Angiography of fluoresceinated anti-vascular endothelial growth factor antibody and dextrans in experimental choroidal neovascularization

Anti-VEGF Drugs in Age-Related Macular Degeneration: A Focus on Dosing Regimen-Related Safety and Efficacy

Age-related macular degeneration (AMD) is one of the main causes of visual impairment and severe visual loss, and can progress to two advanced forms-neovascularization and atrophic. The field of anti-AMD drugs has undergone huge developments in recent years, from single-target intravitreal administration to current clinical studies with multi-target and non-invasive agents, offering interesting new pharmacological opportunities for the treatment of this disease. Hence, we summarize some of the approved anti-vascular endothelial growth factor (VEGF) drugs for neovascular AMD, especially their structural characteristics, clinical manifestations, dosing regimens, and safety issues of the anti-VEGF drugs highlighted. In addition, advances in atrophic AMD drug research are also briefly described.

FITC-Labeled RGD Peptides as Novel Contrast Agents for Functional Fluorescent Angiographic Detection of Retinal and Choroidal Neovascularization

The development of choroidal neovascularization (CNV) is a crucial factor in the pathophysiology and prognosis of exudative age-related macular degeneration (AMD). Therefore, the detection of CNV is essential for establishing an appropriate diagnosis and treatment plan. Current ophthalmic imaging techniques, such as fundus fluorescent angiography and optical coherence tomography, have limitations in accurately visualizing CNV lesions and expressing CNV activity, owing to issues such as excessive dye leakage with pooling and the inability to provide functional information. Here, using the arginine-glycine-aspartic acid (RGD) peptide's affinity for integrin α_vβ₃, which is expressed in the neovascular endothelial cells in ocular tissues, we propose the use of fluorescein isothiocyanate (FITC)-labeled RGD peptide as a novel dye for effective molecular imaging of CNV. FITC-labeled RGD peptides (FITC-RGD₂), prepared by bioconjugation of one FITC molecule with two RGD peptides, demonstrated better visualization and precise localization of CNV lesions than conventional fluorescein dyes in laser-induced CNV rodent models, as assessed using various imaging techniques, including a commercially available clinical fundus camera (Optos). These results suggest that FITC-RGD₂ can serve as an effective novel dye for the diagnosis of neovascular retinal diseases, including AMD, by enabling early detection and treatment of disease occurrence and recurrence after treatment.

Microfluidic outer blood-retinal barrier model for inducing wet age-related macular degeneration by hypoxic stress

Wet age-related macular degeneration (AMD) is a severe ophthalmic disease that develops in the outer blood-retinal barrier (oBRB), involving two types of cells, the retinal pigment epithelium (RPE) and the choriocapillaris endothelium (CCE). Unfortunately, the pathogenesis of AMD is unclear, and the risk of the only effective therapy (Anti-VEGF injection) has been consistently argued. Also, since oBRB is hard to observe in vivo, an in vitro model for the pathological study is necessary. Here, we propose an advanced oBRB model, enhanced in two major ways: fully vascularized CCE and the in vivo analogous distance between RPE and CCE. Our model consists of an RPE (ARPE-19) monolayer with adjacent CCE (HUVEC) embedded fibrin gel in the microfluidic chip and required four days to construct an oBRB. Notably, the intercellular distance was tuned to the in vivo scale (<100 μm) without any extraneous scaffold in between. Thus, the two cell layers can interact freely through the extracellular matrix (ECM) in vivo. This is significant as wet AMD is mainly developed through broken intercellular interaction. Thanks to this in vivo similarity, the model incubated under hypoxic conditions, similar to an oxygen-induced retinopathy animal model, showed upregulated vascularization comparable to the AMD condition. We envisage that our model can be used to assist the investigation of AMD.

Investigational drugs in clinical trials for macular degeneration

INTRODUCTION

Intravitreal anti-vascular endothelial growth factor (VEGF) injections for exudative age-related macular degeneration (eAMD) are effective and safe but require frequent injections and have nonresponding patients. Geographic atrophy/dry AMD (gaAMD) remains an unmet medical need . New therapies are needed to address this leading cause of blindness in the increasing aged population.

AREAS COVERED

This paper reviews the pathogenesis of macular degeneration, current and failed therapeutics, therapies undergoing clinical trials and a rationale for why certain AMD therapies may succeed or fail .

EXPERT OPINION

VEGF- inhibitors reduce both vascular leakage and neovascularization. Experimental therapies that only address neovascularization or leakage will unlikely supplant anti-VEGF therapies. The most promising future therapies for eAMD, are those that target, more potently inhibit and have a more sustained effect on the VEGF pathway such as KSI-301, RGX-314, CLS-AX, EYEP-1901, OTX-TKI.

GaAMD is a phenotype of phagocytic retinal cell loss. Inhibiting phagocytic activity of retinal microglial/macrophages at the border of GA and reducing complement derived activators of microglial/macrophage is the most promising strategy. Complement inhibitors (Pegcetacoplan and Avacincaptad pegol) will likely obtain FDA approval but will serve to pave the way for combined complement and direct phagocytic inhibitors such as AVD-104.

Exudative versus Nonexudative Age-Related Macular Degeneration: Physiopathology and Treatment Options

Age-related macular degeneration (AMD) is an eye disease typically associated with the aging and can be classified into two types—namely, the exudative and the nonexudative AMD. Currently available treatments for exudative AMD use intravitreal injections, which are associated with high risk of infection that can lead to endophthalmitis, while no successful treatments yet exist for the nonexudative form of AMD. In addition to the pharmacologic therapies administered by intravitreal injection already approved by the Food and Drug Administration (FDA) in exudative AMD, there are some laser treatments approved that can be used in combination with the pharmacological therapies. In this review, we discuss the latest developments of treatment options for AMD. Relevant literature available from 1993 was used, which included original articles and reviews available in PubMed database and also information collected from Clinical Trials Gov website using “age-related macular degeneration” and “antiangiogenic therapies” as keywords. The clinical trials search was limited to ongoing trials from 2015 to date.

Laser-Induced Choroidal Neovascularization in Rats

The laser-induced choroidal neovascularization (CNV) model has been widely used for research on wet age-related macular degeneration (wet-AMD) and other ocular neovascular diseases. In this model, the Bruch membrane is perforated by laser injury, resulting in neovascularization formed from the choroidal capillaries. It has become a standard method to evaluate the effect of different treatments on CNV progression in preclinical studies. This protocol can be used in various species, including rat, mouse, pig, and monkey. The rodent laser-induced CNV model is the most commonly used because of the advantages in both cost- and time-efficiency. It takes only 10-15 min to complete the whole laser procedure after adequate training and practicing the technique. Peak CNV formation occurs at approximately 2 weeks after laser application. The entire protocol may require up to 3 weeks to complete the treatment, fundus image acquisition, and tissue collection for histologic analysis. This chapter describes the detailed procedures, protocols, and useful notes on how to induce CNV by laser.

Photothermal Optical Coherence Tomography of Anti-Angiogenic Treatment in the Mouse Retina Using Gold Nanorods as Contrast Agents

Purpose

Optical coherence tomography (OCT) is widely used for ocular imaging in clinical and research settings. OCT natively provides structural information based on the reflectivity of the tissues it images. We demonstrate the utility of photothermal OCT (PTOCT) imaging of gold nanorods (GNR) in the mouse retina in vivo in the laser-induced choroidal neovascularization (LCNV) model to provide additional image contrast within the lesion.

Methods

Wild-type C57BL/6 mice were imaged following the intravenous injection of ICAM2-targeted or untargeted GNR. Mice were also imaged following the injection of ICAM2-targeted GNR with or without the additional ocular delivery of a neutralizing monoclonal anti-vascular endothelial growth factor (anti-VEGF) antibody.

Results

Mice cohorts injected with untargeted or ICAM2-targeted GNR demonstrated increased lesion-associated photothermal signal during subsequent imaging relative to phosphate-buffered saline (PBS)-injected controls. Additionally, intravitreal injection of anti-VEGF antibody caused a detectable reduction in the extent of anatomic laser damage and lesion-associated photothermal signal density in mice treated in the LCNV model and injected with ICAM2-targeted GNR.

Conclusions

These experiments demonstrate the ability of PTOCT imaging of GNR to detect anti-VEGF-induced changes in the mouse retina using the LCNV model.

Translational Relevance

This study shows that PTOCT imaging of GNR in the LCNV model can be used to detect clinically relevant, anti-VEGF-induced changes that are not visible using standard OCT systems. In the future this technology could be used to aid in early detection of disease, monitoring disease progress, and assessing its response to therapies.

Mining for genes related to choroidal neovascularization based on the shortest path algorithm and protein interaction information

BACKGROUND

Choroidal neovascularization (CNV) is a serious eye disease that may cause visual loss, especially for older people. Many factors have been proven to induce this disease including age, gender, obesity, and so on. However, until now, we have had limited knowledge on CNV's pathogenic mechanism. Discovering the genes that underlie this disease and performing extensive studies on them can help us to understand how CNV occurs and design effective treatments.

METHODS

In this study, we designed a computational method to identify novel CNV-related genes in a large protein network constructed using the protein-protein interaction information in STRING. The candidate genes were first extracted from the shortest paths connecting any two known CNV-related genes and then filtered by a permutation test and using knowledge of their linkages to known CNV-related genes.

RESULTS

A list of putative CNV-related candidate genes was accessed by our method. These genes are deemed to have strong relationships with CNV.

CONCLUSIONS

Extensive analyses of several of the putative genes such as ANK1, ITGA4, CD44 and others indicate that they are related to specific biological processes involved in CNV, implying they may be novel CNV-related genes.

GENERAL SIGNIFICANCE

The newfound putative CNV-related genes may provide new insights into CNV and help design more effective treatments. This article is part of a Special Issue entitled "System Genetics" Guest Editor: Dr. Yudong Cai and Dr. Tao Huang.

VEGF: From Discovery to Therapy: The Champalimaud Award Lecture

Purpose

Intraocular vascular diseases are leading causes of adult vision loss, and in the mid-1900s, I. C. Michaelson postulated that the retina releases a soluble, diffusible factor that causes abnormal vascular growth and leakage. What became known as “Factor X” eluded investigators for decades.

Methods

The field of cancer research, where Judah Folkman pioneered the concept of angiogenesis, provided the inspiration for the work honored by the 2014 Champalimaud Vision Award. Recognizing that tumors recruit their own blood supply to achieve critical mass, Dr Folkman proposed that angiogenic factors could be therapeutic targets in cancer. Napoleone Ferrara identified vascular endothelial growth factor (VEGF) as such an angiogenic agent: stimulated by hypoxic tumor tissue, secreted, and able to induce neovascularization. VEGF also was a candidate for Factor X, and the 2014 Champalimaud Laureates and colleagues worked individually and collaboratively to identify the role of VEGF in ocular disease.

Results

The Champalimaud Laureates correlated VEGF with ocular neovascularization in animal models and in patients. Moreover, they showed that VEGF not only was sufficient, but it also was required to induce neovascularization in normal animal eyes, as VEGF inhibition abolished ocular neovascularization in key animal models.

Conclusions

The identification of VEGF as Factor X altered the therapeutic paradigms for age-related macular degeneration (AMD), diabetic retinopathy, retinal vein occlusion, and other retinal disorders.

Translational Relevance

The translation of VEGF from discovery to therapy resulted in the most successful applications of antiangiogenic therapy to date. Annually, over one million patients with eye disease are treated with anti-VEGF agents.

Stem cell therapies in the treatment of diabetic retinopathy and keratopathy

Nonproliferative diabetic retinopathy (DR) is characterized by multiple degenerative changes that could be potentially corrected by stem cell therapies. Most studies so far have attempted to alleviate typical abnormalities of early retinopathy, including vascular hyperpermeability, capillary closure and pericyte dropout. Success was reported with adult stem cells (vascular progenitors or adipose stem cells), as well as induced pluripotent stem cells from cord blood. The cells were able to associate with damaged vessels in both pericyte and endothelial lining positions in models of DR and ischemia-reperfusion. In some diabetic models, functional amelioration of vasculature and electroretinograms was noted. Another approach for endogenous progenitor cell therapy is to normalize dysfunctional diabetic bone marrow and residing endothelial progenitors using NO donors, PPAR-δ and -γ agonists, or inhibition of TGF-β. A potentially important strategy would be to reduce neuropathy by stem cell inoculations, either naïve (e.g., paracrine-acting adipose stem cells) or secreting specific neuroprotectants, such as ciliary neurotrophic factor or brain-derived neurotrophic factor that showed benefit in amyotrophic lateral sclerosis and Parkinson's disease. Recent advances in stem cell therapies for diabetic retinal microangiopathy may form the basis of first clinical trials in the near future. Additionally, stem cell therapies may prove beneficial for diabetic corneal disease (diabetic keratopathy) with pronounced epithelial stem cell dysfunction.

Effects of diabetes on the eye

Hyperglycemia has toxic effects on almost all cells in the body. Ophthalmic complications of hyperglycemia are most profound in cornea and retina. Seventy percent of diabetics suffer from corneal complications, collectively called diabetic keratopathy, which includes include recurrent erosions, delayed wound healing, ulcers, and edema. Confocal microscopy has permitted in vivo imaging of corneal nerves, which are also affected in diabetic subjects. Gene therapies upregulating MNNG HOS transforming gene (cMet) and/or downregulating MMP10 and cathepsin S are potential future therapies for diabetic keratopathy. Diabetic retinopathy (DR) is the most common cause of blindness in people over the age of 50. There is accumulating evidence that DR is an inflammatory disease. The initial events in animal models of DR are increased vascular permeability and leukostasis. This binding of leukocytes to the endothelium results from an increase in intracellular adhesion molecule-1 (ICAM-1) on the retinal capillary endothelium (EC) and expression of CD11/CD18 on the surface of the activated leukocyte. We have observed polymorphonuclear leukocytes (PMNs) at sites of EC vascular dysfunction in diabetic retinas as well as choroid. Anti-inflammatory drugs like etanercept, aspirin, or meloxicam reduce leukostasis and EC death. Future therapies may include repopulation of the acellular capillaries after EC and pericyte death with vascular progenitors made from the patient's own blood cells.

The Harvard angiogenesis story

I shall discuss the work of researchers at Harvard Medical School who came together in the early 1990s. Scattered across various Harvard-affiliated hospitals and research centers, these individuals were unified by their interest in ocular neovascularization. Together and separately, they investigated models of ocular neovascularization, exploring tumor angiogenesis in eye development and disease.

A novel high-resolution in vivo imaging technique to study the dynamic response of intracranial structures to tumor growth and therapeutics

We have successfully integrated previously established Intracranial window (ICW) technology ^1-4 with intravital 2-photon confocal microscopy to develop a novel platform that allows for direct long-term visualization of tissue structure changes intracranially. Imaging at a single cell resolution in a real-time fashion provides supplementary dynamic information beyond that provided by standard end-point histological analysis, which looks solely at 'snap-shot' cross sections of tissue.

Establishing this intravital imaging technique in fluorescent chimeric mice, we are able to image four fluorescent channels simultaneously. By incorporating fluorescently labeled cells, such as GFP+ bone marrow, it is possible to track the fate of these cells studying their long-term migration, integration and differentiation within tissue. Further integration of a secondary reporter cell, such as an mCherry glioma tumor line, allows for characterization of cell:cell interactions. Structural changes in the tissue microenvironment can be highlighted through the addition of intra-vital dyes and antibodies, for example CD31 tagged antibodies and Dextran molecules.

Moreover, we describe the combination of our ICW imaging model with a small animal micro-irradiator that provides stereotactic irradiation, creating a platform through which the dynamic tissue changes that occur following the administration of ionizing irradiation can be assessed.

Current limitations of our model include penetrance of the microscope, which is limited to a depth of up to 900 μm from the sub cortical surface, limiting imaging to the dorsal axis of the brain. The presence of the skull bone makes the ICW a more challenging technical procedure, compared to the more established and utilized chamber models currently used to study mammary tissue and fat pads ^5-7. In addition, the ICW provides many challenges when optimizing the imaging.

Molecular imaging of retinal disease

Imaging of the eye plays an important role in ocular therapeutic discovery and evaluation in preclinical models and patients. Advances in ophthalmic imaging instrumentation have enabled visualization of the retina at an unprecedented resolution. These developments have contributed toward early detection of the disease, monitoring of disease progression, and assessment of the therapeutic response. These powerful technologies are being further harnessed for clinical applications by configuring instrumentation to detect disease biomarkers in the retina. These biomarkers can be detected either by measuring the intrinsic imaging contrast in tissue, or by the engineering of targeted injectable contrast agents for imaging of the retina at the cellular and molecular level. Such approaches have promise in providing a window on dynamic disease processes in the retina such as inflammation and apoptosis, enabling translation of biomarkers identified in preclinical and clinical studies into useful diagnostic targets. We discuss recently reported and emerging imaging strategies for visualizing diverse cell types and molecular mediators of the retina in vivo during health and disease, and the potential for clinical translation of these approaches.

Anti-VEGF Treatment Strategies for Wet AMD

Over the past few years, antivascular endothelial growth factor (VEGF) therapy has become a standard treatment for neovascular age-related macular degeneration (AMD). During this time, treatment strategies have evolved from a monthly dosing schedule to individualized regimens. This paper will review the currently available anti-VEGF agents and evidence-based treatment strategies.

Pazopanib, a multitargeted tyrosine kinase inhibitor, reduces diabetic retinal vascular leukostasis and leakage

OBJECTIVE

To determine the efficacy of pazopanib eye drops in the streptozotocin induced diabetic retinopathy rat model.

METHODS

A 0.5% w/v pazopanib suspension was prepared in phosphate buffered saline (PBS, pH 7.4) in the presence of 0.5% w/v sodium carboxymethyl cellulose. Brown Norway rats were divided into three groups (n=4) - (1) healthy, (2) diabetic, and (3) diabetic with treatment. The drug suspension was administered twice daily as eye drops to group 3 for 30 days. Efficacy parameters including the number of adherent leukocytes in the retinal vasculature (leukostasis), blood-retinal FITC-dextran leakage, and vitreous-to-plasma protein ratio were measured.

RESULTS

Pazopanib suspension in the form of eye drops significantly reduced leukostasis (32%), FITC-dextran leakage (39%), and the vitreous-to-plasma protein ratio (64%) in diabetic animals compared to untreated diabetic group.

CONCLUSION

Pazopanib eye drops can alleviate retinal complications of diabetic retinopathy.

Optimization of laser-induced choroidal neovascularization in African green monkeys

We developed and validated a new nonhuman primate model of laser-induced choroidal neovascularization (CNV) that addresses study design limitations prevalent in laser-induced CNV-based efficacy studies. Laser-induced Bruch's membrane disruption triggers CNV and has been widely utilized in animals to model neovascular ("wet") age-related macular degeneration (AMD). Despite widespread use of the approach, detailed assessment of experimental parameters and their influence on pathophysiological endpoints critical for disease modeling has been extremely limited and largely based on anecdotal observations. We evaluated laser power parameters and endpoint measures to optimize methods for CNV formation and quantification to facilitate drug efficacy screening in African green monkeys. Six laser spots of 350, 550, 750, 950 or 1500 mW laser power were positioned bilaterally 1.5 disc diameters from the fovea, within the macula. Fluorescein angiograms were collected 3-5 weeks later and scored by trained masked investigators using graded (I-IV) and densitometric methods. Histopathology assessments were also performed, including determination of CNV area. Test system sensitivity to angiogenesis inhibition was subsequently assessed by evaluating the effect of intravitreal bevacizumab (Avastin) pretreatment (one day prior to laser photocoagulation) on incidence of CNV. Grade III and grade IV lesions were considered clinically relevant, demonstrating early hyperfluorescence and late leakage within or beyond the lesion borders. By 4 weeks post-laser all treatment groups demonstrated evidence of grade III lesions with greatest incidence observed in lesions induced by 750 and 950 mW laser power (72.9% and 69.4% respectively). Grade IV lesions were confined to eyes receiving 550 mW laser power or higher, with highest incidence of grade IV lesions observed in eyes receiving 950 (19.4%) and 1500 mW (31%) laser spots, incidence peaking 4 weeks post-laser photocoagulation. Densitometric analyses of angiograms corroborated visual scoring. Bevacizumab completely abolished grade IV lesion development and significantly lowered lesion fluorescein signal intensity (P < 0.0001) and CNV area (P = 0.038) compared to vehicle-treated controls. Our studies demonstrate that laser power of 950-1500 mW and angiography analysis 4 weeks post-laser are optimal parameters to evaluate treatment effects on CNV induction following laser photocoagulation. Bevacizumab significantly attenuated CNV development, as determined by fluorescein angiography and histopathology assessments in this model, supporting the application of African green monkeys in preclinical modeling of CNV. Laser parameters and time points for therapeutic dosing and angiography endpoints are critical factors to the laser-induced CNV model and must be validated for robust assessment of efficacy. The newly optimized nonhuman primate model described will facilitate preclinical efficacy assessments of novel therapeutics for CNV.

Transscleral drug delivery to the posterior eye: prospects of pharmacokinetic modeling

Basic biological research has provided new approaches to treat severe diseases of the retina and choroid, such as age related macular degeneration. Although it is possible to deliver drugs from a subconjunctival drug depot to the retina and choroid, the barriers and kinetics of this route of drug administration are not well known. In this review we investigate the pharmacokinetic aspects of transscleral drug delivery into the posterior eye with emphasis on pharmacokinetic modeling. The existing simulation models related to the transscleral drug delivery are reviewed and future directions for the model development are discussed. In addition, a new simulation model for the transscleral drug delivery based on permeability data is introduced. This compartmental model contains several ocular tissues (sclera, choroid, retinal pigment epithelium and vitreous) and it takes into account the clearance of the drug via choroidal circulation. The model is used to simulate the vitreous delivery of macromolecules based on the available data on FITC-dextran 70 kDa.

Development of ranibizumab, an anti-vascular endothelial growth factor antigen binding fragment, as therapy for neovascular age-related macular degeneration

BACKGROUND

Angiogenesis is a key aspect of the wet form of age-related neovascular (AMD), the leading cause of blindness in the elderly population. Substantial evidence indicated that vascular endothelial growth factor (VEGF)-A is a major mediator of angiogenesis and vascular leakage in wet AMD. VEGF-A is the prototype member of a gene family that includes also PlGF, VEGF-B, VEGF-C, VEGF-D and the orf virus-encoded VEGF-E. Several isoforms of VEGF-A can be generated due to alternative mRNA splicing. Various VEGF inhibitors have been clinically developed. Among these, ranibizumab is a high affinity recombinant Fab that neutralizes all isoforms of VEGF-A. The article briefly reviews the biology of VEGF and then focuses on the path that led to clinical development of ranibizumab.

RESULTS

The safety and efficacy of ranibizumab in the treatment of neovascular AMD have been evaluated in two large phase III, multicenter, randomized, double-masked, controlled pivotal trials in different neovascular AMD patient populations. Combined, the trial results indicate that ranibizumab results not only in a slowing down of vision loss but also in a significant proportion of patients experiencing a clinically meaningful vision gain. The visual acuity benefit over control was observed regardless of CNV lesion type. Furthermore, the benefit was associated with a low rate of serious adverse events.

CONCLUSIONS

Ranibizumab represents a novel therapy that, for the first time, appears to have the potential to enable many AMD patients to obtain a meaningful and sustained gain of vision. On June 30 2006, ranibizumab was approved by the US Food and Drug Administration for the treatment of wet AMD.

Promising new treatments for neovascular age-related macular degeneration

Angiogenesis, the growth of new blood vessels from existing blood vessels, is responsible for vision loss in a variety of ophthalmic diseases. In neovascular age-related macular degeneration (AMD), the leading cause for legal blindness in many industrialised countries, abnormal blood vessels grow in the macula and cause blindness. There are a number of factors important in the angiogenic cascade but VEGF-A has been implicated in recent years as the major factor responsible for neovascular and exudative diseases of the eye. Numerous antiangiogenic drugs are in development but anti-VEGF drugs have shown great promise in treating neovascular AMD and other ocular diseases, and many of these drugs have been adopted from oncology where antiangiogenic therapy is gaining wide acceptance. For the first time in neovascular AMD, anti-VEGF drugs have brought the hope of vision improvement to a significant proportion of patients. This review provides an overview on angiogenic mechanisms, potential antiangiogenic treatment strategies and different antiangiogenic drugs with special focus on neovascular AMD.

Single periocular injection of celecoxib-PLGA microparticles inhibits diabetes-induced elevations in retinal PGE2, VEGF, and vascular leakage

PURPOSE

To determine whether celecoxib inhibits VEGF secretion from ARPE-19 cells and to investigate further the safety and effectiveness of periocular celecoxib-poly (lactide-co-glycolide; PLGA) microparticles in inhibiting elevations in retinal PGE(2), VEGF, and blood-tissue barrier leakage at the end of 60 days in a streptozotocin diabetic rat model.

METHODS

VEGF mRNA and protein expression in ARPE-19 cells was evaluated in the presence of 0 to 10 microM celecoxib, and cytotoxicity of celecoxib on ARPE-19 and RF6A cells was evaluated over a 0- to 100-microM concentration range. Celecoxib-PLGA microparticles were prepared by a modified solvent evaporation technique, sterilized by 25 kGy of gamma-irradiation, and characterized for size, zeta potential, drug loading, and in vitro release. Normal and streptozotocin-diabetic male Sprague-Dawley rats were divided into five groups: normal, diabetic, diabetic+placebo, normal+celecoxib, and diabetic+celecoxib. Phosphate-buffered saline (PBS) containing celecoxib-PLGA microparticles, placebo PLGA microparticles, or plain PBS in one eye was injected into the posterior subconjunctival (periocular) space in rats under anesthesia. Sixty days after administration, the animals were killed, and retinal PGE2 secretion, VEGF protein, and blood-retinal barrier leakage were estimated. Blood cell counts, blood chemistry and histology were used to assess the safety of the microparticulate system.

RESULTS

Celecoxib (up to 25 microM) did not cause significant cytotoxicity in ARPE-19 or RF6A cells. Nanomolar concentrations of celecoxib reduced VEGF mRNA and VEGF protein secretion. Celecoxib-PLGA microparticles (diameter: 1140 +/- 15 nm), containing 14.93% +/- 0.21% of celecoxib sustained in vitro drug release and in vivo drug levels in the retina for 60 days. Diabetes elevated PGE2 secretion, VEGF protein, the vitreous-plasma protein ratio, and blood-retinal barrier leakage by 3-, 1.7-, 3.1-, and 2.7-fold, and celecoxib-PLGA microparticles significantly reduced these elevations by 40%, 50%, 40%, and 50%, respectively. Neither the placebo-treated eyes nor the contralateral eyes in celecoxib-PLGA microparticle-treated rats showed significant effects. Celecoxib-PLGA or placebo-PLGA particles had no effect on the body weight or blood sugar level of rats. The celecoxib-PLGA microparticles did not cause any changes in blood cell counts or chemistry and caused no histopathological damage to the retina or periocular tissues.

CONCLUSIONS

Nanomolar concentrations of celecoxib can inhibit VEGF mRNA and protein expression from ARPE-19 cells. Periocular celecoxib microparticles are useful sustained drug delivery systems for inhibiting diabetes-induced elevations in PGE2, VEGF, and blood-retinal barrier leakage. The periocular celecoxib-PLGA microparticles are safe and do not cause any damage to the retina.

Choroidal endothelial cells transmigrate across the retinal pigment epithelium but do not proliferate in response to soluble vascular endothelial growth factor

The purpose of this study was to investigate the effects of soluble VEGF on human choroidal endothelial cell (CEC) transmigration across an RPE monolayer as it relates to choroidal neovascularization in AMD. In coculture assays, ARPE-19 (ARPE) was plated on the undersides of Transwell inserts having 0.4 microm pores. Primary human CECs were then plated into the insert. CECs in the Transwell inserts were counted after 72 hr of growth. CEC proliferation was also measured after culturing CECs in ARPE-CEC coculture-conditioned media or in media with exogenous VEGF121 and/or VEGF165 added. Transmigration assays were performed on Transwells with 8.0 microm pores: green-labelled CECs were plated in Transwell inserts with or without red-labelled ARPE plated on the undersides of the insert. In some transmigration assays, ARPE was plated into the wells to provide a chemotactic gradient for CEC transmigration. After 72 hr CECs were plated, green cells were counted either within the well media as CECs that transmigrated the epithelial monolayer, or on the underside of the insert as CECs that transmigrated the Transwell insert to but not beyond the ARPE monolayer. A neutralizing antibody to VEGF was added to the wells of Transwells at the time the CECs were plated in the insert and transmigrated CECs were counted. VEGF protein was measured in the conditioned media of ARPE and CEC coculture and in transmigration assays. Compared to control, CEC proliferation significantly increased when CECs were cultured in coculture conditioned media (p=0.001) or in coculture assays (p<0.001). However, there was no effect on CEC proliferation when VEGF121, VEGF165, or both were added to solo CECs. Antibody to VEGF did not reduce the proliferative effects of coculture conditioned media on CEC. ARPE plated in the well significantly increased CEC transmigration (p<0.001) compared to transmigration assays without ARPE in the well. VEGF protein measured in the well media of transmigration assays having ARPE within the well was significantly greater than in the assays without ARPE within the well (p<0.004). Exogenous neutralizing antibody to VEGF significantly reduced transmigration, and this effect was dose-dependent. VEGF provides a chemotactic gradient for human CECs to transmigrate across a monolayer of ARPE. Neutralization of VEGF in the media partially reduces transmigration. Whereas soluble VEGF does not increase proliferation of solo CECs, coculture conditioned media enhances proliferation, suggesting that growth factors other than VEGF cause CEC proliferation. These findings may have relevance to the transformation of occult CNV into CNV within the neurosensory retina in AMD.

Drug delivery systems for vitreoretinal diseases

The eye has an environment that is specific unto itself in terms of pharmacokinetics: the inner and outer blood-retinal barriers separate the retina and the vitreous from the systemic circulation and vitreous body, which physiologically has no cellular components, occupies the vitreous cavity, an inner space of the eye, and reduces practical convection of molecules. Considering this, development of a drug delivery system (DDS) is becoming increasingly important in the treatment of vitreoretinal diseases not only to facilitate drug efficacy but also to attenuate adverse effects. The DDS has three major goals: enhances drug permeation (e.g., iontophoresis and transscleral DDS), controls release of drugs (e.g., microspheres, liposomes, and intraocular implants), and targets drugs (e.g., prodrugs with high molecular weight and immunoconjugates). Comprehensive knowledge of these should lead to development of innovative treatment modalities.

Therapeutic applications of viscous and injectable poly(ortho esters)

Poly(ortho esters) (POE) are hydrophobic and bioerodible polymers that have been investigated for pharmaceutical use since the early 1970s. Among the four described generations of POE, the third (POE III) and fourth (POE IV) are promising viscous and injectable materials which have been investigated in numerous biomedical applications. POE III has been extensively studied for ophthalmic drug delivery, it presents an excellent biocompatibility and is currently being investigated as a vehicle for sustained drug delivery to treat diseases of the posterior segment of the eye. POE IV is distinguishable by a highly reproducible and controlled synthesis, a higher hydrophobicity, and an excellent biocompatibility. It is currently under development for a variety of applications, such as ocular delivery, periodontal disease treatment and applications in veterinary medicine. This review will also focus on new perspectives for this promising family of polymers, such as guided tissue regeneration, treatment of osteoarthritis, as well as peptide and protein delivery.

Drug targeting to choroidal neovascularization

Subfoveal choroidal neovascularization (CNV) causes significant visual loss, especially in patients with age-related macular degeneration (AMD). Several pharmaceutical treatments that use anti-angiogenic agents have been tried to inhibit the activity of CNV experimentally and clinically. In general, however, systemically administered drugs may reach not only targeted tissues but also other tissues, resulting in unwanted side effects. Also, to maintain therapeutic levels of the drugs in targeted tissues, frequent administration for an extended period of time is required. To solve these problems, drug delivery systems targeted to the CNV are being developed. Anatomic characteristics of CNV tissues resemble those of tumor vasculature, exhibiting enhanced permeability and retention effect. Drug targeting to CNV may be feasible in the same manner as it is to tumors. In this review, we describe two approaches of drug targeting to CNV: passive targeting and active targeting.