Aflibercept: a Potent Vascular Endothelial Growth Factor Antagonist for Neovascular Age-Related Macular Degeneration and Other Retinal Vascular Diseases

Studies were identified through a comprehensive literature search of electronic databases (PubMed, Science Direct, and Scopus) with no limitations of language or year of publication. The following keywords and combinations of words were used in compiling the above search: ‘aflibercept,’ ‘vascular endothelial growth factor’ (VEGF), ‘VEGF,’ ‘antivascular endothelial growth factor‘ (anti-VEGF), ‘anti-VEGF,’ ‘vascular endothelial growth factor Trap-Eye,’ ‘VEGF Trap-Eye,’ ‘age-related macular degeneration,’ ‘neovascular age-related macular degeneration,’ ‘AMD,’ ‘diabetic macular edema’ (DME), ‘DME,’ ‘retinal vein occlusion’ (RVO), ‘RVO,’ ‘branch retinal vein occlusion’ (BRVO), ‘BRVO,’ ‘central retinal vein occlusion’ (CRVO), and ‘CRVO.’

Current established therapies for the treatment of neovascular AMD include argon laser therapy, photodynamic therapy (PDT), and anti-VEGF therapy.

A variety of molecules are currently being studied for the treatment of neovascular AMD. These drugs target various mediators and receptors involved in the angiogenic pathway. They include tyrosine kinase inhibitors (valatinib, pazopanib, TG100801, TG101095, AG013958, AL39324), integrin inhibitors (JSM6427, volociximab), bioactive lipids (sonepcizumab), nicotine receptor antagonists (mecamylamine), vectors encoding for pigment epithelial derived factor (ADGVPEDF) and small interfering RNAs or siRNAs (PF-04523655, AGN211745, RTP801i-14) [23, 24].

The class of drugs that has shown to be most effective against angiogenesis is the VEGF antagonists [25]. The efficacy of these agents has been studied extensively in several phase 3 trials resulting in a paradigm shift in the management of neovascular AMD. A summary of the properties of anti-VEGFs currently employed in managing patients with neovascular AMD is presented in Table 1 [17, 18, 26‐38].

VEGF is an important mediator of neovascularization. It also increases vessel permeability, and is about 50,000 times more potent than histamine in inducing vascular leakage [39]. The mammalian VEGF family includes VEGF-A, VEGF-B, VEGF-C, VEGF-D, and PlGF (placental growth factor). VEGF-A₁₆₅ is the most abundantly expressed and biologically active form in the human body [40].

VEGF-A acts on two transmembrane receptors located on the vascular endothelium, VEGFR1 and VEGFR2. Each receptor has seven immunoglobulin (Ig) domains in their extracellular regions. Binding of these domains with VEGF initiates the intrinsic tyrosine kinase activity of their cytodomains. Although VEGFR1 binds to VEGF with substantially higher affinity, most of the biologic effects of VEGF appear to be mediated by VEGFR2 [26]. Activation of these tyrosine kinases activates pathways that mediate endothelial migration and proliferation promoting angiogenesis; as well as effecting endothelial barrier functions causing leakage of water and macromolecules [41]. PlGF binds to VEGFR1 and has been shown to facilitate VEGF-A in promoting angiogenesis and vascular permeability, especially in pathological states [42‐44].

VEGF-A₁₆₅ and VEGF-A₁₂₁ are most abundantly expressed in normal eye vasculature and high levels of these isoforms have been found in CNV tissues excised from AMD patients [43]. VEGF-A₁₆₄ and VEGF-A₁₂₀ have also been implicated in the pathogenesis of CNV [45]. VEGF-A and P1GF have both been shown to promote angiogenesis and vascular leakage in the retina of animal and human models [43, 45‐47].

Table 2 [69‐81] summarizes important trials that have influenced current management of AMD with anti-VEGFs. The VEGF Inhibition Study in Ocular Neovascularization (VISION) trials established that pegaptanib (PEG) prevented vision loss over a period of 2 years in all forms of AMD, but no comparison was drawn with the use of PDT. No significant gain in visual acuity (VA) was observed and the majority of patients continued to have vision loss with the use of pegaptanib in these trials [69, 70].

The Minimally Classic/Occult Trial of the Anti-VEGF Antibody Ranibizumab in the Treatment of Neovascular Age-Related Macular Degeneration (MARINA) and Anti-VEGF Antibody for the Treatment of Predominantly Classic Choroidal Neovascularization in Age-Related Macular Degeneration (ANCHOR) trials established that RBZ not only prevented vision loss in all forms of AMD, but also improved vision in a subset of patients [71‐73]. Patients in these trials were followed for 2 years and the results showed that the benefit of RBZ was maintained throughout the study period. In MARINA, there was a mean improvement of 5.4 and 6.6 letters in the treatment arms (vs. a mean decline of 14.9 letters in the sham arm). The ANCHOR study specifically compared RBZ to PDT for the treatment of predominantly classic lesions and showed that patients receiving RBZ maintained vision superiorly compared with PDT. In addition, RBZ improved VA in a larger subset of patients than PDT. Over 2 years, there was a mean improvement of 8.1 and 10.9 letters in the treatment arms (vs. a mean decline of 9.8 letters in the PDT arm).

The RhuFab V2 Ocular Treatment Combining the Use of Visudyne to Evaluate Safety (FOCUS) study has shown that PDT given in conjunction with RBZ is superior to PDT given alone for predominantly classic lesions [74, 75]. Due to the heavy financial burden and inconvenience of monthly injections of RBZ for a prolonged period, the phase 3b, multicenter, randomized, double-masked, sham injectioncontrolled study of the efficacy and safety of RBZ in subjects with subfoveal CNV with or without classic CNV secondary to AMD (PIER) and Prospective optical coherence tomography imaging of patients with intraocular ranibizumab (PrONTO) studies were conducted to explore and conFigure practical and economical regimens for RBZ administration. In the PIER study, monthly injections were given for 3 months followed by quarterly injections. However, it failed to show the same benefits that were seen when monthly injections were given in the MARINA and ANCHOR trials [76, 77]. On the other hand, the PrONTO study established that a regimen of 3 monthly injections followed by monthly follow-ups and PRN (pro re nata/ as needed) administration of RBZ is possible, with results comparable to the ANCHOR and MARINA trials. Patients in this study received an average of 5.6 injections at the end of year 1 and 9.9 injections by the end of year 2. The PrONTO study, however, had a small sample size and was conducted at only one site [78, 79].

The Avastin (BVZ) for choroidal neovascular age-related macular degeneration (ABC) trial has shown that BVZ, being a similar molecule to RBZ, also prevents vision loss along with improving VA in a subset of patients [80]. Both RBZ and BVZ have been shown to have similar efficacy in the Comparison of Age-related Macular Degeneration Treatments Trials: Lucentis-Avastin Trial (CATT) trials, when given in a monthly regimen. RBZ given on a PRN basis also has a comparable efficacy to the monthly regimens. No conclusive comparison could be made for the prnBVZ group from the CATT trial [81].

Another strategy, the “treat and extend” regimen (TER) has been suggested in the clinical setting [82]. TER involves treating patients with an anti-VEGF agent monthly until there is no macular hemorrhage on examination or any intra- or sub-retinal fluid on OCT. The treating interval is prolonged by 2 weeks for every visit that there is no recurrence of exudation until a 12 week interval is established. The patient is then given the option to discontinue treatment with a follow-up in 8 weeks or to continue 12-weekly treatment. If at any time, there is evidence of recurrence of disease on examination, OCT or FA, or if VA is affected, the treatment interval is reduced by 2 weeks. Single-center retrospective studies using RBZ (92 eyes) and BVZ (74 eyes) have reported similar outcomes to those observed in MARINA and ANCHOR in eyes where TER was employed [83, 84]. The superiority of this regimen has been shown over PRN dosing in another retrospective review of 90 eyes [85]. It is clear that the TER approach is more cost-effective than monthly injections; however, the level of evidence for the efficacy of this management approach is currently from retrospective trials. Nevertheless, such a strategy is currently being employed by the majority (60%) of retinal specialists in the US as recently reported in the 2011 Preferences and Trends (PAT) Survey conducted by the American Society of Retina Specialists.

Preclinical studies have demonstrated the potential role of VEGF Trap in a number of vascular eye diseases including AMD [60, 86]. VEGF Trap-Eye was first studied in humans by Nguyen and colleagues at the Wilmer Eye Institute via intravenous administration of 0.3 mg/kg, 1.0 mg/kg and 3.0 mg/kg against placebo in a phase 1 trial [61]. A dose-dependent decrease in foveal thickness (FTh) was noted, but due to two patients developing systemic toxicity in the 3.0 mg group (grade 4 hypertension and grade 2 proteinuria), the trial was halted [61].

The CLinical Evaluation of Anti-angiogenesis in the Retina Intravitreal Trial (CLEAR-IT-1) clinical trial was a two-part phase 1 study designed to investigate the safety of IVT VEGF Trap for AMD. The first part of the study was a dose escalation cohort of increasing concentrations; 0.05, 0.15, 0.5, 1, 2, and 4 mg IVT VEGF Trap in 21 patients. No systemic or ocular adverse events (AEs) were noted. A substantial reduction in FTh was observed, and 95% of the patients remained stable or improved vision at 6 weeks [87]. The second part of the CLEAR-IT-1 study investigated the effect of a single intravitreal injection of 0.15 or 4 mg of VEGF Trap in 28 patients, with the primary endpoint at week 8. No SAE was reported in either group. The effects were substantially more prominent in the 4 mg group compared to the 0.15 group, as expected, illustrating the dose-response characteristics. FTh decreased by 25% and 11% while VA improved by a mean of 4.5 letters and 1.1 letters in the 4.0 mg and 0.15 mg groups, respectively [88].

The CLEAR-IT phase 2 (CLEAR-IT-2) multicenter, double-masked clinical trial followed 159 patients, divided into five groups across 33 sites, for a year. Two groups were administered a monthly injection of 0.5 mg and 2.0 mg VEGF Trap-Eye while three groups were given 0.5, 2.0, and 4.0 mg VEGF Trap-Eye every 3 months. All patients received mandatory monthly or 3 monthly (based on the group designation) treatments for the first 3 months following the first treatment. After month 3, patients were evaluated each month and treated with the same dose of drug on a PRN basis. By the end of the mandatory treatment period, patients in groups 1 and 2 had received four treatments while patients in groups 3, 4, and 5 had received two treatments. The 3-month results showed a mean reduction of 119 μm in central subfield thickness and a mean gain of 5.7 letters across all groups. These improvements were significantly greater in the groups treated monthly compared to the groups treated 3-monthly [56]. Improvements in anatomic and functional parameters were maintained through month 13, with a mean reduction of 130 μm in central subfield thickness and a mean gain of 5.3 letters across all groups. The size of CNV as observed at month 12 on FA decreased in all groups. Overall, 92% of the study population lost fewer than 15 letters and 22% gained more than 15 letters. Patients received an average of two injections in the 9 months following the mandatory treatments [89].

The CLEAR-IT-2 trial showed that the monthly administration of VEGF Trap-Eye provided significantly greater improvement in both VA and foveal thickness (FTh) compared to every-3-month administration. The least number of injections (1.55) and the longest mean initial treatment-free interval (160 days) after mandatory treatments was observed in the 2.0 mg monthly group. As highlighted before, the VEGF Trap-Eye molecule not only has a considerably favorable pharmacodynamic profile over other anti-VEGFs in its ability to bind to VEGF, it binds to PlGF as well. Such ability of persistent VEGF blockade led to the postulation of a possible longer treatment interval between injections of VEGF Trap compared to other anti-VEGFs. A mathematical model predicted VEGF Trap-Eye to maintain biological activity for 73–83 days compared to the activity of RBZ (30 days) [29]. On the basis of these results, phase 3 clinical trials VIEW 1 and VIEW 2 (The Vascular Endothelial Growth Factor [VEGF] Trap-Eye: Investigation of Efficacy and Safety in Wet Age-Related Macular Degeneration [AMD] Study) are being conducted.

VIEW 1 and VIEW 2 are two large, multicenter, randomized clinical trials that were designed to compare different treatment regimens of VEGF Trap-Eye to monthly RBZ. The studies were designed as noninferiority trials between VEGF Trap-Eye and RBZ. VIEW 1 has enrolled 1,217 patients across sites in North America, while VIEW 2 has enrolled 1,240 patients across sites in Europe, Asia, and Latin America. There are four treatment groups: 0.5 mg RBZ monthly, 0.5 mg VEGF Trap-Eye monthly, 2 mg VEGF Trap-Eye monthly, and 2 mg VEGF Trap-Eye every 2 months. All these groups received monthly injections for the first 3 months of the study [90].

At month 12, prevention of moderate vision loss (defined as losing less than 15 letters) was achieved in a similar percentage (94–95%) of patients in all four treatment arms across both trials. Patients in the 2.0 mg VEGF Trap-Eye group had a mean improvement of 10.9 letters in vision compared to 8.1 letters in the 0.5 mg monthly RBZ group. The other two groups were found to be noninferior to 0.5 mg RBZ monthly [62, 91]. The VIEW study design did not compare against a dosing regimen of RBZ given every 2 months; thus, no comparison can be made to such a regimen.

In Year 2, all patients are being treated with the same dose no less frequently than every 3 months but as frequently as every month if required in a “quarterly capped PRN” dosing schedule [64, 92]. According to a news release by Regeneron and Bayer on December 5, 2011, in an integrated analysis of the VIEW 1 and VIEW 2 studies, the VA gain from baseline in the VEGF Trap-Eye 2.0 mg every other month group at week 96 was 7.6 letters compared to 8.4 letters at week 52, with an average of 11.2 injections over 2 years and 4.2 injections during the second year. The VA gain from baseline in the monthly RBZ group at week 96 was 7.9 letters compared to 8.7 letters at week 52, with an average of 16.5 injections over two years and 4.7 injections during the second year. The results of each of the VIEW 1 and VIEW 2 studies were consistent with the integrated analysis [93].

The overall fewer average number of injections in the second year in the VEGF Trap-Eye 2.0 mg every 2 months group compared to the RBZ group (4.2 vs. 4.7) was driven by the fact that fewer patients needed more intense therapy in the VEGF Trap-Eye 2.0 mg every 2 months. The proportion of patients who required frequent injections (six or more) during the second year was 15.9% in the VEGF Trap-Eye 2.0 mg every 2 months group compared to 26.5% in the RBZ group. In the 25% of patients who required the most intense therapy (the greatest number of injections), patients in the VEGF Trap-Eye 2.0 mg every 2 months group required an average of 1.4 fewer injections in the second year compared to the RBZ group (6.6 vs. 8.0). In the 25% of patients in each group who had the fewest number of injections in the second year, the average number of injections was similar (approximately 3 for both groups, corresponding to the protocol-mandated minimum number of injections). The statistical significance of these differences was not disclosed in this press release [93]. In addition, based on the currently available information, it is not clear if the difference between 4.2 and 4.7 injections is clinically significant. Thus, it will be increasingly important to evaluate the efficacy and patterns of usage that are reported by clinicians as they begin to use aflibercept for neovascular AMD.

In addition to neovascular AMD, VEGF Trap-Eye is also being studied as a potential therapy for DME and CRVO.

In an exploratory study of five patients, Do and colleagues at the Wilmer Eye Institute, demonstrated the safety and signals for bioactivity of VEGF Trap-Eye in eyes with DME. Each patient received one ITV injection of VEGF Trap-Eye. Four patients showed improvement in FTh (median 31% reduction from baseline) and VA (median improvement of three letters) at 6 weeks [59]. Following the pilot study, the DME And VEGF Trap-Eye: INvestigation of Clinical Impact (DAVINCI) phase 2 clinical trial compared 0.5 mg and 2.0 mg VEGF Trap-Eye monthly, 2 mg VEGF Trap-Eye bimonthly, and 2 mg VEGF Trap-Eye PRN to the current standard of care (laser therapy) in 221 patients with DME [65, 66]. Six month results showed all four groups to be superior (mean letters gain of 8.5 to 11.4, mean FTh reduction of −127.3μm to −194.5 μm) to macular laser therapy (mean letters gain of 2.4, mean FTh −67.9 μm) [58]. Month 12 results have shown that the superiority of VEGF Trap-Eye over laser has been maintained. Mean change in VA at week 52 was −1.3 letters for the laser group and 11, 13.1, 9.7, and 12 for the 0.5 mg monthly, 2.0 mg monthly, 2.0 mg bimonthly, and 2.0 mg PRN groups, respectively [94]. Two large phase 3 trials, Study of Intravitreal Administration of VEGF Trap-Eye in Patients with Diabetic Macular Edema (VISTA-DME) and VEGF Trap-Eye in Vision Impairment Due to DME (VIVD-DME), are currently investigating two separate dosing regimens of VEGF Trap-Eye compared to focal laser photocoagulation for the treatment of DME [67].

COPERNICUS (Controlled Phase 3 Evaluation of Repeated intravitreal administration of VEGF Trap-Eye In Central retinal vein occlusion: Utility and Safety) and GALILEO (General Assessment Limiting Infiltration of Exudates in central retinal vein Occlusion with VEGF Trap-Eye) are two phase 3 trials following 189 and 172 patients with CRVO respectively. Patients are given monthly 2.0 mg VEGF Trap-Eye or sham injections for the first 6 months followed by PRN treatment for the next 6 months [63, 95]. At month 6, 56.1% and 60.2% of patients treated with VEGF Trap-Eye gained at least 15 letters from baseline compared to 12.3% and 22.1% of patients treated with sham, in the COPERNICUS and GALILEO studies, respectively [57, 94]. The multicenter, randomized, controlled trial, CRUISE (a study of the efficacy and safety of RBZ injection in patients with macular edema secondary to CRVO), in which 392 CRVO patients received 6 monthly RBZ or sham injections followed by PRN treatment, has previously reported that 46.2% and 47.7% of patients in the RBZ groups and 16.9% of patients in the sham group gained at least 15 letters at month 6 [96]. At month 12, 47% and 50.8% in the RBZ groups, and 33.1% in the sham/RBZ group had a gain of at least 15 letters [97]. Three hundred and four patients from CRUISE were followed in the HORIZON (An Open-Label, Multicenter Extension Study to Evaluate the Safety and Tolerability of Ranibizumab in Subjects With Choroidal Neovascularization [CNV] Secondary to AMD or Macular Edema Secondary to RVO Who Have Completed a Genentech-Sponsored Ranibizumab Study) trial and seen at least every 3 months in a PRN regimen. At month 24 after CRUISE, 38.6% and 45.1% in the RBZ groups, and 38.3% in the sham/RBZ groups had a gain of at least 15 letters [98]. Phase 3 studies of VEGF Trap-Eye in branch retinal vein occlusion are being launched and will provide clinicians with additional and more complete data on the role of aflibercept in different types of RVO.

Ocular SAEs after IVT injections in different clinical trials have been fortunately very low, with risks varying with underlying disease process, technique of administration and effect of the drug [99]. SAEs reported for anti-VEGF treatments specifically in multiple clinical trials have also been low with incidence rates per 100 injections as follows: endophthalmitis (0.04–0.11), retinal detachment (0.01–0.08), retinal tear (0.02–0.3), anterior chamber inflammation (0.25–1.06), cataract (0.05–0.64), increased intraocular pressure (IOP; 0.15–3.6) and intraocular hemorrhage (0.03–00.18) [58, 100‐102].

Since VEGF is involved in a variety of physiologic processes such as blood pressure homeostasis [103], the question of AEs due to any systemic circulation of anti-VEGF given intravitreally arises. BVZ and aflibercept when given intravenously as chemotherapeutic agents have been known to cause hypertension and proteinuria, while BVZ has been identified as a risk for arterial thrombotic events (ATEs) and venous thrombotic events (VTEs) [104]. In the ANCHOR and MARINA trials, an increased but not significant rate of nonocular hemorrhages was noted in the treatment arms (9%) versus the sham arm (5.5%), raising some concern [105]. However, in other RBZ trials, including a phase 4 study specifically designed to test the safety of RBZ injections (SAILOR-Safety Assessment of Intravitreal Lucentis for AMD), the rates of ATEs were similar to control groups [106]. In the CATT, the anti-VEGFs’ incidences of ATEs and VTEs were between 2–3% and 0–1.4%, respectively [81]. A large retrospective study of Medicare claims of 146,942 patients with neovascular AMD concluded that there was no increased risk of mortality, myocardial infarction, bleeding, or stroke in patients treated with BVZ and RBZ compared to photodynamic therapy or pegaptanib [107].

Thus far, data from the CLEAR-IT2 and VIEW studies have shown a similar safety profile as other anti-VEGFs. SAEs related to study injection, which included end ophthalmitis, traumatic cataract, and transient IOP elevation, were found to have an incidence of less than 0.1% per injection, consistent with SAEs of IVT therapy. The most commonly reported AEs are conjunctival hemorrhage, eye pain, cataract, vitreous detachment, vitreous floaters, and increased IOP. Data from the VIEW trials has been carefully analyzed to look for any systemic SAEs of VEGF Trap. Only 0.3% of patients were found to have had an SAE pertaining to hypertension, with mean systolic pressure remaining stable in all treatment groups over time. The incidence of ATEs was 1.8% in the VEGF Trap group compared to 1.3% in the RBZ group with no dose response found between drug and ATE events. There also appeared to be no increased risk of immunogenicity to the VEGF Trap molecule either [28]. However, on February 13, 2012, the American Society of Retina Specialists, in a letter to its members, and Regeneron, in a letter to the FDA, described a number of reported cases of ocular inflammation/noninfectious endophthalmitis following intravitreal injection of aflibercept for the treatment of neovascular AMD. It is unclear at this time if such inflammation will continue to be observed in the future and if it will affect the usage of VEGF Trap-Eye among clinicians.

VEGF antagonists have brought better therapeutic outcomes, compared to laser therapy, to patients with neovascular AMD, DME, and RVO. Starting with pegaptanib followed by RBZ, BVZ, and most recently aflibercept, each of these agents has confirmed again the important role of VEGF in the pathogenesis of many retinal vascular diseases. Aflibercept appears to provide longer duration of efficacy compared to RBZ in neovascular AMD, while being investigated further in DME and RVO. The safety profile of anti-VEGF therapy, in published studies thus far, has not shown to be very different among different agents.

Studies are being done and research is being conducted to search for additional therapeutic approaches to enable patients with different retinal vascular diseases, including AMD, DME, and RVO, to achieve further visual gain while confronting no additional safety concerns.