Structure and Function of Cationic and Ionizable Lipids for Nucleic Acid Delivery

Abstract

Hereditary genetic diseases, cancer, and infectious diseases are affecting global health and become major health issues, but the treatment development remains challenging. Gene therapies using DNA plasmid, RNAi, miRNA, mRNA, and gene editing hold great promise. Lipid nanoparticle (LNP) delivery technology has been a revolutionary development, which has been granted for clinical applications, including mRNA vaccines against SARS-CoV-2 infections. Due to the success of LNP systems, understanding the structure, formulation, and function relationship of the lipid components in LNP systems is crucial for design more effective LNP. Here, we highlight the key considerations for developing an LNP system. The evolution of structure and function of lipids as well as their LNP formulation from the early-stage simple formulations to multi-components LNP and multifunctional ionizable lipids have been discussed. The flexibility and platform nature of LNP enable efficient intracellular delivery of a variety of therapeutic nucleic acids and provide many novel treatment options for the diseases that are previously untreatable.

Keywords: cationic lipid; ionizable lipid; lipid nucleic acid nanoparticles; nucleic acid delivery; structural effect.

Fig. 1

Chemical structures of DOTAP and DOTMA, which have different linkage bonds (two ester bonds in DOTAP and two ether bonds in DOTMA).

Fig. 2

Structures of the lipid analogues of DOTMA and DOTAP.

Fig. 3

Structures of commonly used phosphatidylethanolamine (PE), phosphatidylcholine (PC) and cholesterol helper lipids.

Fig. 4

Chemical structures of a lipid library based on DOTAP with various lipid chain lengths and combination.

Fig. 5

Structures of a lipid library containing hydroxyalkyl chain lengths on the quaternary amine head group (A) and different alkyl chains (B).

Fig. 6

Structures of the cationic lipids and poly(ethylene glycol)-ceramides (PEG-Cer) for formulation of stabilized plasmid-lipid particles.

Fig. 7

Chemical structures of 1,2-dioleyloxy-3-dimethylaminopropane (DODMA) and 1,2-dioleoyl-3-dimethylaminopropane (DODAP) lipids.

Fig. 8

SNALP Lipids. (a)1,2-dilinoleyloxy-N,N-dimethyl-3-aminopropane (DLinDMA), (b)cholesterol (Chol), (c)1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), (d)3-N-[(ω-methoxypoly(ethylene glycol)₂₀₀₀)carbamoyl]-1,2-dimyristyloxy-propylamine (PEG-C-DMA).

Fig. 9

Structures of ionizable lipids DODMA analogues for SNALP.

Fig. 10

Structures of DLinDMA analogues.

Fig. 11

Structures of DLin-K-DMA analogues.

Fig. 12

Structures of YSK13 and YSK15 lipids.

Fig. 13

Systematic derivatization of YSK12-C4. The YSK12-C4 is divided into 3 sections, an ionizable head group, distal, and proximal side of hydrophobic tails. Each part of the YSK12-C4 was derivatized to assess structure–activity relationship. The notation for the ionizable lipids used in this study are abbreviated as cationic lipid (CL), followed by the order of the number of carbons in the head group (1 to 15), distal (A to H) and proximal side (6 to 10) of the hydrophobic tails.

Fig. 14

The design of the multifunctional pH-sensitive amino lipids.

Fig. 15

Structural modification of the multifunctional pH-sensitive amino lipids based on EHCO.

Fig. 16

Chemical structures of ionizable lipids in mRNA LNP.