Delivery of nucleic acids and gene therapy
Nucleic acids have considerable potential as therapeutic agents, either as gene expression systems for gene therapy (DNA plasmids or mRNA), or for knockdown gene expression (siRNA). What limits the use of nucleic acids is the difficulty in delivering these anionic macromolecules to their intended sites of action.
Methods for design and construction of mammalian expression plasmids are well known. Such plasmids are used routinely to express genes in cell culture. However, to deliver DNA to the nucleus of a mammalian cell in vivo,it is necessary to protect the DNA from destructive enzymes, and then provide mechanisms to overcome a succession of biological barriers.
Adenoviruses have evolved mechanisms to facilitate particle uptake by endocytosis, transfer of the viral capsid to the cytoplasm, trafficking of the capsid towards the nucleus, and subsequent delivery of viral DNA to the nucleus through the nuclear pore complex. To exploit viral mechanisms, many gene therapy research groups incorporate therapeutic genes into engineered attenuated viruses. However, there are safety concerns with viral vectors, in both manufacture and clinical use, and repeated dosage is often limited by immunogenicity.
D4 is investigating the molecular mechanisms of viral delivery—to learn from these mechanisms, and to introduce analogous transport mechanisms into synthetic gene delivery systems. D4 researchers are developing non-viral DNA vaccines for use in cancer immunotherapy and the treatment and prevention of infectious diseases.
Delivery of mRNA for gene expression or siRNA for knockdown presents a less formidable delivery challenge, in that these molecules are required to be delivered to the cytoplasm but do not need to enter the nucleus. Nevertheless, as with DNA, the key to success is to design and construct stable nanoparticles that can protect the nucleic acid, while allowing tissue distribution and intracellular trafficking.