Comparing exosome-like vesicles with liposomes for the functional cellular delivery of small RNAs

Exosome-like vesicles (ELVs) play an important role in intercellular communication by acting as natural carriers for biomolecule transfer between cells. This unique feature rationalizes their exploitation as bio-inspired drug delivery systems. However, the therapeutic application of ELVs is hampered by the lack of efficient and reproducible drug loading methods, in particular for therapeutic macromolecules. To overcome this limitation, we present a generic method to attach siRNA to the surface of isolated ELVs by means of a cholesterol anchor. Despite a feasible uptake in both a dendritic and lung epithelial cell line, B16F10- and JAWSII-derived ELVs were unable to functionally deliver the associated small RNAs, neither exogenous cholesterol-conjugated siRNA nor endogenous miRNA derived from the melanoma producer cell. The latter results were confirmed both for purified ELVs and ELVs delivered via a transwell co-culture set-up. In contrast, simple anionic fusogenic liposomes were able to induce a marked siRNA-mediated gene knockdown under equal experimental conditions, both indicating successful cytosolic delivery of surface-bound cholesterol-conjugated siRNA and further underscoring the incapacity of the here evaluated ELVs to guide cytosolic delivery of small RNAs. In conclusion, we demonstrate that a more in-depth understanding of the biomolecular delivery mechanism and specificity is required before ELVs can be envisioned as a generic siRNA carrier.