ALC-0315

ALC-0315 is an ionizable cationic lipid and a key component of lipid nanoparticle (LNP) formulations designed to deliver mRNA and other nucleic acids. Its molecular structure comprises a tertiary amine bearing a hydroxybutyl substituent and two hydrophobic branched tails, each linked to the amine through a hexyl spacer and an ester bond.

The amine remains predominantly neutral at physiological pH but becomes protonated in acidic environments. This pH-dependent ionization enables efficient encapsulation of nucleic acids during LNP formulation and facilitates their release following endosomal uptake. The biodegradable ester linkages also provide a defined route for metabolic degradation after delivery.

ALC-0315 is the ionizable lipid used in the Pfizer–BioNTech COVID-19 mRNA vaccine and has become a widely accepted benchmark for mRNA–LNP systems. It is typically incorporated into a four-component formulation alongside a helper phospholipid, cholesterol, and a PEG-lipid, in applications such as mRNA delivery, vaccine development, and comparative studies with other ionizable lipids, including SM-102 and DLin-MC3-DMA.

The saturated lipid tails of ALC-0315 make it considerably less prone to oxidative degradation than dilinoleyl-based lipids. Nevertheless, oxidation of the tertiary amine and the resulting formation of N-oxide impurities remain important quality concerns. These oxidation products may interact with encapsulated mRNA and adversely affect its expression.