PARP inhibition restores extrinsic apoptotic sensitivity in glioblastoma

PLoS One. 2014 Dec 22;9(12):e114583. doi: 10.1371/journal.pone.0114583. eCollection 2014.


Background: Resistance to apoptosis is a paramount issue in the treatment of Glioblastoma (GBM). We show that targeting PARP by the small molecule inhibitors, Olaparib (AZD-2281) or PJ34, reduces proliferation and lowers the apoptotic threshold of GBM cells in vitro and in vivo.

Methods: The sensitizing effects of PARP inhibition on TRAIL-mediated apoptosis and potential toxicity were analyzed using viability assays and flow cytometry in established GBM cell lines, low-passage neurospheres and astrocytes in vitro. Molecular analyses included western blots and gene silencing. In vivo, effects on tumor growth were examined in a murine subcutaneous xenograft model.

Results: The combination treatment of PARP inhibitors and TRAIL led to an increased cell death with activation of caspases and inhibition of formation of neurospheres when compared to single-agent treatment. Mechanistically, pharmacological PARP inhibition elicited a nuclear stress response with up-regulation of down-stream DNA-stress response proteins, e.g., CCAAT enhancer binding protein (C/EBP) homology protein (CHOP). Furthermore, Olaparib and PJ34 increased protein levels of DR5 in a concentration and time-dependent manner. In turn, siRNA-mediated suppression of DR5 mitigated the effects of TRAIL/PARP inhibitor-mediated apoptosis. In addition, suppression of PARP-1 levels enhanced TRAIL-mediated apoptosis in malignant glioma cells. Treatment of human astrocytes with the combination of TRAIL/PARP inhibitors did not cause toxicity. Finally, the combination treatment of TRAIL and PJ34 significantly reduced tumor growth in vivo when compared to treatment with each agent alone.

Conclusions: PARP inhibition represents a promising avenue to overcome apoptotic resistance in GBM.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Caspase 3 / metabolism
  • Cell Line, Tumor
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Cell Proliferation / drug effects
  • Cell Survival / drug effects
  • Drug Interactions
  • Drug Resistance, Neoplasm / drug effects
  • Enzyme Activation / drug effects
  • Enzyme Inhibitors / pharmacology*
  • Gene Expression Regulation, Neoplastic / drug effects
  • Gene Knockdown Techniques
  • Glioblastoma / pathology*
  • Humans
  • Mice
  • Neural Stem Cells / drug effects
  • Neural Stem Cells / metabolism
  • Phthalazines / pharmacology
  • Piperazines / pharmacology
  • Poly(ADP-ribose) Polymerase Inhibitors*
  • Poly(ADP-ribose) Polymerases / deficiency
  • Poly(ADP-ribose) Polymerases / genetics
  • RNA, Small Interfering / genetics
  • Receptors, TNF-Related Apoptosis-Inducing Ligand / metabolism
  • TNF-Related Apoptosis-Inducing Ligand / pharmacology
  • Transcription Factor CHOP / deficiency
  • Transcription Factor CHOP / genetics
  • Transcription Factor CHOP / metabolism
  • Triple Negative Breast Neoplasms / pathology
  • Up-Regulation / drug effects
  • Xenograft Model Antitumor Assays
  • bcl-2-Associated X Protein / metabolism


  • DDIT3 protein, human
  • Enzyme Inhibitors
  • Phthalazines
  • Piperazines
  • Poly(ADP-ribose) Polymerase Inhibitors
  • RNA, Small Interfering
  • Receptors, TNF-Related Apoptosis-Inducing Ligand
  • TNF-Related Apoptosis-Inducing Ligand
  • bcl-2-Associated X Protein
  • Transcription Factor CHOP
  • Poly(ADP-ribose) Polymerases
  • Caspase 3
  • olaparib