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Peter Adamson, Heelam Chan, Janne Turunen, Jiayi Miao, Erik de Vrieze, Margo Dona, Silvia Albert, Erwin van Wijk, Hester van Diepen; QRX-421, an Antisense Oligonucleotide (AON) Targeting Mutations in Exon 13 of USH2A, Associated with Retinitis Pigmentosa in Usher Syndrome Type 2, is Effective in Skipping Exon 13 in the USH2A mRNA of Patients Fibroblasts and Patient-Derived Optic Cups. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2969. doi: https://doi.org/.
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The c.2299delG mutation in the USH2A gene is the most common mutation causing Usher syndrome when present in homozygosity or compound heterozygosity. Patients carrying this mutation suffer from inherited deafness and progressive loss of vision. The c.2299delG mutation is present in exon 13 of the USH2A gene and results in premature termination of translation and the absence of a functional Usherin protein. QRX-421 is a single stranded fully phosphorothioated and 2'-O-methyl modified antisense oligonucleotide designed to skip exon 13, including the c.2299delG mutation, leading to a truncated in-frame mRNA and functional Usherin protein.
Fibroblasts of a homozygous USH2A patient carrying the c.2299delG mutation in the USH2A gene were transfected with QRX-421 and mRNA levels were assessed. Patient-derived optic cup organoids were cultured and treated with QRX-421 for one month and mRNA levels assessed. A mutant zebrafish was developed as a model to assess functional protein restoration. Mutant zebrafish were injected with exon 13 targeting AONs, and mRNA profile, protein levels and ERG activity determined.
QRX-421 treatment of patient fibroblasts and patient-derived optic cups resulted in exon 13 skip in the mRNA transcript profile of USH2A. AON injection in mutant zebrafish showed Usherin protein restoration in the outer nuclear layer of the retina. Mutant zebrafish showed reduced levels of ERG activity which were restored following AON treatment.
QRX-421 demonstrated an ability to skip exon 13 in the mRNA of the USH2A gene in patient fibroblasts and patient-derived optic cups, presumably leading to the formation of a slightly shortened, but functional Usherin protein.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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