Systematically Mitigating the p38α Activity of Triazole-based BET Inhibitors

The Bromodomain and Extra Terminal (BET) family of proteins recognize post-translational N-ϵ-acetylated lysine modifications, regulating transcription as "reader" proteins. Bromodomain inhibitors are interesting targets for the development of potential cancer, inflammation, and heart disease treatments. Several dual kinase-bromodomain inhibitors have been identified by screening kinase inhibitor libraries against BET proteins. Although potentially useful from a polypharmacology standpoint, multitarget binding complicates deciphering molecular mechanisms. This report describes a systematic approach to mitigating kinase activity in a dual kinase-bromodomain inhibitor based on a 1,2,3-triazole-pyrimidine core. By modifying the triazole substituent and altering the pyrimidine core, this structure-activity relationship study enhanced BET activity while reducing the p38α kinase activity >90,000-fold. A BRD4-D1 cocrystal structure indicates that the 1,2,3-triazole is acting as a N-ϵ-acetylated lysine mimic. A BRD4 sensitive cell line, MM.1S, was used to demonstrate activity in cells, which is further supported by reduced c-Myc expression.