Abstract 5157: Comparison of exosomes shed by breast cancer cell lines with varying metastatic potential
Authors: Martin Kelly A. , Hum Nicholas R. , Sebastian Aimy , Loots Gabriela G. 
Published: August 2019

Abstract
Exosomes are endosomal secreted vesicles containing a variety of genetic and non-genetic material that can be transferred between cells (DNA, RNA, protein, lipid, etc.). Cancer derived exosomes have been implicated in a wide range of cancer mechanisms such as promotion of tumor growth, tumor angiogenesis, immune evasion, drug resistance, and metastasis. In addition to functional significance, cancer exosomes may possess novel biomarkers with potential uses for non-invasive liquid biopsies for cancer detection and monitoring of disease progression. Here we examined differences that may exist in extracellular vesicles or exosomes (EVs) shed by cancer cell lines with various metastatic potential (MDA-MB-231, highly metastatic; MCF-7, weakly metastatic; MCF-10a, normal breast epithelial cells). Morphological analysis of EVs was performed using fluorescent Nanosight Tracking Analysis and revealed decreased mean diameter of EVs derived from MCF-7 cells compared to the other two cell lines, there was also increased exosome particle yield in this cell line. Small RNAs from EVs cargo were also analyzed via sequencing (exoRNA-Seq). The majority of sequenced RNA aligned to coding regions of the human genome (~60%) across all cell lines. Non-coding RNA classification also showed little variability across cell lines examined regardless of metastatic potential, with ~38% of RNA reads corresponding to non-coding RNAs. Pairwise comparison of these cell lines demonstrated that each line packaged unique cargos into their shed exosomes. The non-coding regions corresponded to a variety of small RNAs (miRNA, snoRNA, snRNA, miscRNA, rRNA) but included other RNA features such as pseudogenes and antisense RNAs. We found 304 genes significantly up-regulated and 150 genes significantly down-regulated when comparing metastatic cancer exosomes (MCF-7 and MDA-MB-231) to normal, non-tumorigenic exosomes (MCF-10A). Among examined microRNAs we found several miRNAs associated with metastatic behavior that have previously been implicated in cancer biology, which will be prioritized for validation. Also, 21 RNAs were upregulated at high levels in exosomes shed by metastatic cells, and their expression level was directly proportional with the metastatic character, suggesting that these RNAs may be tested for their potential as biomarkers. Future research will expand upon these newly identified genetic signatures of metastatic exosomal cargo and further validate their influence in driving metastasis.
This study received funding from DOD grant BC151687. This work was conducted under the auspices of the USDOE by LLNL (DE-AC52-07NA27344). IM number: LLNL-POST-758941
Citation Format: Kelly A. Martin, Nicholas R. Hum, Aimy Sebastian, Gabriela G. Loots. Comparison of exosomes shed by breast cancer cell lines with varying metastatic potential [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5157.