Multifunctional, pH-sensitive amino lipid (ECO)/pABCA4-based nanoparticles may be a promising candidate for the delivery of nonviral gene therapy to treat Stargardt disease, according to mouse model research results published in the Journal of Controlled Release. 

Following the development of an effective nonviral gene therapy based on self-assembled nanoparticles, investigators conducted further research into the therapeutic ACBA4 plasmid (pRHO-ABCA4). In the current study, they modified ABCA4 plasmid with simian virus 40 enhancer (pRHO-ABCA4-SV40) for enhanced gene expression. Formulations of ECO/pDNA nanoparticles using either sucrose or sorbitol stabilizer were also prepared and examined. 

Investigators found that ECO creates stable nanoparticles within pRHO-ABCA4-SV40 in the presence of sucrose, but not in the presence of sorbitol. In vitro transfection efficiency increased significantly following the introduction of an SV40 enhancer in conjunction with a cytomegalovirus promoter. 


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Results also demonstrated that sucrose did not affect transfection efficiency; sorbitol, though, was associated with a fluctuation of in vitro transfection efficiency. 

Investigators then examined the efficacy of using ECO/pRHO-ABCA4 and ECO/pRHO-ABCA4-SV40 for the prevention of Stargardt disease progression in mouse models. Efficacy was assessed based on A2E accumulation in the retinal pigmented epithelium. Mice were euthanized 8 months after a single subretinal injection of either ECO/pRHO-ABCA4 or ECO/pRHO-ABCA4-SV40 with PBS control; A2E levels were analyzed via high performance liquid chromatography. 

A2E peaks were significantly reduced following ECO/pRHO-ABCA4 and ECO/pRHO-ABCA4-SV40 nanoparticle injections, compared with a control group. Quantitative analysis found average A2E levels of approximately 63.95%and 71.78% in each treatment group, respectively. Large variations of in vivo efficacy were observed in the ECO/pRHO-ABCA4-SV40 group. This group also experienced a “slightly higher” but still nonsignificant ABCA4 mRNA expression at 4 days. These results, the researchers wrote, implies that plasmid pRHO-ABCA4-SV40 with a viral enhancer may be cleared more quickly. 

“Gene therapy holds great promise for the treatment of monogenic retinal disorders, but still faces challenges for the efficient and specific delivery of therapeutic genes, especially large genes,” the researchers note. 

“Modification of ABCA4 plasmids with an SV40 enhancer induced significantly higher gene expression in ARPE-19 cells, and demonstrated the same level of A2E reduction in treated mice as ECO/pRHO-ABCA4 nanoparticles,” the research concludes. “Therefore, the ECO/pABCA4 nanoparticles with a modified enhancer sequence and the stabilizer can be a promising, reliable, and safe nonviral gene therapy platform to deliver large therapeutic genes for the treatment of Stargardt disease.”

Reference

Sun D, Sun W, Gao S-Q, et al. Formulation and efficacy of ECO/pRHO-ABCA4-SV40 nanoparticles for nonviral gene therapy of Stargardt disease in a mouse model. J Control Release. 2020;330:329-340. doi:10.1016/j.jconrel.2020.12.010.