Abstract 5808: The role of breast cancer-derived exosomes in brain metastasis
Authors: Morad Golnaz , Yang Jiang , Moses Marsha A. 
Published: July 2017

The development of brain metastasis is associated with a significant reduction in the survival rate of breast cancer patients. Improving the prognosis of women with brain metastasis from breast cancer relies on the elucidation of the mechanisms underlying this process. Our group and others have shown that the formation of brain metastases occurs along the abluminal side of brain vessels, a process called “vessel co-option”. These observations prompted our hypothesis that the cellular and extracellular matrix (ECM) components of the blood-brain-barrier (BBB) can serve as a pre-metastatic niche for breast cancer brain metastases. The role of tumor-derived exosomes (TEx) in the preparation of a pre-metastatic niche in distant organs has been shown in a number of cancers. To investigate the mechanisms driving the vessel co-option of breast cancer brain metastases, we studied the role of breast cancer-derived exosomes in preparation of the BBB for metastasis formation. Exosomes were isolated from the MDA-MB-231 breast cancer cell line, a brain-seeking variant of these cells, and a bone-seeking variant as a non-brain metastatic control. Brain endothelial cells, astrocytes, and brain vascular pericytes, the three components of the BBB, were treated with exosomes for 3 days to recapitulate the continuous exposure of cells to the circulating TEx in vivo. The treated cells were analyzed for cellular activities relevant to pre-metastatic niche preparation in the brain such as the integrity of the BBB, expression of cytokines, and modulation of the ECM. An initial screen was performed using cytokine antibody arrays and PCR arrays for ECM and adhesion molecules and results were validated in three separate experiments using western blots, ELISA, and Multiplex assays. Exosomes derived from brain-seeking cells significantly increased astrocyte migration and decreased the expression of Integrin β1 in brain endothelial cells, both of which can lead to the disruption of the BBB integrity. Moreover, the expression of Interleukin 8 was increased by TEx in astrocytes. TEx also increased the expression of MMP-3 and -9 (Matrix Metalloproteinases) from an undetectable baseline level and decreased the expression of TIMP-1 and -2 (Tissue Inhibitors of MMPs) in astrocytes. While the importance of these two MMPs for brain metastasis from breast cancer has been previously reported, our study is the first to demonstrate that secretion of these MMPs is triggered by TEx. Surprisingly, we did not observe any significant TEx-derived modulations in the expression of cytokines, ECM, and adhesion molecules in brain pericytes. These findings indicate that within the BBB, astrocytes and endothelial cells, but not pericytes, can be affected by breast cancer-derived exosomes in such a way that can potentially lead to preparation of a suitable niche for future metastasis formation along the brain vasculature. (This work is supported by the Breast Cancer Research Foundation.)

Citation Format: Golnaz Morad, Jiang Yang, Marsha A. Moses. The role of breast cancer-derived exosomes in brain metastasis [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 5808. doi:10.1158/1538-7445.AM2017-5808