ATP-competitive inhibitor of DNA-dependent protein kinase (DNA-PK). Displays selectivity over other PIKK family enzymes (IC50 values are 0.23, 13.0, > 100 and > 100 μM for DNA-PK, PI3K, ATM and ATR respectively). Radiosensitizes both proliferating and quiescent mouse embryonic fibroblast cells to IR and inhibits DSB repair. Purity 98%. MW (observed): 281.31