Small Molecule Antagonists of the Interaction between the Histone Deacetylase 6 Zinc-Finger Domain and Ubiquitin
Inhibitors of HDAC6 have attractive potential in numerous cancers. HDAC6 inhibitors to date target the catalytic domains, but targeting the unique zinc-finger ubiquitin-binding domain (Zf-UBD) of HDAC6 may be an attractive alternative strategy. We developed X-ray crystallography and biophysical assays to identify and characterize small molecules capable of binding to the Zf-UBD and competing with ubiquitin binding. Our results revealed two adjacent ligand-able pockets of HDAC6 Zf-UBD and the first functional ligands for this domain.
Harding, Rachel J.,Ferreira De Freitas, Renato,Collins, Patrick,Franzoni, Ivan,Ravichandran, Mani,Ouyang, Hui,Juarez-Ornelas, Kevin A.,Lautens, Mark,Schapira, Matthieu,Von Delft, Frank,Santhakumar, Vjayaratnam,Arrowsmith, Cheryl H.
Identification and Structure-Activity Relationship of HDAC6 Zinc-Finger Ubiquitin Binding Domain Inhibitors
HDAC6 plays a central role in the recruitment of protein aggregates for lysosomal degradation and is a promising target for combination therapy with proteasome inhibitors in multiple myeloma. Pharmacologically displacing ubiquitin from the zinc-finger ubiquitin-binding domain (ZnF-UBD) of HDAC6 is an underexplored alternative to catalytic inhibition. Here, we present the discovery of an HDAC6 ZnF-UBD-focused chemical series and its progression from virtual screening hits to low micromolar inhibitors. A carboxylate mimicking the C-terminal extremity of ubiquitin, and an extended aromatic system stacking with W1182 and R1155, are necessary for activity. One of the compounds induced a conformational remodeling of the binding site where the primary binding pocket opens up onto a ligand-able secondary pocket that may be exploited to increase potency. The preliminary structure-activity relationship accompanied by nine crystal structures should enable further optimization into a chemical probe to investigate the merit of targeting the ZnF-UBD of HDAC6 in multiple myeloma and other diseases.