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 IC(50) of 0.42 μM. 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.

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Background and purpose: The ATP-gated P2X 7 receptor has been shown to play a role in several inflammatory processes, making it an attractive target for anti-inflammatory drug discovery. We have recently identified a novel set of cyclic imide compounds that inhibited P2X 7 receptor-mediated dye uptake in human macrophage THP-1 cells. In this study the actions and selectivity of one of these compounds, AZ11645373, were characterized. Experimental approach: We measured membrane currents, calcium influx, and YOPRO-1 uptake from HEK cells expressing individual P2X receptors, and YOPRO1 uptake and interleukin-1b release from THP-1 cells in response to ATP and the ATP analogue benzoylbenzoyl ATP (BzATP). Key results: AZ11645373 up to 10 mM, had no agonist or antagonist actions on membrane currents due to P2X receptor activation at human P2X 1 , rat P2X 2 , human P2X 3 , rat P2X 2/3 , human P2X 4 , or human P2X 5 receptors expressed in HEK cells. AZ11645373 inhibited human P2X 7 receptor responses in HEK cells in a non-surmountable manner with K B values ranging from 5 -20 nM, with mean values not significantly different between assays. K B values were not altered by removing extracellular calcium and magnesium. ATP-evoked IL-1b release from lipopolysaccharide-activated THP-1 cells was inhibited by AZ11645373, IC 50 ¼ 90 nM. AZ11645373 was 4 500-fold less effective at inhibiting rat P2X 7 receptor-mediated currents with less than 50% inhibition occurring at 10 mM. Conclusions and implications: AZ11645373 is a highly selective and potent antagonist at human but not rat P2X 7 receptors and will have much practical value in studies of human cells.

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