Abstract 2179: Wnt pathway inhibition by niclosamide: a therapeutic target for ovarian cancer.

Abstract Objective: The majority of patients diagnosed with ovarian cancer initially respond to chemotherapy, but recurrence invariably occurs. The Wnt/β-catenin pathway is known to regulate cellular proliferation and differentiation and has been shown to play a role in chemoresistance and contribute to “stemness” of cancer cells. Wnt co-receptor, LRP6, forms a trimeric complex with Wnt ligand and Frizzled and becomes phosphorylated. This causes cytoplasmic buildup of β-catenin, which acts as a transcriptional activator leading to proliferation. Studies have shown an association of LRP6 degradation with apoptosis and inhibition of cellular proliferation. Niclosamide, an FDA approved salicyclamide derivative used for the treatment of tapeworm infections, causes LRP6 degradation. Therefore, the objective of this study was to investigate niclosamide as a potential therapeutic agent for ovarian cancer. Methods: Two ovarian cancer cell lines A2780, SKOV3ip1 and their carboplatin and paclitaxel chemoresistant derivatives, A2780.cp20 and SKOV3ip2.TRip2, were treated with niclosamide (0.1 to 5 μM) alone or in combination with carboplatin (5 to 150 μM). Tumor cells isolated from the ascites of six patients with primary ovarian cancer were also treated. Cell viability was assessed using the ATP-lite assay. The levels of LRP6, Axin 2 and cytosolic free β-catenin were determined using Western blot analysis. Cell lines were treated with Wnt3A ligand and niclosamide, and Wnt transcriptional activity was measured by the TOPflash reporter assay. Results: Combination treatment produced increased cytotoxicity compared to single agent treatment in all ovarian cancer cell lines, and in the six patient samples. In the cell lines, combination treatment with carboplatin and niclosamide caused synergistic cytotoxicity. Western blot analysis showed a dose-dependent decrease in phosphorylated LRP6, Axin 2 expression, and the level of cytosolic free β-catenin in patient samples and in the A2780 cell line after niclosamide treatment for 24 hours. A significant reduction of Wnt/β-catenin signaling was confirmed by TOPflash assay in both parental (p=0.05) and chemoresistant cell lines (p=0.009). Conclusion: This study demonstrates that niclosamide is a potent Wnt/β-catenin signaling inhibitor by causing a decrease in LRP6, Axin 2 expression, and cytosolic free β-catenin. Targeting the Wnt/β-catenin pathway led to decreased cellular proliferation and increased apoptosis. Niclosamide displays excellent anti-tumor activity in ovarian cancer cell lines and in ovarian cancer cells from patient ascites. These findings warrant further preclinical and clinical evaluation of this drug as a treatment option for ovarian cancer. Citation Format: Rebecca C. Arend, Angelina I. Londoño-Joshi, Yonghe Li, Wenyan Lu, Rajeev S. Samant, Brandon J. Metge, J. Michael Straughn, Donald J. Buchsbaum. Wnt pathway inhibition by niclosamide: a therapeutic target for ovarian cancer. [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 2179. doi:10.1158/1538-7445.AM2013-2179