Phosphorylcholine-based copolymer as synthetic vector for gene delivery
Gene therapy has a great potential for the treatment of a wide range of diseases. However, the development of a safe and efficient delivery vector is the major obstacle for gene therapy. Recently synthesized 2 - (dimethylamino) ethyl methacrylate 2-(methacryloxloxyethyl phosphorylcholine) (DMA-MPC) diblock copolymer was investigated in this work as a novel non-viral vector for gene delivery. It has been previously demonstrated that the cationic DMA block can condense DNA efficiently. The zwitterionic PC head groups are found naturally in the outer leaflet of biomembranes and are extremely biocompatible. It is thus proposed here that the MPC can act as a new steric stabilizer to the system. Different compositions of DMA-MPC diblock copolymers were evaluated. The MPC block with minimum length 30 monomeric units can successfully provide steric stabilization to the system, and reduce nonspecific cellular interaction by providing a steric barrier to the DNA complexes. However, long MPC chain can hinder the interaction between cationic DMA and DNA, leading to the formation of loosely condensed complexes which were more susceptible to enzymatic degradation. Therefore the composition of the copolymer must be carefully adjusted so that the DNA condensing and steric stabilization effect are well balanced. In order to investigate the cellular uptake mechanism DMA homopolymerDNA complexes, the effect of different endocytosis inhibitors was examined. Microtubules and actin filaments were involved in the uptake of DNA complexes, suggesting that the complexes were internalised by endocytosis. Both the clathrin- and caveolae- mediated pathway were responsible for the uptake of DNA complexes, and the former appeared to be the main route of entry. Finally, folic acid ligand was incorporated into the DMA-MPC copolymer in order to improve the specific targeting. Initial data showed that there was selective uptake of the folate conjugated system in folate receptor expressing cells possibly via receptor mediated endocytosis. However, parameters such as the optimum length of MPC component, number of ligands per DNA complex and the composition of the system need to be further investigated in order to maximize the specificity and transfection efficiency.