SAXS/PCS study on the mesoscopic structure of lipid nanoparticle (LNP) formulations for mRNA drug delivery: Comirnaty and drug-free LNP dispersions

Lipid Nanoparticles (LNPs) produced by anti-solvent precipitation (ASP) are used in formulations for mRNA drug delivery. The mesoscopic structure of such complex multicomponent and polydisperse nanoparticulate systems is most relevant for their drug delivery properties, medical efficiency, shelf-life, and possible side effects. However, the knowledge on the structural details of such formulations is very limited. Essentially no such information is publicly available for pharmaceutical dispersions approved by numerous medicine agencies for the use in humans and loaded with mRNA encoding a mimic of the spike protein of the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) as e.g. the Comirnaty formulation (BioNTech). Here, we present a simple preparation method to mimic the Comirnaty drug-free LNPs including a comparison of their structural properties with those of Comirnaty. Strong evidence for the liquid state of the LNPs in both systems is found in contrast to the designation of the LNPs as solid lipid nanoparticles by BioNTech. A detailed structural model for the LNPs i.a. revealing their unexpected narrow size distribution will be presented based on SAXS, DLS, light microscopy, and ¹HNMR studies. The presented results should contribute to better understanding the LNP drug delivery process, enhancing their medical benefit, and reducing side effects.