Despite the implementation of multiple HER2-targeted therapies, patients with advanced HER2⁺ breast cancer ultimately develop drug resistance. Stromal fibroblasts represent an abundant cell type in the tumor microenvironment and have been linked to poor outcomes and drug resistance. Here, we show that fibroblasts counteract the cytotoxic effects of HER2 kinase-targeted therapy in a subset of HER2⁺ breast cancer cell lines and allow cancer cells to proliferate in the presence of the HER2 kinase inhibitor lapatinib. Fibroblasts from primary breast tumors, normal breast tissue, and lung tissue have similar protective effects on tumor cells via paracrine factors. This fibroblast-mediated reduction in drug sensitivity involves increased expression of antiapoptotic proteins and sustained activation of the PI3K/AKT/MTOR pathway, despite inhibition of the HER2 and the RAS-ERK pathways in tumor cells. HER2 therapy sensitivity is restored in the fibroblast cocultures by combination treatment with inhibitors of MTOR or the antiapoptotic proteins BCL-XL and MCL-1. Expression of activated AKT in tumor cells recapitulates the effects of fibroblasts resulting in sustained MTOR signaling and poor lapatinib response. Lapatinib sensitivity was not altered by fibroblasts in tumor cells that exhibited sustained MTOR signaling due to a strong gain-of-function PI3KCA mutation. These findings indicate that in addition to tumor cell-intrinsic mechanisms that cause constitutive PI3K/AKT/MTOR pathway activation, secreted factors from fibroblasts can maintain this pathway in the context of HER2 inhibition. Our integrated proteomic–phenotypic approach presents a strategy for the discovery of protective mechanisms in fibroblast-rich tumors and the design of rational combination therapies to restore drug sensitivity.

尽管实施了多种针对HER2的疗法，晚期HER2 ⁺乳腺癌患者最终仍会产生耐药性。基质成纤维细胞在肿瘤微环境中代表丰富的细胞类型，并与不良结果和耐药性有关。在这里，我们显示成纤维细胞在HER2 ^+的一个子集中抵消了HER2激酶靶向治疗的细胞毒性作用乳腺癌细胞系，并允许癌细胞在HER2激酶抑制剂拉帕替尼的存在下增殖。来自原发性乳腺肿瘤，正常乳腺组织和肺组织的成纤维细胞通过旁分泌因子对肿瘤细胞具有类似的保护作用。尽管抑制了肿瘤细胞中的HER2和RAS-ERK途径，但这种成纤维细胞介导的药物敏感性降低涉及抗凋亡蛋白的表达增加和PI3K / AKT / MTOR途径的持续活化。通过与MTOR抑制剂或抗凋亡蛋白BCL-XL和MCL-1联合治疗，可在成纤维细胞共培养物中恢复HER2治疗敏感性。肿瘤细胞中活化的AKT的表达概括了成纤维细胞的作用，导致持续的MTOR信号传导和不良的拉帕替尼反应。拉帕替尼敏感性并未因肿瘤细胞中的成纤维细胞而改变，这些细胞由于强大的功能性PI3KCA突变而表现出持续的MTOR信号传导。这些发现表明，除了引起组成型PI3K / AKT / MTOR途径活化的肿瘤细胞内在机制外，成纤维细胞分泌的因子还可以在HER2抑制的情况下维持该途径。我们的综合蛋白质组学-表型方法为发现富含纤维母细胞的肿瘤中的保护机制提供了策略，并为恢复药物敏感性设计了合理的联合疗法。成纤维细胞分泌的因子可以在HER2抑制的情况下维持该途径。我们的综合蛋白质组学-表型方法为发现富含纤维母细胞的肿瘤中的保护机制提供了策略，并为恢复药物敏感性设计了合理的联合疗法。成纤维细胞分泌的因子可以在HER2抑制的情况下维持该途径。我们的综合蛋白质组学-表型方法为发现富含纤维母细胞的肿瘤中的保护机制提供了策略，并为恢复药物敏感性设计了合理的联合疗法。