Abstract A30: Angiotensin-(1-7) attenuates triple negative breast cancer progression bytargeting C-Met and downstream ERK1/2 signaling
Authors: Deng Guorui , Tallant Elizabeth Ann , Gallagher Patricia 
Published: May 2015

Abstract
Triple negative breast cancer (TNBC) is an aggressive form of breast cancer that lacks expression of the estrogen receptor (ER) and progesterone receptor (PR) and does not overexpress the HER2/Neu oncoprotein. Patients diagnosed with TNBC have an increased risk of developing distant organ metastasis and disease relapse, contributing to poor prognosis and survival. Without a selective therapeutic target, patients diagnosed with TNBC are treated with chemotherapeutic drugs such as anthracyclines and taxanes that often result in harsh side effects. Angiotensin-(1-7) [Ang-(1-7)] is an endogenous seven amino acid peptide hormone that activates the G protein-coupled receptor mas. Previous studies demonstrated that the heptapeptide hormone exerts anti-proliferative activities in lung, breast and prostate cancer cells and tumor xenografts. In the present study, 4T1 mouse TNBC cells were injected into the mammary fat pad of female Balb/c mice; when the tumors reached a volume of 50 mm3, the animals were treated for 18 days with or without Ang-(1-7) (24 μg/kg/h) via an implanted osmotic mini-pump. Ang-(1-7) significantly reduced tumor volume when compared to the untreated group (a 46% reduction by day 18, n = 6-7, p&lt;0.05), with a concomitant decrease in tumor weight (2.0±0.3 g in untreated mice vs. 1.3±0.1 g in treated mice, p &lt; 0.05). The proliferation marker Ki67 was significantly reduced in Ang-(1-7)-treated tumors compared to untreated tumors [18.1±3.7 Ki67(+) cells in treated vs 103.9±17.2 in untreated tumors, p&lt;0.005]. Phospho-ERK1/2, the final mediators of the Ras/MAPK cascade, were significantly reduced in tumors from treated mice in comparison to tumors from untreated mice (phospho-ERK1: 1.0±0.1 vs. 0.2±0.1, phospho-ERK2: 1.0±0.1 vs. 0.3±0.1, n=5, p&lt;0.05), whereas DUSP1, a dual-specificity phosphatase that negatively regulates ERK1/2 activation, was elevated in response to Ang-(1-7) treatment (1.0±0.3 in untreated mice vs. 3.2±0.8 in treated mice, n=5, p&lt;0.05).
Hepatocyte growth factor/scatter factor (HGF/SF) is a potent inducer of Ras/MAPK signaling by activating the receptor tyrosine kinase (RTK) c-Met; HGF/SF/c-Met signaling is elevated in human TNBC. Ang-(1-7) attenuated c-Met RTK activation by HGF in human MDA-MB-231 and murine 4T1 TNBC cells which was blocked by pretreatment with D-alanine7-Ang-(1-7) [D-Ala], a mas receptor antagonist. A significant decrease in immunoreactive phospho-c-Met RTK was also observed in 4T1 tumors treated with the heptapeptide hormone as compared to untreated tumors (19.7±3.5 phospho-c-Met cells in tumors from treated mice vs. 47.0±9.5 in untreated mice, p&lt;0.05). In addition, Ang-(1-7) reduced HGF-induced activation of the MAPKs ERK1/2 in 4T1 cells. Activation of c-Met by HGF/SF orchestrates a complex biological process termed “invasive growth” by influencing cell proliferation, migration and invasion. The invasive potential of Ang-(1-7)-treated MDA-MB-231 cells in response to HGF/SF was assessed using Matrigel-coated Boyden chambers. HGF/SF significantly increased the number of invading cells (62±5 in untreated cells vs. 117±7 in HGF/SF-treated cells, n=8, p&lt;0.05) which was significantly reduced by treatment with Ang-(1-7) (to 53±2, n=8, p&lt;0.05); the mas receptor antagonist D-ala abrogated the response to the heptapeptide hormone. Collectively, these data suggest that Ang-(1-7) suppresses TNBC progression by activating the mas receptor to attenuate HGF/SF induced c-Met activation, resulting in decreased ERK1/2 signaling, attenuated tumor growth and diminished cell invasion, providing support for the use of Ang-(1-7) as a novel therapeutic agent for TNBC patients.
Citation Format: Guorui Deng, Elizabeth Ann Tallant, Patricia Gallagher. Angiotensin-(1-7) attenuates triple negative breast cancer progression bytargeting C-Met and downstream ERK1/2 signaling. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr A30. doi: 10.1158/1557-3125.RASONC14-A30