Cellular therapy is becoming a widely accepted procedure for patients with end-stage cardiovascular disease. Purified autologous cells that can be re-injected are the obvious choice and primary myoblasts have been the first to be used in clinical post-infarction transplantation. Phase I trials have established feasibility and safety, but efficacy of this procedure remains somewhat skeptical. These primary myoblasts have demonstrated engraftment and improvement in left ventricular function but with adverse event of arrhythmia. However, cardiomyocyte protection and vessel collateralization of the myocardium is not primarily affected. Genetic modification of the injected primary myoblasts to express a pro-angiogenic, anti-apoptotic molecule may reduce myocardial damage and scar formation and elicit a more efficacious response than un-modified cells. Non-viral polymers possess several characteristics that are favorable for use in cellular therapy of ischemic myocardium. Since expression is only required for a short amount of time, the transient expression of non-viral carriers is preferred. There is no integration of the therapeutic genes within the cellular genome to raise the fear of unrestricted growth. Non-viral polymers are biocompatible and non-immunogenic so that little to no toxicity is present upon transfection or subsequent transplantation. We propose that the novel bioreducible polymer, poly(cystamine bisacrylamide-diaminohexane), poly(CBA-DAH) will transfect primary myoblasts with superior efficiency and minimal toxicity compared to other non-viral polymeric carriers. This novel bioreducible polymer has demonstrated high transfection rates and little toxicity in several different cell lines, including primary myoblasts. This has been attributed to the reducible nature of the polymer once it enters the cytosol. Physiochemical properties of the synthesized polymer will be ascertained using established methods such as nuclear magnetic resonance (1H-NMR) and high performance liquid chromatography (HPLC). The poly(CBA-DAH)/pCMV-VEGF polyplexes will be evaluated by electrophoretic mobility shift assay, dynamic light scattering (DLS), zeta potential, and cytosolic degradation kinetics. Effective delivery will be evaluated by in vitro and in vivo expression of VEGF by genetically modified primary myoblasts and its downstream effects (qRT-PCR and Western blot analysis, for apoptosis and angiogenesis assays). Primary characterization of where and how many cells to inject into infarcted myocardium will assist in characterizing initial in vivo experiments. This will be paired with immunogenicity, toxicity and biodistribution studies for safety. Completion of the proposal will include functional studies consisting magnetic resonance imaging, infarct size, left ventricular wall thickness, and leukocyte infiltration in rat model.
Despite advances in cellular transplantation therapies for coronary artery disease, functional recovery following cardiac ischemia remains a major cause of morbidity and mortality. At the present time, there is no clinically reliable means to prevent ischemia/reperfusion injury to the myocardium. In this application, we propose to develop a novel bioreducible polymer to deliver VEGF gene to primary myoblasts for the treatment of acute myocardial infarct to address these short- comings of current therapeutic strategies.
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