Discovery of the First BRD4 Second Bromodomain (BD2)-Selective Inhibitors
Junhua Li, Qingqing Hu, Run Zhu, Ruibo Dong, Hui Shen, Jiankang Hu, Cheng Zhang, Xiaohan Zhang, Tingting Xu, Qiuping Xiang, Yan Zhang, Bin Lin, Linxiang Zhao, Xishan Wu, Yong Xu
Abstract
Pan-BD2 inhibitors have been shown to retain an antileukemia effect and display less dose-limiting toxicities than pan-BET inhibitors. However, it is necessary to consider the potential off-target toxicity associated with the inhibition of four BET BD2 proteins. To date, no BRD4 BD2 domain selective inhibitor has been reported. Based on our previous pan-BD2 inhibitor 12 (XY153), we successfully identified 16o (XY221) as the first BRD4 BD2-selective inhibitor. 16o demonstrated potent binding affinity for BRD4 BD2 (IC 50 = 5.8 nM), along with high pan-BD2 selectivity (667-fold over BRD4 BD1) and BRD4 BD2 domain selectivity (9–32-fold over BRD2/3/T BD2). The BRD4 BD2 selectivity of 16o was further confirmed by the BLI assay, showing 66–144-fold selectivity over other BET BD2 domains. 16o exhibited good liver microsomal stability ( T 1/2 > 120 min) and pharmacokinetic properties ( F = 13.1%). These data indicate that 16o may serve as a valuable candidate for BRD4 BD2 advancing epigenetic research.