To screen for small molecule inhibitors of ATM kinase activity, an in vitro kinase assay is carried out, and an ELISA assay developes which measures the phosphorylation status of the ATM downstream target p53. Recombinant GST-p53(1-101) and full-length Flag-tagged ATM & ATR are purified for use in the ELISA and in vitro kinase assays. Briefly, Nunc 96 well Maxisorp plates are coated overnight (4°C) with 2 μg of purified, recombinant GST-p53(1-101) in PBS. All subsequent incubations are performed at room temperature. The plates are washed (0.05% v/v-Tween/PBS) before addition of purified recombinant full-length ATM kinase (30-60 ng) in a final volume of 80 μL of reaction buffer (20 mM HEPES, 50 mM NaCl₂, 10 mM MgCl₂, 10 mM MnCl₂, 1 mM DTT and 1 μM ATP) in the presence or absence of compound. Compounds including CP-466722 (10 μM) are added to plates in duplicate and the kinase assay is incubated (90 min). Plates are washed (0.05% v/v-Tween/PBS), blocked (1 h, 1% w/v-BSA/PBS) and rinsed before anti-Phospho(Ser15)-p53 antibody (1:1000/PBS) is added to the plates and incubated (1 h). To reduce non-specific binding plates are washed (0.05% v/v-Tween/PBS) prior to incubation (1 h) with HRP-conjugated goat anti-rabbit IgG secondary antibody (1:5000/PBS). Secondary antibody that is linked to the phosphorylated GST-p53(1-101) protein is detected with TMB substrate reagent. Plates are developed (15-30 min) and the reaction is stopped (1M H₂SO₄ final concentration) before absorbance is determined (λ450 nm). Compounds that inhibit ATM kinase activity in ELISA assays, are characterized with respect to inhibition of ATM/ATR kinases using in vitro kinase assays. Western blotting using the anti-Phospho(Ser15)-p53 antibody is used as a readout of ATM/ATR inhibition^[1].

MCE has not independently confirmed the accuracy of these methods. They are for reference only.

Cells are plated in triplicate (40,000 cells/plate), incubated as required before culture media and trypsinsed cells are combined and viability determined: Vi-CELL? XR cell viability analyzer^[1].

MCE has not independently confirmed the accuracy of these methods. They are for reference only.

• [1]. Rainey MD, et al. Transient inhibition of ATM kinase is sufficient to enhance cellular sensitivity to ionizing radiation. Cancer Res. 2008 Sep 15;68(18):7466-74.  [Content Brief]

  [2]. Guo K, et al. Development of a cell-based, high-throughput screening assay for ATM kinase inhibitors. J Biomol Screen. 2014 Apr;19(4):538-46.  [Content Brief]

  [3]. W?sierska-G?dek J, et al. Interactions Between Ataxia Telangiectasia Mutated Kinase Inhibition, Poly(ADP-ribose) Polymerase-1 Inhibition and BRCA1 Status in Breast Cancer Cells. J Cancer Prev. 2014 Jun;19(2):125-36.  [Content Brief]