Targeting Serum Glucocorticoid-Regulated Kinase-1 in Squamous Cell Carcinoma of the Head and Neck: A Novel Modality of Local Control

Purpose: The inhibition of serum glucocorticoid-regulated kinase-1 (SGK-1) has been found to decrease growth of colon and prostate cancer cells. The purpose of this study is to evaluate the therapeutic effect of SGK-1 inhibition in head and neck squamous cell carcinoma (SCC). Experimental Design: Human head and neck tumors (HTB41/43) were established in athymic mice. Growth rates between mice treated with vehicle (PBS) injection (group 1, n=5), SGK-1 Inhibitor GSK 650394 (group 2, n=6), systemic cisplatin (group 3, n=6), and a combination of SGK-1 Inhibitor and cisplatin (group 4, n=6) were compared using repeated measures one-way ANOVA with Newman-Keuls Multiple Comparison Test. Tumor cells were subsequently submitted to further analyses. Results: At the end of the experiment mean tumor sizes were 122.33+/-105.86, 76.73+/-36.09, 94.52+/-75.92, and 25.76+/-14.89 mm(2) (mean +/- SD) for groups 1 to 4. Groups 2 and 3 showed decreased tumor growth compared to controls (p<0.001). Group 4 displayed even greater growth suppression (p<0.0001). Importantly, group 4 fared better than group 3 (p<0.001). CD44 expression was reduced in group 2 (p<0.05), and to an even greater extent in groups 3 and 4 (p<0.0025). A trend towards reduction of HER 2 expression was noted in group 4. Conclusions: SGK-1 inhibition suppresses tumor growth, and in combination with systemic cisplatin exceeds the effect of cisplatin alone. Decreased expression of CD44 and HER 2 implies depletion of tumor stem cells, and less tumorigenicity. SGK-1 inhibition represents a potential modality of local control for palliation in advanced cases.