The antibiotic drug trimethoprim suppresses tumour growth and metastasis via targeting Snail.

The zinc finger transcription factor Snail is aberrantly activated in many human cancers and strongly associated with poor prognosis. As a transcription factor, Snail has been traditionally considered an 'undruggable' target. Here, we identified a potent small-molecule inhibitor of Snail, namely trimethoprim, and investigated its potential antitumour effects and the underlying mechanisms. The inhibitory action of trimethoprim on Snail protein and the related molecular mechanisms were revealed by molecular docking, biolayer interferometry, immunoblotting, immunoprecipitation, qRT-PCR, pull-down and cycloheximide pulse-chase assays. The anti-proliferative and anti-metastatic effects of trimethoprim via targeting Snail were tested in multiple cell-based assays and animal models. This study identified trimethoprim, an antimicrobial drug, as a potent antitumour agent via targeting Snail. Molecular modelling analysis predicted that trimethoprim directly binds to the arginine-174 pocket of Snail protein. We further discovered that trimethoprim strongly interrupts the interaction of Snail with CREB-binding protein (CBP)/p300, which consequently suppresses Snail acetylation and promotes Snail degradation through the ubiquitin-proteasome pathway. Furthermore, trimethoprim sufficiently inhibited the proliferation, epithelial-mesenchymal transition (EMT) and migration of cancer cells in vitro via specifically targeting Snail. More importantly, trimethoprim effectively reduced Snail-driven tumour growth and metastasis to vital organs such as lung, bone and liver. These findings indicate, for the first time, that trimethoprim suppresses tumour growth and metastasis via targeting Snail. This study provides insights for a better understanding of the anticancer effects of trimethoprim and offers a potential anticancer therapeutic agent for clinical treatment.