S-1 mediates the inhibition of lymph node metastasis in oral cancer cells

S-1, an oral fluorouracil antitumor drug, is composed of three agents: tegafur (FT), 5-chloro-2,4-dihydroxypyridine (CDHP), and potassium oxonate (Oxo). Approximately 50% of oral squamous cell carcinomas (OSCC) exhibit cervical lymph node metastasis. The extent of lymph node involvement is a major determinant in both staging and prognosis of the majority of OSCC. The purpose of this study was to examine the effect of S-1 on the metastatic potential of OSCC cells. We used orthotopic green fluorescence protein (GFP) SAS-L1, in BALB/c nu/nu mice. Mice received oral doses of either 5% hydroxypropylmethylcellulose (HPMC) for control or S-1 (20 mg/kg) and were autopsied at 2 weeks. We also performed in vitro experiments using concomitant 5-fluorouracil (5-FU) and CDHP as a drug model of S-1 to determine the effect of S-1 on OSCC invasion and metastasis. Although 100% (11 of 11) of mice not treated with S-1 showed cervical lymph node metastasis, only 54.4% (6 of 11) of S-1 treated mice demonstrated metastasis. In in vitro experiments, OSCC cells treated with 5-FU and CDHP showed a marked reduction in invasiveness and in adhesion to laminin coated plates. Western blot analysis revealed that treatment with 5-FU and CDHP suppressed expression of integrins αv, α3, α6, β1, β3, β4, β5, and β6. These results suggest that S-1 inhibits tumor proliferation and lymph node metastasis in OSCC cells. Moreover, expression of integrin subunits and the integrin signal transduction pathway may be closely related to metastasis suppression.