Resistance to hormone therapy in breast cancer cells promotes autophagy and EGFR signaling pathway.

Breast cancer is the leading cause of cancer deaths for women worldwide. Endocrine therapies represent the cornerstone for hormone-dependent breast cancer treatment. However, in many cases, endocrine resistance is induced with poor prognosis for patients. In the current study, we have developed MCF-7 cell lines resistant to fulvestrant (MCF-7Fulv) and tamoxifen (MCF-7Tam) aiming at investigating mechanisms underlying resistance. Both resistant cell lines exerted lower proliferation capacity in two-dimensional (2-D) cultures but retain estrogen receptor α (ERα) expression and proliferate independent of the presence of estrogens. The established cell lines tend to be more aggressive exhibiting advanced capacity to form colonies, increased expression of epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), and heterodimerization of ERBB family receptors and activation of EGFR downstream pathways like MEK/ERK1/2 and PI3K/AKT. Tyrosine kinase inhibitors tested against resistant MCF-7Fulv and MCF-7Tam cells showed moderate efficacy to inhibit cell proliferation, except for lapatinib, which concomitantly inhibits both EGFR and HER2 receptors and strongly reduced cell proliferation. Furthermore, increased autophagy was observed in resistant MCF-7Fulv and MCF-7Tam cells as shown by the presence of autophagosomes and increased Beclin-1 levels. The increased autophagy in resistant cells is not associated with increased apoptosis, suggesting a cytoprotective role for autophagy that may favor cells' survival and aggressiveness. Thus, by exploiting those underlying mechanisms, new targets could be established to overcome endocrine resistance.NEW & NOTEWORTHY The development of resistance to hormone therapy caused by both fulvestrant and tamoxifen promotes autophagy with concomitant apoptosis evasion, rendering cells capable of surviving and growing. The fact that resistance also triggers ERBB family signaling pathways, which are poorly inhibited by tyrosine kinase inhibitors might attribute to cells' aggressiveness. It is obvious that the development of endocrine therapy resistance involves a complex interplay between deregulated ERBB signaling and autophagy that may be considered in clinical practice.

The Impact of Anti-tumor Agents on ER-Positive MCF-7 and HER2-Positive SKBR-3 Breast Cancer Cells Biomechanics.

Studying human cancer from a biomechanical perspective may contribute to pathogenesis understanding which leads to the malignancy. In this study, biomechanics of suspended and adhered breast cancer cells were investigated via the micropipette aspiration method with special emphasis on comparing the cell stiffness and viscoelastic parameters of estrogen receptor positive, ER+, MCF-7 and human epidermal growth factor receptor 2 positive, HER2 +, SKBR-3 cancer cell lines prior to and post treatment with tamoxifen and trastuzumab, respectively. Alterations of mechanical parameters included significant increase in cell stiffness, especially after treatment with trastuzumab and changes in viscoelastic parameters, in both cancer cell lines post treatment. According to immunofluorescence analysis, the raised cell stiffness was corresponded to remodeling of F-actin, which peripherally located in tamoxifen treated and perinuclear accumulated in trastuzumab treated cancer cell cytoskeleton, implying a reduced potential for cell deformation and motility. Additionally, these results were in line with the study of single and collective cell migration through Boyden chamber and wound healing assays respectively, where the potential for migration was significantly decreased after treatment. Consequently, these findings lead to an increased interest in biomechanics of cancer progression after treatment with anti-tumor agents, importantly in understanding the effect of the alterations of mechanical properties upon the possibility for change in metastatic potential.