Background

With the rapid growth of the gene therapy and vaccine markets, the value of lipid nanoparticles (LNPs), which serve as key delivery vehicles, is also increasing. However, designing the optimal chemical composition to accurately deliver and release genetic material to target cells is a highly complex process. In the past, academia has relied heavily on invasive methods to verify the delivery efficiency of LNPs, sacrificing experimental animals and directly grinding up organ tissues such as the liver and spleen to measure drug accumulation. This approach has been criticized for only showing that the delivery vehicle, the LNP, has simply moved to a specific organ, making it difficult to reflect whether the genetic material is actually released and decoded to synthesize proteins within the cytoplasm, which is 'functional delivery'. Furthermore, due to the physiological differences between mice and non-human primates (NHPs), the phenomenon of interspecies barriers, in which particles that show excellent results in mouse experiments become useless in NHPs or humans, is frequently observed. Large-scale efficacy trials in NHPs involve ethical concerns regarding animal welfare and astronomical costs, making them a major barrier in the early candidate screening stage.

Key Findings

The joint research team from Georgia Institute of Technology and Emory University in the United States has developed snapCode, a non-invasive barcoding technology that directly measures the expression efficiency of nanomedicines through blood analysis, to solve these challenges. The research team adopted a design in which they inject each LNP with mRNA for expressing a fusion protein in which a self-labeling protein, snap-tag, is combined with secreted nanoluciferase (secNluc), which is secreted outside the cell. At the same time, each particle formulation was given a unique DNA barcode, and a benzylguanine (BG) molecule, which causes a chemical reaction with the snap-tag at the barcode end, was conjugated. When the LNP enters the cell and induces mRNA translation, the snap-tag protein is produced, and this protein forms a stable protein-DNA complex by forming a covalent bond with benzylguanine. This complex is then released into the bloodstream and circulates throughout the body. The researchers administered six different LNPs intravenously to mice and NHPs and then collected blood to verify their efficacy. As a result of analyzing the DNA barcode of the complex in the serum using next-generation sequencing (NGS), it was found that the number of secreted barcodes closely matched the actual mRNA delivery and protein expression levels of each LNP.

Significance and Prospects

This study is considered an alternative that can alleviate the chronic interspecies barrier problem, in which nanomedicines that have shown good efficacy in animal studies fail in clinical trials. Above all, by adopting a non-invasive method, it is now possible to continuously track the delivery efficacy over time with experiments on only one NHP. Unlike the past, there is no need to euthanize animals at each measurement point, which greatly increases the flexibility of the experimental design. It is also welcomed as a useful tool for practicing ethical obligations in research by significantly reducing the number of experimental animals sacrificed in the drug development process. However, this platform does not solve all existing limitations. Due to the nature of quantifying the barcode that has leaked into the bloodstream, it is difficult to perfectly depict the long-term in vivo safety of the drug or the precise cellular distribution within the target organ. In addition, there are concerns that the externally derived snap-tag protein may cause adverse reactions or trigger an immune response in NHPs upon repeated administration, so follow-up studies on this should be conducted in the pre-clinical stage.