Restoring visual function to blind mice with photoswitches that selectively target the degenerated retina.

Abstract

Purpose: Degenerative blinding diseases such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD) affect millions of patients around the world. These disorders cause the progressive loss of photoreceptors from the retina, while sparing the remaining amacrine, bipolar and retinal ganglion cells (RGCs). We have developed a small molecule pharmacological therapy that selectively photosensitizes retinal ganglion cells in retinas suffering from degeneration, while leaving healthy retinas unaffected. Our goal is to demonstrate the safety and efficacy of the compounds we've developed in different animal models of blindness with the goal of obtaining FDA approval for clinical testing in human patients.

Methods: We have created several chemical “photoswitches” that can be used to control the activity of neurons by reversibly blocking native ion channels in response to light. Here, we demonstrate that these compounds restore retinal light sensitivity in rodent and canine models of retinal degeneration. We also demonstrate the restoration of visually guided behavior in vivo in blind mice.

Results: We have previously demonstrated that chemical photoswitches restore light responses to blind retinas in vitro and also enable light-aversive behaviors in blind mice. Here, we present improved photoswitch molecules, DENAQ and BENAQ, which photosensitize the blind retina for weeks after a single intravitreal injection, allowing RGCs to respond to white light with an intensity equivalent to ordinary daylight. The compounds show no acute toxicity in mice. DENAQ and BENAQ only photosensitize RGCs from degenerated retinas, but have no effect on RGCs from healthy retinas. We identify a hyperpolarization activated inward current (Ih) as the conductance underlying the photoswitches’ selectivity. We also determine that Ih is upregulated in RGCs from an rd1 mouse model of RP, and may partly mediate the reported increase in spontaneous activity in retinas undergoing photoreceptor degeneration.

Conclusions: The selectivity of our photoswitches for diseased but not healthy retinas implies that our pharmacological therapy could not only restore vision in patients with end stage RP, but also improve vision in less advanced RP and AMD patients, by selectively acting on the parts of the retina undergoing photoreceptor death.

Keywords: 608 nanomedicine • 702 retinitis • 412 age-related macular degeneration