Positron Emission Tomography-Based Pharmacokinetics of mRNA–Lipid Nanoparticles: A Study Quantifying the ApoE and Macrophage Contribution

It is important to clarify the pharmacokinetics of mRNA-loaded lipid nanoparticles (mRNA-LNPs), which have attracted attention as new pharmaceutical modalities for vaccines and therapeutic agents against various diseases. Positron emission tomography (PET) is expected to provide data to ensure the pharmacokinetics of mRNA-LNPs early after administration in detail, especially because of its high temporal resolution. In this study, we have developed a method for the preparation of ⁶⁴Cu-labeled mRNA-LNPs by an approach via hybridization of short oligonucleotides to the 3' UTR region of mRNA, and conducted PET pharmacokinetic studies in normal and functionally deficient mice after intravenous and intramuscular administration, which mainly yielded the following findings. First, the common composition of mRNA-LNPs showed a clearly separated two-step accumulation process in the liver after intravenous administration in normal mice, indicating the involvement of ApoE in the second step. Second, after intravenous administration, the time to protein corona formation, in which blood proteins bind to mRNA-LNPs, was found to be within 5-10 min. Third, liver and spleen clearance was determined using integration plot analysis, and the contribution of hepatocyte uptake via ApoE to hepatic clearance after intravenous administration was approximately twice that of Kupffer cell uptake. Fourth, a comparison with luciferase reporter protein expression suggested that the protein expression ability of hepatocytes taken up via ApoE after intravenous administration and that of antigen-presenting cells transferred to the lymph nodes after intramuscular administration was remarkably high.