Potent, selective and competitive ATM kinase inhibitor (Ki = 2.2 nM, IC50 values are 13, 2500, 9300, 16600, > 100000 and > 100000 nM at ATM, DNA-PK, mTOR, PI 3-kinase, PI 4-K and ATR respectively). Decreases viability of MCF-7, A549 and HCT116 cells and decreases p21CIP1 levels in vitro. Acts as a radio- and chemosensitizer for the treatment of cancer.