Abstract
Ado-trastuzumab emtansine (Kadcyla®; 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 α5β1 and αVβ3 integrins, resulting in enhanced motility and invasion of T-DM1-resistant cells. This study delineates previously unappreciated relationships between α5β1 and αVβ3 and suggests that specific integrins should be carefully selected as therapeutic targets to treat T-DM1-resistant disease. Specifically, silencing β1 integrin expression by siRNA in T-DM1-resistant cells destabilizes α5, but increases expression of αV, 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 β1 integrin blockage induced by an inhibitory antibody, MAB 13, significantly increases invasion of T-DM1-resistant cells. However, the increased cell invasion induced by β1 integrin blockage can be significantly reduced by either EGFR inhibitor or specific siRNA against αV integrin. The discovery of functional cooperation between EGFR and αV 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.