title: Hypoxia Potentiates the Radiation-Sensitizing Effect of Olaparib in Human Non-Small Cell Lung Cancer Xenografts by Contextual Synthetic Lethality.
abstract: Poly(ADP-ribose) polymerase (PARP) inhibitors potentiate radiation therapy in preclinical models of human non-small cell lung cancer (NSCLC) and other types of cancer. However, the mechanisms underlying radiosensitization in vivo are incompletely understood. Herein, we investigated the impact of hypoxia on radiosensitization by the PARP inhibitor olaparib in human NSCLC xenograft models.
  
  
  
  NSCLC Calu-6 and Calu-3 cells were irradiated in the presence of olaparib or vehicle under normoxic (21% O2) or hypoxic (1% O2) conditions. In vitro radiosensitivity was assessed by clonogenic survival assay and γH2AX foci assay. Established Calu-6 and Calu-3 subcutaneous xenografts were treated with olaparib (50 mg/kg, daily for 3 days), radiation (10 Gy), or both. Tumors (n=3/group) were collected 24 or 72 hours after the first treatment. Immunohistochemistry was performed to assess hypoxia (carbonic anhydrase IX [CA9]), vessels (CD31), DNA double strand breaks (DSB) (γH2AX), and apoptosis (cleaved caspase 3 [CC3]). The remaining xenografts (n=6/group) were monitored for tumor growth.
  
  
  
  In vitro, olaparib showed a greater radiation-sensitizing effect in Calu-3 and Calu-6 cells in hypoxic conditions (1% O2). In vivo, Calu-3 tumors were well-oxygenated, whereas Calu-6 tumors had extensive regions of hypoxia associated with down-regulation of the homologous recombination protein RAD51. Olaparib treatment increased unrepaired DNA DSB (P<.001) and apoptosis (P<.001) in hypoxic cells of Calu-6 tumors following radiation, whereas it had no significant effect on radiation-induced DNA damage response in nonhypoxic cells of Calu-6 tumors or in the tumor cells of well-oxygenated Calu-3 tumors. Consequently, olaparib significantly increased radiation-induced growth inhibition in Calu-6 tumors (P<.001) but not in Calu-3 tumors.
  
  
  
  Our data suggest that hypoxia potentiates the radiation-sensitizing effects of olaparib by contextual synthetic killing, and that tumor hypoxia may be a potential biomarker for selecting patients who may get the greatest benefit from the addition of olaparib to radiation therapy.
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom.
authors.forename: Yanyan
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom.
authors.forename: Tom
authors.initials: T
authors.lastname: Verbiest
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom.
authors.forename: Aoife M
authors.initials: AM
authors.lastname: Devery
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom.
authors.forename: Sivan M
authors.initials: SM
authors.lastname: Bokobza
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom.
authors.forename: Anika M
authors.initials: AM
authors.lastname: Weber
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom.
authors.forename: Katarzyna B
authors.initials: KB
authors.lastname: Leszczynska
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom.
authors.forename: Ester M
authors.initials: EM
authors.lastname: Hammond
authors.affiliation: Cancer Research UK/Medical Research Council Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom. Electronic address: anderson.ryan@oncology.ox.ac.uk.
authors.forename: Anderson J
authors.initials: AJ
authors.lastname: Ryan
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000532:radiotherapy*; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D004249:DNA Damage; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D051379:Mice; D008807:Mice, Inbred BALB C; D010793:Phthalazines / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D000067856:Poly(ADP-ribose) Polymerase Inhibitors / Q000494:pharmacology; D051135:Rad51 Recombinase / Q000032:analysis; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
chemical_list: D010793:Phthalazines; D010879:Piperazines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011838:Radiation-Sensitizing Agents; D051135:Rad51 Recombinase; C531550:olaparib