Generation and characterization of a recombinant adenovirus expressing vascular endothelial growth factor for studies of neovascularization in the eye

Gene Therapies for Neovascular Age-Related Macular Degeneration

Pathological neovascularization is a key component of the neovascular form (also known as the wet form) of age-related macular degeneration (AMD) and proliferative diabetic retinopathy. Several preclinical studies have shown that antiangiogenesis strategies are effective for treating neovascular AMD in animal models. Vascular endothelial growth factor (VEGF) is one of the main inducers of ocular neovascularization, and several clinical trials have shown the benefits of neutralizing VEGF in patients with neovascular AMD or diabetic macular edema. In this review, we summarize several preclinical and early-stage clinical trials with intraocular gene therapies, which have the potential to reduce or eliminate the repeated intravitreal injections that are currently required for the treatment of neovascular AMD.

Nonhuman primate models for diabetic ocular neovascularization using AAV2-mediated overexpression of vascular endothelial growth factor

Neovascularization leads to blindness in numerous ocular diseases, including diabetic retinopathy, age-related macular degeneration, retinopathy of prematurity, and sickle cell disease. More effective and stable treatments for ocular neovascularization are needed, yet there are major limitations in the present animal models. To develop primate models of diabetic retinopathy and choroidal neovascularization, rhesus monkeys were injected subretinally or intravitreally with an adeno-associated virus (AAV)-2 vector carrying the cDNA encoding human vascular endothelial growth factor (VEGF). Overexpression of VEGF was measured by intraocular fluid sampling over time. Neovascularization was evaluated by ophthalmoscopy through angiography, optical coherence tomography, and ultimately histopathology. Overexpression of VEGF through AAV2 results in rapid development of features of diabetic retinopathy or macular edema, depending on the targeted cell type/mode of production of VEGF and diffusion of VEGF. Nonhuman primate models will be useful in testing long-term safety and efficacy of novel therapeutic agents for blinding neovascular diseases.

Vascular endothelial growth factor (VEGF) gene transfer enhances surgical revascularization of necrotic bone

Avascular necrosis of bone is a relatively common clinical condition caused by inflammatory conditions, steroid or other drug use, and trauma that affect many different sites in man. Revascularization of the necrotic bone is slow to occur, often resulting in bone resorption and eventual collapse of the involved bone. Rapid revascularization and subsequent bone remodeling may lead to improved outcomes. Surgical revascularization with arterovenous bundles (AV bundles) or vascularized bone grafts results in neoangiogenesis and bone remodeling. Gene transfer of an angiogenic factor to the vessel wall may be an additional strategy to further accelerate this process. In this study, we examined the effectiveness of vascular endothelial growth factor (VEGF) gene transfer to augment surgical revascularization of necrotic bone. An adenoviral vector, either with the VEGF gene (VEGF-A) or identical virus without the cDNA VEGF insert (ADV-DeltaE1) was used to transduce endothelial cells in rabbit saphenous arteries. The artery was then placed with its venae comitantes as an AV bundle into necrotic iliac crest bone in vivo. Angiogenesis in the necrotic bone was quantified by bone blood flow measurement and assessment of vessel density following microangiography. The extent of neoangiogenesis was significantly greater in the VEGF group than the control group at 1 week postoperatively.

Assessment of risks associated with cardiovascular gene therapy in human subjects

Clinical trials of cardiovascular gene therapy, whether using viral (53%) or nonviral (47%) vectors, have thus far disclosed no evidence indicative of inflammatory or other complications, including death, directly attributable to the vector used. Indeed, despite the fact that initial trials of cardiovascular gene therapy targeted patients with end-stage vascular disease, including critical limb ischemia and refractory myocardial ischemia, the mortality for patients enrolled in clinical trials of cardiovascular gene therapy reported to date compares favorably with mortality for similar groups of patients in contemporary controlled studies of medical or interventional therapies. The most common morbidity reported after cardiovascular gene transfer is lower extremity edema; in contrast to data involving genetically engineered mice, however, evidence of life- or limb-threatening edema has not been described in any patients, including patients after gene transfer for myocardial ischemia. Concerns regarding the potential for angiogenic cytokines to promote the progression of atherosclerosis are not supported by angiographic follow-up of patients with coronary or peripheral vascular disease. The levels and duration of gene expression investigated for therapeutic angiogenesis transfer have been unassociated with hemangioma formation. Likewise, there is little evidence from either preclinical or clinical studies to support the notion that the administration of angiogenic growth factors, per se, is sufficient to stimulate the growth of neoplasms. Patients enrolled in clinical studies of angiogenic cytokines, including patients with diabetes and a previous history of retinopathy, have disclosed no evidence to suggest that ocular pathology is a risk of angiogenic growth factor gene transfer.

Adenovirus-mediated gene transfer in canine eyes: a preclinical study for gene therapy of human uveal melanoma

BACKGROUND

Melanomas of the uveal tract are the most common intraocular malignancies in adults, with an incidence of six cases per million adults per year. Enucleation, which may enhance the dissemination of tumour cells into the systemic circulation, is still required for eyes with large tumours. Gene therapy is proposed as a new therapeutic approach for uveal melanoma management.

METHODS

The potential of adenovirus-mediated gene transfer to normal eyes of two laboratory Beagles and in an iris tumour of a Great Dane were evaluated. Replication-defective adenoviral vectors (Adbetagal) were used to assess the feasibility, efficiency and safety of direct adenoviral delivery to the anterior chamber of normal eyes and to an iris tumour. The expression of angiostatin into the aqueous humour following an adenoviral-mediated delivery of human angiostatin (AdK3) was also investigated.

RESULTS

The ciliary body was the area preferentially transduced after adenoviral injection into the anterior chamber. It was also demonstrated that a direct intratumoral injection of a recombinant adenovirus efficiently transduces a canine uveal melanoma. Western blot analysis performed on the aqueous humour revealed that the expression of the angiostatin recombinant protein in the aqueous humour correlated with the dose of AdK3 administered. Lymphocyte infiltrates at the site of AdK3 injection indicated induction of a strong cellular immune response, and humoral immune responses developed in all three dogs.

CONCLUSIONS

The present study involving adenovirus-mediated gene transfer to dog eyes provides an essential basis for gene therapy treatment of uveal melanoma-bearing patients.