Drug delivery to posterior intraocular tissues: third Annual ARVO/Pfizer Ophthalmics Research Institute Conference

Advanced Technologies of Drug Delivery to the Posterior Eye Segment Targeting Angiogenesis and Ocular Cancer

Retinoblastoma (RB), a childhood retinal cancer is caused due to RB1 gene mutation which affects the child below 5 years of age. Angiogenesis has been proven its role in RB metastasis due to the presence of vascular endothelial growth factor (VEGF) in RB cells. Therefore, exploring angiogenic pathway by inhibiting VEGF in treating RB would pave the way for future treatment. In preclinical studies, anti-VEGF molecule have shown their efficacy in treating RB. However, treatment requires recurrent intra-vitreal injections causing various side effects along with patient nonadherence. As a result, delivery of anti-VEGF agent to retina requires an ocular delivery system that can transport it in a non-invasive manner to achieve patient compliance. Moreover, development of these type of systems are challenging due to the complicated physiological barriers of eye. Adopting a non-invasive or minimally invasive approach for delivery of anti-VEGF agents would not only address the bioavailability issues but also improve patient adherence to therapy overcoming the side effects associated with invasive approach. The present review focuses on the eye cancer, angiogenesis and various novel ocular drug delivery systems that can facilitate inhibition of VEGF in the posterior eye segment by overcoming the eye barriers.

Recent Advances in the Excipients Used for Modified Ocular Drug Delivery

In ocular drug delivery, maintaining an efficient concentration of the drug in the target area for a sufficient period of time is a challenging task. There is a pressing need for the development of effective strategies for drug delivery to the eye using recent advances in material sciences and novel approaches to drug delivery. This review summarizes the important aspects of ocular drug delivery and the factors affecting drug absorption in the eye including encapsulating excipients (chitosan, hyaluronic acid, poloxamer, PLGA, PVCL-PVA-PEG, cetalkonium chloride, and gelatin) for modified drug delivery.

Ocular delivery of proteins and peptides: Challenges and novel formulation approaches

The impact of proteins and peptides on the treatment of various conditions including ocular diseases over the past few decades has been advanced by substantial breakthroughs in structural biochemistry, genetic engineering, formulation and delivery approaches. Formulation and delivery of proteins and peptides, such as monoclonal antibodies, aptamers, recombinant proteins and peptides to ocular tissues poses significant challenges owing to their large size, poor permeation and susceptibility to degradation. A wide range of advanced drug delivery systems including polymeric controlled release systems, cell-based delivery and nanowafers are being exploited to overcome the challenges of frequent administration to ocular tissues. The next generation systems integrated with new delivery technologies are anticipated to generate improved efficacy and safety through the expansion of the therapeutic target space. This review will highlight recent advances in formulation and delivery strategies of protein and peptide based biopharmaceuticals. We will also describe the current state of proteins and peptides based ocular therapy and future therapeutic opportunities.

Nanomedicines in the future of pediatric therapy

Nanotechnology has become a key tool to overcome the main (bio)pharmaceutical drawbacks of drugs and to enable their passive or active targeting to specific cells and tissues. Pediatric therapies usually rely on the previous clinical experience in adults. However, there exists scientific evidence that drug pharmacokinetics and pharmacodynamics in children differ from those in adults. For example, the interaction of specific drugs with their target receptors undergoes changes over the maturation of the different organs and systems. A similar phenomenon is observed for toxicity and adverse effects. Thus, it is clear that the treatment of disease in children cannot be simplified to the direct adjustment of the dose to the body weight/surface. In this context, the implementation of innovative technologies (e.g., nanotechnology) in the pediatric population becomes extremely challenging. The present article overviews the different attempts to use nanotechnology to treat diseases in the pediatric population. Due to the relevance, though limited available literature on the matter, we initially describe from preliminary in vitro studies to preclinical and clinical trials aiming to treat pediatric infectious diseases and pediatric solid tumors by means of nanotechnology. Then, the perspectives of pediatric nanomedicine are discussed.

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.

Nanostructured lipid carriers for triamcinolone acetonide delivery to the posterior segment of the eye

Triamcinolone acetonide (TA) is a corticosteroid drug currently administered by intravitreal injection for a broad spectrum of inflammatory, edematous and angiogenic ocular diseases. To increase the drug's bioavailability by ocular instillation, TA was encapsulated in nanostructured lipid carriers (NLC), previously optimized by our group using a factorial design approach. In the present paper, nanometric (∼200 nm), unimodal and negatively charged NLC loaded with the fluorescent lipid marker Nile red (NR-NLC) and drug (TA-NLC) were produced by high pressure homogenization. Based on the selected formulations, in vivo tests were carried out by eye-drop instillation of NR-NLC in mice, revealing the systems' ability of delivering lipophilic actives to the posterior segment of the eye via the corneal and non-corneal pathways. Short and long-term stability of TA-NLC was assessed by high performance stability analysis using the Turbiscan®. The results showed a backscattering of less than 1.5% and during a period of 6 months, anticipated the low tendency of these particles for aggregation during shelf life when stored at room temperature.

Noninvasive, in vivo assessment of mouse retinal structure using optical coherence tomography

Background

Optical coherence tomography (OCT) is a novel method of retinal in vivo imaging. In this study, we assessed the potential of OCT to yield histology-analogue sections in mouse models of retinal degeneration.

Methodology/Principal Findings

We achieved to adapt a commercial 3^rd generation OCT system to obtain and quantify high-resolution morphological sections of the mouse retina which so far required in vitro histology. OCT and histology were compared in models with developmental defects, light damage, and inherited retinal degenerations. In conditional knockout mice deficient in retinal retinoblastoma protein Rb, the gradient of Cre expression from center to periphery, leading to a gradual reduction of retinal thickness, was clearly visible and well topographically quantifiable. In Nrl knockout mice, the layer involvement in the formation of rosette-like structures was similarly clear as in histology. OCT examination of focal light damage, well demarcated by the autofluorescence pattern, revealed a practically complete loss of photoreceptors with preservation of inner retinal layers, but also more subtle changes like edema formation. In Crb1 knockout mice (a model for Leber's congenital amaurosis), retinal vessels slipping through the outer nuclear layer towards the retinal pigment epithelium (RPE) due to the lack of adhesion in the subapical region of the photoreceptor inner segments could be well identified.

Conclusions/Significance

We found that with the OCT we were able to detect and analyze a wide range of mouse retinal pathology, and the results compared well to histological sections. In addition, the technique allows to follow individual animals over time, thereby reducing the numbers of study animals needed, and to assess dynamic processes like edema formation. The results clearly indicate that OCT has the potential to revolutionize the future design of respective short- and long-term studies, as well as the preclinical assessment of therapeutic strategies.