A ribozyme-mediated RNA replacement gene therapy shows efficacy in a pig model of Autosomal Dominant Retinitis Pigmentosa (adRP).

Abstract

Purpose : The P23H mutation in the rhodopsin (RHO) gene represents the most common form of adRP in North Americans. Eliminating the causative mutant allele, while leaving the wild-type (WT) allele intact should prevent vision loss in adRP patients. Group-I intron-based trans-splicing ribozymes reprogram a mutant RNA into a WT gene through RNA replacement. To evaluate RZ-004 (a trans-splicing ribozyme) efficacy, we delivered it via subretinal injection to a preclinical adRP pig model and examined retinal structure and function.

Methods : RZ-004 ribozyme is encoded in an AAV vector and driven by a hRHO promoter. We delivered RZ-004 via subretinal injection (50ul) to both eyes of Tg hRHO P23H pigs between postnatal days 3 to 7 (n=19). Untreated or vehicle injected eyes served as negative controls (n=5 pigs). All pigs were prophylactically treated with prednisone (3 days prior and 30 days after injection). The structural and function efficacy of four viral concentrations were evaluated using the following non-invasive assessment at regular intervals between 4 and 28 weeks post injection (wpi). The structural efficacy was quantified using fundus imaging and optical coherence tomography (OCT). Functional efficacy was quantified using full-field electroretinogram (ffERG). At the terminal assessment, pigs were euthanized and immunohistochemistry/confocal imaging assessed rod morphology.

Results : Treatment with RZ-004 was well tolerated although a mild immune response occurred at the highest titer, 1x10¹¹vg. From birth, untreated TgP23H hRHO pigs have no rod-isolated ffERG response. Eyes injected with RZ-004 gained a significant rod-isolated ffERG response across all viral titers, first observed at 8wpi and lasting through 28wpi. Untreated and vehicle injected retinas had no rod-isolated ffERG response. Within the RZ-004 treated area, Tg rods had elongated inner and outer segments (IS/OS) and thicker ONL. Rods were significantly reduced in number and had abnormal morphology and thinner ONL in untreated areas in the same retinas or untreated/vehicle injected Tg retinas.

Conclusions : RZ-004 ribozyme prevents rod degeneration and induces rod function in the adRP TgP23H hRHO pig model and this AAV-based therapy is well tolerated. Our results suggest, that the RNA replacement based RHO-targeting ribozyme, RZ-004, has the potential to treat rod degeneration in P23H hRHO adRP patients.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.