Synergistic augmentation of rapamycin-induced autophagy in malignant glioma cells by phosphatidylinositol 3-kinase/protein kinase B inhibitors

Hayato Takeuchi, Yasuko Kondo, Keishi Fujiwara, Takao Kanzawa, Hiroshi Aoki, Gordon Mills, Seiji Kondo

Research output: Contribution to journalArticle

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Abstract

The mammalian target of rapamycin (mTOR) is a downstream effector of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway and a central modulator of cell proliferation in malignant gliomas. Therefore, the targeting of mTOR signaling is considered a promising therapy for malignant gliomas. However, the mechanisms underlying the cytotoxic effects of a selective mTOR inhibitor, rapamycin, on malignant glioma cells are poorly understood. The purpose of this study was thus to elucidate how rapamycin exerts its cytotoxic effects on malignant glioma cells. We showed that rapamycin induced autophagy but not apoptosis in rapamycin-sensitive malignant glioma U87-MG and T98G cells by inhibiting the function of mTOR. In contrast, in rapamycin-resistant U373-MG cells, the inhibitory effect of rapamycin was minor, although the phosphorylation of p70S6 kinase, a molecule downstream of mTOR, was remarkably inhibited. Interestingly, a PI3K inhibitor, LY294002, and an Akt inhibitor, UCN-01 (7-hydroxystaurosporine), both synergistically sensitized U87-MG and T98G cells as well as U373-MG cells to rapamycin by stimulating the induction of autophagy. Enforced expression of active Akt in tumor cells suppressed the combined effects of LY294002 or UCN-01, whereas dominant-negative Akt expression was sufficient to increase the sensitivity of tumor cells to rapamycin. These results indicate that rapamycin exerts its antitumor effect on malignant glioma cells by inducing autophagy and suggest that in malignant glioma cells a disruption of the PI3K/Akt signaling pathway could greatly enhance the effectiveness of mTOR inhibitors.

Original languageEnglish (US)
Pages (from-to)3336-3346
Number of pages11
JournalCancer Research
Volume65
Issue number8
StatePublished - Apr 15 2005
Externally publishedYes

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Phosphatidylinositol 3-Kinase
Proto-Oncogene Proteins c-akt
Autophagy
Sirolimus
Protein Kinase Inhibitors
Glioma
2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one

ASJC Scopus subject areas

  • Cancer Research
  • Oncology

Cite this

Synergistic augmentation of rapamycin-induced autophagy in malignant glioma cells by phosphatidylinositol 3-kinase/protein kinase B inhibitors. / Takeuchi, Hayato; Kondo, Yasuko; Fujiwara, Keishi; Kanzawa, Takao; Aoki, Hiroshi; Mills, Gordon; Kondo, Seiji.

In: Cancer Research, Vol. 65, No. 8, 15.04.2005, p. 3336-3346.

Research output: Contribution to journalArticle

Takeuchi, Hayato ; Kondo, Yasuko ; Fujiwara, Keishi ; Kanzawa, Takao ; Aoki, Hiroshi ; Mills, Gordon ; Kondo, Seiji. / Synergistic augmentation of rapamycin-induced autophagy in malignant glioma cells by phosphatidylinositol 3-kinase/protein kinase B inhibitors. In: Cancer Research. 2005 ; Vol. 65, No. 8. pp. 3336-3346.
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