Abstract P2-12-02: discovery of the β-catenin/Tcf inhibitors for treatment of triple negative breast cancer

In triple negative breast cancers (TNBCs), the autocrine activation of Wnt ligands, the epigenetic silencing of Wnt suppressor genes, and the cross talks between signaling pathways stabilize β-catenin in the dephosphorylated state, increase the level of nuclear β-catenin, and aberrantly activate the Wnt/β-catenin signaling pathway. The design of inhibitors for the upstream effectors of the Wnt/β-catenin signaling pathway cannot confer the inhibitory activities to cancer cells that harbor downstream APC, Axin, or β-catenin activation mutations and can perturb the function of β-catenin in cell–cell adhesion. The formation of the β-catenin/T-cell factor (Tcf) complex in the cell nucleus is the penultimate step of the Wnt/β-catenin signaling pathway. The aberrant formation of this protein–protein interaction (PPI) complex has been recognized as a key driving force for many cancers including TNBCs. Since β-catenin was reported in 1992, significant interest has been paid to screen compound libraries to discover small-molecule inhibitors that can bind β-catenin and disrupt the β-catenin/Tcf interaction. Many high-throughput screening campaigns were conducted, but little to no success was obtained. None of the reported compounds were able to deliver any drug candidates to preclinical and clinical trials. We decided to take a rational drug design approach to design new inhibitors based on the electronic properties of the key structural features for β-catenin/Tcf recognition. Our crystallographic and biochemical analyses revealed that the Tcf4 G13ANDE17 binding site of β-catenin could be targeted to design potent small-molecule inhibitors selective for the β-catenin/Tcf interaction. 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 interaction. The most potent inhibitor exhibited submicromolar inhibitory potency for disruption of the β-catenin/Tcf interaction. This potent inhibitor also exhibited dozens to hundreds folds of selectivities for the β-catenin/Tcf over the β-catenin/E-cadherin and β-catenin/APC interactions. 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 Wnt/β-catenin signaling in TNBC cells, and suppressed growth of Wnt/β-catenin-dependent TNBC cells. These inhibitors also exhibited cell-based selectivities for the β-catenin/Tcf over β-catenin/cadherin and β-catenin/adenomatous polyposis coli (APC) interactions. Citation Format: Ji H, Wang Z, Mo C, Zhang M. discovery of the β-catenin/Tcf inhibitors for treatment of triple negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-12-02.