Development of an Experimental Drug Eluting Suprachoroidal Microstent as Glaucoma Drainage Device

Ocular drug delivery systems: glaucoma patient perceptions from a German university hospital eye clinic

PURPOSE

This study aimed to report on glaucoma patients' beliefs and illness perceptions and to investigate their opinion on ocular drug delivery devices (ODD).

METHODS

We performed a cross-sectional study in a large tertiary-referral outpatient glaucoma clinic, with 102 patients. Validated anonymized questionnaires were used. We investigated the awareness and acceptance regarding ODD (contact lenses (CLs), punctal plugs (PPs), subconjunctival implants, anterior chamber (AC) injections, and drug-emitting stents) and looked at factors that could influence a patient's decision for having an ODD.

RESULTS

Sixty-three patients (61.8%) confirmed they would rather have ODD than keep their eye-drops (38.2%). The most important factors influencing their decision were effectiveness and long-lasting effect. A large proportion of patients reported a preference for CLs (48.0%), PPs (52.9%), or drug-emitting stents (44.1%). When comparing patients who preferred ODD (group-1) versus eye-drops (group-2), significantly more patients in group-1 were worried (p < 0.001) or felt disrupted (p < 0.001) by their use of eye-drops. A significantly greater share of patients in group-1 showed acceptance towards CLs (60.3% vs. 38.5%; p = 0.032), AC injections (38.1% vs. 12.8%, p = 0.006), or drug-emitting stents (54% vs. 28.2%, p = 0.023), whilst there were no significant differences regarding the acceptance of PPs (p = 0.363) or subconjunctival implants (p = 0.058).

CONCLUSION

ODD for the treatment of glaucoma were broadly deemed acceptable by patients in this study. Effectiveness and long-lasting effect were the most important factors for a decision towards having an ODD. The majority of patients who preferred an ODD felt severely affected by their disease and were negatively influenced by their glaucoma medication intake.

Recent Advancements in Glaucoma Surgery-A Review

Surgery has long been an important treatment for limiting optic nerve damage and minimising visual loss in patients with glaucoma. Numerous improvements, modifications, and innovations in glaucoma surgery over recent decades have improved surgical safety, and have led to earlier and more frequent surgical intervention in glaucoma patients at risk of vision loss. This review summarises the latest advancements in trabeculectomy surgery, glaucoma drainage device (GDD) implantation, and minimally invasive glaucoma surgery (MIGS). A comprehensive search of MEDLINE, EMBASE, and CENTRAL databases, alongside subsequent hand searches-limited to the past 10 years for trabeculectomy and GDDs, and the past 5 years for MIGS-yielded 2283 results, 58 of which were included in the final review (8 trabeculectomy, 27 GDD, and 23 MIGS). Advancements in trabeculectomy are described in terms of adjunctive incisions, Tenon's layer management, and novel suturing techniques. Advancements in GDD implantation pertain to modifications of surgical techniques and devices, novel methods to deal with postoperative complications and surgical failure, and the invention of new GDDs. Finally, the popularity of MIGS has recently promoted modifications to current surgical techniques and the development of novel MIGS devices.

Quantitative systems pharmacology of the eye: Tools and data for ocular QSP

Good eyesight belongs to the most-valued attributes of health, and diseases of the eye are a significant healthcare burden. Case numbers are expected to further increase in the next decades due to an aging society. The development of drugs in ophthalmology, however, is difficult due to limited accessibility of the eye, in terms of drug administration and in terms of sampling of tissues for drug pharmacokinetics (PKs) and pharmacodynamics (PDs). Ocular quantitative systems pharmacology models provide the opportunity to describe the distribution of drugs in the eye as well as the resulting drug-response in specific segments of the eye. In particular, ocular physiologically-based PK (PBPK) models are necessary to describe drug concentration levels in different regions of the eye. Further, ocular effect models using molecular data from specific cellular systems are needed to develop dose-response correlations. We here describe the current status of PK/PBPK as well as PD models for the eyes and discuss cellular systems, data repositories, as well as animal models in ophthalmology. The application of the various concepts is highlighted for the development of new treatments for postoperative fibrosis after glaucoma surgery.

History, presence, and future of mitomycin C in glaucoma filtration surgery

PURPOSE OF REVIEW

Mitomycin C (MMC) is an alkylating agent with extraordinary ability to crosslink DNA, preventing DNA synthesis. By this virtue, MMC is an important antitumor drug. In addition, MMC has become the gold standard medication for glaucoma filtration surgery (GFS). This eye surgery creates a passage for drainage of aqueous humor (AqH) out of the eye into the sub-Tenon's space with the aim of lowering the intraocular pressure. A major cause of failure of this operation is fibrosis and scarring in the sub-Tenon's space, which will restrict AqH outflow. Intraoperative application of MMC during GFS has increased GFS success rate, presumably mainly by reducing fibrosis after GFS. However, still 10% of glaucoma surgeries fail within the first year.

RECENT FINDINGS

In this review, we evaluate risks and benefits of MMC as an adjuvant for GFS. In addition, we discuss possible improvements of its use by adjusting dose and method of administration.

SUMMARY

One way of improving GFS outcome is to prolong MMC delivery by using a drug delivery system.

Regulation of the Ocular Cell/Tissue Response by Implantable Biomaterials and Drug Delivery Systems

Therapeutic advancements in the treatment of various ocular diseases is often linked to the development of efficient drug delivery systems (DDSs), which would allow a sustained release while maintaining therapeutic drug levels in the target tissues. In this way, ocular tissue/cell response can be properly modulated and designed in order to produce a therapeutic effect. An ideal ocular DDS should encapsulate and release the appropriate drug concentration to the target tissue (therapeutic but non-toxic level) while preserving drug functionality. Furthermore, a constant release is usually preferred, keeping the initial burst to a minimum. Different materials are used, modified, and combined in order to achieve a sustained drug release in both the anterior and posterior segments of the eye. After giving a picture of the different strategies adopted for ocular drug release, this review article provides an overview of the biomaterials that are used as drug carriers in the eye, including micro- and nanospheres, liposomes, hydrogels, and multi-material implants; the advantages and limitations of these DDSs are discussed in reference to the major ocular applications.

Targeting drug delivery within the suprachoroidal space

The suprachoroidal space (SCS), a potential anatomical space between the sclera and choroid, is a novel route for drug delivery targeting the chorioretinal layers of the eye. The safety and efficacy of SCS drug delivery have been shown in multiple clinical trials. Recent studies have developed methods for more precise targeting within the SCS at sites of action at the posterior pole (e.g., macula), near the limbus (e.g., ciliary body), and throughout the SCS using iontophoresis, swollen hydrogels, high-density particle emulsions, highly viscous and non-Newtonian fluids, and microstents. Here, we review novel technologies targeting the posterior, anterior, or entire SCS.

Trabeculectomy with Suprachoroidal Derivation in Eyes with Uncontrolled Glaucoma: A Case Series with a 24-Month Follow-up

Introduction

The aim of this study was to evaluate the efficacy of trabeculectomy with suprachoroidal derivation in eyes with uncontrolled glaucoma after a 24-month follow-up period.

Methods

This was a prospective uncontrolled non-randomized case series. All patients scheduled for a trabeculectomy due to uncontrolled glaucoma at the “Instituto de Glaucoma y Catarata” (Lima, Peru) between 2011 and 2014 were included. Thee patients underwent trabeculectomy with mitomycin C and suprachoroidal derivation with two autologous scleral flaps. Postsurgical follow-up visits took place on day 1, and at 1, 6, 12, 18 and 24 months. Best corrected visual acuity (BCVA), intraocular pressure (IOP) and complications at each control were registered. Main outcome measures were IOP reduction, number of glaucoma medications and complication rate. Postoperative IOP of > 21 mmHg, < 5 mmHg, additional glaucoma surgery or severe complications were considered as indications of failure.

Results

Thirty-three participants (41 eyes) were included in the study, of whom 27 (81.82%) (31 eyes [75.61%]) finished the 24 months of follow-up. At the end of the follow-up, mean IOP had decreased by 11.29 ± 9.32 mmHg (p < 0.001), and glaucoma medication usage in 25 (25/31; 80.65%) eyes had stopped. Ten (10/41; 24.39%) patients complained of blurred vision, and 15 (15/41; 36.59%) patients referred to foreign body sensation the first day after surgery; both sensations resolved spontaneously after 1 week in all cases. No failures, significant changes in BCVA (p = 0.387) or severe complications were found.

Conclusions

In this case series, trabeculectomy with suprachoroidal derivation exhibited high efficacy and safety after a 24-month follow-up. A larger sample with a control group is needed to confirm our initial findings.

Development of a biodegradable antifibrotic local drug delivery system for glaucoma microstents

To prevent implant failure due to fibrosis is a major objective in glaucoma research. The present study investigated the antifibrotic effects of paclitaxel (PTX), caffeic acid phenethyl ester (CAPE), and pirfenidone (PFD) coated microstent test specimens in a rat model. Test specimens based on a biodegradable blend of poly(4-hydroxybutyrate) biopolymer and atactic poly(3-hydroxybutyrate) (at.P(3HB)) were manufactured, equipped with local drug delivery (LDD) coatings, and implanted in the subcutaneous white fat depot. Postoperatively, test specimens were explanted and analyzed for residual drug content. Fat depots including the test specimens were histologically analyzed. In vitro drug release studies revealed an initial burst for LDD devices. In vivo, slow drug release of PTX was found, whereas it already completed 1 week postoperatively for CAPE and PFD LDD devices. Histological examinations revealed a massive cell infiltration in the periphery of the test specimens. Compact fibrotic capsules around the LDD devices were detectable at 4–36 weeks and least pronounced around PFD-coated specimens. Capsules stained positive for extracellular matrix (ECM) components. The presented model offers possibilities to investigate release kinetics and the antifibrotic potential of drugs in vivo as well as the identification of more effective agents for a novel generation of drug-eluting glaucoma microstents.

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.

iDrugs and iDevices Discovery Research: Preclinical Assays, Techniques, and Animal Model Studies for Ocular Hypotensives and Neuroprotectants

Discovery ophthalmic research is centered around delineating the molecular and cellular basis of ocular diseases and finding and exploiting molecular and genetic pathways associated with them. From such studies it is possible to determine suitable intervention points to address the disease process and hopefully to discover therapeutics to treat them. An investigational new drug (IND) filing for a new small-molecule drug, peptide, antibody, genetic treatment, or a device with global health authorities requires a number of preclinical studies to provide necessary safety and efficacy data. Specific regulatory elements needed for such IND-enabling studies are beyond the scope of this article. However, to enhance the overall data packages for such entities and permit high-quality foundation-building publications for medical affairs, additional research and development studies are always desirable. This review aims to provide examples of some target localization/verification, ocular drug discovery processes, and mechanistic and portfolio-enhancing exploratory investigations for candidate drugs and devices for the treatment of ocular hypertension and glaucomatous optic neuropathy (neurodegeneration of retinal ganglion cells and their axons). Examples of compound screening assays, use of various technologies and techniques, deployment of animal models, and data obtained from such studies are also presented.

Ultrahigh field MR imaging of a subconjunctival anti-glaucoma drug delivery system in a rabbit model

Local drug delivery systems (DDS) have become a favourable approach for the treatment of numerous diseases. Biomedical imaging techniques such as ultrahigh field magnetic resonance imaging (UHF-MRI) offer unique insight into DDS biodegradation in vivo. We describe the establishment of a 7 Tesla MRI routine for longitudinal in vivo examinations of a subconjunctival DDS for the treatment of glaucoma in a rabbit model. In initial in vitro examinations the T2-relaxation times of the polymeric DDS components were assessed. Imaging of enzymatically degraded depot samples in vitro did not reveal changes in sample morphology or T2-relaxation time. Ex vivo investigations with an enucleated porcine eye showed good correlation of anatomical MRI and histological data. In longitudinal in vivo studies in rabbits, we repeatedly scanned the depot in the same animal over the course of 5 months with an in-plane resolution of 130 µm at scan times of less than 30 minutes. The degradation was quantified using volumetric analysis showing a volume reduction of 82% between 3 and 21 weeks after depot implantation. We have thereby demonstrated the feasibility of our UHF-MRI protocol as a non-invasive imaging routine for qualitative and quantitative, longitudinal evaluation of biodegradable subconjunctival DDS.

Development of a biodegradable flow resisting polymer membrane for a novel glaucoma microstent

Within this paper we analyzed the technical feasibility of a novel microstent for glaucoma therapy. For lowering of intraocular pressure, the flexible polyurethane (PUR) implant is designed to drain aqueous humour from the anterior chamber of the eye into subconjunctival, or alternatively suprachoroidal, space. The microstent includes a biodegradable, flow resisting polymer membrane serving as temporary flow resistance for the prevention of early postoperative hypotony. A biodegradable local drug delivery (LDD)-device was designed to prevent fibrous encapsulation. Biodegradable components were made of flexible, nonwoven membranes of Poly(4-hydroxybutyrate) (P(4HB)). Polymer samples and microstent prototypes were manufactured by means of dip coating, electrospinning and femtosecond-laser micromachining and characterized in vitro with regard to structural and fluid mechanical properties, degradation behavior and drug release. Bending stiffness of PUR-tubing (62.53 ± 7.57 mN mm²) is comparable to conventional glaucoma drainage devices in a tube-plate design. Microstent prototypes yield a flow resistance of 2.4 ± 0.6 mmHg/μl min^-1 which is close to the aspired value corresponding to physiological pressure (15 mmHg) and aqueous humour flow (2 μl min^-1) conditions inside the eye. Degradation of electrospun P(4HB) specimens was found to be almost completely finished after six months in vitro. Within this time frame, flow capacity of the microstent increases, which is beneficial to compensate potentially increasing flow resistance of fibrous tissue in vivo. Fast drug release of the LDD-device was found. One microstent prototype was implanted into a porcine eye ex vivo. Future preclinical studies will allow further information about Microstent performance.