Enhanced Intramuscular mRNA Activity of Peptide-Lipid Nanoparticles with Hydrophobized Head Groups

A library of xenopeptide-based ionizable lipids (XP-ILs) was evaluated in mRNA lipid nanoparticles (LNPs) to investigate the impact of modifications within the polar oligoamine headgroup. Modifications included hydrophobic or bulky side chains or a reduced number of protonatable amines. The resulting XP-ILs were characterized by their key physicochemical properties (logD, logP, HLB, CMC), which were correlated with LNP transfection efficiency and cytotoxicity. The inverse relationship between computational logP and experimental logD_5.5 is consistent with the HLB, indicating a lower tendency for water-in-oil micelle formation in carriers with larger hydrophobic headgroups. Four-tailed oleic acid (OleA)₄-XP-ILs strongly benefited from a cyclohexyl substituent in the polar ionizable headgroup. Hydrophobization of already highly effective bundle-shaped lipoamino fatty acid (LAF)₄-XP-ILs moderately improved efficiency. Notably, intramuscular LNP administration resulted in enhanced in vivo mRNA activity of hydrophobized carriers over previous lead compounds, LAF₄-XP (2-fold) and OleA₄-XP (12-fold).