mRNA, also known as messenger ribonucleic acid in Chinese, is a type of single stranded ribonucleic acid that is transcribed from a strand of DNA as a template, carries genetic information, and can guide protein synthesis; MRNA has a large molecular weight and strong hydrophilicity, but its single stranded structure is extremely unstable and easily degraded. The limited lifespan of mRNA allows cells to rapidly alter protein synthesis in response to its constantly changing needs, but it is difficult to meet the requirements of drug resistance. In addition, mRNA molecules themselves carry negative charges, making it difficult to penetrate cell membranes with the same negative charge on the surface. Therefore, special modifications or encapsulation delivery systems are needed to achieve intracellular expression of mRNA drugs. Therefore, delivery technology is crucial for the success of mRNA drugs. Lipid nanoparticles (LNPs) are currently the mainstream carrier delivery method. Due to its easy absorption by antigen-presenting cells, it is often used in vaccines. The components of LNP mainly include the following four categories: cationic lipids, cholesterol, polyethylene glycol lipids, and auxiliary lipids; The roles and functions of each component are as follows:
(1) Cationic liposomes are a key component of the LNP delivery system. At present, the specific structures of cationic lipid molecules used by various mRNA companies are different, but they all belong to cationic lipids with positive charges under specific conditions. Ionizable cationic lipids are the key to the delivery function of the LNP system. Due to the negative charge of mRNA itself, it is attracted by positive and negative charges and binds to the interior of the LNP, which can improve the stability of mRNA in the body and escape lysosomal degradation. After LNP is absorbed by cells, the low pH environment of the nuclear body will fuse with LNP and release mRNA into the cytoplasmic colloid.
(2) The main function of cholesterol is to mediate the endocytosis of LNP and help ensure the bilayer structure of LNP and lipid fluidity. Auxiliary neutral lipids (such as various phospholipids) are also used to construct LNP bilayer structures, as the bilayer structure of cationic liposomes is not stable.
(3) Polyethylene glycol modified liposomes can control the particle size of nanoparticles during the synthesis process. Due to the strong hydration effect of polyethylene glycol ethoxy chains, the polyethylene glycol structure can form a hydrophilic protective layer in the aqueous phase, which can effectively prevent the aggregation of nanoparticles during storage and maintain the spatial stability of LNP; At the same time, polyethylene glycol on the surface of LNP particles can protect the particles from being detected by immune proteins in the body, shield the binding particles of plasma proteins and other components, and prevent LNP particles from being cleared in the body.
(4) The representatives of auxiliary lipids are phospholipid lipids such as DOPE, DSPC, and DOPC. In the process of preparing cationic liposomes, auxiliary lipids have a strong synergistic effect, mainly including stabilizing the bilayer membrane and reducing the toxicity of positive components, promoting mRNA release and assisting in the cell penetration of cationic liposomes when LNP is internalized, and determining the morphology of mRNA-LNP complexes, making the complexes have good fusibility and improving transmembrane efficiency.
The mRNA delivery system developed by Ersheng adopts two development paths; One is a delivery system similar to LNP, but with significant differences in component ratio and nanoparticle size compared to existing LNP systems; Another path is to use components completely different from LNP to construct a delivery system; The company has applied for corresponding patents for this.
