title: Stabilization of Ostwald ripening in low molecular weight amino lipid nanoparticles for systemic delivery of siRNA therapeutics.
abstract: Lipid nanoparticles (LNPs) represent the most clinically advanced technology for the systemic delivery of therapeutic siRNA in vivo. Toward this end, a novel class of LNPs comprising low molecular weight (MW) ionizable amino lipids having asymmetric architecture was recently reported.1 LNPs of these amino lipids, termed asymmetric LNPs, were shown to be highly efficacious and well tolerated in vivo; advances were enabled by improved endosomal escape, coupled with enhanced amino lipid metabolism and clearance. In this work, we show that, in contrast to their desirable pharmacological performance, asymmetric LNPs present a significant pharmaceutical developability challenge, namely physical instability limiting extended shelf life. Using orthogonal characterization methods, we identify the mechanism of LNP instability as Ostwald ripening and establish it to be driven predominantly by the asymmetric amino lipid component. Through rational optimization of LNP physical and macromolecular properties, we are able to significantly attenuate or entirely eliminate the Ostwald ripening instability. Modulation of LNP size, for example, effectively halts particle growth. Similarly, optimization of LNP macromolecular packing through deliberate selection of structurally matched colipids significantly diminishes the rate of ripening. This later experimental observation is substantiated by molecular dynamics simulations of LNP self-assembly, which establish a quantitative dependence of LNP macromolecular order on colipid structure. In totality, the experimental and molecular dynamics outcomes of this work support the rational design of LNP physical and chemical properties leading to effective Ostwald ripening stabilization and enable the advance of asymmetric LNPs as a clinic-ready platform for siRNA therapeutics.
authors.affiliation: Department of Pharmaceutical Sciences, ‡Department of RNA Therapeutics, §Department of Chemistry Modeling and Informatics, and ∥Department of RNA Biology, Merck Research Laboratories, Merck and Co., Inc. , West Point, Pennsylvania 19486, United States.
authors.forename: Marian E
authors.initials: ME
authors.lastname: Gindy
authors.forename: Brad
authors.initials: B
authors.lastname: Feuston
authors.forename: Angela
authors.initials: A
authors.lastname: Glass
authors.forename: Leticia
authors.initials: L
authors.lastname: Arrington
authors.forename: R Matthew
authors.initials: RM
authors.lastname: Haas
authors.forename: Joseph
authors.initials: J
authors.lastname: Schariter
authors.forename: Steven M
authors.initials: SM
authors.lastname: Stirdivant
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D001055:Apolipoproteins B / Q000037:antagonists & inhibitors* / Q000235:genetics; D002850:Chromatography, Gel; D016503:Drug Delivery Systems; D005260:Female; D008055:Lipids / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D056004:Molecular Dynamics Simulation; D008970:Molecular Weight; D053758:Nanoparticles / Q000737:chemistry*; D010316:Particle Size; D012333:RNA, Messenger / Q000037:antagonists & inhibitors / Q000235:genetics; D034741:RNA, Small Interfering / Q000008:administration & dosage* / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D013499:Surface Properties
chemical_list: D000596:Amino Acids; D001055:Apolipoproteins B; D008055:Lipids; D012333:RNA, Messenger; D034741:RNA, Small Interfering
keywords: Ostwald ripening; drug delivery; lipid nanoparticle; molecular dynamics; siRNA