A gel-forming antioxidant eye drop for photoreceptor protection in retinitis pigmentosa

Retinitis pigmentosa (RP) is a chronic genetic condition that leads to progressive loss of photoreceptor cells and vision. While gene therapy is available for a small subset of patients with specific mutations, developing a therapeutic that broadly targets the cellular stresses that lead to cell death could address a major unmet need. One such option would be utilizing antioxidant therapies to neutralize reaction oxygen species (ROS) in the retina that underlie RP progression. Here, we describe an approach for delivering the antioxidants N-acetyl cysteine (NAC) or N-acetyl cysteine ethyl ester (NACET) with a gel-forming eye drop previously demonstrated to provide therapeutic drug delivery in the posterior segment in animals. We demonstrated therapeutic protection of photoreceptor structure and function in a chemically-induced rat model of RP (48% increase in photopic b-wave amplitude), as well as some limited protection in an aggressive genetic mouse model (rd10) of retinal degeneration (~ 31% increase in photopic b-wave amplitude) with once daily application. However, antioxidants have inherent stability issues when stored in solution, so we investigated the use of additional excipients to improve stability and retain potency. While a promising approach, future work to address product stability and efficacy in larger eyes is needed for further development.