Delivery of Nucleic Acid Drugs

Abstract

Nucleic acid drugs should be delivered into the corresponding intracellular target site, i.e. the nucleus or cytosol. Because biosystems have developed several barriers to prevent the intrusion of external genetic material, highly sophisticated delivery machinery must be used to overcome those barriers. In this review, we describe the evolution of polymer-based carriers over several decades of research. To prevent deactivation in extracellular circumstances, nucleic acid drugs are condensed with cationic polymers or encapsulated with hydrophobic polymers. The condensed or encapsulated complexes are often crosslinked to enhance the physicochemical stability and coated with biocompatible polymers for safety. Delivery of the nucleic acid drugs to a specific site and subsequent intracellular entry can be partially accomplished by passive targeting based on the enhanced permeability and retention (EPR) effect or nonspecific endocytosis, but more effectively by receptor-mediated endocytosis. After the cell entry, various functionalities help the nucleic acid drugs escape the endosomes to enter the cytosol, release them from the carrier system, and transfer them into nucleoplasm through the nuclear envelope. The development of an ideal delivery carrier with efficiency, specificity, as well as safety has been supported by progress in polymer chemistry and supramolecular chemistry, and accumulated experience in biological and clinical trials.