Abstract.To study the role of TNF-α in tongue cancer metastasis, we made highly metastatic cells from a human oral squamous cell carcinoma cell line (SAS) by repeating the passage in which the cells were injected into a nude mouse tongue and harvested from metastasized cervical lymph nodes. Cancer cells after 5 passages (GSAS/N5) increased invasive activity 7-fold in a TNF-α receptor 1 (TNFR1)-dependent manner and enhanced mRNA expression of TNF-α and TNFR1. In the highly metastatic cells, NF-κB activation was upregulated via elevated phosphorylation of Akt and Ikkα/β in the signaling pathway and secretion of TNF-α, active MMP-2 and MMP-9 increased. Suppression of increase of TNF-α mRNA expression and MMP secretion by NF-κB inhibitor NBD peptide suggested a positive feedback loop in GSAS/N5 cells; TNF-α activates NF-κB and activated NF-κB induces further TNF-α secretion, leading to increase of active MMP release and promotion of invasion and metastasis of the cells. GSAS/N5 cells that had been injected into the nude mouse tongue and harvested from metastasized lungs multiplied angiopoietin-like 4 (Angptl4) expression with enhanced migration activity, which indicated a possible involvement of Angptl4 in lung metastasis of the cells. These results suggest that TNF-α and Angptl4 promote metastasis of the oral cancer cells, thus, these molecules may be therapeutic targets for patients with tongue cancer.
IntroductionThe American Cancer Society estimated 45,780 new cases of oral cavity and pharyngeal cancer, and 8,650 deaths from these tumors, in 2015 in the United States (1). By advances in surgery and radiation therapy, the 5-year survival rate for oropharyngeal cancer has increased to 66%, but the rate is still unsatisfactory in comparison with some other site cancers including prostate, thyroid and breast; the rates of these types of cancer are >90% (1). A primary cause for the unfavorable prognosis is patient death from the cancer metastasized at regional and distant sites (2-5). Squamous cell carcinoma (SCC) accounts for approximately 90% of oral and oropharyngeal malignancies in the United States and tongue is a common site of the malignant diseases (6,7). The rate of nodal metastasis is higher in tongue cancer patients than oral cavity cancer patients whose rate is 30% on their initial evaluation (8,9). Several studies have shown a high rate of occult nodal metastasis (20-40%) in tongue SCC patients with no evidence of regional spread on clinical or radiographic evaluation (8,10-15). There is a tendency that tongue cancer increases in young females in recent 2-3 decades (16-18). Thus, metastasis suppression is a main and urgent subject in the treatments of patients with tongue SCC.The process of metastasis is complex and involves tumor growth, the extra-cellular matrix breakdown, invasion to the vessels, escape from immune surveillance, transport to other sites with adhesion to the vessel, subsequent invasion into an organ where tumor cells proliferate, grow and spread. Various molecules participate in the pr...