HPV-positive HNSCC cell lines but not primary human fibroblasts are radiosensitized by the inhibition of Chk1.
OBJECTIVE
Despite the comparably high cure rates observed for HPV-positive HNSCC, there is still a great need for specific tumor radiosensitization due to the often severe side effects resulting from intense radiochemotherapy. We recently demonstrated that HPV-positive HNSCC cell lines are characterized by a defect in DNA double-strand break repair associated with a pronounced G2-arrest. Here we tested whether abrogation of this radiation-induced G2-arrest by the inhibition of Chk1 results in specific radiosensitization of HPV-positive HNSCC cells.


METHODS
Experiments were performed with five HPV and p16-positive (93-VU-147T, UM-SCC-47, UT-SCC-45, UD-SCC-2, UPCI-SCC-154) and two HPV and p16-negative HNSCC cell lines, as well as two normal human fibroblast strains. Chk1 was inhibited by the selective inhibitor PF-00477736. Cell cycle distribution was determined by flow cytometry, Chk1-activity via Western blot and cell survival by colony formation assay.


RESULTS
With the exception of UPCI-SCC-154, the inhibition of Chk1 was found to abolish the pronounced radiation-induced G2-arrest in all HPV-positive cells utilized. All tumor cell lines that demonstrated the abrogation of G2-arrest also demonstrated radiosensitization. Notably, in G1-arrest-proficient normal human fibroblasts no radiosensitization was induced.


CONCLUSIONS
Abrogation of the G2 checkpoint through the inhibition of Chk1 may be used to selectively increase the cellular radiosensitivity of HPV-positive HNSCC without affecting the surrounding normal tissue.
Department of Otolaryngology and Head and Neck Surgery, University Medical Center Hamburg Eppendorf, Germany.
Chia-Jung
CJ
Busch
Malte
M
Kriegs
Simon
S
Laban
Silke
S
Tribius
Rainald
R
Knecht
Cordula
C
Petersen
Ekkehard
E
Dikomey
Thorsten
T
Rieckmann
D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy* / Q000821:virology; D059447:Cell Cycle Checkpoints / Q000528:radiation effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D000071877:Checkpoint Kinase 1; D005347:Fibroblasts / Q000528:radiation effects*; D016195:G2 Phase / Q000528:radiation effects; D006258:Head and Neck Neoplasms / Q000532:radiotherapy* / Q000821:virology; D006801:Humans; D027383:Papillomaviridae / Q000302:isolation & purification*; D010766:Phosphorylation; D011494:Protein Kinases / Q000502:physiology*; D011836:Radiation Tolerance; D000077195:Squamous Cell Carcinoma of Head and Neck; D016159:Tumor Suppressor Protein p53 / Q000502:physiology
D016159:Tumor Suppressor Protein p53; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1
Chk1; G2-arrest; HNSCC; HPV; Radiosensitivity; p16