Objective:

Mucinous adenocarcinoma of the ovary (MAC) has a poor prognosis. It resists conventional chemotherapy based on platinum or taxane. Recent molecular analyses of various types of ovarian tumors showed that overexpressed epidermal growth factor receptor (EGFR) family proteins and consequent activation of its downstream signaling Akt / mammalian target of rapamycin (mTOR) are found in 48% of tumors.

These are associated with poor patients outcomes. We explored molecular-targeted therapy with NVP-BEZ235 (BEZ235), a dual inhibitor of phosphatidylinositol

3-kinase (PI3K) and mTOR, to treat MAC.

Method:

Seven cell lines of MAC (JHOM-1, JHOM-2B, MCAS, OMC-1, RMUG-L, RMUG-S, and

TU-OM-1) were used. The sensitivity of these cells to BEZ235 was determined with the WST-8 assay. Mutation status of EGFR, KRAS, and PIK3CA genes was analyzed by direct sequencing. Cell cycle distribution was assessed by flow cytometry, and the expression of proteins in apoptotic pathways and molecules downstream of the PI3K/Akt/mTOR signaling pathways were determined by western blot analysis. We also examined the effects of BEZ235 on tumor growth in xenograft models with nude mice. Mice bearing subcutaneous tumors of RMUG-S or OMC-1 received the vehicle or BEZ235 (25 or 50 mg/kg/day) for 3 weeks. Tumor volume was measured using a caliper twice weekly.

Results:

The half-maximal inhibitory concentration (IC50) values of each cell line ranged from 18 to 618 nM for BEZ235. All lines exhibited protein expressions of the PI3K/Akt/mTOR signaling pathways, but had no mutations in

EGFR and PIK3CA genes. A point mutation of the KRAS gene at codon 12 in exon 2 was observed only in the MCAS cell line. The protein expression levels of phosphorylated (p) Akt, pp70S6K and p4E-BP1 were suppressed after exposure to

BEZ235 in a dose-dependent manner. After treatment with BEZ235, the proportions of the cells in the G0/G1 phase increased, and the proportion in the S phase fraction decreased. Moreover, 24 h after treatment with BEZ235, the protein expression of cleaved PARP and cleaved caspase-9 were upregulated in both

RMUG-S and TU-OM-1 cells. BEZ235 increased the number of apoptotic cells in both RMUG-S and TU-OM-1. Treatment of mice bearing OMC-1 or RMUG-S with BEZ235 at 25 or 50 mg/kg/day doses significantly suppressed tumor growth in xenograft models without severe weight loss.

Conclusion:

The PI3K/Akt/mTOR pathway is a potential therapeutic target for MAC using BEZ235 as a therapeutic agent.

Citation Format: Akiko Kudoh, Tetsuro Oishi, Hiroaki Itamochi, Michiko Nonaka, Seiya Sato, Jun Naniwa, Shinya Sato, Muneaki Shimada, Naoki Terakawa, Junzo Kigawa, Tasuku Harada. A novel therapy for mucinous adenocarcinoma of the ovary by using NVP-BEZ235 to inhibit PI3K and mTOR. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3256. doi:10.1158/1538-7445.AM2013-3256