Discovery of Pyrrolopyrimidinone Inhibitors of the BCL6-SMRT Corepressor Interaction.

B-cell lymphoma 6 (BCL6) is a transcriptional repressor protein central to the development and maintenance of germinal centers (GCs) during the humoral immune response. BCL6 is often deregulated in diffuse large B-cell lymphoma (DLBCL), a type of non-Hodgkin's lymphoma, and inhibition of the protein-protein interaction between BCL6 and corepressors has been implicated as a therapeutic strategy. Based on a previously identified small molecule binding site on the BCL6 BTB domain, we carried out a virtual screen and identified a set of high micromolar screening hits. One series was advanced to a low micromolar confirmed hit via iterative rounds of compound optimization guided by structure activity relationships and co-crystal structures. Overall, we were able to use a rational, structure-based drug design approach to identify and advance a novel series of pyrrolopyrimidinone BCL6 BTB inhibitors.