Harnessing stem cells as drug delivery vehicles for therapeutic angiogenesis [electronic resource] : a biomaterials-mediated approach
Keywords: Bioengineering.

Cardiovascular disease (CVD) represents a global medical and economic problem with high morbidity and mortality rates. CVD is often associated with partial occlusion of the blood vessels and tissue ischemia, and restoring blood supply to ischemic tissues is critical to prevent irreversible tissue damage. Therapeutic angiogenesis aims to stimulate the growth of new blood vessels from pre-existing vessels, which offers a valuable tool for treating CVD. Several strategies have been developed to promote angiogenesis, including growth factor delivery and gene therapy. Direct delivery of angiogenic growth factors has the potential to stimulate new blood vessel growth. However, it is limited by short half-lives in vivo, and uncontrolled diffusion of angiogenic factors may also cause undesirable side effects. Gene therapy offers an alternative approach by delivering genes encoding angiogenic factors, but previous approaches often require the use of viral vectors for efficient gene delivery, and are limited by safety concerns such as immunogenicity. The goal of this thesis research is to develop novel strategies for stimulating therapeutic angiogenesis by harnessing stem cells as drug delivery vehicles and to validate the efficacy of non-viral engineered stem cells in vivo using mouse models of hindlimb ischemia. Our strategy takes advantage of the natural homing capacity of stem cells towards ischemic tissues in vivo, and their ability to secrete paracrine signals to stimulate blood vessel growth. Specifically we developed two strategies including: (1) isolating and transfecting stem cells ex vivo using biodegradable polymeric nanoparticles to overexpress therapeutic genes, followed by transplanting non-viral engineered stem cells back to ischemic tissues; and (2) recruiting and programming endogenous stem cells in situ using biomaterials-mediated delivery of biologics. In the first strategy, we have chosen adipose-derived stem cells (ADSCs), an abundantly available autologous cell source that can be easily obtained in a minimally invasive manner. To enhance the paracrine signaling of ADSCs for therapeutic angiogenesis, we transfected ADSCs using in-house developed biodegradable polymeric nanoparticles, which eliminate the dependence on viruses for efficient gene delivery. Using the optimized polymeric vectors, we examined the efficacy of ADSCs overexpressing various angiogenic factors or homing factors on therapeutic angiogenesis in vitro and in vivo. Transplantation of non-viral engineered ADSCs led to significantly enhanced tissue salvage in a murine model of hindlimb ischemia with faster restoration of blood reperfusion and muscle regeneration. Our results suggest that stem cells programmed with biodegradable polymeric nanoparticles can serve as delivery vehicles to express therapeutic factors in situ to promote therapeutic angiogenesis. In the second strategy, we seek to circumvent the need of isolating and manipulating stem cells ex vivo by directly recruiting and transfecting endogenous progenitor cells in situ at the site of ischemia. To achieve this, we developed a biomaterials-mediated delivery platform for sequential release of stem cell homing factors and DNA encoding therapeutic genes. Our results show that biomaterials-mediated release of homing factors followed by delayed DNA delivery enhanced recruitment of endogenous progenitor cells and improved limb salvage in a mouse model of hindlimb ischemia. Finally, we demonstrate the potential of using microfluidic-synthesized microspheres to aid therapeutic angiogenesis using a biomaterials-mediated drug delivery depot.