Preclinical evaluation of a phosphorothioate oligonucleotide in the retina of rhesus monkey

Effects of Topic Delivery of an Inhibitor of Serine Racemase on Laser-Induced Choroidal Vasculopathy

Purpose

Intravitreal injection of anti-VEGF antibodies remains the primary therapy for exudative age-related macular degeneration (exAMD), although its efficacy is limited. Previous research has demonstrated that both a loss-of-function mutation of srr and the intravenous injection of a serine racemase inhibitor, L-aspartic acid β-hydroxamate (L-ABH), significantly inhibit laser-induced choroidal neovascularization (CNV) in mice. Given that L-ABH is a small molecule, this study investigated the effects of L-ABH administered via eye drops on CNV, aiming to develop a noninvasive treatment strategy for exAMD.

Methods

CNV models in mice and rhesus macaques were established through laser photocoagulation. Seven monkeys were randomly assigned to receive either saline solution or L-ABH eye drops. Intraperitoneal or intravenous injection of fluorescein characterized CNV in both mice and monkeys. Fluorescein fundus angiography was used to assess leakage, whereas optical coherence tomography measured retinal thickness in the monkeys.

Results

L-ABH eye drops significantly reduced fluorescein leakage in laser-injured mice (P < 0.001 compared to saline). In laser-injured rhesus macaques, the average percent changes in leakage areas treated with L-ABH were 2.5% ± 25.8% (P = 0.004) and 1.5% ± 75.7% (P = 0.023 compared to saline solution) on day 14 and day 28, respectively. However, L-ABH eye drops did not significantly affect the number of grade IV laser spots or retinal thickness, whereas bevacizumab did.

Conclusions

This study demonstrates the potential efficacy of an SRR inhibitor in two animal models of laser-induced CNV.

Translational Relevance

This represents the first investigation into the effects of topical delivery of an SRR inhibitor on CNV.

Duplex RNAs and ss-siRNAs Block RNA Foci Associated with Fuchs' Endothelial Corneal Dystrophy

Fuchs' endothelial corneal dystrophy (FECD) leads to vision loss and is one of the most common inherited eye diseases. Corneal transplants are the only curative treatment available, and there is a major unmet need for treatments that are less invasive and independent of donor tissue. Most cases of FECD are associated with an expanded CUG repeat within the intronic region of TCF4 and the mutant RNA has been implicated as the cause of the disease. We previously presented preliminary data suggesting that single-stranded antisense oligonucleotides (ASOs) can inhibit CUG RNA foci in patient-derived cells and tissue. We now show that duplex RNAs and single-stranded silencing RNAs (ss-siRNAs) reduce the number of cells with foci and the number of foci per cells. Potencies are similar to those that are achieved with chemically modified ASOs designed to block foci. These data widen the potential for synthetic nucleic acids to be used to treat a widely prevalent and debilitating disease.

Antisense Oligonucleotide-Based Splicing Correction in Individuals with Leber Congenital Amaurosis due to Compound Heterozygosity for the c.2991+1655A>G Mutation in CEP290

Leber congenital amaurosis (LCA) is a rare inherited retinal disorder affecting approximately 1:50,000 people worldwide. So far, mutations in 25 genes have been associated with LCA, with CEP290 (encoding the Centrosomal protein of 290 kDa) being the most frequently mutated gene. The most recurrent LCA-causing CEP290 mutation, c.2991+1655A>G, causes the insertion of a pseudoexon into a variable proportion of CEP290 transcripts. We previously demonstrated that antisense oligonucleotides (AONs) have a high therapeutic potential for patients homozygously harbouring this mutation, although to date, it is unclear whether rescuing one single allele is enough to restore CEP290 function. Here, we assessed the AON efficacy at RNA, protein and cellular levels in samples that are compound heterozygous for this mutation, together with a protein-truncating mutation in CEP290. We demonstrate that AONs can efficiently restore splicing and increase protein levels. However, due to a high variability in ciliation among the patient-derived cell lines, the efficacy of the AONs was more difficult to assess at the cellular level. This observation points towards the importance of the severity of the second allele and possibly other genetic variants present in each individual. Overall, AONs seem to be a promising tool to treat CEP290-associated LCA, not only in homozygous but also in compound heterozygous carriers of the c.2991+1655A>G variant.

Dendrimers as tunable vectors of drug delivery systems and biomedical and ocular applications

Dendrimers are large polymeric structures with nanosize dimensions (1-10 nm) and unique physicochemical properties. The major advantage of dendrimers compared with linear polymers is their spherical-shaped structure. During synthesis, the size and shape of the dendrimer can be customized and controlled, so the finished macromolecule will have a specific "architecture" and terminal groups. These characteristics will determine its suitability for drug delivery, diagnostic imaging, and as a genetic material carrier. This review will focus initially on the unique properties of dendrimers and their use in biomedical applications, as antibacterial, antitumor, and diagnostic agents. Subsequently, emphasis will be given to their use in drug delivery for ocular diseases.

Intravitreal Injection of Splice-switching Oligonucleotides to Manipulate Splicing in Retinal Cells

Leber congenital amaurosis is a severe hereditary retinal dystrophy responsible for neonatal blindness. The most common disease-causing mutation (c.2991+1655A>G; 10-15%) creates a strong splice donor site that leads to insertion of a cryptic exon encoding a premature stop codon. Recently, we reported that splice-switching oligonucleotides (SSO) allow skipping of the mutant cryptic exon and the restoration of ciliation in fibroblasts of affected patients, supporting the feasibility of a SSO-mediated exon skipping strategy to correct the aberrant splicing. Here, we present data in the wild-type mouse, which demonstrate that intravitreal administration of 2'-OMePS-SSO allows selective alteration of Cep290 splicing in retinal cells, including photoreceptors as shown by successful alteration of Abca4 splicing using the same approach. We show that both SSOs and Cep290 skipped mRNA were detectable for at least 1 month and that intravitreal administration of oligonucleotides did not provoke any serious adverse event. These data suggest that intravitreal injections of SSO should be considered to bypass protein truncation resulting from the c.2991+1655A>G mutation as well as other truncating mutations in genes which like CEP290 or ABCA4 have a mRNA size that exceed cargo capacities of US Food and Drug Administration (FDA)-approved adeno-associated virus (AAV)-vectors, thus hampering gene augmentation therapy.

Animal models of age-related macular degeneration and their translatability into the clinic

Age-related macular degeneration (AMD) is a leading cause of blindness in people over the age of 55. Despite its common nature, the etiology of the disease involves both genetic and environmental factors, the interaction of which is not fully understood. Animal models, including the mouse, rat, rabbit, pig and non-human primate, have been developed to study various aspects of the disease and to evaluate novel therapies; however, no single model has been developed to emulate all aspects of the disease. This review will discuss the various existing models of AMD, their strengths and limitations and examples of their use in current AMD research.

Aptamer-based therapeutics of the past, present and future: from the perspective of eye-related diseases

Aptamers have emerged as a novel and powerful class of biomolecules with an immense untapped potential. The ability to synthesise highly specific aptamers against any molecular target make them a vital cog in the design of effective therapeutics for the future. However, only a minutia of the enormous potential of this dynamic class of molecule has been exploited. Several aptamers have been studied for the treatment of eye-related disorders, and one such strategy has been successful in therapy. This review gives an account of several eye diseases and their regulatory biomolecules where other nucleic acid therapeutics have been attempted with limited success and how aptamers, with their exceptional flexibility to chemical modifications, can overcome those inherent shortcomings.

Animal models of age related macular degeneration

Age related macular degeneration (AMD) is the leading cause of vision loss of those over the age of 65 in the industrialized world. The prevalence and need to develop effective treatments for AMD has lead to the development of multiple animal models. AMD is a complex and heterogeneous disease that involves the interaction of both genetic and environmental factors with the unique anatomy of the human macula. Models in mice, rats, rabbits, pigs and non-human primates have recreated many of the histological features of AMD and provided much insight into the underlying pathological mechanisms of this disease. In spite of the large number of models developed, no one model yet recapitulates all of the features of human AMD. However, these models have helped reveal the roles of chronic oxidative damage, inflammation and immune dysregulation, and lipid metabolism in the development of AMD. Models for induced choroidal neovascularization have served as the backbone for testing new therapies. This article will review the diversity of animal models that exist for AMD as well as their strengths and limitations.

Retinal microglial activation and inflammation induced by amadori-glycated albumin in a rat model of diabetes

OBJECTIVE

During diabetes, retinal microglial cells are activated to release inflammatory cytokines that initiate neuronal loss and blood-retinal barrier breakdown seen in diabetic retinopathy (DR). The mechanism by which diabetes activates microglia to release those inflammatory mediators is unclear and was therefore elucidated.

RESEARCH DESIGN AND METHODS

Microglia activation was characterized in streptozocin-injected rats and in isolated microglial cells using immunofluorescence, enzyme-linked immunosorbent assay, RT-PCR, and Western blot analyses.

RESULTS

In 8-week diabetic retina, phospho-extracellular signal-related kinase (ERK) and P38 mitogen-activated protein kinases were localized in microglia, but not in Mueller cells or astrocytes. At the same time, Amadori-glycated albumin (AGA)-like epitopes were featured in the regions of microglia distribution, implicating a pathogenic effect on microglial activation. To test this, diabetic rats were treated intravitreally with A717, a specific AGA-neutralizing antibody, or murine IgG. Relative to nondiabetic rats, diabetic rats (IgG-treated) manifested 3.9- and 7.9-fold increases in Iba-1 and tumor necrosis factor (TNF)-α mRNAs, respectively. Treatment of diabetic rats with A717 significantly attenuated overexpression of these mRNAs. Intravitreal injection of AGA per se in normal rats resulted in increases of Iba-1 expression and TNF-α release. Guided by these results, a cultured retinal microglia model was developed to study microglial response after AGA treatment and the mechanistic basis behind this response. The results showed that formation of reactive oxygen species and subsequent activation of ERK and P38, but not Jun NH2-terminal kinase, are molecular events underpinning retinal microglial TNF-α release during AGA treatment.

CONCLUSIONS

These results provide new insights in understanding the pathogenesis of early DR, showing that the accumulated AGA within the diabetic retina elicits the microglial activation and secretion of TNF-α. Thus, intervention trials with agents that neutralize AGA effects may emerge as a new therapeutic approach to modulate early pathologic pathways long before the occurrence of vision loss among patients with diabetes.

Optimization of laser-induced choroidal neovascularization in African green monkeys

We developed and validated a new nonhuman primate model of laser-induced choroidal neovascularization (CNV) that addresses study design limitations prevalent in laser-induced CNV-based efficacy studies. Laser-induced Bruch's membrane disruption triggers CNV and has been widely utilized in animals to model neovascular ("wet") age-related macular degeneration (AMD). Despite widespread use of the approach, detailed assessment of experimental parameters and their influence on pathophysiological endpoints critical for disease modeling has been extremely limited and largely based on anecdotal observations. We evaluated laser power parameters and endpoint measures to optimize methods for CNV formation and quantification to facilitate drug efficacy screening in African green monkeys. Six laser spots of 350, 550, 750, 950 or 1500 mW laser power were positioned bilaterally 1.5 disc diameters from the fovea, within the macula. Fluorescein angiograms were collected 3-5 weeks later and scored by trained masked investigators using graded (I-IV) and densitometric methods. Histopathology assessments were also performed, including determination of CNV area. Test system sensitivity to angiogenesis inhibition was subsequently assessed by evaluating the effect of intravitreal bevacizumab (Avastin) pretreatment (one day prior to laser photocoagulation) on incidence of CNV. Grade III and grade IV lesions were considered clinically relevant, demonstrating early hyperfluorescence and late leakage within or beyond the lesion borders. By 4 weeks post-laser all treatment groups demonstrated evidence of grade III lesions with greatest incidence observed in lesions induced by 750 and 950 mW laser power (72.9% and 69.4% respectively). Grade IV lesions were confined to eyes receiving 550 mW laser power or higher, with highest incidence of grade IV lesions observed in eyes receiving 950 (19.4%) and 1500 mW (31%) laser spots, incidence peaking 4 weeks post-laser photocoagulation. Densitometric analyses of angiograms corroborated visual scoring. Bevacizumab completely abolished grade IV lesion development and significantly lowered lesion fluorescein signal intensity (P < 0.0001) and CNV area (P = 0.038) compared to vehicle-treated controls. Our studies demonstrate that laser power of 950-1500 mW and angiography analysis 4 weeks post-laser are optimal parameters to evaluate treatment effects on CNV induction following laser photocoagulation. Bevacizumab significantly attenuated CNV development, as determined by fluorescein angiography and histopathology assessments in this model, supporting the application of African green monkeys in preclinical modeling of CNV. Laser parameters and time points for therapeutic dosing and angiography endpoints are critical factors to the laser-induced CNV model and must be validated for robust assessment of efficacy. The newly optimized nonhuman primate model described will facilitate preclinical efficacy assessments of novel therapeutics for CNV.

Unique Homologous siRNA Blocks Hypoxia-Induced VEGF Upregulation in Human Corneal Cells and Inhibits and Regresses Murine Corneal Neovascularization

PURPOSE

To evaluate the results of amniotic membrane transplantation (AMT) for ocular surface reconstruction in chemical and thermal injuries.

METHODS

Retrospective review of case records of patients who had undergone AMT for chemical injuries (January 1998 to May 2001).

RESULTS

Seventy two eyes of 69 patients were studied of which 24 were acute cases (median-2 days, range, 1-20 days) and 48 were chronic cases (median-12.4 months, range, 1.02-95.8 months). Mean age was 22.4 years (SD +/- 13.34 years) and average follow up duration was 7.8 months (SD +/- 7.1). Main clinical findings were symblephara (52.8%), corneal vascularization (51.3%), conjunctivalization (45.8%), Limbal ischemia (45.8%), Limbal stem cell deficiency (55.5%) and epithelial defect (48.6%). 18 cases were due to acid injuries (5 acute, 13 chronic), 52 were due to alkali (18 acute and 34 chronic) and 2 cases were due to thermal burns (1 each acute and chronic). Overall success rate was 87.5% in acute cases and 72.9% in chronic cases. Indication-wise success rates were 94.3% for epithelial defect healing, 88.2% for symptomatic relief, 59.7% for ocular surface reconstruction, and 55% for improving limbal stem cell function. Success was not achieved in any outcome measure in 1/24 (4.2%) in acute group and 6/48 (12.5%) in chronic group.

CONCLUSION

AMT helps in ocular surface reconstruction, promotes rapid epithelial healing and partially restores limbal stem cell function. It can be considered as an effective modality for the ocular surface restoration in chemical and thermal injuries in selected cases. Success rates in acute and chronic cases are comparable.

Non-viral ocular gene therapy: potential ocular therapeutic avenues

Non-viral vectors for potential gene replacement and therapy have been developed in order to overcome the drawbacks of viral vectors. The diversity of non-viral vectors allows for a wide range of various products, flexibility of application, ease of use, low-cost of production and enhanced "genomic" safety. Using non-viral strategies, oligonucleotides (ODNs) can be delivered naked (less efficient) or entrapped in cationic lipids, polymers or peptides forming slow release delivery systems, which can be adapted according to the organ targeted and the therapy purposes. Tissue and cell internalization can be further enhanced by changing by physical or chemical means. Moreover, a specific vector can be selected according to disease course and intensity of manifestations fulfilling specific requirements such as the duration of drug release and its level along with cells and tissues specific targeting. From accumulating knowledge and experience, it appears that combination of several non-viral techniques may increase the efficacy and ensure the safety of these evolving and interesting gene therapy strategies.

Ocular delivery of nucleic acids: antisense oligonucleotides, aptamers and siRNA

Nucleic acids have gained a lot of interest for the treatment of ocular diseases. The first to enter in clinic has been Vitravene an antisense oligonucleotide for the treatment of cytomegalovirus (CMV) infection and more recently, research on aptamers have led to the marketing of anti-vascular endothelial growth factor (VEGF) inhibitor (Macugen) for the treatment of age-related macular degeneration (AMD). The siRNAs appear very promising as they are very potent inhibitors of protein expression. Despite their potential, nucleic acids therapeutic targets of nucleic acid-based drugs are mainly located in the posterior segment of the eye requiring invasive administration which can be harmful if repeated. Their intracellular penetration in some cases needs to be enhanced. This is the reason why adequate delivery systems were designed either to insure cellular penetration, protection against degradation or to allow long-term delivery. A combination of both effects was also developed for an implantable system. In conclusion, the intraocular administration of nucleic acids offers interesting perspectives for the treatment of ocular diseases.

EFFECT OF A NOVEL OCTAPEPTIDE UROKINASE FRAGMENT, A˚6, ON EXPERIMENTAL CHOROIDAL NEOVASCULARIZATION IN THE MONKEY

PURPOSE

To evaluate the inhibitory effects of a urokinase-derived octapeptide, A 6, on laser-induced choroidal neovascularization (CNV) in monkeys.

METHODS

Twenty female cynomolgus monkeys were randomly grouped into weekly or monthly A 6 treatment groups, each consisting of 10 animals. CNV was induced in both eyes by perimacular laser treatment. In each right eye, a single 22.25-mg A 6 dose (monthly group) or 4 22.25-mg A 6 doses each week (weekly group) were given by intravitreal injections. Each left eye received phosphate buffer on the same schedule. Monkeys were observed for 4 weeks by ophthalmic examinations, color photography, and fluorescein angiography.

RESULTS

Weekly treated eyes had a 35% reduction of CNV compared with controls (P = 0.23). In contrast, monthly treated eye had a 71% reduction of CNV compared with controls (P = 0.0009). There was no evidence of toxicity at both clinical and pathologic examinations.

CONCLUSIONS

Intravitreal A 6 injections effectively inhibited CNV in cynomolgus monkeys without evidence of toxicity. The overall reduction in CNV was greater for monthly treated eyes than for weekly treated eyes. This study suggests that A 6 has promise as a local antiangiogenic treatment of CNV. Further work is indicated to evaluate the potential role of A 6 in therapy for human CNV associated with age-related macular degeneration.

Emerging biological therapies for age-related macula degeneration

Age-related macular degeneration (AMD) has emerged as the dominant cause of irretrievable visual loss in most developed countries achieving increasing longevity. The major cause of rapid and severe visual loss is the development of choroidal neovascularisation under the macula (exudative or wet AMD). Physical treatments, especially thermal laser and photodynamic therapy following intravenous verteporfin, have made statistically significant but modest progress in limiting visual loss, whereas surgical translocation of the macula and even light or electrically sensitive retinal implants are spectacular, but likely to only ever benefit a few. Intravitreal fine needle injections and slow release implants of steroid derivatives have opened new areas for investigation. The blocking of endothelial receptors for vascular endothelial growth factor by RNA-based aptamer or immune-protected antibody fragments has been the subject of intensive scientific development and large scale clinical trials. This approach may expand the range of AMD patients amenable to treatment. Additional therapeutic gains await measures to modify photoreceptor cell loss and subretinal fibrosis involving the retinal pigment epithelium as well as prevention or treatment for pigment epithelial detachment. Epidemiological associations with smoking and diet, and antioxidant dietary supplements offer important strategies for prevention.

Long-term Evaluation of AAV-Mediated sFlt-1 Gene Therapy for Ocular Neovascularization in Mice and Monkeys

Vascular endothelial growth factor (VEGF) is one of the major mediators of retinal ischemia-associated neovascularization. We have shown here that adeno-associated virus (AAV)-mediated expression of sFlt-1, a soluble form of the Flt-1 VEGF receptor, was maintained for up to 8 and 17 months postinjection in mice and in monkeys, respectively. The expression of sFlt-1 was associated with the long-term (8 months) regression of neovascular vessels in 85% of trVEGF029 eyes. In addition, it resulted in the maintenance of retinal morphology, as the majority of the treated trVEGF029 eyes (75%) retained high numbers of photoreceptors, and in retinal function as measured by electroretinography. AAV-mediated expression of sFlt-1 prevented the development of laser photocoagulation-induced choroidal neovascularization in all treated monkey eyes. There were no clinically or histologically detectable signs of toxicity present in either animal model following AAV.sFlt injection. These results suggest that AAV-mediated secretion gene therapy could be considered for treatment of retinal and choroidal neovascularizations.

Age-related macular degeneration: etiology, pathogenesis, and therapeutic strategies

Age-related macular degeneration is the principal cause of registered legal blindness among those aged over 65 in the United States, western Europe, Australia, and Japan. Despite intensive research, the precise etiology of molecular events that underlie age-related macular degeneration is poorly understood. However, investigations on parallel fronts are addressing this prevalent public health problem. Sophisticated biochemical and biophysical techniques have refined our understanding of the pathobiology of drusen, geographic atrophy, and retinal pigment epithelial detachments. Epidemiological identification of risk factors has facilitated an intelligent search for underlying mechanisms and fueled clinical investigation of behavior modification. Gene searches have not only brought us to the cusp of identifying the culpable gene loci in age-related macular degeneration, but also localized genes responsible for other macular dystrophies. Recent and ongoing investigations, often cued by tumor biology, have revealed an important role for various growth factors, particularly in the neovascular form of the condition. Transgenic and knockout studies have provided important mechanistic insights into the development of choroidal neovascularization, the principal cause of vision loss in age-related macular degeneration. This in turn has culminated in preclinical and clinical trials of directed molecular interventions.

Potential long-term inhibition of ocular neovascularisation by recombinant adeno-associated virus-mediated secretion gene therapy

Neovascularisation (NV) within the eye often results in visual loss. Vascular endothelial growth factor (VEGF) has been implicated in the development of ocular NV. Previous studies have shown that VEGF antagonists successfully suppressed retinal and choroidal NV in animal models. However, the systemic approach and transient nature of the delivery systems used in these studies hinder therapeutic application. To achieve stable and localised ocular anti-angiogenic therapy, we explored the use of recombinant adeno-associated virus (rAAV)-mediated secretion gene therapy (SGT). In this study, we generated a rAAV vector encoding soluble VEGF receptor 1, sFlt-1 (AAV-CMV.sflt) and determined its ability to inhibit cautery-induced corneal NV and laser-induced choroidal NV. Delivery of AAV-CMV.sflt into the anterior chamber resulted in transgene expression in the iris pigment epithelium and corneal endothelium, which reduced the development of corneal NV in the stroma of cauterised rats by 36% compared with cauterised control groups (P = 0.009). Subretinal delivery of AAV-CMV.sflt near the equator of the eye also suppressed choroidal NV at the laser lesions around the optic nerve by 19% (P = 0.002), indicating that there was diffusion of the secreted anti-angiogenic protein across the retina. Both results suggest that the long-term suppression of ocular NV is possible through the use of stable rAAV-mediated SGT.