Discovery of Potent and Selective Inhibitors of Ataxia Telangiectasia Mutated and Rad3 Related (ATR) Protein Kinase as Potential Anticancer Agents

DNA-damaging agents are among the most frequently used anticancer drugs. However, they provide only modest benefit in most cancers. This may be attributed to a genome maintenance network, the DNA damage response (DDR), that recognizes and repairs damaged DNA. ATR is a major regulator of the DDR and an attractive anticancer target. Herein, we describe the discovery of a series of aminopyrazines with potent and selective ATR inhibition. Compound 45 inhibits ATR with a K-i of 6 nM, shows >600-fold selectivity over related kinases ATM or DNA-PK, and blocks ATR signaling in cells with an IC50 of 0.42 mu M. Using this compound, we show that ATR inhibition markedly enhances death induced by DNA-damaging agents in certain cancers but not normal cells. This differential response between cancer and normal cells highlights the great potential for ATR inhibition as a novel mechanism to dramatically increase the efficacy of many established drugs and ionizing radiation.