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Jasmina Cehajic Kapetanovic, Nina Milosavljevic, Robert Bedford, Robert J Lucas, Paul N Bishop; Efficacy and safety of glycosidic enzymes for improved gene delivery to the retina following intravitreal injection. Invest. Ophthalmol. Vis. Sci. 2016;57(12):777.
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© ARVO (1962-2015); The Authors (2016-present)
Adeno-associated virus (AAV)-mediated gene therapy has shown great promise in treating inherited retinal degenerations and other retinal conditions. Reaching adequate levels of transgene expression following intravitreal delivery represents a major challenge for ocular gene therapy studies, so current clinical trials rely on a more complex delivery approach via subretinal injection. We have previously reported that the extent of transgene expression in the mouse retina following intravitreal injection of AAV serotype 2 (AAV2) can be enhanced by co-injection of glycosidic enzymes targeting the extracellular matrix. Here we set out to determine the optimal combination of enzymes for this approach.
To this end we assessed the transduction efficiency of AAV2 (carrying a reporter gene, enhanced green fluorescent protein, GFP, driven by a ubiquitous promoter) in conjunction with chondroitin ABC lyase, hyaluronan lyase, heparinase III and combinations thereof by qualitative and quantitative analysis of GFP positive cells in the treated wild-type retinas. In addition, using an optimised AAV2-enzyme combination, we qualitatively analysed GFP expression in degenerate retinas from rd1 mice, a model of advanced retinal degeneration, after both untargeted delivery and when GFP was selectively targeted to ON-bipolar cells. Lastly, we performed a functional analysis of the retina by flash electoretinography and pupillometry to determine if glycosidic enzymes had any effects on the retinal function.
We report that a combination of heparinase III and hyaluronan lyase produced the greatest enhancement of gene delivery to the healthy wild-type retinas. This optimised AAV2-enzyme combination also led to a marked improvement in transduction of retinas from rd1 mice compared to AAV2 injected without the enzymes. Safety studies measuring retinal function by flash electroretinography in both scotopic and photopic conditions and pupillometry indicated that retinal function was unaffected in acute period and up to at least 12 months post enzymatic treatment.
Collectively these data confirmed that the glycosidic enzyme approach enhances retinal transduction efficiency by AAV, potentially allowing the development of intravitreal injection of gene therapy vectors for clinical applications.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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