Dynamic carriers for therapeutic RNA delivery

Abstract

Carriers for RNA delivery must be dynamic, first stabilizing and protecting therapeutic RNA during delivery to the target tissue and across cellular membrane barriers and then releasing the cargo in bioactive form. The chemical space of carriers ranges from small cationic lipids applied in lipoplexes and lipid nanoparticles, over medium-sized sequence-defined xenopeptides, to macromolecular polycations applied in polyplexes and polymer micelles. This perspective highlights the discovery of distinct virus-inspired dynamic processes that capitalize on mutual nanoparticle-host interactions to achieve potent RNA delivery. From the host side, subtle alterations of pH, ion concentration, redox potential, presence of specific proteins, receptors, or enzymes are cues, which must be recognized by the RNA nanocarrier via dynamic chemical designs including cleavable bonds, alterable physicochemical properties, and supramolecular assembly-disassembly processes to respond to changing biological microenvironment during delivery.

Keywords: LNP; RNA; lipoplex; polyplex; synthetic virus.

Fig. 1.

LNPs—(A) Examples for cationizable lipids, lipidoids, and lipopeptides, containing cationizable tertiary amines (highlighted in blue). (B) Interaction of cationized lipids with endosomal membrane lipids, leading to endosomal escape. Image credit: Created with BioRender.com.

Fig. 2.

VIPER. (A) Endosomal pH-responsive methacrylate copolymer VIPER. (B) Upon endosomal protonation, the hydrophobic diisopropylamino domain is solubilized, exposing the membrane bilayer disruptive peptide melittin, which promotes release into the cytosol. Reproduced from Cheng et al. (95) with permissions of John Wiley and Sons. 2016 Wiley-VCH Verlag GmbH & CO. KGaA, Weinheim.

Fig. 3.

CARTs. Mechanism of polyplex disassembly and release of mRNA by carrier degradation. Reproduced from Blake et al. (104) with permission of the American Chemical Society. 2023 ACS Publications, Washington D.C.

Fig. 4.

T-shaped lipo-OAAs for siRNA, sgRNA, and mRNA delivery. Optimization by structural variations both in backbone and side chains (dashed lines indicate optional incorporations/variations of distinct motifs). C, cysteine; FA, fatty acid; H, histidine; K(N₃), azido-lysine; LinA, linoleic acid; NonOcA, 8-nonanamido octanoic acid; OHSteA, hydroxystearic acid (hydroxyl group at position C9 or C10); OleA, oleic acid; Y₃, tyrosine-tripeptide; ssbb, cystamine disulfide building block; Stp, succinoyl tetraethylene pentamine. Image credit: Created with BioRender.com.

Fig. 5.

Double pH-responsive lipo-xenopeptides as molecular chameleons. (A) LAF-Stp carriers with both apolar (LAF) and polar (Stp) cationizable units. (B) pH-tunable polarity mediated by tertiary amines results in structural and physicochemical changes, evidenced by a drastic change in the logD value. (C) Effective U-shape and B2-bundle topologies. (D) Hypothetical mechanisms of endosomal escape of lipopolyplexes formed with LAF-Stp carriers. LAF, lipo amino fatty acid; Stp, succinoyl tetraethylene pentamine. Image credit: Created with BioRender.com.