Covalent Fragment Screening and Optimization Identifies the Chloroacetohydrazide Scaffold as Inhibitors for Ubiquitin C‑terminal Hydrolase L1

Dysregulation of the ubiquitin-proteasome systems is
a hallmark
of various disease states including neurodegenerative diseases and
cancer. Ubiquitin C-terminal hydrolase L1 (UCHL1), a deubiquitinating
enzyme, is expressed primarily in the central nervous system under
normal physiological conditions, however, is considered an oncogene
in various cancers, including melanoma, lung, breast, and lymphoma.
Thus, UCHL1 inhibitors could serve as a viable treatment strategy
against these aggressive cancers. Herein, we describe a covalent fragment
screen that identified the chloroacetohydrazide scaffold as a covalent
UCHL1 inhibitor. Subsequent optimization provided an improved fragment
with single-digit micromolar potency against UCHL1 and selectivity
over the closely related UCHL3. The molecule demonstrated efficacy
in cellular assays of metastasis. Additionally, we report a ligand-bound
crystal structure of the most potent molecule in complex with UCHL1,
providing insight into the binding mode and information for future
optimization.