Exploration of mRNA nanoparticles based on DOTAP through optimization of the helper lipids

Lipid nanoparticles (LNPs) are one of the most efficient carriers for RNA packaging and delivery, and vaccines based on mRNA‐LNPs have received substantial attention since the outbreak of the COVID‐19 pandemic. LNPs based on 1,2‐dioleoyl‐3‐trimethylammonium propane (DOTAP) have been widely used in preclinical and clinical settings. A novel non‐viral gene delivery system called LNP3 was previously developed, which was composed of DOTAP, 1,2‐dioleoyl‐sn‐glycero‐3‐phosphoethanolamine (DOPE), and cholesterol. One of the helper lipids in this carrier was DOPE, which belongs to phospholipids. Given that substituting DOPE with non‐phospholipids as helper lipids can increase the delivery efficiency of some LNPs, this study aimed to examine whether non‐phospholipids can be formulated with DOTAP as helper lipids. It was found that monoglycerides with C14:0, C16:0, C18:0, C18:1, and C18:2 mediated mRNA transfection, and the transfection efficiency varied between C18:0, C18:1, and C18:2. Furthermore, substituting of the glycerol with other moieties such as the cholesterol or the ethanolamine similarly mediated mRNA transfection. The introduction of cholesterol can further improve the transfection capacity of some DOTAP‐based LNPs. One of the best‐performing formulations, LNP3‐MO, was used to mediate luciferase‐mRNA expression in vivo, and the luminescence signal was found to be mainly enriched in the lung and spleen. In addition, the level of SARS‐CoV‐2 spike antibody in the serum increased after three doses of LNP3‐MO mediated SARS‐CoV‐2 spike mRNA. Altogether, this study demonstrates that non‐phospholipids are promising helper lipids that can be formulated with DOTAP to facilitate efficient delivery of mRNAs in vitro and in vivo with organ‐specific targeting. Graphical and Lay Summary Non‐phospholipid‐based lipids such as MO can be promising helper lipids formulated with DOTAP to mediate efficient delivery of mRNA in vitro and in vivo with organ‐specific targeting. It was found that the complete replacement of previous helper lipids with an array of non‐phospholipid‐based lipids formulated with DOTAP caused improvement delivery efficacy of mRNA and LNP3‐MO was one of the most efficient formulations in vitro. LNP3‐MO was used to mediate luciferase‐mRNA expression in vivo, and the luminescence signal was mainly enriched in the lung and spleen and the level of SARS‐COV‐2 spike antibody in sera increased after three doses of LNP3‐MO mediated SARS‐COV‐2 spike mRNA. There