Inhibition of ATM blocks the etoposide-induced DNA damage response and apoptosis of resting human T cells

DNA Repair (Amst). 2012 Nov 1;11(11):864-73. doi: 10.1016/j.dnarep.2012.08.006. Epub 2012 Oct 9.


It is believed that normal cells with an unaffected DNA damage response (DDR) and DNA damage repair machinery, could be less prone to DNA damaging treatment than cancer cells. However, the anticancer drug, etoposide, which is a topoisomerase II inhibitor, can generate DNA double strand breaks affecting not only replication but also transcription and therefore can induce DNA damage in non-replicating cells. Indeed, we showed that etoposide could influence transcription and was able to activate DDR in resting human T cells by inducing phosphorylation of ATM and its substrates, H2AX and p53. This led to activation of PUMA, caspases and to apoptotic cell death. Lymphoblastoid leukemic Jurkat cells, as cycling cells, were more sensitive to etoposide considering the level of DNA damage, DDR and apoptosis. Next, we used ATM inhibitor, KU 55933, which has been shown previously to be a radio/chemo-sensitizing agent. Pretreatment of resting T cells with KU 55933 blocked phosphorylation of ATM, H2AX and p53, which, in turn, prevented PUMA expression, caspase activation and apoptosis. On the other hand, KU 55933 incremented apoptosis of Jurkat cells. However, etoposide-induced DNA damage in resting T cells was not influenced by KU 55933 as revealed by the FADU assay. Altogether our results show that KU 55933 blocks DDR and apoptosis induced by etoposide in normal resting T cells, but increased cytotoxic effect on proliferating leukemic Jurkat cells. We discuss the possible beneficial and adverse effects of drugs affecting the DDR in cancer cells that are currently in preclinical anticancer trials.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Phytogenic / toxicity*
  • Apoptosis / drug effects
  • Apoptosis / genetics*
  • Apoptosis Regulatory Proteins / metabolism
  • Ataxia Telangiectasia Mutated Proteins
  • Caspases / metabolism
  • Cell Cycle Proteins / antagonists & inhibitors*
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism
  • Cell Proliferation
  • DNA / metabolism
  • DNA Damage*
  • DNA Repair / drug effects
  • DNA Repair / genetics*
  • DNA-Binding Proteins / antagonists & inhibitors*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Etoposide / toxicity*
  • Histones / metabolism
  • Humans
  • Jurkat Cells
  • Morpholines / pharmacology
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / antagonists & inhibitors*
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism
  • Proto-Oncogene Proteins / metabolism
  • Pyrones / pharmacology
  • T-Lymphocytes / drug effects
  • Transcription, Genetic
  • Tumor Suppressor Protein p53 / metabolism
  • Tumor Suppressor Proteins / antagonists & inhibitors*
  • Tumor Suppressor Proteins / genetics
  • Tumor Suppressor Proteins / metabolism


  • 2-morpholin-4-yl-6-thianthren-1-yl-pyran-4-one
  • Antineoplastic Agents, Phytogenic
  • Apoptosis Regulatory Proteins
  • BBC3 protein, human
  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • H2AX protein, human
  • Histones
  • Morpholines
  • Proto-Oncogene Proteins
  • Pyrones
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins
  • Etoposide
  • DNA
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • Protein-Serine-Threonine Kinases
  • Caspases