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.

Grant Number: 5R01GM150196-04
NIH Institute/Center: NIH
Principal Investigator: Jianfeng Cai