Lipid S4

Lipid S4 is an advanced ionizable lipid engineered for systemic mRNA delivery to the brain, leveraging SR-57227—a high-affinity 5-HT3 receptor ligand—as its core head group to enable targeted blood-brain barrier (BBB) penetration via receptor-mediated transcytosis, while incorporating amino linkers for pH-responsive ionization and biodegradable branched ester tails to facilitate efficient endosomal escape and intracellular mRNA release; optimized through orthogonal screening into OS4 LNP (formulated at S4/DOPE/Chol/DMG-PEG2k = 40:40:60:0.75 molar ratio), it demonstrated a 13.3-fold increase in brain mRNA expression compared to FDA-approved MC3 LNPs, and further conjugation with the Tat cell-penetrating peptide yielded OS4T LNP, boosting delivery efficiency by 12.7-fold over OS4 alone and enabling broad mRNA expression across neurons, astrocytes, microglia, and endothelial cells; validated in orthotopic glioblastoma models, OS4T delivered engineered IL-12 mRNA, suppressing tumor growth and extending median survival to 37 days (vs. 17 days for controls) with minimal systemic toxicity, positioning S4-based LNPs as a robust, translatable platform for CNS-targeted therapeutics.