Low Cytotoxity And Biocompatible Gene Vectors Based On Low Molecular Weight PEI

PEI is one of the most representative synthetic polyions, and it is widely used as genevectors, owing to its high charge density and excellent buffer capacity. However, the highmolecular weight PEI, which exhibits outstanding gene transfection efficiency, shows highcytotoxicity and poor biocompatibility. This shortage limits the clinical use of PEI. Lowmolecular weight PEI shows low cytotoxicity but poor transfection efficiency. It is possible toincrease the transfection efficiency of low molecular PEI with crosslinking or modificationwith macromolecules. The crosslinking and modification could increase the charge density ofPEI. Owing to the electrostatic hydration effect, zwitterions show superhydropholic and caninhibit the nonspecific protein adsorption. To combine the low cytotoxity of low molecularweight PEI and the biocompatibility of betaine, we designed betaine modified gene vectorsbased on hydrozone-crosslinked or nucleobase pair A-U crosslinked low molecular PEI;moreover, we also modified dextran with PEI600Da and betaine. The combination withDNA, buffer capacity, cytotoxicity, biocompatibility and transfection efficiency of vectorswas investigated. The contents of thesis are illustrated as follows:(1) PEI1.8K was crosslinked by hydrazone-containing crosslinker (Hdz) and furthermodified with sulfobetaines (DMAAPS). PEI-Hdz-DMAAPS samples were synthesized andcharacterized by1H NMR. Viscometry was employed to determine the molecular weight anddegradation. The increase of molecular weight after crosslinking and the degradation ofsamples incubated in acid solution were conformed. The titration experiments conformed thebuffer capacity of samples between pH=5to pH=7. The polymer/DNA complexes wereassessed by agarose gel, dynamic light scattering (DLS) and zeta potential. Little hemolysisand low protein adsorption was observed in betaine-modified samples. MTT assays showedthe carriers modified with betaine have good biocompatibility and low cytotoxity.Transfection experiments show that PEI-Hdz-DMAAPS21.2%and PEI-Hdz-DMAAPS36.0%exhibit higher transfection efficiency and good serum tolerance.(2) PEI1.8K modified with Adenines and betaines was crosslinked by Uracil-containingcrosslinkers. The crosslinked PEI was characterized by1H NMR. The molecular weight anddegradation was determined by viscometry. Polymer/DNA complexes were assessed by agarose gel, dynamic light scattering (DLS) and zeta potential. The mean diameters ofcomplexes were about200nm. Little hemolysis and low protein adsorption was observed inbetaine-modified samples. MTT assays showed that polymers modified with betaine havegood biocompatibility and low cytotoxity. In vitro transfection experiments showed thatPEI-A2.3-B2.1-U-U shows high transfection efficiency and good serum tolerance.(3) Dex-PEI-B samples were synthesized by grafting PEI600Da and betaines ontodextran, and characterized by1H NMR. Agarose gel experiments and DLS determined theformation of polymer/DNA complexes. The mean diameter of complexes were around300~400nm. Little hemolysis and low protein adsorption was observed in betaine-modifiedsamples. MTT assays showed that polymers exhibit good biocompatibility and extremely lowcytotoxity. Transfection experiments comformed that Dex-PEI16and Dex-PEI16-B22showcomparable transfection efficiency with PEI25K, and Dex-PEI16-B22has good serumtolerance in transfection experiments.In summary, we have synthesized several gene vectors based on low molecular weightPEI. Owing to the betaine modification, the vectors showed low cytotoxity and excellentbiocompatibility, as well as high transfection efficiency. Especially, when transfected inserum-containing medium, the betaine modified samples stay high transfection efficiency. Thepolymers have great potential to be a new type of safe and efficient gene vectors.