Drying technologies for messenger RNA and other nucleic acid-lipid nanoparticles: advances in freeze-drying and beyond

Nucleic acid therapeutics have emerged as the third major class of therapeutics, following small molecules and antibodies. Lipid nanoparticles (LNPs) serve as the leading platform for nucleic acid delivery. The mRNA-LNPs showed clinical success in COVID-19 vaccines, but they suffer from ultra-low temperature storage requirement that limits global transportation and distribution. Drying technologies, especially freeze-drying, offer solutions to maintain stability at a higher temperature. This review highlights the intrinsic stability of mRNA-LNPs, the status of using freeze-drying for improving the stability of mRNA-LNPs, the potential challenges during freeze-drying, and the strategies for maintaining the stability of mRNA-LNPs during freeze-drying and storage. Beyond mRNA, we compare drying strategies for other nucleic acid-LNPs (NA-LNPs), including siRNA, saRNA, circRNA, pDNA, miRNA, and the CRISPR system, underscoring the impact of structure on the drying of these NA-LNPs. We also discuss alternative freeze-drying and drying methods, including continuous freeze-drying based on spin-freezing, thin film freeze-drying, spray freeze-drying, spray drying, and alcohol dilution freeze-drying, for improving stability and suitability for different routes of administration. Overall, this review provides insight for the development of a solid form of NA-LNPs with maintained stability and potency.