Abstract

RNA therapeutics and mRNA vaccines have emerged as a promising class of medicines for the treatment of various diseases. The successful application of these modalities depends on the safe and effective delivery of mRNA into target cells. Lipid nanoparticle (LNP) is a novel carrier for delivery. Ionizable lipid is a key component of LNP and plays a crucial role in encapsulating and protecting mRNA molecules. Given the incorporation of novel carrier components, such as synthetic lipids, in LNPs, extensive preclinical biodistribution studies are essential to evaluate their in vivo exposure profiles. To assess the biodis- tribution of ionizable lipids, an analytical method using liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for the quantitation of ionizable lipids such as SM-102 and ALC-0315, enabling their precise quantification in biological matrices. The method was successfully established, demonstrating good selectivity, linearity (r 2  0.9950 over the range of 1- 2000 ng/mL), accuracy (ranging from 89.7% to 117.4% for SM-102, from 93.8% to 115.2% for ALC-0315), precision ( 19.7% for SM-102,  15.3% for ALC-0315), and a lower limit of quantification (1.0 ng/mL). This method is expected to contribute to the comprehensive evaluation of biodistribution for novel ionizable lipids in LNP formulations.