Specific mTOR inhibitor rapamycin enhances cytotoxicity induced by alkylating agent 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea (ACNU) in human U251 malignant glioma cells

J Neurooncol. 2007 Sep;84(3):233-44. doi: 10.1007/s11060-007-9371-x. Epub 2007 Mar 28.


Loss of the PTEN tumor suppressor gene and amplification of the epidermal growth factor receptor (EGFR), which is common in malignant gliomas, result in activation of the mammalian target of rapamycin (mTOR). Rapamycin is a highly specific inhibitor of mTOR and induces a cytostatic effect in various glioma cell lines. DNA-damaging agents such as nitrosourea are widely used in malignant glioma treatment; therefore, we investigated the effect of rapamycin on cell growth and death in combination with 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea (ACNU, nimustine hydrochloride) in human glioma cells. In U251 malignant glioma (U251MG) cells, we confirmed that rapamycin enhanced ACNU-induced apoptosis. We found that rapamysin inhibited ACNU-induced p21 induction, and knocking down of p21 protein by siRNA enhanced ACNU-induced apoptosis in U251MG cells. Furthermore, adenovirus-mediated over-expression of p21 protein rescued U251MG cells from apoptosis induced by ACNU and rapamycin. Finally, treatment of intracerebral U251MG xenografts with a combination of rapamycin and ACNU in vivo resulted in statistically prolonged median survival (P<0.05). These results suggest that rapamycin in combination with DNA-damaging agents may be efficacious in the treatment of malignant gliomas.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Combined Chemotherapy Protocols / pharmacology*
  • Apoptosis / drug effects
  • Blotting, Western
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cyclin-Dependent Kinase Inhibitor p21 / metabolism
  • Drug Synergism
  • Glioma / metabolism*
  • Glioma / pathology
  • Humans
  • Immunohistochemistry
  • In Situ Nick-End Labeling
  • Male
  • Neoplasms, Experimental / drug therapy*
  • Nimustine / pharmacology*
  • Protein Kinases / drug effects
  • RNA, Small Interfering
  • Rats
  • Rats, Nude
  • Sirolimus / pharmacology*
  • TOR Serine-Threonine Kinases
  • Xenograft Model Antitumor Assays


  • Cyclin-Dependent Kinase Inhibitor p21
  • RNA, Small Interfering
  • Nimustine
  • Protein Kinases
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • Sirolimus