Epigenetic proteins are intently pursued targets in ligand discovery. So far, successful efforts have been limited to chromatin modifying enzymes, or so-called epigenetic 'writers' and 'erasers'. Potent inhibitors of histone binding modules have not yet been described. Here we report a cell-permeable small molecule (JQ1) that binds competitively to acetyl-lysine recognition motifs, or bromodomains. High potency and specificity towards a subset of human bromodomains is explained by co-crystal structures with bromodomain and extra-terminal (BET) family member BRD4, revealing excellent shape complementarity with the acetyl-lysine binding cavity. Recurrent translocation of BRD4 is observed in a genetically-defined, incurable subtype of human squamous carcinoma. Competitive binding by JQ1 displaces the BRD4 fusion oncoprotein from chromatin, prompting squamous differentiation and specific antiproliferative effects in BRD4-dependent cell lines and patient-derived xenograft models. These data establish proof-of-concept for targeting protein-protein interactions of epigenetic 'readers', and provide a versatile chemical scaffold for the development of chemical probes more broadly throughout the bromodomain family.
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Amino Acid Sequence, Animals, Azirines, Binding Sites, Carcinoma, Squamous Cell, Cell Differentiation, Cell Line, Tumor, Cell Proliferation, Chromatin, Dihydropyridines, Female, Humans, Mice, Mice, Nude, Models, Molecular, Molecular Sequence Data, Nuclear Proteins, Protein Binding, Protein Structure, Tertiary, Recombinant Proteins, Sequence Alignment, Skin Neoplasms, Stereoisomerism, Transcription Factors