Unknown,Transcriptomics,Genomics,Proteomics

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Autophagy is essential for tumor development and survival in hypoxia and in vivo in glioblastoma. (Provisional)

ABSTRACT: Hypoxia is negatively associated with glioblastoma patient survival and contributes strongly to tumor resistance. Unfortunately novel anti-angiogenic therapy increases hypoxia and activates survival pathways in tumor cells leading to inevitable tumor relapse. Here we demonstrate that primary glioma cultures and cell lines depend on autophagy to survive severe hypoxia but also at normal oxygen levels. Positive regulators of autophagy are expressed at higher levels in tumor cells and induction in severe hypoxia is more prominent compared to normal brain cells. We demonstrate that autophagy is an essential/critical target for novel treatment in glioblastoma. We show ATG9A is induced by severe hypoxia and could be a novel player of the autophagic response in glioma cells. ATG9A targeting inhibited tumor growth, suggesting an essential role in glioma cell survival in vivo. While autophagy induction was also observed in normal astrocytes, glioma cells displayed a higher sensitivity towards autophagy inhibitors. Importantly, patient-derived cultures exhibited varying sensitivity towards anti-autophagy treatment, where certain cultures were dependent on autophagy already in normoxic conditions. The treatment of tumor bearing mice with the autophagy inhibitor chloroquine significantly increased mice survival, but combination treatment of the agent with bevacizumab did not reveal additive or synergistic effect. The present study demonstrates that inhibition of autophagy using chloroquine as a single agent provides a novel treatment strategy against glioblastoma. It remains to be seen whether autophagy inhibition will improve current standard of care treatment of newly diagnosed glioblastoma patients and whether more specific inhibitors will lead to stronger therapeutic outcome. (Provisional)

ORGANISM(S): Homo sapiens

SUBMITTER: Arnaud Muller

PROVIDER: E-MTAB-3085 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Although malignant gliomas frequently show aberrant activation of the mammalian target of rapamycin (mTOR), mTOR inhibitors have performed poorly in clinical trials. Besides regulating cell growth and translation, mTOR controls the initiation of autophagy. By recycling cellular components, autophagy can mobilize energy resources, and has thus been attributed cancer-promoting effects. Here, we asked whether the activation of autophagy represents an escape mechanism to pharmacological mTOR inhibition, and explored co-treatment with mTOR and autophagy inhibitors as a therapeutic strategy. Mimicking conditions of the glioma microenvironment, glioma cells were exposed to nutrient starvation and hypoxia. Following treatment with mTOR inhibitor torin2 or rapamycin, and autophagy inhibitors bafilomycin A1 or MRT68921, we analyzed autophagic activity, cell growth, viability and oxygen consumption. Changes in global proteome were quantified by mass spectrometry. In the context of hypoxia and starvation, autophagy was strongly induced in glioma cells, and further increased by mTOR inhibition. While torin2 enhanced glioma cell survival, co-treatment with torin2 and bafilomycin A1 failed to promote cell death. Importantly, treatment with bafilomycin A1 alone also protected glioma cells from cell death. Mechanistically, both compounds significantly reduced glioma growth and oxygen consumption. Mass spectrometry analysis showed that bafilomycin A1 induced broad changes in the cellular proteome. More specifically, proteins downregulated by bafilomycin A1 were associated with the mitochondrial respiratory chain and ATP synthesis. Taken together, our results show that activation of autophagy does not account for the cytoprotective effects of mTOR inhibition in our in vitro model of the glioma microenvironment. Our proteomic findings suggest that the pharmacological inhibition of autophagy induces extensive changes in the cellular proteome that can support glioma cell survival under nutrient-deplete and hypoxic conditions. These findings provide a novel perspective on the complex role of autophagy in gliomas and may have implications for the design of future trials.

Project description:Glioblastoma (GBM) carries a dismal prognosis largely due to acquired resistance to the standard treatment, which incorporates the chemotherapy temozolomide (TMZ). Inhibiting the proteasomal pathway is an emerging strategy, where combination treatments are under clinical investigation. We hypothesized that pre-treatment of GBM with bortezomib (BTZ) might sensitize glioblastoma to TMZ by abolishing autophagy survival signals to augment DNA damage and apoptosis. P3 patient-derived GBM cells as well as the tumor cell lines U87, HF66, A172 and T98G were investigated for clonogenic survival after single or combined treatment with TMZ and BTZ in vitro. Change in autophagic flux was examined after experimental treatments in conjunction with inhibitors of autophagy or downregulation of autophagy-related genes -5 and -7 (ATG5 and ATG7, respectively). Autophagic flux was increased in TMZ-resistant P3 and T98G cells as indicated by diminished levels of the autophagy markers LC3A/B-II and increased STX17, higher protein degradation and no formation of p62 bodies nor induction of apoptosis. In contrast, BTZ treatment attenuated ULK1 mRNA, total and phosphorylated protein, and accumulated LC3A/B-II, p62 and autophagosomes analogously to Baf1 and chloroquine autophagy inhibitors. These autophagosomes did not fuse with lysosomes, indicated by attenuated STX17 expression and reduced degradation of long-lived proteins, which culminated in enhanced caspase-3/8 dependent apoptosis. BTZ synergistically enhanced TMZ efficacy, attenuated tumor cell proliferation, triggered ATM/Chk2 DNA damage signalling to further augment caspase-3/8 mediated apoptosis in the TMZ resistant P3 and T98G GBM cells. Genetic or chemical inhibition of autophagy (with CRISPR-CAs9 ATG5, ATG7 shRNA, MRT68921 or VPS34-IN1) abrogated BTZ efficacy and rescued BTZ+ TMZ treated GBM cells from death. We conclude that Bortezomib ameliorates temozolomide resistance through ATG5/7-dependent abrogated autophagic flux and may be amenable in combination treatment regimens for TMZ refractory GBM patients.

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Autophagy is essential for tumor development and survival in hypoxia and in vivo in glioblastoma. (Provisional)

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