| Therapeutic angiogenesis with angiogenic growth factors has emerged as a promising alternative to conventional invasive therapies for cardiovascular disease. However, clinical trials with vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF) have not yet achieved satisfactory results. Controlled delivery of multiple synergistic angiogenic growth factors is considered as an exciting alternative therapeutic approach to induce a healthy vasculature network. The purpose of this thesis was to develop a poly(lactic-co-glycolic acid)-based combination drug delivery system capable of controlling the release of multiple bioactive angiogenic growth factors over a sustained period of time. There are four parts in the thesis. In part I, a model protein, bovine serum albumin (BSA), was used to optimize protein stability and release from the polymer and to evaluate the correlation between in vitro in vivo stability and release kinetics. The release and stability profile could be modified by adjusting loading of protein and acid neutralizing agent. There was an extremely high correlation of BSA stability and release kinetics between in vitro and in vivo results. In part II, VEGF stability was evaluated in solution and a stabilizing formulation with PLGA impants was developed for VEGF. The stability of VEGF in solution was increased with increased ratios of excess BSA co-encapsulated with the growth factor. With the presence of BSA and the acid-neutralization agent, MgCO3, the bioactivity of VEGF was retained within the polymer and continuous release of VEGF was observed over a month. In part III, the therapeutic effects of VEGF encapsulated in PLGA implants were tested in a hindlimb ischemia model in severe combined immunodeficient mice. The perfusion of hindlimbs was almost fully recovered by the released VEGF. Although VEGF did not rescue all the hindlimbs, it reconstituted significantly more limbs than the blank control. The induced new vasculatures remodeled and became more mature while the number of new vessels decreased over time. In part IV, the dose response was evaluated for VEGF and the combination delivery system with VEGF and bFGF was tested in the hindlimb ischemia model. Ischemic hindlimbs responded in a dose dependent fashion when total dose of controlled release VEGF was increased from 0.3 to 3 microg. Combination delivery of bFGF (0.1 microg) and VEGF (1.0 microg) induced angiogenesis that was comparable to, if not higher than, a 3-fold higher dose of VEGF alone. In conclusion, pH-modified PLGA implants provide a promising delivery system for multiple growth factor delivery and therapeutic angiogenesis.;Keywords: angiogenesis, growth factors, vascular endothelial growth factor, basic fibroblast growth factor, poly(lactic-co-glycolic acid), protein stability, controlled release, bovine serum albumin, hindlimb ischemia, SCID mice... |
