Targeting Wnt signaling pathway - Protein-protein interactions (PPIs) are increasingly important targets for bioorganic and medicinal chemistry, given the critical role of myriad protein complexes in vital biological processes including signal transduction, cell growth and proliferation, etc. Due to enhanced stability and functional diversity, helical peptidomimetics have emerged as a promising strategy for targeting PPIs, however their application is still limited as they generally do not mimic α-helices well owing to their difference in the three-dimensional helical structures. For instance, BCL9/β-catenin and TCF/β-catenin PPIs involved in Wnt signaling pathway play an important role in embryonic development and tissue homeostasis and are linked to several types of cancers. As such, molecules disrupting either BCL9/β-catenin or TCF/β-catenin PPIs could become novel anti-cancer agents by inhibiting Wnt/β-catenin signaling. However, the successful design of helical inhibitors based on unnatural scaffold to block the PPIs is previously unknown. We have recently developed a series of unprecedented helical sulfono-γ-AApeptides that can mimic α-helical domain of proteins. Given by the significance of β−catenin/BCL9 and TCF/β-catenin PPIs, we believe that mod- ulating these PPIs could serve as an excellent opportunity to formulate the general strategy for targeting any other PPIs involving α-helices. Compared to the BCL9 and TCF peptides not exhibiting cellular activity, our preliminary studies indicated that sulfono-γ-AApeptides not only can mimic these helical domains, but also are highly cell permeable and can selectively inhibit growth of cancer cells with hyperactive Wnt/β−catenin signaling. To the best of knowledge, our findings represents the first example of helical peptidomimetics based on unnatural backbone in disrupting these PPIs. As such, our long-term goal is to develop novel helical sulfono-γ-AApeptides that serve as proteolytically stable and cell-penetrating molecular entities capable of modulating a myriad of medicinally relevant PPIs. The objective here, is to establish the design strategy of sulfono-γ-AApeptides as helical domain mimetics to disrupt β−catenin/ BCL9 and TCF/β-catenin PPIs with optimal potency. We will first identify helical sulfono-γ-AApeptides that potently disrupt β−catenin/BCL9 and TCF/β-catenin PPIs in vitro. Fol- lowing that, we will confirm molecular mechanism of lead compounds is through modulation of Wnt signaling, by using confocal spectroscopy, TOPFlash and FOPFlash assay, cellular engagement assay, and related signaling assays to assess the selectivity, specificity and potency of these sequences on the cellular level. Finally, we will use a mouse tumor model to validate the ability of the inhibitors to inhibit Wnt signaling and tumor growth in vivo. The proposed work is significant, as these studies are highly likely to lead to a new generation of therapeutic agents targeting both β−catenin/BCL9 PPI and β-catenin/TCF PPIs, which will secure the goal of inhibiting Wnt signaling. The proposed work is innovative, because our strategy of protein-domain-mimicking using helical sulfono-γ-AApeptides is completely new and can be adopted to target myriad disease-related PPIs in the future.
