Drug delivery trends in clinical trials and translational medicine: challenges and opportunities in the delivery of nucleic acid-based therapeutics.

The ability to deliver nucleic acids (e.g., plasmid DNA, antisense oligonucleotides, siRNA) offers the potential to develop potent vaccines and novel therapeutics. However, nucleic acid-based therapeutics are still in their early stages as a new category of biologics. The efficacy of nucleic acids requires that these molecules be delivered to the interior of the target cell, which greatly complicates delivery strategies and compromises efficiency. Due to the safety concerns of viral vectors, synthetic vectors such as liposomes and polymers are preferred for the delivery of nucleic acid-based therapeutics. Yet, delivery efficiencies of synthetic vectors in the clinic are still too low to obtain therapeutic levels of gene expression. In this review, we focus on some key issues in the field of nucleic acid delivery such as PEGylation, encapsulation and targeted delivery and provide some perspectives for consideration in the development of improved synthetic vectors.