To develop small molecules that modulate protein-protein interactions (PPIs) displays a significant therapeutic potential. However, rational design of small molecule enhancers of PPIs remains elusive. A study from Kyle R. Simonetta, et al. reported the potent small molecules that enhance the interaction between an oncogenic transcription factor, β-Catenin, and its cognate E3 ligase, SCFβ-TrCP.

Firstly, the authors identified a series of potent enhancers in a fluorescence polarization (FP)-based binding assay utilizing β-catenin phosphodegron peptides (residues 17-48) and recombinant β-TrCP/Skp1 complex. Ser37 is a known hotspot for β-catenin mutations and capable of screening the binding molecules robustly. NRX-252262, an optimized isoindoline analog, was identified as a typical enhancer of β-catenin:β-TrCP interaction.

Secondly, cellular assays were carried out to identify the activity of the enhancers. NRX-252262 had suitable drug-like properties for cellular evaluation. However, it did not induce degradation of endogenous S37A mutant β-catenin in TOV-112D cells. And the researchers reasoned that the lack of degradation resulted from to insufficient Ser33 phosphorylation in S37A mutant β-catenin.

In general, NRX-252262 is a potent enhancer of the interaction between β-Catenin, and its cognate E3 ligase, SCFβ-TrCP, with an EC50 of 3.8 nM.

Up to now, only a few enhancers of substrate:ligase interactions have been reported. Therefore, this study represents a prospective discovery for a specific ligase-substrate pair. Transcription factors such as β-catenin play vital roles in many diseases. However, in most cases, it as an undruggable target class. It is now clear that post-translational modification through the ubiquitin proteasome system is a common mechanism in cells regulating transcription factor levels. Disorders often results from mutations of the interaction of transcription factors with their cognate ligases. Ultimately, this strategy could effect different types of PPIs.


Nat Commun. 2019 Mar 29;10(1):1402.