Advances in plasmid gene delivery and expression in skeletal muscle.

One of the most striking recent advances for plasmid delivery in vivo has been that of electropermeabilization, commonly referred to as electroporation. This physical process exposes a muscle tissue to a brief, high intensity electric field that induces temporary and reversible breakdown of the plasma membrane. During the period of membrane destabilization, a variety of molecules, including plasmids, gain intracellular access. Electroporation has been shown to improve the efficiency of plasmid gene delivery to skeletal muscle of small animals by as much as two-orders of magnitude to levels comparable to that of adenoviral gene delivery. This technology will allow the muscle to be used as a bioreactor for the secretion of therapeutic proteins into the circulation. This method of gene delivery, which is simple, efficient and reproducible, has become valuable for basic research, with great potential for gene therapy and DNA vaccination. Moreover, significant progress has been made using a variety of molecular designs to achieve regulation of gene expression by low molecular weight drugs. The enhanced efficiency of plasmid delivery by electroporation and the resultant durability of transgene expression, combined with the effectiveness of drug-dependent transgene regulation systems, provide a powerful set of tools that will be broadly applicable to the development of plasmid-based gene therapies for the treatment of human disease.