HNSCC cell lines positive for HPV and p16 possess higher cellular radiosensitivity due to an impaired DSB repair capacity

Radiother Oncol. 2013 May;107(2):242-6. doi: 10.1016/j.radonc.2013.03.013. Epub 2013 Apr 17.


Background and purpose: 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.

Materials and 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis
  • Carcinoma, Squamous Cell / chemistry
  • Carcinoma, Squamous Cell / genetics
  • Carcinoma, Squamous Cell / radiotherapy*
  • Carcinoma, Squamous Cell / virology
  • Cell Line, Tumor
  • Cyclin-Dependent Kinase Inhibitor p16
  • DNA Breaks, Double-Stranded*
  • DNA Repair*
  • G1 Phase
  • Head and Neck Neoplasms / chemistry
  • Head and Neck Neoplasms / genetics
  • Head and Neck Neoplasms / radiotherapy*
  • Head and Neck Neoplasms / virology
  • Humans
  • Neoplasm Proteins / analysis*
  • Papillomaviridae / isolation & purification*
  • Radiation Tolerance*
  • Squamous Cell Carcinoma of Head and Neck


  • CDKN2A protein, human
  • Cyclin-Dependent Kinase Inhibitor p16
  • Neoplasm Proteins