Click Chemistry-Mediated Surface Protein Assay for Quantifying Subpopulations of Hepatocellular Carcinoma-associated Extracellular Vesicles

Hepatocellular carcinoma (HCC) accounts for 80-85% of primary liver cancers, and mainly occurs in patients with liver cirrhosis or chronic hepatitis B virus (HBV) infection. Prognosis of HCC is dismal primarily due to advanced stage of disease at diagnosis. Current clinical practice guidelines recommend HCC surveillance by biannual liver ultrasound with/without serum alpha-fetoprotein (AFP) for at-risk patients to achieve the goal of detecting HCC at a curative stage. However, their accuracy remains relevantly low with sensitivity between 6070% at a specificity of 90%. As such, novel biomarkers for early detection of HCC are still desperately needed. Extracellular vesicles (EVs) are a heterogeneous group of lipid nanoparticles that are released by all types of cells, and even more so by tumor cells and those cells within tumor microenvironment. Tumor-associated EVs are present in circulation at relatively early stages of disease and are readily accessible across all disease stages. Since the surface proteins of tumor-associated EVs could mirror those of the parental tumor cells and those cells within tumor microenvironment, exploiting the diagnostic potential of HCC-associated EVs’ surface protein signatures as a novel biomarker for early detection of HCC holds great promise to significantly augment the ability of current diagnostic modalities. We propose an HCC EV Surface Protein Assay (SPA) to quantify subpopulations of HCC-associated EVs for detecting early-stage HCC. The proposed HCC EV SPA couples two powerful technologies: Click Chemistrymediated EV Click Beads for isolating different subsets of HCC-associated EVs, and downstream 4-plex realtime immuno-PCR for quantification of the isolated subsets of HCC EVs. One of the major challenges emerging in the field of EV utilization for clinical use is the lack of robust and reproducible methods for the isolation of subpopulations of tumor-associated EVs. Conventional methods for isolating EVs, such as ultracentrifugation, filtration, and precipitation, are incapable of isolating subpopulation of tumor-associated EVs from total EVs. New research efforts have been devoted to exploring immunoaffinity-based capture techniques for enriching tumorassociated EVs from the plasma samples of patients with different solid tumors. However, there are challenges identified for the single antibody-mediated tumor-derived EV enriching approaches, such as limited sensitivity/specificity and a need for multiple capture antibodies to overcome the tumor heterogeneity. In order to address these concerns, our research team developed HCC EV SPA, which combines a click chemistrymediated tumor-associated EV isolation, and downstream 4-plex real-time immuno-PCR. HCC EV SPA is capable of highly sensitive and specific quantification of 32 subpopulations of HCC EVs in patients’ plasma samples, based on the combined use of 8 different HCC-associated surface protein markers and four EV surface markers. The long-term goal of this R01 proposal is to develop, refine, and validate the HCC EV SPA for detecting early-stage HCC from at-risk liver cirrhotic patients by quantifying subpopulations of HCC EVs.