A RNAi screen identified Brd4 as a therapeutic target in acute myeloid leukaemia (AML). The study used a custom library of small hairpin RNAs (shRNAs) targeting known chromatin regulators in a genetically defined AML mouse model to identify genes critical for disease maintenance. Brd4, a bromodomain-containing protein, was found to be essential for AML progression. Suppression of Brd4 using shRNAs or the small-molecule inhibitor JQ1 led to robust antileukaemic effects in vitro and in vivo, accompanied by terminal myeloid differentiation and elimination of leukaemia stem cells. JQ1 showed broad activity in diverse AML subtypes, indicating its potential as a therapeutic agent. The effects of Brd4 suppression were attributed to its role in sustaining Myc expression, which promotes aberrant self-renewal. These findings highlight the utility of RNAi screening in revealing epigenetic vulnerabilities that can be exploited for direct pharmacological intervention. The study also demonstrated that JQ1 effectively inhibits Brd4, leading to reduced Myc expression and limiting self-renewal in AML. The results establish small-molecule inhibition of Brd4 as a promising therapeutic strategy in AML and other cancers. The study underscores the importance of targeting epigenetic pathways in cancer therapy and highlights the potential of Brd4 as a therapeutic target.A RNAi screen identified Brd4 as a therapeutic target in acute myeloid leukaemia (AML). The study used a custom library of small hairpin RNAs (shRNAs) targeting known chromatin regulators in a genetically defined AML mouse model to identify genes critical for disease maintenance. Brd4, a bromodomain-containing protein, was found to be essential for AML progression. Suppression of Brd4 using shRNAs or the small-molecule inhibitor JQ1 led to robust antileukaemic effects in vitro and in vivo, accompanied by terminal myeloid differentiation and elimination of leukaemia stem cells. JQ1 showed broad activity in diverse AML subtypes, indicating its potential as a therapeutic agent. The effects of Brd4 suppression were attributed to its role in sustaining Myc expression, which promotes aberrant self-renewal. These findings highlight the utility of RNAi screening in revealing epigenetic vulnerabilities that can be exploited for direct pharmacological intervention. The study also demonstrated that JQ1 effectively inhibits Brd4, leading to reduced Myc expression and limiting self-renewal in AML. The results establish small-molecule inhibition of Brd4 as a promising therapeutic strategy in AML and other cancers. The study underscores the importance of targeting epigenetic pathways in cancer therapy and highlights the potential of Brd4 as a therapeutic target.