Abstract 1618: Simultaneous isolation of exosomes and cfDNA from liquid biopsies using universal kit based on SubX-MatrixTM technology

In 2016 we have developed novel approach for isolation of circulating cell-free DNA employing the proprietary bi-functional substance SubX® that tightly binds DNA and forms sandwich [cfDNA- SubX®-magnetic particles]. These sandwich aggregates are easily separated from bio-liquid with magnet followed by cfDNA isolation by speedy protocol. Our approach does not require Proteinase K digestion and 2-3-fold dilution of bio-liquid with lysis/binding buffer in contrast to all commercially available kits. Our kit has been evaluated in various research and clinical labs for cfDNA isolation from serum, plasma and urine of patients with different forms of cancer. SubX®-approach also allows for isolation of cfDNA from large volumes of urine samples without its concentration. We demonstrated linear increase of the DNA yield with liquid biopsy volume. Another unique property of the SubX® is that both ends of the molecule display lipid binding groups. This feature allows each molecule of SubX® to anchor two exosomes (i.e. dimerize). Excess of SubX® molecules in the solution results in aggregation of up to 10-15 exosomes and formation of micron-size particles that are easily precipitated in a brief 14K x g (or 30 min 2K x g) centrifugation step. A specially designed buffer allows for reconstitution of the pelleted exosomes back to monomer format for downstream applications. Flow cytometry with specific surface marker CD9 confirmed that SubX®-aggregated vesicles are exosomes. Analysis of membrane-bound protein markers and microRNA profile of exosomes isolated from plasma of prostate cancer patients will be presented. Difference in SubX® binding strength for cfDNA and exosomes allows for consequent isolation from the [cfDNA/exosomes- SubX®-magnetic particles] pellet first exosomes, then cfDNA. Eventually, we combined both approaches in one kit for isolation of cfDNA and exosomes from the same sample. This simultaneous isolation protocol is simple and fast, it allows to employ minimal volume of valuable bio samples as well as to reduce labor and cost. The kit was validated in serum and urine samples from patients with ovarian and pancreatic cancer. Exosome nature of isolated vesicles was confirmed by three independents methods - light scattering, immunological and electron microscopy. Thus, one could analyze both genetic (DNA and RNA) as well as protein markers present in the same liquid biopsy sample. Citation Format: Andrei G. Malykh, Anastasia Malek, Anna Lokshin, Vladimi