In recent years, RNA interference (RNAi) therapeutics, most notably with lipid nanoparticle-based delivery systems, have advanced into human clinical trials. The results from these early clinical trials suggest that lipid nanoparticles (LNPs), and the novel ionizable lipids that comprise them, will be important materials in this emerging field of medicine. A persistent theme in the use of materials for biomedical applications has been the incorporation of biodegradability as a means to improve biocompatibility and/or to facilitate elimination. Therefore, the aim of this work was to further advance the LNP platform through the development of novel, next-generation lipids that combine the excellent potency of the most advanced lipids currently available with biodegradable functionality. As a representative example of this novel class of biodegradable lipids, the lipid evaluated in this work displays rapid elimination from plasma and tissues, substantially improved tolerability in preclinical studies, while maintaining in vivo potency on par with that of the most advanced lipids currently available.

Significance The safe, selective, and efficient delivery of siRNA is a key challenge to the broad application of siRNA therapeutics in humans. Motivated by the structure of lipoproteins, we developed lipopeptide nanomaterials for siRNA delivery. In vivo in mice, siRNA–lipopeptide particles provide the most potent delivery to hepatocytes (ED 50 ∼ 0.002 mg/kg for FVII silencing), with the highest selectivity of delivery to hepatocytes over nontarget cell types (orders of magnitude), yet reported. These materials also show efficacy in nonhuman primates.

Formulation of short interfering RNA (siRNA) into multicomponent lipid nanoparticles (LNP) is an effective strategy for hepatic delivery and therapeutic gene silencing. This study systematically evaluated the effect of polyethylene glycol (PEG) density on LNP physicochemical properties, innate immune response stimulation, and in vivo efficacy. Increased PEG density not only shielded LNP surface charge but also reduced hemolytic activity, suggesting the formation of a steric barrier. In addition, increasing the PEG density reduced LNP immunostimulatory potential as reflected in cytokine induction both in vivo and in vitro. Higher PEG density also hindered in vivo efficacy, presumably due to reduced association with apolipoprotein E (ApoE), a protein which serves as an endogenous targeting ligand to hepatocytes. This effect could be overcome by incorporating an exogenous targeting ligand into the highly shielded LNPs, thereby circumventing the requirement for ApoE association. Therefore, these studies provide useful information for the rational design of LNP-based siRNA delivery systems with an optimal safety and efficacy profile.

The successful formulation of itraconazole and odanacatib into nanoparticle form with diameters of 145 and 350 nm, respectively, using rapid, block copolymer-directed precipitation is presented. These are the smallest stable nanoparticles that have been reported for these compounds. The difference in size of the nanoparticles for the two compounds is explained by the difference in nucleation rate and its dependence on supersaturation. The conditions for stability after formation are presented: storage at 5 degrees C and removal of residual processing solvent. These requirements are explained in terms of solute solubility and its dependence on both temperature and solvent concentration. The theory of Ostwald ripening provides the framework for understanding the differences in stability observed for the two compounds. The dynamics of the hydrophobic polymer block plays a major role in long-term stability as demonstrated by the behavior of nanoparticles stabilized by poloxamer vs polystyrene-b-polyethylene oxide polymers.