RNA-based therapeutics and vaccines represent a novel and expanding class of medicines, the success of which depends on the encapsulation and protection of mRNA molecules in lipid nanoparticle (LNP)-based carriers. With the development of mRNA-LNP modalities, which can incorporate xenobiotic constituents, extensive biodistribution analyses are necessary to better understand the factors that influence their in vivo exposure profiles. This study investigated the biodistribution of heptadecan-9-yl 8-((2-hydroxyethyl)(8-(nonyloxy)-8-oxooctyl)amino)octanoate (Lipid 5)-a xenobiotic amino lipid-and its metabolites in male and female pigmented (Long-Evans) and nonpigmented (Sprague Dawley) rats by using quantitative whole-body autoradiography (QWBA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques. After intravenous injection of Lipid 5-containing LNPs, ¹⁴C-containing Lipid 5 ([¹⁴C]Lipid 5) and radiolabeled metabolites ([¹⁴C]metabolites) were rapidly distributed, with peak concentrations reached within 1 hour in most tissues. After 10 hours, [¹⁴C]Lipid 5 and [¹⁴C]metabolites concentrated primarily in the urinary and digestive tracts. By 24 hours, [¹⁴C]Lipid 5 and [¹⁴C]metabolites were localized almost exclusively in the liver and intestines, with few or no concentrations detected in non-excretory systems, which is suggestive of hepatobiliary and renal clearance. [¹⁴C]Lipid 5 and [¹⁴C]metabolites were completely cleared within 168 hours (7 days). Biodistribution profiles were similar between QWBA and LC-MS/MS techniques, pigmented and nonpigmented rats, and male and female rats, excluding the reproductive organs. In conclusion, the rapid clearance through known excretory systems, with no evidence of redistribution for Lipid 5 or accumulation of [¹⁴C]metabolites, provides confidence for the safe and effective use of Lipid 5-containing LNPs. SIGNIFICANCE STATEMENT: This study demonstrates the rapid, systemic distribution of intact and radiolabeled metabolites of Lipid 5, a xenobiotic amino lipid component of novel mRNA-LNP medicines, and its effective clearance without substantial redistribution after intravenous administration; additionally, findings were consistent between different mRNAs encapsulated within LNPs of similar composition. This study confirms the applicability of current analytical methods for lipid biodistribution analyses, and taken together with appropriate safety studies, supports the continued use of Lipid 5 in mRNA-medicines.

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