Assessment of risks associated with cardiovascular gene therapy in human subjects

Fibroblast transition to an endothelial "trans" state improves cell reprogramming efficiency

Fibroblast reprogramming offers the potential for myocardial regeneration via in situ cell transdifferentiation. We explored a novel strategy leveraging endothelial cell plasticity to enhance reprogramming efficiency. Rat cardiac endothelial cells and fibroblasts were treated with Gata4, Mef2c, and Tbx5 (GMT) to assess the cardio-differentiation potential of these cells. The endothelial cell transdifferentiation factor ETV2 was transiently over-expressed in fibroblasts followed by GMT treatment to assess “trans-endothelial” cardio-differentiation. Endothelial cells treated with GMT generated more cTnT⁺ cells than did cardiac fibroblasts (13% ± 2% vs 4% ± 0.5%, p < 0.01). Cardiac fibroblasts treated with ETV2 demonstrated increased endothelial cell markers, and when then treated with GMT yielded greater prevalence of cells expressing cardiomyocyte markers including cTnT than did fibroblasts treated with GMT or ETV2 (10.3% ± 0.2% vs 1.7% ± 0.06% and 0.6 ± 0.03, p < 0.01). Rat cardiac fibroblasts treated with GMT + ETV2 demonstrated calcium transients upon electrical stimulation and contractility synchronous with surrounding neonatal cardiomyocytes, whereas cells treated with GMT or ETV2 alone failed to contract in co-culture experiments. Human cardiac fibroblasts treated with ETV2 and then GMT likewise demonstrated greater prevalence of cTnT expression than did cells treated with GMT alone (2.8-fold increase, p < 0.05). Cardiac fibroblast transitioning through a trans-endothelial state appears to enhance cardio-differentiation by enhancing fibroblast plasticity.

Angiogenic Abnormalities in Diabetes Mellitus: Mechanistic and Clinical Aspects

CONTEXT

Diabetes causes severe pathological changes to the microvasculature in many organs and tissues and is at the same time associated with an increased risk of coronary and peripheral macrovascular events. We herein review alterations in angiogenesis observed in human and experimental diabetes and how they contribute to diabetes onset and development of vascular complications.

EVIDENCE ACQUISITION

The English language medical literature was searched for articles reporting on angiogenesis/vasculogenesis abnormalities in diabetes and their clinical manifestations, mechanistic aspects, and possible therapeutic implications.

EVIDENCE SYNTHESIS

Angiogenesis is a complex process, driven by a multiplicity of molecular mechanisms and involved in several physiological and pathological conditions. Incompetent angiogenesis is pervasive in diabetic vascular complications, with both excessive and defective angiogenesis observed in various tissues. A striking different angiogenic response typically occurs in the retina vs the myocardium and peripheral circulation, but some commonalities in abnormal angiogenesis can explain the well-known association between microangiopathy and macroangiopathy. Impaired angiogenesis can also affect endocrine islet and adipose tissue function, providing a link to diabetes onset. Exposure to high glucose itself directly affects angiogenic/vasculogenic processes, and the mechanisms include defective responses to hypoxia and proangiogenic factors, impaired nitric oxide bioavailability, shortage of proangiogenic cells, and loss of pericytes.

CONCLUSIONS

Dissecting the molecular drivers of tissue-specific alterations of angiogenesis/vasculogenesis is an important challenge to devise new therapeutic approaches. Angiogenesis-modulating therapies should be carefully evaluated in view of their potential off-target effects. At present, glycemic control remains the most reasonable therapeutic strategy to normalize angiogenesis in diabetes.

Comparison of Mean VEGF-A Expression Between Acute Ischemic Stroke Patients and Non-Ischemic Stroke Subjects

BACKGROUND

Glucose and oxygen supply to neurons are disrupted during acute ischemic stroke, resulting in hypoxia. This event, in turn, activates the transcription of hypoxia-inducible factor (HIF-1), which is responsible for activating genes responsible for angiogenesis, including vascular endothelial growth factor (VEGF). VEGF and their receptor systems exert complex mechanisms of angiogenesis, including the stimulator, inhibitors, angiogenic and modulator. VEGF-A is the primary regulator of angiogenesis, both during physiological and pathological conditions. Nevertheless, the role of VEGF on the prognosis of hypoxia remains controversial.

AIM

The purpose of this study was to address if there is any difference between the mean expression of VEGF-A between acute ischemic patients and non-ischemic stroke subjects.

METHODS

This was an observational study with a cross-sectional design, the population in this research is the acute ischemic stroke patients and non-ischemic stroke subjects, which were admitted on Emergency Room and later treated in the Stroke Unit, Dr Sardjito General Hospital, Yogyakarta, Indonesia. Subjects were recruited using the purposive method, yielding a total of 64 subjects on both groups. Diagnosis of acute ischemic stroke was established using a head CT scan. Patients who meet the inclusion criteria and willing to participate in the study were asked to provide informed consent. Laboratory analysis was conducted during the first 24 hours after being treated at Stroke Unit, Dr Sardjito General Hospital, Yogyakarta, Indonesia, with venous blood was withdrawn VEGF-A levels between acute ischemic stroke and non-ischemic stroke subjects were subsequently compared. Categorical variables (including gender) were tested using either chi-square or Fisher exact test. Interval data was examined using student t-test if data distribution was normal.

RESULTS

As many as 35 acute ischemic stroke and 35 non-ischemic stroke patients were included in the study, among whom were 18 men (51.43%) and 17 women (48.57%) among stroke patients and 21 (60%) men and 14 (40%) women among subjects without stroke. The average of the subject's age on stroke and non-ischemic stroke group was 58.51 and 48.57 years old. VEGF-A levels were significantly higher in the non-stroke group (561.77 ± 377.92) compared with stroke group (397.78 ± 181.53) with p = 0.02.

CONCLUSION

expression of VEGF-A in acute ischemic stroke group was lower when compared with the non-stroke group.

Adenovirus-mediated transfer of VEGF into marrow stromal cells combined with PLGA/TCP scaffold increases vascularization and promotes bone repair in vivo

INTRODUCTION

Large osseous defect remains a serious clinical problem due to the lack of sufficient blood supply and it has been proposed that this situation can be relieved by accelerating the formation of new vessels in the process of bone defect repair. The aim of this study was to develop a new type of artificial bone by transferring the VEGF gene into marrow stromal cells (MSCs) and seeding them into a porous scaffold.

MATERIAL AND METHODS

An adenovirus vector was employed to transfer the VEGF gene into MSCs and expression of the exogenous gene was confirmed by ELISA. Next the transduced cells were seeded into a collagen I modified PLGA/TCP scaffold. The constructed new complex artificial bone was then assessed for biocompatibility in vitro and blood vessel formation and bone formation in vivo.

RESULTS

We found that adenovirus mediated VEGF gene transfer into MSCs sustained VEGF expression in MSCs for 3 weeks. Porous scaffold PLGA/TCP made by rapid prototyping technology exhibited improved biocompatibility resulting from crosslinking with collagen I. Furthermore, the in vivo study showed that large amounts of blood vessels were detected histologically 1 week after artificial bone implantation, and significant bone formation was detected 8 weeks after implantation.

CONCLUSIONS

Our findings suggest that gene transfer of VEGF into MSCs combined with PLGA/TCP scaffold enhances bone repair in vivo by promoting vascularization.

Arteriogenic therapy based on simultaneous delivery of VEGF-A and FGF4 genes improves the recovery from acute limb ischemia

Background

Gene therapy stimulating the growth of blood vessels is considered for the treatment of peripheral and myocardial ischemia. Here we aimed to achieve angiogenic synergism between vascular endothelial growth factor-A (VEGF-A, VEGF) and fibroblast growth factor 4 (FGF4) in murine normoperfused and ischemic limb muscles.

Methods

Adeno-associated viral vectors (AAVs) carrying β-galactosidase gene (AAV-LacZ), VEGF-A (AAV-VEGF-A) or two angiogenic genes (AAV-FGF4-IRES-VEGF-A) were injected into the normo-perfused adductor muscles of C57Bl/6 mice. Moreover, in a different experiment, mice were subjected to unilateral hindlimb ischemia by femoral artery ligation followed by intramuscular injections of AAV-LacZ, AAV-VEGF-A or AAV-FGF4-IRES-VEGF-A below the site of ligation. Post-ischemic blood flow recovery was assessed sequentially by color laser Doppler. Mice were monitored for 28 days.

Results

VEGF-A delivered alone (AAV-VEGF-A) or in combination with FGF4 (AAV-FGF4-IRES-VEGF-A) increased the number of capillaries in normo-perfused hindlimbs when compared to AAV-LacZ. Simultaneous overexpression of both agents (VEGF-A and FGF4) stimulated the capillary wall remodeling in the non-ischemic model. Moreover, AAV-FGF4-IRES-VEGF-A faster restored the post-ischemic foot blood flow and decreased the incidence of toe necrosis in comparison to AAV-LacZ.

Conclusions

Synergy between VEGF-A and FGF4 to produce stable and functional blood vessels may be considered a promising option in cardiovascular gene therapy.

Mechanistic, technical, and clinical perspectives in therapeutic stimulation of coronary collateral development by angiogenic growth factors

Stimulation of collateral vessel development in the heart by angiogenic growth factor therapy has been tested in animals and humans for almost two decades. Discordance between the outcome of preclinical studies and clinical trials pointed to the difficulties of translation from animal models to patients. Lessons learned in this process identified specific mechanistic, technical, and clinical hurdles, which need to be overcome. This review summarizes current understanding of the mechanisms leading to the establishment of a functional coronary collateral network and the biological processes growth factor therapies should stimulate even under conditions of impaired natural adaptive vascular response. Vector delivery methods are recommended to maximize angiogenic gene therapy efficiency and reduce side effects. Optimization of clinical trial design should include the choice of clinical end points which provide mechanistic proof-of-concept and also reflect clinical benefits (e.g., surrogates to assess increased collateral flow reserve, such as myocardial perfusion imaging). Guidelines are proposed to select patients who may respond to the therapy with high(er) probability. Both short and longer term strategies are outlined which may help to make therapeutic angiogenesis (TA) work in the future.

Non-invasive bioluminescence imaging of myoblast-mediated hypoxia-inducible factor-1 alpha gene transfer

PURPOSE

We tested a novel imaging strategy, in which both the survival of transplanted myoblasts and their therapeutic transgene expression, a recombinant hypoxia-inducible factor-1α (HIF-1α-VP2), can be monitored using firefly luciferase (fluc) and Renilla luciferase (hrl) bioluminescence reporter genes, respectively.

PROCEDURES

The plasmid pUbi-hrl-pUbi-HIF-1α-VP2, which expresses both hrl and HIF-1α-VP2 using two ubiquitin promoters, was characterized in vitro. C2c12 myoblasts stably expressing fluc and transiently transfected with pUbi-hrl-pUbi-HIF-1α-VP2 were injected into the mouse hindlimb. Both hrl and fluc expression were monitored using bioluminescence imaging (BLI).

RESULTS

Strong correlations existed between the expression of hRL and each of HIF-1α-VP2, VEGF, and PlGF (r(2) > 0.83, r(2) > 0.82, and r(2) > 0.97, respectively). In vivo, both transplanted cells and HIF-1α-VP2 transgene expression were successfully imaged using BLI.

CONCLUSIONS

An objective evaluation of myoblast-mediated gene transfer in living mice can be performed by monitoring both the survival and the transgene expression of transplanted myoblasts using the techniques developed herein.

Tissue-engineered provisional matrix as a novel approach to enhance diabetic wound healing

Inherent pathologies associated with diabetic wound microenvironment including increased proteolysis, inflammatory dysregulation, and impaired neovascularization prevent timely resolution of chronic diabetic ulcers. It is hypothesized that augmentation of local wound microenvironment with a stable provisional matrix formed by proteolysis-resistant angiogenic peptide nanofibers (NFs) will create permissive environment for attenuated inflammation, enhanced neovascularization, and improved diabetic wound healing. Using murine excisional wound healing models, full-thickness dorsal skin wounds were treated with either NFs or control solutions (phosphate buffered saline; hyaluronic acid) and analyzed for morphology, inflammatory response, neovascularization, and biomechanical properties. NF treatment of diabetic wounds stimulated formation of a robust pro-angiogenic in situ tissue-engineered provisional matrix leading to a significant decrease in wound inflammatory cell infiltration and proinflammatory interleukin-6 levels, a significant increase in endothelial and endothelial progenitor cell infiltration, vascular endothelial growth factor levels, and neovascularization (day 7), as well as improved wound morphology, accelerated wound closure, and significantly stronger repair tissue (day 28). These results suggest that appropriate design of provisional matrix may compensate for some of the complex disruptions in diabetic wound microenvironment and provide missing cues to cells and direct in situ responses toward improved healing, which is promising for future development of new therapies for diabetic ulcers.

Capillary enlargement, not sprouting angiogenesis, determines beneficial therapeutic effects and side effects of angiogenic gene therapy

AIMS

Currently, it is still unclear which mechanisms drive metabolic benefits after angiogenic gene therapy. The side-effect profile of efficient angiogenic gene therapy is also currently incompletely understood. In this study, the effects of increasing doses of adenoviral (Ad) vascular endothelial growth factor-A (VEGF-A) were evaluated on vascular growth, metabolic benefits, and systemic side effects.

METHODS AND RESULTS

Adenoviral vascular endothelial growth factor-A or AdLacZ control was injected intramuscularly (10(9)-10(11) vp/mL) or intra-arterially (5 × 10(11) vp/mL) into rabbit (n = 102) hindlimb muscles and examined 6 or 14 days later. Blood flow, tissue oedema, metabolic benefits, and the structure of angiogenic vessels were assessed using ultrasound imaging, modified Miles assay, arterial blood gas and metabolite analyses, and light and confocal microscopy, respectively. Safety analyses included cardiac ultrasound, electrocardiograms, and blood and tissue samples. Sprouting angiogenesis was already induced with low AdVEGF-A concentrations, whereas higher concentrations were needed to reach efficient capillary enlargement and increases in target muscle perfusion. Interestingly, metabolic benefits, such as improved aerobic energy metabolism and decreased metabolic acidosis during exercise, after AdVEGF-A administration were highly correlated to the level of capillary enlargement but not to sprouting angiogenesis. Several systemic dose-dependent side effects, including transient increases in liver, kidney, and pancreatic enzymes, and signs of cardiac effects were observed.

CONCLUSION

Efficient capillary enlargement leading to significant increases in tissue perfusion is needed to gain metabolic benefits after angiogenic gene therapy. However, the risk of systemic side effects can increase as the efficiency of angiogenic gene therapy is improved. Importantly, the unstable wall structure of the newly formed vessels seems not to compromise the metabolic benefits.

Active Rac1 improves pathologic VEGF neovessel architecture and reduces vascular leak: mechanistic similarities with angiopoietin-1

Architecturally defective, leaky blood vessels typify pathologic angiogenesis induced by vascular endothelial growth factor-A (VEGF-A). Such neovascular defects aggravate disease pathology and seriously compromise the therapeutic utility of VEGF. Endothelial cell (EC) transduction with active L61Rac1 strongly improved VEGF-driven angiogenesis in vivo as measured by increased neovascular density, enhanced lumen formation, and reduced vessel leakiness. Conversely, transduction with dominant-negative N17Rac1 strongly inhibited neovascularization. In vitro, active L61Rac1 promoted organization of cortical actin filaments and vascular cords and improved EC-EC junctions, indicating that improved cytoskeletal dynamics are important to the mechanism by which active L61Rac1 rectifies VEGF-driven angiogenesis. SEW2871, a sphingosine 1-phosphate receptor-1 agonist that activates Rac1 in ECs, improved cord formation and EC-EC junctions in vitro similarly to active L61Rac. Moreover, SEW2871 administration in vivo markedly improved VEGF neovessel architecture and reduced neovascular leak. Angiopoietin-1, a cytokine that "normalizes" VEGF neovessels in vivo, activated Rac1 and improved cord formation and EC-EC junctions in vitro comparably to active L61Rac1, and a specific Rac1 inhibitor blocked these effects. These studies distinguish augmentation of Rac1 activity as a means to rectify the pathologic angioarchitecture and dysfunctionality of VEGF neovessels, and they identify a rational pharmacologic strategy for improving VEGF angiogenesis.

Current strategies for myocardial gene delivery

Existing methods of cardiac gene delivery can be classified by the site of injection, interventional approach and type of cardiac circulation at the time of transfer. General criteria to assess the efficacy of a given delivery method include: global versus regional myocardial transduction, technical complexity and the pathophysiological effects associated with its use, delivery-related collateral expression and the delivery-associated inflammatory and immune response. Direct gene delivery (intramyocardial, endocardial, epicardial) may be useful for therapeutic angiogenesis and for focal arrhythmia therapy but with gene expression which is primarily limited to regions in close proximity to the injection site. An often unappreciated limitation of these techniques is that they are frequently associated with substantial systemic vector delivery. Percutaneous infusion of vector into the coronary arteries is minimally invasive and allows for transgene delivery to the whole myocardium. Unfortunately, efficiency of intracoronary delivery is highly variable and the short residence time of vector within the coronary circulation and significant collateral organ expression limit its clinical potential. Surgical techniques, including the incorporation of cardiopulmonary bypass with isolated cardiac recirculation, represent novel delivery strategies that may potentially overcome these limitations; yet, these techniques are complex with inherent morbidity that must be thoroughly evaluated before safe translation into clinical practice. Characteristics of the optimal technique for gene delivery include low morbidity, increased myocardial transcapillary gradient, extended vector residence time in the coronary circulation and exclusion of residual vector from the systemic circulation after delivery to minimize extracardiac expression and to mitigate a cellular immune response. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Treatment of heart failure by calcium cycling gene therapy

Heart failure is a major cause of morbidity and mortality in Western countries. While progress in conventional treatment modalities is making steady and incremental gains to reduce this disease burden, there remains a need to explore new and potentially therapeutic approaches. Gene therapy, for example, was initially envisioned as a treatment strategy for inherited monogenic disorders. It is now apparent that gene therapy has broader potential, which also includes acquired polygenic diseases such as heart failure. Advances in the understanding of the molecular basis of conditions such as these, together with the evolution of increasingly efficient gene transfer technology, has placed congestive heart failure within the reach of gene-based therapy.

Apelin induces enlarged and nonleaky blood vessels for functional recovery from ischemia

The efficacy of therapeutic angiogenesis for revascularization in ischemia using genes, proteins, and cells has been established. For further improvement, processes allowing enlargement of the luminal cavity to facilitate efficient blood flow need to be facilitated. Recently, we found that expression of APJ and its specific ligand, apelin, is seen in endothelial cells when angiogenesis is taking place during embryogenesis. Apelin-deficient mice are viable but have narrow intersomitic vessels during embryogenesis and narrow blood vessels in the trachea and skin after birth. Apelin induces the formation of larger cords of endothelial cells, mainly mediated by cell-cell aggregation, resulting in the generation of larger blood vessels. Here we report that transgenic overexpression of apelin in keratinocytes induces enlarged but not leaky blood vessels in the dermis. In the hind limb ischemia model, apelin together with vascular endothelial growth factor (VEGF) effectively induced functional vessels larger than with VEGF alone. Endogenous apelin is required for the suppression of VEGF-, histamine-, or inflammation-induced vascular hyperpermeability. Apelin inhibited the down-modulation of vascular endothelial-cadherin by VEGF, resulting in suppression of hyperpermeability. Our results suggest apelin efficacy for therapeutic angiogenesis.

Indirect imaging of cardiac-specific transgene expression using a bidirectional two-step transcriptional amplification strategy

Transcriptional targeting for cardiac gene therapy is limited by the relatively weak activity of most cardiac-specific promoters. We have developed a bidirectional plasmid vector, which uses a two-step transcriptional amplification (TSTA) strategy to enhance the expression of two optical reporter genes, firefly luciferase (fluc) and Renilla luciferase (hrluc), driven by the cardiac troponin T (cTnT) promoter. The vector was characterized in vitro and in living mice using luminometry and bioluminescence imaging to assess its ability to mediate strong, correlated reporter gene expression in a cardiac cell line and the myocardium, while minimizing expression in non-cardiac cell lines and the liver. In vitro, the TSTA system significantly enhanced cTnT-mediated reporter gene expression with moderate preservation of cardiac specificity. After intramyocardial and hydrodynamic tail vein delivery of an hrluc-enhanced variant of the vector, long-term fluc expression was observed in the heart, but not in the liver. In both the cardiac cell line and the myocardium, fluc expression correlated well with hrluc expression. These results show the vector's ability to effectively amplify and couple transgene expression in a cardiac-specific manner. Further replacement of either reporter gene with a therapeutic gene should allow non-invasive imaging of targeted gene therapy in living subjects.

Stem cell-mediated neovascularization in heart repair

Accumulating clinical and experimental evidence indicates that stem cells from various sources are promising in the treatment of cardiac dysfunction. They may be incorporated into neovascular foci and thus contribute to postnatal physiological and pathological vasculogenesis and/or produce a variety of growth factors for angiogenesis and cytokines that home other stem cells from other organs for cardiac regeneration. This review focuses on the neovascularization of stem cells from different sources in cardiac repair, with emphasis on adult stem cells.

Human studies of angiogenic gene therapy

Despite significant advances in medical, interventional, and surgical therapy for coronary and peripheral arterial disease, the burden of these illnesses remains high. To address this unmet need, the science of therapeutic angiogenesis has been evolving for almost two decades. Early preclinical studies and phase I clinical trials achieved promising results with growth factors administered as recombinant proteins or as single-agent gene therapies, and data accumulated through 10 years of clinical trials indicate that gene therapy has an acceptable safety profile. However, more rigorous phase II and phase III clinical trials have failed to unequivocally demonstrate that angiogenic agents are beneficial under the conditions and in the patients studied to date. Investigators have worked to understand the biology of the vascular system and to incorporate their findings into new treatments for patients with ischemic disease. Recent gene- and cell-therapy trials have demonstrated the bioactivity of several new agents and treatment strategies. Collectively, these observations have renewed interest in the mechanisms of angiogenesis and deepened our understanding of the complexity of vascular regeneration. Gene therapy that incorporates multiple growth factors, approaches that combine cell and gene therapy, and the administration of "master switch" agents that activate numerous downstream pathways are among the credible and plausible steps forward. In this review, we examine the clinical development of angiogenic gene therapy, summarize several of the lessons learned during the conduct of these trials, and suggest how this prior experience may guide the conduct of future preclinical investigations and clinical trials.

In vivo properties of the proangiogenic peptide QK

The main regulator of neovascularization is Vascular Endothelial Growth Factor (VEGF). We recently demonstrated that QK, a de novo engineered VEGF mimicking peptide, shares in vitro the same biological properties of VEGF, inducing capillary formation and organization. On these grounds, the aim of this study is to evaluate in vivo the effects of this small peptide. Therefore, on Wistar Kyoto rats, we evaluated vasomotor responses to VEGF and QK in common carotid rings. Also, we assessed the effects of QK in three different models of angiogenesis: ischemic hindlimb, wound healing and Matrigel plugs. QK and VEGF present similar endothelium-dependent vasodilatation. Moreover, the ability of QK to induce neovascularization was confirmed us by digital angiographies, dyed beads dilution and histological analysis in the ischemic hindlimb as well as by histology in wounds and Matrigel plugs. Our findings show the proangiogenic properties of QK, suggesting that also in vivo this peptide resembles the full VEGF protein. These data open to new fields of investigation on the mechanisms of activation of VEGF receptors, offering clinical implications for treatment of pathophysiological conditions such as chronic ischemia.

Advances in gene-based therapy for heart failure

Heart failure is a major cause of morbidity and mortality in western countries. While progress in current treatment modalities is making steady and incremental gains to reduce this disease burden, there remains a need to explore novel therapeutic strategies. Clinicians and researchers alike have thus looked towards novel adjunctive therapeutic strategies, including gene-based therapy for congestive heart failure (CHF). Advances in the understanding of the molecular basis of CHF, combined to the evolution of increasingly efficient gene transfer technology, have placed congestive heart failure within reach of gene-based therapy. This review will discuss issues related to gene vector systems, gene delivery strategies, and gene targets for intervention in the setting of CHF.

Gene and stem cell therapy in peripheral arterial occlusive disease

Abstract

Peripheral arterial occlusive disease (PAOD) is a manifestation of systemic atherosclerosis strongly associated with a high risk of cardiovascular morbidity and mortality. In a considerable proportion of patients with PAOD, revascularization either by endovascular means or by open surgery combined with best possible risk factor modification does not achieve limb salvage or relief of ischaemic rest pain. As a consequence, novel therapeutic strategies have been developed over the last two decades aiming to promote neovascularization and remodelling of collaterals. Gene and stem cell therapy are the main directions for clinical investigation concepts. For both, preclinical studies have shown promising results using a wide variety of genes encoding for growth factors and populations of adult stem cells, respectively. As a consequence, clinical trials have been performed applying gene and stem cell-based concepts. However, it has become apparent that a straightforward translation into humans is not possible. While several trials reported relief of symptoms and functional improvement, other trials did not confirm this early promise of efficacy. Ongoing clinical trials with an improved study design are needed to confirm the potential that gene and cell therapy may have and to prevent the gaps in our scientific knowledge that will jeopardize the establishment of angiogenic therapy as an additional medical treatment of PAOD. This review summarizes the experimental background and presents the current status of clinical applications and future perspectives of the therapeutic use of gene and cell therapy strategies for PAOD.

Brain-derived neurotrophic factor: a newly described mediator of angiogenesis

Recent studies indicate that, in addition to its neuropoietic actions, brain derived neurotrophic factor (BDNF) promotes endothelial cell survival and induces neoangiogenesis in ischemic tissues. Unlike many vascular growth factors that act on many vascular beds, BDNF activity is relatively restricted to central arteries, vessels of cardiac and skeletal muscle, and skin. Studies of newly described biologic mediators that act on large-vessel and microvascular beds in these organs will help us to better understand organ-specific vascular development, as well as to develop novel therapeutic strategies to improve the condition of patients with cardiac and peripheral vascular disease. In this review, we summarize dual proangiogenic actions of BDNF, which, through local activation of TrkB receptor, expressed on a subpopulation of endothelial cells and, in addition, by recruitment of bone marrow-derived cells, contribute to neoangiogenesis.

Engineering blood vessels by gene and cell therapy

Cardiovascular-related syndromes are the leading cause of morbidity and mortality worldwide. Arterial narrowing and blockage due to atherosclerosis cause reduced blood flow to the brain, heart and legs. Bypass surgery to improve blood flow to the heart and legs in these patients is performed in hundreds of thousands of patients every year. Autologous grafts, such as the internal thoracic artery and saphenous vein, are used in most patients, but in a significant number of patients such grafts are not available and synthetic grafts are used. Synthetic grafts have higher failure rates than autologous grafts due to thrombosis and scar formation within graft lumen. Cell and gene therapy combined with tissue engineering hold a great promise to provide grafts that will be biocompatible and durable. This review describes the field of vascular grafts in the context of tissue engineering using cell and gene therapies.

Angiogenesis therapies for cardiovascular disease

PURPOSE OF REVIEW

The purpose was to summarize the findings of the proangiogenic clinical trials using protein and gene therapy, with analysis of the problems and an interpretation of the results.

RECENT FINDINGS

Recent findings include several new large clinical trials, using both gene and protein therapies. There has been development of new basic science concepts, especially with regard to endothelial activation and stabilization of newly formed microvessels. This review provides a critical analysis of the most recent clinical trials, both in efforts to understand the pitfalls of earlier clinical trials, and also to focus on requirements for future studies.

SUMMARY

This article reviews many of the clinical trials utilizing proangiogenic therapy, assesses the pitfalls seen within the current trials, and discusses the conclusions drawn and the future of angiogenesis therapy.

Cardiovascular gene therapy: current status and therapeutic potential

Gene therapy is emerging as a potential treatment option in patients suffering from a wide spectrum of cardiovascular diseases including coronary artery disease, peripheral vascular disease, vein graft failure and in-stent restenosis. Thus far preclinical studies have shown promise for a wide variety of genes, in particular the delivery of genes encoding growth factors such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) to treat ischaemic vascular disease both peripherally and in coronary artery disease. VEGF as well as other genes such as TIMPs have been used to target the development of neointimal hyperplasia to successfully prevent vein graft failure and in-stent restenosis in animal models. Subsequent phase I trials to examine safety of these therapies have been successful with low levels of serious adverse effects, and albeit in the absence of a placebo group some suggestion of efficacy. Phase 2 studies, which have incorporated a placebo group, have not confirmed this early promise of efficacy. In the next generation of clinical gene therapy trials for cardiovascular disease, many parameters will need to be adjusted in the search for an effective therapy, including the identification of a suitable vector, appropriate gene or genes and an effective vector delivery system for a specific disease target. Here we review the current status of cardiovascular gene therapy and the potential for this approach to become a viable treatment option.

Therapeutic Prospects of Cardiac Gene Transfer

Cardiovascular diseases remain a major cause of morbidity and mortality. Despite significant gains in medical and surgical treatment of these conditions, the burden imposed continues to increase, particularly as the population ages. Hence, there exists an impetus to explore novel therapeutic approaches. Gene therapy, broadly defined as the use of nucleic acid sequences as medicine, is an example of such a novel approach. The potential of gene therapy has been explored in several models of both inherited monogenic and acquired polygenic cardiovascular diseases, such as heart failure and arrhythmia. Exciting developments in gene transfer technology and important insights into the molecular basis of these common diseases have placed them within reach of gene-based therapy.

Gene Therapy in the Treatment of Heart Failure

Heart failure is a major cause of morbidity and mortality in contemporary societies. Although progress in conventional treatment modalities is making steady and incremental gains to reduce this disease burden, there remains a need to explore new and potentially therapeutic approaches. Gene therapy, for example, was initially envisioned as a treatment strategy for inherited monogenic disorders. It is now apparent that gene therapy has broader potential that also includes acquired polygenic diseases, such as heart failure. Advances in the understanding of the molecular basis of conditions such as these, together with the evolution of increasingly efficient gene transfer technology, has placed congestive heart failure within reach of gene-based therapy.

New vectors and strategies for cardiovascular gene therapy

Cardiovascular diseases are the major cause of morbidity and mortality in both men and women in industrially developed countries. These disorders may result from impaired angiogenesis, particularly in response to hypoxia. Despite many limitations, gene therapy is still emerging as a potential alternative for patients who are not candidates for traditional revascularization procedures, like angioplasty or vein grafts. This review focuses on recent approaches in the development of new gene delivery vectors, with great respect to newly discovered AAV serotypes and their modified forms. Moreover, some new cardiovascular gene therapy strategies have been highlighted, such as combination of different angiogenic growth factors or simultaneous application of genes and progenitor cells in order to obtain stable and functional blood vessels in ischemic tissue.

Gene-based therapy for hypertension--do preclinical data suggest a promising future?

Many experimental studies have obtained a prolonged control of blood pressure through gene treatment. This consists in the administration of genes coding for vasodilator proteins (the 'sense' approach), or of nucleotide sequences that are complementary to the mRNA of vasoconstrictor proteins, which are consequently synthesized in smaller amounts (the 'antisense' approach). Examples of the sense approach include the genes encoding endothelial nitric oxide synthase and kallikrein. Examples of the second type of approach are the antisense oligodeoxynucleotides to angiotensin-converting enzyme and endothelin-1. Also, RNA molecules, such as ribozymes and small interfering RNAs, are capable to inhibit RNA function. Whole sense genes are usually administered through viral vectors, while antisense oligonucleotides may be administered with plasmids or liposomes. Both viral and non-viral vectors have advantages and disadvantages. Despite the still persisting limitations, the possibility exists that in the future some forms of genetic treatment will be extended to the clinical setting, allowing a prolonged control of essential hypertension and its end-organ sequelae.

Cardiovascular gene delivery: The good road is awaiting

Atherosclerotic cardiovascular disease is a leading cause of death worldwide. Despite recent improvements in medical, operative, and endovascular treatments, the number of interventions performed annually continues to increase. Unfortunately, the durability of these interventions is limited acutely by thrombotic complications and later by myointimal hyperplasia followed by progression of atherosclerotic disease over time. Despite improving medical management of patients with atherosclerotic disease, these complications appear to be persisting. Cardiovascular gene therapy has the potential to make significant clinical inroads to limit these complications. This article will review the technical aspects of cardiovascular gene therapy; its application for promoting a functional endothelium, smooth muscle cell growth inhibition, therapeutic angiogenesis, tissue engineered vascular conduits, and discuss the current status of various applicable clinical trials.

Efficient transduction and seeding of human endothelial cells onto metallic stents using bicistronic pseudo-typed retroviral vectors encoding vascular endothelial growth factor

BACKGROUND

Stents seeded with genetically modified endothelial cells (EC) may provide an attractive therapeutic modality for treating vascular diseases by combining the mechanical properties of the metallic stent with the biologic activity of native or genetically engineered ECs. The clinical feasibility of implanting seeded stents depends on the ability to achieve adequate stent coverage within a clinically applicable time frame. We tested the hypothesis that this goal could be achieved by seeding stents with human ECs overexpressing vascular endothelial growth factor (VEGF) and by using an efficient gene transfer system.

METHODS AND RESULTS

Efficiency of gene transfer to human ECs using an amphotropic retroviral vector and a gibbon ape leukemia virus (GALV) pseudo-typed retroviral vector was examined and compared. For assessment of transduction rates, LacZ-encoding vectors were used and beta-galactosidase activity was determined 48 h after gene transfer. The transduction rate of primary human ECs using the amphotropic retroviral vector encoding the LacZ gene was low (2.9+/-2% of cells). Under the same conditions, the GALV pseudo-typed vector encoding LacZ transduced 94+/-2% of cells (P<.001). To test the effect of VEGF gene transfer on stent coverage, we transduced ECs using a bicistronic GALV pseudo-typed retroviral vector encoding either GFP alone or both VEGF and GFP. Since all transduced cells expressed GFP, stent coverage by ECs could be assessed by fluorescent inverted microscopy, which demonstrated that stent coverage by ECs overexpressing VEGF was more rapid and effective than coverage by ECs overexpressing GFP. Progressively increasing quantities of VEGF protein were detected in the conditioned medium of stents seeded with endothelia cells expressing VEGF 2, 3, and 5 days after seeding.

CONCLUSIONS

High-rate gene transfer to human primary ECs was observed 48 h after transduction with GALV pseudo-typed retroviral vectors, eliminating the need for the time-consuming process of cell selection. Seeding with ECs overexpressing VEGF improved stent coverage and was associated with continuing secretion of the protein. The findings provide support for the feasibility of implanting genetically engineered biologically active cellular-coated stents.

Identification of HIV-1 Tat peptides for future therapeutic angiogenesis

Therapeutic angiogenesis represents a novel approach to treat critical limb ischemia when revascularization is no more an option. The clinical use of the vascular endothelial growth factor is questioned, because of its side effects. This study was designed to identify and characterize human immunodeficiency virus type 1 (HIV-1) Tat-derived peptides based on their pro-angiogenic properties. A series of Tat-derived peptides were synthesized containing mutations in the basic domain. To minimize side effects Tat peptides were selected exerting no effects on the proteasome and on the viability of human umbilical vein endothelial cells (HUVEC). Tatpep5, 15, and 16 increased the endogenous levels of the pro-angiogenic transcription factors c-Jun and SP-1 as well as the production of the plasminogen activator inhibitor-1 (PAI-1) by HUVEC. A significant induction of endothelial cell invasion was observed upon treatment of HUVEC with Tat peptides. In addition, selected Tat peptides induced tube formation by HUVEC as visualized and quantified in a Matrigel matrix. Our data demonstrate that the selected Tat peptides fulfill essential criteria for pro-angiogenic substances. They represent the basis for the development of novel pro-angiogenic drugs for future therapeutic angiogenesis, which might be applied for treatment of unreconstructible critical limb ischemia.

Gene therapy of the ischemic lower limb--Therapeutic angiogenesis

The limitations of surgical revascularisation and pharmacological treatment in peripheral arterial occlusive disease (PAOD) are well recognized. Therapeutic options for critical leg ischemia are consequently limited to percutaneous transluminal angioplasty (PTA) or surgical revascularisation. Unfortunately, many patients with critical leg ischemia are poor candidates for either procedure. Therapeutic angiogenesis is a novel promising tool to treat these patients. Experimental and clinical and trials of gene transfer for therapeutic angiogenesis have already shown some clinical efficacy. This review is focused on gene transfer techniques in preclinical and clinical therapeutic angiogenesis, angiogenic growth factors, vectors, delivery methods and routes. The results of clinical and experimental studies, safety and side effects of gene therapy, and the perspectives of future research are also discussed.

Angiogenic and antiangiogenic gene therapy

Gene therapy is thought to be a promising method for the treatment of various diseases. One gene therapy strategy involves the manipulations on a process of formation of new vessels, commonly defined as angiogenesis. Angiogenic and antiangiogenic gene therapy is a new therapeutic approach to the treatment of cardiovascular and cancer patients, respectively. So far, preclinical and clinical studies are successfully focused mainly on the treatment of coronary artery and peripheral artery diseases. Plasmid vectors are often used in preparations in angiogenic gene therapy trials. The naked plasmid DNA effectively transfects the skeletal muscles or heart and successfully expresses angiogenic genes that are the result of new vessel formation and the improvement of the clinical state of patients. The clinical preliminary data, although very encouraging, need to be well discussed and further study surely continued. It is really possible that further development of molecular biology methods and advances in gene delivery systems will cause therapeutic angiogenesis as well as antiangiogenic methods to become a supplemental or alternative option to the conventional methods of treatment of angiogenic diseases.

From endothelium-derived hyperpolarizing factor (EDHF) to angiogenesis: Epoxyeicosatrienoic acids (EETs) and cell signaling

Epoxyeicosatrienoic acids (EETs) are generated from arachidonic acid by cytochrome P450 (CYP) epoxygenases. The expression of CYP epoxygenases in endothelial cells is determined by a number of physical (fluid shear stress and cyclic stretch) and pharmacological stimuli as well as by hypoxia. The activation of CYP epoxygenases in endothelial cells is an important step in the nitric oxide and prostacyclin (PGI2)-independent vasodilatation of several vascular beds and EETs have been identified as endothelium-derived hyperpolarizing factors (EDHFs). However, in addition to regulating vascular tone, EETs modulate several signaling cascades and affect cell proliferation, cell migration, and angiogenesis. Signaling molecules modulated by EETs include tyrosine kinases and phosphatases, mitogen-activated protein kinases, protein kinase A (PKA), cyclooxygenase (COX)-2, and several transcription factors. This review summarizes the role of CYP-derived EETs in cell signaling and focuses particularly on their role as intracellular amplifiers of endothelial cell hyperpolarization as well as in cell proliferation and angiogenesis. The angiogenic properties of CYP epoxygenases and CYP-derived EETs implicate that these enzymes may well be accessible targets for anti-angiogenic as well as angiogenic therapies.

Gene transfer for ischemic cardiovascular disease: is this the end of the beginning or the beginning of the end?

The past decade has represented a period of high expectations for cardiovascular gene transfer on the basis of the findings from preclinical experiments and promising early clinical results. Yet, randomized studies have not demonstrated similar results. Do these poor results mean that gene transfer for ischemic cardiovascular disease has failed in its promise, or do they merely signify the inherent challenges of a pioneering field? In this paper we briefly review the clinical experience of gene transfer for ischemic cardiovascular disease and propose future directions for research.

Serum hepatocyte growth factor levels predict long-term clinical outcome after percutaneous coronary revascularization

AIMS

To evaluate, in patients referred for elective percutaneous coronary revascularization (PCR) without heparin pre-treatment, the relationship between baseline serum levels of the angiogenic growth factors, vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF), and clinical outcome.

METHODS AND RESULTS

In 488 consecutive patients undergoing elective coronary angioplasty, hsC-reactive protein, HGF, and VEGF levels were measured before heparin administration. The primary endpoint, a composite of death and myocardial infarction, occurred in 44 patients at a median follow-up of 14.9 months. At baseline, VEGF levels were related to C-reactive protein levels and inversely related to age; HGF levels were related to C-reactive protein levels, diabetes, and recent clinical instability. In the univariate analysis, HGF had a significant positive relationship (P=0.003) with the primary endpoint. A similar trend was observed for VEGF (P=0.11). The only three variables significantly associated with the primary endpoint in the multivariable Cox model were HGF (P=0.004), C-reactive protein (P=0.007), and diabetes (P=0.04).

CONCLUSION

Our results demonstrate that in patients, without heparin pre-treatment, referred for PCR, a high serum level of HGF is an independent predictor of clinical events during follow-up and is correlated with other surrogate measures of the activity of atherosclerosis.

Targeting cerebral arteries for gene therapy

After the steady progress towards application of gene therapy to cerebral arterial diseases, several applications, including modification of gene expression in cerebral arteries, are now feasible. There are several possible targets for cerebrovascular gene therapy, and numerous studies have tested gene therapy strategies in animal models of cerebrovascular disorders. However, some major obstacles, especially issues of safety, must be overcome before clinical use in humans. Gene therapy for cerebral arterial diseases is still in its infancy, and many basic and preclinical studies are yet to be done in order to develop effective and safe techniques.

Management of Peripheral Vascular Disease

The management of patients with peripheral arterial occlusive disease (PAD) has to be planned in the context of natural history, epidemiology, and apparent risk factors that predict deterioration. The ankle-brachial index to date has proved to be the most effective, accurate, and practical method of PAD detection. Given that PAD is a powerful indicator of systemic atherosclerosis and (independent of symptoms) is associated with an increased risk of myocardial infarction and stroke, as well as a six times greater likelihood of death, the prevalence and demographic distribution of measurable PAD becomes particularly relevant. Reliable information on interventions to confer symptom relief is much weaker and reflects discrepancies between published reports from centers of excellence and the experience of patients routinely treated in communities around the world. The impact of newer treatment modalities, such as complex endovascular procedures and therapeutic angiogenesis, has been a subject of recent controversy.

Long-term BMP-2-induced bone formation in rat island and free flaps

Ectopic osteoinduction by exogenous bone morphogenetic proteins (BMPs) is rapid but heretofore characterized as transient. A rat model of carrier-free recombinant human BMP-2 intramuscular implantation was used, followed by creation of either an island flap or transplantation of a free flap. BMP-2 injection into an unaltered gastrocnemius, thigh adductor, or cutaneous trunci (thoracic wall) muscle site led to bone resorption at 4 weeks. In contrast, creation of an island or free flap of the muscle/injection site caused the newly formed ossicle to maintain its bony composition with active osteoblastic presence, from 3-8 weeks. Muscle denervation or sectioning of the Achilles tendon (for gastrocnemius injections) did not prevent bone resorption at 4 weeks. There was little osteoclastic activity within de novo bone sites of island- and free flap-injected muscles at 4 and 8 weeks. These data demonstrate that simple injection of BMP-2 into a surgically isolated flap site results in the prolonged presence of de novo bone. These findings suggest that BMP-injected island or free muscle flaps may be used to generate new bone for reconstruction of a bony defect.

Non‐Viral Vectors for Gene Therapy: Clinical Trials in Cardiovascular Disease

The population of patients with end-stage symptomatic coronary and peripheral vascular disease is ever-expanding. Many of these patients no longer have options for mechanical revascularization, and despite maximal medical therapy, they remain physically limited due to angina or critical limb ischemia. The fundamental problem in these patients is insufficient blood supply to muscle due to severely diseased conduit vessels to the target tissue. Therefore, it seems logical that increasing the blood supply to ischemic tissue will relieve symptoms. One potential means to achieving this goal is via therapeutic angiogenesis. The molecular mechanisms behind vascular development are being elucidated, and animal models have shown that mediators of vascular development can be harnessed to produce new capillaries in ischemic tissue. These mediators include cytokines such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF). Angiogenic cytokines can be delivered in several forms including recombinant protein or via gene delivery as a naked plasmid or via viral vector. This chapter will describe the clinical trial experience to date with delivery of non-viral gene therapy for therapeutic angiogenesis in humans with disabling myocardial ischemia and peripheral vascular disease.

VP22-mediated intercellular transport correlates with enhanced biological activity of MybEngrailed but not (HSV-I) thymidine kinase fusion proteins in primary vascular cells following non-viral transfection

BACKGROUND

The intercellular transport properties of the herpes simplex virus (HSV) protein VP22 have been harnessed to enhance the effectiveness of viral gene transfer. We investigated the intercellular transport and biological effects of VP22 fused with the dominant negative c-Myb chimera, MybEngrailed (MybEn) and HSV-I thymidine kinase (TK), in primary vascular smooth muscle cells (VSMC) following non-viral transfection.

MATERIALS AND METHODS

Porcine VSMC transfected with plasmids encoding MybEn, TK and their respective N- and C-terminal VP22 fusion proteins were assayed for the extent and distribution of transgene expression (by immunohistochemistry), culture growth and apoptosis.

RESULTS

The N-terminal MybEn fusion with VP22 (MybEnVP22) and both TK fusions, but not VP22MybEn, exhibited intercellular spread from primary transfected to up to 200 surrounding cells. pMybEnVP22-transfected cultures exhibited growth inhibition and apoptosis rates that were 10.6 +/- 3.6 and 3.2 +/- 1.0 fold higher than in pMybEn-transfected cultures; pVP22MybEn-transfected cultures showed no difference in these parameters. pTK-transfected cultures underwent 60-70% cell death in the presence of ganciclovir despite <2% primary transfection, which was not increased in cultures transfected with plasmids encoding VP22-TK fusions.

CONCLUSIONS

The close correlation between immunocytochemical and biological assays suggests that intercellular transport is crucial to the enhanced biological activity of the MybEnVP22 fusion. The "intrinsic" bystander activity of TK was 4-fold greater than was "engineered" by VP22 fusion, probably reflecting the abundance of gap junctions between VSMC. VP22 fusion may enhance the efficiency of non-viral gene delivery when combined with the appropriate therapeutic transgene, target tissue and transfection method.

Gene Therapy for Chronic Peripheral Arterial Disease: What Role for the Vascular Surgeon?

The incidence of peripheral arterial disease is rising and despite advances in clinical management, many problems remain unsolved. Better knowledge of the mechanisms and consequences associated with chronic muscle ischemia has opened the way for development of new treatment strategies, including therapeutic angiogenesis. Therapeutic angiogenesis is a promising technique based on experimental studies showing that growth factors or genes able to increase capillary density can be used to reduce the impact of muscle ischemia and increase blood flow to ischemic tissue. Enthusiasm for this technique has prompted numerous clinical trials with encouraging results, but data are still inconclusive. Optimal indications for gene therapy must be defined and further experimental progress is needed to respond to ethical issues. Therapeutic angiogenesis should be viewed as an adjunct to rather than as a competitor of current surgical revascularization techniques.

Identification of Placenta Growth Factor Determinants for Binding and Activation of Flt-1 Receptor

Placenta growth factor (PlGF) belongs to the vascular endothelial growth factor (VEGF) family and represents a key regulator of angiogenic events in pathological conditions. PlGF exerts its biological function through the binding and activation of the seven immunoglobulin-like domain receptor Flt-1, also known as VEGFR-1. Here, we report the first detailed mutagenesis studies that provide a basis for understanding molecular recognition between PlGF-1 and Flt-1, highlighting some of the residues that are critical for receptor recognition. Mutagenesis analysis, performed on the basis of a structural model of interaction between PlGF and the minimal binding domain of Flt-1, has led to the identification of several PlGF-1 residues involved in Flt-1 recognition. The two negatively charged residues, Asp-72 and Glu-73, located in the beta3-beta4 loop, are critical for Flt-1 binding. Other mutations, which bring about a significant decrease in PlGF binding activity, are Gln-27, located in the N-terminal alpha-helix, and Pro-98 and Tyr-100 on the beta6 strand. The mutation of one of the two glycosylated residues of PlGF, Asn-84, generates a PlGF variant with reduced binding activity. This indicates that, unlike in VEGF, glycosylation plays an important role in Flt-1 binding. The double mutation of residues Asp-72 and Glu-73 generates a PlGF variant unable to bind and activate the receptor molecules on the cell surface. This variant failed to induce in vitro capillary-like tube formation of primary endothelial cells or neo-angiogenesis in an in vivo chorioallantoic membrane assay.

Vascular endothelial growth factor - basic science and its clinical implications

Vascular endothelial growth factor (VEGF) is the most important signaling molecule involved in the regulation of the formation of new vessels. Results of recent studies have provided new insights into the molecular mechanisms of the VEGF signaling pathways. VEGF local or systemic application represents a new approach in the therapy of ischemic diseases, especially of the coronary artery disease. Inhibition of the VEGF action on various levels is, on the other hand, assumed to be a promising therapeutic concept against cancer. Moreover, VEGF has been recently shown to be associated with some other physiological and pathophysiological processes. In this article we summarize the latest results of VEGF related studies and present the concluding theoretical resource for further research on the role of VEGF in understanding of pathophysiology of diseases and in therapeutic interventions in clinical biomedicine.

A problem-oriented approach to safety issues in drug development and beyond

Human safety issues arise throughout the life cycle of pharmaceutical products and relevant information comes from a multitude of sources. Assessment and management of risks to humans requires a problem-based analysis to bring together relevant information regardless of source. The Safety Evaluation Plan (SEP) is a tool to support problem-oriented safety analysis. Safety issues are specified and the evaluation and management of each problem is based on a status summary that integrates the most current information from all relevant sources. The status summary is updated regularly during the course of clinical development to reflect the results of new studies and new clinical trials. In the postmarketing period, relevant postmarketing data is incorporated. Recent regulatory initiatives emphasise early identification of product safety risks so that appropriate risk-management measures can be instituted at the time of approval. A problem-oriented approach supports growing regulatory expectations regarding risk assessment and risk management. The problem-oriented approach facilitates early identification of safety issues and an evidence-based approach to their evaluation. Proactive management of safety problems leads to prompt assessment of risks and timely and appropriate steps aimed at risk reduction. The SEP provides a single global assessment for each safety issue. Regulatory submissions for pharmaceutical and biological products are organised by type of information. International Conference of Harmonisation documents covering clinical safety issues structure and analyse information separately by type, for example, adverse events, serious adverse events, laboratory data, vital signs, etc. A problem-oriented analysis would need to find a place in the regulatory process. A problem-oriented approach to safety cuts across typical structures in the pharmaceutical industry where different groups handle preclinical, clinical and postmarketing safety information. The SEP can improve communication within the company and externally. Nonetheless, supporting structures need to be adapted to support such an interdisciplinary process. Overall, the problem-oriented approach, supported by a SEP, contributes to realistic expectations and sustained credibility when dealing with safety issues.

Autologous vascular smooth muscle cell-based myocardial gene therapy to induce coronary collateral growth

For therapeutic angiogenesis to achieve clinical relevance, it must be effective, with minimal side effects to other end organ systems. We developed a cardiac-specific gene delivery mechanism by transfecting autologous vascular smooth muscle cells (VSMC) with VEGF and administering these cells via intracoronary injection. We evaluated the efficacy of this protocol by its ability to stimulate angiogenesis in the presence of a subthreshold stimulus for collateralization. A modified canine repetitive coronary occlusion model was utilized in these experiments with left anterior descending coronary artery occlusions for 2 min every 2 h four times per day for 21 days. An intramyocardial catheter in the perfusion territory of the left anterior descending coronary artery measured proteins in the myocardial interstitial fluid. VSMC from jugular vein explants were isolated, amplified in culture for 3 wk, and transfected with a plasmid expressing VEGF-165 and/or enhanced green fluorescent protein. Cells were injected before commencement of occlusions. VEGF levels in myocardial interstitial fluid were significantly higher in VEGF-transfected animals than in sham (repetitive occlusions without cell transplantation) and control (repetitive occlusions with enhanced green fluorescent protein-transfected cells) animals at the onset of occlusions (P < 0.05). In the VEGF group, collateral flow was increased at day 7 and remained higher than in sham and control groups thereafter. We found that intracoronary administration of VEGF-transfected autologous VSMC effectively promotes collateral development. This approach may provide a way to confine delivery of a gene to a specified organ, thus minimizing complications related to gene transfection in nontargeted organ systems.

Therapeutic Angiogenesis in Peripheral Arterial Disease: Can Biotechnology Produce an Effective Collateral Circulation?

The physiological processes of angiogenesis, vasculogenesis and arteriogenesis contribute to the growth of collateral vessels in response to obstructive arterial disease causing lower limb or myocardial ischaemia, but in clinical practice the endogenous angiogenic response is often suboptimal or impaired, e.g. by factors such as ageing, diabetes or drug therapies. Therapeutic angiogenesis is an application of biotechnology to stimulate new vessel formation via local administration of pro-angiogenic growth factors in the form of recombinant protein or gene therapy, or by implantation of endothelial progenitor cells that will synthesize multiple angiogenic cytokines. Numerous experimental and clinical studies have sought to establish 'proof of concept' for therapeutic angiogenesis in PAD and myocardial ischaemia using different treatment modalities, but the results have been inconsistent. This review summarises the mechanisms of angiogenesis and the results of recent trials evaluating the efficacy and safety of different gene therapy, recombinant protein and cellular-based treatment approaches to enhance collateral vessel formation.