Targeting Tumor-Associated Hypoxia To Overcome Chemoresistance In Pancreatic Ductal Adenocarcinoma (Pda)

Abstract Background: PDA will become the 2nd leading cause of cancer-related mortality in the US by 2020. A recent Phase III randomized controlled trial revealed a 4 month overall survival benefit in metastatic PDA with FOLFIRINOX (Folinic acid, 5-Fluorouracil (5FU), Irinotecan, and Oxaliplatin) compared to gemcitabine, the standard of care. However, the long-term clinical efficacy of FOLFIRINOX and other chemotherapy regimens are limited by tumor-associated drug resistance driven by factors in the tumor microenvironment (e.g., hypoxia). We identified a novel drug resistance mechanism driven by the hypoxia-inducible pro-oncogenic kinase PIM1 and regulated by the RNA binding protein HuR. Herein, we launched into developing a strategy to target this tractable mechanism in an effort to optimize current therapeutic treatments for PDA. Methods: To model hypoxia, PDA cells were incubated in 1% O2 and responses to 5FU or oxaliplatin assessed to obtain IC50 doses. Stabilizing interactions between the RNA-binding protein HuR and PIM1 mRNA were quantified in vitro through binding assays, and confirmed in patients by immunohistochemistry in resected PDAs (n = 44). The contribution of HuR-mediated regulation of PIM1 to resistance to 5FU or oxaliplatin in hypoxia was examined using MS-444 (Novartis), a low-molecular-weight HuR inhibitor. Results: In response to hypoxia, HuR translocates from the nucleus to the cytoplasm where it binds and stabilizes the PIM1 mRNA transcript, thus amplifying PIM1 translation and protein expression. Clinically, we identified a positive correlation (p = 0.011) between cytoplasmic HuR and PIM1 protein expression in a cohort of PDA patients from our institution. In vitro mechanistic studies demonstrated that hypoxia-mediated induction of PIM1 overexpression enhanced DNA repair and evaded the apoptotic response elicited by hypoxic stress. Targeted inhibition of HuR by the HuR inhibitor MS-444 abrogated hypoxia-induced PIM1 overexpression, enhancing PDA cell sensitivity to oxaliplatin and 5FU (P<0.001). Conclusion: The mRNA-stability factor HuR post-transcriptionally induces PIM1 expression under hypoxic conditions, and thereby promotes hypoxia-induced chemoresistance. Ongoing pre-clinical studies will evaluate pharmacologic inhibition of HuR's regulation of PIM1 (e.g., MS-444) as a novel modality to enhance the therapeutic value of FOLFIRINOX for the treatment of metastatic PDA. Citation Format: Fernando F. Blanco, Masaya Jimbo, Liz Enyenihi, Nicole Meisner-Kober, Eric Londin, Isidore Rigoutsos, Makarand Risbud, Peter McCue, Charles Yeo, Jordan Winter, Jonathan R. Brody. Targeting tumor-associated hypoxia to overcome chemoresistance in pancreatic ductal adenocarcinoma (PDA). [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 2113. doi:10.1158/1538-7445.AM2015-2113