Chemopreventive and chemotherapeutic actions of mTOR inhibitor in genetically defined head and neck squamous cell carcinoma mouse model.

PURPOSE To assess the efficacy of rapamycin treatment in chemoprevention and chemotherapy of tumorigenesis in a genetically defined mouse model of head and neck squamous cell carcinoma (HNSCC). EXPERIMENTAL DESIGN Knockdown of Tgfbr1 and/or Pten using siRNA-mediated RNA interference was carried out in human HNSCC cell lines to analyze molecular changes in the mTOR pathway. Tgfbr1(flox/flox); Pten(flox/flox); K14-CreER(tam) mice were treated with oral gavage of tamoxifen for the conditional deletion of Tgfbr1 and Pten in oral mucosa, resulting in HNSCC. Tgfbr1 and Pten conditonal deletion (2cKO) mice were treated with rapamycin before or after the onset of HNSCC, and the efficacy of this treatment was assessed by determining tumor burden, longevity, and molecular analysis of the mTOR pathway. Molecular changes observed in human HNSCC cell lines and 2cKO mice were compared to identify key alterations in the mTOR pathway. RESULTS Knockdown of Tgfbr1 and/or Pten in human HNSCC cell lines resulted in activation of mTOR activity complex 1 and increased levels of survivin. Furthermore, we observed similar changes in HNSCC of the 2cKO mouse. In the human HNSCC tissue array, a loss of Tgfbr1 expression correlated with increased survivin levels. Chemopreventive rapamycin treatment significantly delayed the onset of the HNSCC tumors and prolonged survival in 2cKO mice. In addition, we also found that rapamycin had a therapeutic effect on squamous cell carcinomas in these mice. In 2cKO HNSCC tongue tumors, rapamycin treatment induced apoptosis, inhibited cell proliferation and phosphorylation of Akt and S6, and decreased survivin expression. CONCLUSIONS These findings indicate that tumorigenesis in 2cKO HNSCC is associated with activation of the Akt/mTOR/survivin pathway, and inhibition of this pathway by rapamycin treatment successfully ameliorates the onset and progression of tumorigenesis.