Hereditary Retinal Dystrophy.

As our understanding of the genetic basis for inherited retinal disease has expanded, gene therapy has advanced into clinical development. When the gene mutations associated with inherited retinal dystrophies were identified, it became possible to create animal models in which individual gene were altered to match the human mutations. The retina of these animals were then characterized to assess whether the mutated genes produced retinal phenotypes characteristic of disease-affected patients. Following the identification of a subpopulation of patients with the affected gene and the development of techniques for the viral gene transduction of retinal cells, it has become possible to deliver a copy of the normal gene into the retinal sites of the mutated genes. When this was performed in animal models of monogenic diseases, at an early stage of retinal degeneration when the affected cells remained viable, successful gene augmentation corrected the structural and functional lesions characteristic of the specific diseases in the areas of the retina that were successfully transduced. These studies provided the essential proof-of-concept needed to advance monogenic gene therapies into clinic development; these therapies include treatments for: Leber's congenital amaurosis type 2, caused by mutations to RPE65, retinoid isomerohydrolase; choroideremia, caused by mutations to REP1, Rab escort protein 1; autosomal recessive Stargardt disease, caused by mutations to ABCA4, the photoreceptor-specific ATP-binding transporter; Usher 1B disease caused by mutations to MYO7A, myosin heavy chain 7; X-linked juvenile retinoschisis caused by mutations to RS1, retinoschisin; autosomal recessive retinitis pigmentosa caused by mutations to MERTK, the proto-oncogene tyrosine-protein kinase MER; Leber's hereditary optic neuropathy caused by mutations to ND4, mitochondrial nicotinamide adenine dinucleotide ubiquinone oxidoreductase (complex I) subunit 4 and achromatopsia, caused by mutations to CNGA3, cyclic nucleotide-gated channel alpha 3 and CNGB3, cyclic nucleotide-gated channel beta 3. This review includes a tabulated summary of treatments for these monogenic retinal dystrophies that have entered into clinical development, as well as a brief summary of the preclinical data that supported their advancement into clinical development.

Opportunities and challenges in the development of combination therapy for the treatment of retinal diseases.

Ranibizumab, a humanized monoclonal antibody fragment (fragment, antigen binding, FAB) that neutralizes all of the soluble isoforms of vascular endothelial growth factor (VEGF)-A, was a significant step forward in the control of age-related macular degeneration. However, this agent, like others with the same mechanism, has several limitations. Although ranibizumab preserves vision in almost all patients, only a fraction achieves a halving of the visual angle. By inhibiting the activities of VEGF, ranibizumab blocks the continued growth of choroidal neovascularization, but existing neovascular lesions do not regress. Further, ranibizumab addresses only the increased production of VEGF; it does not address the underlying cause of enhanced cytokine production. Although ranibizumab is well tolerated, the course of the disease is unpredictable, necessitating frequent patient monitoring and treatment. Although strategies that guide retreatment based on the reoccurrence of retinal edema can be used to reduce treatment burden, this strategy may not provide optimal patient benefit. Because of these limitations, the identification of effective adjunctive therapies is considered an urgent goal.

Double-Masked, Randomized, Phase 2 Evaluation of Abicipar Pegol (an Anti-VEGF DARPin Therapeutic) in Neovascular Age-Related Macular Degeneration.

Purpose: To evaluate safety and efficacy of the vascular endothelial growth factor binding protein abicipar pegol (abicipar) versus ranibizumab for neovascular age-related macular degeneration. Methods: Phase 2, multicenter, randomized, double-masked comparison (REACH study, stage 3). Patients (n = 64) received intravitreal injections of abicipar 1 mg or 2 mg at baseline, week 4, and week 8 (3 injections) or ranibizumab 0.5 mg at baseline and monthly (5 injections). Results: In the abicipar 1 mg (n = 25), abicipar 2 mg (n = 23), and ranibizumab (n = 16) arms, respectively, least-squares mean best-corrected visual acuity (BCVA) change from baseline was +6.2, +8.3, and +5.6 letters at week 16 (primary endpoint) and +8.2, +10.0, and +5.3 letters at week 20. Least-squares mean central retinal thickness (CRT) reduction from baseline was 134, 113, and 131 µm at week 16 and 116, 103, and 138 µm at week 20. Intraocular inflammation adverse events (AEs), reported in 5/48 (10.4%) abicipar-treated patients, resolved without sustained vision loss or other sequelae. Conclusions: Abicipar demonstrated durability of effect: BCVA and CRT improvements were similar between abicipar and ranibizumab at weeks 16 and 20 (8 and 12 weeks after the last abicipar injection and 4 weeks after the last ranibizumab injection). No serious AEs were reported.

Functional Characterization of Abicipar-Pegol, an Anti-VEGF DARPin Therapeutic That Potently Inhibits Angiogenesis and Vascular Permeability.

Purpose: DARPin molecules are a novel class of small proteins that contain engineered ankyrin repeat domain(s) and bind to target proteins with high specificity and affinity. Abicipar-pegol (abicipar), a DARPin molecule targeting vascular endothelial growth factor-A (VEGF-A), is currently under evaluation in patients with age-related macular degeneration. The pharmacodynamic properties of abicipar were characterized using in vivo and in vitro assays. Methods: The binding affinity of abicipar was assessed using a kinetic exclusion assay (KinExA). In vitro assays evaluated abicipar effects on VEGF-A165-induced calcium mobilization and tube formation in human umbilical vein endothelial cells. Abicipar was tested in vivo in a mouse model of corneal neovascularization and a rabbit model of chronic retinal neovascularization. The efficacies of abicipar and ranibizumab were compared in a rabbit model of VEGF-A165-induced retinal vasculopathy. Results: Abicipar has a high affinity for the soluble isoforms of VEGF-A; binding affinities for human VEGF-A165 are approximately 100-fold greater than those of ranibizumab and bevacizumab and are similar for rat VEGF-A164 but approximately 20-fold lower for rabbit VEGF-A165. Abicipar was effective in cell-based and in vivo models of angiogenesis and vascular leak, blocking neovascularization in a mouse model of corneal neovascularization and vascular permeability in a rabbit model of chronic neovascularization. In a rabbit model of VEGF-A165-induced vasculopathy, the duration of effect of abicipar was longer than ranibizumab when the two compounds were administered at molar-equivalent doses. Conclusions: These data support the testing of abicipar as a treatment for retinal diseases characterized by neovascularization and vascular leak.

Drug intervention can correct subnormal retinal oxygenation response in experimental diabetic retinopathy.

PURPOSE: Early subnormal retinal oxygenation response to a hyperoxic provocation (DeltaPo2) is strongly associated with subsequent experimental diabetic retinopathy and can be reversed by drug treatments started with the induction of diabetes. It is not yet known whether drug treatment can reverse an established subnormal DeltaPo2. METHODS: Retinal DeltaPo2 was measured in two separate experimental paradigms in streptozotocin-induced diabetic rats. In a prevention study, measurements were performed in untreated diabetic rats, 3 months after the initiation of hyperglycemia (D3mo), in age-matched nondiabetic rats (C3mo), and in diabetic rats treated orally for 3 months with celecoxib, a cyclooxygenase (COX)-2-selective inhibitor, (D3mo+COX2i). In an intervention study, measurements were performed in untreated diabetic rats 4 months after the initiation of diabetes (D4mo), in age-matched nondiabetic rats (C4mo), and in diabetic rats that were untreated for 3 months and then were orally treated for an additional month with either celecoxib (D4mo+COX2i) or l-N (6)-(1-iminoethyl)lysine 5-tetrazole amide, a prodrug of an inhibitor of inducible nitric oxide synthase (iNOS, D4mo+ iNOSi). RESULTS: In the prevention arm, subnormal (P < 0.05) retinal DeltaPo2 was found in the D3mo group, but not in the D3mo+COX2i group (P > 0.05). In a previous study, it was reported that retinal DeltaPo2 also corrected in a D3mo+iNOSi group. In the intervention arm, retinal DeltaPo2 levels in the D4mo and D4mo+iNOSi, but not the D4mo+COX2i, groups were (P < 0.05) subnormal. CONCLUSIONS: These results demonstrate, for the first time, that drug treatment can reverse an established subnormal DeltaPo2. Furthermore, this effect could not be predicted by a drugs' ability to prevent the development of subnormal DeltaPo2.

Optical coherence tomography and autofluorescence findings in areas with geographic atrophy due to age-related macular degeneration.

PURPOSE: To analyze outer retinal changes within the atrophic lesion in patients with geographic atrophy (GA) secondary to age-related macular degeneration. METHODS: Twenty-one simultaneously obtained fundus autofluorescence (FAF, excitation, 488 nm; emission, 500-700 nm) and spectral-domain optical coherence tomography (SD-OCT) scans (Spectralis HRA+OCT; Heidelberg Engineering, Heidelberg, Germany) of 21 GA patients (mean age, 75.1 ± 7.4 years) were included and separately exported. Two readers independently graded the following parameters: width of the atrophic lesion on the FAF image at the site where the SD-OCT scan had been placed; and on the SD-OCT image, widths of the linear disruption of the outer nuclear layer, the external limiting membrane, and the inner and outer segments of the photoreceptor layer (IPRL) and width of the disruption of choroidal signal enhancement. Results. The mean width of the atrophic lesion by FAF imaging was 2.83 mm (95% confidence interval, 2.37-3.29). The linear disruption of choroidal hyperreflectivity showed the closest agreement with 2.83 mm (2.37-3.28), whereas the linear width of disrupted IPRL was larger (3.10 mm; 2.65-3.55). Overall, the width of the atrophic lesion correlated significantly with all five SD-OCT parameters (P < 0.0001, r = 0.96-0.99). CONCLUSIONS: These findings demonstrate that the atrophic lesions identified with FAF represent irreversible underlying outer retinal damage. The observation that the width of the atrophic lesion identified with FAF, although significantly correlated but not identical with the width of disruption within the cellular layers of the retina, is consistent with the dynamic nature of the disease. (ClinicalTrials.gov numbers, NCT00393692, NCT00599846.).

Reticular drusen associated with geographic atrophy in age-related macular degeneration.

PURPOSE: To characterize reticular drusen (RDR) in patients with geographic atrophy (GA) secondary to age-related macular degeneration (AMD) in a prospective, multicenter, natural history study. METHODS: Confocal scanning laser ophthalmoscopy (cSLO) three-field fundus autofluorescence (FAF; exc., 488; em., 500-700 nm), near-infrared reflectance (IR; 820 nm), and blue reflectance (BR; 488 nm) images as well as red-free (RF) and color fundus (CF) camera photographs were recorded in 458 GA patients. The digital images were evaluated by two independent readers with subsequent senior reader arbitration for prevalence and topographic distribution of RDR using a modified Early Treatment Diabetic Retinopathy Study grid. RESULTS: RDR were detected with at least one cSLO modality in 286 of 458 (62%) patients in either eye (bilateral 207 [45%]) and were visible in fundus camera photographs in 66 of 371 (18%) patients (bilateral 48 [13%]). Prevalence of RDR by cSLO imaging was associated with increasing age (P = 0.007) and female sex (P = 0.007), but not with GA total lesion area (P = 0.38). Cohen kappa statistics showed good interobserver agreement for FAF (0.81) and IR (0.82) imaging modes, and moderate agreement was found for BR (0.48), RF (0.48), and CF (0.40). On three-field FAF images RDR were present most frequently superior to the fovea (99%). CONCLUSIONS: RDR represent a common phenotypic hallmark in GA eyes. RDR are readily identified using cSLO imaging technology. These observations may explain the high prevalence determined herein, in contrast to previous reports based on fundus photographs. Incorporation of these novel imaging modalities in future natural history studies may facilitate efforts aimed at defining the role and predictive value of RDR in the progression of AMD. (ClinicalTrials.gov number, NCT00599846.)

Minalrestat, an aldose reductase inhibitor, corrects the impaired microvascular reactivity in diabetes.

We demonstrated that aldose reductase inhibition corrects the impaired microvascular responses to inflammatory mediators in diabetic rats. To study the mechanism involved in the restoring effect of aldose reductase inhibition, we examined the effects of minalrestat, another aldose reductase inhibitor, on the responses of mesenteric microvessels studied in vivo to permeability-increasing agents in diabetic and galactosemic rats. The diabetic group was treated from 3 days after the alloxan injection with minalrestat (10 mg/kg/day) for 30 days and the minalrestat treatment (10 mg/kg/day/7 days) of galactosemic rats started concomitantly with the induction of galactosemia. The mesenteric microvessel reactivity was studied using intravital microscopy and changes in vessel diameters were estimated after the topical application of vasoactive agents. The impaired responses to bradykinin, histamine, and platelet-activating factor of arterioles and venules observed in diabetic and galactosemic rats were completely prevented by minalrestat. Neither diabetes nor galactosemia affected responses to acetylcholine and sodium nitroprusside. Responses to these agents were not modified by aldose reductase inhibition. The restoring effect of minalrestat was reversed by inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester, by blocking K(+) channel with tetraethylammonium but not by cyclooxygenase inhibition with diclofenac. Therefore, we concluded that NO, membrane hyperpolarization, but not cyclooxygenase products are involved in the beneficial effect of minalrestat on the microvascular reactivity in diabetes. Together, these findings led us to suggest that aldose reductase inhibition might ameliorate diabetic complications through the correction of the altered microvascular reactivity by a mechanism that involves NO and membrane hyperpolarization.

Complicaciones diabéticas: progresos en el desarrollo del tratamiento / Diabetic complications: progress in the development of treatment

A pesar de los avances en el tratamiento de la diabetes, las complicaciones de la enfermedad a largo plazo, tales como la retinopatía, la nefropatía y la neuropatía, siguen siendo la mayor causa de morbilidad y mortalidad en los pacientes diabéticos. Los estudios clínicos prospectivos con insulinoterapia intensificada han establecido una clara correlación entre la hiperglucemiay el desarrollo de las complicaciones diabéticas estudios en animales han demostrado el vínculo entre el incremento del metabolismo de la glucosa inducido por la hiperglucemia diabética a través de la vía del sorbitol y el desarrollo de lascomplicaciones. Por otra parte, una mejor comprensión de los mecanismos patogénicos de la neuropatía diabética ha promovido la utilización de las mediciones electrofisiológicas como medio confiable de cuantificar la progresión de la neuropatía diabética y también ha redefinido metas realistas de tratamiento para las complicaciones diabéticas, como la detención o atenuación de los procesos de la enfermedad en vez de su reversión. Estudios clínicos recientes con insulinoterapiaintensificada e inhibidores de aldosareductasa, apoyan claramente estos nuevos objetivos de tratamiento. En estudios a largo plazo de 5 a 8 años, la insulinoterapia intensificada no revirtió los signos clínicos y los síntomas de la neuropatía diabética, pero si evitó su aparición en pacientes sin evidencia de neuropatía al comienzo del estudio.La insulinoterapia intensificada tampoco restauró la pérdida preexistente de la función,pero redujo la pérdida acelerada de esa función,característica de la neuropatía diabética