Gene therapy refers to the introduction of normal foreign genes into target cells to compensate or correct diseases caused by gene defects or abnormalities, so as to achieve the purpose of treatment. Naked DNA usually requires physical methods to enter tissues or cells, and DNA is easily digested and degraded by various enzymes in tissues or cells, resulting in a very low expression level of the encoded protein, which affects the effect of gene therapy. Therefore, the development of gene carriers with low toxicity and high efficiency is one of the urgent problems to be solved in gene therapy.

Gene vectors are generally divided into two categories: viral vectors and non-viral vectors. Viral vectors use viral shells to wrap foreign genes, and then use their infectivity to cells to carry genes into host cells. Viral vectors are widely used because of their strong transport ability and high efficiency of exogenous gene expression in target cells. However, viral vectors also have some disadvantages: such as high cytotoxicity and immunogenicity, easy to cause inflammation, high cost, limited size and quantity of loaded DNA, etc..

In order to make up for the above-mentioned defects of viral vectors, some non-viral vectors with low toxicity and low immune response have been gradually developed. Its DNA loading capacity is high, its chemical structure is controllable, and it is easy to prepare in large quantities. Although its transfection efficiency is slightly lower than that of viral vector-mediated transfection, it still has a high level of assistance in the process of gene delivery to target cells. Eukaryotic cells without phagocytosis can only internalize particles with a diameter of less than 1 micron, such as pathogens, liposome-encapsulated drugs or gene delivery complexes, etc.. And the larger the particle, the more difficult it is to enter the cell. The size of the non-nanometer gene carrier is large, and the volume of the complex formed after interacting with the foreign gene is further increased, which is not conducive to entering the cell, so the transfection efficiency is generally low. Due to their unique physical and chemical properties, nanocarriers have some potential advantages in mediating gene transfection:1) Usually have good biocompatibility, and some carriers are biodegradable, so they are harmful to cell growth and Metabolism has little effect; 2) The particle size is very small, and it is easy to penetrate the tissue into the cell, thus increasing the delivery efficiency of the gene; 3) It is relatively easy to prepare, and the structure is controllable, and some nano-gene carriers have more surface active groups, easy to modify, and can realize the targeted delivery of genes; 4) It has high potential and specific surface area, so the gene load is large, and it can effectively prevent genes from being degraded by nucleases in the body; 5) Some nanomaterials have special Magnetic, optical, or thermal properties enable targeted gene delivery or controlled release.

Nanoparticle-based Gene Carrier Classification

With the development of nanotechnology, more and more nanoparticles are used for gene delivery. At present, the nanoparticles used as gene carriers mainly include the following types:

Gene Delivery Based on Metal Nanoparticles
Metal nanoparticles are developing rapidly as gene delivery carriers. Usually, these carriers are nanoparticles with a core-shell structure, that is, the metal is the core and the functional material is the shell. Such a structure determines that this type of gene carrier has the advantages of good biocompatibility, storage stability, easy preparation, multi-functionality, and less toxic and side effects. At present, magnetic nanoparticles and gold nanoparticles are mostly studied as gene carriers.

Gene Carriers Based on Inorganic Non-Metallic Nanomaterials
Similar to metal nanoparticles, gene carriers with superior performance can also be obtained by hybridizing some inorganic non-metallic nanomaterials with functional molecules. Carbon materials and silicon materials are commonly used materials for nano-gene carriers.

Nano-gene Carrier Based on Cationic Polymer
Cationic polymers are another major class of non-viral gene delivery vehicles. So far, many cationic polymers have been used in gene delivery research, such as polyethyleneimine (PEI), chitosan (CS), polylysine and polyamide-amine dendrimer (PAMAM) and so on. Here, we focus on poly-PEI and CS.

PEI nanoparticles

Among cationic polymer nanogene carriers, PEI is the cationic polymer with the most potential to deliver genes. Because of its strong ability to bind to DNA, it has a unique buffering ability called the proton sponge effect, which can promote the release of genes from lysosomes into the cytoplasm through osmotic expansion. There are two common ways for PEI nanoparticles to combine with DNA to form nanocomposites. One is that PEI nanoparticles are directly combined with DNA to form a complex; the other is to form cross-linked polyethylene glycol-PEI nanoparticles first. Then load the DNA on its surface.

CS nanoparticles

As a natural cationic polymer, CS can combine with DNA through electrostatic interaction and carry out gene transfer. As a gene carrier, CS has the characteristics of low cytotoxicity, good biocompatibility, low immunogenicity and high transfection efficiency. CS is biodegradable and has the ability to cross cell membranes and has been reported in many biological applications.

Liposomal Nanoparticles
Liposomes mainly include positive, neutral and negative liposomes, and as gene carriers, cationic liposomes are the most widely studied. Since Felgner et al. first used cationic liposome dioleoyl propyl trimethyl ammonium chloride (DOTMA) and neutral liposome dioleoyl-phosphatidylethanolamine (DOPE) in equal mass ratio to load DNA for successful transfection in 1987, many cationic liposomes have been used to synthesize highly efficient transfection reagents.

Nano-gene carriers have attracted much attention due to their good biocompatibility, low toxicity and low immunogenicity in cells, but their low transfection efficiency limits their application in animal experiments and clinical trials. In order to improve transfection efficiency, targeting ligands can be connected to nanoparticles to improve the cell targeting of nanogene carriers; modify the structure of nanoparticles to enhance their interaction with cell membranes and improve the efficiency of genes entering the nucleus; synthesis Nano-gene carriers that are sensitive to the endogenous environment or pH can improve the release efficiency of exogenous genes in target cells, etc.

With the rapid development of nanotechnology, combined with the special physical and chemical properties and surface functionalization of nanomaterials, future research may be more inclined to the design and synthesis of multifunctional nanoparticles, which can realize real-time tracking of genes, targeted transport and Controlled release, gradually breaking through the bottleneck of gene therapy.

Author's Bio: 

CD Bioparticles is an established drug delivery company which provides customized solutions for developing and producing new, biocompatible drug delivery systems.