Abstract 3542: Inhibition of HuR effectively suppresses ovarian tumor growth in mice (2015)

Abstract Ovarian cancer is the most deadly gynecologic cancer. To address the clinical need for a more effective therapy than currently exists, this investigation focused on targeting a post-transcriptional (RNA to protein) regulatory RNA-binding protein, HuR (Human antigen R, aka ELAVL1). HuR regulates the expression of multiple genes known to function in tumor cell survival and in drug resistance. It is abundant and hyper-functional in ovarian cancer cells as compared to normal cells, thus providing a therapeutic window. We investigated the effect of inhibiting HuR expression in ovarian tumor cells in culture and in ovarian tumors in mice. We generated A2780 and OVCAR5 cells that constitutively express either shHuR or a control shRNA, and assayed cell proliferation and the ability of these cells to produce colonies in a soft agar. Cell proliferation in both shRNA-expressing cell lines was significantly reduced compared to control shRNA-expressing cells (19% and 11% in A2780 and OVCAR5, respectively; p&amp;lt;0.005). A2780-shRNA cells produced 65% fewer colonies in soft agar a compared to parental A2780 cells and control shRNA-expressing cells. To evaluate the effect of HuR suppression on tumor growth, C57BL/6 female mice were injected intraperitoneally with ID8-luc murine ovarian cancer cells; mice developed tumors throughout the peritoneal cavity. Approximately 4 weeks following cell injection, tumor-bearing mice were optically imaged to establish baseline biolumiscence, an indicator of ID8-luc-derived tumor load. A novel CpG-free DNA dendrimer vector, 3DNA, was derivatized with folate, aiming for tumor-targeted siHuR delivery upon systemic administration to mice. Mice were treated twice a week for four weeks (retro-orbital injection) with one of three 3DNA formulations or with 0.9% saline (n = 5-6/group). The 3DNA formulations were: 1) Folate-derivatized 3DNA/siHuR; 2) 3DNA/siHuR; and 3) Folate-derivatized 3DNA/control siRNA. Tumor response to treatment was assessed once a week by optical imaging. Using baseline tumor load as the comparator, tumor growth was suppressed ∼3-fold in mice treated for 4 weeks with folate-derivatized 3DNA/siHuR, the highest suppression of all treatment groups, including non-folate derivatized 3DNA/siHuR (p = 0.01), folate-derivatized 3DNA/control siRNA (p = 0.05), and 0.9% saline (p = 0.04). No overt toxicity was observed. A biodistribution study in which CY3-labeled folate-derivatized 3DNA was systemically administered resulted in very high fluorescence in ovarian tumors with little to no fluorescence in normal tissues, thus supporting the tumor-targeting potential of folate and the enhanced therapeutic effect observed in folate-derivatized 3DNA/siHuR treated mice. These results support further pursuit of HuR-targeted therapy as a complementary approach to current, active therapies for ovarian cancer for overcoming drug resistance and inhibiting tumor growth. Citation Format: Janet A. Sawicki, Yu-Hung Huang, Jonathan R. Brody, Robert C. Getts, Kelly Rhodes, Jackie Gerhart. Inhibition of HuR effectively suppresses ovarian tumor growth in mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3542. doi:10.1158/1538-7445.AM2015-3542