Improved Retinal Function in a Mouse Model of Dominant Retinitis Pigmentosa Following AAV-delivered Gene Therapy

Abstract

Mutational heterogeneity represents one of the greatest barriers impeding the progress toward the clinic of gene therapies for many dominantly inherited disorders. A general strategy of gene suppression in conjunction with replacement has been proposed to overcome this mutational heterogeneity. In the current study, various aspects of this strategy are explored for a dominant form of the retinal degeneration, retinitis pigmentosa (RP), caused by mutations in the rhodopsin gene (RHO-adRP). While > 200 mutations have been identified in rhodopsin (RHO), in principle, suppression and replacement may be employed to provide a single mutation-independent therapeutic for this form of the disorder. In the study we demonstrate in a transgenic mouse simulating human RHO-adRP that RNA interference-based suppression, together with gene replacement utilizing the endogenous mouse gene as the replacement, provides significant benefit as evaluated by electroretinography (ERG). Moreover, this is mirrored histologically by preservation of photoreceptors. AAV-based vectors were utilized for in vivo delivery of the therapy to the target cell type, the photoreceptors. The results demonstrate that RNAi-based mutation-independent suppression and replacement can provide benefit for RHO-adRP and promote the therapeutic approach as potentially beneficial for other autosomal dominantly inherited disorders.

An experimental platform for systemic drug delivery to the retina

“…Although degenerative retinopathies, including age-related macular degeneration (AMD), diabetic retinopathy, and RP represent major causes of world blindness, treatment options are currently exceedingly limited (15,(21)(22)(23)(24). No form of prevention is available for the nonexudative (dry) form of AMD, apart from dietary intervention.…”

Emerging Gene Therapies for Retinal Degenerations

“…Vectors expressing such genes or knock-down cassettes have been developed and tested in animal models (LaVail et al, 2000;Schlichtenbrede et al, 2003;Pang et al, 2008;Chadderton et al, 2009;Raz-Prag et al, 2009;Palfi et al, 2010;Zou et al, 2011). While this approach may be successful for individual disease genes, and is a good one to establish the use of gene therapy vectors for ocular diseases, it likely will not be possible to extend such a targeted approach to all disease genes.…”

Gene-based therapies for dominantly inherited retinopathies

“…The approach involves the use of two components, suppression of both mutant and wild-type RHO alleles and provision of a suppression-resistant replacement RHO gene, engineered using codonredundancy. [7][8][9][10][11][12][13][14] In the context of dominant retinopathies, suppression and replacement is also being explored as a therapy for peripherin/ retinal degeneration slow-linked adRP, the next most common form of adRP after RHO-adRP. 15,16 In principle, replacement genes could be modified in a number of ways, for example, at degenerate sites as stated above.…”

“…RNAi molecules have been shown to suppress human RHO by approximately 90% in transduced photoreceptor cells. 12 Using the same P347S murine model of RHO-adRP, a ZFP (expressed from an AAV vector) targeting the RHO promoter has also been shown to provide benefit by suppression of the mutant P347S RHO, again in conjunction with expression of the endogenous mouse RHO gene. 14 It is worth highlighting that an additional challenge, particularly relevant to RHO-adRP, is associated with the substantial levels of endogenous RHO expression present in mammalian rod photoreceptors.…”