Clinical lipid-nanoparticle (LNP) predominately targets the liver upon systemic administration, which significantly limited the general application of IVT-mRNA as a systemic therapy. Current approach to enhance the extra-hepatic delivery of mRNAs focuses on tuning the apparent pKa of LNPs, which can direct selective mRNA expression in the spleen and lung. However, the apparent pKa does not predict the organ selectivity of some benchmark LNP systems, such as SM-102. Recent studies from us and others also revealed contradictory results between the apparent pKa and LNP’s organ selectivity. The lipophilicity of nanoparticles can affect their interactions with serum proteins such as Apolipoprotein E (ApoE), which mediates the liver-targeting of systemically administrated LNPs. In this study, we hypothesize that the lipophilicity of LNPs, together with their apparent pKa, can direct the extra-hepatic delivery of mRNAs. To test this hypothesis, we rationally designed a library of dendrimer-based LNPs (dLNPs) with different lipophilicities by changing levels of lipids grafted to the dendrimer surface (dendrimers with 100%, 50%, or 0% lipid grafting). Using a hydrophobic fluorescence probe-based assay, we showed that the dLNPs with 100% lipid grafting (100% series) have higher hydrophobicity than dLNPs with 50% lipid grafting (50% series). 100% series dLNPs showed liver-selective mRNA expression, while the 50% series dLNPs showed spleen-selective mRNA expression. In the meantime, increasing the apparent pKa of the dLNPs enhances mRNA expression in the spleen while reducing expression in the liver. Further mechanism study reveals a fundamental difference in the surface structures and protein corona composition for the 100% and 50% series dLNPs. Guided by this mechanistic discovery, we designed 9 patentable low-hydrophobicity mRNA formulations with superior in vivo splenic or lung transfection than clinical LNPs. Implemented in clinics, this delivery platform can be used for targeted delivery of therapeutic RNAs to spleens for the treatment of a wide spectrum of immune-related disorders.
Learning Objectives:
Upon completion, participants will be able to learn the status quo of the approach to modulate the organ-selective mRNA expression.
Upon completion, the participant will be able to learn how lipid nanoparticle hydrophobicity and apparent pKa both affect their tissue tropism
Upon completion, participants will be able to understand endogenous mechanisms that mediate the lipid nanoparticles biodistribution in the liver, spleen, and lung.
