4A3-LNSC8 is a strategically designed thiourea-functionalized ionizable lipid that serves as the foundational core for a novel anion-coordination delivery platform. Its structure features a central 4A3 amine headgroup symmetrically extended with four hydrophobic tails, each incorporating a biodegradable ester linkage and a key thiourea-bridged linker. The inclusion of the thiourea group is the pivotal innovation, as it provides specific hydrogen-bonding sites capable of interacting with various halide anions (F⁻, Cl⁻, I⁻). When formulated into lipid nanoparticles (LNPs) without anion coordination, 4A3-LNSC8 itself exhibits a characteristic liver tropism, efficiently delivering mRNA to hepatocytes following systemic administration, with a measured surface pKa of approximately 5.54. However, its primary significance lies in its role as a versatile precursor. The strong anion-binding capability of its thiourea linkers allows for predictable modulation of the LNP's properties. Upon binding with anions like Cl⁻, the resulting complex (e.g., Cl-4A3-LNSC8) undergoes a significant pKa shift, which reprograms the LNP's in vivo fate, redirecting mRNA delivery from the liver to secondary lymphoid organs such as the spleen and lymph nodes. Thus, 4A3-LNSC8 is not merely an efficient ionizable lipid but a programmable scaffold that enables precise control over organ-targeting specificity through simple anion coordination, offering a powerful rational design strategy for advanced mRNA therapeutics.
