T-DM1-resistant cells gain high invasive activity via EGFR and integrin cooperated pathways

Ado-trastuzumab emtansine (Kadcyla (R); T-DM1) is an antibody-drug conjugate developed to treat trastuzumab-resistant disease. Despite initial favorable outcomes, most patients eventually cease to respond due to developing acquired resistance to T-DM1. Currently, there is no targeted therapy to treat T-DM1-resistant disease. To explore novel therapeutic targets to improve therapeutic efficacy of T-DM1, we generated T-DM1-resistant cells using trastuzumab-resistant JIMT1 cells. We found that the loss of human epidermal growth factor receptor 2 confers T-DM1 resistance, which in turn activates a compensatory mechanism that increases epidermal growth factor receptor (EGFR) expression. Upregulation of EGFR increases the protein levels of alpha 5 beta 1 and alpha V beta 3 integrins, resulting in enhanced motility and invasion of T-DM1-resistant cells. This study delineates previously unappreciated relationships between alpha 5 beta 1 and alpha V beta 3 and suggests that specific integrins should be carefully selected as therapeutic targets to treat T-DM1-resistant disease. Specifically, silencing beta 1 integrin expression by siRNA in T-DM1-resistant cells destabilizes alpha 5, but increases expression of alpha V, a critical integrin mediating the invasion and metastases in many different cancers. As a consequence, T-DM1-resistant cells gain metastatic potential and become more invasive. This finding is underscored by the fact that beta 1 integrin blockage induced by an inhibitory antibody, MAB 13, significantly increases invasion of T-DM1-resistant cells. However, the increased cell invasion induced by beta 1 integrin blockage can be significantly reduced by either EGFR inhibitor or specific siRNA against alpha V integrin. The discovery of functional cooperation between EGFR and alpha V integrin in regulating cell growth and invasion provides an opportunity to develop novel therapeutic strategy by dual-targeting EGFR and specific integrin to overcome T-DM1 resistance.