Chemoproteomics-Enabled Covalent Ligand Screening Reveals a Thioredoxin-Caspase 3 Interaction Disruptor That Impairs Breast Cancer Pathogenicity

Covalent
ligand discovery is a promising strategy to develop small-molecule
effectors against therapeutic targets. Recent studies have shown that
dichlorotriazines are promising reactive scaffolds that preferentially
react with lysines. Here, we have synthesized a series of dichlorotriazine-based
covalent ligands and have screened this library to reveal small molecules
that impair triple-negative breast cancer cell survival. Upon identifying
a lead hit from this screen KEA1-97, we used activity-based protein
profiling (ABPP)-based chemoproteomic platforms to identify that this
compound targets lysine 72 of thioredoxina site previously
shown to be important in protein interactions with caspase 3 to inhibit
caspase 3 activity and suppress apoptosis. We show that KEA1-97 disrupts
the interaction of thioredoxin with caspase 3, activates caspases,
and induces apoptosis without affecting thioredoxin activity. Moreover,
KEA1-97 impairs in vivo breast tumor xenograft growth.
Our study showcases how the screening of covalent ligands can be coupled
with ABPP platforms to identify unique anticancer lead and target
pairs.