Delayed repletion of O6-methylguanine-DNA methyltransferase resulting in failure to protect the human glioblastoma cell line SF767 from temozolomide-induced cytotoxicity

J Neurosurg. 2003 Mar;98(3):591-8. doi: 10.3171/jns.2003.98.3.0591.


Object: Temozolomide (TMZ)-induced O6-methylguanine (MG) DNA lesions, if not removed by MG-DNA methyltransferase (MGMT), mispair with thymine, trigger rounds of futile mismatch repair (MMR), and in glioma cells lead to prolonged G2-M arrest and ultimately cell death. Depletion of MGMT by O6-benzylguanine (BG) sensitizes tumor cells to TMZ, and this combination is currently used in clinical trials. The use of the TMZ+BG combination in gliomas, however, is complicated by the prolonged TMZ-induced G2-M arrest, which may delay activation of poorly defined cell death pathways and allow for MGMT repletion and reversal of toxicity.

Methods: To address these issues, the actions of TMZ were monitored in DNA MMR-proficient SF767 glioma cells depleted of MGMT by BG, and in cells in which BG was removed at various times after TMZ exposure. In MGMT-depleted cells, TMZ exposure led to DNA single-strand breaks and phosphorylation of cdc2, followed by G2-M arrest, induction of p53/p21, and DNA double-strand breaks. Although DNA single-strand breaks, phosphorylation of cdc2, and G2-M arrest could be reversed by repletion of MGMT up to 5 days after TMZ exposure, TMZ-induced cytotoxicity could only be prevented if MGMT was replenished within 24 hours of the onset of G2-M arrest, and before the creation of DNA double-strand breaks.

Conclusions: These results indicate that although SF767 glioma cells undergo a prolonged G2-M arrest in response to TMZ, their ability to escape TMZ-induced cytotoxicity by MGMT repletion is limited to an approximately 24-hour period after the onset of G2-M arrest.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antineoplastic Agents / pharmacology
  • Antineoplastic Agents, Alkylating / pharmacology*
  • Cell Cycle Proteins / metabolism
  • Cell Survival / drug effects
  • Colony-Forming Units Assay
  • Dacarbazine / analogs & derivatives*
  • Dacarbazine / pharmacology*
  • G2 Phase / drug effects
  • Glioma / metabolism
  • Glioma / pathology*
  • Guanine / analogs & derivatives*
  • Guanine / pharmacology
  • Humans
  • Mitosis / drug effects
  • O(6)-Methylguanine-DNA Methyltransferase / metabolism*
  • Temozolomide
  • Time Factors
  • Tumor Cells, Cultured / drug effects


  • Antineoplastic Agents
  • Antineoplastic Agents, Alkylating
  • Cell Cycle Proteins
  • O(6)-benzylguanine
  • Guanine
  • Dacarbazine
  • O(6)-Methylguanine-DNA Methyltransferase
  • Temozolomide