Potent and Selective CK2 Kinase Inhibitors with Effects on Wnt Pathway Signaling <i>in Vivo</i>

The Wnt pathway is an evolutionarily conserved and tightly regulated signaling network with important roles in embryonic development and adult tissue regeneration. Impaired Wnt pathway regulation, arising from mutations in Wnt signaling components, such as Axin, APC, and β-catenin, results in uncontrolled cell growth and triggers oncogenesis. To explore the reported link between CK2 kinase activity and Wnt pathway signaling, we sought to identify a potent, selective inhibitor of CK2 suitable for proof of concept studies <i>in vivo</i>. Starting from a pyrazolo­[1,5-<i>a</i>]­pyrimidine lead (<b>2</b>), we identified compound <b>7h</b>, a potent CK2 inhibitor with picomolar affinity that is highly selectivity against other kinase family enzymes and inhibits Wnt pathway signaling (IC₅₀ = 50 nM) in DLD-1 cells. In addition, compound <b>7h</b> has physicochemical properties that are suitable for formulation as an intravenous solution, has demonstrated good pharmacokinetics in preclinical species, and exhibits a high level of activity as a monotherapy in HCT-116 and SW-620 xenografts

Discovery of Pyrazolo[1,5‑<i>a</i>]pyrimidine B‑Cell Lymphoma 6 (BCL6) Binders and Optimization to High Affinity Macrocyclic Inhibitors

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-<i>a</i>]­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