Direct gene transfer with compacted DNA nanoparticles in retinal pigment epithelial cells: expression, repeat delivery and lack of toxicity

Aim: To evaluate the safety of compacted DNA nanoparticles (NPs) in retinal pigment epithelial (RPE) cells. Materials & methods: Enhanced GFP expression cassettes controlled by the RPE-specific vitelloform macular dystrophy promoter were constructed with and without a bacterial backbone and compacted into NPs formulated with polyethylene glycol-substituted lysine 30-mers. Single or double subretinal injections were administered in adult BALB/c mice. Expression levels of enhanced GFP, proinflammatory cytokines and neutrophil/macrophage mediators, and retinal function by electroretinogram were evaluated at different time-points postinjection. Results: Immunohistochemistry and real-time PCR demonstrated that NPs specifically transfect RPE cells at a higher efficiency than naked DNA and similar results were observed after the second injection. At 6 h postinjections, a transient inflammatory response was observed in all cohorts, including saline, indicating an adverse effect to the injection procedure. Subsequently, no inflammation was detected in all experimental groups. Conclusion: This study demonstrates the safety and efficacy of NP-mediated RPE gene transfer therapy following multiple subretinal administrations.