title: The natural compound gambogic acid radiosensitizes nasopharyngeal carcinoma cells under hypoxic conditions.
abstract: OBJECTIVE
  Hypoxia is an important factor that causes decreased local disease control as well as increased distant metastases and resistance to radiotherapy in patients with advanced nasopharyngeal carcinoma (NPC). Gambogic acid (GA), the major active ingredient of gamboge, exerts antitumor effects in vitro and in vivo. However, the molecular mechanism by which GA inhibits tumor radioresistance remains unclear. The present study aimed to investigate the radiosensitizing effects of GA on NPC and explore the underlying mechanisms.
  
  
  METHODS
  CNE-1 and CNE-2 cells exposed to hypoxia and radiation were treated with GA at different concentrations. CCK-8 assay, clonogenic assay, and flow cytometry were performed to analyze cell proliferation, colony formation, apoptosis, and cell cycle. The expression levels of hypoxia-inducible factor-1α (HIF-1α), Bcl-2, Bax, caspase-3, cyclin B1/p-cdc2 and γ-H2AX were assessed using Western blot and/or immunofluorescence analysis.
  
  
  RESULTS
  Results of the CCK-8 assay, clonogenic assay, and flow cytometry showed that treatment of NPC cells with growth-suppressive concentrations of GA resulted in G2/M phase arrest and apoptosis. Western blot analysis demonstrated that GA-induced cell cycle arrest and apoptosis in CNE-2 cells was associated with upregulated expression of caspase-3 and Bax and downregulated expression of Bcl-2 and cyclin B1/p-cdc2 in hypoxia. Treatment with GA markedly decreased the expression of HIF-1α under hypoxic conditions.
  
  
  CONCLUSIONS
  The results of this study suggest that GA efficiently radiosensitizes NPC cells and the effect may be significant in hypoxic conditions.
authors.affiliation: Department of Radiotherapy, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province - China.
authors.forename: Meilin
authors.initials: M
authors.lastname: Yang
authors.affiliation: Department of Radiotherapy, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province - China.
authors.forename: Yuehua
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Radiotherapy, Second People's Hospital of Lianyungang, Lianyungang Hospital Affiliated to Bengbu Medical College, Lianyungang, Jiangsu Province - China.
authors.forename: Heqing
authors.initials: H
authors.lastname: Cui
authors.affiliation: Department of Radiotherapy, The Affiliated Tumor Hospital of Nantong University, Nantong, Jiangsu Province - China.
authors.forename: Zhifeng
authors.initials: Z
authors.lastname: Guan
authors.affiliation: Department of Radiotherapy, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province - China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Radiotherapy, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province - China.
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Radiotherapy, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province - China.
authors.forename: Xiaochen
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Radiotherapy, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province - China.
authors.forename: Hongchen
authors.initials: H
authors.lastname: Zhu
authors.affiliation: Department of Radiotherapy, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province - China.
authors.forename: Xi
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Radiotherapy, The Affiliated Tumor Hospital of Nantong University, Nantong, Jiangsu Province - China.
authors.forename: Jing
authors.initials: J
authors.lastname: Cai
authors.affiliation: Department of Synthetic Internal Medicine, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province - China.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Cheng
authors.affiliation: Department of Radiotherapy, The First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu Province - China.
authors.forename: Xinchen
authors.initials: X
authors.lastname: Sun
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D015153:Blotting, Western; D002277:Carcinoma; D053148:Caspase 3 / Q000032:analysis; D002453:Cell Cycle / Q000187:drug effects* / Q000528:radiation effects*; D002455:Cell Division / Q000187:drug effects / Q000528:radiation effects; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D056744:Cyclin B1 / Q000032:analysis; D015536:Down-Regulation; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D015972:Gene Expression Regulation, Neoplastic; D006657:Histones / Q000032:analysis; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000032:analysis*; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000737:chemistry / Q000188:drug therapy* / Q000473:pathology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D014410:Tumor Stem Cell Assay; D015854:Up-Regulation; D044004:Xanthones / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein / Q000032:analysis
chemical_list: C494826:BAX protein, human; C534699:CCNB1 protein, human; D056744:Cyclin B1; C468783:H2AX protein, human; C497442:HIF1A protein, human; D006657:Histones; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D019253:Proto-Oncogene Proteins c-bcl-2; D011838:Radiation-Sensitizing Agents; D044004:Xanthones; D051028:bcl-2-Associated X Protein; C052659:gambogic acid; D053148:Caspase 3