Regulation of hypoxia-induced autophagy in glioblastoma involves ATG9A

Br J Cancer. 2017 Sep 5;117(6):813-825. doi: 10.1038/bjc.2017.263. Epub 2017 Aug 10.

Abstract

Background: Hypoxia is negatively associated with glioblastoma (GBM) patient survival and contributes to tumour resistance. Anti-angiogenic therapy in GBM further increases hypoxia and activates survival pathways. The aim of this study was to determine the role of hypoxia-induced autophagy in GBM.

Methods: Pharmacological inhibition of autophagy was applied in combination with bevacizumab in GBM patient-derived xenografts (PDXs). Sensitivity towards inhibitors was further tested in vitro under normoxia and hypoxia, followed by transcriptomic analysis. Genetic interference was done using ATG9A-depleted cells.

Results: We find that GBM cells activate autophagy as a survival mechanism to hypoxia, although basic autophagy appears active under normoxic conditions. Although single agent chloroquine treatment in vivo significantly increased survival of PDXs, the combination with bevacizumab resulted in a synergistic effect at low non-effective chloroquine dose. ATG9A was consistently induced by hypoxia, and silencing of ATG9A led to decreased proliferation in vitro and delayed tumour growth in vivo. Hypoxia-induced activation of autophagy was compromised upon ATG9A depletion.

Conclusions: This work shows that inhibition of autophagy is a promising strategy against GBM and identifies ATG9 as a novel target in hypoxia-induced autophagy. Combination with hypoxia-inducing agents may provide benefit by allowing to decrease the effective dose of autophagy inhibitors.

MeSH terms

  • Angiogenesis Inhibitors / pharmacology
  • Animals
  • Autophagy / drug effects*
  • Autophagy / physiology
  • Autophagy-Related Proteins / metabolism
  • Autophagy-Related Proteins / physiology*
  • Bevacizumab / pharmacology*
  • Brain Neoplasms / blood supply
  • Brain Neoplasms / drug therapy*
  • Brain Neoplasms / metabolism
  • Cell Line, Tumor
  • Cell Survival / drug effects
  • Cell Survival / physiology
  • Chloroquine / pharmacology*
  • Drug Synergism
  • Gene Expression Profiling
  • Gene Knockdown Techniques
  • Gene Silencing
  • Glioblastoma / blood supply
  • Glioblastoma / drug therapy*
  • Glioblastoma / metabolism
  • Heterografts
  • Humans
  • Membrane Proteins / metabolism
  • Membrane Proteins / physiology*
  • Mice
  • Mice, Inbred NOD
  • Mice, SCID
  • Molecular Targeted Therapy / methods
  • Neoplasm Proteins / metabolism
  • Neoplasm Proteins / physiology*
  • Neoplasm Transplantation
  • Random Allocation
  • Spheroids, Cellular / pathology
  • Tumor Hypoxia / physiology*
  • Vesicular Transport Proteins / metabolism
  • Vesicular Transport Proteins / physiology*

Substances

  • Angiogenesis Inhibitors
  • Atg9a protein, human
  • Autophagy-Related Proteins
  • Membrane Proteins
  • Neoplasm Proteins
  • Vesicular Transport Proteins
  • Bevacizumab
  • Chloroquine