑制剂（TKIs）是EGFR突变非小细胞肺癌（NSCLC）的标准疗法；然而，这些肿瘤最终获得化学抗性。U3-1402是一种抗HER3抗体-药物偶联物，具有新型拓扑异构酶I抑制剂DXd。在当前的研究中，我们评估了U3-1402在具有EGFR-TKIs获得性耐药的EGFR突变NSCLC细胞中的抗癌作用。HCC827GR5和PC9AZDR7分别是吉非替尼和奥西替尼的EGFR-TKI耐药克隆。使用体外生长抑制试验和体内异种移植小鼠模型，单独或与EGFR-TKI厄洛替尼组合的U3-1402在HCC827GR5细胞中显示出有效的抗癌功效。U3-1402伴随着组蛋白H2A.X的磷酸化而诱导HCC827GR5细胞凋亡，组蛋白H2A.X是DNA损伤的标志物，但并未阻止HER3 / PI3K / AKT信号转导。此外，我们使用流式细胞仪发现，HCC827GR5细胞中的细胞表面HER3表达水平是HCC827细胞中的两倍，这表明U3-1402的内在化在抗性细胞中增加了。另外，U3-1402的施用显着抑制了EGFR-TKI耐奥西替尼的PC9AZDR7异种移植肿瘤的生长，并且PC9AZDR7细胞表达的细胞表面HER3是PC9细胞的五倍。此外，使用免疫荧光显微镜观察，HER3主要在PC9细胞核中观察到，但位于PC9AZDR7细胞的细胞质中。该发现表明HER3-U3-1402复合物的改变的运输可加速胞质溶酶体酶对接头有效载荷的切割，从而导致DNA损伤。