Background: Dysregulated Wnt/?-catenin signaling has been implicated in the pathogenesis of many common human cancers, making this an attractive clinical target. However, this has proven challenging because i) ?- catenin plays critical roles in normal tissue homeostasis, ii) its signaling pathways form part of a complex network of intersecting pathways, and iii) ?-catenin's mode of interaction with active sites on its partner proteins makes it difficult to identify molecular probes that specifically and selectively disrupt its oncogenic activity. Preliminary data: i) Development of peptidomimetics of the BCL9-HD2 domain that selectively suppress oncogenic Wnt activity by blocking interaction of ?-catenin with its transcriptional co-activator BCL9; ii) A high-throughput screening (HTS) AlphaScreen assay allowing identification of several small-molecule inhibitors of ?-catenin/BCL9 interaction has been implemented; iii) An in vivo model using BCL9 transgenic mice that develop lymphomas as well as lung and gastric adenocarcinomas has been put into place. These studies offer compelling proof-of-concept for i) a therapeutic strategy addressing a known oncogenic role of the Wnt/?-catenin/BCL9 transcriptional complex, and ii) a pharmacologic intervention via targeted disruption of this complex. Working hypothesis: i) The Wnt/?-catenin/BCL9 transcriptional complex performs critical roles in cancer pathogenesis, and targeted disruption of this complex represents a promising pharmacologic strategy for blocking oncogenic Wnt activity in cancer; ii) Potent, specific, competitive inhibition of the ?-catenin/BCL9 interaction can be accomplished by using small organic molecules that bind tightly to the BCL9-HD2 binding domain on ?-catenin. Goals: i) to characterize HTS ?hits? biophysically via rapid calorimetry-based assay; ii) to test inhibitors for functional activity in Wnt-relevant cell-based assays to ensure that the inhibitors have the desired molecular specificity. Experimental tools: i) Homogeneous biophysical assays (i.e. enthalpy change measurement and Isothermal titration calorimetry) that will robustly monitor disruption of ?-catenin/BCL9 binding in vitro, ii) X-ray crystallography to unequivocally establish the structural basis of this interaction and will lay groundwork for possible future structure-guided synthetic chemistry; iii) Cellular assays that will enable us to monitor the consequences of disrupting the ?-catenin/BCL9 complex in intact cells; and iv) Established xenograft and transgenic mouse models of cancers with a dysregulated Wnt/?-catenin/BCL9 complex will allow evaluation of the possible clinical usefulness of small-molecule inhibitors of BCL9/?-catenin interaction. Expected results: Structurally validated small-molecule chemical probes that i) target ?-catenin, ii) dissociate native ?-catenin/BCL9 complexes, iii) selectively suppress Wnt transcriptional activity, and iv) possess mechanism-based antitumor activity in vitro, and in vivo with minimal toxicity, will be identified. Implications to Medicine: Our work in this project is expected to afford highly selective clinical probes of oncogenic Wnt activity and innovative targeted therapies against Wnt/?-catenin/BCL9 dependent human cancers.
Dysregulation of DNA transcription mediated by the Wnt/?-catenin signaling pathway is responsible for a wide range of common human cancers, making it an attractive target for cancer therapy. Here, we propose an innovative strategy designed to identify small-molecule inhibitors of ?-catenin/BCL9/B9L interaction that can be used to treat cancers with dysregulated Wnt/?-catenin/BCL9/B9L signaling. The proposed studies are significant to public health in that they will (i) augment our understanding of the molecular events driving cancer and (ii) improve patient outcome by providing therapies that more effectively alleviate patient suffering while decreasing cost of treatment.
