Gene transfer to induce angiogenesis in myocardial and limb ischaemia

Angiogenesis: Bench to Bedside, Have We Learned Anything?

End-stage ischemic cardiomyopathy patients are an ever-increasing group of coronary artery disease patients, often with no options in our current treatment armamentarium. Angiogenesis therapy pre-clinical and phase I clinical trials showed great promise, however, the benefits of single growth factor treatments have not been borne out in the larger phase II randomized trials. The complexity of angiogenesis process and the challenges in creating animal models to replicate and study this process in ischemic adult human myocardium have been major limitations to progress in this field. In addition failure to control for the powerful placebo effect in the clinical trials and inadequate methods of outcomes measures assessment have created difficult to overcome road blocks in establishing the efficacy of angiogenic strategies. Herein we review the challenges of angiogenesis research and development of treatment strategies. We also propose a structured model for further investigations of angiogenic therapies. The adherence to such a regimented approach as proposed here is, in our opinion, the only way to achieve success in angiogenesis approach development to treatment of patients with end-stage cardiac ischemia refractory to other established therapies.

Therapeutic angiogenesis for myocardial ischemia

Therapeutic angiogenesis offers promise as a novel treatment for ischemic heart disease, particularly for patients who are not candidates for current methods of revascularization. The goal of treatment is both relief of symptoms of coronary artery disease and improvement of cardiac function by increasing perfusion to the ischemic region. Protein-based therapy with cytokines including vascular endothelial growth factor and fibroblast growth factor demonstrated functionally significant angiogenesis in several animal models. However, clinical trials have yielded largely disappointing results. The attenuated angiogenic response seen in clinical trials of patients with coronary artery disease may be due to multiple factors including endothelial dysfunction, particularly in the context of advanced atherosclerotic disease and associated comorbid conditions, regimens of single agents, as well as inefficiencies of current delivery methods. Gene therapy has several advantages over protein therapy and recent advances in gene transfer techniques have improved the feasibility of this approach. The safety and tolerability of therapeutic angiogenesis by gene transfer has been demonstrated in phase I clinical trials. The utility of therapeutic angiogenesis by gene transfer as a treatment option for ischemic cardiovascular disease will be determined by adequately powered, randomized, placebo-controlled Phase II and III clinical trials. Cell-based therapies offer yet another approach to therapeutic angiogenesis. Although it is a promising therapeutic strategy, additional preclinical studies are warranted to determine the optimal cell type to be administered, as well as the optimal delivery method. It is likely the optimal treatment will involve multiple agents as angiogenesis is a complex process involving a large cascade of cytokines, as well as cells and extracellular matrix, and administration of a single factor may be insufficient. The promise of therapeutic angiogenesis as a novel treatment for no-option patients should be approached with cautious optimism as the field progresses.

A New Technique With Calcium Phosphate Precipitate Enhances Efficiency of In Vivo Plasmid DNA Gene Transfer

In vivo gene transfer with plasmid vector has been applied experimentally and clinically; however, the low level of gene transfer efficiency with plasmid vector is a problem. We speculated that the combination of calcium phosphate precipitate (CaP) and plasmid vector could solve this problem because CaP stabilizes plasmid DNA. In the present study, we used a plasmid exression vector encoding enhanced green fluorescent protein and combined the vector with CaP. Then, this combination was mixed with bovine type I atelocollagen. After incubating this mixture in phosphate-buffered saline, the amount of the plasmid DNA in the supernatant was low when the plasmid DNA was combined with CaP. Furthermore, the plasmid DNA, which was combined with CaP, was stable in DNase digestion in vitro. The plasmid vector with or without CaP, together with the atelocollagen, was transplanted subcutaneously or injected in the bone marrow of the femurs of rats. Then, the fluorescence was observed under a confocal laser scanning microscope and the fluorescence intensity in the tissue homogenates was measured. In these animal experiments, the fluorescence was extensive when the plasmid DNA was combined with CaP. These results indicate that our formula, collagen/CaP/DNA, appeared efficient for in vivo gene transfer.

Primer on medical genomics. Part X: Gene therapy

Gene therapy is defined as any therapeutic procedure in which genes are intentionally introduced into human somatic cells. Both preclinical and clinical gene therapy research have been progressing rapidly during the past 15 years; gene therapy is now a highly promising new modality for the treatment of numerous human disorders. Since the first clinical test of gene therapy in 1989, more than 600 gene therapy protocols have been approved, and more than 3000 patients have received gene therapy. However, at the time of writing this article, no gene therapy products have been approved for clinical use. This article explains the potential clinical scope of gene therapy and the underlying pharmacological principles, describes some of the major gene transfer systems (or vectors) that are used to deliver genes to their target sites, and discusses the various strategies for controlling expression of therapeutic transgenes. Safety issues regarding clinical use of gene therapy are explored, and the most important technical challenges facing this field of research are highlighted. This review should serve as an introduction to the subject of gene therapy for clinician investigators, physicians and medical scientists in training, practicing clinicians, and other students of medicine.

Gene therapy progress and prospects: therapeutic angiogenesis for limb and myocardial ischemia

After extensive investigation in preclinical studies and recent clinical trials, gene therapy has been established as a potential method to induce therapeutic angiogenesis in ischemic myocardial and limb disease. Advancements in viral and nonviral vector technology including cell-based gene transfer will continue to improve transgene transmission and expression efficiency. An alternative strategy to the use of transgenes encoding angiogenic growth factors is therapy based on transcription factors such as hypoxia-inducible factor-1alpha (HIF-1alpha) that regulate the expression of multiple angiogenic genes. Further understanding of the underlying biology of neovascularization is needed to determine the ability of growth factors to induce functionally significant angiogenesis in patients with atherosclerotic disease and associated comorbid conditions including endothelial dysfunction, which may inhibit blood vessel growth. The safety and tolerability of therapeutic angiogenesis by gene transfer has been demonstrated in phase I clinical trials. However, limited evidence of efficacy resulted from early phase II studies of angiogenic gene therapy for ischemic myocardial and limb disease. The utility of therapeutic angiogenesis by gene transfer as a treatment option for ischemic cardiovascular disease will be determined by adequately powered, randomized, placebo-controlled phase II and III clinical trials.

Therapeutic angiogenesis: protein-based therapy for coronary artery disease

Therapeutic angiogenesis is a promising treatment for ischaemic heart disease, particularly for patients who are not candidates for current methods of revascularisation. The goal of angiogenic therapy is the relief of symptoms of coronary artery disease and improvement of cardiac function by increasing perfusion to the ischaemic myocardium. Angiogenic cytokines such as fibroblast growth factor and vascular endothelial growth factor have been studied extensively in preclinical studies. Protein-based therapy with these growth factors has produced functionally significant angiogenesis in several animal models. Enthusiasm following these preclinical results led the way to clinical trials, which so far have shown only modest improvements in myocardial perfusion and clinical outcome. The attenuated angiogenic response to growth factor therapy observed in patients with coronary artery disease may be related to associated conditions such as endothelial dysfunction, regimens of single as opposed to multiple angiogenic agents and inefficiency of current delivery modalities, as illustrated by the disappointing results of the Phase II clinical trials using intravascular techniques of administration. The ultimate role angiogenesis will play clinically in the treatment of ischaemic heart disease will be determined by adequately powered, randomised, double-blind, placebo-controlled trials that include multi-agent angiogenic therapy and intramyocardial methods of delivery.

The role of fibroblast growth factors in vascular development

Fibroblast growth factors (FGFs) are considered angiogenic factors, yet the exact relationship between FGF and vascular development in normal and pathological tissue has long remained elusive. However, recent results from gene inactivation and transgenic studies in mice and in culture systems have demonstrated the role of FGFs in vessel assembly and sprouting. FGFs also promote blood-vessel branching and induce lymphangiogenesis. Novel players in FGF-mediated angiogenesis have been identified, such as p38 mitogen-activated protein kinase. Tumour angiogenesis is regulated by FGFs directly or indirectly via secondary angiogenesis factors, such as vascular endothelial growth factor. The newly established angiogenic role of FGFs makes FGF or molecules targeting FGF and its receptor promising candidates for the development of novel therapeutics.

Myogenic Akt signaling regulates blood vessel recruitment during myofiber growth

Blood vessel recruitment is an important feature of normal tissue growth. Here, we examined the role of Akt signaling in coordinating angiogenesis with skeletal muscle hypertrophy. Hypertrophy of C2C12 myotubes in response to insulin-like growth factor 1 or insulin and dexamethasone resulted in a marked increase in the secretion of vascular endothelial growth factor (VEGF). Myofiber hypertrophy and hypertrophy-associated VEGF synthesis were specifically inhibited by the transduction of a dominant-negative mutant of the Akt1 serine-threonine protein kinase. Conversely, transduction of constitutively active Akt1 increased myofiber size and led to a robust induction of VEGF protein production. Akt-mediated control of VEGF expression occurred at the level of transcription, and the hypoxia-inducible factor 1 regulatory element was dispensable for this regulation. The activation of Akt1 signaling in normal mouse gastrocnemius muscle was sufficient to promote myofiber hypertrophy, which was accompanied by an increase in circulating and tissue-resident VEGF levels and high capillary vessel densities at focal regions of high Akt transgene expression. In a rabbit hind limb model of vascular insufficiency, intramuscular activation of Akt1 signaling promoted collateral and capillary vessel formation and an accompanying increase in limb perfusion. These data suggest that myogenic Akt signaling controls both fiber hypertrophy and angiogenic growth factor synthesis, illustrating a mechanism through which blood vessel recruitment can be coupled to normal tissue growth.