PARP inhibition restores extrinsic apoptotic sensitivity in glioblastoma.

Abstract

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.

• Authors: Georg Karpel-Massler, Fresia Pareja, Pascaline Aimé, Chang Shu, Lily Chau, Mike-Andrew Westhoff, Marc-Eric Halatsch, John F Crary, Peter Canoll, Markus D Siegelin
• Journal: PloS one (PLoS One) Vol. 9 Issue 12 Pg. e114583 ( 2014) ISSN: 1932-6203 [Electronic] United States
• PMID: 25531448 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• 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

Topics

• Animals
• Apoptosis (drug effects)
• Caspase 3 (metabolism)
• Cell Line, Tumor
• Cell Membrane (drug effects, 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, metabolism)
• Phthalazines (pharmacology)
• Piperazines (pharmacology)
• Poly(ADP-ribose) Polymerase Inhibitors
• Poly(ADP-ribose) Polymerases (deficiency, genetics)
• RNA, Small Interfering (genetics)
• Receptors, TNF-Related Apoptosis-Inducing Ligand (metabolism)
• TNF-Related Apoptosis-Inducing Ligand (pharmacology)
• Transcription Factor CHOP (deficiency, genetics, metabolism)
• Triple Negative Breast Neoplasms (pathology)
• Up-Regulation (drug effects)
• Xenograft Model Antitumor Assays
• bcl-2-Associated X Protein (metabolism)