Rationally designed BCL6 inhibitors target activated B cell diffuse large B cell lymphoma
Mariano G. Cardenas, … , Alexander D. MacKerell Jr., Ari M. Melnick
Mariano G. Cardenas, … , Alexander D. MacKerell Jr., Ari M. Melnick
Published August 2, 2016
Citation Information: J Clin Invest. 2016;126(9):3351-3362. https://doi.org/10.1172/JCI85795.
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Research Article Oncology

Rationally designed BCL6 inhibitors target activated B cell diffuse large B cell lymphoma

Abstract

Diffuse large B cell lymphomas (DLBCLs) arise from proliferating B cells transiting different stages of the germinal center reaction. In activated B cell DLBCLs (ABC-DLBCLs), a class of DLBCLs that respond poorly to current therapies, chromosomal translocations and amplification lead to constitutive expression of the B cell lymphoma 6 (BCL6) oncogene. The role of BCL6 in maintaining these lymphomas has not been investigated. Here, we designed small-molecule inhibitors that display higher affinity for BCL6 than its endogenous corepressor ligands to evaluate their therapeutic efficacy for targeting ABC-DLBCL. We used an in silico drug design functional-group mapping approach called SILCS to create a specific BCL6 inhibitor called FX1 that has 10-fold greater potency than endogenous corepressors and binds an essential region of the BCL6 lateral groove. FX1 disrupted formation of the BCL6 repression complex, reactivated BCL6 target genes, and mimicked the phenotype of mice engineered to express BCL6 with corepressor binding site mutations. Low doses of FX1 induced regression of established tumors in mice bearing DLBCL xenografts. Furthermore, FX1 suppressed ABC-DLBCL cells in vitro and in vivo, as well as primary human ABC-DLBCL specimens ex vivo. These findings indicate that ABC-DLBCL is a BCL6-dependent disease that can be targeted by rationally designed inhibitors that exceed the binding affinity of natural BCL6 ligands.

Authors

Mariano G. Cardenas, Wenbo Yu, Wendy Beguelin, Matthew R. Teater, Huimin Geng, Rebecca L. Goldstein, Erin Oswald, Katerina Hatzi, Shao-Ning Yang, Joanna Cohen, Rita Shaknovich, Kenno Vanommeslaeghe, Huimin Cheng, Dongdong Liang, Hyo Je Cho, Joshua Abbott, Wayne Tam, Wei Du, John P. Leonard, Olivier Elemento, Leandro Cerchietti, Tomasz Cierpicki, Fengtian Xue, Alexander D. MacKerell Jr., Ari M. Melnick

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Figure 5

FX1 suppresses the growth of ABC-DLBCLs.

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FX1 suppresses the growth of ABC-DLBCLs. (A) ABC-DLBCL cells were treate...
(A) ABC-DLBCL cells were treated with increasing doses of FX1 versus vehicle. Cell viability was measured after 48 hours of treatment by resazurin reduction. The y axis shows percentage of growth-suppressive effect of the compound compared with vehicle-treated cells. Effect = 100% – 100% × (fluorescence of FX1-treated cells/fluorescence of vehicle-treated cells). The graph represents an average of 3 independent experiments. (B) Tumor volume of established HBL-1 xenografts implanted in NOD/SCID mice during treatment with daily 50 mg/kg FX1 versus vehicle for 10 days (n = 10, 2-tailed Mann-Whitney unpaired test). (C) Tumor burden is shown (AUC) for the same mice as in B and calculated between the initial tumor volume (t0: 100 mm3) and the final volume at day 9 (n = 10, 2-tailed Mann-Whitney unpaired test). (D) TUNEL IHC was performed in the same mice as in B. Scale bars: 100 μm. (E) Three primary DLBCL specimens were maintained in a coculture system and treated with FX1 50 μM versus vehicle. The y axis represents viability of 2 biological replicates (represented as percentage of vehicle-treated cells) determined using annexin V/DAPI flow cytometry after 48 hours. Live cells are defined as CD20+CD3– cells that are annexin V/DAPI double negative (unpaired t test, **P < 0.005). Hans and gene expression classification is shown below each sample number. (F) Combinatorial dosing of FX1 and doxorubicin is shown in the indicated cell lines, in cells treated with both agents simultaneously. The y axis represents the dose-reduction index (DRI) of 3 independent experiments, based on the DRI for both doxorubicin and FX1. (DRI > 1 = favorable combination.) Values in A and D represent mean ± SD. Values in B, C, E, and F are shown as mean ± SEM.