Design and Characterization of Bivalent BET Inhibitors

Cellular signaling is often propagated by multivalent interactions. Multivalency creates avidity, allowing stable biophysical recognition. Multivalency is an attractive strategy for achieving potent binding to protein targets, as the affinity of bivalent ligands is often greater than the sum of monovalent affinities. The BET family of transcriptional coactivators features tandem bromodomains, through which BET proteins naturally bind acetylated histones and transcription factors. All reported BRD4 antagonists bind in a monovalent fashion. Here, we report the first bivalent BET bromodomain inhibitor, MT1 that has unprecedented potency. Biophysical and biochemical studies suggest MT1 is an intramolecular bivalent BRD4 binder that is over 100-fold more potent in cellular assays compared to the corresponding monovalent antagonist, JQ1. MT1 significantly delayed leukemia progression in mice (Mus musculus) compared to JQ1. These data qualify a powerful chemical probe for BET bromodomains and extensible rationale for further development of multidomain epigenetic reader protein inhibitors.