ABSTRACT
Polyplexes are based on the condensation of negatively charged DNA by electrostatic attraction with polycationic condensing compounds. The resulting compact particles protect the nucleic acid and also improve the uptake into the cells. Numerous polycations have been used for formulating DNA into complexes. Ideally, the cationic polymer will carry out multiple tasks which include compacting DNA into particles that can migrate to the target tissue, shielding the particles against degradation and undesired interactions, and enhancing cell binding and intracellular delivery into cytoplasm and the nucleus. In practical terms, the polymer is unable to carry out all these tasks. Additional functional domains have to be integrated into the formulation. Advantageously, polymers can be chemically linked to molecules such as cell-targeting ligands, including proteins (antibodies, growth factors) and small molecules (carbohydrates, peptides, vitamins). Various polymer–ligand gene delivery systems have been demonstrated to facilitate receptor-cell-mediated delivery into cultured cells. Targeted delivery to the lung, the liver, or tumors has been achieved in experimental animals, either by localized or systemic application.
