Abstract 2551: Acquisition of epithelial-mesenchymal transition phenotype of chemoresistant ovarian cancer cells is linked with activation of the endothelin signaling pathway

Abstract Chemoresistance is a major challenge in ovarian cancer (OC). High-throughput analysis has shown that the endothelin A receptor (ETAR) is overexpressed in post-chemotherapy OCs, suggesting a role in the chemoresistance onset. To identify ETAR-driven molecular determinants involved in chemoresistance to cisplatin and paclitaxel, we used the A2780 WT, cisplatin-resistant A2780 CIS, and taxol-resistant A2780 TAX human OC cells. ET-1 and ETAR mRNA and protein expression as well as ET-1 secretion were higher in the resistant OC cells, associated with increased ET-1-induced MAPK and AKT activation and cell proliferation. These effects were reverted by treatment with zibotentan (ZD4054), a specific ETAR antagonist. In sensitive OC cells, zibotentan enhanced the number of early apoptotic cells, similar to cisplatinum. Furthermore, zibotentan sensitized resistant A2780 CIS cells to cisplatinum-induced apoptosis, confirming the role of ET-1 as survival factor. Given the documented role of the epithelial to mesenchymal transition (EMT) in the chemoresistance development and the ability of the ET-1/ETAR axis to regulate EMT effectors, such as Snail and β-catenin, we analyzed whether ETAR-driven EMT molecular changes were linked with the chemoresistance in EOC cells. Decreased expression of the epithelial adhesion molecule E-cadherin and an increased expression of mesenchymal markers, such as Snail and Slug, the principal transcriptional repressor of E-cadherin, as well as Snail promoter activity were observed in sensitive OC cells after ET-1 treatment. Moreover, these effects were upregulated in resistant OC cells and were blocked in the presence of zibotentan, providing molecular evidence that the ETAR-mediated EMT signaling in EOC can represent a “salvage pathway” occurring during chemoresistance development. In sensitive A2780, as well as in resistant A2780 CIS and TAX xenografts, zibotentan induced a significant tumor growth inhibition, associated with reduction of Snail and upregulation of E-cadherin, suggesting a specific therapeutic window in which combination therapy of zibotentan with cytotoxic drugs is effective also in resistant OC. Finally immunohistochemical analysis of human OC, with different responses to chemotherapy, showed that ET-1 and ETAR are overexpressed in the resistant tumors, associated with upregulation of E-cadherin and with downregulation of N-cadherin and β-catenin. In conclusion, our study suggest that ETAR blockade with the specific antagonist zibotentan can revert EMT and increase the sensitivity to chemotherapeutic agents, representing a potential strategy to overcome chemoresistance in OC. Supported by AIRC, Ministero della Salute, AstraZeneca. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2551.