Cytoplasmic expression systems triggered by mRNA yield increased gene expression in post-mitotic neurons.

Non-viral vectors are promising vehicles for gene therapy but delivery of plasmid DNA to post-mitotic cells is challenging as nuclear entry is particularly inefficient. We have developed and evaluated a hybrid mRNA/DNA system designed to bypass the nuclear barrier to transfection and facilitate cytoplasmic gene expression. This system, based on co-delivery of mRNA(A64) encoding for T7 RNA polymerase (T7 RNAP) with a T7-driven plasmid, produced between 10- and 2200-fold higher gene expression in primary dorsal root ganglion neuronal (DRGN) cultures isolated from Sprague-Dawley rats compared to a cytomegalovirus (CMV)-driven plasmid, and 30-fold greater expression than the enhanced T7-based autogene plasmid pR011. Cell-free assays and in vitro transfections highlighted the versatility of this system with small quantities of T7 RNAP mRNA required to mediate expression at levels that were significantly greater than with the T7-driven plasmid alone or supplemented with T7 RNAP protein. We have also characterized a number of parameters, such as mRNA structure, intracellular stability and persistence of each nucleic acid component that represent important factors in determining the transfection efficiency of this hybrid expression system. The results from this study demonstrate that co-delivery of mRNA is a promising strategy to yield increased expression with plasmid DNA, and represents an important step towards improving the capability of non-viral vectors to mediate efficient gene transfer in cell types, such as in DRGN, where the nuclear membrane is a significant barrier to transfection.

Emerging developments in RNA therapeutics.

Exciting developments have recently emerged in the field of RNA therapeutics, with potential applications in the treatment of human diseases. The second International Conference on RNA in drug development was held to highlight several novel RNA-based technologies, including different approaches to silence gene expression, the broad range of diagnostic and therapeutic applications for aptamers, and the targeting of RNA with small molecules. Highlights of the meeting included the utilisation of RNA interference to silence genes, with applications for the treatment of both cancer and viral infections, and for systemic silencing of gene expression. Novel approaches to safer drug design using aptamers were presented, which would enable control of their therapeutic activity to be achieved with antidote oligonucleotides. Updates were also presented on the clinical and preclinical development of ribozymes and aptamers, including good progress in increasing the half-life of these molecules in serum.