Abstract 932: Structure-based design of selective inhibitors for the β-catenin/T-cell factor protein-protein interaction

Abstract

Abstract INTRODUCTION: Significant compound screening efforts have been made to discover the inhibitors for the Wnt/β-catenin signaling pathway, but little success was obtained. Even so, most of the identified inhibitors act on Wnt upstream effectors, which can cause the cross-regulatory effects on the noncanonical Wnt signaling pathways, cannot confer the inhibitory activities to cancer cells that harbor downstream APC, Axin, or β-catenin activation mutations, and perturb the function of β-catenin in cell-cell adhesions. The formation of the β-catenin/T-cell factor (Tcf) complex in the cell nucleus is the penultimate step of canonical Wnt signaling. The aberrant formation of this protein-protein interaction (PPI) complex has been recognized as the key driving force for many cancers including triple negative breast cancers (TNBCs). The crystallographic and biochemical analyses reveal that the binding mode of Tcf, cadherin and adenomatous polyposis coli (APC) with β-catenin is identical. In the previous studies, we identified that the Tcf4 G13ANDE17 binding site of β-catenin can be targeted to design potent small-molecule inhibitors selective for the β-catenin/Tcf over β-catenin/cadherin and β-catenin/APC PPIs. EXPERIMENTAL PROCEDURE: In combination of peptidomimetic strategy, structure-based drug design, and chemical synthesis, and biochemical and cell-based characterizations, we successfully designed and synthesized potent and selective small-molecule inhibitors for the β-catenin/Tcf over β-catenin/cadherin and β-catenin/APC interactions. RESULTS AND DISCUSSION: The most potent inhibitor exhibited submicromolar inhibitory potency for disruption of the β-catenin/Tcf PPI. The potent inhibitors also exhibited dozens to hundreds folds selectivities for the β-catenin/Tcf PPI over the β-catenin/E-cadherin and β-catenin/APC PPIs. The binding mode of new inhibitors was characterized by the site-directed mutagenesis and structure-activity relationship studies. The cell-based studies demonstrated that new inhibitors passed the cell membrane, significantly attenuated canonical Wnt signaling in cancer cells, and suppressed growth of Wnt/β-catenin-dependent cancer cells. These inhibitors also exhibited cell-based selectivity for the β-catenin/Tcf over β-catenin/cadherin and β-catenin/APC PPIs. CONCLUSION: In TNBCs, the autocrine activation of Wnt ligands, the epigenetic silencing of Wnt suppressor genes, and the cross talks between signaling pathways stabilize beta-catenin in the dephosphorylated state, increase the level of nuclear β-catenin, and aberrantly activate the Wnt/β-catenin signaling pathway. The potent and selective β-catenin/Tcf inhibitors will provide the starting points for development of a class of targeted therapy for the treatment of triple negative breast cancers. Citation Format: Min Zhang, Zhen Wang, Cheng Mo, Haitao Mark Ji. Structure-based design of selective inhibitors for the β-catenin/T-cell factor protein-protein interaction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 932.