Extracellular vesicles (EVs) are biological nanoparticles that transfer proteins and nucleic acids between cells and have great potential as tunable therapeutic delivery vehicles; they are relatively easy to engineer, well-tolerated in vivo, and naturally capable of intracellular delivery of functional biomolecules. In order for this promise to be realized, robust and general methods for delivering therapeutic cargo molecules via EVs and targeting therapeutic EVs to specific destinations in vivo are required.
Although EVs are known to load native RNAs and deliver them to recipient cells, functional delivery of exogenous cargo molecules has proven challenging. Many questions remain, including how the cargo of endocytosed EVs is released into the cytoplasm, and how this process can be enhanced. The degree to which RNAs loaded into EVs are intact and functional is also not fully understood. To answer these questions, we investigated functional RNA delivery by EVs with or without expression of the membrane fusion-inducing viral protein, VSVG. We found that expression of VSVG enhanced RNA delivery by EVs. We also investigated the relationship between RNA levels (intact or fragmented) in EVs and functional delivery to recipient cells and determined that increased intact RNA loading does not necessarily lead to increased expression in recipient cells. We determined the time course over which EV-delivered RNAs are expressed in recipient cells and found significant expression of EV-delivered RNA over 48 hours. Altogether, we have developed a system for robust EV-mediated delivery of functional RNA to recipient cells and investigated the details of this system allowing for optimal RNA delivery by EVs.
To enhance delivery of therapeutic EVs to target recipient cells, we have also developed a technology for enhancing the display of targeting ligands on the exterior of EVs. Previous attempts to target EVs to specific recipient cells have been hindered by inconsistent targeting using different ligands or different EV-producing cell types. We determined that degradation of targeting peptides by endosomal proteases occurs during EV biogenesis. To overcome this challenge, we have developed a glycosylation strategy that protects peptides from degradation while maintaining their ability to bind target proteins. We applied this peptide targeting strategy to achieve enhanced delivery of EVs to neuroblastoma cells. The tools we have developed enable programming EVs for targeted delivery of RNA cargos in a robust and straightforward manner that can be applied to a wide variety of therapeutic targets.