Abstract 5083: Using proteomics profiling to elucidate the interactions of breast cancer-derived exosomes with the blood-brain barrier
Authors: Morad Golnaz , Otu Hasan H. , Dillon Simon T. , Moses Marsha A. 
Published: August 2018

Breast cancer metastasis to brain is associated with a dismal prognosis commonly attributed to a limited understating of the mechanisms driving this pathological process. Elucidation of the early events leading to brain metastasis is essential to the development of more effective therapeutic and diagnostic approaches. With an interest in the role of breast cancer-derived exosomes in brain metastasis, our group has previously shown that exosomes derived from a brain-seeking variant of the breast cancer cell line MDA-MB-231 (Br-Ex) can facilitate brain metastasis by inducing alterations in the protein expression profile of astrocytes, one of the components of the blood brain barrier (BBB). This observation led us to hypothesize that the interaction(s) between exosomes and astrocytes is more efficient compared to brain endothelial cells (ECs) or pericytes, the two additional major components of the BBB, resulting in more prominent alterations in the protein expression profile of astrocytes. To test this hypothesis, we first quantified and compared the uptake of exosomes by brain ECs, astrocytes, and pericytes in vitro. The uptake of Br-Ex by astrocytes was significantly greater than that of brain ECs (P&lt;4e-3) and pericytes (P&lt;1e-3). In contrast, exosomes derived from parental or bone-seeking MDA-MB-231 cells (P-Ex and Bo-Ex, respectively) did not show a preferential uptake by astrocytes. We have also demonstrated the uptake of Br-Ex by astrocytes in vivo. The uptake of exosomes by different cell types predominantly relies on the interaction of exosomal proteins with different receptors on the recipient cells. To determine the exosomal proteins potentially involved in the preferential uptake of Br-Ex by astrocytes, we performed quantitative mass spectrometry on the P-, Bo-, and Br-Ex via Isobaric Tag for Relative and Absolute Quantitation (iTRAQ) analysis. Database searches were performed against human proteins in the SwissProt database and a total of 126 proteins were detected with over 95% confidence. Pairwise comparisons identified a total of 27 and 21 proteins with statistically significant differential expression (P &lt; 0.05) in the Br-Ex compared to the P- and Bo-Ex, respectively. Functional enrichment analysis of the detected proteins demonstrated that proteins belonging to the cell migration and focal adhesion categories were over-represented in the Br-Ex. Among these proteins, a number of integrins and annexins were highly enriched in the Br-Ex and can potentially be involved in the preferential uptake of these exosomes by astrocytes.

These findings indicate that exosomes derived from brain-seeking breast cancer cells can preferentially interact with astrocytes and these interactions can be driven by exosomal integrins and annexins. (The authors are grateful for the support of the Breast Cancer Research Foundation and the Advanced Medical Research Foundation.)

Citation Format: Golnaz Morad, Hasan H. Otu, Simon T. Dillon, Marsha A. Moses. Using proteomics profiling to elucidate the interactions of breast cancer-derived exosomes with the blood-brain barrier [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 5083.