Whole-Body Pharmacokinetics of Ionizable Lipid, mRNA, and the Expressed Antibody following Intravenous Administration of mRNA-Loaded Lipid Nanoparticles

Lipid nanoparticles (LNPs) containing mRNA that encodes therapeutic proteins have emerged as a promising therapeutic modality for a myriad of diseases. However, the pharmacokinetic (PK) relationships between the nanoparticle carrier, its mRNA payload, and the expressed protein remain poorly understood. Here we have investigated whole-body PK of these components in mice following intravenous administration of an mRNA-LNP that expresses a non-cross-reactive monoclonal antibody. LNPs encapsulating mRNA were prepared via microfluidic mixing and characterized for physicochemical properties and encapsulation efficiency. Following a single intravenous administration of mRNA-LNP, blood, plasma, and tissues were collected for PK measurement over 2 weeks. Ionizable lipid (i.e., ALC-0315) concentrations were determined using LC-MS, mRNA concentrations were measured using qPCR, and the expressed antibody concentrations were determined using ELISA. It was found that each component exhibited a distinct PK profile. For example, lipid exposure was highest in liver and spleen, while mRNA accumulation peaked in spleen and heart. Strikingly, the expressed antibody demonstrated a distribution pattern that did not mirror mRNA exposure, with the lung showing the greatest antibody levels despite only modest mRNA delivery. Tissue-to-plasma ratios for the expressed antibody exceeded values reported for intravenously administered antibodies, suggesting localized production or enhanced retention following in situ translation. These findings highlight that functional protein exposure is governed by tissue-specific translational efficiency and protein properties, rather than just nanoparticle delivery. The comprehensive PK data presented here also provides a foundation for the development of systems-based PK models for antibody expressing mRNA-LNPs.