Abstract
BackgroundHuman epidermal growth factor receptor-2 (HER2) is amplified and a clinical target in a subset of human breast cancers with high rates of metastasis. Targeted therapies involving the antibody trastuzumab and trastuzumab-emtansine (T-DM1) have greatly improved outcomes for HER2-positive (HER2+) breast cancer patients. However, resistance to these targeted therapies can develop and limit their efficacy. Here, we test the involvement of the endocytic adaptor protein endophilin A2 (Endo II) in HER2+ breast cancer models, and their responses to treatments with trastuzumab and T-DM1.MethodsEndo II expression in human breast tumors and lymph node metastases were analyzed by immunohistochemistry. Stable silencing of Endo II was achieved in HER2+ cancer cell lines (SK-BR-3 and HCC1954) to test Endo II effects on HER2 levels, localization and signaling, cell motility and tumor metastasis. The effects of Endo II silencing on the responses of HER2+ cancer cells to trastuzumab or T-DM1 treatments were tested using real-time cell motility and cytotoxicity assays.ResultsHigh Endo II protein expression was detected in HER2-positive tumors, and was linked to worse overall survival in node-positive HER2+ breast cancers at the mRNA level. Stable silencing of Endo II in HER2+ cell lines led to elevated levels of HER2 on the cell surface, impaired epidermal growth factor-induced HER2 internalization, and reduced signaling to downstream effector kinases Akt and Erk. Endo II silencing also led to decreased migration and invasion of HER2+ cancer cells in vitro, and impaired lung seeding following tail vein injection in mice. In addition, Endo II silencing also impaired HER2 internalization in response to Trastuzumab, and led to reduced cytotoxicity response in HER2+ cancer cells treated with T-DM1.ConclusionsOur study provides novel evidence of Endo II function in HER2+ cancer cell motility and trafficking of HER2 that relates to effective treatments with trastuzumab or T-DM1. Thus, differential expression of Endo II may relate to sensitivity or resistance to trastuzumab-based therapies for HER2+ cancers.
Highlights
Human epidermal growth factor receptor-2 (HER2) is amplified and a clinical target in a subset of human breast cancers with high rates of metastasis
High Endo Endophilin A2 (II) expression in metastatic HER2+ breast cancers and association with patient outcomes We previously reported high endophilin A2 (Endo II) expression in triple-negative breast cancer (TNBC) tumors compared to luminal tumors, an association with poor prognosis, and a metastasis-promoting role for Endo II in TNBC xenograft models [22]
At much lower doses than that used for TZ, we observed a significant increase in cytotoxicity (PI+ cells) in NT control cells treated with Trastuzumab emtansine (T-DM1) for 36–48 hours of treatment (Fig. 7b)
Summary
Human epidermal growth factor receptor-2 (HER2) is amplified and a clinical target in a subset of human breast cancers with high rates of metastasis. Targeted therapies involving the antibody trastuzumab and trastuzumab-emtansine (T-DM1) have greatly improved outcomes for HER2-positive (HER2+) breast cancer patients. Resistance to these targeted therapies can develop and limit their efficacy. Mortality in patients with breast cancer is primarily due to the development of metastatic disease [1, 2] This progression involves the acquisition of adaptive changes within tumor cells and the tumor microenvironment [3]. Trastuzumab treatment leads to reduced HER2 signaling, reduced tumor angiogenesis, cell cycle arrest, and enhanced anti-tumor immune responses [9] Despite these beneficial outcomes, resistance to trastuzumab is common, and can occur early in the treatment regime [10]. Defining the underlying mechanisms of trastuzumab-induced HER2 internalization could provide insights into trastuzumab resistance
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