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Engineering insulin-like growth factor-1 for local delivery

Tomotake Tokunou^*, Rachel Miller, Parth Patwari^*, Michael E. Davis^*, Vincent F. M. Segers^*, Alan J. Grodzinsky and Richard T. Lee^*,,1

^* Cardiovascular Division, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA; and

Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

¹Correspondence: Partners Research Facility, 65 Landsdowne St., Cambridge, MA 02139, USA. E-mail: rlee{at}partners.org

Insulin-like growth factor-1 (IGF-1) is a small protein that promotes cell survival and growth, often acting over long distances. Although for decades IGF-1 has been considered to have therapeutic potential, systemic side effects of IGF-1 are significant, and local delivery of IGF-1 for tissue repair has been a long-standing challenge. In this study, we designed and purified a novel protein, heparin-binding IGF-1 (Xp-HB-IGF-1), which is a fusion protein of native IGF-1 with the heparin-binding domain of heparin-binding epidermal growth factor-like growth factor. Xp-HB-IGF-1 bound selectively to heparin as well as the cell surfaces of 3T3 fibroblasts, neonatal cardiac myocytes and differentiating ES cells. Xp-HB-IGF-1 activated the IGF-1 receptor and Akt with identical kinetics and dose response, indicating no compromise of biological activity due to the heparin-binding domain. Because cartilage is a proteoglycan-rich environment and IGF-1 is a known stimulus for chondrocyte biosynthesis, we then studied the effectiveness of Xp-HB-IGF-1 in cartilage. Xp-HB-IGF-1 was selectively retained by cartilage explants and led to sustained chondrocyte proteoglycan biosynthesis compared to IGF-1. These data show that the strategy of engineering a "long-distance" growth factor like IGF-1 for local delivery may be useful for tissue repair and minimizing systemic effects.—Tokunou, T., Miller, R., Patwari, P., Davis, M. E., Segers, V. F. M., Grodzinsky, A. J., Lee, R. T. Engineering insulin-like growth factor-1 for local delivery.

Key Words: heparin binding domain • tissue repair • biosynthesis