Discovery of tankyrase scaffolding inhibitor specifically targeting the ARC4 peptide binding domain

Tankyrases are poly-ADP-ribosyltransferases that orchestrate numerous biological processes involved in disease. Their established regulatory roles, particularly within the WNT/β-catenin pathway, have driven notable drug discovery efforts aimed at inhibiting their catalytic activity. Targeting tankyrases' interaction with proteins through their ARC domains represents an alternative strategy to be explored as a therapeutic approach against specific protein-protein interactions. In this article, we employed a pre-established FRET-based assay to screen the EU-OPENSCREEN libraries for identification of ARC4 inhibitors. We discovered a series of pyrrolone-based compounds, and we synthesized compound S8 (ARCher-142), which binds selectively to ARC4 with a potency of 8 μM. NMR analysis and X-ray crystallography allowed us to identify the binding site and to rationalize the observed selectivity. Despite binding exclusively to ARC4, the inhibitor can attenuate the WNT/β-catenin signaling pathway in cells. Our work demonstrates that targeting single ARC domains is possible, offering an inhibition approach tailored to tankyrase ARC4.