Abstract
Purpose: :
Challenges associated with any potential RNAi therapeutic include successful delivery to and entry into the cell. We have developed a new class of stable, self-delivering RNAi compounds (sd-rxRNATM) that incorporate features of RNAi and antisense technologies and result in spontaneous cellular uptake. Our ultimate goal is to develop a novel RNAi therapeutic platform that enables a wide range of treatments for retinal disorders. To this end, we have carried out studies to establish mRNA silencing in the retina and initiated safety evaluation of this new class of RNAi compounds.
Methods: :
sd-rxRNA was administered by single intravitreal injection to C57 mice. Non-targeting control (NTC), sd-rxRNA or PBS was injected in the contralateral eye as a control. mRNA reduction was evaluated by qPCR. For safety evaluation, fluorescein angiography, fundus photography and optical coherence tomography were performed 1, 2, and 3 weeks post dose. Electroretinography (ERG) was performed at 3 weeks.
Results: :
Previously, confocal microscopy revealed robust cellular internalization of Fl-sd-rxRNA for up to 2 days post intravitreal injection, compared to that of a chemically stabilized small interfering RNA (Fl-rxRNA). To assess whether uptake correlated with silencing, 3 µg of sd-rxRNA targeting ubiquitously expressed genes (e.g. cyclophilin-B or Map4K4) was administered via intravitreal injection and resulted in statistically significant reduction of target mRNA levels in the retina for 14-21 days, with maximum mRNA silencing (51% and 41%, p<0.01 vs. NTC) observed at 1-2 days. Normal retinal architecture with no overt damage was noted up to 3 weeks post injection. ERG was equivalent to PBS treated eyes. The occasional cataract was believed to be injection related.
Conclusions: :
Results from these studies show that sd-rxRNA efficiently distributes to retinal cells without a delivery vehicle, and can sustain statistically significant silencing of an mRNA target for up to 21 days depending upon target. Prolonged silencing observed with sd-rxRNAs supports the potential value of sd-rxRNA as a treatment for retinal disease.
Keywords: gene/expression • retina • detection