To test the activity of (+)-JQ1-ASO conjugates, we initially chose a splice-switching ASO (SSO). The 18mer SSO we used contained a fully phosphorothioated (PS) backbone and all sugars with a 2′-OMe modification (Figure ). We used the gold-standard SSO sequence developed for the HeLa pLuc/705 cell line , which expresses a luciferase-encoding gene interrupted by a mutated ß-globin intron. The mutation generates a 5′-splice site which activates a cryptic 3′-splice site, resulting in incorrect mRNA splicing and non-functional luciferase production (Figure ). The SSO binds to the mutant 5′-splice site and promotes the exclusion of the aberrant intron, restoring the pre-mRNA splicing to produce functional luciferase.