Novel Vitronectin: Growth Factor Complexes for Wound Repair and Tissue Regeneration

We recently discovered novel links between insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs) and vitronectin (VN) and have reported that IGF-II can bind directly to VN (Upton et al. 1999, Endo 140:2928-2931), while IGF-I binds indirectly via IGFBP-2, -3, -4 and -5 (Kricker et al. 2003. Endo 144:2807-2815). On-going studies have revealed that these complexes (generically referred to as VitroGro) also stimulate significant migration and proliferation in a variety of skin and corneal epithelial cell lines, including CHO, as well as human mesenchymal cell lines. Importantly, studies in primary cultures derived from adult human skin and cornea have validated these findings. Interestingly, the complexes appear to stimulate enhanced cell growth and migration without affecting differentiation. Furthermore, functional assays using IGF analogues with reduced affinity for the IGF receptor (IGF-IR) (but which retain binding to IGFBPs and VN) and a function-blocking antibody against the VN-binding ￡V integrins, indicate that these complexes enhance proliferation and migration through coordinate activation of both the IGF-IR and VN-binding integrins. Our recent studies have identified structural motifs that are critical for complex formation and conversely, identify potential targets for antagonists. Recognising the fundamental significance of our discoveries, and realising that this phenomenon of matricellular signalling could be exploited as a biological system to deliver growth factors in situations where cell proliferation and migration are wanted, has led us to examine the potential of the complexes in wound repair and ex vivo expansion of progenitor cells for wound repair and tissue regeneration. Thus far we have developed mulitmeric vitronectin complexes that can incorporate IGF, EGF, bFGF and IGFBPs. We are examining these novel complexes in a range of applications including wound healing and tissue engineering. For example, VitroGro has the potential to replace serum and feeder cells for the growth of keratinocytes for use in skin grafts. Our studies have revealed that cells seeded at low density on VitroGro-coated dishes are not only able to survive, but also, to expand more rapidly than cells grown using current clinical protocols (ie. seeded at the same density and grown in the presence of bovine serum and growth-arrested murine feeder cells). In view of these results, we are currently collaborating with the Australian Red Cross Blood Services to further develop the technology to provide a safe, animal-product free, autologous cell-based therapy for burns patients. Clinical trials are scheduled to commence in 2004. We anticipate that a similar approach will be useful to develop safe cell-based therapies for diabetic and venous ulcers, or other cell-based applications that use similar culture technologies, including human embryonic stem cells. Indeed our recent preliminary studies with these cells strongly suggest that this will be the case. Vitronectin is a "sticky" protein and hence can be used to localise growth factors to surfaces where we want cells to migrate and grow. Our preliminary data obtained using osteoblasts (derived from alveolar bone chips) cultured on these scaffolds for 2 weeks, indicate that these cells grow and migrate deeper into VitroGro-treated scaffolds compared to scaffolds treated with foetal calf serum. Thus the complexes have potential as coatings for prosthetics and in the development of "bioactive" dressings for wounds. Research data illustrating addressing these concepts, as well as mechanistic studies examining the molecular basis underlying the responses of cells to these complexes will be presented