238. A Comparison of Gene Delivery and Vector Systems To Achieve High Levels of Sustained Skeletal Muscle Gene Expression

Abstract

Skeletal muscle has several features that make it attractive as a site for therapeutic gene expression - it is accessible to most of the current gene delivery systems, abundant, and displays a relatively slow turn over rate. A variety of gene delivery systems have been tested for high levels of sustainable gene expression from the skeletal muscle. Unfortunately, these studies have generally focused on optimization of one of the systems and have not made direct comparisons to other currently available gene delivery systems. To better understand the potential of these different systems to achieve high, sustained levels of gene expression from the skeletal muscle, we compared the viral-based gene delivery systems derived from human adenovirus (Ad) and adeno-associated virus (AAV) to optimized (electroporation, synthetic polymers) plasmid-based delivery. Using the HCMV promoter driven luciferase gene expression cassette as a reporter system for these studies, gene expression levels in the murine skeletal muscle were quantitated by both direct measurement of luciferase gene expression from excised skeletal muscle and by in vivo CCD camera intensity images. Initial expression levels (day 2 post infection/transduction) were highest from plasmid-based delivery by electroporation, slightly (approx. 2 fold ) higher than Ad and AAV-1 and significantly (100-1000X) higher than plasmid + poloxamer or plasmid alone. By day 6, the rank order of expression had changed, with AAV-1-based expression generating levels superior to the other systems tested (AAV-1>plasmid+electroporation>Ad>plasmid+poloxamer>plasmid). Gene expression has been detected out to 8 months for all the vectors examined. AAV-1 mediated expression levels at the 8 month time point are approximately 2-logs over both plasmid + electroporation and Ad as measured by CCD camera imaging. Consequently, AAV-1 based gene delivery results in superior expression levels and duration in the skeletal muscle relative to many of the other current gene delivery systems available.