Abstract 4386: Identification of microRNA which regulates paclitaxel resistance of ovarian cancer cells - a potential of miR-194 by attenuating paclitaxel resistance through the down-regulation of oncogene BMI-1

Abstract

Abstract Purpose: Ovarian cancer remains a deadly disease. Despite developments in current chemotherapy, overall survival rate for patients with advanced disease remains approximately 30%, mainly due to primary or acquired drug resistance. Therefore, overcoming chemoresistance is one of the greatest challenges in ovarian cancer management. However, mechanisms underlying chemoresistance to paclitaxel, a key drug, have not been fully understood. MicroRNAs (miRNAs) are non-coding small RNAs and more than 50% of miRNA genes are located in cancer-associated genomic regions, suggesting that miRNAs are deeply involved in the pathogenesis of cancers, including acquiring chemoresistance. In this study, we attempted to identify miRNAs that regulate paclitaxel resistance and to analyze the therapeutic potential of targeting these. Methods: Two ovarian cancer cell lines, SKOV3ip1 and HeyA-8, were continuously exposed by gradually increasing concentrations of paclitaxel and finally, paclitaxel resistant cell lines, SKOV3ip1-TR and HeyA8-TR were established. MicroRNA PCR arrays were performed and miRNA expressional patterns were compared with those of parental cells. miR-194 was found to be one of down-regulated miRNAs in both resistant cell lines. The effect of miR-194 was assessed by the enforced expression of precursor miRNA. In silico analyses found that Bmi-1 is a possible target gene. miR-194 expression was examined by quantitative RT-PCR and BMI expression by Western blotting. In order to investigate whether miR-194 directly targets the 3′-UTR of Bmi-1 mRNA, a luciferase reporter assay was performed. The stably miR-194 expressing HeyA8-TR cells were constructed and injected subcutaneously onto female nude mice. Two weeks after the inoculation, paclitaxel was treated to mice and the effect of paclitaxel was assessed by measuring tumor volumes. Results: IC50 values of parentally paclitaxel sensitive cell lines, SKOV3ip1 and HeyA-8, were 2nM and 19nM, respectively, while those of SKOV3ip1-TR and HeyA8-TR were both over 300nM. The enforced expression of miR-194 attenuated paclitaxel resistance significantly. While miR-194 expression was down-regulated in SKOV3ip1-TR and HeyA8-TR cells compared parental cells, BMI-1 expression was highly expressed in these cell lines. Transfection of precursor miR-194 into resistant cells reduced BMI-1 expression. In a luciferase reporter assay, miR-194 directly suppressed BMI-1 transcriptional activity. In a xenograft model, the transduction of miR-194 enhanced the effect of paclitaxel and significantly shrunk the tumor volumes. Conclusion: MiR-194 attenuated paclitaxel resistance by inhibiting BMI-1 expression. The overcome of chemoresistace is a critical issue for ovarian cancer treatment and herein we suggest that miR-194 is a potential therapeutic target. Citation Format: Koji Nakamura, Kenjiro Sawada, Yasuto Kinose, Kae Hashimoto, Seiji Mabuchi, Tadashi Kimura. Identification of microRNA which regulates paclitaxel resistance of ovarian cancer cells - a potential of miR-194 by attenuating paclitaxel resistance through the down-regulation of oncogene BMI-1. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4386. doi:10.1158/1538-7445.AM2014-4386