Discovery of an Chemical Probe for BCL6 Inhibition by Optimization of Tricyclic Quinolinones.

B-cell lymphoma 6 (BCL6) is a transcriptional repressor and oncogenic driver of diffuse large B-cell lymphoma (DLBCL). Here, we report the optimization of our previously reported tricyclic quinolinone series for the inhibition of BCL6. We sought to improve the cellular potency and exposure of the non-degrading isomer, , of our recently published degrader, .

Improved Binding Affinity and Pharmacokinetics Enable Sustained Degradation of BCL6 .

The transcriptional repressor BCL6 is an oncogenic driver found to be deregulated in lymphoid malignancies. Herein, we report the optimization of our previously reported benzimidazolone molecular glue-type degrader to , a highly potent probe suitable for sustained depletion of BCL6 . We observed a sharp degradation SAR, where subtle structural changes conveyed the ability to induce degradation of BCL6.

Into Deep Water: Optimizing BCL6 Inhibitors by Growing into a Solvated Pocket.

We describe the optimization of modestly active starting points to potent inhibitors of BCL6 by growing into a subpocket, which was occupied by a network of five stably bound water molecules. Identifying potent inhibitors required not only forming new interactions in the subpocket but also perturbing the water network in a productive, potency-increasing fashion while controlling the physicochemical properties. We achieved this goal in a sequential manner by systematically probing the pocket and the water network, ultimately achieving a 100-fold improvement of activity.

Achieving Target Depletion through the Discovery and Optimization of Benzimidazolone BCL6 Degraders.

Deregulation of the transcriptional repressor BCL6 enables tumorigenesis of germinal center B-cells, and hence BCL6 has been proposed as a therapeutic target for the treatment of diffuse large B-cell lymphoma (DLBCL). Herein we report the discovery of a series of benzimidazolone inhibitors of the protein-protein interaction between BCL6 and its co-repressors. A subset of these inhibitors were found to cause rapid degradation of BCL6, and optimization of pharmacokinetic properties led to the discovery of 5-((5-chloro-2-((3,5)-4,4-difluoro-3,5-dimethylpiperidin-1-yl)pyrimidin-4-yl)amino)-3-(3-hydroxy-3-methylbutyl)-1-methyl-1,3-dihydro-2-benzo[]imidazol-2-one (CCT369260), which reduces BCL6 levels in a lymphoma xenograft mouse model following oral dosing.

Dual blockade of the PI3K/AKT/mTOR (AZD8055) and RAS/MEK/ERK (AZD6244) pathways synergistically inhibits rhabdomyosarcoma cell growth in vitro and in vivo.

Purpose: To provide rationale for using phosphoinositide 3-kinase (PI3K) and/or mitogen-activated protein kinase (MAPK) pathway inhibitors to treat rhabdomyosarcomas, a major cause of pediatric and adolescent cancer deaths.

Experimental Design: The prevalence of PI3K/MAPK pathway activation in rhabdomyosarcoma clinical samples was assessed using immunohistochemistry. Compensatory signaling and cross-talk between PI3K/MAPK pathways was determined in rhabdomyosarcoma cell lines following p110α short hairpin RNA-mediated depletion.