UC San Diego

Plant virus-based nanoparticles (VNPs) offer a bio-inspired approach to the delivery of drugs and imaging agents. The chemical addressability, biocompatibility, and scalable manufacturability make VNPs a promising alternative to synthetic delivery platforms. However, proteinaceous VNPs and synthetic nanoparticles (NPs) alike are readily recognized and cleared by critical defense mechanisms such as opsonization and phagocytosis by cells of the mononuclear phagocytic system (MPS) when systemically administered. Here, I investigate if polyethylene glycol (PEG) coatings on tobacco mosaic virus (TMV) as a model nanocarrier system impart ‘stealth’ properties in vitro. Specifically, I evaluated the effects of linear and multivalent PEG coatings at varying chain lengths on serum protein adsorption, antibody recognition, and macrophage uptake. Linear and multivalent PEGs of MW 2000 and 5000 Da were successfully grafted onto TMV at ~20-40% conjugation efficiencies, and the degree of crosslinking as a function of PEG arm valency and length was outlined. While linear and 4-arm PEG coatings on TMV showed a significant reduction (> 7-fold) in macrophage uptake, the bivalent PEG 2000 coating did not, highlighting the impact of PEG conformation and length in ‘stealthing’ NPs. PEGylation altered the composition of the hard protein corona formed around TMV and reduced the adsorption of complement proteins and immunoglobulins. Furthermore, linear and multivalent PEG 5000 formulations reduced α-TMV antibody recognition, while shorter, multivalent PEG coatings significantly reduced α-PEG recognition – this highlights an interesting interplay between the NP and PEG itself in potential antigenicity and should be an important consideration in PEGylation strategies. Lastly, I report that PEGylated TMV formulations were stable for at least a week at body temperature and 24 hours in organic solvents further supporting TMV’s potential as a nanocarrier platform. This work provides insight in PEGylation strategies of VNPs which may improve their possibility of implementation in clinical applications.