Abstract 348: Prognostic value of mTOR activation and therapeutic effects of everolimus in esophageal squamous cell carcinoma

Background: The mammalian target of rapamycin (mTOR) plays central roles in cell growth and homeostasis. Aberrant activation of mTOR in relation to clinical outcome has been reported in several types of cancers. mTOR inhibitor, particularly everolimus (RAD001), has been attracting attentions as a promising anticancer drug. Nonetheless, no study has shown the prognostic value of mTOR activation in oesophageal squamous cell carcinoma (ESCC) and the therapeutic effect of everolimus on human ESCC cell lines. The aims of this study are [1] to evaluate phosphorylated-mTOR (i.e., mTOR activation) expression in ESCC and to clarify its clinical, pathologic, and prognostic features and [2] to examine the therapeutic effect of everolimus on ESCC cell lines. Methods: We examined p-mTOR expression (i.e., mTOR activation) by immunohistochemistry using 143 ESCC specimens. The present study involved 143 consecutive patients with ESCC who underwent the curative surgical resection at Kumamoto University Hospital from January 1996 to December 2006. We determined its clinical, pathologic, and prognostic features. Prognostic significance of p-mTOR expression was examined by Cox regression and Kaplan-Meier analysis. Subsequently. the effects of everolimus on ESCC cell lines were evaluated by in vitro assays (proliferation, cell cycle, apoptosis, invasion). Results: p-mTOR expression was detected in 71 (49.7 %) tumors and was independently associated with higher overall mortality. Compared to p-mTOR negative patients, p-mTOR positive patients experienced high overall mortality [HR 2.44; 95% confidence interval (CI), 1.24-4.83, P = 0.01], which persisted in multivariate analysis (adjusted HR 2.92; 95% CI, 1.48-5.78, P = 0.002). p-mTOR expression was not related with clinical or pathologic variables including age at diagnosis, sex, tumor location, histological grading, T classification (tumor invasion) or N classification (lymph-node metastasis). In vitro, in both TE4 (p-mTOR expression-high in vitro) and TE11 (p-mTOR expression-low in vitro) squamous cell carcinoma cell lines, everolimus suppressed the phosphorylation of downstream p70S6 kinase and 4E-BP1in a dose-dependent manner. Everolimus significantly inhibited cancer cells proliferation and invasion, and induced cells apoptosis in vitro. Conclusion: p-mTOR expression in ESCC was independently associated with poor prognosis, supporting the potential for mTOR as a therapeutic target for ESCC. Everolimus may be useful as an an