Crystal structure of the BCL6 BTB domain in complex with pyrazolo-pyrimidine ligand

Experimental Data Snapshot

  • Resolution: 1.58 Å
  • R-Value Free: 0.192 
  • R-Value Work: 0.163 
  • R-Value Observed: 0.165 

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Discovery of Pyrazolo[1,5-a]pyrimidine B-Cell Lymphoma 6 (BCL6) Binders and Optimization to High Affinity Macrocyclic Inhibitors.

McCoull, W.Abrams, R.D.Anderson, E.Blades, K.Barton, P.Box, M.Burgess, J.Byth, K.Cao, Q.Chuaqui, C.Carbajo, R.J.Cheung, T.Code, E.Ferguson, A.D.Fillery, S.Fuller, N.O.Gangl, E.Gao, N.Grist, M.Hargreaves, D.Howard, M.R.Hu, J.Kemmitt, P.D.Nelson, J.E.O'Connell, N.Prince, D.B.Raubo, P.Rawlins, P.B.Robb, G.R.Shi, J.Waring, M.J.Whittaker, D.Wylot, M.Zhu, X.

(2017) J Med Chem 60: 4386-4402

  • DOI: https://doi.org/10.1021/acs.jmedchem.7b00359
  • Primary Citation of Related Structures:  
    5N1V, 5N1X, 5N1Z, 5N20, 5N21

  • PubMed Abstract: 

    Inhibition of the protein-protein interaction between B-cell lymphoma 6 (BCL6) and corepressors has been implicated as a therapeutic target in diffuse large B-cell lymphoma (DLBCL) cancers and profiling of potent and selective BCL6 inhibitors are critical to test this hypothesis. We identified a pyrazolo[1,5-a]pyrimidine series of BCL6 binders from a fragment screen in parallel with a virtual screen. Using structure-based drug design, binding affinity was increased 100000-fold. This involved displacing crystallographic water, forming new ligand-protein interactions and a macrocyclization to favor the bioactive conformation of the ligands. Optimization for slow off-rate constant kinetics was conducted as well as improving selectivity against an off-target kinase, CK2. Potency in a cellular BCL6 assay was further optimized to afford highly selective probe molecules. Only weak antiproliferative effects were observed across a number of DLBCL lines and a multiple myeloma cell line without a clear relationship to BCL6 potency. As a result, we conclude that the BCL6 hypothesis in DLBCL cancer remains unproven.

  • Organizational Affiliation

    IMED Oncology and Discovery Sciences, AstraZeneca , 310 Cambridge Science Park, Milton Road, Cambridge, CB4 0WG, U.K.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
B-cell lymphoma 6 protein
A, B
122Homo sapiensMutation(s): 0 
UniProt & NIH Common Fund Data Resources
Find proteins for P41182 (Homo sapiens)
Explore P41182 
Go to UniProtKB:  P41182
GTEx:  ENSG00000113916 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP41182
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 2 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on 8HN

Download Ideal Coordinates CCD File 
D [auth A],
F [auth B]
2-[(2~{S})-1-[3-cyano-7-[(2-oxidanylidene-3,4-dihydro-1~{H}-quinolin-6-yl)amino]pyrazolo[1,5-a]pyrimidin-5-yl]pyrrolidin-2-yl]ethanoic acid
C22 H21 N7 O3
Query on CL

Download Ideal Coordinates CCD File 
C [auth A],
E [auth B]
Experimental Data & Validation

Experimental Data

  • Resolution: 1.58 Å
  • R-Value Free: 0.192 
  • R-Value Work: 0.163 
  • R-Value Observed: 0.165 
  • Space Group: P 1
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 30.4α = 83.36
b = 38.97β = 75.39
c = 54.93γ = 67.21
Software Package:
Software NamePurpose
XDSdata reduction
Aimlessdata scaling

Structure Validation

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Ligand Structure Quality Assessment 

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2017-05-17
    Type: Initial release
  • Version 1.1: 2017-06-07
    Changes: Data collection, Database references
  • Version 1.2: 2024-05-08
    Changes: Data collection, Database references