To test the activity of the (+)-JQ1-MALAT1 gapmer conjugate, we measured MALAT1 transcript levels using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) at 24 hours, comparing the knockdown to the unconjugated MALAT1 gapmer, normalised to the house keeping gene GAPDH. As with the SSO conjugate, the (+)-JQ1-MALAT1 gapmer conjugate outperformed the unconjugated MALAT1 gapmer at all tested concentrations. We measured 20.1%, 25 30.2%, 56.8%, and 54% less transcript with the (+)-JQ1 modified gapmer treatment, compared to the unmodified gapmer, at 5, 50, 100, and 200 nM respectively (Figure ). Again, similar to the SSO, this enhanced activity was found to depend on specific (+)-JQ1-BET bromodomain protein interactions, as it was lost in the presence of excess quantities of small molecule (+)-JQ1. At 200 nM (+)-JQ1, the enhanced activity of the (+)-JQ1-MALAT1 gapmer at 50-200 nM was completely inhibited (Figure , SI Figure ). Furthermore, no increase in toxicity was observed for the (+)-JQ1-MALAT1 gapmer conjugate compared to the unconjugated MALAT1 gapmer at all concentrations (SI Figure ). This demonstrated that (+)-JQ1 conjugation can effectively increase both the splice-switching and gene-knockdown activity of ASOs. While MALAT1 ASOs are being evaluated for their therapeutic effect, Oblimersen (G3139), an 18-mer ASO containing a fully PS backbone designed to target apoptosis factor BCL-2, reached phase III clinical trials. BCL-2 is a crucial inhibitor of apoptosis that is overexpressed in various cancers. Despite promising phase I-II results as a sensitiser for chemotherapy, G3139 failed to show efficacy in multiple phase III trails. As this drug was well tolerated by patients , the limiting factor is likely target engagement and efficacy. Therefore, given that G3139 functions as an RNase H-active ASO (Figure ), like the MALAT1 gapmer, we aimed to measure whether a (+)-JQ1-G3139 conjugate could result in a more potent drug molecule (Figure ).