Noninvasive Ocular Drug Delivery System of Dexamethasone Sodium Phosphate in the Treatment of Experimental Uveitis Rabbit

Retinal Diseases: The Next Frontier in Pharmacodelivery

The future continuous growth of the global older population augments the burden of retinal diseases worldwide. Retinal characteristics isolating and protecting the sensitive neuro-retina from the rest of the ocular tissues challenge drug delivery and promote research and development toward new horizons. In this review, we wish to describe the unmet medical needs, discuss the novel modes of delivery, and disclose to the reader a spectrum of older-to-novel drug delivery technologies, innovations, and the frontier of pharmacodelivery to the retina. Treating the main retinal diseases in the everlasting war against blindness and its associated morbidity has been growing steadily over the last two decades. Implants, new angiogenesis inhibitor agents, micro- and nano-carriers, and the anchored port delivery system are becoming new tools in this war. The revolution and evolution of new delivery methods might be just a few steps ahead, yet its assimilation in our daily clinical work may take time, due to medical, economical, and regulatory elements that need to be met in order to allow successful development and market utilization of new technologies. Therefore, further work is warranted, as detailed in this Pharmaceutics Special Issue.

Ocular Drug Delivery to the Retina: Current Innovations and Future Perspectives

Treatment options for retinal diseases, such as neovascular age-related macular degeneration, diabetic retinopathy, and retinal vascular disorders, have markedly expanded following the development of anti-vascular endothelial growth factor intravitreal injection methods. However, because intravitreal treatment requires monthly or bimonthly repeat injections to achieve optimal efficacy, recent investigations have focused on extended drug delivery systems to lengthen the treatment intervals in the long term. Dose escalation and increasing molecular weight of drugs, intravitreal implants and nanoparticles, hydrogels, combined systems, and port delivery systems are presently under preclinical and clinical investigations. In addition, less invasive techniques rather than intravitreal administration routes, such as topical, subconjunctival, suprachoroidal, subretinal, and trans-scleral, have been evaluated to reduce the treatment burden. Despite the latest advancements in the field of ophthalmic pharmacology, enhancing drug efficacy with high ocular bioavailability while avoiding systemic and local adverse effects is quite challenging. Consequently, despite the performance of numerous in vitro studies, only a few techniques have translated to clinical trials. This review discusses the recent developments in ocular drug delivery to the retina, the pharmacokinetics of intravitreal drugs, efforts to extend drug efficacy in the intraocular space, minimally invasive techniques for drug delivery to the retina, and future perspectives in this field.

Sirolimus-Loaded Intravitreal Implant for Effective Treatment of Experimental Uveitis

Non-infectious uveitis, an ocular inflammatory condition that affects the iris, ciliary body, choroid, and adjacent tissues (retina, optic nerve, and vitreous), is an important cause of blindness worldwide. Sirolimus (SRL), a potent immunomodulatory drug, has shown promising results in the treatment of inflammatory ocular diseases. Despite this therapeutic potential, its clinical use is a major challenge due to low bioavailability and poor solubility. Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable polymer commonly used for ophthalmic drug delivery due to its suitable characteristics such as biocompatibility, good mechanical properties, and improvement of the pharmacokinetic profile of the drug. In the present study, we investigated the effects of SRL-PLGA implant on experimental autoimmune uveitis in rabbits. Clinical and histopathological examinations were performed, followed by assessment of protein levels and determination of myeloperoxidase (MPO) and N-acetylglucosaminidase (NAG) activity in the aqueous humor/vitreous. As a result, treated eyes had decreased average inflammatory scores, protein significant decreases in treated eyes, assessed after 35 days. Histopathological examination showed less severe intraocular inflammation and decreased tissue damage in treated eyes. According to these results, the SRL-PLGA implant evaluated in this study was apparently safe, reducing inflammation in treated eyes, with an extended effect possibly associated with prolonged release of SRL in the posterior segment of the eye. Therefore, intravitreal SRL-PLGA implant could be a promising alternative for treatment of non-infectious uveitis.

Development and Clinical Application of Phosphorus-Containing Drugs

Phosphorus-containing drugs belong to an important class of therapeutic agents and are widely applied in daily clinical practices. Structurally, the phosphorus-containing drugs can be classified into phosphotriesters, phosphonates, phosphinates, phosphine oxides, phosphoric amides, bisphosphonates, phosphoric anhydrides, and others; functionally, they are often designed as prodrugs with improved selectivity and bioavailability, reduced side effects and toxicity, or biomolecule analogues with endogenous materials and antagonistic endoenzyme supplements. This review summarized the phosphorus-containing drugs currently on the market as well as a few promising molecules at clinical studies, with particular emphasis on their structural features, biological mechanism, and indications.

A review of the clinical applications of drug delivery systems for the treatment of ocular anterior segment inflammation

Ocular anterior segment inflammation is a medical problem that is seen in cases of cataract surgery and non-infectious anterior uveitis. Inadequately treated anterior segment inflammation can lead to sight-threatening conditions such as corneal oedema, glaucoma and cystoid macular oedema. The mainstay of treatment for anterior segment inflammation is topical steroid eye-drops. However, several drawbacks limit the critical value of this treatment, including low bioavailability, poor patient compliance, relatively difficult administration manner and risk of blurring of vision and ocular irritation. A drug delivery system (DDS) that can provide increased bioavailability and sustained delivery while being specifically targeted towards inflamed ocular tissue can potentially replace daily eye-drops as the gold standard for management of anterior segment inflammation. The various DDS for anti-inflammatory drugs for the treatment of anterior segment inflammation are listed and summarised in this review, with a focus on commercially available products and those in clinical trials. Dextenza, INVELTYS, Dexycu and Bromsite are examples of DDS that have enjoyed success in clinical trials leading to FDA approval. Nanoparticles and ocular iontophoresis form the next wave of DDS that have the potential to replace topical steroids eye-drops as the treatment of choice for anterior segment inflammation. With the current relentless pace of ophthalmic drug delivery research, the pursuit of a new standard of treatment that eliminates the problems of low bioavailability and patient compliance may soon be realised.

Steroid-eluting contact lenses for corneal and intraocular inflammation

Ocular inflammation is one of the leading causes of blindness worldwide, and steroids in topical ophthalmic solutions (e.g. dexamethasone eye drops) are the mainstay of therapy for ocular inflammation. For many non-infectious ocular inflammatory diseases, such as uveitis, eye drops are administered as often as once every hour. The high frequency of administration coupled with the side effects of eye drops leads to poor adherence for patients. Drug-eluting contact lenses have long been sought as a potentially superior alternative for sustained ocular drug delivery; but loading sufficient drug into contact lenses and control the release of the drug is still a challenge. A dexamethasone releasing contact lens (Dex-Lens) was previously developed by encapsulating a dexamethasone-polymer film within the periphery of a hydrogel-based contact lens. Here, we demonstrate safety and efficacy of the Dex-Lens in rabbit models in the treatment of anterior ocular inflammation. The Dex-Lens delivered drug for 7 days in vivo (rabbit model). In an ocular irritation study (Draize test) with Dex-Lens extracts, no adverse events were observed in normal rabbit eyes. Dex-Lenses effectively inhibited suture-induced corneal neovascularization and inflammation for 7 days and lipopolysaccharide-induced anterior uveitis for 5 days. The efficacy of Dex-Lenses was similar to that of hourly-administered dexamethasone eye drops. In the corneal neovascularization study, substantial corneal edema was observed in rabbit eyes that received no treatment and those that wore a vehicle lens as compared to rabbit eyes that wore the Dex-Lens. Throughout these studies, Dex-Lenses were well tolerated and did not exhibit signs of toxicity. Dexamethasone-eluting contact lenses may be an option for the treatment of ocular inflammation and a platform for ocular drug delivery. STATEMENT OF SIGNIFICANCE: Inflammation of the eye can happen either on the ocular surface (i.e. the cornea) or inside the eye, both of which can result in loss of vision or even blindness. Ocular inflammation is normally treated by steroid eye drops. Depending on the type and severity of inflammation, patients may have to take drops every hour for days at a time. Such severe dosing regimen can lead to patients missing doses. Also, more than 95% drug in an eye drop never goes inside the eye. Here we present a contact lens that release a steroid (dexamethasone) for seven days at a time. It is much more efficient than eye drops and a significant improvement since once worn, the patient will avoid missing doses.

Efficacy of Sub-Tenon Micro-Perfusion of Cyclophosphamide in Rabbits with Severe Ocular Inflammation

Purpose

To explore the feasibility of cyclophosphamide (CP) via a sub-Tenon micro-perfusion system (SMS) in rabbits, and assess its therapeutic efficacy in severe ocular inflammation.

Materials and Methods

Distribution and pharmacokinetics of CP were evaluated in vivo, and the concentrations of CP in plasma, vitreous humor, and retina/choroid were quantitated by ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) at different time points. After induction of severe experimental uveitis, rabbits were divided into three groups (n=8 in each): the SMS group, subconjunctival injection (SI) group, and control group. Clinical inflammatory score was assessed in rabbits. Electroretinography and histopathology were performed on post-treatment day 8. Statistical analyses were performed using Mann–Whitney and Kruskal–Wallis tests. P-value less than 0.05 was considered significant.

Results

The concentrations of CP in vitreous humor and retina/choroid in the SMS group were significantly higher than that of the SI group at 3, 6, 10, and 24 hours (P<0.01), while plasmatic CP concentrations were comparable at all time points in the SMS group and SI group (P>0.05). The SMS group showed significantly less inflammation compared to the control group and SI group. Furthermore, the restoration of retinal structure and function were more obvious in the SMS group compared with conventional SI application.

Conclusion

Sub-Tenon micro-perfusion of CP exhibited satisfied therapeutic efficacy in rabbits with severe ocular inflammation and may provide a promising alternative for controlling ocular inflammatory disease and immune-mediated ocular diseases.

Transscleral Iontophoresis for Noninvasive Ocular Drug Delivery of Macromolecules

Purpose: The objectives were to investigate the effect of transscleral iontophoresis of macromolecules in vitro and in vivo, to study the importance of electroosmosis on macromolecules of low charge to mass ratio, and to evaluate transscleral iontophoresis efficacy in a choroidal neovascularization (CNV) animal model. Methods: Through in vitro transport experiments, the permeability coefficients of macromolecules [eg, immunoglobulin G (IgG), dextran 70 kDa] were determined under different conditions. The effect of ionic strength formulations and iontophoretic conditions was studied on the distribution of IgG and bevacizumab into the eye in vivo. Magnetic resonance imaging (MRI) was utilized to evaluate in vivo real time distribution of gadolinium-labeled albumin (Galbumin) following iontophoresis. The efficacy between no treatment, intravitreal injection (IVT), and iontophoresis of bevacizumab on a CNV model of subretinal injection of adeno-associated virus encoding human VEGF-165 was investigated. Results: The permeability data suggested a significant effect of ionic strength on the iontophoretic transport of macromolecules. Transscleral iontophoresis of IgG at 4 mA with a low ionic strength formulation was about 600 times greater than passive diffusion and 14-fold over a conventional formulation in vitro. Approximately 0.6 mg of bevacizumab can be delivered into the rabbit eye in vivo with a 20-min treatment of iontophoresis. MRI showed that Galbumin was in the posterior tissues after iontophoresis. In the CNV model, the iontophoresis and IVT methods of bevacizumab delayed retinal neovascularization by 4 and 8 weeks, respectively. Conclusions: Transscleral iontophoresis is capable of delivering macromolecule drugs through the conjunctiva and sclera, eventually exposing the retina/choroid to the drugs.

Sub-Tenon Sustained Controllable Delivery of Dexamethasone for Treating Severe Acute Experimental Uveitis

PURPOSE

To evaluate the efficacy of dexamethasone (DXM) through sub-tenon sustained controllable drug delivery system (SSCDDS) for treating severe acute experimental uveitis.

METHODS

Rabbits were treated with either DXM (treated group) or normal saline (control group) through SSCDDS. Clinical signs of uveitis were assessed at days 1, 3, 5, 7, and 14 after treatment. Histopathologic examinations were performed to evaluate inflammatory cell infiltration on posttreatment days 7 and 14.

RESULTS

All signs of experimental uveitis were reduced by SSCDDS of DXM according to clinical criteria, and the treated group had significantly less inflammation than the control group (p<0.05). Histopathologic examinations showed severe inflammation and marked inflammatory cell infiltration in the control group, but minimal inflammation in the treated group.

CONCLUSIONS

Sub-tenon sustained controllable delivery of DXM effectively suppresses severe acute inflammation in a rabbit model of uveitis. The proposed minimal invasive system might be a promising candidate for managing severe ocular diseases.

Novel Dexamethasone Sodium Phosphate Treatment (DSP-Visulex) for Noninfectious Anterior Uveitis: A Randomized Phase I/II Clinical Trial

PURPOSE

Frequent steroid drops represent a challenge in patient compliance. This study evaluated the safety and efficacy of 5 minute topical dexamethasone sodium phosphate-Visulex (DSP-Visulex) treatment regimen (two applications on the first week then weekly after) compared to daily prednisolone acetate 1% (PA) for noninfectious anterior uveitis.

MATERIALS AND METHODS

Forty-four patients were randomized to 8% DSP-Visulex with placebo eye drops (8% group, n = 14), 15% DSP-Visulex with placebo eye drops (15% group, n = 15), or Vehicle-Visulex with PA eye drops (PA group, n = 15). Patients received daily eye drops and Visulex treatments on days 1, 3, 8, and 15 with an optional treatment on day 22. Efficacy measures were change in anterior chamber cell (ACC) count from baseline and proportion of patients with zero ACC count at days 8, 15, and 29. Safety measures were adverse events (AEs), visual acuity, ocular symptoms, and intraocular pressure (IOP).

RESULTS

ACC resolution over time was similar among the three groups. The percentage of patients with clear ACC was 18%, 22%, and 15% on day 8; 27%, 56%, and 54% on day 15; and 90%, 88%, and 77% on day 29 for the 8%, 15%, and PA groups, respectively. The numbers of reported AEs were 10, 36, and 12 for the 8%, 15%, and PA groups, respectively. Ten patients among all groups experienced treatment-related AEs, which included headache, eye pain, corneal abrasion, conjunctival/corneal staining, conjunctivitis, visual acuity reduction, and keratitis all of which were resolved during the timeframe of patients' participation in the study. IOP elevation was noted in the PA group throughout the study, whereas IOP elevation in the DSP-Visulex groups was observed at day 3 but not thereafter.

CONCLUSIONS

The efficacy of the DSP-Visulex applications was comparable to the daily PA drops in the treatment of noninfectious anterior uveitis. Both 8% and 15% DSP-Visulex treatments were safe and well tolerated.

Ocular Drug Distribution and Safety of a Noninvasive Ocular Drug Delivery System of Dexamethasone Sodium Phosphate in Rabbit

PURPOSE

To determine the ocular toxicity, systemic exposure, and amounts of dexamethasone sodium phosphate (DSP) in ocular tissues after administration of DSP with the Visulex system (DSP-Visulex).

METHODS

DSP-Visulex was applied onto healthy rabbit eyes. DSP concentrations (4%, 8%, 15%, and 25%) and treatment durations (5, 10, and 20 min) were evaluated for the amounts of DSP in the ocular tissues and in plasma after single administrations of DSP-Visulex. The drug in eye tissues and plasma was analyzed by high-performance liquid chromatography-UV/VIS and by liquid chromatography-mass spectrometry, respectively. The safety and tolerability were ascertained based on clinical observations and histopathological examinations from repeat weekly DSP-Visulex treatments (4%, 8%, 15%, and 25% for 20 min) for 12 weeks.

RESULTS

Significant amounts of DSP (ie, higher than 1 μg/g) were found in the anterior chamber, retina-choroid, cornea, vitreous, conjunctiva, and sclera after single applications of DSP-Visulex. The DSP concentrations in the ocular tissues and in plasma increased with increased DSP concentrations in the Visulex applicator and with increased application times. Systemic DSP was rapidly detected. The plasma half-life was 2-3 h. C_max was 148 and 1,844 ng/mL, and the area under the plasma drug concentration versus time curve (AUC) was 418 and 3,779 ng · h/mL for the low dose (4% DSP-Visulex for 5 min) and the high dose (15% DSP-Visulex for 20 min), respectively. Ocular findings over 12 weeks were mostly conjunctival injection and eye discharge. These were transient and mild. Histopathological examinations indicated the eyes to be normal.

CONCLUSIONS

DSP can be administered safely and effectively into the rabbit eye with the Visulex system. Treatment duration and DSP concentration are important factors in achieving therapeutic levels. Repeat applications of DSP-Visulex are safe and well tolerated for weekly administrations over 4-12 weeks. DSP-Visulex has clinical potential for the noninvasive treatment of ocular diseases.