Identification of a Novel Small Molecule That Enhances the Release of Extracellular Vesicles with Immunostimulatory Potency via Induction of Calcium Influx.

Extracellular vesicles (EVs) transfer antigens and immunomodulatory molecules in immunologic synapses as a part of intracellular communication, and EVs equipped with immunostimulatory functions have been utilized for vaccine formulation. Hence, we sought small-molecule compounds that increase immunostimulatory EVs released by antigen-presenting dendritic cells (DCs) for enhancement of vaccine immunogenicity. We previously performed high-throughput screening on a 28K compound library using three THP-1 reporter cell lines with CD63 Turbo-Luciferase, NF-κB, and interferon-sensitive response element (ISRE) reporter constructs, respectively. Because intracellular Ca elevation enhances EV release, we screened 80 hit compounds and identified compound as a Ca influx inducer. enhanced EV release in murine bone marrow-derived dendritic cells (mBMDCs) and increased costimulatory molecule expression on the surface of EVs and the parent cells. EVs isolated from -treated mBMDCs induced T cell proliferation in the presence of antigenic peptides. To assess the roles of intracellular Ca elevation in immunostimulatory EV release, we performed structure-activity relationship (SAR) studies of . The analogues that retained the ability to induce Ca influx induced more EVs with immunostimulatory properties from mBMDCs than did those that lacked the ability to induce Ca influx. The levels of Ca induction of synthesized analogues correlated with the numbers of EVs released and costimulatory molecule expression on the parent cells. Collectively, our study presents that a small molecule, , enhances the release of EVs with immunostimulatory potency via induction of Ca influx. This agent is a novel tool for EV-based immune studies and vaccine development.