Comparison of suprachoroidal drug delivery with subconjunctival and intravitreal routes using noninvasive fluorophotometry

An update on the latest strategies in retinal drug delivery

INTRODUCTION

Retinal drug delivery has witnessed significant advancements in recent years, mainly driven by the prevalence of retinal diseases and the need for more efficient and patient-friendly treatment strategies.

AREAS COVERED

Advancements in nanotechnology have introduced novel drug delivery platforms to improve bioavailability and provide controlled/targeted delivery to specific retinal layers. This review highlights various treatment options for retinal diseases. Additionally, diverse strategies aimed at enhancing delivery of small molecules and antibodies to the posterior segment such as implants, polymeric nanoparticles, liposomes, niosomes, microneedles, iontophoresis and mixed micelles were emphasized. A comprehensive overview of the special technologies currently under clinical trials or already in the clinic was provided.

EXPERT OPINION

Ideally, drug delivery system for treating retinal diseases should be less invasive in nature and exhibit sustained release up to several months. Though topical administration in the form of eye drops offers better patient compliance, its clinical utility is limited by nature of the drug. There is a wide range of delivery platforms available, however, it is not easy to modify any single platform to accommodate all types of drugs. Coordinated efforts between ophthalmologists and drug delivery scientists are necessary while developing therapeutic compounds, right from their inception.

Rapidly Dissolving Trans-scleral Microneedles for Intraocular Delivery of Cyclosporine A

Cyclosporine A (CsA) is a cyclic peptide immunosuppressant drug that is beneficial in the treatment of various ocular diseases. However, its ocular bioavailability in the posterior eye is limited due to its poor aqueous solubility. Conventional CsA formulations such as a solution or emulsion permeate poorly across the eye due to various static and dynamic barriers of the eye. Dissolvable microneedle (MN)-based patches can be used to overcome barrier properties and, thus, enhance the ocular bioavailability of CsA in the posterior eye. CsA-loaded dissolvable MN patches were fabricated using polyvinylpyrrolidone (PVP) and characterized for MN uniformity and sharpness using SEM. Further characterization for its failure force, penetration force, and depth of penetration were analyzed using a texture analyzer. Finally, the dissolution time, ex vivo permeation, and ocular distribution of cyclosporine were determined in isolated porcine eyes. PVP MNs were sharp, uniform with good mechanical properties, and dissolved within 5 min. Ocular distribution of CsA in a whole porcine eye perfusion model showed a significant increase of CsA levels in various posterior segment ocular tissues as compared to a topically applied ophthalmic emulsion (Restasis®) (P < 0.001). Dissolving MNs of CsA were prepared, and the MN arrays can deliver CsA to the back of the eye offering potential for treating various inflammatory diseases.

Discovery and Potential Utility of a Novel Non-Invasive Ocular Delivery Platform

To this day, the use of oily eye drops and non-invasive retinal delivery remain a major challenge. Oily eye drops usually cause ocular irritation and interfere with the normal functioning of the eye, while ocular injections for retinal drug delivery cause significant adverse effects and a high burden on the healthcare system. Here, the authors report a novel topical non-invasive ocular delivery platform (NIODP) through the periorbital skin for high-efficiency anterior and posterior ocular delivery in a non-human primate model (NHP). A single dose of about 7 mg JV-MD2 (omega 3 DHA) was delivered via the NIODP and reached the retina at a Cmax of 111 µg/g and the cornea at a Cmax of 66 µg/g. The NIODP also delivered JV-DE1, an anti-inflammatory agent in development for dry eye diseases, as efficiently as eye drops did to the anterior segments of the NHP. The topical NIODP seems to transport drug candidates through the corneal pathway to the anterior and via the conjunctiva/sclera pathway to the posterior segments of the eye. The novel NIODP method has the potential to reshape the landscape of ocular drug delivery. This is especially the case for oily eye drops and retinal delivery, where the success of the treatment lies in the ocular tolerability and bioavailability of drugs in the target tissue.

Refractory post-surgical cystoid macular edema managed following suprachoroidal microcatheterization and delivery of triamcinolone

BACKGROUND

Post-surgical macular edema (ME) is a common cause of prolonged visual impairment. Here we report on the feasibility and clinical outcomes from the use of a novel suprachoroidal microcatheter to treat post-surgical chronic ME by the posterior suprachoroidal placement of a triamcinolone acetonide (TA) suspension.

METHODS

Two patients were catheterized with the Oxulumis suprachoroidal delivery system on two separate occasions starting 5 and 10 mm posterior to the limbus. The catheter only remains in the suprachoroidal space for the time of the drug administration. Visual acuity and spectral domain optical coherence tomography (SD-OCT) changes were followed over several weeks to months to determine the duration of ME resolution.

RESULTS

Suprachoroidal microcatheterization for posterior delivery of triamcinolone was possible in all attempts using the illuminated Oxulumis catheter. No reflux, scleral or choroidal trauma was observed. There was no intraocular pressure rise during the follow-up period. The triamcinolone deposit was visible on infrared imaging and on SD-OCT a choroidal elevation was visible. Both progressively disappeared over time. A rapid resolution of ME associated with improved vision was observed following each injection for 3 to 7 months with a TA dose of 2.4 mg or 4 mg.

CONCLUSIONS

In these patients with poorly responsive ME, posterior suprachoroidal TA led to a visible suprachoroidal drug deposit and prolonged visual improvement. The Oxulumis microcatheterization device performed as expected and was not associated with any complications.

Suprachoroidal Injection: A Novel Approach for Targeted Drug Delivery

Treating posterior segment and retinal diseases poses challenges due to the complex structures in the eye that act as robust barriers, limiting medication delivery and bioavailability. This necessitates frequent dosing, typically via eye drops or intravitreal injections, to manage diseases, often leading to side effects with long-term use. Suprachoroidal injection is a novel approach for targeted drug delivery to the posterior segment. The suprachoroidal space is the region between the sclera and the choroid and provides a potential route for minimally invasive medication delivery. Through a more targeted delivery to the posterior segment, this method offers advantages over other routes of administration, such as higher drug concentrations, increased bioavailability, and prolonged duration of action. Additionally, this approach minimizes the risk of corticosteroid-related adverse events such as cataracts and intraocular pressure elevation via compartmentalization. This review focuses on preclinical and clinical studies published between 2019 and 2023, highlighting the potential of suprachoroidal injection in treating a variety of posterior segment diseases. However, to fully harness its potential, more research is needed to address current challenges and limitations, such as the need for technological advancements, refinement of injection techniques, and consideration of cost and accessibility factors. Future studies exploring its use in conjunction with biotech products, gene therapies, and cell-based therapies can lead to personalized treatments that can revolutionize the field of ophthalmology.

A Physiology-Based Mathematical Model to Understand Drug Delivery from Contact Lenses to the Back of the Eye

OBJECTIVE

Therapeutic contact lenses, able to store drug and deliver it to the eye surface in a sustained fashion, gained interest as an effective and patient-friendly alternative to eye drops. Recent animal studies also demonstrated the presence of therapeutic drug levels in the back of the eye after wearing drug-loaded contact lenses, thus opening the possibility of treating the posterior segment without need of invasive intraocular injections. The drug pathways from contact lenses to the back of the eye require further investigation.

METHODS

A mechanistic mathematical model was developed to evaluate the drug concentration over time in the tears, sclera and choroid, retina, aqueous humor and vitreous humor after the application of a therapeutic contact lens. The main drug transport mechanisms of the eye and the barrier properties of the different tissues were included in the model. Validation was performed by comparison with experimental data in literature.

RESULTS

The model predictions of drug concentration over time reflected the experimental data both in the anterior and posterior segment of the eye. The model can differentiate between contributions to transport from different pathways.

CONCLUSIONS

The model constitutes a first step towards the possibility of predicting the ocular drug distribution and the treatment efficacy in the early stage of contact lens development, and it may help reduce both the need for in vivo tests (with ethical and economic advantages) and the gap between the lens design and clinical application. It also allows for an improved understanding of drug transport in the eye.

Ocular immunosuppressive microenvironment and novel drug delivery for control of uveitis

Ocular immune privilege is a phenomenon described by Peter Medawar in relation to the indefinite survival of the placement of foreign tissue grafts into the eye. Several mechanisms have been described that contribute to ocular immune privilege, such as a blood-ocular barrier and lack of lymphatics in the eye, the production of immune-suppressing molecules inside the ocular microenvironment, and the induction of systemic regulatory immunity against antigens found in the eye. Because ocular immune privilege is not absolute, failure of it can result in uveitis. Uveitis is a group of inflammatory disorders that can lead to vision loss if not treated properly. The current uveitis treatments involve the use of immunosuppressive and anti-inflammatory medications. Researching mechanisms of ocular immune privilege and the development of novel treatments for uveitis is ongoing. This review discusses mechanisms of ocular immune privilege, followed by an overview of uveitis treatments and ongoing clinical trials.

Ocular barriers as a double-edged sword: preventing and facilitating drug delivery to the retina

In recent decades, the growing of the aging population in the world brings increasingly heavy burden of vision-threatening retinal diseases. One of the biggest challenges in the treatment of retinal diseases is the effective drug delivery to the diseased area. Due to the existence of multiple anatomical and physiological barriers of the eye, commonly used oral drugs or topical eye drops cannot effectively reach the retinal lesions. Innovations in new drug formulations and delivery routes have been continuously applied to improve current drug delivery to the back of the eye. Unique ocular anatomical structures or physiological activities on these ocular barriers, in turn, can facilitate drug delivery to the retina if compatible formulations or delivery routes are properly designed or selected. This paper focuses on key barrier structures of the eye and summarizes advances of corresponding drug delivery means to the retina, including various local drug delivery routes by invasive approaches, as well as systemic eye drug delivery by non-invasive approaches.

Nanomedicine and drug delivery to the retina: current status and implications for gene therapy

Blindness affects more than 60 million people worldwide. Retinal disorders, including age-related macular degeneration (AMD), diabetic retinopathy (DR), and glaucoma, are the leading causes of blindness. Finding means to optimize local and sustained delivery of drugs or genes to the eye and retina is one goal to advance the development of new therapeutics. Despite the ease of accessibility of delivering drugs via the ocular surface, the delivery of drugs to the retina is still challenging due to anatomic and physiologic barriers. Designing a suitable delivery platform to overcome these barriers should enhance drug bioavailability and provide a safe, controlled, and sustained release. Current inventions for posterior segment treatments include intravitreal implants and subretinal viral gene delivery that satisfy these criteria. Several other novel drug delivery technologies, including nanoparticles, micelles, dendrimers, microneedles, liposomes, and nanowires, are now being widely studied for posterior segment drug delivery, and extensive research on gene delivery using siRNA, mRNA, or aptamers is also on the rise. This review discusses the current state of retinal drug/gene delivery and highlights future therapeutic opportunities.

Long-acting formulation strategies for protein and peptide delivery in the treatment of PSED

The invigoration of protein and peptides in serious eye disease includes age-related macular degeneration, choroidal neovascularization, retinal neovascularization, and diabetic retinopathy. The transportation of macromolecules like aptamers, recombinant proteins, and monoclonal antibodies to the posterior segment of the eye is challenging due to their high molecular weight, rapid degradation, and low solubility. Moreover, it requires frequent administration for prolonged therapy. The long-acting novel formulation strategies are helpful to overcome these issues and provide superior therapy. It avoids frequent administration, improves stability, high retention time, and avoids burst release. This review briefly enlightens posterior segments of eye diseases with their diagnosis techniques and treatments. This article mainly focuses on recent advanced approaches like intravitreal implants and injectables, electrospun injectables, 3D printed drug-loaded implants, nanostructure thin-film polymer devices encapsulated cell technology-based intravitreal implants, injectable and depots, microneedles, PDS with ranibizumab, polymer nanoparticles, inorganic nanoparticles, hydrogels and microparticles for delivering macromolecules in the eye for intended therapy. Furthermore, novel techniques like aptamer, small Interference RNA, and stem cell therapy were also discussed. It is predicted that these systems will make revolutionary changes in treating posterior segment eye diseases in future.

Protein and polypeptide mediated delivery to the eye

Hybrid or recombinant protein-polymers, peptide-based biomaterials, and antibody-targeted therapeutics are widely explored for various ocular conditions and vision correction. They have been noted for their potential biocompatibility, potency, adaptability, and opportunities for sustained drug delivery. Unique to peptide and protein therapeutics, their production by cellular translation allows their precise modification through genetic engineering. To a greater extent than drug delivery to other systems, delivery to the eye can benefit from the combination of locally-targeted administration and protein-based specificity. Consequently, a range of delivery platforms and administration methods have been exploited to address the ocular delivery of peptide and protein biomaterials. This review discusses a sample of preclinical and clinical opportunities for peptide-based drug delivery to the eye.

Suprachoroidal versus Intravitreal Triamcinolone Acetonide for the Treatment of Diabetic Macular Edema

Purpose

This article aims to compare between intravitreal (IV) and suprachoroidal (SC) triamcinolone acetonide (TA) injection for the treatment of diabetic macular edema (DME) in terms of improvement in both best-corrected visual acuity (BCVA) and central macular thickness (CMT), and development of complications (intraocular pressure (IOP) rise and cataract progression), and to identify the efficient dose of TA using the SC route.

Patients and Methods

This prospective interventional randomized comparative study included 45 eyes of 32 patients, randomly divided into three groups, group I received 4 mg/0.1 mL intravitreal TA (IVTA), group II received 4 mg/0.1 mL suprachoroidal TA (SCTA), and group III received 2mg/0.1 mL SCTA. Patients were followed up for 6 months.

Results

At 1 month, a maximum reduction in CMT (147.33 ± 110.97 µm, 160.80 ± 98.25 µm and 65.64 ± 46.19 µm in groups I, II, and III, respectively) was observed, which was associated with the greatest improvement of BCVA (0.09 ± 0.09, 0.19 ± 0.10 and 0.10 ± 0.09 logMAR lines) in groups I, II, and III, respectively. At 3 months, CMT started to increase, and reduction was not statistically significant compared to baseline, except in group II (4 mg SCTA group) (149.80 ± 106.57 µm with P-value = 0.013). At 6 months, CMT and BCVA returned close to baseline except for group II which had a sustained reduction of 60.16 µm from baseline. Regarding steroid-related complications, IOP elevation of 10 mmHg or more was noted in 1 eye (6.7%), 2 eyes (13.3%), and 1 eye in groups I, II, and III, respectively. Three phakic eyes per group showed cataract progression.

Conclusion

SCTA is a safe and effective route for the treatment of DME, which has comparable effects to IVTA, and may even last longer.

A Review of Ocular Drug Delivery Platforms and Drugs for Infectious and Noninfectious Uveitis: The Past, Present, and Future

Uveitis refers to a broad group of inflammatory disorders of the eye that often require medical and surgical management to improve or stabilize vision and prevent vision-threatening pathological changes to the eye. Drug delivery to the eye to combat inflammation and subsequent complications from uveitic conditions is complex as there are multiple barriers to absorption limiting availability of the needed drug in the affected tissues. As such, there has been substantial interest in developing new drugs and drug delivery platforms to help reduce intraocular inflammation and its complications. In this review, we discuss the challenges of drug delivery, novel technologies recently approved for uveitis patient care and promising drug delivery platforms for uveitis and sequelae of ocular inflammation.

Suprachoroidal Injection of Triamcinolone- Review of a Novel Treatment for Macular Edema Caused by Noninfectious Uveitis

Macular edema is the most frequent cause of visual deterioration in noninfectious uveitis. The treatment of noninfectious uveitis with associated macular edema commonly includes systemic or locally administered corticosteroids, with long-term use limited by significant side effects. The need for a treatment with an improved safety profile has driven the development of a novel ophthalmic therapy: a proprietary triamcinolone acetonide suspension (CLS-TA) administered in the suprachoroidal space (XIPERE^™; Clearside Biomedical, Alpharetta, GA, USA). Suprachoroidal delivery of corticosteroids allows higher steroid concentration in the posterior segment and decreases the risk of other adverse ocular events. Recent results from the PEACHTREE trial (ClinicalTrials.gov Identifier: NCT02595398), a phase III trial with two suprachoroidal injections of CLS-TA at 0 and 12 weeks with follow up lasting 24 weeks, showed the significant improvement in visual acuity and reduction in central subfield thickness, all without increasing the risk of elevated intraocular pressure or accelerated cataract progression.

Drug Delivery via the Suprachoroidal Space for the Treatment of Retinal Diseases

The suprachoroidal space (SCS), a potential space between the sclera and choroid, is becoming an applicable method to deliver therapeutics to the back of the eye. In recent years, a vast amount of research in the field has been carried out, with new discoveries in different areas of interest, such as imaging, drug delivery methods, pharmacokinetics, pharmacotherapies in preclinical and clinical trials and advanced therapies. The SCS can be visualized via advanced techniques of optical coherence tomography (OCT) in eyes with different pathologies, and even in healthy eyes. Drugs can be delivered easily and safely via hollow microneedles fitted to the length of the approximate thickness of the sclera. SCS injections were found to reach greater baseline concentrations in the target layers compared to intravitreal (IVT) injection, while agent clearance was faster with highly aqueous soluble molecules. Clinical trials with SCS injection of triamcinolone acetonide (TA) were executed with promising findings for patients with noninfectious uveitis (NIU), NIU implicated with macular edema and diabetic macular edema (DME). Gene therapy is evolving rapidly with viral and non-viral vectors that were found to be safe and efficient in preclinical trials. Here, we review these novel different aspects and new developments in clinical treatment of the posterior segment of the eye.

Age-related ocular conditions: Current treatments and role of cyclodextrin-based nanotherapies

Age-related eye disorders are chronic diseases that affect millions of people worldwide. They cause visual impairment and, in some cases, irreversible blindness. Drug targeting to the retina is still a challenge due to the difficulties with drug distribution, crossing eye barriers, and reaching intraocular tissues in an effective therapeutic concentration. Although intravitreal injections can directly deliver drugs to the posterior segment of the eye, it remains an invasive technique and leads to several side effects. Conventional formulations such as emulsions, suspensions, or ointments have been related to frequent instillation and inability to reach intraocular tissues. New drug delivery systems and medical devices have also been designed. Nevertheless, these treatments are not always effective and sometimes require the presence of a specialist for the administration of the dose. Therefore, treatments for age-related ocular diseases remain as one of the major unmet clinical needs to manage these widespread eye conditions. Nanotechnology may become the adequate tool for developing effective and non-invasive therapies suitable for self-administration. In this review, we discuss emerging therapeutic options based on nanoengineering of cyclodextrin nanocarriers for the treatment of age-related eye disorders, including their pathophysiology, pharmacological options, and feasibility of clinical translation.

Extraocular, periocular, and intraocular routes for sustained drug delivery for glaucoma

Although once daily anti-glaucoma drug therapy is a current clinical reality, most therapies require multiple dosing and there is an unmet need to develop convenient, safe, and effective sustained release drug delivery systems for long-term treatment to improve patient adherence and outcomes. One of the first sustained release drug delivery systems was approved for the reduction of intraocular pressure in glaucoma patients. It is a polymeric reservoir-type insert delivery system, Ocusert™, placed under the eyelid and on the ocular surface for zero-order drug release over one week. The insert, marketed in two strengths, released pilocarpine on the eye surface. While many clinicians appreciated this drug product, it was eventually discontinued. No similar sustained release non-invasive drug delivery system has made it to the market to date for treating glaucoma. Drug delivery systems under development include punctal plugs, ring-type systems, contact lenses, implants, microspheres, nanospheres, gels, and other depot systems placed in the extraocular, periocular, or intraocular regions including intracameral, supraciliary, and intravitreal spaces. This article discusses the advantages and disadvantages of the various routes of administration and delivery systems for sustained glaucoma therapy. It also provides the reader with some examples and discussion of drug delivery systems that could potentially be applied for glaucoma treatment. Interestingly, one intracamerally injected implant, Durysta™, was approved recently for sustained intraocular pressure reduction. However, long-term acceptance of such devices has yet to be established. The ultimate success of the delivery system will depend on efficacy relative to eye drop dosing, safety, reimbursement options, and patient acceptance. Cautious development efforts are warranted considering prior failed approaches for sustained glaucoma drug delivery. Neuroprotective approaches for glaucoma therapy including cell, gene, protein, and drug-combination therapies, mostly administered intravitreally, are also rapidly progressing towards assessment in humans.

Dexamethasone delivery to the ocular posterior segment by sustained-release Laponite formulation

This paper presents a novel nanoformulation for sustained-release delivery of dexamethasone (DEX) to the ocular posterior segment using a Laponite (LAP) carrier-DEX/LAP 1:10 w w^-1 formulation; 10 mg ml^-1. In vivo ocular feasibility and pharmacokinetics after intravitreal (IV) and suprachoroidal (SC) administration in rabbit eyes are compared against IV administration of a DEX solution (1 mg ml^-1). Thirty rabbit eyes were injected with the DEX/LAP formulation (15 suprachoroid/15 intravitreous). Ophthalmological signs were monitored at day 1 and at weeks 1-4-12-24 post-administration. Three eyes per sample time point were used to quantify DEX concentration using high-performance liquid chromatography-mass spectrometry. The ocular tissues' pharmacokinetic parameters (lens, vitreous humour, choroid-retina unit and sclera) were studied. DEX/LAP was well tolerated under both administration methods. Peak intraocular DEX levels from the DEX/LAP were detected in the vitreous humour after both deliveries soon after administration. The vitreous area under the curve was significantly greater after both DEX/LAP deliveries (IV: 205 968.47; SC: 11 442.22 ng g^-1 d^-1) than after IV administration of the DEX solution (317.17 ng g^-1 d^-1). Intravitreal DEX/LAP delivery extended higher vitreous DEX levels up to week 24 (466.32 ± 311.15 ng g^-1). With SC delivery, DEX levels were detectable in the choroid-retina unit (12.04 ± 20.85 ng g^-1) and sclera (25.46 ± 44.09 ng g^-1) up to week 24. This study demonstrated the intraocular feasibility of both SC and IV administration of the DEX/LAP formulation. The LAP increased the intraocular retention time of DEX when compared with conventional solutions. DEX/LAP could be considered a biocompatible and useful sustained-release formulation for treating posterior-pole eye diseases.

Nanoformulations for Ocular Delivery of Drugs - A Patent Perspective

Efficient delivery of ocular therapeutics with improved efficacy, enhanced bioavailability, and acceptable patient compliance presents unique challenges. This can be attributed to the presence of protective mechanisms, physicobiological barriers, and structural obstacles in the eye. Nanotherapeutic interventions have been explored extensively over the past few years to overcome these limitations. The present review focusses on the nanoformulations developed for the diagnosis and treatment of various ocular diseases besides providing an in-depth insight into the patents reported for the same.

Recent advances in the management of non-infectious posterior uveitis

PURPOSE

To review the current regimens and novel therapeutic modalities in various stages of research and development for the management of non-infectious posterior uveitis (NIPU).

METHODS

We performed a thorough review of current literature using PubMed, Google Scholar and Clinicaltrials.gov to identify the published literature about the available therapeutics and novel drugs/therapies in different stages of clinical trials.

RESULTS

The current management regimen for non-infectious posterior uveitis includes corticosteroids, immunomodulatory therapies and anti-metabolites. However, NIPU requires long-term management for efficacious remission of the disease and to prevent disease relapse. Long-term safety issues associated with steroids have led to efforts to develop novel therapeutic agents including biological response modulators and immunosuppressants. The current therapeutic agents in various stages of development include calcineurin inhibitors, biologic response modifiers and a more a comprehensive modalities like ocular gene therapy as well as novel drug delivery mechanisms for higher bioavailability to the target tissues, with minimal systemic effects.

CONCLUSION

Novel efficacious therapeutic modalities under development will help overcome the challenges associated with the traditional therapeutic agents.

Noninvasive Monitoring of Choroid-Retina Autofluorescence and Intravitreal Nanoparticle Disposition in Royal College of Surgeon Rats of Different Ages and Retinal Thinning

Purpose: To determine the baseline choroid-retina fluorescence signal in Royal College of Surgeon (RCS) rats of various ages with different degrees of retinal degeneration and assess the persistence of intravitreal nanoparticles. Methods: In RCS rats of age 6, 12, and 20 weeks and Sprague Dawley (SD) rats of age 6 and 20 weeks, baseline eye tissue fluorescence and retinal thickness were recorded noninvasively using fluorophotometry and optical coherence tomography (OCT), respectively. Further, 20-nm carboxylate-modified fluorescent particles were injected intravitreally in the above groups of rats, and the depth-wise fluorescence signal was monitored over 7 days using fluorophotometry and confocal laser scanning ophthalmoscopy (cSLO). Additionally, 200 nm particles of the same material were injected intravitreally into about 7-week-old RCS rats and the fluorescence signal was monitored up to 35 days using fluorophotometry. Results: Reduction in retinal thickness and an increase in choroid-retina and lens baseline fluorescence was observed with increasing age of RCS and SD rats. The 20 nm particles persisted in the vitreous of animals from all age groups for at least 7 days postadministration, irrespective of the differences in retinal thickness. cSLO confirmed nanoparticle persistence in the eye. The fluorescence signal from 200 nm particles persisted for 35 days in the vitreous humor. Conclusions: Choroid-retina and lens autofluorescence monitored using fluorophotometry increase with age. Intravitreally injected nanoparticles can be monitored noninvasively in rats using fluorophotometry and cSLO imaging. Both 20 and 200 nm particles persist in the back of the eye tissues, for several days following intravitreal injection.

Suprachoroidally injected pharmacological agents for the treatment of chorio-retinal diseases: a targeted approach

Delivery of pharmaceuticals to the posterior segment presents challenges that arise from the anatomy and clearance pharmacokinetics of the eye. Systemic and several local administration options [topical, periocular, intravitreal (IVT) and subretinal] are in clinical use, each with a unique benefit to risk profile shaped by factors including the administered agent, frequency of dosing, achievable pharmaceutical concentrations within posterior segment structures versus elsewhere in the eye or the body, invasiveness of the procedure and the inherent challenges with some administration methods. The use of the suprachoroidal space (SCS), which is the region between the sclera and the choroid, is being explored as a potential approach to target pharmacotherapies to the posterior segment via a minimally invasive injection procedure. Preclinical data on agents such as vascular endothelial growth factor inhibitors and triamcinolone acetonide (TA) indicate that administration via suprachoroidal injection results in more posterior distribution of the pharmacologic agent, with higher exposure to the sclera, choroid, retinal pigment epithelium cells and retina, and lesser exposure to the anterior segment, than observed with IVT administration. Based in part on these findings, clinical trials have explored the efficacy and safety of suprachoroidal administration of pharmacologic therapies in conditions affecting the posterior segment. Data on a proprietary formulation of TA administered by suprachoroidal injection show improvement in anatomic and visual outcomes in subjects with noninfectious uveitis, with the potential to mitigate the known risks of cataract and increased intraocular pressure (IOP) associated with the use of intraocular corticosteroids. Suprachoroidal administration appears to be a promising treatment modality and is also in the early stages of investigation for other possible applications, such as injection of antiglaucoma agents into the anterior SCS for long-lasting control of elevated IOP, and as a mode of delivery for gene- or cell-based therapies for retinal disorders.

Targeted Drug Delivery in the Suprachoroidal Space by Swollen Hydrogel Pushing

Purpose

The purpose is to target model drug particles to the posterior region of the suprachoroidal space (SCS) of the eye controlled via pushing by hydrogel swelling.

Methods

A particle formulation containing 1% hyaluronic acid (HA) with fluorescent polymer particles and a hydrogel formulation containing 4% HA were introduced in a single syringe as two layers without mixing, and injected sequentially into the SCS of the rabbit eye ex vivo and in vivo using a microneedle. Distribution of particles in the eye was determined by microscopy.

Results

During injection, the particle formulation was pushed toward the middle of the SCS by the viscous hydrogel formulation, but less than 12% of particles reached the posterior SCS. After injection, the particle formulation was pushed further toward the macula and optic nerve in the posterior SCS by hydrogel swelling and spreading. Heating the eye to 37°C, or injecting in vivo decreased viscosity and mechanical strength of the hydrogel, thereby allowing it to swell and flow further in the SCS. A high salt concentration (9% NaCl) in the hydrogel formulation further increased hydrogel swelling due to osmotic flow into the hydrogel. In this way, up to 76% of particles were delivered to the posterior SCS from an injection made near the limbus.

Conclusions

This study shows that model drug particles can be targeted to the posterior SCS by HA hydrogel swelling and pushing without particle functionalization or administering external driving forces.

The route of administration influences the therapeutic index of an anti-proNGF neutralizing mAb for experimental treatment of Diabetic Retinopathy

Many neurodegenerative retinal diseases are treated with monoclonal antibodies (mAb) delivered by invasive intravitreal injection (IVT). In Diabetic Retinopathy there is a scarcity of effective agents that can be delivered using non-invasive methods, and there are significant challenges in the validation of novel therapeutic targets. ProNGF represents a potential novel target, and IVT administration of a function-blocking anti-proNGF mAb is therapeutic in a mouse model of DR. We therefore compared invasive IVT to less invasive systemic intravenous (IV) and local subconjunctival (SCJ) administration, for therapy of Diabetic Retinopathy. The IV and SCJ routes are safe, afford sustained pharmacokinetics and tissue penetration of anti-proNGF mAb, and result in long–term therapeutic efficacy that blocks retinal inflammation, edema, and neuronal death. SCJ may be a more convenient and less-invasive approach for ophthalmic use and may enable reduced frequency of intervention for the treatment of retinal pathologies.

Transcleral approach for closing retinal tears using DuraSeal™ hydrogel sealant

Purpose:

The aim of this study was to evaluate an innovative approach for closing retinal tears using DuraSeal™ (DS) hydrogel sealant in a rabbit model.

Methods:

Retinal detachment with a small tear was performed on 20 New Zealand rabbits. Thereafter, rabbits were divided into two groups; the experimental group received a transscleral injection of 0.1 ml DS into the subretinal space whereas the control group received sham injection of saline. Eyes were clinically evaluated using indirect ophthalmoscopy, retinal function was recorded in ten rabbits by electroretinography and the sealant's toxicity was evaluated histopathologically.

Results:

We found that the DS hydrogel was easily injected transsclerally into the subretinal space of the detached retinas with no major complications. Retinal reattachment was seen in both groups within 2 weeks with no toxicity to the sensory retina. There were no significant differences in retinal function between groups.

Conclusion:

Subretinal injection of hydrogel through a transscleral route is easy to perform and may open a new avenue in the treatment of retinal detachment. However, the efficacy of the DS as a tamponade for sealing retinal tear is yet to be definite. Long-term clinical, functional, and toxicological studies are needed to evaluate its full potential for clinical applications.

Ocular drug delivery targeted by iontophoresis in the suprachoroidal space using a microneedle

Treatment of many posterior-segment ocular indications would benefit from improved targeting of drug delivery to the back of the eye. Here, we propose the use of iontophoresis to direct delivery of negatively charged nanoparticles through the suprachoroidal space (SCS) toward the posterior pole of the eye. Injection of nanoparticles into the SCS of the rabbit eye ex vivo without iontophoresis led to a nanoparticle distribution mostly localized at the site of injection near the limbus and <15% of nanoparticles delivered to the most posterior region of SCS (>9 mm from the limbus). Iontophoresis using a novel microneedle-based device increased posterior targeting with >30% of nanoparticles in the most posterior region of SCS. Posterior targeting increased with increasing iontophoresis current and increasing application time up to 3 min, but further increasing to 5 min was not better, probably due to the observed collapse of the SCS within 5 min after injection ex vivo. Reversing the direction of iontophoretic flow inhibited posterior targeting, with just ~5% of nanoparticles reaching the most posterior region of SCS. In the rabbit eye in vivo, iontophoresis at 0.14 mA for 3 min after injection of a 100 μL suspension of nanoparticles resulted in ~30% of nanoparticles delivered to the most posterior region of the SCS, which was consistent with ex vivo findings. The procedure was well tolerated, with only mild, transient tissue effects at the site of injection. We conclude that iontophoresis in the SCS using a microneedle has promise as a method to target ocular drug delivery within the eye, especially toward the posterior pole.

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.

In vitro and ex vivo models to study drug delivery barriers in the posterior segment of the eye

Many ocular disorders leading to blindness could benefit from efficient delivery of therapeutics to the retina. However, despite extensive research into drug delivery vehicles and administration techniques, efficacy remains limited because of the many static and dynamic barriers present in the eye. Comprehension of the various barriers and especially how to overcome them can improve our ability to estimate the potential of existent drug delivery vectors and support the design of new ones. To this end, this review gives an overview of the most important ocular barriers for each administration route to the back of the eye. For each barrier, its biological composition and its role as an obstacle towards macromolecules, nanoparticles and viral vectors will be discussed; special attention will be paid to the influence of size, charge and lipophilicity of drug(s) (carrier) on their ability to overcome each barrier. Finally, the most significant available in vitro and ex vivo methods and models to test the potential of a therapeutic to cross each barrier are listed.

The suprachoroidal space as a route of administration to the posterior segment of the eye

The suprachoroidal space (SCS) is a potential space between the sclera and choroid that traverses the circumference of the posterior segment of the eye. The SCS is an attractive site for drug delivery because it targets the choroid, retinal pigment epithelium, and retina with high bioavailability, while maintaining low levels elsewhere in the eye. Indeed, phase III clinical trials are investigating the safety and efficacy of SCS drug delivery. Here, we review the anatomy and physiology of the SCS; methods to access the SCS; kinetics of SCS drug delivery; strategies to target within the SCS; current and potential clinical indications; and the safety and efficacy of this approach in preclinical animal studies and clinical trials.

Choroidal Changes After Suprachoroidal Injection of Triamcinolone Acetonide in Eyes With Macular Edema Secondary to Retinal Vein Occlusion

PURPOSE

To evaluate choroidal and suprachoroidal changes following suprachoroidal injection of triamcinolone acetonide injectable suspension (CLS-TA), in eyes with macular edema due to retinal vein occlusion (RVO).

DESIGN

Prospective cohort study within a randomized, controlled phase 2 clinical trial.

METHODS

Enhanced depth imaging optical coherence tomography (EDI-OCT) images were analyzed from 38 eyes of 38 treatment-naïve patients with macular edema due to RVO, enrolled in the prospective Suprachoroidal Injection of Triamcinolone Acetonide with Intravitreal Aflibercept in Subjects with Macular Edema Due to Retinal Vein Occlusion (TANZANITE) study who received either a suprachoroidal injection of CLS-TA with an intravitreal injection of aflibercept (combination arm) or only an intravitreal injection of aflibercept (monotherapy arm), followed by monthly intravitreal aflibercept injections in both arms based on pro re nata criteria.

RESULTS

Macular choroidal thickness measured to the outer choroidal vessel lumen (vascular choroidal thickness, VCT), outer choroid stroma (stromal choroidal thickness, SCT), or inner scleral border (total choroidal thickness, TCT) showed no significant changes over 3 months in both study arms (P = .231-.342). Eyes that received combination therapy showed a trend toward thickening of the suprachoroidal space (SCS) compared with monotherapy alone (13.4 μm vs 5.3 μm at 3 months; P = .077). In the 15 eyes that demonstrated a visible SCS at baseline, the SCS expanded significantly after suprachoroidal CLS-TA injection (16.2 μm to 27.8 μm at 3 months; P = .033).

CONCLUSIONS

Suprachoroidal injection of CLS-TA does not alter choroidal thickness in eyes with macular edema due to RVO, but may result in expansion of the SCS.

Clearance Kinetics and Clearance Routes of Molecules From the Suprachoroidal Space After Microneedle Injection

Purpose

To determine clearance kinetics and routes of clearance of molecules from the suprachoroidal space (SCS) of live New Zealand White rabbits.

Methods

Suprachoroidal space collapse rate and pressure changes after microneedle injection into SCS were determined. Fluorescent fundus images were acquired to determine clearance rates of molecules ranging in size from 332 Da to 2 MDa. Microneedle injections of fluorescein were performed, and samples were taken from various sites over time to determine amount of fluorescein exiting the eye. Clearance transport was modeled theoretically and compared with experimental data.

Results

After injection, pressures in SCS and vitreous humor spiked and returned to baseline within 20 minutes; there was no difference between these two pressures. Suprachoroidal space collapse occurred within 40 minutes. One hour after fluorescein injection, 46% of fluorescein was still present in the eye, 15% had transported across sclera, 6% had been cleared by choroidal vasculature, and 4% had exited via leakage pathways. Characteristic clearance time increased in proportion with molecular radius, but total clearance of 2 MDa FITC-dextran was significantly slower (21 days) than smaller molecules. These data generally agreed with predictions from a theoretical model of molecular transport.

Conclusions

Guided by experimental data in the context of model predictions, molecular clearance from SCS occurred in three regimes: (1) on a time scale of approximately 10 minutes, fluid and molecules exited SCS by diffusion into sclera and choroid, and by pressure-driven reflux via transscleral leakage sites; (2) in approximately 1 hour, molecules cleared from choroid by blood flow; and (3) in 1 to 10 hours, molecules cleared from sclera by diffusion and convection.

Thickness and Closure Kinetics of the Suprachoroidal Space Following Microneedle Injection of Liquid Formulations

Purpose

To determine the effect of injection volume and formulation of a microneedle injection into the suprachoroidal space (SCS) on SCS thickness and closure kinetics.

Methods

Microneedle injections containing 25 to 150 μL Hanks' balanced salt solution (HBSS) were performed in the rabbit SCS ex vivo. Distribution of SCS thickness was measured by ultrasonography and three-dimensional (3D) cryo-reconstruction. Microneedle injections were performed in the rabbit SCS in vivo using HBSS, Discovisc, and 1% to 5% carboxymethyl cellulose (CMC) in HBSS. Ultrasonography was used to track SCS thickness over time.

Results

Increasing HBSS injection volume increased the area of expanded SCS, but did not increase SCS thickness ex vivo. With SCS injections in vivo, the SCS initially expanded to thicknesses of 0.43 ± 0.06 mm with HBSS, 1.5 ± 0.4 mm with Discovisc, and 0.69 to 2.1 mm with 1% to 5% CMC. After injection with HBSS, Discovisc, and 1% CMC solution, the SCS collapsed to baseline with time constants of 19 minutes, 6 hours, and 2.4 days, respectively. In contrast, injections with 3% to 5% CMC solution resulted in SCS expansion to 2.3 to 2.8 mm over the course of 2.8 to 9.1 hours, after which the SCS collapsed to baseline with time constants of 4.5 to 9.2 days.

Conclusions

With low-viscosity formulations, SCS expands to a thickness that remains roughly constant, independent of the volume of fluid injected. Increasing injection fluid viscosity significantly increased SCS thickness. Expansion of the SCS is hypothesized to be controlled by a balance between the viscous forces of the liquid formulation and the resistive biomechanical forces of the tissue.

Past, Present, and Future Concepts of the Choroidal Scleral Interface Morphology on Optical Coherence Tomography

The choroid is the most vascular tissue in the eye and it has been implicated in the pathophysiology of a variety of ocular diseases. A new era of research in the choroid began with the improved ability to visualize this layer and its inner and outer boundaries using spectral domain optical coherence tomography (OCT) with enhanced depth imaging and swept source OCT. The accuracy and precision of qualitative and quan-titative assessments of the choroidal layer support the potential use of OCT-derived choroidal parameters for diagnosis, monitoring of disease progression, planning surgical access, and evaluating treatment response. Although there is increasing interest in measuring choroidal thickness, there is currently no consensus nomenclature to classify choroidal layers and boundaries. Furthermore, the definition and description of the choroidal scleral interface is inconsistent in the literature, contributing to interstudy variation in choroidal thickness measurements. The purpose of this review is to provide an overview of the literature on the definition of choroidal layers and choroidal scleral boundary, review the discrepan-cies, and harmonize the terminology so that a consensus nomenclature can be proposed.

Nanomedicine in the application of uveal melanoma

Rapid advances in nanomedicine have significantly changed many aspects of nanoparticle application to the eye including areas of diagnosis, imaging and more importantly drug delivery. The nanoparticle-based drug delivery systems has provided a solution to various drug solubility-related problems in ophthalmology treatment. Nanostructured compounds could be used to achieve local ocular delivery with minimal unwanted systematic side effects produced by taking advantage of the phagocyte system. In addition, the in vivo control release by nanomaterials encapsulated drugs provides prolong exposure of the compound in the body. Furthermore, certain nanoparticles can overcome important body barriers including the blood-retinal barrier as well as the corneal-retinal barrier of the eye for effective delivery of the drug. In summary, the nanotechnology based drug delivery system may serve as an important tool for uveal melanoma treatment.

Dexamethasone – PAMAM dendrimer conjugates for retinal delivery: preparation, characterization and in vivo evaluation

Objective

Ocular diseases affecting retina, such as diabetic retinopathy (DR), age-related macular degeneration (AMD) and glaucoma are the major causes of blindness, and their treatment is still a challenge due to the special structure of the eye. The purpose of this study was to prepare a sustained release DEX conjugate formulation with enhanced ocular permeation using poly(amidoamine) (PAMAM) dendrimers and to evaluate the effects of conjugation on DEX release and ocular residence time.

Methods

PAMAM G3.5 and PAMAM G4.5 dendrimers were used to prepare DEX conjugates, and conjugation was confirmed using 1H-NMR. Formulations were evaluated in terms of drug release in the presence of ocular enzymes and cytotoxicity on ARPE19 cell lines. Fluorotron analysis was performed and ocular pharmacokinetic properties of DEX–PAMAM conjugates were studied in Sprague Dawley rats following intravitreal and subconjunctival applications.

Key Findings

The results indicated that DEX–PAMAM conjugates were able to enhance ocular permeability and ocular tissue levels of DEX following subconjunctival injection, and results were encouraging when compared to the literature that has reported DEX getting cleared from vitreous in 3 h.

Conclusion

Current studies are focused on formulation improvement to enhance hydrolysis and clearance time.

Swept-Source Optical Coherence Tomography Correlations Between Retina and Choroid Before and After Vitrectomy for Epiretinal Membranes

PURPOSE

To describe retinal and choroidal morphology before and after surgery for epiretinal membranes (ERM) in swept-source OCT (SS-OCT). Additionally, to evaluate factors responsible for visibility of the suprachoroidal layer (SCL) and suprachoroidal space (SCS).

DESIGN

Prospective consecutive case series.

METHODS

Twenty-nine eyes of 29 patients with symptomatic, idiopathic ERM were included. Pars plana vitrectomy with ERM removal and ILM peeling was performed. We examined patients with SS-OCT twice preoperatively (9-12 months and 1 week before surgery), then postoperatively at 1 week and 6 and 12 months.

RESULTS

Twelve months after surgery visual acuity improved to 20/50 (0.48 logMAR), statistically significantly higher as compared to 1 week preoperatively (P < .001). Preoperative loss of visual acuity was commonly associated with progression of deformation of the plexiform layers, as central retinal thickness (CRT) did not decrease in this period, nor did photoreceptor defects increase. Choroidal thickness decreased 6 months after surgery (P = .02) and remained stable until 12 months postoperatively (P = .2). The outer choroidoscleral boundary was irregular in 16 eyes preoperatively but only in 4 eyes 12 months post surgery. SCS and SCL were visible in 15 eyes.

CONCLUSION

During the natural course of idiopathic ERM, deformation of the outer plexiform layer progresses and is associated with decreased visual acuity. Eyes with an initially irregular outer choroidoscleral boundary (CSB) recover visual acuity faster after vitrectomy with ILM peeling for ERM. Three factors are independently associated with the visibility of the SCS: disarrangement of plexiform layers, CRT, and multiple adhesion points between retina and ERM.

Specialized Diagnostic Investigations to Assess Ocular Status in Hypertensive Diseases of Pregnancy

This review describes specialized diagnostic investigations to assess ocular status in hypertensive diseases of pregnancy. Ocular assessment can aid in early detection for prompt multidisciplinary treatment, obstetric intervention and follow-up. The investigations accurately predict the possible causes of blindness in hypertensive diseases of pregnancy. The investigations include fluorescein angiography, ophthalmodynamometry, fluorophotometry, imaging modalities, OCT, ultrasonography, doppler velocimetry and blood chemistry analysis. The review includes a summary of imaging techniques and related recent developments to assess the neuro-ophthalmic aspects of the disease. The imaging modalities have been instrumental in understanding the complex neuropathophysiological mechanisms of eclamptic seizures. The importance of blood chemistry analysis in hypertensive diseases of pregnancy has been emphasized. The investigations have made a significant contribution in improving the standards of antenatal care and reducing maternal and fetal morbidity and mortality.

Circumferential flow of particles in the suprachoroidal space is impeded by the posterior ciliary arteries

Microneedle injection into the suprachoroidal space (SCS) enables targeted drug delivery for treatment of posterior segment diseases. This study sought to identify and characterize anatomical barriers to circumferential spread of particles in the SCS of rabbit and human cadaver eyes. These barriers could make targeting specific regions within the SCS challenging. A hollow microneedle (33-gauge, 750 μm long) was used to inject fluorescent particles into albino New Zealand White rabbit eyes ex vivo at six different positions around the limbus and a limited number of conditions in vivo. SCS injections were also performed in human cadaver eyes 8 mm and 2 mm from the optic nerve (ON). Eyes were dissected and particle distribution was quantified. In rabbit eyes, injections made in the superior or inferior hemispheres (even when injected temporally immediately adjacent to the long posterior ciliary artery (LPCA)) did not significantly cross into the other hemisphere, apparently due to a barrier formed by the LPCA. The vortex veins had a minor effect on particle deposition, limited to only around the vortex vein root. In human eyes, the short posterior ciliary arteries (SPCAs) prevented circumferential spread towards the macula and ON. In conclusion, the rabbit LPCA and the human SPCA were anatomical barriers to particle spread within the SCS. Therefore, design of drug delivery protocols targeting the SCS need to account for barriers formed by anatomical structures in order for injected drug to reach target tissues.

Anti-tubercular therapy for intraocular tuberculosis: A systematic review and meta-analysis

Intraocular tuberculosis remains a diagnostic and management conundrum for both ophthalmologists and pulmonologists. We analyze the efficacy and safety of anti-tubercular therapy (ATT) in patients with intraocular tuberculosis and factors associated with favorable outcome. Twenty-eight studies are included in this review, with a total of 1,917 patients. Nonrecurrence of inflammation was observed in pooled estimate of 84% of ATT-treated patients (95% CI 79-89). There was minimal difference in the outcome between patients treated with ATT alone (85% successful outcome; 95% CI 25-100) and those with concomitant systemic corticosteroid (82%; 95% CI 73-90). The use of ATT may be of benefit to patients with suspected intraocular tuberculosis; however, this conclusion is limited by the lack of control group analysis and standardized recruitment and treatment protocols. We propose further prospective studies to better establish the efficacy of ATT and ascertain the factors associated with favorable treatment outcomes.

Imaging Suprachoroidal Layer in Exudative Age-Related Macular Degeneration

PURPOSE

To evaluate the prevalence of a visible suprachoroidal layer (SCL) on optical coherence tomography (OCT) in exudative age-related macular degeneration (AMD).

MATERIALS AND METHODS

This retrospective study included 252 eyes of 252 patients with treatment-naive typical exudative AMD (n = 80), polypoidal choroidal vasculopathy (PCV) (n = 138) and retinal angiomatous proliferation (RAP) (n = 34). The presence of SCL was identified based on enhanced-depth imaging OCT images, and the prevalence was compared among the three disease groups. In addition, subfoveal choroidal thickness was compared between patients with and without SCL.

RESULTS

The SCL was noted in 56 eyes (22.2%). The prevalence was 22.5% in typical exudative AMD (18 of 80 eyes), 18.8% in PCV (26 of 138 eyes) and 35.3% in RAP (12 of 34 eyes) (p = 0.118). Patients with SCL showed significantly thinner choroid (207.5 ± 83.9 µm versus 279.7 ± 116.5 µm, p < 0.001) and were relatively older (72.1 ± 8.1 versus 70.1 ± 8.7 years, p = 0.124) than those without SCL.

CONCLUSION

The prevalence of visible SCL was 22.2% in patients with exudative AMD. Age-related changes, including choroidal thinning, may contribute to the development of a visible SCL.

Safety and pharmacodynamics of suprachoroidal injection of triamcinolone acetonide as a controlled ocular drug release model

Suprachoroidal injection is an emerging technique for drug delivery to the posterior segment, which is hard to reach by non-invasive approaches. However, the injection technique varies and the associated ocular safety is not well understood. In addition, it is not clear if drug formulation is a major factor in optimizing pharmacodynamics using this technique. The current study was designed to compare the suprachoroidal injection of different drug formulations and to characterize the safety and pharmacodynamics of triamcinolone acetonide (TA) delivered by this technique. Both indocyanine green (ICG) solution and TA suspension, at 50μL, 100μL, and 150μL, were suprachoroidally injected and intraocular pressure (IOP) tonometry, fundus photography, and electroretinography were performed over multiple time points up to eight weeks. After 50μL TA (Kenalog-40) suprachoroidal injection, 4-5 animals at 7 time points were sacrificed for aqueous, vitreous, retina, and plasma collections. TA was quantitated using ultra-performance liquid chromatography tandem mass spectrometry. For comparative efficacy study, 50μL (2mg) suprachoroidal TA versus 20mg subtenon TA were performed 4weeks before induction of experimental uveitis with 10ng of intravitreal lipopolysaccharide. After suprachoroidal injection, IOP had an acute elevation, higher volume caused higher IOP (p<0.0001). Equivalent volume of ICG solution led to a significantly smaller IOP elevation than after TA suprachoroidal injection. This finding suggests better distribution of ICG solution than TA suspension in the suprachoroidal space. Following a 50μL suprachoroidal injection, peak TA concentration in the aqueous was below 1ng/mL. In contrast, the posterior vitreous and retina had 1912ng/mL and 400,369ng/mL TA, respectively. Maximum TA in plasma was 11.6ng/mL. Drug exposure to the posterior retina was 523,910 times more than that to the aqueous and 29,516 times more than systemic TA exposure. In the treatment of lipopolysaccharide-induced uveitis, compared with 20mg subtenon injection, suprachoroidal 2mg TA demonstrated much better efficacy with significantly less aqueous humor cells and lower vitreous opacity scores (p<0.05). Histology showed much less vitreous inflammation in the suprachoroidal injection group (p<0.0001). It seems that a 50μL suprachoroidal injection of TA was well tolerated in rabbit eyes and demonstrated excellent penetration into the posterior retina, providing better therapeutic effect than subtenon 20mg TA.

Nanoparticles in porous microparticles prepared by supercritical infusion and pressure quench technology for sustained delivery of bevacizumab

Nanoparticles in porous microparticles (NPinPMP), a novel delivery system for sustained delivery of protein drugs, was developed using supercritical infusion and pressure quench technology, which does not expose proteins to organic solvents or sonication. The delivery system design is based on the ability of supercritical carbon dioxide (SC CO2) to expand poly(lactic-co-glycolic) acid (PLGA) matrix but not polylactic acid (PLA) matrix. The technology was applied to bevacizumab, a protein drug administered once a month intravitreally to treat wet age related macular degeneration. Bevacizumab coated PLA nanoparticles were encapsulated into porosifying PLGA microparticles by exposing the mixture to SC CO2. After SC CO2 exposure, the size of PLGA microparticles increased by 6.9-fold. Confocal and scanning electron microscopy studies demonstrated the expansion and porosification of PLGA microparticles and infusion of PLA nanoparticles inside PLGA microparticles. In vitro release of bevacizumab from NPinPMP was sustained for 4 months. Size exclusion chromatography, fluorescence spectroscopy, circular dichroism spectroscopy, SDS-PAGE, and ELISA studies indicated that the released bevacizumab maintained its monomeric form, conformation, and activity. Further, in vivo delivery of bevacizumab from NPinPMP was evaluated using noninvasive fluorophotometry after intravitreal administration of Alexa Fluor 488 conjugated bevacizumab in either solution or NPinPMP in a rat model. Unlike the vitreal signal from Alexa-bevacizumab solution, which reached baseline at 2 weeks, release of Alexa-bevacizumab from NPinPMP could be detected for 2 months. Thus, NPinPMP is a novel sustained release system for protein drugs to reduce frequency of protein injections in the therapy of back of the eye diseases.

Light-activated, in situ forming gel for sustained suprachoroidal delivery of bevacizumab

A light-activated polycaprolactone dimethacrylate (PCM) and hydroxyethyl methacrylate (HEMA) based gel network was developed to sustain the release of stable, active bevacizumab (an anti-VEGF antibody used to treat choroidal neovascularization) and used to assess sustained ex vivo delivery in rabbit eyes and in vivo delivery in rat eyes following in situ gel formation in the suprachoroidal space. PCM was synthesized from polycaprolactone diol (PCD) and evaluated using NMR spectroscopy. PCM was used to cross-link HEMA in the presence of 365 nm UV light and 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a photoinitiator. Bevacizumab was entrapped in the gel using three different cross-linking durations of 3, 7, and 10 min. In vitro release of bevacizumab in PBS pH 7.4 at 37 °C during a 4 month study was quantified using a VEGF-binding based ELISA. The stability of released bevacizumab was monitored by size exclusion chromatography (SEC) and circular dichroism. Alexa Fluor 488 dye conjugated bevacizumab mixed with polymers was injected suprachoroidally in rabbit eyes to study the effect of different cross-linking durations on the spread of the dye conjugated bevacizumab. In vivo delivery was assessed in Sprague-Dawley (SD) rats by injecting Alexa Fluor 488 dye conjugated bevacizumab mixed with polymers followed by cross-linking for 10 min. Spread in the rabbit eyes and in vivo delivery in rat eyes was monitored noninvasively using a fundus camera and Fluorotron Master. The formation of PCM was confirmed by the disappearance of hydroxyl peak in NMR spectra. A cross-linking duration of 10 min resulted in a burst release of 21% of bevacizumab. Other cross-linking durations had ≥62% burst release. Bevacizumab release from 10 min cross-linked gel was sustained for ∼4 months. Release samples contained ≥96.1% of bevacizumab in the monomeric form as observed in SEC chromatograms. Circular dichroism confirmed that secondary β-sheet structure of bevacizumab was maintained after release from the gel. As the cross-linking duration was increased to 10 min, the gel/antibody was better confined at the injection site in excised rabbit eye suprachoroidal space. Delivery of Alexa Fluor 488 dye conjugated bevacizumab was sustained for at least 60 days in the suprachoroidal space of SD rats. PCM and HEMA gel sustained bevacizumab release for 4 months and maintained the stability and VEGF-binding activity of bevacizumab. Therefore, light-activated PCM and HEMA gel is suitable for in situ gel formation and sustained protein delivery in the suprachoroidal space.

Effect of choroidal perfusion on ocular tissue distribution after intravitreal or suprachoroidal injection in an arterially perfused ex vivo pig eye model

PURPOSE

To compare tissue distribution of dye-drug surrogates after intravitreal (IVT) and suprachoroidal (SCS) delivery to determine the influence of drug lipophilicity and choroidal circulation.

METHODS

Thirty-two pig eyes were collected immediately after euthanasia. Sixteen eyes were perfused for 30 min through one long posterior ciliary artery with nondye containing nutrient media. An IVT or SCS injection was performed with either a 100 μL balanced salt solution (BSS, n=8), 1% sodium fluorescein (NaF, n=12) or 0.12% lipophilic carbocyanine dye (DiI, n=12). Globes were maintained at 37°C for 15 min, and then snap-frozen and dissected. Aqueous extraction and measurement of NaF or DiI concentration was performed using spectrophotometry and spectrofluorometry, respectively.

RESULTS

After SCS delivery of NaF scleral, iris-ciliary body, choroidal and vitreous dye levels were higher in nonperfused eyes compared to perfused eyes. After DiI SCS or IVT delivery, no significant differences were found in dye tissue concentrations in perfused eyes compared to nonperfused eyes. Following perfusion, a better and even drug distribution was found in the retinal pigmented epithelium (RPE)-choroid following IVT and SCS delivery of the hydrophilic drug and after IVT injection of the lipophilic drug compared to nonperfused eyes.

CONCLUSIONS

Choroidal circulation reduces the tissue drug concentration of the hydrophilic drug suggesting an early clearance mechanism after SCS delivery. SCS injections of lipid and hydrophilic drugs allowed direct drug delivery to the retina and RPE-choroid with limited exposition to the anterior segment.

Nanomedicines for back of the eye drug delivery, gene delivery, and imaging

Treatment and management of diseases of the posterior segment of the eye such as diabetic retinopathy, retinoblastoma, retinitis pigmentosa, and choroidal neovascularization is a challenging task due to the anatomy and physiology of ocular barriers. For instance, traditional routes of drug delivery for therapeutic treatment are hindered by poor intraocular penetration and/or rapid ocular elimination. One possible approach to improve ocular therapy is to employ nanotechnology. Nanomedicines, products of nanotechnology, having at least one dimension in the nanoscale include nanoparticles, micelles, nanotubes, and dendrimers, with and without targeting ligands. Nanomedicines are making a significant impact in the fields of ocular drug delivery, gene delivery, and imaging, the focus of this review. Key applications of nanotechnology discussed in this review include a) bioadhesive nanomedicines; b) functionalized nanomedicines that enhance target recognition and/or cell entry; c) nanomedicines capable of controlled release of the payload; d) nanomedicines capable of enhancing gene transfection and duration of transfection; f) nanomedicines responsive to stimuli including light, heat, ultrasound, electrical signals, pH, and oxidative stress; g) diversely sized and colored nanoparticles for imaging, and h) nanowires for retinal prostheses. Additionally, nanofabricated delivery systems including implants, films, microparticles, and nanoparticles are described. Although the above nanomedicines may be administered by various routes including topical, intravitreal, intravenous, transscleral, suprachoroidal, and subretinal routes, each nanomedicine should be tailored for the disease, drug, and site of administration. In addition to the nature of materials used in nanomedicine design, depending on the site of nanomedicine administration, clearance and toxicity are expected to differ.