Background

Lipid nanoparticles (LNPs) have become a core technology for vaccines and therapeutics, delivering messenger RNA (mRNA) into cells to induce protein production. However, existing LNP systems still exhibit limitations, including low cell membrane permeability, insufficient safety, and physical instability during storage. In particular, cell-level experiments (in vitro) conducted in the early stages of drug discovery and animal-level experiments (in vivo) aimed at clinical translation require different particle characteristics. In cell culture experiments, rapid and robust protein expression is a priority, while in vivo administration prioritizes immune response control, targeted delivery to specific organs, and in vivo stability. Previously, both academia and industry attempted to address both areas with a single LNP composition, which led to reduced efficacy or unexpected toxicity. Therefore, research is actively underway to design delivery systems that are tailored to the intended use and target environment.

Key Findings

Recently, a domestic and international collaborative research team developed two complementary, customized delivery platforms with optimized compositions and structures to overcome the limitations of LNPs.

First, for cell culture LNPs, the existing cholesterol component was replaced with a plant-derived sterol compound, beta-sitosterol. Cryogenic transmission electron microscopy (Cryo-TEM) analysis successfully confirmed a unique internal fingerprint structure that is clearly distinguishable from existing particles. This structural change enhances the fusion efficiency with cell membranes, resulting in a more than 100-fold increase in intracellular protein expression compared to existing LNPs. However, beta-sitosterol LNPs did not enhance protein expression in the in vivo environment and showed a significant decrease in formulation stability, indicating that it is suitable as a tool for cell culture only.

For in vivo LNPs, a new strategy was adopted to introduce biocompatible vitamin molecules. The researchers chemically synthesized a total of eight vitamin-conjugated ionizable lipids and screened six candidate lipids with high potential efficacy in an animal model. The results confirmed that the two selected vitamin-based LNPs showed a significant advantage in in vivo target protein expression levels compared to commercially available LNPs. In addition, accelerated stability tests showed that it maintained better physical properties than existing formulations, demonstrating the possibility of long-term storage.

To verify the efficacy of the in vivo-optimized LNP as a vaccine formulation, mRNA encoding varicella-zoster virus (VZV) and respiratory syncytial virus (RSV) was loaded and administered to mice in an immunization experiment. The animal experiment showed that the customized LNP induced superior in vivo immunogenicity at a lower dose than the commercial delivery system. In addition, in vivo safety evaluation showed that the systemic toxicity and inflammatory side effects observed in the existing LNP administration group were significantly reduced, supporting the possibility of clinical application.

Significance and Prospects

This research provides a clue to shorten the development process of gene therapy drugs based on LNPs and improve safety. The diversified strategy that divides the roles of cell-based and in vivo-based LNPs has the potential to strengthen the connection between research results at the laboratory stage and the derivation of actual new drug candidates. However, in order for this platform to be expanded to the level of targeted delivery of mRNA to various organs and tissues, additional engineering steps are required to precisely control receptor binding ability. In addition, it is an important task in the future to verify whether the vitamin-conjugated ionizable lipids can maintain uniform particle size and quality in large-scale production processes and to optimize the large-scale production process.