Abstract LB-232: A novel approach for liquid biopsy by using nExo

Abstract

Abstract Exosomes are small extracellular vesicles secreted from all living cells; its contents are highly varied, including proteins, small RNAs and recently discovered, genomic DNA (gDNA). The presence of nuclear content in exosomes suggests that different cell compartments can contribute to exosome cargo; however, little is known about this sub population of nuclear derived exosomes (nExo). Here, we analyzed nExo isolated from ovarian cancer cells and characterized them to explore potential clinical relevance such as cancer detection and therapeutic response. Exosomes were isolated from ovarian cancer cell lines, normal human fallopian epithelial tube cells and bio-fluids from mouse and human samples. To determine the purity of exosomes, nanoparticle tracking system, immunoblotting assay and cryo-transmission electron microscopy were used. To analyze the content of exosomes, protein mass spectrometry and imaging flow cytometry analysis was performed. First, we determined that mass spectrometry analyses for ovarian cancer cell exosomes revealed that 12.5% of proteins are derived from the cell nucleus sub-population. Additionally, using a novel imaging flow cytometry technique which enables us to identify single exosome and to quantify them, we determined that 10% of exosomes carried gDNA. Conversely, normal cells secreted only 0.2% of nExo. Then we hypothesized that the prevalence of gDNA is affected by genotoxic drugs. Treating cells with either the PARP inhibitor olaparib or topoisomerase inhibitor topotecan increased the proportion of nExo secreted from ovarian cancer cells. In addition, PARP proteins exist in ovarian cancer cell exosomes and 80.4 % of the exosome co-localized with gDNA. Using in vivo preclinical models, serum from ovarian cancer bearing mice contained a higher number of nExo than non-tumor controls, and this population was increased in response to treatment of genotoxic drugs. Furthermore, plasma and ascites from ovarian cancer patients contain around 0.3 % of nExo, which include nuclear proteins and gDNA. We demonstrate that nExo are predominantly secreted from cancer cells and could serve as an important biomarker. Although the subpopulation is relatively rare, their presence in bio-fluids isolated from cancer patients holds the potential of serving as novel biomarkers for early detection and therapeutic response to genotoxic agents. Citation Format: Akira Yokoi, Alejandro Villar-Prados, Paul Allen Oliphint, Theresa J. O'Halloran, Jason Roszik, Anil K. Sood. A novel approach for liquid biopsy by using nExo [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 LB-232.