Abstract 3730: 2-Methoxyestradiol induces differentiation of epithelial ovarian cancer-initiating cells sensitizing them to chemotherapy.
Authors: Cuello Mauricio A. , Kato Sumie , Hormazábal Katherine , Abarzua Lorena , Bravo Loreto , Barriga Isabel , Barrena Nicanor , Brañes Jorge , Bravo Erasmo , Gejman Roger , Castellón Enrique , Owen Gareth 
Published: August 2014

Ovarian cancer is the most deadly gynecological malignancy. Its lethality is mainly due to late diagnosis and acquisition of resistance to available therapies. Current evidence considers “tumor cell heterogeneity” as a cancer hallmark. A subset of cancer cells, named "cancer-initiating cells" (CICs), possesses stem cell-like capabilities allowing self-renewal, differentiation and dedifferentiation into other cell types, some of them evolved to a more invasive and resistant phenotype. Thus, the existence of CICs allows tumor to overcome therapy and regrowth as resistant kind over time. Finding therapeutic strategies effective against this subset of cells remain a major goal in cancer therapeutics. Previously we have shown that 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite, induces cell death in ovarian cancer cells. Objective: In the present work we investigated the potential effects of 2-ME on CICs isolated from either ovarian cancer cell lines or primary tissue cultures obtained from ovarian cancer patients. Methods: CICs were isolated from both ovarian cancer cell lines (SKOV3, UCI 101, HEY) as well as primary tissue cultures established from ascites samples. Stemness, epithelial-mesenchymal transition (EMT), and anti-apoptotic markers were studied by immunoblotting (W-B), RT-PCR and immunohistochemistry in CICs cultured under stem-selection medium/non-attachment conditions and after treatment with different concentrations of 2-ME (5 to 10 uM, up to 24h). CICs treated under similar conditions were then exposed to different concentrations of chemotherapeutic reagents (i.e. paclitaxel, 0,5-5 uM, for up to 48 h). Cell death was measured by Tunel assay and PARP cleavage (measured by W-B). Results: Isolated CICs grow forming ovospheres that express higher levels of Oct-4, Nanog, Snail, N-Cadherin, CD44, CD133, survivin, and lower levels of E-cadherin compared with non-selected cell population (whole cell population, WP). In contrast to WP, CICs did not undergo apoptosis upon 2-ME exposure (5 uM for 24 h) measured by PARP cleavage. However, 2-ME treatment results in a decrease of Nanog, N-cadherin, Snail, Survivin and an increase in E-cadherin protein expression levels. In addition, a decrease in mRNA levels of Twist, Zeb2 (but not Zeb1) is observed under similar conditions (5 uM for 6 h). 2-ME pretreatment increases paclitaxel-induced cell death in CICs compared to those treated with paclitaxel alone, measured by Tunel assay. Conclusions: 2-ME induces the loss of stemness and EMT markers in epithelial ovarian CICs. This differentiating effect induced by 2-ME results in sensitization of this subset of resistant cells to chemotherapeutic agents. Further studies might be conducted to assess the clinical usefulness of this combination. (FONDECYT 1120292, and BMRC CTU06)

Citation Format: Mauricio A. Cuello, Sumie Kato, Katherine Hormazábal, Lorena Abarzua, Loreto Bravo, Isabel Barriga, Nicanor Barrena, Jorge Brañes, Erasmo Bravo, Roger Gejman, Enrique Castellón, Gareth Owen. 2-Methoxyestradiol induces differentiation of epithelial ovarian cancer-initiating cells sensitizing them to chemotherapy. [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 3730. doi:10.1158/1538-7445.AM2013-3730