Background

In the development of messenger RNA (mRNA) therapeutics and vaccines, technology that delivers drugs intact into the target cytoplasm is a key factor determining therapeutic efficacy. The currently widely used delivery vehicle is the Lipid Nanoparticle (LNP), and the primary component that drives in vivo delivery efficiency and endosomal escape after cellular uptake is the ionizable lipid. To maximize biocompatibility and delivery efficiency, a diverse pool of lipid scaffolds must be employed.

The realistic barrier lay in the process of synthesizing and discovering new lipid scaffolds. Conventional synthetic methods required multi-step chemical reactions and complex separation and purification processes, imposing significant time and cost burdens. Consequently, the diversity of available geological structures was limited, making it difficult to implement a high-throughput screening system capable of rapidly constructing and searching new libraries numbering in the thousands. There was an urgent need for alternative technologies that could resolve the synthesis bottlenecks of existing platforms and rapidly combine diverse molecular structures under mild conditions.

Key Discovery

Researchers have established a Photochemistry-based Ionizable Lipid Library (PILL) platform that utilizes visible light energy to synthesize lipid scaffolds in a single step. Based on irradiation with blue visible light at a wavelength of 427 nanometers (nm), they designed a one-pot multicomponent photochemical reaction that reacts three precursors—amine, aldehyde, and boronic acid—within a single vessel. The reaction proceeded smoothly in a mild, room-temperature environment without the need for complex heating or harsh catalytic conditions.

Based on this strategy, 275 types of new ionizable lipids containing $\alpha$-branched amine structures were synthesized in a short period. The researchers directly linked the process so that in vitro delivery efficiency screening at the cellular level could be performed immediately, bypassing separate separation and purification steps. By removing the purification bottleneck, they were able to rapidly evaluate the activity of hundreds of candidate compounds and quickly advance to the in vivo validation stage.

The lead candidate exhibiting the best delivery performance during the screening process was named A18B8C14. Comparative evaluation following administration to animal models demonstrated that the optimized A18B8C14-LNP formulation induces significantly higher in vivo gene expression than the existing commercial benchmark lipid, MC3-based LNP. It also met a favorable safety profile, without inducing significant signs of toxicity during the in vivo metabolic process. When integrated with the Selective Organ Targeting (SORT) strategy, tissue-specific control of lipid nanoparticles for targeted drug delivery to specific organs was successfully achieved.

Significance and Outlook

This study demonstrates that photochemical reactions can be practically applied to the discovery of lipid delivery vehicles, overcoming the limitations of classical organic synthesis. Through a highly reactive photochemical multicomponent coupling process, the diversity of molecular scaffolds was dramatically expanded, and the cycle for deriving candidate compounds was significantly shortened via a purification-free screening pipeline. It is expected to provide a solid foundation for research into rapidly designing customized vaccine formulations during new pandemic outbreaks or searching for treatments for rare genetic diseases.

However, establishing a photochemical fluidic reaction process that can uniformly scale up the synthesis efficiency of 275 types proven in laboratory-scale photochemical reactors to pilot and commercial production units remains a challenge. Maintaining particle stability during long-term storage and securing immunogenicity data in large animal models, such as primates, are also key challenges that must be verified before entering clinical trials. Subsequent engineering research is expected to continue, precisely extending long-term target specificity beyond the liver to fine tissues such as the heart and central nervous system.