Enhancing the Potency of Growth Factor-Mimicking Peptides via Cross-Presentation With Integrin Ligands

Abstract

Growth factors enhance survival and integration of transplanted Mesenchymal Stromal Cells (MSC), but successful supplementation often requires supraphysiological growth factor doses, risking off-target effects. Short peptide mimics like the knuckle epitope (KE) of Bone Morphogenetic Protein 2 (BMP-2) can be covalently immobilized to biomaterials, localizing bioactivity at the delivery site. However, these short peptides often lack the potency of full-length growth factors. We sought to improve the potency of alginate-grafted KE to encourage MSC osteogenic differentiation. When alginate gels co-presented KE and integrin-binding cyclo-RGD (cRGD) peptides, MSC expressed early markers of osteogenesis (Runt-related Transcription Factor2, RUNX2, Alkaline Phosphatase, ALP, and osteocalcin, OCN) in a KE-dose dependent manner. When co-presented with cRGD, high concentrations of KE partially mimicked the osteogenic potential (ALP induction) of full-length BMP-2. Proximity between KE and cRGD may be the mechanism through which high dose KE induces osteogenesis in the presence of cRGD. To investigate this possibility, we used orthogonal strain-promoted azide-alkyne cycloaddition (SPAAC) and maleimide-thiol chemistries to graft KE and cRGD in a bivalent (same alginate chain) and a monovalent (different alginate chain) manner, at constant bulk peptide concentration. Bivalent presentation of peptides (separation distance of 5.5 ± 0.5 nm verified by FRET) ultimately increased RUNX2 and ALP expression compared to monovalent presentation. This platform technology can be used in future studies to control peptide nanopatterning to enhance potency, in the context of MSC-based therapies and beyond.