title: HNSCC cell lines positive for HPV and p16 possess higher cellular radiosensitivity due to an impaired DSB repair capacity.
abstract: OBJECTIVE
  When treated by radiotherapy, patients with squamous cell carcinomas of the head and neck (HNSCC) positive for HPV and p16(INK4a) possess a clearly favorable prognosis as compared to those with HPV-negative HNSCC. The aim of this work was to study whether the better outcomes might be caused by an enhanced cellular radiosensitivity.
  
  
  METHODS
  The radiation response of five HPV/p16(INK4a)-positive and five HPV-negative cell lines was characterized with regard to cellular radiosensitivity by colony formation assay. Furthermore G1- and G2-arrest, apoptosis and residual DNA double-strand breaks (DSB) were analyzed by the colcemid-based G1-efflux assay, propidium iodide staining, the detection of PARP cleavage, the fluorescence-based detection of caspase activity and the immunofluorescence staining of γH2AX and 53BP1 foci.
  
  
  RESULTS
  On average, the cellular radiosensitivity of the HNSCC cell lines positive for HPV and p16(INK4a) was higher as compared to the sensitivity of a panel of five HPV-negative HNSCC cell lines (SF3=0.2827 vs. 0.4455). The higher sensitivity does not result from increased apoptosis or the execution of a permanent G1-arrest, but is rather associated with both, elevated levels of residual DSBs and extensive G2-arrest.
  
  
  CONCLUSIONS
  Increased cellular radiosensitivity due to compromised DNA repair capacity is likely to contribute to the improved outcome of patients with HPV/p16(INK4a)-positive tumors when treated by radiotherapy.
authors.affiliation: Laboratory of Radiobiology & Experimental Radiooncology, University Medical Center Hamburg Eppendorf, Germany. t.rieckmann@uke.uni-hamburg.de
authors.forename: Thorsten
authors.initials: T
authors.lastname: Rieckmann
authors.forename: Silke
authors.initials: S
authors.lastname: Tribius
authors.forename: Tobias J
authors.initials: TJ
authors.lastname: Grob
authors.forename: Felix
authors.initials: F
authors.lastname: Meyer
authors.forename: Chia-Jung
authors.initials: CJ
authors.lastname: Busch
authors.forename: Cordula
authors.initials: C
authors.lastname: Petersen
authors.forename: Ekkehard
authors.initials: E
authors.lastname: Dikomey
authors.forename: Malte
authors.initials: M
authors.lastname: Kriegs
mesh_terms: D017209:Apoptosis; D002294:Carcinoma, Squamous Cell / Q000737:chemistry / Q000235:genetics / Q000532:radiotherapy* / Q000821:virology; D045744:Cell Line, Tumor; D019941:Cyclin-Dependent Kinase Inhibitor p16; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D016193:G1 Phase; D006258:Head and Neck Neoplasms / Q000737:chemistry / Q000235:genetics / Q000532:radiotherapy* / Q000821:virology; D006801:Humans; D009363:Neoplasm Proteins / Q000032:analysis*; D027383:Papillomaviridae / Q000302:isolation & purification*; D011836:Radiation Tolerance; D000077195:Squamous Cell Carcinoma of Head and Neck
chemical_list: C000614131:CDKN2A protein, human; D019941:Cyclin-Dependent Kinase Inhibitor p16; D009363:Neoplasm Proteins