Identification and Targeting of Therapeutic Resistance Mechanisms in Inflammatory Breast Cancer

Abstract

<p>Inflammatory breast cancer (IBC) is a rare and highly aggressive form of breast cancer that is characterized by survival signaling through overexpression and/or activation of the epidermal growth factor receptors EGFR/ErbB1 and Her2/ErbB2 and defects in the apoptotic program. The development of therapeutic resistance is a significant barrier to successful treatment in IBC, and thus, strategies targeting the mechanisms that drive drug resistance could prevent or reverse therapeutic resistance, significantly improving patient prognosis. Based on analysis of previously developed models of therapeutic resistant IBC, we hypothesized that apoptotic dysregulation and redox adaptive mechanisms were central to the drug resistant phenotype in IBC cells, and that targeting of these mechanisms could overcome therapeutic resistance. Our objectives to address this hypothesis were: 1. to develop and characterize an isotype-matched IBC cellular model to investigate the mechanisms of acquired therapeutic resistance; 2. to characterize IAP-specific small molecule inhibitors as a means of targeting the mechanism of apoptotic dysregulation in IBC; and 3. to characterize a novel redox modulatory combination as a means of targeting redox adaptive mechanisms in IBC.</p><p>Analysis of cell viability, proliferation, and growth parameters, evaluation of protein expression and signaling via western immunoblot, and measurement of reactive oxygen species (ROS), antioxidants, and apoptosis in patient-derived IBC cell lines and isogenic derivatives revealed that resistance to the ErbB1/2 inhibitor lapatinib was protective against other targeted agents and chemotherapeutics. Additionally, reversal of resistance was associated with enhanced ability to accumulate ROS and downregulation of anti-apoptotic and antioxidant proteins. Targeting of resistance mechanisms using small molecule IAP inhibitors and a redox modulatory strategy both effectively induced apoptosis in therapy resistant IBC cells. Together, these results confirm XIAP and the redox adaptive phenotype as promising therapeutic targets for IBC and demonstrate the feasibility of targeting those mechanisms in order to reverse therapeutic resistance.</p>