Sensitization of breast carcinoma cells to ionizing radiation by small molecule inhibitors of DNA-dependent protein kinase and ataxia telangiectsia mutated

Biochem Pharmacol. 2005 Dec 19;71(1-2):13-20. doi: 10.1016/j.bcp.2005.09.029. Epub 2005 Nov 15.


DNA-PK and ATM are members of the phosphatidylinositol 3'-kinase like kinase (PIKK) family of serine/threonine protein kinases and have critical roles in the cellular response to DNA double-strand breaks. Genetic loss of either activity leads to pronounced sensitivity to ionizing radiation (IR). Hence, these enzymes are potential targets to confer enhanced radiosensitivity on tumour cells. We show that novel inhibitors of either DNA-PK or ATM sensitize breast carcinoma cells to IR. Radiosensitization was accompanied by an apparent DNA repair deficit as measured by the persistence of IR-induced foci of phosphorylated histone H2AX (gammaH2AX foci). These specific inhibitors also allowed us to probe the biochemistry and kinetics of histone H2AX phosphorylation following gamma-irradiation in breast cancer cells with the aim of validating H2AX as a biomarker for DNA-PK or ATM inhibition in vivo. ATM inhibition reduced the initial average intensity of gammaH2AX foci while inhibition of DNA-PK had only a small effect on the initial phosphorylation of H2AX. However, simultaneous treatment with both compounds dramatically reduced gammaH2AX focus intensity, consistent with the reported role of ATM and DNA-PK in IR induced phosphorylation of H2AX.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ataxia Telangiectasia Mutated Proteins
  • Breast Neoplasms / enzymology
  • Breast Neoplasms / genetics
  • Breast Neoplasms / pathology*
  • Cell Cycle Proteins / antagonists & inhibitors*
  • Cell Line, Tumor
  • Chromones / pharmacology
  • DNA-Activated Protein Kinase / antagonists & inhibitors*
  • DNA-Binding Proteins / antagonists & inhibitors*
  • Enzyme Inhibitors / pharmacology*
  • Fluorescent Antibody Technique
  • Humans
  • Morpholines / pharmacology
  • Photosensitizing Agents / pharmacology*
  • Protein Serine-Threonine Kinases / antagonists & inhibitors*
  • Pyrones / pharmacology
  • Radiation, Ionizing*
  • Radiation-Sensitizing Agents / pharmacology*
  • Tumor Suppressor Proteins / antagonists & inhibitors*


  • 2-morpholin-4-yl-6-thianthren-1-yl-pyran-4-one
  • 8-dibenzothiophen-4-yl-2-morpholin-4-yl-chromen-4-one
  • Cell Cycle Proteins
  • Chromones
  • DNA-Binding Proteins
  • Enzyme Inhibitors
  • Morpholines
  • Photosensitizing Agents
  • Pyrones
  • Radiation-Sensitizing Agents
  • Tumor Suppressor Proteins
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • DNA-Activated Protein Kinase
  • Protein Serine-Threonine Kinases