In vitro activity: Compared to KU-55933, KU-60019 is an improved more water-soluble inhibitor of the ATM kinase, while displaying similar target selectivity. KU-60019 has little activity against DNA-PKcs and ATR with IC50 values of 1.7 μM and>10 μM, respectively, as well as 229 other protein kinases such as PI3K, mTOR and mTOR/FKBP12. KU-60019 displays 3- to 10-fold more potency than KU-55933 at blocking radiation-induced phosphorylation of key ATM protein targets such as p53, γ-H2AX, and CHK2, in human glioma U87 and U1242 cells, as 1 μM of KU-60019 significantly induces>70% decrease of p53 (S15) phosphorylation to which extent ~10 μM of KU-55933 is required to achieve. KU-60019 effectively radiosensitizes human glioma cells with dose-enhancement ratio of 1.7 and 4.4 at 1 μM and 10 μM, respectively, and also radiosensitizes the normal fibroblasts but not the A-T fibroblasts. KU-60019 treatment (3 μM) blocks basal and insulin-induced AKT S473 phosphorylation by 70% and ~50%, respectively, and completely reduces radiation-induced AKT phosphorylation below the level of control. The effect of KU-60019 on AKT S473 phosphorylation can be seen in glioma cell lines and normal fibroblasts but not in A-T (h-TERT) cells, and can be significantly blocked by phosphatase inhibitor okadaic acid, suggesting a critical role of ATM kinase in regulating AKT phosphorylation via unknown phosphatase. Consistent with the inhibition of prosurvival AKT signaling, KU-60019 at 3 μM significantly inhibits migration and invasion of human glioma U87 cells by>70% and ~60%, respectively, as well as U1242 cells by>50% and ~60% respectively.

Kinase Assay: KU-55933 has an IC50 of 13 nM and Ki of 2.2 nM in vitro and is highly specific for the ATM kinase using a panel of 60 protein kinases. KU-60019 is an improved inhibitor of the ATM kinase with an IC50 of 6.3 nM, approximately half that of KU-55933. The IC50 values for DNA-PKcs and ATR are 1.7 and>10 μM, respectively, almost 270-and 1600-fold higher than for ATM. KU-60019 is 10-fold more effective than KU-55933 at blocking radiation-induced phosphorylation of key ATM targets in human glioma cells. In human U87 glioma cells, KU-55933 completely inhibits phosphorylation of p53 (S15) at 10 μM but not at 3 μM, whereas γ-H2AX levels are only partly reduced with 10 μM 1 h after irradiation. By comparison, 3 μM KU-60019 completely inhibits p53 phosphorylation and partial inhibits at 1 μM.

Cell Assay: Cells (U87 and U1242) are exposed to KU-60019 for 1, 3, and 5 days. Cell growth is determined by AlamarBlue. AlamarBlue is added to the medium to the recommended final concentration. Plates are incubated for 1 hour at 37 °C, fluorescence is determined on a Fluoro-Count plate reader (excitation 530 nm, emission 590 nm), and values are taken as a measure of cell growth. Cell survival is determined by trypan blue/fluorescence activated cell sorting (FACS) assay.