Journal of Neuro-Oncology

, Volume 110, Issue 3, pp 349–357 | Cite as

ATM inhibitor KU-55933 increases the TMZ responsiveness of only inherently TMZ sensitive GBM cells

  • Aditi Nadkarni
  • Meena Shrivastav
  • Ann C. Mladek
  • Paul M. Schwingler
  • Patrick T. Grogan
  • Junjie Chen
  • Jann N. Sarkaria
Laboratory Investigation


Ataxia telangiectasia mutated (ATM) kinase is critical in sensing and repairing DNA double-stranded breaks (DSBs) such as those induced by temozolomide (TMZ). ATM deficiency increases TMZ sensitivity, which suggests that ATM inhibitors may be effective TMZ sensitizing agents. In this study, the TMZ sensitizing effects of 2 ATM specific inhibitors were studied in established and xenograft-derived glioblastoma (GBM) lines that are inherently sensitive to TMZ and derivative TMZ-resistant lines. In parental U251 and U87 glioma lines, the addition of KU-55933 to TMZ significantly increased cell killing compared to TMZ alone [U251 survival: 0.004 ± 0.0015 vs. 0.08 ± 0.01 (p < 0.001), respectively, and U87 survival: 0.02 ± 0.005 vs. 0.04 ± 0.002 (p < 0.001), respectively] and also elevated the fraction of cells arrested in G2/M [U251 G2/M fraction: 61.8 ± 1.1 % vs. 35 ± 0.8 % (p < 0.001), respectively, and U87 G2/M fraction 25 ± 0.2 % vs.18.6 ± 0.4 % (p < 0.001), respectively]. In contrast, KU-55933 did not sensitize the resistant lines to TMZ, and neither TMZ alone or combined with KU-55933 induced a G2/M arrest. While KU-55933 did not enhance TMZ induced Chk1/Chk2 activation, it increased TMZ-induced residual γ-H2AX foci in the parental cells but not in the TMZ resistant cells. Similar sensitization was observed with either KU-55933 or CP-466722 combined with TMZ in GBM12 xenograft line but not in GBM12TMZ, which is resistant to TMZ due to MGMT overexpression. These findings are consistent with a model where ATM inhibition suppresses the repair of TMZ-induced DSBs in inherently TMZ-sensitive tumor lines, which suggests an ATM inhibitor potentially could be deployed with an improvement in the therapeutic window when combined with TMZ.


Temozolomide Glioblastoma DNA repair ATM inhibitor 



The authors thank James Tarara and the Mayo Flow Cytometry and Optical Morphology Core personnel. Funding: Grant support provided by NIH SPORE grant CA108961, NIH RO1 CA127716, and the Brain Tumor Funder’s Consortium (all to JNS)

Conflict of interest

JNS is a recipient of a research grant from Merck Pharmaceuticals for unrelated research

Supplementary material

11060_2012_979_MOESM1_ESM.pptx (47 kb)
Supplementary material 1 (PPTX 47 kb)


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Copyright information

© Springer Science+Business Media New York 2012

Authors and Affiliations

  • Aditi Nadkarni
    • 1
  • Meena Shrivastav
    • 1
  • Ann C. Mladek
    • 1
  • Paul M. Schwingler
    • 2
  • Patrick T. Grogan
    • 3
  • Junjie Chen
    • 4
  • Jann N. Sarkaria
    • 1
  1. 1.Mayo ClinicRochesterUSA
  2. 2.Eastern Virginia Medical SchoolNorfolkUSA
  3. 3.University of Kansas Medical SchoolLawrenceUSA
  4. 4.University of Texas MD Anderson Cancer CenterHoustonUSA

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