Abstract 2850: Characterization of circulating extracellular vesicles isolated from plasma of cancer subjects using novel AC electrokinetics platform
Authors: Krishnan Rajaram , Lewis Jean , Searson David , Perrera Orlando , Kinana Alfred , Balcer Heath , Clark Iryna , Hinestrosa Juan Pablo 
Published: September 2020

Introduction: Extracellular vesicles (EVs) contain protein and nucleic cargo that has been shown to be reflective of physiological and pathological states, or their originating cells, in many diseases including cancer. Specifically, these EV-associated biomarkers have been shown to fluctuate with the change in pathological processes. As a result, characterization of blood-based circulating EVs have been widely investigated for diagnostic applications such as disease monitoring and treatment selection. The heterogeneity of blood-based EVs present significant challenges to current rapid isolation methods due to enrichment with unwanted sub-populations, e.g. apoptotic bodies, or contamination with lipids, e.g. APOB, for both capture-based chemistry-based isolation methods. We have developed a novel lab-on-a-chip technology for isolation and on-chip characterization of EVs from blood-based matrices using an AC electrokinetics (ACE) methodology.

Methods: Blood samples were collected from 10 healthy volunteers and 10 donors with known cancer diagnosis into K2EDTA tubes under IRB approved protocols. Plasma was processed from the blood and stored at -80C. 120 µL of thawed plasma was applied to the microelectrode array flow cell (ExoVerita Flex, Biological Dynamics, San Diego, CA) and the EVs were isolated on the microelectrodes. Following isolation, the flow cell was washed, the isolated material was released from the array and eluted from the flow cell. For comparison, isolation of EVs from the same amount of plasma was performed using a chemistry-based method (ExoQuick Ultra, System Biosciences, Palo Alto, CA) according to manufacturer's instructions. Following isolation, the eluates were evaluated for the presence of EV-associated biomarkers using Western blotting capillary electrophoresis and mass spectrometry (Orbitrap Fusion Lumos, TFS). Nanoparticle tracking analysis (qNano Gold, Izon Science, New Zealand) was performed to determine EV concentration and size distribution. Quantitative qRT-PCR analysis of the purified plasma Evs was performed to confirm presence of EV-bound mRNA.

Results: Western Blotting demonstrated that eluates from both ACE-based methodology and chemistry-based isolation contain the expected CD9 and CD63. The ACE-isolated EVs showed a single prominent band for CD63, whereas chemistry-based isolated EVs display multiple smaller CD63-reactive species, which was suggestive of proteolysis. Mass spectrometry analysis confirmed presence of CD9 and CD81 in EVs isolated by ACE method; but not in EVs purified by chemistry-based method. APOB contamination was present in chemistry-based EVs, but not in ACE-isolated EVs. For RT-PCR experiments, EVs were purified from 5 subjects with lung cancer and 3 subjects with melanoma patient plasma using ACE method. Quantitative PCR confirmed presence of mRNA, via successful amplification of the housekeeping genes PGK1 and β-actin, in all ACE-isolated EVs.

Conclusions: The novel ACE-based platform successfully demonstrated direct isolation of EVs from plasma while preserving the integrity of protein and mRNA biomarkers. The compatibility of the eluted EVs with multiple downstream technologies, such as mass spectrometry, Western blotting and qRT-PCR, may enable novel biomarker discovery and use of EV-associated biomarkers in diagnostic assays.

Citation Format: Rajaram Krishnan, Jean Lewis, David Searson, Orlando Perrera, Alfred Kinana, Heath Balcer, Iryna Clark, Juan Pablo Hinestrosa. Characterization of circulating extracellular vesicles isolated from plasma of cancer subjects using novel AC electrokinetics platform [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2850.