Recent advances in siRNA delivery mediated by lipid-based nanoparticles

Abstract

Small interfering RNA (siRNA) has been expected to be a unique pharmaceutic for the treatment of broad-spectrum intractable diseases. However, its unfavorable properties such as easy degradation in the blood and negative-charge density are still a formidable barrier for clinical use. For disruption of this barrier, siRNA delivery technology has been significantly advanced in the past two decades. The approval of Patisiran (ONPATTRO™) for the treatment of transthyretin-mediated amyloidosis, the first approved siRNA drug, is a most important milestone. Since lipid-based nanoparticles (LNPs) are used in Patisiran, LNP-based siRNA delivery is now of significant interest for the development of the next siRNA formulation. In this review, we describe the design of LNPs for the improvement of siRNA properties, bioavailability, and pharmacokinetics. Recently, a number of siRNA-encapsulated LNPs were reported for the treatment of intractable diseases such as cancer, viral infection, inflammatory neurological disorder, and genetic diseases. We believe that these contributions address and will promote the development of an effective LNP-based siRNA delivery system and siRNA formulation.

Keywords: Lipid nanoparticles; pH-responsive ionizable lipid; siRNA.

Graphical abstract

Fig. 1

Schematic illustration of liposome-mediated delivery of siRNA. a) siRNA is encapsulated in the inner water phase of liposomes. b) siRNA is complexed with liposomes containing cationic lipids.

Fig. 2

Schematic illustration of LNPs. LNPs can be prepared by mixing a lipid mixture dissolved in an organic solvent and siRNA in aqueous solution with a microfluidic device followed by dialysis in water to remove the organic solvent. siRNA is encapsulated in the core of LNPs after dialysis.

Fig. 3

Structural formulae of ionizable lipids used for preparation of SNALP. a) DLin-DMA, b) DODAP, c) DLin-KC2-DMA, d) DLin-MC3-DMA.

Fig. 4

Schematic illustration of MEND. a) siRNA is enclosed in the internal aqueous phase. The surface of MEND is made up of various functional lipid derivatives to give it multi-functionality to control internal and intracellular kinetics. b) Chemical structures of pH-responsive ionizable lipids YSK05, YSK13 and CL4H6.

Fig. 5

Structural formulae of ssPalms. a) ssPalmM is characterized by having miristic acid, 2 tertiary amines, and a disulfide bond, b) ssPalmA contains Vitamin A, c) ssPalmE contains Vitamin E. The tertiary amine of ssPalm is positively charged in response to the acidic pH in the endosome. The disulfide bond is cleaved in response to the reducing environment in the cytoplasm.

Fig. 6

Structural formulae of lipidoids, lipid-like materials. a) C12–200. b) 304O₁₃. c) cKK-E12.

Fig. 7

Schematic illustration of SLN. a) SLN has a crystalline triolein core surrounded by phospholipids, cationic lipids, and PEGylated lipids. siRNA interacts with cationic lipids. b) HIP consists of siRNA and cationic lipids is incorporated in the crystalline core of SLN.

Fig. 8

Mechanisms of enhanced cellular retention of LNPs in cells treated with NP3.47, a NPC1 inhibitor. a) LNPs are often exocytosed to the outside of the cells. b) Endosomal recycling mechanism is impaired by NP3.47 treatment, resulting in enhanced retention of LNPs. c) In cells treated with NP3.47, infection of the Ebola virus is suppressed by inhibiting endosomal recycling mechanism. d) The Ebola virus is exocytosed to the outside of the cells, resulting in infection spread. By NP3.47 treatment, LNP increases the chance of exerting its function by endosomal escape, but Ebola virus reduces the chance of infection because it cannot endosomal escape.