2024 AIChE Annual Meeting

Lipid Nanoparticle Modifications for Improved mRNA Delivery through Microneedle Patches

mRNA is a powerful technology developed for a diverse set of uses, such as vaccination, cancer treatment, and protein therapeutics.1 The development of lipid nanoparticles (LNPs) has aided in the delivery of mRNA into cells, but intramuscular injection of liquid LNP formulations poses a challenge, as they are not stable at low temperatures and require extensive resources for distribution and administration.2 Microneedle patches (MNPs) are arrays of micron-scale needles made from dissolvable polymers used to delivery therapeutics transdermally, and they offer a viable solution.3 MNPs are less painful, are easier to transport, store, and administer, and may increase thermostability compared to intramuscular injection.3 However, research pertaining to drying LNP formulations for MNP use is limited, and initial tests determined that LNPs are destabilized during MNP manufacturing. Optimizing LNP design may improve the stability and functionality of LNPs for mRNA delivery in an MNP.

Nanoluciferase encoding mRNA was formulated into LNPs using microfluidic mixing. LNP composition included ionizable lipid SM-102, cholesterol, DMG-PEG2000, and distearoylphosphatidylcholine at various molar ratios, with 50:38.5:1.5:10 used as a positive control to mimic Moderna’s SpikeVax COVID vaccine LNP formulation. LNPs were then mixed into a solution of 6.25% polyvinyl alcohol and 10% sucrose, dried under a vacuum in PDMS molds, and backed with epoxy to make MNPs. The dried MNPs were reconstituted in phosphate-buffered saline and evaluated for size using dynamic light scattering, encapsulation efficiency (EE) using Ribogreen assay, and in-vitro cellular expression in a RAW 264.7 cell line.

A variety of lipid molar ratios were screened to determine their effect on LNP stability during the MNP fabrication process. Increasing SM-102 had a stabilizing effect on MNPs, indicated by small LNP size, high EE, and high cellular expression post-drying. Increasing distearoylphosphatidylcholine content had a destabilizing effect. Increasing cholesterol content or DMG-PEG2000 content did not have a significant effect on markers of stability. The mass ratio of lipid: mRNA was also modified to improve the function and biophysical characterization of dried LNPs ranging from 20:1 to 100:1. Increasing mass ratios to 50:1 and 75:1 generated high cellular expression in particles but had minimal effect on EE and size. Large mass ratios decrease the loading capacity of mRNA in MNPs, which is undesirable in a low-dose MNP. Finally, phospholipids were screened, and initial data suggest that positively charged DOTMA increases in vitro expression before and after MNP manufacturing.

Modifications to LNP molar and mass ratios suggest an improvement in MNP drying stability. Additional formulation optimization can improve the function of LNPs post-drying. Future directions of this work include investigating the effect of ionizable lipid identity on stability and further investigations of alternate phospholipids.

References:

1. Schlake, T., Thess, A., Fotin-Mleczek, M., & Kallen, K.-J. (2012). Developing mrna-vaccine technologies. RNA Biology, 9(11), 1319–1330. https://doi.org/10.4161/rna.22269

2. Wilson, B., & Geetha, K. M. (2022). Lipid nanoparticles in the development of mrna vaccines for COVID-19. Journal of Drug Delivery Science and Technology, 74, 103553. https://doi.org/10.1016/j.jddst.2022.103553

3. Prausnitz, M. R. (2017). Engineering microneedle patches for vaccination and drug delivery to skin. Annual Review of Chemical and Biomolecular Engineering, 8(1), 177–200. https://doi.org/10.1146/annurev-chembioeng-060816-101514