Small molecule promotes β-catenin citrullination and inhibits Wnt signaling in cancer.

Wnt (wingless)/β-catenin signaling is critical for tumor progression and is frequently activated in colorectal cancer as a result of the mutation of adenomatous polyposis coli (APC); however， therapeutic agents targeting this pathway for clinical use are lacking. Here we report that nitazoxanide (NTZ)， a clinically approved antiparasitic drug， efficiently inhibits Wnt signaling independent of APC. Using chemoproteomic approaches， we have identified peptidyl arginine deiminase 2 (PAD2) as the functional target of NTZ in Wnt inhibition. By targeting PAD2， NTZ increased the deamination (citrullination) and turnover of β-catenin in colon cancer cells. Replacement of arginine residues disrupted the transcriptional activity， and NTZ induced degradation of β-catenin. In Wnt-activated colon cancer cells， knockout of either PAD2 or β-catenin substantially increased resistance to NTZ treatment. Our data highlight the potential of NTZ as a modulator of β-catenin citrullination for the treatment of cancer patients with Wnt pathway mutations.