# Anti-VEGF Agents: Pharmacology, Biosimilars, and Port Delivery Systems

## Introduction

Anti-vascular endothelial growth factor (anti-VEGF) therapy has revolutionized the treatment of neovascular retinal diseases. Since the landmark MARINA and ANCHOR trials, intravitreal anti-VEGF agents have become the standard of care for neovascular age-related macular degeneration (nAMD), diabetic macular edema (DME), retinal vein occlusion (RVO), and other conditions involving pathologic angiogenesis. The field continues to evolve with biosimilars, new molecules, and novel delivery platforms.

## VEGF Biology

### VEGF Family

**VEGF-A**: principal mediator of pathologic ocular angiogenesis; multiple isoforms (VEGF-121, VEGF-165, VEGF-189, VEGF-206) VEGF-B, VEGF-C, VEGF-D: roles in lymphangiogenesis and other vascular functions. **Placental growth factor (PlGF)**: synergizes with VEGF-A in angiogenesis and inflammation.

### VEGF Receptors

**VEGFR-1 (Flt-1)**: binds VEGF-A, VEGF-B, PlGF; decoy receptor and signaling receptor. **VEGFR-2 (KDR)**: primary mediator of VEGF-A-driven angiogenesis, vascular permeability, and cell survival. **Neuropilin-1 and -2**: co-receptors enhancing VEGF signaling.

### Pathologic Effects of VEGF in the Eye

Neovascularization (choroidal, retinal, iris) Vascular hyperpermeability leading to macular edema. Leukocyte adhesion and inflammation. Endothelial cell proliferation and migration.

## Anti-VEGF Agents

### Pegaptanib (Macugen)

**RNA aptamer** binding VEGF-165 selectively. First FDA-approved anti-VEGF for nAMD (2004) Largely replaced by more effective agents; historical significance.

### Bevacizumab (Avastin)

**Full-length humanized monoclonal antibody** against all VEGF-A isoforms. FDA-approved for colorectal cancer; used **off-label** intravitreally (1.25 mg/0.05 mL) CATT trial demonstrated non-inferiority to ranibizumab for nAMD. Very low cost (~$50 per dose); widely used globally. Compounded from systemic vial; concerns about compounding-related contamination (rare endophthalmitis clusters)

### Ranibizumab (Lucentis)

**Humanized monoclonal antibody Fab fragment** against all VEGF-A isoforms. Smaller molecule (48 kDa vs. 149 kDa for bevacizumab); theoretically better retinal penetration. FDA-approved for nAMD, DME, RVO, diabetic retinopathy, myopic CNV. Dose: 0.5 mg/0.05 mL intravitreal injection. Intravitreal half-life: approximately 9 days.

### Aflibercept (Eylea)

**Recombinant fusion protein** (VEGF-Trap): extracellular domains of VEGFR-1 and VEGFR-2 fused to Fc portion of IgG1. Binds VEGF-A (all isoforms), VEGF-B, and **PlGF** with higher affinity than native receptors. FDA-approved for nAMD, DME, RVO, diabetic retinopathy, retinopathy of prematurity. Dose: 2 mg/0.05 mL. Intravitreal half-life: approximately 11.5 days. **Aflibercept 8 mg (Eylea HD)**: higher dose formulation allowing extended dosing intervals (every 12-16 weeks after loading); PULSAR and PHOTON trials.

### Anti-VEGF Agents Comparison

| Agent | Structure | MW | Targets | Dose | Half-life (IVT) | Cost | Key Feature |
|-------|-----------|----|---------|----- |-----------------|------|-------------|
| Bevacizumab (Avastin) | Full-length mAb | 149 kDa | VEGF-A | 1.25 mg | ~10 days | ~$50 | Off-label; lowest cost |
| Ranibizumab (Lucentis) | Fab fragment | 48 kDa | VEGF-A | 0.5 mg | ~9 days | ~$1,200 | First purpose-designed ocular anti-VEGF |
| Aflibercept (Eylea) | Fusion protein | 115 kDa | VEGF-A, VEGF-B, PlGF | 2 mg | ~11.5 days | ~$1,800 | Higher binding affinity |
| Aflibercept 8 mg (Eylea HD) | Fusion protein | 115 kDa | VEGF-A, VEGF-B, PlGF | 8 mg | Extended | ~$2,200 | Q12-16 wk maintenance |
| Faricimab (Vabysmo) | Bispecific mAb | 150 kDa | VEGF-A + Ang-2 | 6 mg | ~7 days | ~$2,200 | Dual pathway; extended intervals |
| Brolucizumab (Beovu) | scFv | 26 kDa | VEGF-A | 6 mg | ~4.5 days | ~$1,100 | Smallest; Q12 wk; IOI risk |

### Brolucizumab (Beovu)

**Single-chain antibody fragment (scFv)** against VEGF-A; smallest anti-VEGF molecule (26 kDa) High molar concentration enables more drug per injection. FDA-approved for nAMD; 6 mg/0.05 mL. HAWK and HARRIER trials: non-inferior to aflibercept with potential for longer durability (every 12 weeks) **Safety concern**: increased risk of **intraocular inflammation** (3.3%), retinal vasculitis, and retinal vascular occlusion. Requires careful patient selection and monitoring.

### Faricimab (Vabysmo)

**Bispecific antibody** targeting both **VEGF-A and angiopoietin-2 (Ang-2)**. Ang-2 destabilizes blood vessels; dual inhibition addresses complementary pathways. FDA-approved for nAMD and DME. TENAYA/LUCERNE (nAMD) and YOSEMITE/RHINE (DME) trials: non-inferior to aflibercept with potential for extended dosing (up to every 16 weeks) Dose: 6 mg/0.05 mL.

![Schematic diagram comparing molecular structures of anti-VEGF agents](images/anti-vegf-molecular-structures.jpg)

## Treatment Regimens

### Fixed Monthly Dosing

Every 4-week injection regardless of disease activity. Maximum efficacy but highest treatment burden. MARINA and ANCHOR protocols for ranibizumab.

### PRN (Pro Re Nata / As Needed)

Inject only when disease activity is present on OCT or FA. Monthly monitoring visits; inject when fluid recurs. Reduces injection burden but requires frequent visits.

### Treat-and-Extend (T&E)

Extend interval between injections stepwise (by 2 weeks) if disease is controlled. Shorten interval if disease recurs. Preferred by many retina specialists; optimizes both outcomes and visit burden. Typical range: 4-16 week intervals depending on disease stability.

### Loading Dose Phase

Most protocols begin with 3-4 monthly loading injections before transitioning to maintenance.

## Biosimilars

### Definition and Regulatory Framework

A **biosimilar** is a biologic product highly similar to an approved reference product with no clinically meaningful differences in safety, purity, or potency. FDA pathway: abbreviated Biologics License Application (aBLA) under the Biologics Price Competition and Innovation Act (BPCI Act) Biosimilars are NOT generic drugs; biologics are complex proteins that cannot be identically replicated.

### Approved Ophthalmic Biosimilars

**Ranibizumab biosimilars**: multiple approved (e.g., Byooviz/SB11, Cimerli/FYB201); interchangeable with Lucentis. **Aflibercept biosimilars**: emerging in the market. **Bevacizumab**: already low cost; biosimilar development less commercially driven.

### Clinical Considerations

Rigorous analytical, preclinical, and clinical comparability studies required. Immunogenicity assessment is critical (anti-drug antibodies) Potential for significant cost savings (estimated 15-35% reduction) Switching between reference product and biosimilar appears safe based on available data.

![Timeline of anti-VEGF agent development and biosimilar approvals](images/anti-vegf-timeline-biosimilars.jpg)

## Port Delivery System

### Ranibizumab Port Delivery System (Susvimo)

**Permanently implanted, refillable reservoir** placed in the pars plana via a surgical procedure. Contains a custom formulation of ranibizumab (100 mg/mL) Drug diffuses continuously from the reservoir into the vitreous through a **release-control element**. Refilled in-office via a specialized needle every **approximately 6 months**. **Archway trial**: non-inferior to monthly ranibizumab injections for nAMD.

### Surgical Implantation

Performed in the operating room under local or general anesthesia. Conjunctival peritomy and scleral dissection; pars plana placement (3.5 mm posterior to limbus) Reservoir sutured to the sclera; laser to any vitreous in the wound. Postoperative recovery period of 2-4 weeks.

### Advantages and Limitations

Markedly reduces treatment burden (2 refills per year vs. 12+ injections) Maintains continuous drug levels (avoids peaks and troughs of bolus injections) Surgical risks: vitreous hemorrhage, endophthalmitis, retinal detachment, implant erosion. Patient selection important; not suitable for all patients. Temporarily withdrawn from market (2022) for manufacturing issues; returned with updated formulation.

## Safety Considerations for All Anti-VEGF Agents

### Ocular Adverse Events

**Endophthalmitis**: 0.02-0.05% per injection; risk mitigation with povidone-iodine prep. Retinal detachment, vitreous hemorrhage (rare) Increased IOP (sustained elevation in some patients with repeated injections) Cataract progression (from needle contact) RPE tears (associated with large PEDs)

### Systemic Safety

Theoretical risk of thromboembolic events (stroke, MI); large meta-analyses show no significant increase. Avoid in the perioperative period for major surgery (wound healing concerns) Pregnancy: contraindicated (anti-VEGF agents are teratogenic in animal models)

![Port delivery system implant showing reservoir placement in the pars plana](images/port-delivery-system-pds.jpg)

## Key Clinical Pearls

Bevacizumab and ranibizumab showed equivalent visual outcomes in the CATT trial, but bevacizumab costs a fraction of the price. Faricimab's dual mechanism (anti-VEGF-A and anti-Ang-2) represents a paradigm shift toward multi-target therapy with extended durability. Biosimilars undergo rigorous comparability testing and offer significant cost savings without clinically meaningful differences in efficacy or safety. The port delivery system reduces nAMD treatment burden to two refills per year by providing continuous drug release, but requires a surgical implantation procedure.

## References

1. Rosenfeld PJ, Brown DM, Heier JS, et al. Ranibizumab for neovascular age-related macular degeneration (MARINA study). *N Engl J Med*. 2006;355(14):1419-1431.
2. CATT Research Group. Ranibizumab and bevacizumab for neovascular age-related macular degeneration. *N Engl J Med*. 2011;364(20):1897-1908.
3. Heier JS, Khanani AM, Quezada Ruiz C, et al. Efficacy, durability, and safety of intravitreal faricimab up to every 16 weeks (TENAYA and LUCERNE). *Ophthalmology*. 2022;129(8):838-855.
4. Holekamp NM, Campochiaro PA, Chang MA, et al. Archway randomized phase 3 trial of the port delivery system with ranibizumab. *Ophthalmology*. 2022;129(3):295-307.