Epigenetic proteins are intently pursued targets in ligand discovery.,To date, 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) which binds competitively to acetyl-lysine recognition motifs, or bromodomains.,High potency and specificity toward a subset of human bromodomains is explained by co-crystal structures with 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 anti-proliferative 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.
Resistance to BRAF inhibitors is an emerging problem in the melanoma field.,Strategies to prevent and overcome resistance are urgently required.,The dynamics of cell signalling, BrdU incorporation and cell-cycle entry after BRAF inhibition was measured using flow cytometry and western blot.,The ability of combined BRAF/MEK inhibition to prevent the emergence of resistance was demonstrated by apoptosis and colony formation assays and in 3D organotypic cell culture.,BRAF inhibition led to a rapid recovery of phospho-ERK (pERK) signalling.,Although most of the cells remained growth arrested in the presence of drug, a minor population of cells retained their proliferative potential and escaped from BRAF inhibitor therapy.,A function for the rebound pERK signalling in therapy escape was demonstrated by the ability of combined BRAF/MEK inhibition to enhance the levels of apoptosis and abrogate the onset of resistance.,Combined BRAF/MEK inhibition may be one strategy to prevent the emergence of drug resistance in BRAF-V600E-mutated melanomas.