VEGF in Clinical Trials and in Practice

By Naomi Fischer, MD; Michaela Goldstein, MD; and Anat Loewenstein, MD

Vascular endothelial growth factor (VEGF) plays a key role in ocular angiogenesis and vascular permeability. Several VEGF family members have been discovered, including VEGF-A, -B, -C, and -D as well as placental growth factor. Several known isoforms of VEGF may account for different effects in ocular pathologies and may differ in their neuroprotective abilities.1;2 Isoforms exert their effects through multiple receptors, which are predominantly expressed on endothelial cells and are also found on monocytes and macrophages.3

VEGF is upregulated by hypoxia,4 and it is found in elevated levels in neovascular and macular edema pathologies.1 Moreover, several case-controlled studies have found specific VEGF single-neucleotide polymorphisms to be associated with an increased risk of neovascular age- related macular degeneration (AMD).5,6 Therefore, VEGF is an attractive target for combating neovascular and ischemic eye disease such as choroidal neovascularization, diabetic macular edema, neovascularization that may occur in retinal vein occlusion, retinopathy of prematurity, neovascular glaucoma and, more rarely, in white dot syndromes, macular telangiectasia, and Stargardt's disease. VEGF is also being investigated in wound modulation after trabeculectomy.7

Several anti-VEGF drugs have been shown to be effective, but long-term drug delivery remains a challenge. There is a lack of multicenter randomized controlled trials comparing the VEGF drugs available as well as limited data comparing these drugs to other antiangiogenic and anti-inflammatory drugs. This article provides an overview of the clinical trials conducted thus far for the major anti-VEGF drugs that have been studied.

VEGF INHIBITORS

Pegaptanib

Pegaptanib sodium (Macugen; Eyetech, Inc.), an intravitreal RNA aptamer drug, was the first FDA- approved anti-VEGF drug for use in neovascular AMD. It targets VEGF165 and possibly its larger isoforms.8 The recommended dose is 0.3 mg every 6 weeks. The phase 3 VISION (VEGF Inhibition Study in Ocular Neovascularization) trial, which included patients with neovascular AMD, showed no serious systemic side effects and no increase in severe ocular inflammation, cataract, or glaucoma compared with sham injection.9,10 Over the first year, 70% of patients treated with pegaptanib lost fewer than 15 letters of visual acuity compared with 55% of sham-treated patients. However, only 6% gained three lines of vision.10 As early as 6 weeks, and at all subsequent points, mean visual acuity among patients receiving pegaptanib 0.3 mg was better than those receiving sham injections. The proportion of patients losing more than three lines between 1 and 2 years was double (14% vs 7%) if treatment was discontinued compared with those who continued to receive pegaptanib injections. This suggests that there is a more favorable outcome when treatment is delivered consistently for at least 2 years.11

A multicenter randomized controlled trial for diabetic macular edema showed that mean and median visual acuity at 36 weeks was 20/50 for treated patients versus 20/63 for patients in the sham group (P = .04). There was a significant decrease in mean retinal thickness for patients treated with pegaptanib compared with sham (P = .02).12 Additionally, 62% of the patients who also had retinopathy showed regression of neovascularization by 36 weeks compared with none in the sham group or untreated fellow eye.13 Small-scale studies have also shown pegaptanib to be effective for macular edema due to retinal vein occlusion.14,15

Ranibizumab

Ranibizumab (Lucentis; Genentech, Inc.) is a small 48-kDa recombinant humanized monoclonal antibody fragment that binds to all VEGF-A isoforms and has a good systemic and ocular safety profile. The phase 3 MARINA (Minimally Classic/Occult Trial of the Anti- VEGF Antibody Ranibizumab in the Treatment of Neovascular AMD) and ANCHOR (Anti-VEGF Antibody for the Treatment of Predominantly Classic Choroidal Neovascularization in AMD) trials found ranibizumab to be superior to sham injection and photodynamic therapy (PDT). The trials established that monthly intravitreal injections of ranibizumab prevent vision loss over a 24-month period. In comparison, 52.9% of MARINA control patients and 65.7% of ANCHOR patients treated with PDT lost fewer than three lines of visual acuity (P < .001).16,17 In the MARINA trial, a gain in visual acuity of three lines or more was seen in 24.8% patients treated with ranibizumab 0.3 mg and in 33.8% of patients treated with ranibizumab 0.5 mg compared with 5% treated with sham injections (P < .001).16 In ANCHOR, a three-line improvement was observed in 34% to 41% of patients in the ranibizumab group compared with 6.3% in the PDT group (P < .001).16, 17

The 2-year PIER (Phase 3b, Multi-Center, Randomized, Double-Masked, Sham Injection-Controlled Study of the Efficacy and Safety of Ranibizumab in Subjects with Subfoveal Choroidal Neovascularization with or without Classic CNV Secondary to AMD) trial showed less beneficial results when ranibizumab was given consecutively for the first 3 months and then quarterly.18 However, the PRONTO (Prospective OCT Imaging of Patients With Neovascular AMD Treated With Intraocular Ranibizumab) and SAILOR (Safety Assessment of Intravitreous Lucentis for AMD) studies demonstrated that clinical and optical coherence tomography-guided treatment can be used for effective as-needed dosing.19,20 Even so, results were better when three initial monthly injections were administered.21 The READ-2 (Ranibizumab for Edema of the Macula in Diabetes) study demonstrated a significantly better visual outcome for ranibizumab versus focal laser, with a mean improvement of 7.4 letters in the ranibizumab- treated group compared with 0.5 letters in the laser- treated group at 6 months and 7.7 letters in the ranibizumab-treated group compared with 5.1 letters in the laser-treated group at 24 months.22,23

Furthermore, the BRAVO (a Phase 3, Multicenter, Randomized, Sham Injection-Controlled Study of the Efficacy and Safety of Ranibizumab Injection Compared With Sham in Patients With Macular Edema Secondary to BRVO) and CRUISE (A Phase 3, Multicenter, Randomized, Sham Injection-Controlled Study of the Efficacy and Safety of Ranibizumab Injection Compared With Sham in Patients With Macular Edema Secondary to CRVO) trials showed improvement in visual acuity for ranibizumab versus sham injection.24-26 In BRAVO, the mean gain from baseline at month 6 was 16.6 letters in patients receiving 0.3 mg of ranibizumab, 18.3 letters in those receiving 0.5 mg, and 7.3 in those receiving sham injection. Improvement in BCVA was evident as early as 1 week, with patients achieving a mean gain of 7.6, 7.4, and 1.9 letters in the 0.3- and 0.5-mg ranibizum- ab and sham groups at 1 week, respectively. By month 6, most patients in the two ranibizumab groups gained at least three lines of BCVA (55.2% in the 0.3-mg and 61.1% in the 0.5-mg group), whereas most of those in the sham group did not (28.8%).

In CRUISE, the mean gain from baseline BCVA at 6 months was 12.7 letters in patients who received 0.3 mg of ranibizumab, 14.9 letters in patients who received 0.5 mg of ranibizumab, and 0.8 letters in those who received sham injections. Again, improvements in BCVA were seen as early as 1 week, with patients achieving mean gains of 8.8, 9.3, and 1.1 let- ters in the 0.3- and 0.5-mg ranibizumab and sham groups at 1 week, respectively. At 6 months, gains of three lines or more in BCVA were seen in 46.2% of patients receiving 0.3 mg of ranibizumab, 47.7% of those receiving 0.5 mg of ranibizumab, and 16.9% of those receiving sham injections.

Bevacizumab

Bevacizumab (Avastin; Genentech, Inc.) is a full- length recombinant humanized monoclonal antibody (149 kDa) that binds to all VEGF-A isoforms. Ranibizumab is derived from this molecule. Whereas ranibizumab has only one binding site, bevacizumab has two. It was first approved by the FDA for metastatic colorectal cancer and has been adopted for off-label use in ocular disease. Although systemic administration of bevacizumab has been associated with increased adverse systemic cardiovascular effects, these appear to be rare for intravitreal dosing.27,28 Given its relatively low cost and availability compared with ranibizumab, bevacizumab has become a leading treatment option during the past few years. A larger molecule than ranibizumab, bevacizumab has a longer-acting effect in vitro, but it may penetrate the retina less effectively.29-32

Bevacizumab has been found effective in neovascular and edematous disease. Most small-scale and retrospective studies have found no significant difference between the efficacy or safety of bevacizumab and ranibizumab.33-36 Others have noted differences in short-term outcomes,37 but evidence based on large randomized controlled trials is not available. Several trials comparing bevacizumab and ranibizumab are currently being conducted in the United States and Europe, including the CATT (Comparison of AMD Treatments Trials), IVAN (a Randomized Controlled Trial of Alternative Treatments to Inhibit VEGF in Age- Related Choroidal Neovascularization), VIBERA (Prevention of Vision Loss in Patients With Age-Related Macular Degeneration by Intravitreal Injection of Bevacizumab and Ranibizumab), EQUAL (a Randomized Trial to Study the Equivalence of Three Monthly Intravitreal Injections and Additional Injections as Needed of Bevacizumab and Ranibizumab on Visual Acuity in Patients with Exudative Age-Related Macular Degeneration), and MANTA (Avastin Versus Lucentis in Age-Related Macular Degeneration) studies.38-42

Aflibercept

Aflibercept (VEGF Trap-Eye; Regeneron Pharmaceuticals, Inc.) is a 110-kDa soluble decoy receptor that binds with high affinity to all VEGF members, except un- processed VEGF-C and D1. Its safety and efficacy was evaluated in the CLEAR-IT 1 (Clinical Evaluation of Anti- angiogenesis in the Retina) study, which found that aflibercept was well tolerated with no serious side effects.43 At 6 weeks, 95% of patients had stable or improved visual acuity. The VIEW (VEGF Trap-Eye: Investigation of Efficacy and Safety in Wet AMD) trial aims to compare this drug to ranibizumab.44,45 The DA VINCI (DME and VEGF Trap-Eye: Investigation of Clinical Impact) trial included 219 patients with diabetic macular edema and compared different doses of aflibercept and macular laser.46 The best result was observed after three monthly loading doses of 2.0 mg of aflibercept followed by injection as needed. Patients gained an average of 10.3 letters after 4.4 injections.

Small-Interfering RNAs

Small-interfering RNA (siRNA) is a 21- to 23- nucleotide double-stranded RNA that binds specifically to messenger RNA and prevents translation at the ribo- somal level. The phase 2 CARE (Acuity Cand5 Anti-VEGF RNAi Evaluation) assessed bevasiranib siRNA (Opko Health, Inc.) for neovascular AMD. Continuing deterioration was observed in the first 3 weeks, and it is hypothesized that bevasiranib may have a delayed effect. AGN211745 (Allergan, Inc.) siRNA showed stabilized visual acuity in 92% of patients with neovascular AMD at 3 months. Kleinman et al47 indicated that the antiangiogenic effect of siRNA may be due to activation of toll-like receptor-3, which could be potentially harmful, as activation of this receptor may promote geographic atrophy in genetically susceptible individuals.48

Pazopanib

Pazopanib (GalxoSmithKline) is a tyrosine kinase inhibitor of VEGF receptors 1, 2 and 3, PDGFR-α/β, and c-kit, and it has been approved for use in renal-cell carcino- ma. It is currently being investigated in a phase 2b study comparing pazopanib eye drops with ranibizumab for neovascular AMD.49 An open-label pilot study is also underway for oral pazopanib dosed daily over 28 days for wet AMD.50

COMBINATION THERAPY

Combination therapy potentially has a synergestic effect with possible longer-lasting effects. Small-scale studies have compared anti-VEGF in combination with triamcinolone, vitrectomy, and PDT in a range of ocular diseases with mixed results.51-56 Preclinical studies have shown a cumulative effect of combining ranibizumab and bevacizumab with the pegylated aptamer E10030 (Ophthotech Corp.). E10030 targets platelet-derived growth factor. Therefore, the combi- nation of these two treatments is targeting two inde- pendent angiogenic activities. Sorafenib (Bayer HealthCare and Onyx Pharmaceuticals, Inc.) is a tyro- sine kinase inhibitor that acts upon the VEGF receptor 2. Its off-label use has been described in two patients dosed orally three times per week (200 mg) in combi- nation with intravitreal ranibizumab with promising results.57 Currently, focal strontium-90 beta radiation (Epi-Rad90; Neovista, Inc.) delivered in combination with ranibizumab is being investigated in the phase 3 CABERNET (CNV Secondary to AMD Treated With Beta Radiation Epiretinal Therapy) trial.58

CONCLUSION

The VEGF pathway plays a key role in angiogenesis and permeability. Clinical trials show promising results for antiangiogenic agents in ocular diseases. However, there is a lack of large long-term randomized con- trolled trials as well as comparative studies between the various drugs. Simultaneously targeting several independent factors in this pathway may provide synergistic effects with fewer adverse events and less frequent treatment interventions.

Naomi Fischer, MD, is a senior resident in the Department of Ophthalmology at the Tel Aviv Sourasky Medical Center in Tel Aviv, Israel. She acknowledged no financial interest in the products or companies mentioned herein. Dr. Fischer may be reached at +972-3-6973408; naomi797@hotmail.com.

Michaella Goldstein, MD, is vice director of the Department of Ophthalmology and director of the Medical Retinal Unit in the Department of Ophthalmology at the Tel Aviv Sourasky Medical Center in Tel Aviv, Israel. She acknowledged no financial interest in the products or companies mentioned herein. Dr. Goldstein may be reached at michgold@netvision.net.il.

Anat Loewenstein, MD, is director of the Department of Ophthalmology at the Tel Aviv Medical Center, and she is a professor of ophthal- mology and vice dean of the Sackler School of Medicine at Tel Aviv University in Tel Aviv, Israel. She is a consultant to Allergan, Inc. Dr. Loewenstein may be reachedatanatlow@tasmc.health.gov.il.