Sirna-027 to silence other contributory genes, such as that for VEGFR-2.

Anti-VEGFR Vaccine Therapy

A study showed CD8+ cytotoxic T-lymphocyte mediated regression of physiologic and pathologic new vessels [36]. An animal model demonstrated CNV regression by inducing cellular immunity specific for VEGFR-2 [37]. Currently, a phase 1 study is recruiting patients [38]. Patients will be vaccinated weekly for 12 weeks with sub- cutaneousVEGFR-1peptide(1mg)andVEGFR-2 (1 mg) mixed with Montanide ISA 51 [39].

Pearl

Tyrosine kinase inhibitors, siRNAs, and vaccine therapy can inhibit VEGF receptors to block the angiogenic effects of VEGF.

E10030

E10030 (Ophthotech Corporation, Princeton, NJ, USA) is an aptamer directed against PDGF-B. Pericytes, which are recruited and matured by PDGF, protect endothelial cells from anti-VEGF agents and thus promote resistance to therapy [22]. E10030 decreases pericyte density in neovascular vessels, and therefore improves the effect of antiVEGF agents [22]. A phase I study of 22 patients evaluated intravitreal E10030 as monotherapy and in combination with ranibizumab [40]. The results in the combination group were promising, with 59% of patients experiencing at least a three-line visual acuity gain at 12 weeks. Further, there was an 86% mean decrease in CNV area at 12 weeks with a progressive decrease in macular thickness. E10030 was well tolerated without drug-related adverse effects [41, 42]. Of note, the choroidal neovascular lesions had to have evidence of classic CNV, and had to be less than five disc areas.

Radiation

Radiation therapy has antiangiogenic, antiinflammatory, and antifibrotic characteristics; it is not

new to the treatment of neovascular AMD. However, prior studies evaluating monotherapy with either external beam [43–45] or proton beam irradiation [46] failed to show a treatment benefit [43–46]. The external delivery of radiation, and subsequent exposure to nonpathologic tissues, limited its efficacy. Localized radiation may provide a novel treatment modality with a distinct mechanism of action compared to current anti-VEGF therapies. Localized radiation has been shown to inhibit neovascularization and fibroblast proliferation [47, 48], affording it the potential to induce choroidal neovascular regression and inhibit scar formation in neovascular AMD. Moreover, targeted radiation, which may induce CNV regression, theoretically does not affect the overlying retina when delivered below threshold levels.

Radiation therapy may have an additive effect when combined with anti-VEGF treatment. Adjunctive bevacizumab with standard chemoradiotherapy proved efficacious in a phase II study treating advanced colorectal carcinoma [49]. Researchers feel that in addition to its antivascular effect, VEGF-targeted therapy may sensitize tumors to radiation through two mechanisms: by normalizing the tumor vasculature, leading to greater tumor oxygenation and thereby increasing the cytotoxicity of radiation to cancer cells, and by increasing the radiosensitivity of tumorassociated endothelial cells [50]. This same additive response may prove beneficial in the treatment of neovascular AMD.

Pearl

Radiation therapy has antiangiogenic, antiinflammatory, and antifibrotic characteristics; localized therapy holds promise in the treatment of neovascular AMD.

Epi-Rad90™ Ophthalmic System

The Epi-Rad90™ Ophthalmic System (NeoVista, Fremont, CA, USA) delivers strontium 90 directly to the neovascular complex during a vitrectomy, thereby delivering localized radiation (brachytherapy) while minimizing collateral exposure to

surrounding tissues. The device is a handheld intraocular instrument with a retractable tip. The tip contains the radiation source, which remains protected and insulated until engaged over the fovea. The target dose is 24 Gy to the fovea, a level that decreases dramatically (10% every 0.1 mm) as a function of distance from the radiation source.

Preclinical studies in animal models demonstrated safety of this device, with no reported cases of radiation-induced optic neuropathy or retinopathy. A feasibility trial of 34 patients, NVI-068, evaluated the safety and effectiveness of delivering a single treatment of either 15 Gy (8 patients) or 24 Gy (26 patients) beta radiation using the Epi-Rad90™ Ophthalmic System [51]. During the course of the study, the investigators altered eligibility requirements and excluded 11 patients from the analysis (five were diabetic, two had lesions greater than 5.4 mm, two had baseline visual acuity outside the inclusion criteria parameters, one displayed Alzheimer-like symptoms, and one was treated outside of the establish protocol, having received an initial 24 Gy dose and an additional 24 Gy dose after the six-month visit). Twelve-month data were available for 21 patients. All lost fewer than three lines of vision. In the 24 Gy group, 5 of 17 (29%) gained three or more lines of vision. There were no adverse events attributed to radiation exposure.

Another prospective feasibility study, protocol NVI-111, treated 34 patients with 24 Gy by the Epi-Rad90™ Ophthalmic System with concomitant intravitreal bevacizumab [52, 53]. Patients were randomized to two groups. Group I (n = 12) received bevacizumab prior to surgery (10 ± 4 days) and at one month after surgery. Group II (n = 22) received bevacizumab intraoperatively and at one month post surgery. After the two mandatory intravitreal bevacizumab injections, 25 patients (74%) did not require further injections at 24 months of follow-up. Retreatment was entirely based upon investigator evaluation, not on strict retreatment criteria [52]. As a result, patients may have been undertreated based on current practices. Patients achieved visual gains despite this possible undertreatment. Seven patients (20.6%) gained at least three lines of

vision at two years, while 22 patients (64.7%) maintained vision, losing less than or equal to three lines. Visual outcomes appeared confounded by cataract formation; half of phakic patients (12 of 24) developed cataract. Though all patients lost a mean of 2.4 letters, phakic patients lost 4.8 letters while pseudophakes gained 3.8. Researchers felt cataract formation was due to vitrectomy and not radiation, as the lens only receives 0.6 mGy during the procedure. Two patients developed subretinal fibrosis. Most importantly, there were no cases of radiation retinopathy.

The results of these pilot studies prompted the CNV Secondary to AMD Treated with Beta Radiation Epiretinal Therapy (CABERNET) trial, a phase III study that completed enrollment in September 2009. A total of 450 patients were randomized to either the experimental arm of the 24 Gy Epi-Rad90™ Ophthalmic System and two injections of ranibizumab, one at the time of surgery and another at one month, or the control arm of monthly ranibizumab for the first three months followed by quarterly injections for two years. Retreatment injections are possible in both arms at monthly intervals per specific retreatment criteria. If proven efficacious and safe, the EpiRad90™ Ophthalmic System would add a surgical option for neovascular AMD and has the potential to decrease the treatment burden of monthly injections.

Preliminary successes with the Epi-Rad90™ Ophthalmic System have spawned additional trials. MERITAGE I is a phase I/II study evaluating the Epi-Rad90™ Ophthalmic System for patients with neovascular AMD who require relatively frequent anti-VEGF therapy for adequate response [54]. ROSE is a phase II feasibility study evaluating epiretinal beta radiation in suboptimal responders to anti-VEGF therapy [55]. MERLOT is a phase IV study in the United Kingdom comparing epiretinal beta radiation to monthly ranibizumab [56].

IRay

IRay (Oraya Therapeutics, Inc., Newark, CA, USA) is an externally-applied stereotactic orthovoltage irradiation device. This office-based procedure allows noninvasive application of ionizing

radiation to the submacular choroidal neovascular membrane. The device uses three sequential beams, which pass through the pars plana and overlap at the macula. Phase I data of 16 Gy IRay demonstrated safety with no retinal, choroidal, retinal pigment epithelium, or optic nerve toxicity, and no cataract progression. All patients developed mild, self-limited punctate keratopathy secondary to the superficial corneal guidance device. The trial suggested therapeutic effect, with improvement of fluid on OCT and shrinkage of lesion size on fluorescein angiography [57]. Researchers are designing a phase II study in Europe [58], as well as a second study for the United States. If proven efficacious, IRay’s noninvasive, office-based delivery system would be an attractive means of applying ionizing radiation directly to choroidal neovascular membranes.

Antiinflammatory/Antiimmune

Pathways

Studies have suggested an inflammatory component in the pathogenesis of neovascular AMD [59–61]. A histologic study found macrophages in choroidal neovascular membranes; these macrophages secrete tissue factor, which is involved in fibrinogenesis [61]. Further, several genes in the complement pathway are implicated in neovascular AMD [60]. The bioactive forms of complement 3 and 5 (C3a and C5a) are present in AMD drusen, and they induce VEGF expression in vivo and in vitro [62]. Overexpression of the pleiotropic cytokine tumor necrosis factor (TNF), which is mainly produced by T cells and monocytes, has been found in neovascular membranes of eyes with AMD [63]. Thus, inhibition of inflammatory and immune pathways may play a therapeutic role in neovascular AMD.

Pearl

Inhibition of inflammatory and immune pathways may play a therapeutic role in neovascular AMD.

POT-4

Complement 3 (C3) is a central component of all known complement activation pathways. Thus, inhibition of C3 disables all downstream complement cascade activation that could lead to local inflammation, tissue damage, and upregulation of VEGF [39, 64]. POT-4 (Potentia Pharmaceuticals, Louisville, KY, USA) binds and inhibits C3. A phase I, dose-escalating trial of intravitreal POT-4 exhibited safety in all doses tested. POT-4 demonstrated signs of activity in a few end-stage wet AMD patients. Researchers measured sustained serum levels of POT-4 in patients receiving the highest dose, and expect a single intravitreal POT-4 injection to provide sustained therapeutic levels for several months. A phase II study to further define the safety, efficacy, and pharmacokinetic profile of POT-4 is under design [64, 65].

ARC1905

ARC1905 (Ophthotech Corporation, Princeton, NY, USA) inhibits complement factor 5 (C5), preventing the formation of key terminal fragments C5a and C5b-9. C5a induces vascular permeability, and recruitment and activation of phagocytes. C5b-9 is involved in membrane attack complex formation, which initiates cell lysis [39, 62]. A phase I study is evaluating intravitreal ARC1905 with either an induction dose or multiple doses of ranibizumab for neovascular AMD [66]. In addition, another phase I study is evaluating intravitreal ARC1905 for dry AMD [67].

Infliximab

The anti-TNF-a monoclonal antibody infliximab (Remicade®, Centocor, Inc., Horsham, PA, USA) is used for various inflammatory conditions, such as rheumatoid arthritis, inflammatory bowel disease, psoriasis, and noninfectious uveitis. Researchers observed regression of CNV and improvement of visual acuity in three neovascular AMD patients treated with intravenous infliximab for inflammatory arthritis [63]. Intravitreal infliximab has regressed laser-induced CNV in rats [68]. Subsequent experiments of intravitreal infliximab found doses up to 2 mg were safe in the rabbit eye [69]. Intravitreal infliximab was administered to three patients with neovascular