Abstract LB-215: Astrocytes promote brain metastasis of triple-negative great cancer through TGF-β2/ANGPTL4 axis
Authors: Wang Ling , Hou Zhimin , Gronseth Emily , Rader Janet , Harder David , Ramchandran Ramani 
Published: July 2017

Abstract
Breast cancer has a high propensity for brain metastasis (BM), especially in triple negative (ER-/PR-/Her2-) breast cancer (TNBC) subsets. To date, the underlying mechanism for BM is poorly understood, and no targeted therapies have been developed. Metastatic outcome depends on the interactions of metastatic cells with a specific organ microenvironment. Astrocyte is the most abundant cell type in the brain microenvironment. Previous observations suggest a role for astrocytes in tumor BM, but the underlying mechanism is unknown. Our goal is to determine how astrocytes promote TNBC cell BM and to develop novel therapeutic strategies to treat this deadly disease
To investigate the effect of astrocyte on BM formation of TNBC cells, we passaged TNBC cells in astrocyte-cultured medium (ACM), and compared these cells to DMEM passaged cells (control) for their genetic and functional difference. Next, we determined the role of a significant ACM up-regulated gene, angiopoietin-like 4 (Angptl4), in BM formation in a mouse model. Furthermore, we investigated the mechanisms for how TNBC cells and astrocytes interaction to up-regulate the ANGPTL4 expression, and how ANGPTL4 contributes to BM formation. Finally, we analyzed the ANGPTL4 expression in brain metastatic tumors and plasma from TNBC patients.
We found that 1) ACM-conditioned MDA-MB-231 cell facilitated BM formation and up-regulated ANGPTL4 expression. In addition to 231 cells, other TNBC cells (MDA-MB-468 and HCC1937) showed similar up-regulation of ANGPTL4 expression; 2) knockdown of Angptl4 by shRNA reduced ACM-induced BM formation and mortality; 3) astrocytes produced transforming growth factor-beta2 (TGF-β2), which was enhanced by tumor cell-derived IL-1β and TNF-α. The TGF-β2 through Smad signaling in part is responsible for the up-regulation of ANGPTL4 in TNBCs; 4) passaging TNBC cells in ACM led to a large amount of cells died, but cells survived in ACM revealed cancer stem cell like phenotype with CD44+/CD24-, α-SMA high and ID1 low. They started to gradually grow when extended to passage them in ACM. However, knockdown of ANGPTL4 resulted to a contrary consequence; and 5) the higher ANGPTL4 level was observed in brain mets compared to primary tumors, and the higher ANGPTL4 level in plasma was also identified in TNBC patients with BM compared to without BM.
Collectively, our results suggest that TNBC cells interact with astrocytes to promote astrocytes secrete TGF-β2, which in turn up-regulates ANGPTL4 expression in TNBC cells. This up-regulation of ANGPTL4 attributes to the survival and activation of a small population of breast cancer stem like cells from TNBC to facilitate BM formation. This work presents a novel mechanism of how astrocytes and tumor cells communicate in a paracrine and autocrine manner to facilitate BM of TNBC. Our work suggests that ANGPTL4 is a potential therapeutic molecule that can be targeted for the treatment of BM of TNBCs.
Note: This abstract was not presented at the meeting.
Citation Format: Ling Wang, Zhimin Hou, Emily Gronseth, Janet Rader, David Harder, Ramani Ramchandran. Astrocytes promote brain metastasis of triple-negative great cancer through TGF-β2/ANGPTL4 axis [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 LB-215. doi:10.1158/1538-7445.AM2017-LB-215