AdPEDF.11 in a murine model resulted in transduction of episcleral cells that produced PEDF [83]. The PEDF penetrated the sclera with high choroidal levels that induce regression of CNV.

A phase I trial of AdPEDF.11 in 28 patients failed to identify any dose-related toxicities and suggested a sustained anti-angiogenic effect for several months after a single intravitreal injection of at least 108 particle units [84–86]. Moreover, repeated adenovector administration into the eye does not appear to incite a systemic immune response [87], affording the possibility of repeat injections. This study demonstrates the viability of ocular gene transfer via an adenoviral vector. Further study is warranted to fully appreciate AdPEDF.11’s potential as a therapy in this disease.

AAV2-sFLT01

The high-affinity VEGF receptor Flt-1 is one of the most potent naturally occurring VEGF binders. sFLT01 is a novel chimeric VEGF-binding molecule that consists of one Flt-1 domain linked to the human IgG1 heavy-chain Fc region, resulting in a forced homodimer with high affinity for VEGF. Pechan and colleagues integrated sFLT01 into an adeno-associated virus serotype 2 (AAV2) vector, so called AAV2-sFLT01 (Genzyme, Cambridge, MA, USA). AAV2-mediated intravitreal gene delivery of sFLT01 inhibited angiogenesis in the mouse oxygen-induced retinopathy model [88].

A phase 1 trial to evaluate the safety and feasibility of AAV2-sFLT01 in treating patients with neovascular AMD is underway [89].

Other Pathways

ATG-3

ATG-3 (CoMentis, formerly Athenagen, South San Francisco, CA, USA) is the proprietary eye drop formulation of mecamylamine, which antagonizes the nicotinic acetylcholine receptor pathwaythatmediatesangiogenesisanddownregulates VEGF. Mecamylamine suppressed CNV in a

murine model, both by subcutaneous and topical application [90]. A phase I trial treated 80 patients with ATG-3 eye drops twice daily up to 14 days. ATG-3 was well tolerated and safe, with very low levels of the compound found in the blood following application. However, a phase II trial examining two doses of ATG-3 in 343 patients was terminated [91]. Another phase II trial is evaluating the safety and efficacy of ATG-3 drops in patients receiving maintenance intravitreal injections of ranibizumab or bevacizumab. This trial is currently ongoing, but not recruiting [92].

Squalamine Lactate

Squalamine lactate (Evizon®, Genaera Corporation, Plymouth Meeting, PA) is an antiangiogenic amino sterol derived from dogfish shark (Squalus acanthus) cartilage. It blocks cell membrane ion transport that controls pH and cell metabolism. It also blocks VEGF action and integrin expression when bound to calmodulin. Squalamine must be administered intravenously, as it is ineffective intravitreally [15, 93]. Systemically administered squalamine lactate partially reduced choroidal neovascular membrane development induced by laser trauma in a rat model [94]. In a phase I/II trial of 40 patients receiving 25 or 50 mg/m2 weekly for four weeks, no patients lost vision and 26% gained three or more lines [15]. Despite these results, Genaera abandoned this product. Phase II [95–97] and III [98] trials have been terminated.

Combretastatin A4 Phosphate/CA4P

Combretastatin A4 Phosphate, or CA4P (Zybrestat, OXiGENE, South San Francisco, CA, USA), is a microtubule-disrupting agent that rapidly shuts off blood flow in new vessels and induces regression [99, 100]. In a murine model of tumor angiogenesis, CA4P selectively targeted endothelial cells, but not smooth muscle cells, and induced regression of unstable nascent tumor neovessels by rapidly disrupting the molecular engagement of vascular endothelial-cadherin, an endothelial cell-specific junctional molecule. CA4P increased endothelial cell permeability,

while inhibiting endothelial cell migration and capillary tube formation, thereby leading to rapid vascular collapse and tumor necrosis [100]. Interestingly, however, CA4P failed to induce regression of diabetes-like retinal neovascularization in a canine model [101].

A phase I/II trial in patients with neovascular AMD treated with intravenous CA4P demonstrated side effects, namely hypertension and increased QTc interval [102]. A phase II study in patients with myopic CNV showed weakly positive results [103, 104]. OXiGENE is currently testing a topical application that achieved good retinal and choroidal concentrations in a rabbit model [105].

JSM6427

Integrin a5b1is the principal fibronectin receptor and plays a key role in angiogenesis [106]. Inhibition of a5b1 integrin function induces apoptosis of actively proliferating but not quiescent cells [106]. JSM6427 (Jerini AG, Berlin, Germany) is a potent a5b1 integrin antagonist that has been shown to modulate hypoxia-induced neovascularization in mice [107]. Preclinical work was done in rabbit and monkey models of CNV. Intravitreal JSM6427 inhibited CNV in a dose-dependent manner without any ocular adverse effects or systemic safety signals [108]. Interestingly, JSM6427 may also prove beneficial in proliferative retinopathies. It has a strong inhibitory effect on human retinal pigment epithelial cell attachment, proliferation, and migration [109].

A phase I dose-escalation trial [110] demonstrated safety and some degree of biologic activity in end-stage lesions. However, the relatively short half life led to concerns regarding treatment duration. Further study is on hold until researchers develop extended delivery of the drug.

Volociximab

Volociximab(OphthotechCorporation,Princeton, NY, USA) is a monoclonal antibody that targets a 5b 1 integrin. It appears to inhibit neovascularization independent of the growth factor stimulation, either by VEGF or other angiogenic factors

[106]. A phase I study evaluated the safety of intravitreal volociximab combined with ranibizumab for neovascular AMD [111]. Volociximab was used in combination with ranibizumab because the integrin antagonist likely needs antiVEGF cotreatment due to the lack of a significant antipermeability effect. Preliminary results from 10 subjects receiving two doses of volociximab in combination with ranibizumab revealed a visual acuity improvement of 10.8 letters at nine weeks, with a mean decrease in central macular thickness of 136 mm. These results do not separate the independent contributions from ranibizumab and volociximab. Dose escalation of volociximab has been completed without evidence of dose-limiting toxicity or drug-related adverse events [112].

NT-501, Ciliary Neurotrophic Factor

Ciliary neurotrophic factor (CNTF) (Neurotech Pharmaceuticals, Lincoln, RI) is a potent neuroprotective agent capable of protecting photoreceptors in animal models of retinal degeneration [113]. The definitive neuroprotective mechanism of CNTF in the degenerating retina remains unknown [114]. Indirect rescue of photoreceptors by CNTF is a function of reversible biochemical and morphological changes in rod photoreceptors that lead to reduced photoresponsiveness [115].

Researchers have adapted encapsulated cell technology to permit CNTF-producing transfected cells to release CNTF for a year or longer after implantation into the vitreous cavity. The intravitreal implant, known as NT-501, requires surgical implantation through the pars plana with scleral fixation. NT-501 is being evaluated in patients with dry AMD or retinitis pigmentosa, but may someday hold promise in protecting photoreceptors of neovascular AMD patients.

NT-501 was safe and well tolerated in a phase II study of geographic atrophy [116], with stability of visual acuity and improvement in macular volume. There was evidence that implants continued to elute CNTF for up to 18 months [117]. Both CNTF and encapsulated cell technology