Abstract 1971: A novel approach to overcome resistance to HER2 targeted therapy in a new syngeneic model of breast cancer brain metastasis
Authors: Pouliot Normand , Nagpal Aadya , Fuentes Miriam , Mouhtouris Effie , Avogadri-Connors Francesca , Lalani Alshad S. , Araujo Heloisa Sobreiro Selistre de 
Published: August 2018

Abstract
The human epidermal growth factor receptor-2 (HER2) subtype of breast cancer is aggressive and associated with a high propensity to metastasize to the brain. Whilst the introduction of HER2-targeted therapies has significantly improved survival outcomes in affected patients, effective treatment of brain metastasis remains a challenge due to acquired resistance and limited drug permeability across the blood brain barrier. Moreover, progress in identifying more effective treatments, particularly against therapy-resistant brain-metastatic HER2 breast cancer, has been hampered by the lack of robust and clinically relevant preclinical models. Here, we introduce a new Balb/c syngeneic model of spontaneous breast cancer brain metastasis that naturally expresses HER2 (RCSI-Her2). In vivo metastasis assays confirmed that this model gives rise to high incidence of spontaneous brain metastases from mammary tumors or experimental brain metastases following intra-cardiac inoculation. RT-PCR, western blotting and immunohistochemical analyses of RCSI-Her2 cells, tumors or brain metastases confirmed the lack of hormone receptor expression but high levels of HER2. Accordingly, RCSI-Her2 cell proliferation is inhibited by HER2 inhibitors, lapatinib or neratinib, but not by anti-estrogens, indicating phenotypic and functional similarities to human HER2 breast cancer. Importantly, short term in vitro proliferation assays show that the combination of neratinib with αvβ3 integrin inhibitors (Cilengitide or DisBa-01) potently and synergistically inhibits the proliferation of RCSI-HER2 or brain-metastatic triple negative breast cancer cells (4T1Br4). Moreover, treatment of neratinib-resistant RCSI-Her2 variants with Cilengitide or DisBa-01 restores sensitivity to neratinib. Preliminary in vivo experiments indicate that neratinib is well-tolerated in immune-competent mice, inhibits RCSI-HER2 primary tumour growth and extends survival. Transcriptomic analysis (RNAseq) of neratinib-sensitive and resistant variants treated or not with neratinib to identify signaling pathways implicated in resistance is underway. The results from this analysis will be presented. To our knowledge, RCSI-Her2 is the only model that fully recapitulates the spontaneous spread of HER2 breast cancer to the brain in immune-competent hosts. This model provides a unique tool to validate the efficacy of neratinib/αvβ3 integrin inhibitors in vivo against advanced brain-metastatic and therapy-resistant HER2 breast cancer.
Citation Format: Normand Pouliot, Aadya Nagpal, Miriam Fuentes, Effie Mouhtouris, Francesca Avogadri-Connors, Alshad S. Lalani, Heloisa Sobreiro Selistre de Araujo. A novel approach to overcome resistance to HER2 targeted therapy in a new syngeneic model of breast cancer brain metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1971.