title: Identification and characterization of a novel and specific inhibitor of the ataxia-telangiectasia mutated kinase ATM.
abstract: The serine/threonine protein kinase ATM signals to cell cycle and DNA repair components by phosphorylating downstream targets such as p53, CHK2, NBS1, and BRCA1. Mutation of ATM occurs in the human autosomal recessive disorder ataxia-telangiectasia, which is characterized by hypersensitivity to ionizing radiation and a failure of cells to arrest the cell cycle after the induction of DNA double-strand breaks. It has thus been proposed that ATM inhibition would cause cellular radio- and chemosensitization. Through screening a small molecule compound library developed for the phosphatidylinositol 3'-kinase-like kinase family, we identified an ATP-competitive inhibitor, 2-morpholin-4-yl-6-thianthren-1-yl-pyran-4-one (KU-55933), that inhibits ATM with an IC(50) of 13 nmol/L and a Ki of 2.2 nmol/L. KU-55933 shows specificity with respect to inhibition of other phosphatidylinositol 3'-kinase-like kinases. Cellular inhibition of ATM by KU-55933 was demonstrated by the ablation of ionizing radiation-dependent phosphorylation of a range of ATM targets, including p53, gammaH2AX, NBS1, and SMC1. KU-55933 did not show inhibition of UV light DNA damage induced cellular phosphorylation events. Exposure of cells to KU-55933 resulted in a significant sensitization to the cytotoxic effects of ionizing radiation and to the DNA double-strand break-inducing chemotherapeutic agents, etoposide, doxorubicin, and camptothecin. Inhibition of ATM by KU-55933 also caused a loss of ionizing radiation-induced cell cycle arrest. By contrast, KU-55933 did not potentiate the cytotoxic effects of ionizing radiation on ataxia-telangiectasia cells, nor did it affect their cell cycle profile after DNA damage. We conclude that KU-55933 is a novel, specific, and potent inhibitor of the ATM kinase.
authors.affiliation: KuDOS Pharmaceuticals Ltd., Cambridge Science Park, Milton Road, Cambridge, UK.
authors.forename: Ian
authors.initials: I
authors.lastname: Hickson
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Caroline J
authors.initials: CJ
authors.lastname: Richardson
authors.forename: Sharon J
authors.initials: SJ
authors.lastname: Green
authors.forename: Niall M B
authors.initials: NM
authors.lastname: Martin
authors.forename: Alisdair I
authors.initials: AI
authors.lastname: Orr
authors.forename: Philip M
authors.initials: PM
authors.lastname: Reaper
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Jackson
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Curtin
authors.forename: Graeme C M
authors.initials: GC
authors.lastname: Smith
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D002867:Chromones / Q000737:chemistry / Q000494:pharmacology; D020650:Combinatorial Chemistry Techniques; D004268:DNA-Binding Proteins; D006367:HeLa Cells; D006801:Humans; D020128:Inhibitory Concentration 50; D007700:Kinetics; D009025:Morpholines / Q000737:chemistry / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011753:Pyrones / Q000737:chemistry / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000737:chemistry / Q000494:pharmacology; D025521:Tumor Suppressor Proteins
chemical_list: C495818:2-morpholin-4-yl-6-thianthren-1-yl-pyran-4-one; D018797:Cell Cycle Proteins; D002867:Chromones; D004268:DNA-Binding Proteins; D009025:Morpholines; D047428:Protein Kinase Inhibitors; D011753:Pyrones; D011838:Radiation-Sensitizing Agents; D025521:Tumor Suppressor Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases