Potent Liver-Tropic mRNA Lipid Nanoparticles: ApoE-Mediated Delivery Through a Low-Density Lipoprotein Receptor Independent Uptake Mechanism.

The development of nucleic acid therapeutics using non-viral delivery systems requires efficient payload delivery to target organs for higher potency and tolerability. While lipid nanoparticle (LNP) formulations influence biodistribution, cellular uptake, and therapeutic efficacy, underlying mechanisms remain incompletely understood. This study develops potent mRNA-LNP formulations and investigates determinants of liver tropism using ornithine transcarbamylase (OTC) deficiency as a protein replacement therapy model. Systematic screening of ionizable and helper lipids, optimization of composition and process, and biophysical characterization identify a liver-tropic helper lipid-1,2-dierucoyl-sn-glycero-3-phosphoethanolamine (DEPE) that modulates LNP structure and apolipoprotein E (ApoE) binding, enhancing liver-specific delivery. Analysis of ionizable lipid chemistry reveals its role in cellular uptake mechanisms, leading to the identification of a novel ionizable lipid designed with N-(2-Hydroxyethyl)piperazine-N'-(4-butanesulfonic acid) (HEPBS) core that enables efficient delivery independent of the low-density lipoprotein receptor (LDLR) pathway. The optimized formulation achieves robust dose responsiveness, sustained therapeutic expression, and favorable tolerability in preclinical models. Therapeutic levels of OTC protein expression are observed with minimal toxicity, as indicated by stable liver function markers and cytokine levels. These findings provide mechanistic insights and establish a platform for mRNA-based protein replacement therapies, supporting broader applications in rare genetic diseases requiring hepatic gene expression.