Aflibercept (VEGF Trap-Eye) for the treatment of exudative age-related macular degeneration

Aflibercept, a soluble receptor molecule that binds VEGF, has been recently approved for the treatment of exudative age-related macular degeneration. This fusion protein with binding sequences from VEGF receptors 1 and 2 possesses high binding affinity for isomers of VEGF-A, VEGF-B and PlGF, and prevents VEGF from initiating proliferation and migration of vascular endothelial cells. Phase III trials showed that intravitreal aflibercept given monthly or every 2 months produces visual improvement and decrease in macular thickness comparable with monthly ranibizumab. The second year of the trials demonstrated that as-needed aflibercept maintained vision with few required injections. Aflibercept promises to decrease the treatment burden faced by patients with exudative age-related macular degeneration.     

Targeted pharmacotherapy of retinal diseases with ranibizumab

Diseases of retinal and/or choroidal blood vessels are the most prevalent causes of moderate and severe vision loss in developed countries. Vascular endothelial growth factor (VEGF)-A plays a critical role in the pathogenesis of many of these diseases. Ranibizumab is a humanized antigen-binding fragment that binds all isoforms of VEGF-A. Intraocular injections of ranibizumab cause significant visual improvement in approximately 40% of patients with choroidal neovascularization due to age-related macular degeneration (AMD). Pilot trials have indicated that intraocular injections of ranibizumab also provide benefits in patients with macular edema due to diabetic retinopathy or retinal vein occlusions. Based upon several case series, bevacizumab, a full-length humanized monoclonal antibody that binds all isoforms of VEGF-A, improves vision in patients with choroidal neovascularization due to AMD and other diseases. Case series also suggest that bevacizumab can cause regression of retinal neovascularization in patients with proliferative diabetic retinopathy. Taken together, results with ranibizumab and bevacizumab suggest that potent antagonists of VEGF will provide the foundation of treatment for a wide variety of diseases complicated by retinal or choroidal neovascularization, or by excessive vascular leakage leading to macular edema.     

Drug delivery techniques for treating age-related macular degeneration

Introduction: Currently, the standard therapy for neovascular age-related macular degeneration involves the use of anti-vascular endothelial growth factor (VEGF) drugs, which are delivered by repeated office-based intravitreal injections. This treatment is generally very effective in stabilizing or improving vision, although repeated injections create a burden for patients, family members and physicians. In addition, the cumulative risks of endophthalmitis and other complications increase with the number of injections.

Areas covered: In the clinic, much attention is focused on the relative efficacies of the three major anti-VEGF medications (bevacizumab, ranibizumab and aflibercept) as well as the most popular re-injection regimens (monthly, as-needed and treat-and-extend). In theory, intravitreal anti-VEGF drug delivery with sustained-release devices would offer similar visual results with fewer required re-injections. Various approaches have been studied, including noninvasive techniques, intraocular implants and colloidal carriers, such as liposomes, microparticles and nanoparticles.

Expert opinion: Despite its theoretical appeal, sustained-release drug delivery will not replace current techniques unless it offers one or more advantages in efficacy, safety, convenience or cost. Currently, many patients maintain stable vision with intravitreal injections at intervals of 2 months or longer, so sustained-release techniques will have to lengthen these intervals substantially to become widely accepted. As we continue to collect data from clinical trials, the role of sustained-release techniques will become better defined.     

Aflibercept for the treatment of neovascular age-related macular degeneration

Age-related macular degeneration (AMD) can have devastating effects on vision, especially in its neovascular form. In the last decade, the use of intravitreal pharmacotherapy targeted to vascular endothelial growth factor (VEGF) has significantly improved the visual outcomes in patients with neovascular AMD. Although we have become accustomed to these unprecedented improvement outcomes, maintaining good visual results with anti-VEGF therapy requires tremendous effort, time and cost, typically involving monthly clinic visits and intravitreal injections. The introduction of aflibercept, an anti-VEGF drug that targets all isoforms of VEGF as well as placenta growth factor, has shown promise throughout recent clinical trials as an equally effective treatment for neovascular AMD that requires less frequent dosing than either ranibizumab or bevacizumab. Based on clinical trial results, the U.S. Food and Drug Administration approved aflibercept in November 2011 for use in neovascular AMD, giving patients the hope of alleviating some of the burden associated with treatment.     

VEGF Trap-Eye for the treatment of neovascular age-related macular degeneration

Background: Age-related macular degeneration (AMD) affects > 14 million individuals worldwide. Although 90% of patients with AMD have the dry form, neovascular AMD accounts for the vast majority of patients who develop legal blindness. Until recently, few treatment options existed for treatment of neovascular AMD. The advent of anti-VEGF therapy has significantly improved the safe and effective treatment of neovascular AMD. In addition to two anti-VEGF drugs currently in widespread use, ranibizumab and bevacizumab, a number of medications that interrupt angiogenesis are currently under investigation. One promising new drug is aflibercept (VEGF Trap-Eye), a fusion protein that blocks all isoforms of VEGF-A and placental growth factors-1 and -2. Objective: To review the current literature and clinical trial data regarding VEGF Trap-Eye for the treatment of neovascular AMD. Methods: Literature review. Results/conclusion: VEGF Trap-Eye is a novel anti-VEGF therapy, with Phase I and II trial data indicating safety, tolerability and efficacy for the treatment of neovascular AMD. Two Phase III clinical trials (VIEW-1 and VIEW-2) comparing VEGF Trap-Eye to ranibizumab are currently continuing and will provide vital insight into the clinical applicability of this drug.     

Effects of receptor tyrosine kinase inhibitors on VEGF165a- and VEGF165b-stimulated gene transcription in HEK-293 cells expressing human VEGFR2

Background and Purpose

Receptor tyrosine kinase inhibitors (RTKIs) targeted at VEGF receptor 2 (VEGFR2) have proved to be attractive approaches to cancer therapy based on their ability to reduce angiogenesis. Here we have undertaken a quantitative analysis of the interaction of RTKIs and two VEGF splice variants, VEGF₁₆₅a and VEGF₁₆₅b, with VEGFR2 by studying nuclear factor of activated T-cells (NFAT) reporter gene activity in live HEK-293 cells.

Experimental Approach

HEK-293 cells expressing the human VEGFR2 and a firefly luciferase reporter gene regulated by an NFAT response element were used for quantitative analysis of the effect of RTKIs on VEGF₁₆₅a- and VEGF₁₆₅b-stimulated luciferase gene expression.

Key Results

VEGF₁₆₅a produced a concentration-dependent activation of the NFAT-luciferase reporter gene in living cells that was inhibited in a non-competitive fashion by four different RTKIs (cediranib, pazopanib, sorafenib and vandetanib). The potency obtained for each RTKI from this analysis was similar to those obtained in binding studies using purified VEGFR2 kinase domains. VEGF₁₆₅b was a lower-efficacy agonist of the NFAT-luciferase response when compared with VEGF₁₆₅a. Analysis of the concentration–response data using the operational model of agonism indicated that both VEGF₁₆₅ isoforms had similar affinity for VEGFR2.

Conclusions and Implications

Quantitative pharmacological analysis of the interaction of VEGF₁₆₅ isoforms and RTKIs with VEGFR2 in intact living cells has provided important insights into the relative affinity and efficacy of VEGF₁₆₅a and VEGF₁₆₅b for activation of the calcineurin- NFAT signalling pathway by this tyrosine kinase receptor.     

An update on the pharmacotherapy of neovascular age-related macular degeneration

Introduction: Neovascular age-related macular degeneration (AMD) is currently the most common cause of legal blindness in industrialized countries. The advent of pharmacotherapy with intravitreal VEGF inhibitors has greatly improved outcomes for the treatment of this disease.

Areas covered: The present review is divided into two major sections: the period prior to the use of anti-VEGF agents (triamcinolone acetonide, verteporfin photodynamic therapy) and the period following their introduction (pegaptanib sodium, bevacizumab, ranibizumab, aflibercept). The main pharmacological and clinical characteristics of each therapy are summarized.

Expert opinion: Monotherapy with anti-VEGF agents is currently the ‘gold standard' for treating neovascular AMD, but, with several drug choices and various different dosing regimens available, there is still wide variability in how individual clinicians manage their patients. Despite improved visual outcomes, there remains a significant unmet need for better treatments as the frequent office visits and injections associated with anti-VEGF therapy are costly and place a significant burden on patients, their family members and physicians.     

Comparative efficacy of bevacizumab,ranibizumab, and aflibercept for treatment of macular edema secondary to retinal vein occlusion: a systematic review and network meta-analysis

Introduction: Anti-vascular endothelial growth factor (VEGF) therapy has become the most commonly used treatment for macular edema secondary to retinal vein occlusion (RVO). Although its superior efficacy as compared to other interventions has been proven, there is a lack of evidence for relative efficacy among anti-VEGF drugs.

Areas covered: This work systematically reviewed and compared the efficacy of intravitreal bevacizumab, ranibizumab, and aflibercept for treating macular edema due to RVO. PubMed, EMBASE, and the Cochrane Library were searched from their inception until October 2017. Eleven randomized controlled trials (18 articles; 1830 adult patients) were identified. The proportion of patients who gained at least 15 letters in best-corrected visual acuity (BCVA), mean change from baseline in BCVA, and mean change from baseline in central macular thickness (CMT) were reported and these efficacy outcomes at 6 months were analyzed in network meta-analysis.

Expert commentary: Apparently, bevacizumab, ranibizumab, and aflibercept were significantly superior to sham injection in terms of BCVA improvement and CMT reduction and had good safety profiles. However, there were no statistically significant differences in any outcomes among anti-VEGF drugs. In selecting an anti-VEGF drug for individual patients, other factors including affordability, drug availability, and patient characteristics should be considered.     

A positive circuit of VEGF increases Glut-1 expression by increasing HIF-1α gene expression in human retinal endothelial cells

Treatment of human retinal microvascular endothelial cells (HRMECs) with vascular endothelial growth factor 165 (VEGF₁₆₅) increased hypoxia-inducible factor 1α (HIF-1α), VEGF, and glucose transporter 1 (Glut-1) mRNA expression and Glut-1 protein localization to the membrane. In contrast, treatment of human retinal pigment epithelium cells with VEGF₁₆₅ did not induce HIF-1α, VEGF, and Glut-1 gene expression. Microvascular endothelial cells are surrounded by astrocytic end feet in the retina. Astrocyte-derived A-kinase anchor protein 12 overexpression during hypoxia downregulated VEGF secretion, and this conditioned medium reduced VEGF and Glut-1 expression in HRMECs, suggesting that communications between astrocytes and endothelial cells may be the determinants of the blood vessel network. In HRMECs, HIF-1α small interfering RNA transfection blocked the VEGF₁₆₅-mediated increase in VEGF and Glut-1 gene expression. Inhibition of protein kinase C (PKC) with inhibitor GF109203X or with a small interfering RNA targeting PKCζ attenuated the VEGF₁₆₅-induced Glut-1 protein expression and VEGF and Glut-1 mRNA expression. In addition, results of an immunoprecipitation assay imply an interaction between VEGF receptor 2 (VEGFR2) and PKCζ in HRMECs. Therefore, VEGF secretion by hypoxic astrocytes may upregulate HIF-1α gene expression, inducing VEGF and Glut-1 expression via the VEGFR2–PKCζ axis in HRMECs.     

Real world evidence of use of anti-VEGF therapy in Denmark

Objective: This study evaluates real-world evidence regarding the frequency of anti-vascular-endothelial-growth-factor (VEGF) injections during the first year of therapy of treatment-naïve patients with neovascular age-related macular degeneration (nAMD), diabetic macular edema (DME) and retinal vein occlusion (RVO) from the Danish National Patient Registry. There was a switch in anti-VEGF treatment for naïve nAMD patients during the study period, following the introduction of aflibercept, which was expected to reduce the injection frequency relative to ranibizumab due to a perception of prolonged treatment duration of aflibercept.

Methods: All treatment-naïve nAMD, DME or RVO patients who received an intravitreal injection in Denmark from 1 January 2012 to 31 July 2015 were eligible for inclusion. Patients were required to have been treated for at least one year and, for nAMD, to have received at least three injections during the first four months of treatment. Patients were allocated to half-year groupings (2012/1 to 2014/1) based on registration of their first intravitreal injection. Injection frequency during the first year of treatment was calculated for each group and t-tests investigated whether injection frequencies changed over time.

Results: In treatment naïve nAMD patients (n?=?500), the mean (SD) number of anti-VEGF injections increased significantly from 6.04 (1.71) in 2012/1 to 6.73 (1.62) in 2014/1 (p?=?.001; 2012/1 and 2012/2 vs. 2014/1) across all treatments. A similar trend was found for DME patients (n?=?76) from 2012/1 to 2014/1 and RVO patients (n?=?82) from 2012/2 to 2014/1, with mean injection frequencies increasing significantly from 5.14 (2.29) to 5.93 (1.98) (p?=?.007), and from 4.83 (1.21) to 6.08 (1.55) (p?=?.024), respectively. Post hoc sensitivity analysis also found a significant increase in injection frequency in nAMD patients who did not receive a loading phase (4.55 in 2012/1 and 5.05 in 2014/1; p?=?.006; n?=?616).

Conclusions: In contrast to the decrease in injection frequency predicted with a switch to aflibercept treatment for nAMD, our study showed that injection frequencies increased significantly from 2012 to 2014 in patients initiating therapy across the three diseases.     

Systemic safety of anti-VEGF drugs: a commentary

Introduction: VEGF is a mediator of angiogenesis. Thus, concerns have been expressed following the use of VEGF inhibitors for the treatment of neovascular age-related macular degeneration (nAMD). Ranibizumab, and more recently aflibercept, are VEGF inhibitors licensed for the treatment of nAMD. Bevacizumab is also used but unlicensed for this application.

Areas covered: A non-systematic review of nAMD trials was undertaken to investigate four outcomes: all-cause mortality, all systemic serious adverse events (SSAEs), arteriothrombotic events (ATEs) and gastrointestinal (GI) complications. Differences in event rates with injections of ranibizumab compared to bevacizumab, aflibercept, photodynamic therapy (PDT) and sham were explored and quantified using fixed-effect meta-analyses.

Expert opinion: Anti-VEGF agents can influence vascular health; however, the data suggest no difference in the risk of an ATE or death between anti-VEGF agents. Clinical trials are limited in their size and eligibility criteria and databases of patients treated in routine practice should also be scrutinized.     

Novel anti-angiogenic therapeutic strategies in colorectal cancer

Introduction: Anti-angiogenetic agents are currently the standard of care in metastatic CRC patients. Bevacizumab, aflibercept, regorafenib and recently ramucirumab have significantly improved both progression-free and overall survival in different lines of treatment. Since bevacizumab’s approval, a number of novel anti-VEGF agents have been tested in preclinical and clinical models.

Areas covered: This review is focused on the most recent clinical results of novel agents targeting VEGF and its receptors with a major focus on those investigated recently in clinical trials.

Expert opinion: In the last 15 years, a number of new anti-angiogenetic agents have been tested. Unfortunately, most of them have demonstrated unacceptable toxicities or failed to show activity. When tested as single agents, encouraging preliminary results were reported with fruquintinib, famitinib, and nintedanib. Interesting novel mechanisms of action are also being explored: VGX-100 is a monoclonal antibody (mAb) which binds to VEGF-C, inhibiting activation of VEGFR-2 and VEGFR-3 when combined with bevacizumab; tanibirumab is a mAb which binds to VEGFR-2 and vanucizumab is a bispecific mAb binding both to VEGF-A and Angiopoietin-2. Data about the combination of these agents with chemotherapy are very encouraging, even though preliminary. However, the definition of specific predictive biomarkers remains a priority.     

A safety evaluation of ranibizumab in the treatment of age-related macular degeneration

Introduction: The use of intravitreal ranibizumab has transformed the outcomes for thousands of patients with wet age related macular degeneration (AMD), which is the leading cause of blindness in developed countries. Prior to its introduction, most patients with wet AMD would rapidly lose central vision. The use of intravitreal ranibizumab has been shown to reduce certifiable visual loss by about a half. Current treatment regimens with ranibizumab in wet AMD require multiple injections over several years and so it is highly relevant to review the safety record of this important drug.

Areas covered: This review considers the important ocular and systemic adverse events (AE) that have been reported in the literature, particularly in the context of the pivotal clinical trials that have been performed. It also reviews the safety of other anti-VEGF drugs that are used in wet AMD, namely bevacizumab and aflibercept, and compares these drugs with ranibizumab.

Expert opinion: Overall, intravitreal ranibizumab can be considered a safe and highly effective drug for patients with wet AMD. However recent concerns about retinal thinning following ranibizumab therapy, possible systemic AE associated with all anti-VEGF drugs and the occurrence of complications relating to drug preparation and delivery must be considered.     

Long-Term Stability of Anti-Vascular Endothelial Growth Factor (a-VEGF) Biologics Under Physiologically Relevant Conditions and Its Impact on the Development of Long-Acting Delivery Systems

The port delivery system with ranibizumab (PDS) is an investigational long-acting drug delivery system for the continuous release of ranibizumab, an anti-VEGF biologic, in the vitreous humor. The efficacy of the PDS implant relies on the maintenance of long-term drug stability under physiological conditions. Herein, the long-term stability of three anti-VEGF biologics - ranibizumab, bevacizumab and aflibercept - was investigated in phosphate buffered saline (PBS) at 37 °C for several months. Comparison of stability profiles shows that bevacizumab and aflibercept are increasingly prone to aggregation whereas ranibizumab undergoes minimal aggregation. Ranibizumab also shows the smallest loss in antigen binding capacity after long-term incubation in PBS. Even though the aggregated forms of bevacizumab and aflibercept bind to VEGF, the consequences of aggregation on immunogenicity, implant function and efficacy are unknown. These results highlight the importance of maintaining long-term drug stability under physiologically relevant conditions which is necessary for achieving efficacy with an in vivo continuous drug delivery device such as the PDS implant.     

Toxicological considerations for intravitreal drugs

INTRODUCTION: Intravitreal injections are a very common procedure and are the most effective route of drug delivery to the retina. There are currently several drugs available and even more are in development; therefore, safety is a very important concern. AREAS COVERED: The toxicological considerations of the most common drugs used for intravitreal pharmacotherapy such as anti-VEGFs, corticosteroids and antibiotics. Emerging agents such as anti-TNFs, VEGF-trap and kinase inhibitors are also discussed. An assessment of the efficacy and safety issues of the most relevant drugs including bevacizumab, ranibizumab and triamcinolone is presented. EXPERT OPINION: The toxicology and safety profiles are available for several drugs that are either in use or will be available for intravitreal injections. Retinal pharmacotherapy is very effective for different retinal diseases; however safety is a very important issue when intravitreal injections are applied and the possibility of retinal toxicity should always be kept in mind. Bevacizumab and ranibizumab are effective for the therapy of wet-age-related macular degeneration and macular edema, while triamcinolone remains an alternative agent to treat secondary macular edema. It is important, as some of these drugs will be used for extended periods of time, that their long-term toxicological effects are better understood.     

Long-term intraocular pressure changes after intravitreal injection of bevacizumab

Purpose: To assess the long-term intraocular pressure (IOP) changes after the intravitreal injection of bevacizumab (Avastin; Genentech, Inc., South San Francisco, CA) for treatment of age-related macular degeneration (AMD) and diabetic macular edema (DME) patients and evaluate the correlation factors.

Material and methods: Patients with neovascular AMD or DME underwent treat-and-extended anti-VEGF regimen in one eye and followed more than 12 months were enrolled in this study. We set three criteria of IOP elevation: (1) the IOP of the treated eye increased above the contralateral eye for at least two consecutive visits; (2) the IOP of the treated eye increased above the pre-injection IOP for at least two consecutive visits; (3) and the IOP of the treated eye increased more than 5?mmHg above the baseline IOP for at least two consecutive visits. We used mixed model univariate and multivariate analysis to assess the association between IOP elevation and independent parameters including age, sex, lens status, the number of injections, and underlying disease.

Results: In total 152 patients, 83 patients with AMD and 69 patients with DME, were included in this study. Mean follow-up time was 18.7 months, with a maximum of 50 months. In IOP elevation, 54 eyes (35.6%) showed an IOP increase above that of the contralateral eye (criteria 1), 50 eyes (33.4%) showed an IOP increase above the baseline IOP (criteria 2), and an IOP increase greater than 5?mmHg above the baseline IOP observed in nine eyes (5.9%) (criteria 3). In the univariate analysis, lens status and total number of injections were statistically significant for criteria 2 and 3 (all ps?<?0.05). However, in the multivariable analysis, only the number of intravitreal injections was statistically correlated with sustained IOP elevation for criteria 2 and 3 (p?<?0.001 and p?=?0.039, respectively).

Conclusions: Our results suggest that under long-term monitoring, with a treat-and-extended regimen, intravitreal bevacizumab injections were associated with sustained IOP elevation. In particular, multiple intravitreal injections could be associated with sustained IOP elevation.     

Emerging treatments for wet age-related macular degeneration

Introduction: Wet or exudative age-related macular degeneration (AMD) is the leading cause of blindness in the United States for individuals over the age of 65 years. Wet AMD is characterized by the formation of choroidal neovascularization, which can lead to edema, hemorrhage and scarring of the macula. This leads to metamorphopsia and vision loss. Without treatment, the loss of vision is permanent. The current gold standard treatment of wet AMD consists of intravitreal injections of anti-vascular endothelial growth factor (VEGF) medications.

Areas covered: Numerous new therapies in the drug pipeline aim at addressing limitations of current treatments. Future therapies involve novel compounds that attack different parts of the VEGF cascade, novel delivery systems aimed at reducing the frequency of intraocular injections, combination therapies and the use of radiation in conjunction with intravitreal therapies.

Expert opinion: Limitations of current treatments include the need for repeated injections, the high financial costs and treatment burdens of repeated injections, the risk of adverse ocular and systemic adverse events, and the inability to completely reverse the disease process of wet AMD. There are many new therapies and approaches in the pipeline which hold promise for improving the treatment of wet AMD.     

Hydrodynamic Radii of Ranibizumab,Aflibercept and Bevacizumab Measured by Time-Resolved Phosphorescence Anisotropy

Purpose

To measure the hydrodynamic radii of intravitreal anti-VEGF drugs ranibizumab, aflibercept and bevacizumab with μs time-resolved phosphorescence anisotropy.

Methods

Ruthenium-based dye Ru(bpy)₂(mcbpy???O???Su???ester)(PF₆)₂, whose lifetime of several hundred nanoseconds is comparable to the rotational correlation time of these drugs in buffer, was used as a label. The hydrodynamic radii were calculated from the rotational correlation times of the Ru(bpy)₂(mcbpy???O???Su???ester)(PF₆)₂-labelled drugs obtained with time-resolved phosphorescence anisotropy measurements in buffer/glycerol solutions of varying viscosity.

Results

The measured radii of 2.76±0.04 nm for ranibizumab, 3.70±0.03 nm for aflibercept and 4.58±0.01 nm for bevacizumab agree with calculations based on molecular weight and other experimental measurements.

Conclusions

Time-resolved phosphorescence anisotropy is a relatively simple and straightforward method that allows experimental measurement of the hydrodynamic radius of individual proteins, and is superior to theoretical calculations which cannot give the required accuracy for a particular protein.