Bone repair with a form of BMP-2 engineered for incorporation into fibrin cell ingrowth matrices

Abstract

Most growth factors naturally involved in development and regeneration demonstrate strong binding to the extracellular matrix and are retained there until being locally mobilized by cells. In spite of this feedback between cell activity and growth factor mobilization in the extracellular matrix, this approach has not been extensively explored in therapeutic situations. We present an engineered bone morphogenetic protein-2 (BMP-2) fusion protein that mimics such function in a surgically relevant matrix, fibrin, incorporated into the matrix until it is locally liberated by cell surface-associated proteases. A tripartite fusion protein, denoted TG-pl-BMP-2, was designed and produced recombinantly. An N-terminal transglutaminase substrate (TG) domain provides covalent attachment to fibrin during coagulation under the influence of the blood transglutaminase factor XIIIa. A central plasmin substrate (pl) domain provides a cleavage site for local release of the attached growth factor from the fibrin matrix under the influence of cell-activated plasmin. A C-terminal human BMP-2 domain provides osteogenic activity. TG-pl-BMP-2 in fibrin was evaluated in vivo in critical-size craniotomy defects in rats, where it induced 76% more defect healing with bone at 3 weeks with a dose of 1 mug/defect than wildtype BMP-2 in fibrin. After a dosing study in rabbits, the engineered growth factor in fibrin was evaluated in a prospective clinical study for pancarpal fusion in dogs, where it induced statistically faster and more extensive bone bridging than equivalent treatment with cancellous bone autograft. The strong healing response shown by fibrin including a bound BMP-2 variant suggests that with the combination of bound growth factor and ingrowth matrix, it may be possible to improve upon the natural growth factor and even upon tissue autograft.

Peptide-based biopolymers in biomedicine and biotechnology

“…The Hubbell group has turned their attention to designing and synthesizing hydrogels that mimic the bi-directional biomolecular interactions that naturally occur between cells and the extracellular matrix (ECM) surrounding them [184,[273][274][275][276][277][278][279][280][281][282][283][284][285]. They have found that signals such as cell adhesion sites, bound growth factors, and cleavage sites for proteolytic activity are essential for cells to be able to remodel the ECM and sustain tissue regeneration.…”

“…To impart these additional functionalities to artifical ECMs, peptides are covalently incorporated into one of two types of chemically crosslinked hydrogels. The first class of hydrogels is based on naturally occurring fibrin, which is spontaneously formed by the polymerization of fibrinogen in the presence of thrombin and further cross-linked by the transglutaminase activity of factor XIIIa [273][274][275][276][277][278]. Ehrbar et al engineered a vascular endothelial growth factor (VEGF) fusion protein that includes a substrate for binding to the fibrin matrix by transglutaminase during polymerization as well as a plasmin cleavage site for invading cells to release the bound growth factor [276].…”

“…The injectable hydrogels containing bound VEGF were able to induce endothelial cell proliferation better than hydrogels containing only native soluble VEGF. Fibrin matrices were also successfully augmented with bone morphogenetic protein-2 (BMP-2) to promote bone growth and healing [275] and with heparin-binding proteins to promote neurite extension [277].…”

Innovative Strategies for Treatment of Soft Tissue Injuries in Human and Animal Athletes

“…Another approach is to chemically modify titanium prostheses or other materials, if necessary including reactive groups that are able to bind growth factors and to release them slowly. We and others could show that such an approach is able to induce biological activity in model cell lines and in vivo as well, see, e. g. [7,8]. Despite many successful efforts to solve the problem of long-term delivery by strategies like the one just discussed many researchers may prefer gene-therapeutic strategies (cf.…”

Microenvironmental regulation of biomacromolecular therapies

“…Furthermore, coupling oligopeptides that contain the RGD sequence to protein delivery vehicles may also improve the cellular response to growth factors by facilitating cell migration into the material, activating the cells to the desired responsive state and subsequently exposing the cells to the drug in a controlled manner 84 . For example, binding BMP2 to fibrin gels has stimulated the growth of bone into gels in several animal models 85 . In a similar manner, binding of VEGF and RGD-containing oligopeptides to synthetic hydrogels have also stimulated vascularization of the gels 86 .…”