Abstract LB-B19: Re-sensitizing Pancreatic Cancer, targeted siRNA inhibition of HuR

Abstract

Abstract We have demonstrated that 3DNA nanocarriers can specifically, effectively, and safely deliver siRNA oligos targeted against a pro-survival hub, HuR (the ELAVL1 gene) in an in vivo, pre-clinical model of pancreatic cancer. Pancreatic cancer remains one of the deadliest cancers with an overall 5 year survival rate of 9%; and is on pace to become the second leading cause of cancer related deaths in the U.S. by 2020. Pancreatic cancer is so deadly, in part, because it is highly refractory to standard chemotherapeutics. In fact, new standard of care regiments such as FOLFIRINOX have only improved survival by a few months. Our previous work has established HuR as a target in pancreatic cancer. HuR is an RNA binding protein that is primarily retained in the nucleus, but upon exposure to cancer associated stressors translocates to the cytoplasm. In the cytoplasm, HuR functions to bind, stabilize, and up-regulate expression of pro-survival target mRNAs. CRISPR-mediated deletion of HuR causes a xenograft lethal phenotype in vivo and increases sensitivity to a variety of drugs, particularly PARP inhibitor therapy, enhancing Olaparib therapy over 20-fold in vitro. In an independent doxycycline inducible knockdown model, HuR depletion combined with Olaparib treatment resulted in a 9.3 fold (p<.001) decrease in tumor volume in vivo. Based on these findings and our previous published work, we have launched into a line of investigation attempting to target HuR in pancreatic cancer cells. We have delivered siHuR oligos tethered to 3DNA nanostructures (Genisphere, LLC) in a targeted fashion using either a folic acid targeting moiety, a transferrin receptor targeted antibody, or an EGFR targeted antibody (i.e., siHuR nanotherapy). Additionally, we are working to combine siHuR nanotherapy with conventional therapeutics. 3DNA nanocarriers are constructed using stable DNA strands assembled and crosslinked in a stepwise fashion, to create a layered nanoscaffold capable of attaching multiple different targeting moieties and deliverables. The siRNA oligos hybridized to the 3DNA were modified in order to withstand systemic RNases during treatment. We first validated the modified siHuR nanotherapy in vitro by evaluating protein and RNA levels of HuR. Second, we validated the expression of our intended targeting moieties in both human cell lines and a tissue microarray consisting of patient derived pancreatic cancer tumors. For the mouse studies, athymic female nude mice were injected with 4 million MIA PaCa-2 cells per flank, and randomized to treatment arms when tumors reached 100mm3. Mice were then treated intraperitoneally twice weekly with either siHuR or siControl nanotherapies (3ug siRNA per treatment) with one of the three targeting moieties. We demonstrated efficacy of systemic targeted delivery of siHuR nanotherapy which improved average overall survival by 35% (p=.012) compared to the control arm, with an increase in survival using a Kaplan-Meier survival analysis (p=.01). We are currently setting up treatments with siHuR nanotherapy in conjunction with a targeted treatment strategy, Olaparib, which has previously been shown to work in conjunction with dox-inducible HuR silencing (i.e.,shRNA targeting) in vivo. Herein, we describe the development of siHuR nanotherapy that, as a monotherapy or most likely with clinically available drugs, may improve outcomes for patients with pancreatic cancer. Citation Format: Chris W. Schultz, Kevin O'Hayer, Kathryn M. Bormes, Teena Dhir, Samantha Brown, Avinoam Nevlar, Saswati Chand, Henry Thomsett, Wei Jiang, Jessica Bowers, Kelly Rhodes, Michael Pishvaian, Robert Getts, Jonathan Brody. Re-sensitizing Pancreatic Cancer, targeted siRNA inhibition of HuR [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-B19.