Abstract 1227: Angiotensin-(1-7) reduces triple negative breast cancer brain metastatic growth in association with decreased c-Met signaling

Patients with triple negative breast cancer often develop metastatic brain disease and have limited treatment options due to the lack of targeted therapeutics that efficiently cross the blood brain barrier. In the current study, we investigated the effect of angiotensin-(1-7) [Ang-(1-7)], a heptapeptide hormone with anti-proliferative and anti-metastatic activities, on the growth of murine brain tumors using brain trophic BR.5-4T1 cells in a model of metastatic triple negative breast tumor growth. BR.5-4T1 cells (1.25 x 104) were injected into the internal carotid artery of female BALB/c mice; after two days, mice were implanted with osmotic mini-pumps to deliver 24 µg/kg/h Ang-(1-7) and all mice were sacrificed after 20 days of treatment. Ang-(1-7) treatment significantly reduced metastatic tumor number in the brain; an average of 20 metastatic lesions per mouse was observed in the brains of an untreated control cohort while an average of 3 metastatic tumors per mouse was observed in the Ang-(1-7)-treated cohort. Tumor size was also reduced 17-fold by treatment with Ang-(1-7). Ki67, a marker of proliferation, was decreased from 29.1±6.7% to 6.4±2.2% in tumors from mice treated with Ang-(1-7), indicating that the heptapeptide hormone decreased metastatic tumor burden in the brain. Aberrant activation of the c-Met receptor tyrosine kinase signaling pathway facilitates tumor cell invasion and metastasis. Treatment with Ang-(1-7) significantly reduced the percentage of metastatic tumor cells exhibiting phospho-c-Met immunoreactivity, from 20.8±3.4% in tumors from untreated mice to 6.7±2.6% in mice treated with Ang-(1-7). Protein phosphatase 1b (PTB1b), which dephosphorylates and negatively regulates phospho-c-Met, was increased in the tumor cells of mice treated with Ang-(1-7) compared to tumor cells from untreated animals, from 4.1±1.4% in sections of tumors from control mice compared to 8.8±0.9% in sections of tumors from mice treated with Ang-(1-7). These results suggest that Ang-(1-7) increases PTP1b to antagonize c-Met signaling and decrease triple negative breast cancer brain metastasis. In support of a role for c-Met signaling in the regulation of metastatic brain disease in breast cancer patients, analysis of publicly available breast cancer cohort databases demonstrated a significant correlation between low c-Met/high PTP1b expression and improved survival outcome, including an increase in brain metastasis-free survival and distant-metastasis free survival. This is the first report to demonstrate that Ang-(1-7) reduces metastatic triple negative breast cancer localized to the brain in association with increased protein phosphatase PTP1b and decreased phospho-c-Met, suggesting that the heptapeptide hormone may serve as a novel targeted therapy to reduce metastatic brain tumor burden in triple negative breast cancer patients. Citation Format: E. Ann Tallant, Guorui Deng, Wenhong Chen, Linda J. Metheny-Barlow, Patricia E. Gallagher. Angiotensin-(1-7) reduces triple negative breast cancer brain metastatic growth in association with decreased c-Met signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1227. doi:10.1158/1538-7445.AM2017-1227