Synthesis Of Sulfonium Modified PEI Compounds And Study Of Their Ability As Gene Vectors

Polyethylenimine(PEI)is a kind of widely used non-viral gene vector.Its surface contains many amino groups that can be protonated under physiological pH conditions,so that it has good ability of cell uptake and endosome escape.However,the positive charge density of unmodified PEI is big in high molecular weight PEI which present raised cytotoxicity,poor blood compatibility.The shortcomings limit its clinical application.In order to improve the properties of PEI,a novel PEI modified polymer was developed by combining sulfonium compound(SI)containing carboxylic acid group with low molecular weight PEI through amide bonds.The newly modified PEI(SIPEI)possessed biodegradable amide bond,lower charge density and was expected to be better gene delivery vector with low toxicity and high transfection activity.In this experiment,36 SIPEIs were synthesized from the reactions of three SI compounds with four low molecular weight PEIs in three condensation ratios,and were characterized by IR and ~1H-NMR.The condensing abilities of SIPEIs towards DNA were assessed with agarose gel experiments.The formed SIPEI/DNA complexes were detected the particle size and Zeta potential of with a Nano-ZS 90 Laser Particle Size and Zeta Potential Analyzer.The cytotoxicity of SIPEI was evaluated with MTT assay.The intracellular distribution and transfection effects of SIPEI/DNA complexes were observed with fluorescence microscope.Through the analysis of IR and ~1H-NMR,the SIPEIs have been successfully condensed,and the modification degree of PEI is positively varied with the ratio of reactants.16 SIPEIs with better solubility are selected by solubility test.Agarose gel experiments have shown that 10SIPEIs have the ability to combine plasmid DNA to form nanoparticles which particle size ranging between 150 nm and 300 nm,and Zeta potential ranging from+5 m V to+25 m V.The MTT tests showed that the cytotoxicity of 10 SIPEIs are not significantly different from that of the control PEI 25k,and rise along with the increase of concentration or duration of SIPEIs.The results of intracellular distribution experiments showed that 7 SIPEI/DNA complexes have better cell uptake rates and most of them are distributed around the nucleus.In transfection experiments,4 SIPEIs which are 5SIPEI 1.8k-0.25,5SIPEI 1.8k-0.5,8SIPEI1.8k-0.25,10SIPEI 1.8k-0.25,were found stronger transfection effect than that of PEI 1.8k,and their transfection effects were comparable to PEI 25k.This study demonstrates that the positive charge on the SI functional group can effectively bond with the phosphate in the DNA,so that the modified low molecular weight PEI can condense DNA to form nanoparticles with improving the transfection efficiency.But comparing with lower molecular weight PEI,the modified products have higher cytotoxicity which indicating that SI functional group is lightly toxic and needs to be further optimized so as to obtain low cytotoxicity and high transfection efficiency gene vector.