A fluorescent splice-switching mouse model enables high-throughput, sensitive quantification of antisense oligonucleotide delivery and activity.

While antisense oligonucleotides (ASOs) are used in the clinic, therapeutic development is hindered by the inability to assay ASO delivery and activity in vivo. Accordingly, we developed a dual-fluorescence, knockin mouse model that constitutively expresses mKate2 and an engineered EGFP that is alternatively spliced in the presence of ASO to induce expression. We first examined free ASO activity in the brain following intracerebroventricular injection revealing EGFP splice-switching is both ASO concentration and time dependent in major central nervous system cell types. We then assayed the impact of lipid nanoparticle delivery on ASO activity after intravenous administration. Robust EGFP fluorescence was observed in the liver and EGFP+ cells were successfully isolated using fluorescence-activated cell sorting. Together, these results show the utility of this animal model in quantifying both cell-type- and organ-specific ASO delivery, which can be used to advance ASO therapeutics for many disease indications.