title: Discovery and optimization of small-molecule ligands for the CBP/p300 bromodomains.
abstract: Small-molecule inhibitors that target bromodomains outside of the bromodomain and extra-terminal (BET) sub-family are lacking. Here, we describe highly potent and selective ligands for the bromodomain module of the human lysine acetyl transferase CBP/p300, developed from a series of 5-isoxazolyl-benzimidazoles. Our starting point was a fragment hit, which was optimized into a more potent and selective lead using parallel synthesis employing Suzuki couplings, benzimidazole-forming reactions, and reductive aminations. The selectivity of the lead compound against other bromodomain family members was investigated using a thermal stability assay, which revealed some inhibition of the structurally related BET family members. To address the BET selectivity issue, X-ray crystal structures of the lead compound bound to the CREB binding protein (CBP) and the first bromodomain of BRD4 (BRD4(1)) were used to guide the design of more selective compounds. The crystal structures obtained revealed two distinct binding modes. By varying the aryl substitution pattern and developing conformationally constrained analogues, selectivity for CBP over BRD4(1) was increased. The optimized compound is highly potent (Kd = 21 nM) and selective, displaying 40-fold selectivity over BRD4(1). Cellular activity was demonstrated using fluorescence recovery after photo-bleaching (FRAP) and a p53 reporter assay. The optimized compounds are cell-active and have nanomolar affinity for CBP/p300; therefore, they should be useful in studies investigating the biological roles of CBP and p300 and to validate the CBP and p300 bromodomains as therapeutic targets.
authors.affiliation: Department of Chemistry, University of Oxford , South Parks Road, Oxford OX1 3TA, U.K.
authors.forename: Duncan A
authors.initials: DA
authors.lastname: Hay
authors.forename: Oleg
authors.initials: O
authors.lastname: Fedorov
authors.forename: Sarah
authors.initials: S
authors.lastname: Martin
authors.forename: Dean C
authors.initials: DC
authors.lastname: Singleton
authors.forename: Cynthia
authors.initials: C
authors.lastname: Tallant
authors.forename: Christopher
authors.initials: C
authors.lastname: Wells
authors.forename: Sarah
authors.initials: S
authors.lastname: Picaud
authors.forename: Martin
authors.initials: M
authors.lastname: Philpott
authors.forename: Octovia P
authors.initials: OP
authors.lastname: Monteiro
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Rogers
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Conway
authors.forename: Timothy P C
authors.initials: TP
authors.lastname: Rooney
authors.forename: Anthony
authors.initials: A
authors.lastname: Tumber
authors.forename: Clarence
authors.initials: C
authors.lastname: Yapp
authors.forename: Panagis
authors.initials: P
authors.lastname: Filippakopoulos
authors.forename: Mark E
authors.initials: ME
authors.lastname: Bunnage
authors.forename: Susanne
authors.initials: S
authors.lastname: Müller
authors.forename: Stefan
authors.initials: S
authors.lastname: Knapp
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Schofield
authors.forename: Paul E
authors.initials: PE
authors.lastname: Brennan
mesh_terms: D001665:Binding Sites; D050882:CREB-Binding Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D060326:Chemistry Techniques, Synthetic; D018360:Crystallography, X-Ray; D055808:Drug Discovery; D004353:Drug Evaluation, Preclinical / Q000379:methods; D050881:E1A-Associated p300 Protein / Q000737:chemistry* / Q000378:metabolism; D036681:Fluorescence Recovery After Photobleaching; D016158:Genes, p53; D006367:HeLa Cells / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000737:chemistry; D007555:Isoxazoles / Q000737:chemistry; D008024:Ligands; D008862:Microsomes, Liver / Q000187:drug effects; D008958:Models, Molecular; D015394:Molecular Structure; D017434:Protein Structure, Tertiary; D054852:Small Molecule Libraries / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D007211:Indoles; D007555:Isoxazoles; D008024:Ligands; D054852:Small Molecule Libraries; D050882:CREB-Binding Protein; C494363:CREBBP protein, human; D050881:E1A-Associated p300 Protein; C494360:EP300 protein, human