Synthesis and characterization of Poly(L-lysine-co-L-proline) as a non-viral gene delivery vector

Abstract

Gene therapy, the expression of genetic materials with therapeutic activity, has been considered as an encouraging approach to heal life threatening diseases with genetic deficiency. Since direct delivery of the DNA in the absence of a carrier experiences rapid degradation by nuclease and generally exhibits poor cellular uptake, it is one of the main challenges facing today’s gene therapy to establish safe and efficient vectors for delivering therapeutic genes to specific cells. Gene delivery systems investigated so far include viral and non-viral vectors. Viral vectors are intensively used in clinical applications because they efficiently integrate their genetic information into the host chromosomes; however, toxic immunological reactions and recombination events into virulent products still remain as major drawbacks. Non-viral vectors, including liposomes and cationic polymers, display nonimmunogenicity, low acute toxicity, and flexibility to design a carrier with well-defined structures and chemical properties, while they have major problems in transfection efficiency which is limited as only few percentage of that by viral vectors. Among non-viral vectors, poly(L-lysine) (PLL) has been widely used due to the reasonable efficiency and biocompatible nature of peptide bonds in the backbones. However, transfection efficiency of PLL is not so high enough that modification of PLL, such as introduction of targeting ligands or endosomal escape moieties, has been investigated for the use of PLL in vivo. Proline is the only amino acid with a cyclic structure containing a secondary α-amino group and this structural feature gives unique stereochemical and biological properties to the peptides containing proline residue. Water soluble prolinerich peptides have been reported as naturally occurring cellpermeant peptides, which are able to break the cell membrane and deliver the attached carriers into the cells without causing lethal membrane disruption. In this communication, we report the synthesis of lysine and proline based amino acid copolymers. Characterization of the copolymer and the effect of proline content on the formation of copolymer/DNA complex, in vitro cytotoxicity and transfection efficiency were investigated to examine the possibility of the synthesized copolymers as a polymeric gene delivery carrier.