Abstract 1961: Gaps in the armor: Targeting HuR to sensitize pancreatic cancer

Abstract

Abstract HuR is an RNA binding protein involved in a coordinated cellular response to stressors. Upon insults such as chemotherapy or radiation treatment, HuR translocates from the nucleus to the cytoplasm where it binds the 3'UTR of target mRNAs. HuR's interaction with target mRNAs leads to the upregulation of target genes and ultimately treatment resistance. This is particularly relevant in the case of pancreatic ductal adenocarcinoma (PDA). PDA is highly resistant to standard chemotherapy such as FOLFIRINOX or gemcitabine/nab-paclitaxel. Using a tumor microarray (TMA), we found 79% of patient tumor samples (n=70) were positive for active cytoplasmic HuR, while little to no cytoplasmic localization was detected in normal tissue. In addition, HuR CRISPR knockout cell lines have a xenograft lethal phenotype. Previously published data also demonstrated that reduction of HuR in xenografts with a DOX-inducible shRNA system caused a 3.6 fold decrease in tumor size. HuR reduction was also shown to potentiate a PARP-inhibitor (olaparib) treatment from a 5.6-fold reduction alone to 9.3-fold reduction in tumor size when combined with shHuR, demonstrating the role of HuR in drug resistance. The aim of our current study was: A) to target HuR directly using nanoparticle delivery of siRNA against HuR; and B) to use the FDA approved small molecule pyrvinium pamoate (PP) to inhibit HuR's translocation and sensitize PDA cells to concurrent therapies. Using 3DNA, a 60nm nanoparticle composed of a sphere of crosslinked DNA, we have successfully delivered siRNA against HuR in vivo utilizing targeting moieties against receptors known to be overexpressed on the surface of PDA cells: EGFR, folic acid receptor, and transferrin receptor. Bi-weekly IP treatment of siHuR bound to 3DNA was safe and effective at extending life in a xenograft model as indicated by Kaplan Meier analysis (p=0.01). We are currently testing siHuR-3DNA dendrimer therapy's ability to sensitize PDA cells to oxaliplatin or olaparib in vivo. We are also investigating the use of PP to target HuR's localization. PP has previously been shown in bladder cancer to inhibit the translocation of HuR in vitro and in vivo. We have reproduced this finding in PDA cells, and have shown impressive drug potency with IC50s as low as 38nM in 2D cultures and 16nM in a 3D mouse PDA organoid model. Combination index (CI) values determine drugs interactions where 1 is additive, <1 is synergistic and >1 is antagonistic. We have determined that PP can enhance therapies such as gemcitabine (CI of 0.55), olaparib (CI of 0.40) and palbociclib (CI of 0.37) in vitro, and are currently validating these findings in vivo. Taken together, our data demonstrate that HuR inhibition via 3DNA delivery of siHuR and/or PP treatment can sensitize PDA cells to chemotherapy and targeted therapies. By inhibiting a resistance driver (HuR) in pancreatic cancer we aim to improve current therapies for this devastating disease. Citation Format: Christopher W. Schultz, Kevin O'Hayer, Teena Dhir, Oloruntoba Bolaji, Kathryn M. Bormes, Samantha Z. Brown, Henry Thomsett, Saswati Chand, Aditi Jain, Wei Jiang, Grace McCarthy, Charles J. Yeo, Austin Goetz, Avinoam Nevler, Jonathan R. Brody, Jordan M. Winter, Ranjan Preet, Dan Dixon, Jessica Bowers, Kelly Rhodes, Robert Getts. Gaps in the armor: Targeting HuR to sensitize pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1961.