Biodegradable lipid nanoparticles induce a prolonged RNA interference-mediated protein knockdown and show rapid hepatic clearance in mice and nonhuman primates

Abstract Lipid nanoparticles based on ionizable lipids have been clinically validated as a means of delivery for RNA interference (RNAi) therapeutics. The ideal properties of RNAi carriers are efficient delivery of oligonucleotides into target cells and rapid elimination after the function is performed. Here, we report that degradable lipid nanoparticles are effective carriers of small interfering RNA (siRNA) and have a high therapeutic index. The newly developed degradable lipid nanoparticles carrying siRNA showed potent gene-silencing activity in mouse hepatocytes (ED 50  ≈ 0.02 mg/kg siRNA). The ester bond in the lipid tail was hydrolyzed in the liver, resulting in rapid metabolism of the lipid. Toxicity assays showed that the degradable lipid was well-tolerated at siRNA doses of up to 16 mg/kg in rats (over 800-fold higher than ED 50 ). A single intravenous injection of siRNA targeting proprotein convertase subtilisin/kexin type 9 (PCSK9) in cynomolgus monkeys resulted in more than 90% protein silencing, and a 50% decrease in plasma low-density lipoprotein (LDL) cholesterol, with a measurable reduction for 2 months. Moreover, quantification of lipids in liver biopsies revealed rapid hepatic clearance of the degradable lipid in nonhuman primates. These degradable lipid nanoparticles with a high therapeutic index hold promise for RNA-based treatments.