Topically applied antibody fragments penetrate into the back of the rabbit eye

Topical Solution for Retinal Delivery: Bevacizumab and Ranibizumab Eye Drops in Anti-Aggregation Formula (AAF) in Rabbits

PURPOSE

Wet age-related macular degeneration (AMD) is a blinding retinal disease. Monthly intravitreal anti-VEGF antibody injections of bevacizumab (off-label) and ranibizumab (FDA approved) are the standard of care. Antibody aggregation may interfere with ocular absorption/distribution. This study assessed topical delivery of dilute antibodies to the posterior segment of rabbit eyes using a novel anti-aggregation formula (AAF).

METHODS

Bevacizumab, or biosimilar ranibizumab was diluted to 5 mg/ml in AAF. All rabbits were dosed twice daily. Substudy 1 rabbits (bevacizumab, 100 µl eye drops): Group 1 (bevacizumab/AAF, n = 6); Group 2 (bevacizumab/PBS, n = 7) and Vehicle control (AAF, n = 1). Substudy 2 rabbits (ranibizumab biosimilar/AAF, 50 µl eye drops): (ranibizumab biosimilar/AAF, n = 8). At 14.5 days, serum was drawn from rabbits. Aqueous, vitreous and retina samples were recovered from eyes and placed into AAF aliquots. Tissue analyzed using AAF as diluent.

RESULTS

Bevacizumab in AAF permeated/accumulated in rabbit aqueous, vitreous and retina 10 times more, than when diluted in PBS. AAF/0.1% hyaluronic acid eye drops, dosed twice daily, provided mean tissue concentrations (ng/g) in retina (29.50), aqueous (12.34), vitreous (3.46), and serum (0.28 ng/ml). Additionally, the highest concentration (ng/g) of ranibizumab biosimilar was present in the retina (18.0), followed by aqueous (7.82) and vitreous (1.47). Serum concentration was negligible (< 0.04 ng/ml). No irritation was observed throughout the studies.

CONCLUSIONS

Bevacizumab and ranibizumab, in an AAF diluent eye drop, can be delivered to the retina, by the twice daily dosing of a low concentration mAb formulation. This may prove to be an adjunct to intravitreal injections.

Ultrasound-Mediated Ocular Drug Delivery: From Physics and Instrumentation to Future Directions

Drug delivery to the anterior and posterior segments of the eye is impeded by anatomical and physiological barriers. Increasingly, the bioeffects produced by ultrasound are being proven effective for mitigating the impact of these barriers on ocular drug delivery, though there does not appear to be a consensus on the most appropriate system configuration and operating parameters for this application. In this review, the fundamental aspects of ultrasound physics most pertinent to drug delivery are presented; the primary phenomena responsible for increased drug delivery efficacy under ultrasound sonication are discussed; an overview of common ocular drug administration routes and the associated ocular barriers is also given before reviewing the current state of the art of ultrasound-mediated ocular drug delivery and its potential future directions.

Optimization and Characterization of Novel ALCAM-Targeting Antibody Fragments for Transepithelial Delivery

Activated leukocyte cell adhesion molecule (ALCAM) is a cell adhesion molecule that supports T cell activation, leukocyte migration, and (lymph)angiogenesis and has been shown to contribute to the pathology of various immune-mediated disorders, including asthma and corneal graft rejection. In contrast to monoclonal antibodies (mAbs) targeting ALCAM's T cell expressed binding partner CD6, no ALCAM-targeting mAbs have thus far entered clinical development. This is likely linked with the broad expression of ALCAM on many different cell types, which increases the risk of eliciting unwanted treatment-induced side effects upon systemic mAb application. Targeting ALCAM in surface-exposed tissues, such as the lungs or the cornea, by a topical application could circumvent this issue. Here, we report the development of various stability- and affinity-improved anti-ALCAM mAb fragments with cross-species reactivity towards mouse, rat, monkey, and human ALCAM. Fragments generated in either mono- or bivalent formats potently blocked ALCAM-CD6 interactions in a competition ELISA, but only bivalent fragments efficiently inhibited ALCAM-ALCAM interactions in a leukocyte transmigration assay. The different fragments displayed a clear size-dependence in their ability to penetrate the human corneal epithelium. Furthermore, intranasal delivery of anti-ALCAM fragments reduced leukocyte infiltration in a mouse model of asthma, confirming ALCAM as a target for topical application in the lungs.

Topical ocular protein delivery based on protein powder suspensions in semifluorinated alkanes

The field of ocular diseases, specifically retinal diseases is a successful target area for protein drugs with various marketed products. Besides the intraocular treatment of the retina, the topical treatment of corneal or conjunctival diseases is a promising approach. Topical ocular protein formulations face the challenges of poor penetration and potentially low stability. In this study we tested suspensions based on the semifluorinated alkane F6H8 to improve the topical ocular protein delivery. Such suspensions are well known for the increased protein stability compared to aqueous solutions. Furthermore, F6H8 is well known as vehicle for ocular delivery due to its easy spreading on the cornea. Penetration of a model mAb and its Fab fragment was tested in an ex vivo corneal penetration test. The amount of penetrated protein was increased when the protein powder suspensions were used compared to the respective aqueous solutions. Sodium caprate as penetration enhancer at 5mg/ml substantially increased the Fab fragment (7-fold) and the mAB (3-fold) concentration in the corneal tissue when applied as an aqueous solution. The effect was surprisingly more pronounced, when Fab fragment (31-fold) or mAb (13-fold) and the penetration enhancer were formulated as F6H8 suspensions. The same penetration enhancement from suspensions could be achieved with 2.5mg/ml, but the penetration was reduced compared to 2.5 mg/ml in the aqueous solution. A test based on stratified human keratinocytes did not indicate eye irritation by the tested formulations. Furthermore, stability studies for bevacizumab suspensions in semifluorinated alkanes were investigated and showed superior long-term stability compared to the marketed aqueous solution. Overall results demonstrate the high potential of topical ocular protein delivery using powder suspensions in non-aqueous vehicles based on semifluorinated alkanes.

Topical Drug Delivery to the Posterior Segment of the Eye

Topical drug delivery to the posterior segment of the eye is a very complex challenge. However, topical delivery is highly desired, to achieve an easy-to-use treatment option for retinal diseases. In this review, we focus on the drug characteristics that are relevant to succeed in this challenge. An overview on the ocular barriers that need to be overcome and some relevant animal models to study ocular pharmacokinetics are given. Furthermore, a summary of substances that were able to reach the posterior segment after eye drop application is provided, as well as an outline of investigated delivery systems to improve ocular drug delivery. Some promising results of substances delivered to the retina suggest that topical treatment of retinal diseases might be possible in the future, which warrants further research.

Recent trends in drug-delivery systems for the treatment of diabetic retinopathy and associated fibrosis

Diabetic retinopathy is a frequent microvascular complication of diabetes and a major cause of visual impairment. In advanced stages, the abnormal neovascularization can lead to fibrosis and subsequent tractional retinal detachment and blindness. The low bioavailability of the drugs at the target site imposed by the anatomic and physiologic barriers within the eye, requires long term treatments with frequent injections that often compromise patient's compliance and increase the risk of developing more complications. In recent years, much effort has been put towards the development of new drug delivery platforms aiming to enhance their permeation, to prolong their retention time at the target site and to provide a sustained release with reduced toxicity and improved efficacy. This review provides an overview of the etiology and pathophysiology of diabetic retinopathy and current treatments. It addresses the specific challenges associated to the different ocular delivery routes and provides a critical review of the most recent developments made in the drug delivery field.

Topical Drug Delivery to the Posterior Segment of the Eye: Addressing the Challenge of Preclinical to Clinical Translation

Topical delivery of therapeutics to the posterior segment of the eye remains the “holy grail” of ocular drug delivery. As an example, anti–vascular endothelial growth factor biologics, such as ranibizumab, aflibercept, and bevacizumab, are delivered by intravitreal injection to treat neovascular age-related macular degeneration and, although these drugs have revolutionized treatment of the disease, less invasive alternatives to intravitreal injection are desired. Multiple reports in the literature have demonstrated topical delivery of both small and large molecules to the back of the eye in small animal models. Despite this progress, successful translation to larger species, and ultimately humans, has yet to be demonstrated. Selection of animal models with relevant ocular anatomy and physiology, along with appropriate experimental design, is critical to enable more relevant feasibility assessments and increased probability of successful translation.

Ocular delivery of proteins and peptides: Challenges and novel formulation approaches

The impact of proteins and peptides on the treatment of various conditions including ocular diseases over the past few decades has been advanced by substantial breakthroughs in structural biochemistry, genetic engineering, formulation and delivery approaches. Formulation and delivery of proteins and peptides, such as monoclonal antibodies, aptamers, recombinant proteins and peptides to ocular tissues poses significant challenges owing to their large size, poor permeation and susceptibility to degradation. A wide range of advanced drug delivery systems including polymeric controlled release systems, cell-based delivery and nanowafers are being exploited to overcome the challenges of frequent administration to ocular tissues. The next generation systems integrated with new delivery technologies are anticipated to generate improved efficacy and safety through the expansion of the therapeutic target space. This review will highlight recent advances in formulation and delivery strategies of protein and peptide based biopharmaceuticals. We will also describe the current state of proteins and peptides based ocular therapy and future therapeutic opportunities.

Ocular tissue distribution and pharmacokinetic study of a small 13kDa domain antibody after intravitreal, subconjuctival and eye drop administration in rabbits

Domain antibodies (dAb's) comprise the smallest functional unit of human IgG and can be targeted to a range of different soluble cytokine and receptor targets in the eye. In particular their small size may offer advantage for ocular tissue penetration and distribution. To investigate this we used a 13kDa tool molecule to undertake a preliminary short term ocular tissue distribution and pharmacokinetic study in the rabbit eye. The dAb was administered by the intravitreal or subconjunctival route or, as topical eye drops for up to five days and dAb concentrations measured in vitreous, aqueous, conjunctiva, choroid-RPE, retina, iris, sclera, and ciliary body. The observed elimination half-live of the dAb (~3 days) in vitreous showed a similar elimination rate to that of a much larger (∼50kDa) Fab fragment whilst the half-life following subconjunctival administration was ∼24 h and, after eye drop dosing the dAb was detectable in aqueous and conjunctiva. These preliminary data show that the intravitreal half-life of dAb's are similar to much larger antibody fragments, offering the potential to deliver significantly more drug to target on a molar basis with a single intravitreal injection potentially enabling dosing frequencies of once a month or less. Subconjunctival injection may provide short duration therapeutic levels of dAb to the anterior and posterior chamber whilst topical eye drop delivery of dAbs may be useful in front-of-eye disease. These data indicate that small domain antibodies may have utility in ophthalmology. Further studies are warranted.

Eye drop delivery of pigment epithelium-derived factor-34 promotes retinal ganglion cell neuroprotection and axon regeneration

Axotomised retinal ganglion cells (RGCs) die rapidly by apoptosis and fail to regenerate because of the limited availability of neurotrophic factors and a lack of axogenic stimuli. However, we have recently showed that pigment epithelium-derived factor (PEDF) promotes RGC survival and axon regeneration after optic nerve crush injury. PEDF has multiple fragments of the native peptide that are neuroprotective, anti-angiogenic and anti-inflammatory. Here we investigated the neuroprotective and axogenic properties of a fragment of PEDF, PEDF-34, in retinal neurons in vitro and when delivered by intravitreal injection and eye drops in vivo. We found that PEDF-34 was 43% more neuroprotective and 52% more neuritogenic than PEDF-44 in vitro. Moreover, in vivo, intravitreal delivery of 1.88 nM PEDF-34 was 71% RGC neuroprotective at 21 days after optic nerve crush compared to intact controls, whilst daily eye drops containing 1.88 nM PEDF-34 promoted 87% RGC survival. After topical eye drop delivery, PEDF-34 was detected in the vitreous body within 30 min and attained physiologically relevant concentrations in the retina by 4 h peaking at 1.4 ± 0.05 nM by 14 days. In eye drop- compared to intravitreal-treated PEDF-34 animals, 55% more RGC axons regenerated 250 μm beyond the optic nerve lesion. We conclude that daily topical eye drop application of PEDF-34 is superior to weekly intravitreal injections in promoting RGC survival and axon regeneration through both direct effects on retinal neurons and indirect effects on other retinal cells.

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PEDF-34 is more neuroprotective and neuritogenic than PEDF-44.

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PEDF-34 is more neuroprotective and neuritogenic than full-length PEDF.

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PEDF-34 can reach the retina after topical application to the eyes.

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PEDF-34 eye drops are more neuroprotective and axogenic than intravitreal injection.

Delivery of Topically Applied Calpain Inhibitory Peptide to the Posterior Segment of the Rat Eye

We developed an inhibitory peptide that specifically acts against mitochondrial μ-calpain (Tat-μCL, 23 amino acid, 2857.37 Da) and protects photoreceptors in retinal dystrophic rats. In the present study, we topically administered Tat-μCL to the eyes of Sprague-Dawley rats for 7 days to determine both the delivery route of the peptide to the posterior segment of the eye and the kinetics after topical application in adult rats. Distribution of the peptide was determined by immunohistochemical analysis, and enzyme-linked immune-absorbent assay was used to quantify the accumulation in the retina. Peptides were prominently detected in both the anterior and posterior segments of the eye at 1 h after the final eye drop application. Immunohistochemically positive reactions were observed in the retina, optic nerve, choroid, sclera and the retrobulbar tissues, even in the posterior portion of the eye. Immunoactivities gradually diminished at 3 and 6 h after the final eye drop. Quantitative estimations of the amount of peptide in the retina were 15.3, 5.8 and 1.0 pg/μg protein at 1, 3 and 6 h after the final instillation, respectively. Current results suggest that while the topically applied Tat-μCL peptide reaches the posterior segment of the retina and the optic nerve, the sufficient concentration (> IC50) is maintained for at least 6 h in the rat retina. Our findings suggest that delivery of topically applied peptide to the posterior segment and optic nerve occurs through the conjunctiva, periocular connective tissue, sclera and optic nerve sheath.

Ocular distribution, spectrum of activity, and in vivo viral neutralization of a fully humanized anti-herpes simplex virus IgG Fab fragment following topical application

Herpes simplex ocular infection is a major cause of corneal blindness. Local antiviral treatments exist but are associated with corneal toxicity, and resistance has become an issue. We evaluated the biodistribution and efficacy of a humanized anti-herpes simplex virus (anti-HSV) IgG FAb fragment (AC-8; 53 kDa) following repeated topical administration. AC-8 was found in the corneal epithelium, anterior stroma, subepithelial stromal cells, and retinal glial cells, with preferential entry through the ocular limbus. AC-8 was active against 13 different strains of HSV-1, with 50% and 90% mean effective concentrations (MEC(50) and MEC(90), respectively) ranging from 0.03 to 0.13 μg/ml, indicating broad-spectrum activity. The in vivo efficacy of AC-8 was evaluated in a mouse model of herpes-induced ocular disease. Treatment with low-dose AC-8 (1 mg/ml) slightly reduced the ocular disease scores. A greater reduction of the disease scores was observed in the 10-mg/ml AC-8-treated group, but not as much as with trifluridine (TFT). AC-8 treatment reduced viral titers but less than trifluridine. AC-8 did not display any toxicity to the cornea or other structures in the eye. In summary, topical instillation of an anti-HSV FAb can be used on both intact and ulcerated corneas. It is well tolerated and does not alter reepithelialization. Further studies to improve the antiviral effect are needed for AC-8 to be considered for therapeutic use.

Corneal penetration of topical and subconjunctival bevacizumab

PURPOSE

To investigate the ability of bevacizumab to penetrate the cornea after topical application or subconjunctival injection.

METHODS

Bevacizumab 1% was topically applied three times a day to the corneas of mice (BALB/c) with intact corneas (n = 14), and with corneal neovascularization (n = 14). Animals were euthanized at 1, 6, 12, and 24 hours, and 2, 4, and 7 days for immunohistochemical analyses. Donkey anti-human IgG labeled with Cy3 was used for bevacizumab immunoreactivity detection. Additionally, one-time topical bevacizumab 1% was tested in corneas with denuded epithelium (n = 16). In another group (n = 16), a single dose of 0.5 mg bevacizumab was injected subconjunctivally. Animals were euthanized at 1, 6, and 24 hours, and 2, 4, 7, 14, and 21 days for immunohistochemical studies.

RESULTS

Bevacizumab was barely detected beyond the very superficial layer of the corneal epithelium in mice with intact corneas even after 7 days of topical administration. Application of bevacizumab in mice with corneal neovascularization; however, showed variable penetration into the corneal stroma. Experimentation with single application of topical bevacizumab in corneas with denuded epithelium or subconjunctivally injected bevacizumab showed intense staining for bevacizumab.

CONCLUSIONS

Topically applied bevacizumab has limited capacity to penetrate the corneas with intact epithelium. However, bevacizumab can penetrate the neovascularized cornea after topical application. This study demonstrates that subconjunctivally injected bevacizumab in eyes with an intact cornea penetrates well into the corneal stroma.

Potential penetration of topical ranibizumab (Lucentis) in the rabbit eye

PURPOSE

To assess ranibizumab (Lucentis) penetration into the retina after topical administration in a rabbit model.

METHODS

Ranibizumab was topically applied to the right eye of rabbits according to three regimens: every 2 h (q2hr), four times daily (qid), and twice daily (bid). Intraocular penetration of ranibizumab was assessed at 3, 7, 14, 21, and 28 days following initiation of drops. At each time point, the anterior chambers, vitreous cavities, and blood of one of the rabbits from each subgroup were sampled for ranibizumab detection using enzyme-linked immunosorbent assay (ELISA), and both eyes were then enucleated for ranibizumab detection in the retina by confocal immunohistochemistry (CI). Another group of rabbits received intravitreal ranibizumab and was similarly sampled for comparison.

RESULTS

CI showed ranibizumab staining in the right retina after 7 and 14 days of q2hr topical administration in two out of four experiments. No ranibizumab was detected in the left retina at any of the sampling time points. ELISA was positive in the vitreous of the right eye at 14 and 21 days in the q2hr treated rabbits in one out of four experiments. No ranibizumab was detected in the qid and bid subgroups. CI and ELISA of the aqueous and vitreous were consistently positive in the intravitreal group. Mild ranibizumab levels were detected in the blood in both the topical and intravitreal groups.

CONCLUSIONS

Topically applied ranibizumab can be detected in the retina following high-frequency administration in a rabbit model. A trans-scleral route of penetration is suggested.

Protein delivery for retinal diseases: from basic considerations to clinical applications

Because the eye is protected by ocular barriers but is also easily accessible, direct intravitreous injections of therapeutic proteins allow for specific and targeted treatment of retinal diseases. Low doses of proteins are required in this confined environment and a long time of residency in the vitreous is expected, making the eye the ideal organ for local proteic therapies. Monthly intravitreous injection of Ranibizumab, an anti-VEGF Fab has become the standard of care for patients presenting wet AMD. It has brought the proof of concept that administering proteins into the physiologically low proteic concentration vitreous can be performed safely. Other antibodies, Fab, peptides and growth factors have been shown to exert beneficial effects on animal models when administered within the therapeutic and safe window. To extend the use of such biomolecules in the ophthalmology practice, optimization of treatment regimens and efficacy is required. Basic knowledge remains to be increased on how different proteins/peptides penetrate into the eye and the ocular tissues, distribute in the vitreous, penetrate into the retinal layers and/or cells, are eliminated from the eye or metabolized. This should serve as a basis for designing novel drug delivery systems. The later should be non-or minimally invasive and should allow for a controlled, scalable and sustained release of the therapeutic proteins in the ocular media. This paper reviews the actual knowledge regarding protein delivery for eye diseases and describes novel non-viral gene therapy technologies particularly adapted for this purpose.

Production of scFv antibody fragments from a hybridoma with functional activity against human vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) plays a major role in the development of aberrant neovascularization in ocular diseases such as diabetic retinopathy and age-related macular degeneration (ARMD), and is an important therapeutic target for these diseases. Monoclonal antibodies specific for VEGF are in clinical use for some patients with ARMD, delivered by intraocular injection. We have shown previously that single chain antibody fragments (scFv) penetrate into the eye when applied topically to the ocular surface. Here we describe the production of a scFv from a monoclonal antibody specific for human VEGF and demonstrate its ability to decrease proliferation of human umbilical vein endothelial cells in culture. A suitably formulated anti-VEGF scFv may have potential as a less invasive topical treatment for potentially blinding neovascular diseases of the eye.

Antibody-based immunosuppressive agents for corneal transplantation

The progress in antibody engineering over the last 20 years has created the tools for the development of novel antibody-based drugs and constructs, such as small antibody fragments, suitable for topical administration. In rheumatology, oncology, transplantation medicine and ophthalmology, therapeutic antibody constructs, and antibody fragments have been responsible for the clinical progress seen over the last decade. Although antibody-based therapies have become a well-established immunosuppressive option in solid organ transplantation, there are only very few reports with regard to corneal transplantation. The following review explains some of the important aspects of engineered antibody-based therapeutic agents and summarises the current use of such immunosuppressive therapies in transplantation medicine and corneal transplantation.

Single chain antibody fragments for ocular use produced at high levels in a commercial wheat variety

We are investigating the use of single chain antibody fragments (scFv) in eye drops for diagnosis and treatment of eye diseases. For ocular use, recombinant proteins must be free of bacterial endotoxin that causes inflammation in the eye. We required a means of generating high yields of scFvs with little endotoxin contamination. Using microprojectile bombardment we produced transgenic lines of the commercial wheat variety, Westonia, that express two scFvs that bind to CD4 or CD28 on the surface of rat thymocytes. A high level of expression of active scFv in the range 50-180 microg/g was measured by quantitative flow cytometry in crude extracts made from mature seeds. The levels of expression were stable over four generations of transgenic plants and mature seeds were stored for one year with little loss of scFv activity. Substantial purification of scFv was achieved by immobilised metal affinity chromatography. Compared to bacterial extracts, crude transgenic seed extracts contained only a small amount of endotoxin (150 EU/ml) that will be easily removed by purification. The transgenic wheat lines express functional scFv at levels comparable to production in bacteria and promise to be superior to bacteria for production of scFv pharmaceuticals for ocular use.

Ability of Poly-L-arginine to Enhance Drug Absorption into Aqueous Humor and Vitreous Body after Instillation in Rabbits

The effect of poly-L-arginine with a molecular weight of 35.5 kDa (PLA) on the ocular absorption of hydrophilic molecules after instillation was examined in rabbits in vivo. FITC-labeled dextran (3.8 kDa, FD-4) and pyridoxamine were used as model hyprophilic molecules for absorption. The potential toxicity of PLA was evaluated by microscopic observation of the cornea, production of TNF-alpha, and the thickness of the corneal epithelia and stroma. The concentration of pyridoxamine and FD-4 in aqueous humor 30 min after a single instillation of a solution of PLA was 29- and 16-fold higher than that without PLA, respectively, but the drug concentrations were not determined in the vitreous body. Repetitive instillation of PLA every 30 min for 150 min achieved 31.1- and 13.3-fold increases in pyridoxamine and FD-4 in aqueous humor, respectively. Furthermore, significant amounts of pyridoxamine and FD-4 were detected in the vitreous body after the repetitive instillation of PLA, even although very little of these drugs was detected in the vitreous body in the control eye without PLA. On the other hand, repetitive instillation of PLA did not induce any alteration of corneal epithelial and stromal thickness, production of TNF-alpha, and disruption of the epithelial and stromal morphologies and neutrophil infiltration. Our findings suggest that PLA may be useful in promoting drug delivery of hydrophilic drugs to the ocular tissues without producing any significant corneal damage and inflammation.