A lipid nanoparticle (LNP) composed of a series of disulfide bridge cleavable and pH-reponsive lipid-like materials (COATOSOME SS-E-P4C2) was developed as a platform of a gene delivery system. The LNP showed good stability in the serum. The tertiary amine and disulfide bridge of COATOSOME SS-E-P4C2 lead to destabilization of the endosomal membrane and for intracellular collapse. We would like to present our development of a hepatocyte-targeting siRNA carrier by the molecular tuning of the hydrophobic scaffold, and tertiary amine structures. The gene knockdown activity against a hepatocyte-specific marker (factor VII) was improved when a more fat-soluble vitamin (vitamin E) was employed as a hydrophobic scaffold. Moreover, to allow the tertiary amines to accept protons by sensing a slight change in endosomal acidification, its structural flexibility was minimized by fixing it in a piperidine structure, and the distance between the surface of the particle to the ternary amine was increased. As a result, the pKa value was increased to the approximately 6.18 depending on its distance, while the pKa reached plateau when the tertiary amine was linked by an excess number of linear carbon chains. The pH-dependent membrane destabilization activity, as assessed by a hemolysis assay, was increased in parallel with the pKa value. Moreover, the gene knockdown activity was improved in parallel with hemolytic activity. Finally, further optimization of the lipid/siRNA ratio, and the use of chemically (2′-fluoro) modified siRNA synergistically improved the gene knockdown efficacy to an effective dose (ED50) of 0.035 mg/kg. The developed COATOSOME SS-E-P4C2 represents a promising platform for use as a hepatocyte-targeting siRNA carrier.
Audience take away:
• How to optimize the chemical environment around amine groups of ionizable lipids in order to transfect nucleic acids into cells.
• How to utilize the difference in the redox-potential between the plasma and the cytoplasm for in-vivo delivery of nucleic acids.
• How to optimize the stability of lipid nanoparticles with RNA.
• The audience will learn how to design lipids for transfection and in-vivo delivery of nucleic acids.
• Specific targeting of nanoparticles to the liver after intravenous injection.
• Optimization of lipid nanoparticles for transfection of nucleic acids.
• Methods for in-vitro optimization of ionizable lipids for efficient complexation of nucleic acids and transfection.
• Strategies to develop biodegradable lipids with low toxicity.