Discovery of a Potent and Selective Covalent Inhibitor and Activity-Based Probe for the Deubiquitylating Enzyme UCHL1, with Antifibrotic Activity

Ubiquitin carboxy-terminal hydrolase L1 (UCHL1) is a deubiquitylatingenzyme which is proposed as a potential therapeutic target inneurodegeneration, cancer, and liver and lung fibrosis. Herein we report thediscovery of the most potent and selective UCHL1 probe (IMP-1710) to date basedon a covalent inhibitor scaffold and apply this probe to identify and quantifytarget proteins in intact human cells. IMP-1710 stereoselectively labels thecatalytic cysteine of UCHL1 at low nanomolar concentration in cells, and weshow that a previously claimed UCHL1 inhibitor (LDN-57444) fails to engageUCHL1 in cells. We further demonstrate that potent UCHL1 inhibitors blockpro-fibrotic responses in a cellular model of idiopathic pulmonary fibrosis,supporting a potential therapeutic role for UCHL1 inhibition and providing abasis for future therapeutic development of selective UCHL1 inhibitors.