Bioinspired Lipid Nanocarriers for RNA Delivery

Abstract

RNA therapy is a disruptive technology comprising a rapidly expanding category of drugs. Further translation of RNA therapies to the clinic will improve the treatment of many diseases and help enable personalized medicine. However, in vivo delivery of RNA remains challenging due to the lack of appropriate delivery tools. Current state-of-the-art carriers such as ionizable lipid nanoparticles still face significant challenges, including frequent localization to clearance-associated organs and limited (1-2%) endosomal escape. Thus, delivery vehicles must be improved to further unlock the full potential of RNA therapeutics. An emerging strategy is to modify existing or new lipid nanocarriers by incorporating bioinspired design principles. This method generally aims to improve tissue targeting, cellular uptake, and endosomal escape, addressing some of the critical issues facing the field. In this review, we introduce the different strategies for creating bioinspired lipid-based RNA carriers and discuss the potential implications of each strategy based on reported findings. These strategies include incorporating naturally derived lipids into existing nanocarriers and mimicking bioderived molecules, viruses, and exosomes. We evaluate each strategy based on the critical factors required for delivery vehicles to succeed. Finally, we point to areas of research that should be furthered to enable the more successful rational design of lipid nanocarriers for RNA delivery.

Figure 1

Schematics illustrating current research focused on bioinspired nanocarriers incorporating natural lipids. (A) Schematic of lipopeptide nanoparticles developed by Dong et al. (Adapted with permission from ref (59). Copyright 2014, National Academy of Sciences). (B) Schematic and lipid structures of pSar-LNPs developed by Nogueira et al. (Adapted from ref (113). Copyright 2020, American Chemical Society). (C) Left: The chemical structure of β-sitosterol differs from cholesterol by one ethyl group (highlighted in red). Right: Schematic of endosomal escape of eLNPs developed by Patel et al. Shows desorption of PEG-lipids from LNPs, which allows ApoE binding to occur and causes LDL-mediated cellular uptake in cells. Subsequently, a small amount of RNA escapes the endosome while most is recycled back by lysosomal transporters or directed to degradative endocytic compartments. (Adapted with permission under a Creative Commons CC-BY License https://creativecommons.org/licenses/by/4.0/ from ref (117). Copyright 2020, Nature Portfolio). (D) Chemical structures of two helper lipids, DSPC and DGTS, used by Kim et al. in their LNP formulations. (E) Chemical structure of ionizable phospholipid PL1 developed by Li et al. (Adapted with permission under a Creative Commons CC-BY License https://creativecommons.org/licenses/by/4.0/ from ref (123). Copyright 2021, Nature Portfolio). (F) Chemical structures of three helper lipids used by LoPresti et al. in their LNP formulations. (Adapted with permission under a Creative Commons CC-BY License https://creativecommons.org/licenses/by/4.0/ from ref (125). Copyright 2022, Elsevier).

Figure 2

Schematics illustrating current research focused on bioinspired nanocarriers mimicking endogenous molecules. (A) Schematic of synthesis procedure and components of siRNA-TLPs developed by McMahon et al. In Step 1, TLPs are synthesized. In Step 2, TLPs are mixed with single-stranded RNA (ssRNA), complement strands of a siRNA duplex, complexed with DOTAP. (Adapted from ref (132). Copyright 2016, with permission from John Wiley & Sons, Inc.). (B) Schematic illustration of dual-targeting HDL-mimics developed by Jiang et al., showing how they dynamically enhance plaque targeting via a positive feedback loop and lower intracellular lipid disposition. (Adapted from ref (139). Copyright 2019, with permission from Elsevier). (C) The components and outline for the preparation of siRNA-CaP-rHDLs developed by Huang et al.. (Adapted with permission under a Creative Commons CC-BY License http://creativecommons.org/licenses/by/4.0/ from ref (131). Copyright 2017, Nature Portfolio). (D) Chemical structure and the ratio of lipids used in GDNP-mimicking nLNPs developed by Sung et al. (Adapted from ref (142). Copyright 2022, with permission from Elsevier).

Figure 3

Schematics illustrating current research focused on bioinspired nanocarriers mimicking viruses. (A) Shows the critical steps involved in HA-mediated membrane fusion. (1) HA binds to the cell membrane through sialic acid groups (green); (2) pH reduction in endosome causes a conformation change that causes fusion peptides (red) to interact with the cell membrane; (3) Another conformation change fuses the membranes to form a “stalk”; (4) multiple HA proteins work to accomplish this, and eventually the stalk collapses to form a pore. (Adapted from ref (110). Copyright 2022, with permission from Elsevier). (B) Outlines the modifications to cationic liposomes made by Kim et al. to form EGFR-targeting Viroplexes that deliver siRNA. (C) Schematic showing the cell-free synthesis of HA2 virosomes and the mechanism of siRNA delivery (Adapted from ref (154). Copyright 2022, with permission from Elsevier). (D) Illustrates the design of PS-LNPs inspired by viral membrane lipids and provides an overview of methods to evaluate their ability to deliver RNA. (Adapted with permission under a Creative Commons CC-BY License https://creativecommons.org/licenses/by/4.0/ from ref (111). Copyright 2022, Elsevier.) (E) Schematic showing PS-LNP nanoparticles and their ability to target SLOs through macrophage/monocyte mediated delivery, enabling mRNA delivery to the spleen and lymph nodes (Adapted from ref (171). Copyright 2022, American Chemical Society).

Figure 4

Schematics illustrating current research focused on bioinspired nanocarriers mimicking exosomes. (A) Illustrates the chemical structures of the lipids used in exosome mimetic liposomes, reported by Lu et al. (B) Visual representation of a one-step microfluidic synthesis method to prepare exosome-like NPs (Adapted from ref (180). Copyright 2021, American Chemical Society). (C) Structure of tumor-suppressing exosome mimetic nanosystem functionalized with tumor-targeting integrin α6β4 reported. (Adapted with permission under a Creative Commons CC-BY License license http://creativecommons.org/licenses/by/4.0/ from ref (177). Copyright 2019, BioMed Central Ltd.). (D) Schematic for the preparation of exosome-mimetic Cx43/L/CS-siRNA NPs. siRNA was complexed with CS and subsequently coated with an exosome-like lipid bilayer. Cell-free synthesis was then used to incorporate Cx43 proteins in the lipid bilayer. (Adapted from ref (112). Copyright 2019, with permission from Elsevier).