Tankyrases 1 and 2 (TNKS1/2) are promising pharmacological targets that recently gained interest for anticancer therapy in Wnt pathway dependent tumors. 2-Aryl-quinazolinones were identified and optimized into potent tankyrase inhibitors through SAR exploration around the quinazolinone core and the 4'-position of the phenyl residue. These efforts were supported by analysis of TNKS X-ray and WaterMap structures and resulted in compound 5k, a potent, selective tankyrase inhibitor with favorable pharmacokinetic properties. The X-ray structure of 5k in complex with TNKS1 was solved and confirmed the design hypothesis. Modulation of Wnt pathway activity was demonstrated with this compound in a colorectal xenograft model in vivo.