Retinal delivery of celecoxib is several-fold higher following subconjunctival administration compared to systemic administration

Comprehensive ocular and systemic pharmacokinetics of dexamethasone after subconjunctival and intravenous injections in rabbits

Even though subconjunctival injections are used in clinics, their quantitative pharmacokinetics has not been studied systematically. For this purpose, we evaluated the ocular and plasma pharmacokinetics of subconjunctival dexamethasone in rabbits. Intravenous injection was also given to enable a better understanding of the systemic pharmacokinetics. Dexamethasone concentrations in plasma (after subconjunctival and intravenous injections) and four ocular tissues (iris-ciliary body, aqueous humour, neural retina and vitreous) were analysed using LC-MS/MS. Population pharmacokinetic modelling for plasma data from both injection routes were used, and for first time the constant rate of absorption of dexamethasone from the subconjunctival space into plasma was estimated (ka,plasma = 0.043 min-1, i.e. absorption half-life of 17.3 min). Non-compartmental analysis was used for the ocular data analysis and resulting in ocular drug exposure of iris-ciliary body (AUC0-∞= 41984 min·ng/g) > neural retina (AUC0-∞= 25511 min·ng/g) > vitreous (AUC0-∞= 7319 min·ng/mL) > aqueous humour (AUC0-∞= 6146 min·ng/mL). The absolute bioavailability values after subconjunctival injection, reported for the first time, were 0.74 % in aqueous humour (comparable to topical dexamethasone suspensions), and 0.30 % in vitreous humour (estimated to be higher than in topical administration). These novel and comprehensive pharmacokinetic data provide valuable information on the potential for exploiting this route in ocular drug development for treating both, anterior and posterior segment ocular diseases. Moreover, the new generated dexamethasone-parameters are a step-forward in building predictive pharmacokinetic models to support the design of new subconjunctival dexamethasone formulations, which may sustain drug effect for longer period of time.

Challenges and Opportunities for Celecoxib Repurposing

Drug repositioning, also known as drug repurposing, reprofiling, or rediscovery, is considered to be one of the most promising strategies to accelerate the development of new original drug products. Multiple examples of successful rediscovery or therapeutic switching of old molecules that did not show clinical benefits or safety in initial trials encourage the following of the discovery of new therapeutic pathways for them. This review summarizes the efforts that have been made, mostly over the last decade, to identify new therapeutic targets for celecoxib. To achieve this goal, records gathered in MEDLINE PubMed and Scopus databases along with the registry of clinical trials by the US National Library of Medicine at the U.S. National Institutes of Health were explored. Since celecoxib is a non-steroidal anti-inflammatory drug that represents the class of selective COX-2 inhibitors (coxibs), its clinical potential in metronomic cancer therapy, the treatment of mental disorders, or infectious diseases has been discussed. In the end, the perspective of a formulator, facing various challenges related to unfavorable physicochemical properties of celecoxib upon the development of new oral dosage forms, long-acting injectables, and topical formulations, including the latest trends in the pharmaceutical technology, such as the application of mesoporous carriers, biodegradable microparticles, lipid-based nanosystems, or spanlastics, was presented.

Large-scale phenotypic drug screen identifies neuroprotectants in zebrafish and mouse models of retinitis pigmentosa

Retinitis pigmentosa (RP) and associated inherited retinal diseases (IRDs) are caused by rod photoreceptor degeneration, necessitating therapeutics promoting rod photoreceptor survival. To address this, we tested compounds for neuroprotective effects in multiple zebrafish and mouse RP models, reasoning drugs effective across species and/or independent of disease mutation may translate better clinically. We first performed a large-scale phenotypic drug screen for compounds promoting rod cell survival in a larval zebrafish model of inducible RP. We tested 2934 compounds, mostly human-approved drugs, across six concentrations, resulting in 113 compounds being identified as hits. Secondary tests of 42 high-priority hits confirmed eleven lead candidates. Leads were then evaluated in a series of mouse RP models in an effort to identify compounds effective across species and RP models, that is, potential pan-disease therapeutics. Nine of 11 leads exhibited neuroprotective effects in mouse primary photoreceptor cultures, and three promoted photoreceptor survival in mouse rd1 retinal explants. Both shared and complementary mechanisms of action were implicated across leads. Shared target tests implicated parp1-dependent cell death in our zebrafish RP model. Complementation tests revealed enhanced and additive/synergistic neuroprotective effects of paired drug combinations in mouse photoreceptor cultures and zebrafish, respectively. These results highlight the value of cross-species/multi-model phenotypic drug discovery and suggest combinatorial drug therapies may provide enhanced therapeutic benefits for RP patients.

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.

Drug Delivery to the Posterior Segment of the Eye: Biopharmaceutic and Pharmacokinetic Considerations

The treatment of the posterior-segment ocular diseases, such as age-related eye diseases (AMD) or diabetic retinopathy (DR), present a challenge for ophthalmologists due to the complex anatomy and physiology of the eye. This specialized organ is composed of various static and dynamic barriers that restrict drug delivery into the target site of action. Despite numerous efforts, effective intraocular drug delivery remains unresolved and, therefore, it is highly desirable to improve the current treatments of diseases affecting the posterior cavity. This review article gives an overview of pharmacokinetic and biopharmaceutics aspects for the most commonly-used ocular administration routes (intravitreal, topical, systemic, and periocular), including information of the absorption, distribution, and elimination, as well as the benefits and limitations of each one. This article also encompasses different conventional and novel drug delivery systems designed and developed to improve drug pharmacokinetics intended for the posterior ocular segment treatment.

Dendrimers for Ocular Drug Delivery

Existing methods of administering ocular drugs are limited in either their safety or efficiency. Nanomedicine therapies have the potential to address this deficiency by creating vehicles that can control drug biodistribution. Dendrimers are synthetic polymeric nanoparticles with a unique highly organized branching structure. In recent years, promising results using dendrimer vehicles to deliver ocular drugs through different routes of administration have been reported. In this review, we briefly summarize these results with emphasis on the dendrimer modifications used to target different ocular structures.

Stability and Ocular Pharmacokinetics of Celecoxib-Loaded Nanoparticles Topical Ophthalmic Formulations

A spontaneous emulsification and/or solvent diffusion method was used for the preparation of celecoxib-loaded nanoparticles (NPs) using polymers, including chitosan (CS), sodium alginate, poly-ε-caprolactone (PCL), poly-l-lactide, and poly-d,l-lactide-co-glycolide. NPs were incorporated into vehicles (eye drops, in situ gelling system, and gel). Formulations were subjected to an accelerated stability study by storing them at elevated temperatures of 30, 35, and 45°C for 6 months. Formulations were evaluated monthly for general appearance, pH, viscosity, particle size, polydispersity index, zeta potential, and drug content. Gels containing CS-NPs and PCL-NPs were selected for an ocular pharmacokinetics study using Sprague-Dawley rats due to their high stability and long shelf lives (24.56 and 33.76 months, respectively). The gel improved NP stability by keeping it inside its network structure, which protected them from aggregation and interacting with water. Our formulations improved celecoxib bioavailability due to their bioadhesivness, thus preventing their rapid removal. Also, NPs acted as drug reservoirs that adhered to eye surface and continuously released the drug. The availability of celecoxib in all eye tissues and its absence in plasma suggests that our formulation could be used for anterior eye disorders and also for treatment of diseases associated with the posterior eye with no systemic side effects.

Influence of freeze-drying and γ-irradiation in preclinical studies of flurbiprofen polymeric nanoparticles for ocular delivery using d-(+)-trehalose and polyethylene glycol

This study investigated the suspension of poly(ε-caprolactone) nanoparticles as an ocular delivery system for flurbiprofen (FB-PεCL-NPs) in order to overcome the associated problems, such as stability, sterility, tolerance, and efficacy, with two different FB-PεCL-NP formulations. The formulations were stabilized with poloxamer 188 (1.66% and 3.5%) and submitted individually for freeze-drying and γ-irradiation with polyethylene glycol 3350 (PEG3350) and d-(+)-trehalose (TRE). Both formulations satisfied criteria according to all physicochemical parameters required for ocular pharmaceuticals. The FB-PεCL-NP formulations showed non-Newtonian behavior and sustained drug release. Ex vivo permeation analysis using isolated ocular pig tissues suggested that the presence of PEG3350 results in a reduction of FB transcorneal permeation. Moreover, TRE improved the penetration of FB across the cornea, especially after γ-irradiation. In addition, both formulations did not show a significant affinity in increasing FB transscleral permeation. Both formulations were classified as nonirritating, safe products for ophthalmic administration according to hen’s egg test-chorioallantoic membrane and Draize eye test. Furthermore, an in vivo anti-inflammatory efficacy test showed that irradiated FB-PεCL-NPs prepared with PEG3350 (IR-NPsPEG) have longer anti-inflammatory effects than those presented with irradiated FB-PεCL-NPs prepared with TRE (IR-NPsTRE). IR-NPsPEG showed a suitable physical stability after an aqueous reconstitution over >30 days. This study concludes that both formulations meet the Goldman’s criteria and demonstrate how irradiated nanoparticles, with innovative permeation characteristics, could be used as a feasible alternative to a flurbiprofen solution for ocular application in clinical trials.

Effect of periocular injection of celecoxib and propranolol on ocular level of vascular endothelial growth factor in a diabetic mouse model

AIM

To investigate the effects of periocular injection of propranolol and celecoxib on ocular levels of vascular endothelial growth factor (VEGF) in a diabetic mouse model.

METHODS

Forty 4-6wk BALB-C male mice weighing 20-25 g were used. The study groups included: non-diabetic control (group 1), diabetic control (group 2), diabetic propranolol (group 3), and diabetic celecoxib (group 4). After induction of type 1 diabetes by streptozotocin, propranolol (10 µg) and celecoxib (200 µg dissolved in carboxymethylcellulose 0.5%) were injected periocularly. The ocular level of VEGF was measured in all the study groups using enzyme-linked immuno sorbent assay (ELISA) method.

RESULTS

Ocular VEGF level was significantly increased (1.25 fold) in the diabetic control group when compared to the non-diabetic group one week after induction with streptozotocin (P=0.002). Both periocular propranolol and celecoxib significantly reduced ocular VEGF levels (P=0.047 and P<0.001, respectively). The effect was more pronounced with celecoxib.

CONCLUSION

The periocular administration of propranolol and celecoxib can significantly reduce ocular VEGF levels in a diabetic mouse model.

Lipid mediators are critical in resolving inflammation: a review of the emerging roles of eicosanoids in diabetes mellitus

The biosynthesis pathway of eicosanoids derived from arachidonic acid, such as prostaglandins and leukotrienes, relates to the pathophysiology of diabetes mellitus (DM). A better understanding of how lipid mediators modulate the inflammatory process may help recognize key factors underlying the progression of diabetes complications. Our review presents recent knowledge about eicosanoid synthesis and signaling in DM-related complications, and discusses eicosanoid-related target therapeutics.

Corticosteroid-loaded biodegradable nanoparticles for prevention of corneal allograft rejection in rats

Immunologic graft rejection is one of the main causes of short and long-term graft failure in corneal transplantation. Steroids are the most commonly used immunosuppressive agents for postoperative management and prevention of corneal graft rejection. However, steroids delivered in eye drops are rapidly cleared from the surface of the eye, so the required frequency of dosing for corneal graft rejection management can be as high as once every 2h. Additionally, these eye drops are often prescribed for daily use for 1 year or longer, which can result in poor patient compliance and steroid-related side effects. Here, we report a biodegradable nanoparticle system composed of Generally Regarded as Safe (GRAS) materials that can provide sustained release of corticosteroids to prevent corneal graft rejection following subconjunctival injection provided initially during transplant surgery. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles containing dexamethasone sodium phosphate (DSP) exhibited a size of 200 nm, 8 wt.% drug loading, and sustained drug release over 15 days in vitro under sink conditions. DSP-loaded nanoparticles provided sustained ocular drug levels for at least 7 days after subconjunctival administration in rats, and prevented corneal allograft rejection over the entire 9-week study when administered weekly. In contrast, control treatment groups that received weekly injections of either placebo nanoparticles, saline, or DSP in solution demonstrated corneal graft rejection accompanied by severe corneal edema, neovascularization and opacity that occurred in ≤ 4 weeks. Local controlled release of corticosteroids may reduce the rate of corneal graft rejection, perhaps especially in the days immediately following surgery when risk of rejection is highest and when typical steroid eye drop administration requirements are particularly onerous.

Vitreous pharmacokinetics and bioavailability of memantine after subtenon, intravenous, and intravitreal administration in rabbits

PURPOSE

This study evaluated the vitreous pharmacokinetics and vitreous bioavailability of memantine following posterior-subtenon administration (PST) compared to intravitreal (INT) and intravenous routes (INV) in rabbits.

METHODS

Vitreous pharmacokinetic analysis was performed on female New Zealand (NZ) albino rabbits after PST, INT, and INV administration and calculating the pharmacokinetic parameters that describe memantine vitreous distribution. The vitreous bioavailability (F) and the relative vitreous bioavailability of memantine was estimated after posterior-subtenon administration (Frel (pst/int)) and after intravenous route (Frel (inv/int)) compared with intravitreal administration. Relative vitreous bioavailability of memantine was also estimated following PST administration compared with vitreous concentrations after intravenous administration (Frel (pst/inv)).

RESULTS

Memantine kinetics in the vitreous of NZ albino rabbits after PST administration can be explained by a one-compartment model, which was characterized by a fast absorption process, and a short terminal half-life. Vitreous pharmacokinetics following INV administration was also characterized by a fast absorption process, a terminal half-life significantly longer than the subtenon route, and low area under the curve values. High vitreous bioavailability after PST was observed, and the relative vitreous bioavailability of memantine following PST administration (0.53%) was greater than for intravenous administration (0.02%).

CONCLUSIONS

Our results suggest that memantine reaches the vitreous after PST administration by local diffusion. These data also show that local diffusion of the drug is responsible for greater vitreous availability of memantine following PST administration compared with INV administration.

Drug delivery to the posterior segment of the eye for pharmacologic therapy

Treatment of diseases of the posterior segment of the eye, such as age-related macular degeneration, cytomegalovirus retinitis, diabetic retinopathy, posterior uveitis and retinitis pigmentosa, requires novel drug delivery systems that can overcome the many barriers for efficacious delivery of therapeutic drug concentrations. This challenge has prompted the development of biodegradable and nonbiodegradable sustained-release systems for injection or transplantation into the vitreous as well as drug-loaded nanoparticles, microspheres and liposomes. These drug delivery systems utilize topical, systemic, subconjunctival, intravitreal, transscleral and iontophoretic routes of administration. The focus of research has been the development of methods that will increase the efficacy of spatiotemporal drug application, resulting in more successful therapy for patients with posterior segment diseases. This article summarizes recent advances in the research and development of drug delivery methods of the posterior chamber of the eye, with an emphasis on the use of implantable devices as well as micro- and nanoparticles.

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.

Dendrimer nanoparticles for ocular drug delivery

Eye is a unique organ of perfection and complexity, and is a microcosm of the body in many ways. It represents a great opportunity for nanomedicine, since it is readily accessible-allowing for direct drug/gene delivery to maximize the therapeutic effect and minimize side effects. The development of appropriate delivery systems that can sustain and deliver therapeutics to the target tissues is a key challenge that can be addressed by nanotechnology. Dendrimers are tree-like, nanostructured polymers that have received significant attention as ocular drug delivery systems, due to their well-defined size, tailorable structure, and potentially favorable ocular biodistribution. In this review, we highlight recent developments in dendrimer-based ocular therapies for both anterior and posterior segment diseases.

Nanoparticle-based topical ophthalmic formulations for sustained celecoxib release

Celecoxib-loaded NPs were prepared from biodegradable polymers such as poly-ε-caprolactone (PCL), poly(L-lactide) (PLA), and poly(D,L-lactide-co-glycolide) (PLGA) by spontaneous emulsification solvent diffusion method. Different concentrations of polymers, emulsifier, and cosurfactants were used for formulation optimization. Nanoparticles (NPs) were characterized regarding their particle size, PDI, zeta potential, shape, morphology, and drug content. Celecoxib-loaded NPs were incorporated into eye drops, in situ gelling system, and gel and characterized regarding their pH, viscosity, uniformity of drug content, in vitro release, and cytotoxicity. The results of optimized celecoxib-loaded PCL-, PLGA-, and PLA-NPs, respectively, are particle size 119 ± 4, 126.67 ± 7.08, and 135.33 ± 4.15 nm; zeta potential -22.43 ± 2.91, -25.46 ± 2.35, and -31.81 ± 2.54 mV; and encapsulation efficiency 93.44 ± 3.6%, 86.00 ± 1.67%, and 79.04 ± 2.6%. TEM analyses revealed that NPs have spherical shapes with dense core and distinct coat. Formulations possessed uniform drug content with pH and viscosity compatible with the eye. Formulations showed sustained release without any burst effect with the Higuchi non-fickian diffusion mechanism. Cytotoxicity studies revealed that all formulations are nontoxic. Our formulations provide a great deal of flexibility to formulation scientist whereby sizes and zeta potentials of our NPs can be tuned to suit the need using scalable and robust methodologies. These formulations can thus serve as a potential drug delivery system for both anterior and posterior eye diseases.

Recent advances in ophthalmic drug delivery

Topical ocular drug bioavailability is notoriously poor, in the order of 5% or less. This is a consequence of effective multiple barriers to drug entry, comprising nasolacrimal drainage, epithelial drug transport barriers and clearance from the vasculature in the conjunctiva. While sustained drug delivery to the back of the eye is now feasible with intravitreal implants such as Vitrasert (-6 months), Retisert (-3 years) and Iluvien (-3 years), currently there are no marketed delivery systems for long-term drug delivery to the anterior segment of the eye. The purpose of this article is to summarize the resurgence in interest to prolong and improve drug entry from topical administration. These approaches include mucoadhesives, viscous polymer vehicles, transporter-targeted prodrug design, receptor-targeted functionalized nanoparticles, iontophoresis, punctal plug and contact lens delivery systems. A few of these delivery systems might be useful in treating diseases affecting the back of the eye. Their effectiveness will be compared against intravitreal implants (upper bound of effectiveness) and trans-scleral systems (lower bound of effectiveness). Refining the animal model by incorporating the latest advances in microdialysis and imaging technology is key to expanding the knowledge central to the design, testing and evaluation of the next generation of innovative ocular drug delivery systems.

Intraocular distribution of melanin in human, monkey, rabbit, minipig and dog eyes

The purpose of this study was to quantify the melanin pigment content in sclera, choroid-RPE, and retina, three tissues encountered during transscleral drug delivery to the vitreous, in human, rabbit, monkey, minipig, and dog models. Strain differences were assessed in NZW × NZR F1 and Dutch belted rabbits and Yucatan and Gottingen minipigs. The choroid-RPE and retina tissues were divided into central (posterior pole area) and peripheral (away from posterior pole) regions while the sclera was analyzed without such division. Melanin content in the tissues was analyzed using a colorimetric assay. In all species the rank order for pigment content was: choroid-RPE >retina ≥ sclera, except in humans, where scleral melanin levels were higher than retina and central choroid. The melanin content in a given tissue differed between species. Further, while the peripheral tissue pigment levels tended to be generally higher compared to the central regions, these differences were significant in human in the case of choroid-RPE and in human, monkey, and dogs in the case of retina. Strain difference was observed only in the central choroid-RPE region of rabbits (NZW × NZR F1 >Dutch Belted). Species, strain, and regional differences exist in the melanin pigment content in the tissues of the posterior segment of the eye, with Gottingen minipig being closest to humans among the animals assessed. These differences in melanin content might contribute to differences in drug binding, delivery, and toxicity.

Systematic evaluation of supported liquid extraction in reducing matrix effect and improving extraction efficiency in LC-MS/MS based bioanalysis for 10 model pharmaceutical compounds

In past a few years, there has been a large increase in the application of supported liquid extraction (SLE) for LC-MS/MS based bioanalysis due to its distinct practical advantage in reduced time cost, ease of operation and the feasibility for automation. The main purpose of this study was to systematically evaluate supported liquid extraction in reducing matrix effect and improving extraction efficiency/recovery under various extraction conditions with 10 model pharmaceutical compounds in liquid chromatography coupled to electrospray tandem mass spectrometry (LC-ESI-MS/MS) analysis. Selected compounds have diverse physicochemical properties where logP ranges from 0.1 to 6.24 and pK(a) ranges from 4.0 to 11.1. The factors that may have the impact on the recovery of analytes and phospholipids (PL) were assessed. Over 75% recovery was achieved for every analyte under its respectively optimized extraction conditions where the selection of the polarity of extraction solvent and buffered pH can be critical for efficient recovery. Furthermore, the matrix effect was assessed by postextraction spike and postcolumn infusion method. The matrix effect was considerably reduced for all analytes under most extraction conditions evaluated for SLE, compared with protein precipitation (PPT) method. The correlation between matrix effect and residual phospholipids in sample extract was clearly shown. Although analyte-dependent matrix effect was observed prominently in sample extract prepared by PPT, it was minimized by SLE sample preparation process that effectively removes the majority of phospholipids. Sample extracted by ethyl acetate contained more phospholipids and demonstrated stronger matrix effect than by other organic solvents. Water-miscible organic content, such as methanol and acetonitrile in samples prior to loading has significant impact on PL recovery when eluting with methyl tert-butyl ether. However, isopropanol does not enhance the recovery of PL when adding to dichloromethane for elution. In addition, the compromise between improved extraction efficiency by SLE and reduced matrix effect is sometimes necessary to yield clean extract with acceptable recovery. The effective removal of phospholipids and reduction of matrix effect, while achieving good recovery for all pharmaceutical compounds with diverse physicochemical properties, demonstrated that SLE is a valuable alternative technique to liquid-liquid extraction (LLE) in high throughput LC-MS/MS based bioanalysis.

Hydrophilic prodrug approach for reduced pigment binding and enhanced transscleral retinal delivery of celecoxib

Transscleral retinal delivery of celecoxib, an anti-inflammatory and anti-VEGF agent, is restricted by its poor solubility and binding to the melanin pigment in choroid-RPE. The purpose of this study was to develop soluble prodrugs of celecoxib with reduced pigment binding and enhanced retinal delivery. Three hydrophilic amide prodrugs of celecoxib, celecoxib succinamidic acid (CSA), celecoxib maleamidic acid (CMA), and celecoxib acetamide (CAA) were synthesized and characterized for solubility and lipophilicity. In vitro melanin binding to natural melanin (Sepia officinalis) was estimated for all three prodrugs. In vitro transport studies across isolated bovine sclera and sclera-choroid-RPE (SCRPE) were performed. Prodrug with the highest permeability across SCRPE was characterized for metabolism and cytotoxicity and its in vivo transscleral delivery in pigmented rats. Aqueous solubilities of CSA, CMA, and CAA were 300-, 182-, and 76-fold higher, respectively, than celecoxib. Melanin binding affinity and capacity were significantly lower than for celecoxib for all three prodrugs. Rank order for the % in vitro transport across bovine sclera and SCRPE was CSA > CMA ~ CAA ~ celecoxib, with the transport being 8-fold higher for CSA than celecoxib. CSA was further assessed for its metabolic stability and in vivo delivery. CSA showed optimum metabolic stability in all eye tissues with only 10-20% conversion to parent celecoxib in 30 min. Metabolic enzymes responsible for bioconversion included amidases, esterase, and cytochrome P-450. In vivo delivery in pigmented BN rats showed that CSA had 4.7-, 1.4-, 3.3-, 6.0-, and 4.5-fold higher delivery to sclera, choroid-RPE, retina, vitreous, and lens than celecoxib. CSA has no cytotoxicity in ARPE-19 cells in the concentration range of 0.1 to 1000 μM. Celecoxib succinamidic acid, a soluble prodrug of celecoxib with reduced melanin binding, enhances transscleral retinal delivery of celecoxib.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

Pazopanib eye drops can alleviate retinal complications of diabetic retinopathy.

Inflammation in diabetic retinopathy

Diabetes causes a number of metabolic and physiologic abnormalities in the retina, but which of these abnormalities contribute to recognized features of diabetic retinopathy (DR) is less clear. Many of the molecular and physiologic abnormalities that have been found to develop in the retina in diabetes are consistent with inflammation. Moreover, a number of anti-inflammatory therapies have been found to significantly inhibit development of different aspects of DR in animal models. Herein, we review the inflammatory mediators and their relationship to early and late DR, and discuss the potential of anti-inflammatory approaches to inhibit development of different stages of the retinopathy. We focus primarily on information derived from in vivo studies, supplementing with information from in vitro studies were important.

Influence of drug solubility and lipophilicity on transscleral retinal delivery of six corticosteroids

The influence of drug properties including solubility, lipophilicity, tissue partition coefficients, and in vitro transscleral permeability on ex vivo and in vivo transscleral delivery from corticosteroid suspensions was determined. Solubility, tissue/buffer partition coefficients for bovine sclera and choroid-retinal pigment epithelium (CRPE), and in vitro bovine sclera and sclera-choroid-retinal pigment epithelium (SCRPE) transscleral transport were determined at pH 7.4 for triamcinolone, prednisolone, dexamethasone, fluocinolone acetonide, triamcinolone acetonide, and budesonide in solution. Ex vivo and in vivo transscleral delivery was assessed in Brown Norway rats after posterior subconjunctival injection of a 1 mg/ml suspension of each corticosteroid. Corticosteroid solubility and partition coefficients ranged from ∼ 17 to 300 μg/ml and 3.0 to 11.4 for sclera and from 7.1 to 35.8 for CRPE, respectively, with the more lipophilic molecules partitioning more into both tissues. Transport across sclera and SCRPE was in the range of 3.9 to 10.7% and 0.3 to 1.8%, respectively, with the transport declining with an increase in lipophilicity. Ex vivo and in vivo transscleral delivery indicated tissue distribution in the order CRPE ≥ sclera > retina > vitreous. Tissue partitioning showed a positive correlation with drug lipophilicity (R(2) = 0.66-0.96). Ex vivo and in vivo sclera, CRPE, retina, and vitreous tissue levels of all corticosteroids showed strong positive correlation with drug solubility (R(2) = 0.91-1.0) but not lipophilicity (R(2) = 0.24-0.41) or tissue partitioning (R(2) = 0.24-0.46) when delivered as suspensions. In vivo delivery was lower in all eye tissues assessed than ex vivo delivery, with the in vivo/ex vivo ratios being the lowest in the vitreous (0.085-0.212). Upon exposure to corticosteroid suspensions ex vivo or in vivo, transscleral intraocular tissue distribution was primarily driven by the drug solubility.

Delivery of celecoxib for treating diseases of the eye: influence of pigment and diabetes

IMPORTANCE OF THE FIELD

Age-related macular degeneration (AMD) and diabetic retinopathy (DR) are two major causes of blindness. In these disorders, growth factors such as vascular endothelial growth factor (VEGF) are upregulated, leading to either enhanced vascular permeability or proliferation of endothelium. While corticosteroid therapies available at present suffer from side effects including cataracts and elevated intraocular pressure, anti-VEGF antibody therapies require frequent intravitreal injections, a procedure that can potentially lead to retinal detachment or endophthalmitis. Thus, there is a need to develop safe, sustained release therapeutic approaches for treating AMD and DR.

AREAS COVERED IN THIS REVIEW

This review discusses the pharmacological basis for using celecoxib, an anti-inflammatory drug capable of selectively inhibiting cycloxygenase 2, in treating AMD and DR. In addition, this article discusses the safety, delivery advantage and efficacy of celecoxib by transscleral retinal delivery, a periocular delivery approach that is less invasive to the globe compared with intravitreal injections.

WHAT THE READER WILL GAIN

The reader will gain insights into the development of a pharmacological agent and a sustained release delivery system for treating DR and AMD. Further, the reader will gain insights into the influence of eye physiology including pigmentation and disease states such as DR on retinal drug delivery.

TAKE HOME MESSAGE

Transscleral sustained delivery of anti-inflammatory agents is a viable option for treating retinal disorders.

Nonsteroidal anti-inflammatory drugs in ophthalmology

Nonsteroidal anti-inflammatory drugs (NSAIDs) are increasingly employed in ophthalmology to reduce miosis and inflammation, manage scleritis, and prevent and treat cystoid macular edema associated with cataract surgery. In addition, they may decrease postoperative pain and photophobia associated with refractive surgery and may reduce the itching associated with allergic conjunctivitis. In recent years, the U.S. Food and Drug Administration has approved new topical NSAIDs, and previously approved NSAIDs have been reformulated. These additions and changes result in different pharmacokinetics and dosing intervals, which may offer therapeutic advantages. For example, therapeutic effects on diabetic retinopathy and age-related macular degeneration may now be achievable. We provide an updated review on NSAIDs and a summary of their current uses in ophthalmology with attention to potential future applications.

Influence of lipophilicity on drug partitioning into sclera, choroid-retinal pigment epithelium, retina, trabecular meshwork, and optic nerve

In vitro bovine eye tissue/phosphate-buffered saline, pH 7.4, partition coefficients (Kt:b), in vitro binding to natural melanin, and in vivo delivery at 1 h after posterior subconjunctival injection in Brown Norway rats were determined for eight beta-blockers. The Kt:b was in the order intact tissue, dry weight method >or= intact tissue, wet weight method corrected for tissue water and drug in tissue water >> intact tissue, wet weight method > homogenized tissue. In intact tissue methods, Kt:b followed the order choroid-retinal pigment epithelium (RPE) > trabecular meshwork > retina > sclera approximately optic nerve; propranolol > betaxolol > pindolol approximately timolol approximately metoprolol > sotalol approximately atenolol approximately nadolol. Intact tissue, wet weight log (Kt:b) correlated positively with log D for all tissues (R(2) of 0.7-0.9). Log (melanin binding capacity) correlated positively with choroid-RPE log (Kt:b) (R(2) of 0.5). With an increase in concentration, Kt:b decreased in trabecular meshwork for all beta-blockers and for some lipophilic beta-blockers in choroid-RPE and sclera. With an increase in drug lipophilicity, in vivo tissue distribution increased in choroid-RPE, iris-ciliary body, sclera, and cornea but exhibited a declining trend in retina, vitreous, and lens. In vitro bovine intact tissue, wet weight Kt:b correlated positively with rat in vivo tissue/vitreous humor distribution for sclera, choroid-RPE, and retina (R(2) of 0.985-0.993). In vitro tissue partition coefficients might be useful in predicting in vivo drug distribution after trans-scleral delivery. Less lipophilic solutes exhibiting limited nonproductive binding in choroid-RPE might exhibit greater trans-scleral delivery to the retina and vitreous.

Subconjunctival nanoparticle carboplatin in the treatment of murine retinoblastoma

OBJECTIVE

To evaluate the efficacy of subconjunctival nanoparticle carboplatin in the treatment of transgenic murine retinoblastoma.

METHODS

Dendrimeric nanoparticles loaded with carboplatin were prepared. Forty LHbeta-Tag mice were randomly assigned into 4 groups and treated at 10 weeks of age. Each mouse received a single subconjunctival injection in one eye, and the opposite eye was left untreated as a control. Group 1 (high-dose nanoparticle carboplatin) received 37.5 mg/mL of nanoparticle carboplatin; group 2 (low-dose nanoparticle carboplatin) received 10 mg/mL of nanoparticle carboplatin; group 3 (conventional carboplatin) received 10 mg/mL of carboplatin in aqueous solution; and group 4 (phosphate-buffered saline) received phosphate-buffered saline. Mice were killed on day 22 after treatment. Eyes were serially sectioned, and retinal tumor burden was quantified by histopathologic analysis.

RESULTS

Mean tumor burden in the treated eyes was significantly smaller compared with the untreated eyes in the same mice in both nanoparticle carboplatin groups (group 1, P = .02; group 2, P = .02) and the treated eyes in the conventional carboplatin group (group 1 vs group 3, P < .01; group 2 vs group 3, P = .01) and phosphate-buffered saline group (group 1 vs group 4, P < .01; group 2 vs group 4, P = .01). The untreated eyes in the high-dose nanoparticle carboplatin group showed significantly smaller tumor mass compared with the conventional carboplatin (P = .03) and PBS (P = .04) groups. No toxic effects were observed in any of the groups.

CONCLUSION

A single injection of subconjunctival nanoparticle carboplatin was effective in the treatment of transgenic murine retinoblastoma, with no associated toxic effects. The higher dose of subconjunctival nanoparticle carboplatin decreased the tumor burden in the contralateral eye.

CLINICAL RELEVANCE

This model provides a basis to test carboplatin nanoparticles for the treatment of human retinoblastoma.

Cyclooxygenase-2 plays a critical role in retinal ganglion cell death after transient ischemia: real-time monitoring of RGC survival using Thy-1-EGFP transgenic mice

The exact role of cyclooxygenase-2 (COX-2) in neurodegeneration of retinal ganglion cells (RGCs) in vivo following ischemia-reperfusion injury of the retina was unknown. We made transgenic mice in which the Thy-1.2 promoter drives the expression of EGFP cDNA (Thy-1-EGFP) in RGCs to monitor RGC survival and death in retinal whole mount preparations and in live animals. We show that celecoxib, a selective COX-2 inhibitor, blocks RGC death after ischemic injury. Furthermore, in COX-2 knockout (COX-2(-/-)) mice, RGCs are resistant to ischemia-reperfusion injury. Finally, we performed time-lapse monitoring of RGC death after ischemia in Thy-1-EGFP; COX-2(-/-) mice. Our data show that COX-2 plays a crucial role in ischemia-reperfusion injury-induced RGC death. Inhibition of COX-2 activity may therefore be an effective therapy for neurodegenerative diseases of the retina and optic nerve.

Pathophysiology of cyclooxygenase inhibition in animal models

Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid into prostaglandins (PGs), which play a significant role in health and disease in the gastrointestinal tract (GI) and in the renal, skeletal, and ocular systems. COX-1 is constitutively expressed and found in most normal tissues, whereas COX-2 can be expressed at low levels in normal tissues and is highly induced by pro-inflammatory mediators. Inhibitors of COX activity include: (1) conventional nonselective, nonsteroidal anti-inflammatory drugs (ns-NSAIDs) and (2) COX-2 selective nonsteroidal anti-inflammatory drugs (COX-2 s-NSAIDs). Inhibition of COX-1 often elicits GI toxicity in animals and humans. Therefore, COX-2 s-NSAIDs were developed to provide a selective COX-2 agent, while minimizing the attendant COX-1-mediated GI toxicities. Rats and dogs overpredict COX inhibition for renal effects such as renal handling of electrolytes in humans. COX inhibitors are shown to have both beneficial and detrimental effects, such as on healing of ligament or tendon tears, on the skeletal system in animal models. Certain ophthalmic conditions such as glaucoma and keratitis are associated with increased COX-2 expression, suggesting a potential role in their pathophysiology.

Human scleral diffusion of anticancer drugs from solution and nanoparticle formulation

PURPOSE

To determine the transscleral permeability of chemotherapeutic drugs vinblastine and doxorubicin for treatment of intraocular tumors, and to compare the use of doxorubicin encapsulated in PLGA and liposome nanoparticles.

METHODS

Human sclera was isolated and mounted in a Lucite chamber. Fluorescently tagged vinblastine (VIN), innately fluorescent free doxorubicin (DOX), PLGA doxorubicin (PLGA-DOX), or Doxil (Tibotec Therapeutics) were added to the episcleral donor chamber. The choroidal side was perfused with Balanced Salt Solution. Perfusate fractions were collected over 24 h and measured for fluorescence. Following the experiment, tissue sections were imaged, underwent a drug wash out procedure, and tissue drug content was analyzed using an LC-MS/MS method.

RESULTS

Within 24 h, a total of 68%, 74%, 29%, and 1.9% of the drug dose from VIN, DOX, PLGA-DOX, and Doxil, respectively, diffused across the sclera. VIN and DOX scleral tissue showed strong fluorescence after 24 h. PLGA-DOX displayed scattered fluorescence, and Doxil indicated minimal fluorescence. LC-MS/MS revealed strong tissue binding of DOX.

CONCLUSIONS

This study suggests both vinblastine and doxorubicin are able to diffuse across human sclera. In addition, PLGA nanoparticles delivered doxorubicin at a slower rate across the sclera, and the liposome preparation resulted in the slowest delivery of drug.

Effect of diabetes on transscleral delivery of celecoxib

PURPOSE

To investigate the effects of diabetes on transscleral retinal delivery of celecoxib in albino and pigmented rats.

METHODS

Albino (Sprague Dawley-SD) and pigmented (Brown Norway-BN) rats were made diabetic by a single intraperitoneal injection of streptozotocin (60 mg/kg) following 24 h of fasting and diabetes was confirmed (blood glucose>250 mg/dL). Two months after diabetes induction, the integrity of blood-retinal-barrier in control versus diabetic rats from both strains was compared by using FITC-dextran leakage assay. Fifty microliter suspension of celecoxib (3 mg/rat) was injected periocularly in both the strains in one eye, 2 months following diabetes induction. The animals were euthanized at the end of 0.25, 0.5, 1, 2, 3, 4, 8, and 12 h post-dosing and celecoxib levels in ocular tissues and plasma were estimated using a HPLC assay.

RESULTS

Diabetes (2-month duration) resulted in 2.4 and 3.5 fold higher blood-retinal barrier leakage in diabetic SD and BN rats, respectively, compared to controls. The area under tissue celecoxib concentration versus time curves (AUC) for sclera, cornea, and lens were not significantly different between control and diabetic animals. However, retinal and vitreal AUCs of celecoxib in treated eyes were approximately 1.5-fold and 2-fold higher in diabetic SD and BN rats, respectively, as compared to the controls.

CONCLUSIONS

Transscleral retinal and vitreal delivery of celecoxib is significantly higher in diabetic animals of both strains. The increase in retinal delivery of celecoxib due to diabetes is higher in pigmented rats compared to albino rats. Higher delivery of celecoxib in diabetic animals compared to control animals can be attributed to the disruption of blood-retinal barrier due to diabetes.

Computer modeling of drug delivery to the posterior eye: effect of active transport and loss to choroidal blood flow

PURPOSE

The direct penetration route following transscleral drug administration presents several barrier and clearance mechanisms-including loss to choroidal blood flow, active transport by the retinal pigment epithelium (RPE), and loss to the conjunctival lymphatics and episcleral blood vessels. The objective of this research was to quantify the role of choroidal and episcleral losses.

MATERIALS AND METHODS

A finite element model was created for drug distribution in the posterior human eye. The volumetric choroidal loss constant, active transport component and mass transfer from the scleral surface were unknown parameters in the model. The model was used to simulate drug distribution from a systemic source, and the results were compared to existing experimental results to obtain values for the parameters.

RESULTS

The volumetric choroidal loss constant, mass transfer coefficient from the scleral surface and active transport component were evaluated to be (2.0 +/- 0.6) x 10(-5) s(-1), (2.0 +/- 0.35) x 10(-5) cm/s and 8.54 x 10(-6) cm/s respectively.

CONCLUSION

Loss to the choroidal circulation was small compared to loss from the scleral surface. Active transport was predicted to induce periscleral movement of the drug, resulting in more rapid distribution and elevated drug concentrations in the choroid and sclera.

Effect of eye pigmentation on transscleral drug delivery

PURPOSE

To determine the influence of eye pigmentation on transscleral retinal delivery of celecoxib.

METHODS

Melanin content in ocular tissues of both the strains was determined by sodium hydroxide solubilization

METHOD

The affinity of celecoxib to synthetic and natural melanin was estimated by co-incubating celecoxib and melanin in isotonic phosphate-buffered saline. The binding affinity (k) and the maximum binding (r(max)) for celecoxib to both natural and synthetic melanin were estimated. Suspension of celecoxib (3 mg/rat) was injected periocularly into one eye of Sprague-Dawley (SD, albino) and Brown Norway (BN, pigmented) rats. The animals were euthanatized at the end of 0.25, 0.5, 1, 2, 3, 4, 8, or 12 hours after the drug was administered, and celecoxib levels in ocular tissues (sclera, choroid-RPE, retina, vitreous, lens, and cornea) were estimated with an HPLC assay. In addition, celecoxib-poly(lactide) microparticles (750 microg drug/rat) were administered periocularly in SD and BN rats, and celecoxib levels in these eye tissues were assessed on day 8, to determine the effectiveness of the sustained release system.

RESULTS

The r(max) and k for celecoxib's binding to natural melanin were (3.92 +/- 0.06) x 10(-7) moles/mg of melanin and (0.08 +/- 0.01) x 10(6) M(-1), respectively. The affinity and the extent of celecoxib's binding to natural melanin were not significantly different from those observed with synthetic melanin. The concentrations of melanin in choroid-RPE, sclera, and retina of BN rats were 200 +/- 30, 12 +/- 4, and 3 +/- 0.2 mug/mg tissue, respectively. Melanin was not detectable in the vitreous, lens, and cornea of BN rats. In SD rats, melanin was not detected in all tissues assessed except in the choroid-RPE, wherein melanin-like activity was 100-fold less than in BN rats. The area under the curve (AUC) for tissue concentration versus time profiles for animals administered with celecoxib suspension was not significantly different between the two strains for sclera, cornea, and lens. However, the retinal (P = 0.001) and vitreal (P = 0.001) AUCs of celecoxib in the treated eyes were approximately 1.5-fold higher in SD rats than in BN rats. Further, the choroid-RPE AUC in the treated and untreated eyes, respectively, were 1.5-fold (P = 0.001) and 2-fold (P = 0.0001) higher in BN rats than in SD rats. With celecoxib-poly(lactide) microparticles, choroid-RPE, retina, and vitreous concentrations on day 8 exhibited similar trends in differences between the two strains, with the differences being greater than those recorded for the celecoxib suspension.

CONCLUSIONS

Transscleral retinal and vitreal drug delivery of lipophilic celecoxib is significantly lower in pigmented rats than in albino rats. This difference may be attributable to significant binding of celecoxib to melanin and its accumulation/retention in the melanin-rich choroid-RPE of pigmented rats. The hindrance of retinal and vitreal drug delivery by the choroid-RPE in pigmented rats is also true of sustained-release microparticle systems.

Modeling of corneal and retinal pharmacokinetics after periocular drug administration

PURPOSE

To develop pharmacokinetics models to describe the disposition of small lipophilic molecules in the cornea and retina after periocular (subconjunctival or posterior subconjunctival) administration.

METHODS

Compartmental pharmacokinetics analysis was performed on the corneal and retinal data obtained after periocular administration of 3 mg of celecoxib (a selective COX-2 inhibitor) to Brown Norway (BN) rats. Berkeley Madonna, a differential and difference equation-based modeling software, was used for the pharmacokinetics modeling. The data were fit to different compartment models with first-order input and disposition, and the best fit was selected on the basis of coefficient of regression and Akaike information criteria (AIC). The models were validated by using the celecoxib data from a prior study in Sprague-Dawley (SD) rats. The corneal model was also fit to the corneal data for prednisolone at a dose of 2.61 mg in albino rabbits, and the model was validated at two other doses of prednisolone (0.261 and 26.1 mg) in these rabbits. Model simulations were performed with the finalized model to understand the effect of formulation on corneal and retinal pharmacokinetics after periocular administration.

RESULTS

Celecoxib kinetics in the BN rat cornea can be described by a two-compartment (periocular space and cornea, with a dissolution step for periocular formulation) model, with parallel elimination from the cornea and the periocular space. The inclusion of a distribution compartment or a dissolution step for celecoxib suspension did not lead to an overall improvement in the corneal data fit compared with the two-compartment model. The more important parameter for enhanced fit and explaining the apparent lack of an increase phase in the corneal levels is the inclusion of the initial leak-back of the dose from the periocular space into the precorneal area. The predicted celecoxib concentrations from this model also showed very good correlation (r = 0.99) with the observed values in the SD rat corneas. Similar pharmacokinetics models explain drug delivery to the cornea in rat and rabbit animal models. Retinal pharmacokinetics after periocular drug administration can be explained with a four-compartment (periocular space, choroid-containing transfer compartment, retina, and distribution compartment) model with elimination from the periocular space, retina, and choroid compartment. Inclusion of a dissolution-release step before the drug is available for absorption or elimination better explains retinal t(max). Good fits were obtained in both the BN (r = 0.99) and SD (r = 0.99) rats for retinal celecoxib using the same model; however, the parameter estimates differed.

CONCLUSIONS

Corneal and retinal pharmacokinetics of small lipophilic molecules after periocular administration can be described by compartment models. The modeling analysis shows that (1) leak-back from the site of administration most likely contributes to the apparent lack of an increase phase in corneal concentrations; (2) elimination via the conjunctival or periocular blood and lymphatic systems contributes significantly to drug clearance after periocular injection; (3) corneal pharmacokinetics of small lipophilic molecules can be explained by using similar models in rats and rabbits; and (4) although there are differences in some retinal pharmacokinetics parameters between the pigmented and nonpigmented rats, the physiological basis of these differences has yet to be ascertained.

Celecoxib inhibits proliferation of retinal pigment epithelial and choroid-retinal endothelial cells by a cyclooxygenase-2-independent mechanism

Age-related macular degeneration (ARMD) is a leading cause of blindness. The major reason for severe vision loss in ARMD is choroidal neovascularization due to an elevation in the expression of angiogenic factors such as vascular endothelial growth factor (VEGF). Drugs with anti-VEGF and antiproliferative activities can be beneficial for the treatment of this disorder. We have previously demonstrated that celecoxib [a selective cyclooxygenase (Cox)-2 inhibitor] inhibits VEGF expression in retinal pigment epithelial cells. In this study, we investigated the antiproliferative effects of celecoxib in adult retinal pigment epithelial (ARPE-19) and choroidal endothelial (RF/6A) cells. The results indicate that celecoxib 1) causes a dose-dependent antiproliferative effect in ARPE-19 and RF/6A cells (IC(50) of 23 and 13 microM, respectively); 2) leads to a G(2)-M phase cell cycle arrest in these cell types; and 3) inhibits VEGF-induced proliferation of RF/6A cells (IC(50) of 20 microM). In addition, 4) the concentrations of celecoxib required for antiproliferative effects are lower than those required for the cytotoxicity. These effects of celecoxib are by mechanisms independent of its Cox-2 inhibitory activity because rofecoxib (another Cox-2 inhibitor) had no effects on the proliferation or cell cycle distribution of the two cell types, and flurbiprofen (an inhibitor of Cox-1 and Cox-2) had weak antiproliferative effects on ARPE-19 cells, with IC(50) of 90 microM. In summary, celecoxib has potent antiproliferative effects in RF/6A and ARPE-19 cells; thus, it can be a potential new treatment in proliferative disorders of the choroid-retina such as choroidal neovascularization in age-related macular degeneration.

Sustained-release ophthalmic drug delivery systems for treatment of macular disorders: present and future applications

Macular disease currently poses the greatest threat to vision in aging populations. Historically, most of this pathology could only be dealt with surgically, and then only after much damage to the macula had already occurred. Current pathophysiological insights into macular diseases have allowed the development of effective new pharmacotherapies. The field of drug delivery systems has advanced over the last several years with emphasis placed on controlled release of drug to specific areas of the eye. Its unique location and tendency toward chronic disease make the macula an important and attractive target for drug delivery systems, especially sustained-release systems. This review evaluates the current literature on the research and development of sustained-release posterior segment drug delivery systems that are primarily intended for macular disease with an emphasis on age-related macular degeneration.Current effective therapies include corticosteroids and anti-vascular endothelial growth factor compounds. Recent successes have been reported using anti-angiogenic drugs for therapy of age-related macular degeneration. This review also includes information on implantable devices (biodegradable and non-biodegradable), the use of injected particles (microspheres and liposomes) and future enhanced drug delivery systems, such as ultrasound drug delivery. The devices reviewed show significant drug release over a period of days or weeks. However, macular disorders are chronic diseases requiring years of treatment. Currently, there is no 'gold standard' for therapy and/or drug delivery. Future studies will focus on improving the efficiency and effectiveness of drug delivery to the posterior chamber. If successful, therapeutic modalities will significantly delay loss of vision and improve the quality of life for patients with chronic macular disorders.

2nd Ophthalmic Drug Development and Delivery Summit

The Second Annual Ophthalmic Drug Development and Delivery Summit was held on 19 - 20 September 2006 in San Diego, CA, US. The 2-day symposium, having a highly focused theme, was packed with cutting-edge science, insightful overviews and networking opportunities. With a total of 11 recognized specialists presenting reviews and recent results in the advancement of ocular drug development and delivery, the invited expert speaking faculty presented the latest preclinical and clinical developments in novel ophthalmic therapies and drug delivery technology. The talks included various case studies from primary investigators and pharmaceutical companies touching upon key topics: updates on current clinical trials, study design issues, sustained delivery to the eye, views of the vitreous space as a drug reservoir, new developments in dry and wet age-related macular degeneration and diabetic retinopathy, formulation for optimal drug delivery, differences and similarities in developing drugs for the eye compared with other targets, pharmacokinetics, novel ocular delivery methods and devices, delivery of proteins and peptides, focal drug delivery, non-invasive drug delivery to the eye, neuroprotection challenges, in vitro and in vivo models for glaucoma and angiogenesis for early efficacy estimation, and toxicology. Overall, the 2-day annual symposium continues to grow as an efficient platform for fostering discussion on a range of scientific topics and challenges and avenues for building collaborative partnerships in ophthalmic drug development.

New Dosage Formulations for Targeted Delivery of Cyclo-Oxygenase-2 Inhibitors

NSAIDs are a widely used class of analgesic and anti-inflammatory drugs that act by inhibiting the cyclo-oxygenase (COX) enzyme. However, because of their nonspecificity of action, use of these agents as long-term therapy for chronic pain in diseases such as rheumatoid arthritis (RA) and osteoarthritis (OA) is often discouraged. Among NSAIDs, COX-2 inhibitors are promising candidates for long-term therapy of chronic diseases, particularly in the elderly, because of their reduced incidence of gastrointestinal adverse effects. However, in recent times these agents have also been shown to cause adverse effects such as cardiovascular effects (myocardial infarction, stroke and hypertension) and renal effects (decreased renal blood flow/glomerular filtration rate), which in 2004 led to the withdrawal of rofecoxib and in 2005 the withdrawal of valdecoxib from the US market. Importantly, these adverse effects can be effectively reduced by achieving site specific/targeted delivery through new formulation approaches. These formulations not only restrict the drug supply to specific organs but also reduce the dose required. As a result, use of new delivery systems such as nanoparticles, microparticles, microemulsions and nanogels has gained widespread applicability in the management of chronic disease, especially in the elderly, and particularly when there is a need to decrease dose-dependent adverse effects (as is the case with COX-2 inhibitors). This article reviews various new approaches to the delivery of COX-2 inhibitors and highlights issues related to the development of delivery systems for these agents for RA, OA, cancer (familial adenomatous polyposis, prostate, breast and non-small cell lung cancer), ocular diseases (such as diabetic retinopathy) and inflammatory diseases of the skin, with emphasis on their potential for use in the elderly. Emphasis is also placed on the preparation of these particulate systems, their release profile and behaviour in biological systems.

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

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

Bovine and porcine transscleral solute transport: influence of lipophilicity and the Choroid-Bruch's layer

PURPOSE

To determine the influence of the choroid-Bruch's layer and solute lipophilicity on in vitro transscleral drug permeability in bovine and porcine eyes.

METHODS

The in vitro permeability of two VEGF inhibitory drugs, budesonide and celecoxib, which are lipophilic and neutral at physiologic pH, and of three marker solutes, 3H-mannitol (hydrophilic, neutral), sodium fluorescein (hydrophilic, anionic), and rhodamine 6G (lipophilic, cationic), were determined across freshly excised scleras, with or without the underlying choroid-Bruch's layer. Select studies were performed using porcine sclera with and without choroid-Bruch's layer. Neural retina was removed by exposure of the eyecup to isotonic buffer and wherever required, the retinal pigment epithelial (RPE) layer of the preparation was disrupted and removed by exposure to hypertonic buffer. Because of the poor solubility of celecoxib and budesonide, permeability studies were conducted with 5% wt/vol of hydroxypropyl-beta-cyclodextrin (HPbetaCD). For other solutes, permeability studies were conducted, with and without HPbetaCD. Partitioning of the solutes into bovine sclera and choroid-Bruch's layer was also determined.

RESULTS

The calculated log (distribution coefficient) values were -2.89, -0.68, 2.18, 3.12, and 4.02 for mannitol, sodium fluorescein, budesonide, celecoxib, and rhodamine 6G, respectively. Removal of RPE was confirmed by transmission electron microscopy and differences in the transport of mannitol. The order of the permeability coefficients (Papp) across sclera and sclera-choroid-Bruch's layers in bovine and porcine models was 3H-mannitol > fluorescein > budesonide > celecoxib > rhodamine 6G, with HPbetaCD, and 3H-mannitol > fluorescein > rhodamine 6G, without HPbetaCD. The presence of choroid-Bruch's layer reduced the bovine scleral permeability by 2-, 8-, 16-, 36-, and 50-fold and porcine tissue permeability by 2-, 7-, 15-, 33-, and 40-fold, respectively, for mannitol, sodium fluorescein, budesonide, celecoxib, and rhodamine 6G. The partition coefficients measured in bovine tissues correlated positively with the log (distribution coefficient) and exhibited a trend opposite that of transport. The partition coefficient ratio of bovine choroid-Bruch's layer to sclera was approximately 1, 1.5, 1.7, 2, and 3.5, respectively, for the solutes, as listed earlier.

CONCLUSIONS

The choroid-Bruch's layer is a more significant barrier to drug transport than is sclera. It hinders the transport of lipophilic solutes, especially a cationic solute, more than hydrophilic solutes and in a more dramatic way than does sclera. The reduction in transport across this layer directly correlates with solute binding to the tissue. Understanding the permeability properties of sclera and underlying layers would be beneficial in designing better drugs for transscleral delivery.

Size-dependent disposition of nanoparticles and microparticles following subconjunctival administration

The purpose of this study was to determine the retention and ocular distribution of subconjunctivally administered nanoparticles and microparticles. Fluorescent polystyrene particles (carboxylate modified, negatively charged) of various sizes (20 nm, 200 nm and 2 microm; Fluospheres, dose 400 microg) were administered to male Sprague-Dawley rats by subconjunctival injection under anaesthesia. The disposition of the particles in the periocular and ocular tissues was studied for up to 60 days by quantifying the particle amounts using liquid extraction followed by spectrofluorimetric analysis. The effect of dose on the particle disposition was investigated with a 40-microg dose of the particles. The effect of an increase in surface hydrophobicity was evaluated for the 20 and 200 nm particles at 1 day post administration. Following periocular administration, penetration into the ocular tissues was negligible for the carboxylate-modified microparticles as well as nanoparticles. Almost the entire dose of the 200 nm and 2 microm particles was retained in the periocular tissue at 60 days post-administration. The 20 nm particles disappeared rapidly from the periocular tissue with 15 and 8% of administered dose remaining after 1 and 7 days, respectively. The 20 nm particles could not be detected in the periocular tissue at 60-days post-administration. An increase in the surface hydrophobicity did not affect the periocular retention of 200 nm particles but elevated that of the 20 nm particles, at the end of day 1. It was concluded that subconjunctivally administered 200 nm and larger particles can be almost completely retained at the site of administration for at least two months. Periocular administration of particulate systems of this size would likely be useful as sustained drug delivery systems.