Induction of autophagy in temozolomide treated malignant gliomas

Natsumeda, Manabu; Aoki, Hiroshi; Miyahara, Hiroaki; Yajima, Naoki; Uzuka, Takeo; Toyoshima, Yasuko; Kakita, Akiyoshi; Takahashi, Hitoshi; Fujii, Yukihiko

doi:10.1111/j.1440-1789.2010.01197.x

Cited by 55 publications

(45 citation statements)

References 42 publications

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“…Induction of autophagy by TMZ has been documented in glioma cell lines and surgical specimens (11,12). In agreement with this, the current results showed that treatment with 100 µM TMZ induced autophagy as shown by a significant increase of AVOs and enhanced cleavage of LC3B (Fig.…”

Section: Tmz Treatment Induces Autophagy In Gliomasupporting

confidence: 78%

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Temozolomide induces autophagy via ATM-AMPK-ULK1 pathways in glioma

Zou

Wang

et al. 2014

Molecular Medicine Reports

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Abstract. Autophagy is a cytoprotective process, which occurs following temozolomide (TMZ) treatment, and contributes to glioma chemoresistance and TMZ treatment failure. However, the molecular mechanisms by which TMZ induces autophagy are largely unknown. In the current study, the ataxia-telangiectasia mutated (ATM) inhibitor KU-55933, adenosine monophosphate-activated protein kinase (AMPK) inhibitor compound C, and U87MG and U251 cell lines were employed to investigate the molecular mechanisms of TMZ-induced autophagy in glioma, and to evaluate the effects of autophagy inhibition on TMZ cytotoxicity. KU-55933 and compound C were observed to inhibit the activation of autophagy-initiating kinase ULK1 and result in a significant decrease of autophagy as indicated by depressed LC3B cleavage and acidic vesicular organelle formation. The activation of AMPK-ULK1 was ATM dependent. Autophagy inhibition via the AMPK inhibitor compound C augmented TMZ cytotoxicity as observed by depressed cell viability, increased γH2AX-marked double-strand breaks (DSBs) and elevated numbers of apoptotic glioma cells. In conclusion, TMZ induced autophagy via ATM-AMPK-ULK1 pathways. TMZ chemoresistance may therefore be overwhelmed by targeting AMPK, particularly for the treatment of O 6 -methylguanine DNA methyltransferase-negative gliomas.

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Section: Tmz Treatment Induces Autophagy In Gliomasupporting

confidence: 78%

“…Induction of autophagy by TMZ has been documented in glioma cell lines and surgical specimens, and inhibition of autophagy augments TMZ-induced apoptosis in glioma cells (11,12). However, the molecular mechanism by which TMZ induces autophagy is largely unknown.…”

Section: Introductionmentioning

confidence: 99%

Temozolomide induces autophagy via ATM-AMPK-ULK1 pathways in glioma

Zou

Wang

et al. 2014

Molecular Medicine Reports

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“…Sometimes, autophagy induces the death of damaged cells, and yet at other times, autophagy confers protection [47] . Indeed, autophagy induction functions as a pro-death mechanism (also called type II programmed cell death) in different tumors [48][49][50] . Treatment with NVP-BEZ235 increased autophagy, as measured by studying LC3-I to LC3-II conversion over an extended period of treatment.…”

Section: Discussionmentioning

confidence: 99%

NVP-BEZ235, a novel dual PI3K/mTOR inhibitor, enhances the radiosensitivity of human glioma stem cells in vitro

et al. 2013

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Aim: NVP-BEZ235 is a novel dual PI3K/mTOR inhibitor and shows dramatic effects on gliomas. The aim of this study was to investigate the effects of NVP-BEZ235 on the radiosensitivity and autophagy of glioma stem cells (GSCs) in vitro. Methods: Human GSCs (SU-2) were tested. The cell viability and survival from ionizing radiation (IR) were evaluated using MTT and clonogenic survival assay, respectively. Immunofluorescence assays were used to identify the formation of autophagosomes. The apoptotic cells were quantified with annexin V-FITC/PI staining and flow cytometry, and observed using Hoechst 33258 staining and fluorescence microscope. Western blot analysis was used to analyze the expression levels of proteins. Cell cycle status was determined by measuring DNA content after staining with PI. DNA repair in the cells was assessed using a comet assay. Results: Treatment of SU-2 cells with NVP-BEZ235 (10-320 nmol/L) alone suppressed the cell growth in a concentration-dependent manner. A low concentration of NVP-BEZ235 (10 nmol/L) significantly increased the radiation sensitivity of SU-2 cells, which could be blocked by co-treatment with 3-MA (50 µmol/L). In NVP-BEZ235-treated SU-2 cells, more punctate patterns of microtubule-associated protein LC3 immunoreactivity was observed, and the level of membrane-bound LC3-II was significantly increased. A combination of IR with NVP-BEZ235 significantly increased the apoptosis of SU-2 cells, as shown in the increased levels of BID, Bax, and active caspase-3, and decreased level of Bcl-2. Furthermore, the combination of IR with NVP-BEZ235 led to G 1 cell cycle arrest. Moreover, NVP-BEZ235 significantly attenuated the repair of IR-induced DNA damage as reflected by the tail length of the comet. Conclusion: NVP-BEZ235 increases the radiosensitivity of GSCs in vitro by activating autophagy that is associated with synergistic increase of apoptosis and cell-cycle arrest and decrease of DNA repair capacity.

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“…However, autophagic cell death could also be initiated in response to sustained intracellular damage caused by hypoxia, chemotherapeutic agents, virus infection, or toxins, especially in gliomas (17). Recent studies found that GBM is resistant to chemotherapy protocols that induce apoptosis but seems to be less resistant to therapies that induce autophagy (18)(19)(20). As an effective cytotoxic drug, temozolomide (TMZ) induces significant autophagic cell death in many GBM cells, such as U251 human glioma cell line (18,21,22).…”

Section: Introductionmentioning

confidence: 99%

Knockdown of Nrf2 enhances autophagy induced by temozolomide in U251 human glioma cell line

et al. 2012

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Abstract. Glioblastoma multiforme (GBM) and oxidative stress are closely linked. Oxidative stress affects many signaling pathways and may cause the induction of autophagy. The NF-E2-related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1) signaling pathway is the main pathway responsible for cell defense against oxidative stress and Nrf2 is a critical transcription factor related with cancer multidrug resistance. However, the relation between Nrf2 and regulation of autophagy is not well understood. In this study, we used temozolomide (TMZ), which inhibited the viability of GBM cells mainly by inducing autophagic cell death and explored the role of Nrf2 downregulation on autophagy induced by TMZ in GBM cells. In U251-Si-Nrf2 48 h after transfection the protein levels of Nrf2 were significantly downregulated, while the protein levels of LC3B-II increased by western blot analysis. Knockdown of Nrf2 also led to a significant increase of autophagic vacuoles and acidic vesicular organelles (AVOs), revealed by trans mission electron microscopy (TEM) and acridine orange (AO) staining using flow cytometry. Collectively, these findings demonstrate that knockdown of Nrf2 can enhance the basal level of autophagy in the U251 glioma cell line. Furthermore, after the treatment with TMZ (100 µM) for 3 days, the U251-Si-Nrf2 transfected cells showed less viability rate by cell counting kit-8 (CCK-8) assay and the levels of autophagy increased obviously through analysis of western blot and AO staining using flow cytometry. Taken together, our results suggest that knockdown of Nrf2 may enhance autophagy induced by TMZ in the U251 glioma cell line, which should be further evaluated for novel anticancer activity.

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Induction of autophagy in temozolomide treated malignant gliomas

Cited by 55 publications

References 42 publications

Temozolomide induces autophagy via ATM-AMPK-ULK1 pathways in glioma

Temozolomide induces autophagy via ATM-AMPK-ULK1 pathways in glioma

NVP-BEZ235, a novel dual PI3K/mTOR inhibitor, enhances the radiosensitivity of human glioma stem cells in vitro

Knockdown of Nrf2 enhances autophagy induced by temozolomide in U251 human glioma cell line

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