Efficacy, biodistribution and safety comparison of chemically modified antisense oligonucleotides in the retina

Antisense oligonucleotides (AONs) are a versatile tool for treating inherited retinal diseases. However, little is known about how different chemical modifications of AONs can affect their biodistribution, toxicity, and uptake in the retina. Here, we addressed this question by comparing splice-switching AONs with three different chemical modifications commonly used in a clinical setting (2'O-methyl-phosphorothioate (2-OMe/PS), 2'O-methoxyethyl-phosphoriate (2-MOE/PS), and phosphorodiamidite morpholino oligomers (PMO)). These AONs targeted genes exclusively expressed in certain types of retinal cells. Overall, studies in vitro and in vivo in C57BL/6J wild-type mouse retinas showed that 2-OMe/PS and 2-MOE/PS AONs have comparable efficacy and safety profiles. In contrast, octa-guanidine-dendrimer-conjugated in vivo PMO-oligonucleotides (ivPMO) caused toxicity. This was evidenced by externally visible ocular phenotypes in 88.5% of all ivPMO-treated animals, accompanied by severe alterations at the morphological level. However, delivery of unmodified PMO-AONs did not cause any toxicity, although it clearly reduced the efficacy. We conducted the first systematic comparison of different chemical modifications of AONs in the retina. Our results showed that the same AON sequence with different chemical modifications displayed different splicing modulation efficacies, suggesting the 2'MOE/PS modification as the most efficacious in these conditions. Thereby, our work provides important insights for future clinical applications.