Abstract 1397: Antisense oligo nucleotide of Annexin A4 improved platinum resistance in ovarian clear cell cancer
Authors: Kakubari Reisa , Nakagawa Satoshi , Iwamiya Tadashi , Kobayashi Eiji , Matsuzaki Shinnya , Ueda Yutaka , Yoshino Kiyoshi , Kasahara Yuya , Obika Satoshi , Kimura Tadashi , Serada Satoshi , Naka Tetsuji , Fujimoto Minoru 
Published: July 2017

Abstract
Introduction: Ovarian cancer in Japan are classified as clear cell carcinoma (CCC) more than 20 %, this percentage is higher than in Europe and United States. Besides, it is well known that CCC of ovary is highly resistant to cancer chemotherapy including carboplatin and paclitaxel treatment. We reported that Annexin A4 protein was overexpressed in ovarian CCC tissues by immunohistochemical analysis. Elevated Annexin A4 level has been detected in various epithelial cancer cell lines and have reported associating with chemoresistance to platinum-based cancer drugs. To overcome the platinum chemoresistance, we thought antisense oligonucleotides (ASOs) to be a good therapeutic option in a way of highly specific therapy for improving chemoresistance by suppressing the expression of Annexin A4 in cancer cells.
Methods: We generated ASO targeting Annexin A4 with 2’, 4’-bridged nucleic acid. And we analyzed suppression of Annexin A4 in ASO-transfected RMG-I cell line (CCC) in vitro using real time PCR and western blotting. In 16 types of ASOs targeting Annexin A4, 2 ASOs were eligible. Cells were seeded in 96-well plates (2,000 cells per well). Next day, cells were transfected with ASOs using lipofectamine 2000 and were exposed to various concentrations of cisplatin (0 - 100 μM) for 72 hr. Then, drug concentrations resulting in a 50% inhibition of cell growth (IC50 values) were calculated. Intracellular platinum accumulation in Annexin A4 overexpressing cells was analyzed. To assess the improvement of platinum resistance in vivo, we used ICR nu/nu mice xenografted subcutaneously with RMG-I cells. Intraperitoneal injection of cisplatin 3mg/kg after intratumoral administration of ASO 1mg/kg each twice a week were given to xenograft mice.
Results: By realtime PCR analysis, among strong 16 types of ASOs targeting Annexin A4, 2 ASOs showed strong knockdown efficiency (about 80% knockdown) compared to negative control ASOs. Western blotting analysis showing knockdown of Annexin A4 expression was observed in Annexin A4 ASO transfected cells compared to no treatment or control ASOs in vitro. ASO-transfected RMG-I cells was less resistant to cisplatin (IC50 = 3.3μM) compared with control cells (IC50 = 5.2μM) Same result were obtained with carboplatin. Platinum resistance was significantly improved in treated with Annexin A4 ASO and cisplatin compared to control ASO and cisplatin treated group in vivo.
Conclusion: By transfection of ASOs targeting Annexin A4, platinum resistance have improved in vivo and in vitro, Annexin A4 have associated with efflux of platinum anti-tumor drug. In conclusion, antisense oligonucleotides for Annexin A4 will be a therapeutic option for ovarian clear cell carcinoma with chemoresistance to platinum antitumor drug.
Citation Format: Reisa Kakubari, Satoshi Nakagawa, Tadashi Iwamiya, Eiji Kobayashi, Shinnya Matsuzaki, Yutaka Ueda, Kiyoshi Yoshino, Yuya Kasahara, Satoshi Obika, Tadashi Kimura, Satoshi Serada, Tetsuji Naka, Minoru Fujimoto. Antisense oligo nucleotide of Annexin A4 improved platinum resistance in ovarian clear cell cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1397. doi:10.1158/1538-7445.AM2017-1397