Myoblast‐mediated gene transfer for therapeutic angiogenesis and arteriogenesis

Abstract

Therapeutic angiogenesis aims at generating new blood vessels by delivering growth factors such as VEGF and FGF. Clinical trials are underway in patients with peripheral vascular and coronary heart disease. However, increasing evidence indicates that the new vasculature needs to be stabilized to avoid deleterious effects such as edema and hemangioma formation. Moreover, a major challenge is to induce new vessels that persist following cessation of the angiogenic stimulus. Mature vessels may be generated by modulating timing and dosage of growth factor expression, or by combination of 'growth' factors with 'maturation' factors like PDGF-BB, angiopoietin-1 or TGF-b. Myoblastmediated gene transfer has unique characteristics that make it a useful tool for studying promising novel approaches to therapeutic angiogenesis. It affords robust and long-lasting expression, and can be considered as a relatively rapid form of 'adult transgenesis' in muscle. The combined insertion of different gene constructs into single myoblasts and their progeny allows the simultaneous expression of different 'growth' and 'maturation' factors within the same cell in vivo. The additional insertion of a reporter gene makes it possible to analyze the phenotype of the vessels surrounding the transgenic muscle fibers into which the myoblasts have fused. The effects of timing and duration of gene expression can be studied by using tetracycline-inducible constructs, and dosage effects by selecting subpopulations consistently expressing distinct levels of growth factors. Finally, the autologous cellbased approach using transduced myoblasts could be an alternative gene delivery system for therapeutic angiogenesis in patients, avoiding the toxicities seen with some viral vectors.

Controlled Angiogenesis in the Heart by Cell-Based Expression of Specific Vascular Endothelial Growth Factor Levels

“…In particular, VEGF overexpression has been shown to induce angioma growth in the heart both with cell-based expression (Lee et al, 2000) and gene therapy vectors (Schwarz et al, 2000). Furthermore, such aberrant vessels failed to contribute to blood flow recovery in ischemic tissue (von Degenfeld et al, 2006) and even generated functional arteriovenous shunts that excluded the downstream microcirculation (Choi et al, 2011). Clinical angioma formation has been reported only once, after intra-arterial delivery of a plasmid DNA vector (Isner et al, 1996).…”

“…Four weeks posttreatment, rats were sacrificed by exsanguination under the same anesthesia conditions as already described, and the hearts were then collected, embedded in OCT compound (Sakura Finetek, Torrance, CA), and frozen in isopentane cooled in liquid nitrogen. In some experiments, fluorescein isothiocyanate (FITC)-labeled Lycopersicon esculentum lectin (250 lg in 250 ll; Vector Laboratories, Burlingame, CA) was injected into the femoral vein and allowed to circulate for 4 min before sacrifice in order to label perfused vessels as previously described (von Degenfeld et al, 2006).…”

“…On the other hand, excessive VEGF expression has the potential to induce the growth of angioma-like vascular tumors (Lee et al, 2000;Schwarz et al, 2000). We previously found that, since VEGF binds tightly to extracellular matrix, the induction of normal or aberrant angiogenesis depends strictly on its amount localized in the microenvironment around each producing cell and not on the total dose delivered (Ozawa et al, 2004;von Degenfeld et al, 2006). This finding helps to explain the apparently narrow therapeutic window for VEGF gene delivery and its lack of efficacy at safe doses in clinical trials of therapeutic angiogenesis (Ylä -Herttuala et al, 2004), in which only the total dose of vector could be controlled, but not its expression in individual cells, leading to a heterogeneous distribution of microenvironmental levels within the tissue (Banfi et al, 2005).…”

Angiogenesis and hypertension: an update

“…70 Likewise, an intervention that controlled the level of VEGF in the microenvironment by using the implantation of engineered myoblasts converted pathological angiogenesis into therapeutic angiogenesis in mice. 71 Combinations of several angiogenic factors induce a more secured and stable vasculature than the administration of single growth factors. 72 This concept has been tested recently in a clinical phase-I trial by introducing the pro-angiogenic transcription factor hypoxia-inducible factor 1a, which is expected to activate all genes needed for proper microvessel growth.…”

Myoblast Therapy: From Bench to Bedside

“…They also demon-(hGH) (14). This approach, which used transduced myoblasts, could also function as an alternative gene delivstrated that the adverse event of arrhythmia did occur, but was found to be controlled by medication, without ery system for therapeutic angiogenesis in patients, avoiding the toxicities seen with some viral vectors (61). hospitalization or the implantation of a cardioverterdefibrillator.…”