Osteoinduction by repeat plasmid injection of human bone morphogenetic protein-2

Background Bone morphogenetic protein‐2 (BMP‐2) is an osteoinductive protein and is considered useful for the treatment of skeletal disorders. Previous studies using BMP‐2 in clinical applications have encountered difficulties, including the lack of an efficient, safe, inexpensive and simple delivery system. The gene transfer approach is a promising option for utilizing BMP‐2. Although viral vector‐mediated gene transfer is efficient, safety concerns prevent its clinical application for common diseases. On the other hand, plasmid‐based gene transfer is a safe method and can be harnessed for practical applications. Methods A plasmid encoding human BMP‐2 (pCAGGS‐BMP‐2) was used and injected repeatedly (one to eight times) into the skeletal muscle of mice at a divided dose. We compared the capability of osteoinduction in the skeletal muscle of mice after gene transfer by repeat injection. BMP‐2 production was assessed via immunohistochemistry, and osteoinduction was evaluated using radiography, histology and biochemical assays. Results The BMP‐2 gene was transferred into the skeletal muscle of mice by repeat injection using pCAGGS‐BMP‐2. Mature bone was frequently observed in mice injected repeatedly with pCAGGS‐BMP‐2 at a divided dose. This confirms that, if the total dose is fixed, repeat injection with pCAGGS‐BMP‐2 at a divided dose causes osteoinduction more frequently in the skeletal muscle of mice. Conclusions These results suggest the possibility of the effective clinical use of human BMP‐2 gene therapy by direct DNA injection, and facilitate the clinical application of BMP‐2 gene therapy. Copyright © 2010 John Wiley & Sons, Ltd.