Development of safe and effective gene delivery systems is essential in treating ocular genetic disorders. A hybrid nonviral system composed of a multifunctional lipid ECO and a G4 nanoglobule was designed for efficient gene delivery into RPE cells at low charge ratios. This system formed stable DNA nanoparticles at low N/P ratios, exhibited low cytotoxicity, and induced higher GFP expression in ARPE-19 cells at N/P = 6. The hybrid nanoparticles mediated significant reporter gene GFP expression ex-vivo in the retina from wild type C57 mice and in vivo in BALB/c mice. These hybrid nanoparticles are promising for in vitro and in vivo gene delivery at low charge ratios.

Development of a gene delivery system with high efficiency and a good safety profile is essential for successful gene therapy. Here we developed a targeted non-viral delivery system using a multifunctional lipid ECO for treating Lebers congenital amaurosis type 2 (LCA2) and tested this in a mouse model. ECO formed stable nanoparticles with plasmid DNA (pDNA) at a low amine to phosphate (N/P) ratio and mediated high gene transfection efficiency in ARPE-19 cells because of their intrinsic properties of pH-sensitive amphiphilic endosomal escape and reductive cytosolic release (PERC). All-trans-retinylamine, which binds to interphotoreceptor retinoid-binding protein (IRBP), was incorporated into the nanoparticles via a polyethylene glycol (PEG) spacer for targeted delivery of pDNA into the retinal pigmented epithelium. The targeted ECO/pDNA nanoparticles provided high GFP expression in the RPE of 1-month-old Rpe65-/- mice after subretinal injection. Such mice also exhibited a significant increase in electroretinographic activity, and this therapeutic effect continued for at least 120 days. A safety study in wild-type BALB/c mice indicated no irreversible retinal damage following subretinal injection of these targeted nanoparticles. All-trans-retinylamine-modified ECO/pDNA nanoparticles provide a promising non-viral platform for safe and effective treatment of RPE-specific monogenic eye diseases such as LCA2.

PURPOSE: Apply manganese-enhanced magnetic resonance imaging (MEMRI) to assess ion channel activity and structure of retinas from mice subject to light-induced retinal degeneration treated with prophylactic agents. METHODS: Abca4(-/-)Rdh8(-/-) double knockout mice with and without prophylactic retinylamine (Ret-NH2) treatment were illuminated with strong light. Manganese-enhanced MRI was used to image the retina 2 hours after intravitreous injection of MnCl2 into one eye. Contrast-enhanced MRIs of the retina and vitreous humor in each experimental group were assessed and correlated with the treatment. Findings were compared with standard structural and functional assessments of the retina by optical coherence tomography (OCT), histology, and electroretinography (ERG). RESULTS: Manganese-enhanced MRI contrast in the retina was high in nonilluminated and illuminated Ret-NH2-treated mice, whereas no enhancement was evident in the retina of the light-illuminated mice without Ret-NH2 treatment (P < 0.0005). A relatively high signal enhancement was also observed in the vitreous humor of mice treated with Ret-NH2. Strong MEMRI signal enhancement in the retinas of mice treated with retinylamine was correlated with their structural integrity and function evidenced by OCT, histology, and a strong ERG light response. CONCLUSIONS: Manganese-enhanced MRI has the potential to assess the response of the retina to prophylactic treatment based on the measurement of ion channel activity. This approach could be used as a complementary tool in preclinical development of new prophylactic therapies for retinopathies.

Stargardt disease (STGD) is an autosomal recessive retinal disorder caused by a monogenic ABCA4 mutation. Currently, there is no effective therapy to cure Stargardt disease. The replacement of mutated ABCA4 with a functional gene remains an attractive strategy. In this study, we have developed a non-viral gene therapy using nanoparticles self-assembled by a multifunctional pH-sensitive amino lipid ECO and a therapeutic ABCA4 plasmid. The nanoparticles mediated efficient intracellular gene transduction in wild-type (WT) and Abca4^-/- mice. Specific ABCA4 expression in the outer segment of photoreceptors was achieved by incorporating a rhodopsin promoter into the plasmids. The ECO/pRHO-ABCA4 nanoparticles induced substantial and specific ABCA4 expression for at least 8 months, 35% reduction in A2E accumulation on average, and a delayed Stargardt disease progression for at least 6 months in Abca4^-/- mice. ECO/plasmid nanoparticles constitute a promising non-viral gene therapy platform for Stargardt disease and other visual dystrophies.

Dysfunctions caused by gene mutations in the retinal pigment epithelium (RPE) lead to retinal degeneration, visual function loss, and even blindness. RPE-specific gene replacement therapy holds great promise for treating monogenic ocular disorders in the RPE. Although the adeno-associated virus (AAV) has been approved for gene therapy to treat monogenic visual disorders, broad clinical applications of AAV-based gene therapy are limited by its gene loading capacity. In this work, we intended to design and develop a stable retinylamine analogue ACU4429-modified dual pH-sensitive ECO/pDNA nanoparticles for specific delivery of large therapeutic genes to the RPE. ACU4429 was first conjugated to a PEG 3.4 kD spacer with a pH-sensitive hydrazone linker at the distal end (ACU-PEG-HZ-MAL). The targeted dual pH-sensitive ECO/pDNA nanoparticles were then prepared by self-assembly of ACU-PEG-HZ-MAL, pH-sensitive lipid carrier ECO, and a plasmid DNA expressing the large ABCA4 gene. The formation of targeted ACU-PEG-HZ-ECO/pDNA nanoparticles was characterized by dynamic light scattering and gel electrophoresis. The incorporation of a hydrazone linker enhanced the cytosolic gene delivery, which translated to high ABCA4 expression in ARPE-19 cells for ACU-PEG-HZ-ECO/pABCA4 nanoparticles. The targeted nanoparticles also demonstrated excellent targeting efficiency in the interphotoreceptor matrix of Abca4-/- mice, resulting in enhanced expression of the ABCA4 gene in the RPE. The ACU4429 PEG hydrazone-modified ECO/pDNA nanoparticles provide a promising nonviral platform to safely and effectively deliver therapeutic genes with unlimited sizes for the treatment of monogenic visual disorders.