title: 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.affiliation: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York, United States of America.
authors.forename: Georg
authors.initials: G
authors.lastname: Karpel-Massler
authors.affiliation: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York, United States of America.
authors.forename: Fresia
authors.initials: F
authors.lastname: Pareja
authors.affiliation: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York, United States of America.
authors.forename: Pascaline
authors.initials: P
authors.lastname: Aimé
authors.affiliation: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York, United States of America.
authors.forename: Chang
authors.initials: C
authors.lastname: Shu
authors.affiliation: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York, United States of America.
authors.forename: Lily
authors.initials: L
authors.lastname: Chau
authors.affiliation: Department of Pediatrics and Adolescent Medicine, Ulm University Medical Center, Ulm, Germany.
authors.forename: Mike-Andrew
authors.initials: MA
authors.lastname: Westhoff
authors.affiliation: Department of Neurosurgery, Ulm University Medical Center, Ulm, Germany.
authors.forename: Marc-Eric
authors.initials: ME
authors.lastname: Halatsch
authors.affiliation: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York, United States of America.
authors.forename: John F
authors.initials: JF
authors.lastname: Crary
authors.affiliation: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York, United States of America.
authors.forename: Peter
authors.initials: P
authors.lastname: Canoll
authors.affiliation: Department of Pathology & Cell Biology, Columbia University Medical Center, New York, New York, United States of America.
authors.forename: Markus D
authors.initials: MD
authors.lastname: Siegelin
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004347:Drug Interactions; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D055785:Gene Knockdown Techniques; D005909:Glioblastoma / Q000473:pathology*; D006801:Humans; D051379:Mice; D058953:Neural Stem Cells / Q000187:drug effects / Q000378:metabolism; D010793:Phthalazines / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000172:deficiency / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology; D051742:Transcription Factor CHOP / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D064726:Triple Negative Breast Neoplasms / Q000473:pathology; D015854:Up-Regulation / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: C497249:DDIT3 protein, human; D004791:Enzyme Inhibitors; D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D034741:RNA, Small Interfering; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053221:TNF-Related Apoptosis-Inducing Ligand; D051028:bcl-2-Associated X Protein; D051742:Transcription Factor CHOP; D011065:Poly(ADP-ribose) Polymerases; D053148:Caspase 3; C531550:olaparib