New Nucleotide-Competitive Non-Nucleoside Inhibitors of Terminal 2 Deoxynucleotidyl Transferase: Discovery, Characterization, and 3 Crystal Structure in Complex with the Target

Terminal deoxynucletidyl transferase (TdT) is overex- pressed in some cancer types, where it might compete with pol μ during the mutagenic repair of double strand breaks (DSBs) through the non- homologous end joining (NHEJ) pathway. Here we report the discovery and characterization of pyrrolyl and indolyl diketo acids that speci fi cally target TdT and behave as nucleotide-competitive inhibitors. These com- pounds show a selective toxicity toward MOLT-4 compared to HeLa cells that correlate well with in vitro selectivity for TdT. The binding site of two of these inhibitors was determined by cocrystallization with TdT, ex- plaining why these compounds are competitive inhibitors of the deoxy- nucleotide triphosphate (dNTP). In addition, because of the observed dual localization of the phenyl substituent, these studies open the possibility of rationally designing more potent compounds