As regulators of transcription, epigenetic proteins that interpret post-translational modifications to N-terminal histone tails are essential for maintaining cellular homeostasis. When dysregulated, "reader" proteins become drivers of disease. In the case of bromodomains, which recognize N-ϵ-acetylated lysine, selective inhibition of individual bromodomain-and-extra-terminal (BET)-family bromodomains has proven challenging. We describe the >55-fold N-terminal-BET bromodomain selectivity of 1,4,5-trisubstituted-imidazole dual kinase-bromodomain inhibitors. Selectivity for the BRD4 N-terminal bromodomain (BRD4(1)) over its second bromodomain (BRD4(2)) arises from the displacement of ordered waters and the conformational flexibility of lysine-141 in BRD4(1). Cellular efficacy was demonstrated via reduction of c-Myc expression, inhibition of NF-κB signaling, and suppression of IL-8 production through potential synergistic inhibition of BRD4(1) and p38α. These dual inhibitors provide a new scaffold for domain-selective inhibition of BRD4, the aberrant function of which plays a key role in cancer and inflammatory signaling.
Bibliographical noteFunding Information:
This work was supported by the NSF (Grant CHE-1352019, W.C.K.P.) AHA (Grant 15SDG25710427, W.C.K.P.), NIGMS (Grant R35GM124718), and the University of Minnesota Masonic Cancer Center (Pre-R01 pilot grant D.A.H. and W.C.K.P.). A.D. was supported by the NIH Chemistry-Biology Interface Training Grant at the University of Minnesota (5T32GM008700-18). Isothermal-titration calorimetry and nuclear-magnetic-resonance spectroscopy were carried out using instruments funded by NIH Shared Instrumentation Grants (S10-OD017982 and S10-OD011952, respectively). We also thank the Moffitt Chemical Biology Core for use of the protein crystallography facility (NCI Grant P30-CA076292). BI-BODIPY was a generous gift from Wei Zhang at the University of Massachusetts, Boston. We thank Prof. Brian Smith for providing the BRD4 Bromodomain construct BRD4 (1 + 2) spanning residues 38-460.