title: Chloroquine Sensitizes Nasopharyngeal Carcinoma Cells but Not Nasoepithelial Cells to Irradiation by Blocking Autophagy.
abstract: BACKGROUND
  Treatment of nasopharyngeal carcinoma requires the application of high dosages of radiation, leading to severe long-term complications in the majority of patients. Sensitizing tumor cells to radiation could be a means to increase the therapeutic window of radiation. Nasopharyngeal carcinoma cells display alterations in autophagy and blockade of autophagy has been shown to sensitize them against chemotherapy.
  
  
  METHODS
  We investigated the effect of chloroquine, a known inhibitor of autophagy, on sensitization against radiation-induced apoptosis in a panel of five nasopharyngeal carcinoma cell lines and a SV40-transformed nasoepithelial cell line. Autophagy was measured by immunoblot of autophagy-related proteins, immunofluorescence of autophagosomic microvesicles and electron microscopy. Autophagy was blocked by siRNA against autophagy-related proteins 3, 5, 6 and 7 (ATG3, ATG5, ATG6 and ATG7).
  
  
  RESULTS
  Chloroquine sensitized four out of five nasopharyngeal cancer cell lines towards radiation-induced apoptosis. The sensitizing effect was based on the blockade of autophagy as inhibition of ATG3, ATG5, ATG6 and ATG7 by specific siRNA could substitute for the effect of chloroquine. No sensitization was seen in nasoepithelial cells.
  
  
  CONCLUSIONS
  Chloroquine sensitizes nasopharyngeal carcinoma cells but not nasoepithelial cells towards radiation-induced apoptosis by blocking autophagy. Further studies in a mouse-xenograft model are warranted to substantiate this effect in vivo.
authors.affiliation: Division of Pediatric Hematology, Oncology and Stem Cell Transplantation, Medical Faculty, RWTH Aachen University, Aachen, Germany.
authors.forename: Anna
authors.initials: A
authors.lastname: Makowska
authors.affiliation: Department of Radiation Oncology, Medical Faculty, RWTH Aachen University, Aachen, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Eble
authors.affiliation: Department of Radiation Oncology, Medical Faculty, RWTH Aachen University, Aachen, Germany.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Prescher
authors.affiliation: Electron Microscopic Facility, Institute of Pathology, Medical Faculty, RWTH Aachen University, Aachen, Germany.
authors.forename: Mareike
authors.initials: M
authors.lastname: Hoß
authors.affiliation: Division of Pediatric Hematology, Oncology and Stem Cell Transplantation, Medical Faculty, RWTH Aachen University, Aachen, Germany.
authors.forename: Udo
authors.initials: U
authors.lastname: Kontny
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects*; D001343:Autophagy / Q000187:drug effects* / Q000235:genetics*; D000071187:Autophagy-Related Protein 5 / Q000235:genetics; D000071193:Autophagy-Related Protein 7 / Q000235:genetics; D000071183:Autophagy-Related Proteins / Q000235:genetics; D000071186:Beclin-1 / Q000235:genetics; D002277:Carcinoma / Q000188:drug therapy / Q000532:radiotherapy*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D002738:Chloroquine / Q000494:pharmacology*; D004847:Epithelial Cells / Q000187:drug effects / Q000528:radiation effects*; D006801:Humans; D020287:In Situ Nick-End Labeling; D009297:Nasal Mucosa / Q000166:cytology; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000188:drug therapy / Q000532:radiotherapy*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics
chemical_list: C502778:ATG5 protein, human; D000071187:Autophagy-Related Protein 5; D000071183:Autophagy-Related Proteins; D000071186:Beclin-1; D034741:RNA, Small Interfering; D011838:Radiation-Sensitizing Agents; D002738:Chloroquine; D044763:Ubiquitin-Conjugating Enzymes; C509349:ATG7 protein, human; D000071193:Autophagy-Related Protein 7; C455621:ATG3 protein, human