Molecular medicine uses genetic materials that are transported into cells with the assistance of specific delivery vectors, in order to treat those diseases that do not respond well to conventional therapies. Non-viral DNA vectors have been extensively studied as such delivery vehicles, because of their desirable properties, such as the ability to induce relatively low toxicity and generate hardly any immune responses. Other potential advantages of the non-viral gene delivery systems include their capability to deal with large DNA plasmids, their simple preparation method, and flexibility in their use, as well as cell-type specificity after chemical conjugation of a targeting ligand.
Different Methods of Gene Delivery Vectors Used for the Central Nervous System (CNS)
Our lab at the National University of Singapore has been working with the development of synthetic polymer-, peptide-, and recombinant protein-based gene delivery vectors that have been tuned to fit into the application in the central nervous system (CNS). The PEGylation (where PEG is polyethylene glycol) approach was adopted to modify polyethylenimine (PEI), a polycation that is potent in mediating gene transfer in vitro and in vivo, to improve its biocompatibility in the CNS, without sacrificing its gene delivery efficiency. Of particular interest, PEGylated PEI allows repeated intrathecal administration of DNA/polymer nanoparticles, leading to prolonged transgene expression in the spinal cord.
Using Cyclodextrin (CD) to Improve the Biocompatibility of Polyethylenimine (PEI)
The use of cyclodextrin (CD) to link low molecular weight PEI, is another method of improving the biocompatibility of PEI. The copolymers comprise ester bonds for hydrolysis, and are capable of mediating gene transfection in various types of cells as efficiently as high molecular weight PEI.
Using Ligand-Receptor Interaction and Receptor-Mediated Endocytosis to Enter DNA Nanoparticles into Neurons
To explore the feasibility of targeting entry of DNA nanoparticles into neurons through specific ligand-receptor interaction and receptor-mediated endocytosis, recombinant DNA technology has been used to produce chimeric polypeptides, containing a nucleic acid binding domain linked to a receptor-binding domain of neurotrophins. The polypeptides form complexes with DNA, and target the complexes to the neurons expressing neurotrophin receptors. Receptor binding of the polypeptides triggers receptor-mediated endocytosis, delivering DNA into the neurons selectively.