Abstract 2063: Reversal of chemoresistance to Paclitaxel by reintroduction of microRNA-200c in ovarian cancer cells
Authors: Richer Jennifer K. , Dimitrova Irina , Post Miriam , Behbakht Kian 
Published: February 2011

Abstract
MircoRNAs control the post-translational regulation of many genes involved in tumorigenesis including those involved in epithelial to mesenchymal transition (EMT), cellular migration, adhesion, invasion and sensitivity to chemotherapy. The transcription factor ZEB1, which represses E-cadherin and other genes involved in maintaining polarity, is normally not expressed in epithelial cells. However, it is inappropriately expressed in high-grade carcinomas, which lack microRNA −200c (miR-200c). Class III beta-tubulin (TUBB3) is abnormally expressed in carcinomas resistant to microtubule-targeting chemotherapies. We have demonstrated previously that miR-200c, in addition to directly targeting ZEB1/2, also directly targets TUBB3 (as well as other genes typically only expressed in mesenchymal or neuronal cells) resulting in increased sensitivity to paclitaxel in breast and endometrial cancer. TUBB3 has been found to be overexpressed in ovarian cancers resistant to We hypothesized that restoration of miRNA-200c would enhance ovarian cancer chemosensitivity to paclitaxel.
Results: Restoration of miR-200c into Hey ovarian cancer cells using microRNA mimic reduced in vitro migration and invasion by 84 and 86% respectively. Restoration of miR-200c also restored chemosensitivity to paclitaxel in cell death assays (85% increase in cell death) and reduced cell survival in clonogenic assays (49-55% decrease in total colony area and 67-70% decrease in the number of colonies). We proved that this was a direct result of miR-200c targeting of TUBB3 since introduction of exogenous TUBB3 expression vector lacking the miR-200c target site inhibited the miR-200c-mediated increase in sensitivity to paclitaxel. In addition, ovarian cancer cells transiently transfected with miR-200c mimic demonstrate statistically significantly decrease in adhesion to basement membrane complex and its components. We are currently in the process of analyzing 20 patient samples of high-grade serous carcinoma for expression of ZEB1 and TUBB3 by IHC and miR-200c by in-situ hybridization and correlating this data with clinical course and response to chemotherapy. In addition we have created Hey ovarian cancer cells expressing miR-200c in a constitutive manner and are evaluating the effect of restoration of miR-200c on intraperitoneal tumor burden and chemoresistance in a pre-clinical mouse model of ovarian cancer.
Conclusions: Re-introduction of miR-200c restores chemosensitivity to paclitaxel through down-regulation of TUBB3 in Hey ovarian cancer cells. Because restoration of miR-200c is crucial to maintenance of epithelial identity, reduces adherence to various substrates, and increases sensitivity to paclitaxel, it is holds potential as a therapeutic strategy for chemoresistant ovarian cancers.
Funded by the Colorado Cancer League grant to JKR and ID.
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 2063.