Abstract 473: PRKRA/PACT expression promotes chemoresistance in mucinous ovarian cancer
Authors: Hisamatsu Takeshi , McGuire Michael , Wu Sherry Y. , Rupaimoole Rajesha , Pradeep Sunila , Noh Kyunghee , Filant Justyna , Hansen Jean M. , Lyons Yasmin , Gharpure Kshipra M. , Nagaraja Archana S. , Mangala Lingegowda S. , Mitamura Takashi , Rodriguez-Aguayo Cristian , Bartholomeusz Geoffrey A. , Ivan Cristina , Lee Ju-Seong , Matsuo Koji , Frumovitz Michael , Wong Kwong K. , Lopez-Berestein Gabriel , Sood Anil K. 
Published: July 2017

Abstract
Purpose: To investigate the mechanisms of chemotherapy resistance and developing strategies to enhance therapeutic responses in mucinous ovarian cancer (MOC).
Experimental design: We carried out a kinome-based siRNA screen using human MOC to identify novel targets to enhance the efficacy of chemotherapy in MOC cell lines. In vitro and in vivo validation studies were carried out using MOC models. We specifically interrogated the role of PRKRA in MOC based on our screen results.
Results: Among the 939 genes in the screen, we focused on PRKRA/PACT because it was one of the top 5 target genes that exhibited the greatest extent of synthetic lethality in the target gene-siRNA plus oxaliplatin group relative to the target gene-siRNA group. The combination of oxaliplatin plus siPRKRA treatment resulted in significantly reduced cell viability compared with oxaliplatin plus control siRNA in RMUG-L-ip1 or RMUG-S-ip1 MOC cells (p&lt;0.001), while knockdown of PRKRA did not result in a significant change in cell viability compared with the control. We also observed a 2.1-fold increase in cell apoptosis in vitro after treatment with oxaliplatin plus siPRKRA in both MOC cells (p&lt;0.05). Using orthotopic mouse models of MOC, we observed an 88% reduction (p&lt;0.01) in tumor weight and 75% reduction in the number of tumor nodules (p&lt;0.01) in the siPRKRA plus oxaliplatin group compared with the control siRNA plus oxaliplatin group. PRKRA expression in human MOC was significantly higher relative to high-grade serous ovarian tumors as evaluated by immunohistochemistry. Furthermore, we found that the interaction between PACT and Dicer can regulate maturation of microRNA. In particular, mature-miR-515-3p was found to be inhibited by the interaction between PACT and Dicer. Expression of miR-515-3p promotes chemosensitivity in MOC by targeting the mRNA of the anti-apoptotic gene AXL.
Conclusion: The PRKRA/PACT axis represents an important therapeutic opportunity in MOC for enhancing oxaliplatin efficacy.
Citation Format: Takeshi Hisamatsu, Michael McGuire, Sherry Y. Wu, Rajesha Rupaimoole, Sunila Pradeep, Kyunghee Noh, Justyna Filant, Jean M. Hansen, Yasmin Lyons, Kshipra M. Gharpure, Archana S. Nagaraja, Lingegowda S. Mangala, Takashi Mitamura, Cristian Rodriguez-Aguayo, Geoffrey A. Bartholomeusz, Cristina Ivan, Ju-Seong Lee, Koji Matsuo, Michael Frumovitz, Kwong K. Wong, Gabriel Lopez-Berestein, Anil K. Sood. PRKRA/PACT expression promotes chemoresistance in mucinous ovarian 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 473. doi:10.1158/1538-7445.AM2017-473