Abstract 4494: In vivo antitumor activity of NVP-BEZ235, a dual PI3K/mTOR inhibitor, and RAD001 (everolimus), an mTOR inhibitor, in endometrial cancer

Purpose; PI3K (phosphatidylinositol-3-kinase) and its downstream mTOR (mammalian target of rapamycin) pathway play a critical role in diverse cellular functions, including proliferation, growth and cell survival. PI3K-mTOR pathway is frequently activated in endometrial cancer through various PI3K/AKT activating genetic alterations, such as mutations in PTEN, PIK3CA, and K-Ras. It has not been well analyzed whether mTOR inhibition alone is as effective as dual PI3K/mTOR inhibition to cancer cells with the activating PI3K pathway mutations, especially in vivo. In this study, we compared in vivo anti-tumor activity of a dual PI3K.inhibitor, NVP-BEZ235, with an mTOR inhibitor, RAD001, in endometrial cancer cell lines with the PI3K/AKT activating mutations.Experimental procedure; We screened 13 endometrial cancer cell lines, 11 of which possess one or more PI3K/AKT activating mutations. Among them, we selected two cell lines; AN3CA with a nonsense mutation in PTEN, and Hec-59 with double mutations in PIK3CA and PTEN. The IC50 values for cell proliferation by RAD001 were 14nM in AN3CA and 220nM in Hec-59, whereas the values by NVP-BEZ235 were 20nM in AN3CA and 24nM in Hec-59. We examined the effect of RAD001 (2.5mg/kg/day) and BEZ235 (40mg/kg/day) on tumor growth in vivo, using mice inoculated with endometrial cancer cells. We analyzed the phosphorylation levels of Akt, FOXO, GSK3beta and S6 in the tumors by immunoblotting. Results;Both BEZ and RAD001, compared with placebo, significantly suppressed the tumor growth in xenograft mice in the two cell lines. No significant adverse effects were observed with either compounds in any of the mice. Inconsistent with the in vitro data, the effect was comparable between BEZ235 and RAD001 even in Hec-59 cells, although the IC50 value was much higher with RAD001 than NVP-BEZ235. In Hec-59, NVP-BEZ235 clearly suppressed all the phosphorylation level of Akt, FOXO, GSK3beta and S6 in one hour from the treatment. However, all the phosphorylation levels were completely recovered to the base level within 24 hours. RAD001 clearly suppressed the p-S6 level in 1 hour and the effect partly remained even after 24 hours from the treatment. Conclusion; We demonstrated that both NVP-BEZ235 and RAD001 suppressed tumor growth in vivo in endometrial cancer cell lines with PIK3CA and/or PTEN mutations. The comparable effect of NVP-BEZ235 and RAD001 might be explained by the recovery of the phosphorylation levels of the target proteins, such as p-Akt, suggesting that sufficient suppression of the PI3K/mTOR pathway for full time-course might be required to robustly induce the anti-tumor effect by these inhibitors. In clinical trials, both pharmacokinetic and pharmacodinamic analyses would be important to appropriately assess the effect of these inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4494. doi:10.1158/1538-7445.AM2011-4494