1 [Background] Ovarian clear cell carcinoma (CCC) has shown the resistance to the standard chemotherapy for epithelial ovarian cancer (EOC). Therefore, patients with CCC have a worse prognosis than those with ovarian serous adenocarcinoma (SAC), which is a dominant subtype in EOC. Recently, it has shown that CCC has a high frequency of activating mutations of PIK3CA. Thus, PI3K-Akt pathways may be an attractive target of therapy. NVP-BEZ235 (BEZ235) is a novel, orally bioavailable imidazoquinoline that potently and reversibly inhibits class 1 PI3K activity. BEZ235 also binds directly to the mTOR ATP-binding domain and directly inhibits its catalytic activity, thereby inhibiting both mTOR complex 1 (mTORC1) and mTORC2. There are few reports on the activity of BEZ235 against ovarian carcinoma cells. The purpose of the present study was to determine whether the drug targeting the PI3K-Akt-mTOR pathway suppresses cell proliferation and tumorigenicity of CCC. [Material& Methods] We used eight CCC cell lines (OVISE, SMOV-2, KK, TU-OC-1, OVTOKO, KOC-7c, OVMANA, and RMG-I) and five SAC cell lines (KOC-2s, KF, TU-OS-3, TU-OS-4, SHIN-3). IC50 to BEZ235 was determined on the basis of the dose-effect curves, using WST-8 assay. Protein expressions of Akt, phospho(p)-Akt, mTOR, pmTOR, p70S6K, pp70S6K, 4E-BP1, and p4E-BP1 were examined by western blotting. Cell cycle distribution was analyzed by flow cytometry. Apoptotic cells were assessed by Annexin V-FITC/PI double staining. We also investigated the effects of BEZ235 on tumor growth in a nude mice xenograft model. Mice bearing subcutaneous tumor of OVISE were received 3-weeks treatment with vehicle or BEZ235 (25mg/kg/day or 50mg/kg/day). The two perpendicular axes of the tumor diameter was measured in control and treated groups using a caliper twice weekly, and tumor volume was calculated, using the following formula: length x (width)*2 x (≥/6). [Results] IC50 to BEZ235 for CCC cell lines ranged from 44 to 777 nM (median:332.5nM) and those for SAC cell lines ranged from 779 to 25400 nM (median: 1004nM). We confirmed that all CCC cell lines exhibited protein expressions of pAkt and pmTOR. pAkt, p-p70S6K and p4E-BP1 expressions in CCC cells (OVISE and KK) were suppressed after exposure to BEZ235 in a dose-dependent manner. The both cell lines exhibited G1 cell cycle arrest after exposure to 10 or 100nM BEZ235, and apoptotic cells were induced by higher concentrations of the agent. Finally, treatment of the mice with BEZ235 at doses 25mg/kg/day or 50mg/kg/day significantly suppressed tumor growth in a xenograft model. [Conclusion] These results suggest that the PI3K-Akt-mTOR pathway is a potential therapeutic target for CCC and that NVP-BEZ235 is worth exploring as a therapeutic agent for CCC. 1

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3740. doi:1538-7445.AM2012-3740