Increased radiation sensitivity of head and neck squamous cell carcinoma with sphingosine kinase 1 inhibition.
BACKGROUND
Sphingosine kinase 1 (SphK1) is an important regulator of apoptosis, survival, and proliferation in cancer cells. SphK1 expression in head and neck squamous cell cancer (HNSCC) cell lines and tumor tissue was assessed, and the efficacy of SphK1 knockdown in increasing tumor radiosensitivity was evaluated in vitro and in vivo.


METHODS
Expression of SphK1 was determined by immunohistochemistry, Western blot, and real-time polymerase chain reaction (RT-PCR) in 34 prospectively collected HNSCC tumor samples. HNSCC cell lines squamous cell carcinoma (SCC)-15 and SCC-25 were treated with SphK1 inhibitor SKI-II and siRNA targeting SphK1 with and without radiation, and the cell viability was assessed. SCC-15 cells with and without transfection of SphK1 siRNA were then injected into athymic nude mice to develop tumor xenografts, and these 2 groups were further divided into 1 group that received radiation and 1 group that did not. Tumor size was measured over 18 days, when the animals were killed and the tumors were evaluated by immunohistochemistry.


RESULTS
SphK1 is found in both HNSCC cell lines and human tumor samples, with higher expression correlated with advanced tumor stage, nodal involvement, and recurrence. In vitro, both SCC-15 and SCC-25 were found to be radioresistant; however, they were sensitized by administration of SKI-II and transfection with siRNA targeting SphK1. In vivo, SphK1-siRNA transfected xenografts were decreased in size compared with both nonradiated control and radiated control mice, whereas mice with both SphK1-siRNA and radiation treatment showed a synergistic reduction in tumor volume. Histopathologic analysis demonstrated a decreased proliferative state in SphK1-siRNA transfected tumors.


CONCLUSIONS
SphK1 is upregulated in HNSCC, and inhibition of SphK1 sensitizes HNSCC to radiation-induced cytotoxicity.
Sinha
Uttam K
UK
Department of Otolaryngology - Head and Neck Surgery, University of Southern California, Keck School of Medicine, Los Angeles, California, USA.
Schorn
Victor J
VJ
Hochstim
Christian
C
Chinn
Steven B
SB
Zhu
Sutao
S
Masood
Rizwan
R
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D002277:Carcinoma / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D002294:Carcinoma, Squamous Cell; D004195:Disease Models, Animal; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D018307:Neoplasms, Squamous Cell / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors*; D016133:Polymerase Chain Reaction; D011836:Radiation Tolerance / Q000187:drug effects*; D000077195:Squamous Cell Carcinoma of Head and Neck; D013844:Thiazoles / Q000494:pharmacology*; D016896:Treatment Outcome; D000099157:Sphingosine Kinase
D004791:Enzyme Inhibitors; D017853:Phosphotransferases (Alcohol Group Acceptor); D013844:Thiazoles; D000099157:Sphingosine Kinase; C525025:4-(4-(4-chloro-phenyl)thiazol-2-ylamino)phenol