Targeting polo-like kinase 1 enhances radiation efficacy for head-and-neck squamous cell carcinoma.
OBJECTIVE
To investigate the efficacy of targeting polo-like kinase 1 (Plk1) combined with ionizing radiotherapy (RT) for head-and-neck squamous cell carcinoma (HNSCC).


METHODS
Polo-like kinase 1 messenger ribonucleic acid (mRNA) was targeted by small interfering RNA (siRNA) transfection into the FaDu HNSCC cell line; reduction was confirmed using quantitative real-time polymerase chain reaction. The cellular effects were assessed using [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium], clonogenic, flow cytometric, and caspase assays. In vivo efficacy of siPlk1 was evaluated using mouse xenograft models.


RESULTS
Small interfering Plk1 significantly decreased Plk1 mRNA expression, while also increasing cyclin B1 and p21(Waf1/CIP1) mRNA levels after 24 h. This depletion resulted in a time-dependent increase in FaDu cytotoxicity, which was enhanced by the addition of RT. Flow cytometric and caspase assays demonstrated progressive apoptosis, DNA double-strand breaks (gamma-H2AX), G2/M arrest, and activation of caspases 3 and 7. Implantation of siPlk1-treated FaDu cells in severe combined immunodeficient mice delayed tumor formation, and systemic administration of siPlk1 inhibited tumor growth enhanced by RT.


CONCLUSIONS
These data demonstrate the suitability of Plk1 as a potential therapeutic target for HNSCC, because Plk1 depletion resulted in significant cytotoxicity in vitro and abrogated tumor-forming potential in vivo. The effects of Plk1 depletion were enhanced with the addition of RT, indicating that Plk1 represents an important potential radiation sensitizer for HNSCC.
Gerster
Kate
K
Division of Applied Molecular Oncology, Ontario Cancer Institute, Toronto, ON, Canada.
Shi
Wei
W
Ng
Benjamin
B
Yue
Shijun
S
Ito
Emma
E
Waldron
John
J
Gilbert
Ralph
R
Liu
Fei-Fei
FF
D000818:Animals; D017209:Apoptosis; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000532:radiotherapy*; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D056744:Cyclin B1 / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D005260:Female; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000532:radiotherapy*; D006657:Histones / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000037:antagonists & inhibitors* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000627:therapeutic use*; D013778:Tetrazolium Salts; D013844:Thiazoles; D014162:Transfection; D014410:Tumor Stem Cell Assay / Q000379:methods; D000097869:Polo-Like Kinase 1
D053148:Caspase 3; D053179:Caspase 7; D018797:Cell Cycle Proteins; D056744:Cyclin B1; D050759:Cyclin-Dependent Kinase Inhibitor p21; D006657:Histones; D009363:Neoplasm Proteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D013778:Tetrazolium Salts; D013844:Thiazoles; D000097869:Polo-Like Kinase 1; C493956:CDKN1A protein, human; C468783:H2AX protein, human; C070380:3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium