Abstract
Purpose :
Morpholino (MO) and 2′ O-methoxyethyl (MOE) are two chemical modifications frequently applied to antisense oligonucleotides (ASOs) that are being used to manipulate gene expression for therapeutic applications. The fate of the ASO-targeted RNA depends on the ASO mechanism of action, which can be influenced by its chemical modifications. MO and MOEs are chemical modifications to the ribose sugar, which, when combined with modifications to the phosphate backbone, significantly improve ASO pharmacokinetic properties, innate immune response, and stability, making them ideal drugs for the treatment of diseases with defined genetic targets. Retinitis pigmentosa (RP) affects 1 in 4000 individuals worldwide, yet there are no effective treatments. In this study, we tested ASOs with MO or MOE modifications for the treatment of visual dysfunction in a mouse model of Usher syndrome (USH). USH is a form of RP that includes hearing impairment. Transgenic mice with a splicing mutation (216A) in the Ush1c gene, which causes USH in humans, have retinal dysfunction characteristic of RP, as well as profound hearing and vestibular deficits. Previously, we showed short-term rescue of hearing, balance, and vision in USH mice treated with a 216A-targeted-MOE-ASO. Here, we demonstrate that a combination of MO- and MOE-ASOs (Combo-ASO) significantly extends the duration of improved visual function in USH mice.
Methods :
Juvenile USH mice were treated with MOE-, MO-, or Combo-ASOs by intravitreal injection. Visual function was then measured at 3-12 months of age using electroretinogram (ERG) analysis. Retinal Ush1c and protein expression was measured by Next generation sequencing (NGS) and immunohistochemistry (IHC), respectively.
Results :
At 3 months of age, ERGs were significantly increased in all USH mice treated with ASOs compared with untreated USH control mice. The increased ERGs persisted for up to 12 months of age in USH mice treated one time with Combo-ASOs, compared with 3-6 months of age after treatment with MOE- or MO-ASOs alone. Further, NGS and IHC showed significantly improved Ush1c splicing and protein expression in the retinas of ASO-treated USH mice.
Conclusions :
These data demonstrate that a single dose of Combo-ASO significantly extends the duration of improved vision in USH mice and the potential for annual administration of ASO therapy for a long-term benefit to vision.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.