Intelligent polymers as nonviral vectors.

The successful gene therapy largely depends on the vector type that allows a selective and efficient gene delivery to target cells with minimal toxicity. Nonviral vectors are much safer and cheaper, can be produced easily in large quantities, and have higher genetic material carrying capacity. However, they are generally less efficient in delivering DNA and initiating gene expression as compared to viral vectors, particularly when used in vivo. As nonviral vectors, polycations may work well for efficient cell uptake and endosomal escape, because they do form compact and smaller complexes with plasmid DNA and carry amine groups, which give positive charge and buffering ability that allows safe escape from endosome/lysosome. However, this is a disadvantage in the following step, which is releasing the plasmid DNA within the cytosol. In order to initiate transcription and enhance gene expression, the polymer/plasmid complex should dissociate after releasing from endosome safely and effectively. There are also other limitations with some of the polycationic carriers, for example, aggregation, toxicity, etc. Intelligent polymers, also called as 'stimuli responsive polymers', have a great potential as nonviral vectors to obtain site-, timing-, and duration period-specific gene expression, which is already exhibited in recent studies that are briefly summarized here.