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

In the past, development of tankyrases inhibitors has focused on the ADP-ribosyltransferase domain. Targeting tankyrases' ability to interact with protein substrates through their ARC domains represents an alternative strategy to be explored as therapeutic approach against specific protein-protein interactions. In this paper, we employed a FRET-based assay to identify ARC4-binding compounds by screening the EU-OPENSCREEN Pilot and Commercials Diversity libraries. We discovered an effective series of compounds with the same scaffold and through chemical synthesis we obtained the compound S8 (ARCher-142), which binds selectively to ARC4 with potency of 8 μM. NMR analysis and X-ray crystallography allowed us to identify the binding site in ARC4 and to rationalize the observed selectivity. Despite binding exclusively to ARC4, the inhibitor can attenuate the WNT/β-catenin signalling pathway in cells. Our work demonstrates that targeting single ARC domains is possible, offering an inhibition approach tailored to tankyrase ARC4 inhibition.