Transscleral sustained ranibizumab delivery using an episcleral implantable device: Suppression of laser-induced choroidal neovascularization in rats

Solid implantable devices for sustained drug delivery

Implantable drug delivery systems (IDDS) are an attractive alternative to conventional drug administration routes. Oral and injectable drug administration are the most common routes for drug delivery providing peaks of drug concentrations in blood after administration followed by concentration decay after a few hours. Therefore, constant drug administration is required to keep drug levels within the therapeutic window of the drug. Moreover, oral drug delivery presents alternative challenges due to drug degradation within the gastrointestinal tract or first pass metabolism. IDDS can be used to provide sustained drug delivery for prolonged periods of time. The use of this type of systems is especially interesting for the treatment of chronic conditions where patient adherence to conventional treatments can be challenging. These systems are normally used for systemic drug delivery. However, IDDS can be used for localised administration to maximise the amount of drug delivered within the active site while reducing systemic exposure. This review will cover current applications of IDDS focusing on the materials used to prepare this type of systems and the main therapeutic areas of application.

Recent advances and future prospects: current status and challenges of the intraocular injection of drugs for vitreoretinal diseases

Effective drug therapy for vitreoretinal disease is a major challenge in the field of ophthalmology; various protective systems, including anatomical and physiological barriers, complicate drug delivery to precise targets. However, as the eye is a closed cavity, it is an ideal target for local administration. Various types of drug delivery systems have been investigated that take advantage of this aspect of the eye, enhancing ocular permeability and optimizing local drug concentrations. Many drugs, mainly anti-VEGF drugs, have been evaluated in clinical trials and have provided clinical benefit to many patients. In the near future, innovative drug delivery systems will be developed to avoid frequent intravitreal administration of drugs and maintain effective drug concentrations for a long period of time. Here, we review the published literature on various drugs and administration routes and current clinical applications. Recent advances in drug delivery systems are discussed along with future prospects.

A comparative study between a transscleral sustained-release device and eyedrops on intraocular distribution of carteolol hydrochloride

The objectives of this study were to develop a sustained-release device for carteolol hydrochloride (CH) and investigate any potential difference in the intraocular distribution of this agent between the transscleral administration of the device and treatment with eyedrops. The device was formulated with photocurable resin, poly (ethyleneglycol) dimethacrylate, to fit within the curve of the rabbit eyeball. In vitro study showed that CH was released in a sustained-release manner for 2 weeks. The concentration of CH in the retina, choroid/retinal pigment epithelium, sclera, iris, and aqueous humor was determined by high-performance liquid chromatography. Transscleral administration was able to deliver CH to the posterior segment (i.e., retina and choroid/retinal pigment epithelium) rather than the anterior segment (i.e., aqueous humor), while eyedrops delivered CH only to the anterior segment. Transscleral administration could deliver CH to aqueous humor at half the concentration versus treatment with eyedrops and reduced intraocular pressure (IOP) at 1 day after implantation; however, the IOP-lowering effect was not sustained thereafter. In conclusion, transscleral drug delivery may be a useful method for the reduction of IOP. Notably, the aqueous concentration must be equal to that delivered by the eyedrops, and this approach might be preferable for drug delivery to the posterior segment of the eye.

Implantable sustained-release drug delivery systems: a revolution for ocular therapeutics

PURPOSE

Due to the inimitable anatomical structure of the eyeball and various physiological barriers, conventional ocular local administration is often complicated by apparent shortcomings, such as limited bioavailability and short drug retention. Thus, developing methods for sustainable, safe and efficient drug delivery to ocular target sites has long been an urgent need. This study briefly summarizes the barriers to ocular drug administration and various ocular drug delivery routes and highlights recent progress in ocular implantable sustained-release drug delivery systems (DDSs) to provide literature evidence for developing novel ocular implants for sustained drug delivery.

METHODS

We conducted a comprehensive search of studies on ocular implantable sustained-release DDSs in PubMed and Web of Science using the following keywords: ocular, implantable and drug delivery system. More than 400 papers were extracted. Publications focused on sustained and controlled drug release were primarily considered. Experimental articles involving DDSs that cannot be implanted into the eye through surgeries and cannot be inserted into ocular tissues in solid form were excluded. Approximately 143 publications were reviewed to summarize the most current information on the subject.

RESULTS

In recent years, numerous ocular sustained-release DDSs using lipids, nanoparticles and hydrogels as carriers have emerged. With unique properties and systematic design, ocular implantable sustained-release DDSs are able to continuously maintain drug release, effectively sustain the therapeutic concentration in target tissues, and substantially enhance the therapeutic efficacy. Nevertheless, few ocular implantable sustained-release DDSs have been available in clinical use.

CONCLUSIONS

Ocular implantable sustained-release DDSs have become a new focus in the field of ocular drug development through unique designs and improvements in the materials of drug carriers, administration methods and dosage forms. With more ocular implantable sustained-release DDSs being commercialized, ocular therapeutics may be revolutionized.

Release of ranibizumab using a porous poly(dimethylsiloxane) capsule suppressed laser-induced choroidal neovascularization via the transscleral route

The administration of anti-vascular endothelial growth factor drugs in the posterior eye segment with sustained release through less invasive methods is a challenge in the treatment of age-related macular disease. We developed a flexible capsule device using porous poly(dimethylsiloxane) (PDMS) that was able to release ranibizumab. The porous PDMS sheet was fabricated by salt-leaching of a micro-sectioned PDMS sheet containing salt microparticles. Observation with scanning electron microscopy revealed that the pore densities could be adjusted by the concentration of salt. The in vitro release study showed that the release rate of fluorescein isothiocyanate-tagged albumin could be adjusted based on the pore density of the porous PDMS sheet. Ranibizumab could be released in a sustained-release manner for 16 weeks. The device was implanted on the sclera; its efficacy in terms of the suppression of laser-induced choroidal neovascularization (CNV) in rats was compared with that of monthly intravitreal injections of ranibizumab. At 8 and 18 weeks after implantation, the CNV area was significantly reduced in rats that received the ranibizumab-releasing device compared with those that received the placebo device. However, although monthly intravitreal injections of ranibizumab reduced CNV for 8 weeks, this reduction was not sustained for 18 weeks. In conclusion, we demonstrated a novel controlled-release device using a porous PDMS sheet that could suppress CNV via a less invasive transscleral route versus intravitreal injections. This device may also reduce the occurrence of side effects associated with frequent intravitreal injections.

Progress and Challenges of Anti-VEGF Agents and Their Sustained-Release Strategies for Retinal Angiogenesis

Currently, the treatment for ocular neovascular diseases, including diabetic macular edema (DME) and age-related macular degeneration (AMD), mainly involves repeated intravitreal injection of anti-vascular endothelial growth factor (VEGF) drugs. Although it can preserve vision, repeated injections are an invasive treatment modality, leading to serious complications and reducing patient adherence to treatment. To reduce the frequency of administration, prolong the time of drug action, and avoid repeated intravitreal injections, the combination of sustained-release materials with anti-VEGF drug therapy has become an emphasis in ophthalmology. In this review, we highlight the current state of anti-VEGF technology, its challenges, and the sustained-release strategies under investigation or being used in clinical practice. Both continuous release and considerable therapeutic effects can be achieved by encapsulating anti-VEGF drugs in sustained-release materials to minimize the number of intravitreal injections. At present, two sustained-release materials are being tested in clinical research, and although basic research shows the strong therapeutic application prospects of extended-release drugs, its challenges mainly involve the discrepancy between the release rates in vitro and the efficiency of the drugs in vivo. Briefly, sustained release of anti-VEGF agents is an advantageous strategy for treating retinal angiogenesis.

A 3D Printed Self-Sustainable Cell-Encapsulation Drug Delivery Device for Periocular Transplant-Based Treatment of Retinal Degenerative Diseases

Self-sustainable release of brain-derived neurotrophic factor (BDNF) to the retina using minimally invasive cell-encapsulation devices is a promising approach to treat retinal degenerative diseases (RDD). Herein, we describe such a self-sustainable drug delivery device with human retinal pigment epithelial (ARPE-19) cells (cultured on collagen coated polystyrene (PS) sheets) enclosed inside a 3D printed semi-porous capsule. The capsule was 3D printed with two photo curable polymers: triethylene glycol dimethacrylate (TEGDM) and polyethylene glycol dimethylacrylate (PEGDM). The capsule's semi-porous membrane (PEGDM) could serve three functions: protecting the cells from body's immune system by limiting diffusion (5.97 ± 0.11%) of large molecules like immunoglobin G (IgG)(150 kDa); helping the cells to survive inside the capsule by allowing diffusion (43.20 ± 2.16%) of small molecules (40 kDa) like oxygen and necessary nutrients; and helping in the treatment of RDD by allowing diffusion of cell-secreted BDNF to the outside environment. In vitro results showed a continuous BDNF secretion from the device for at least 16 days, demonstrating future potential of the cell-encapsulation device for the treatment of RDD in a minimally invasive and self-sustainable way through a periocular transplant.