Structure-Based Optimization of Small-Molecule Inhibitors for the β-Catenin/B-Cell Lymphoma 9 Protein-Protein Interaction

Structure-based optimization was conducted to improve the potency, selectivity, and cell-based activities of beta-catenin/B-cell lymphoma 9 (BCL9) inhibitors based on the 4'-fluoro-N-phenyl-[1,1'-biphenyl]-3-carboxamide scaffold, which was designed to mimic the side chains of the hydrophobic a-helical hot spots at positions i, i + 3, and i + 7. Compound 29 was found to disrupt the beta-catenin/BCL9 protein-protein interaction (PPI) with a K-i of 0.47 mu M and >1900-fold selectivity for beta-catenin/BCL9 over beta-catenin/E-cadherin PPIs. The proposed binding mode of new inhibitors was consistent with the results of site-directed mutagenesis and structure-activity relationship studies. Cell-based studies indicated that 29 disrupted the beta-catenin/BCL9 interaction without affecting the beta-catenin/E-cadherin interaction, selectively suppressed transactivation of Wnt/beta-catenin signaling, downregulated expression of Wnt target genes, and inhibited viability of Wnt/beta-catenin-dependent cancer cells in dose-dependent manners. A comparison of the biochemical and cell-based assay results offered the directions for future inhibitor optimization.