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J Med Chem. 2017 May 25;60(10):4386-4402. doi: 10.1021/acs.jmedchem.7b00359. Epub 2017 May 9.

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

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IMED Oncology and Discovery Sciences, AstraZeneca , 310 Cambridge Science Park, Milton Road, Cambridge, CB4 0WG, U.K.
IMED Oncology, AstraZeneca , Mereside, Alderley Park, Macclesfield, SK10 4TG, U.K.
IMED Oncology and Discovery Sciences, AstraZeneca , Gatehouse Park, Waltham, Massachusetts 02451, United States.
Pharmaron Beijing Co., Ltd. 6 Taihe Road BDA, Beijing 100176 P. R. China.


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.

[Indexed for MEDLINE]

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