Anti-proliferative and anti-migratory effects of EGFR and c-Met tyrosine kinase inhibitors in triple negative breast cancer cells

Background: There is increasing need to develop targeted therapies for triple negative breast cancer (TNBC) as conventional therapies are ineffective at combatting systemic disease. Triple negative breast tumors often have increased expression of receptor tyrosine kinases (RTKs) such as epidermal growth factor receptor (EGFR) and the hepatocyte growth factor receptor c-Met; presenting as potential targets for treatment. However, targeted anti-EGFR and anti-c-Met therapies have faced mixed results in clinical trials due to acquired resistance. In this study, we explore the potential of EGFR and c-Met as potential targets for treatment of metastatic TNBC, including assessment of potential mechanisms of response. Methods: To help define the clinical context, we first evaluated EGFR and c-Met expression data from The Cancer Genome Atlas (TCGA) and Clinical Proteomic Tumor Analysis Consortium (CPTAC). Using MDA-MB-468 and MDA-MB-231 TNBC cell lines, we also investigated the effects of the c-Met inhibitor cabozantinib and the EGFR inhibitor erlotinib on in vitro cell proliferation, migration, invasion and downstream signaling pathways. Results: TCGA and CPTAC data demonstrated increased expression of both EGFR and c-Met in patients with TNBC relative to other breast cancer subtypes (P<0.05). We observed that MDA-MB-468 cells were more sensitive to the anti-proliferative effects of erlotinib (IC50 =9.70 nM) compared to MDA-MB-231 cells (IC50 =5.48 µM), whereas MDA-MB-231 cells were more sensitive to cabozantinib (IC50 =1.68 µM) than MDA-MB-468 cells (IC50 =8.89 µM). In erlotinib-treated MDA-MB-468 cells, we observed a decrease in both phosphorylated EGFR (Y1086) and total EGFR as well as decreased activation of ERK1/2 (T202, Y204) (P<0.05). Cabozantinib, although not directly affecting the activation of c-Met, attenuated activation of AKT1 (S473) in MDA-MB-231 cells (P<0.05). Finally, we observed a reduction in cell migration and invasion of erlotinib-treated MDA-MB-468 cells and cabozantinib-treated MDA-MB-231 cells compared to controls (P<0.05). Conclusions: Erlotinib and cabozantinib have varying anti-proliferative and anti-migratory effects in different TNBC models. Elucidation of the underlying mechanisms that define the heterogenous response to tyrosine kinase inhibitors (TKIs) in TNBC could help identify biomarkers to stratify patients for treatment and/or facilitate discovery of targets to attenuate acquired resistance.