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Abstract LB-231: Therapeutic targeting of multiple pancreatic tumor promoting-pathways in vivo: nanotherapeutic silencing of HuR

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL

HuR is an mRNA binding protein that is localized to the cytoplasm upon pancreatic cancer associated stressors. In normal cells, the HuR network is utilized to protect cells from harmful stimuli. In pancreatic cancer cells, HuR post-transcriptionally regulates core pathways involved in the tumorigenesis process, such as invasion and growth. We therefore hypothesized that silencing HuR may be detrimental to the growth and survival of pancreatic cancer cells. Thus, we designed a highly specific therapeutic strategy to suppress HuR expression in pancreatic cancer cells. We first transfected pancreatic cancer cell lines growing in culture to test a siRNA oligo designed to target HuR mRNA specifically. Efficiency of siRNA silencing of HuR in transfected cells was evaluated by immunoblot and qPCR assays. Anchorage-independent growth in soft agar (a hallmark of malignancy) of pancreatic cancer cells (MiaPaCa2, CAPAN1, and PL5 lines) transfected with HuR siRNA was evaluated 2–3 weeks post-transfection. Nanoparticle delivery of HuR siRNA into representative pancreatic cancer cell xenografts (MiaPaCa2 cells) in mice was used for pre-clinical analysis of this approach. Growth of HuR siRNA-treated mouse tumors was measured over a 2-week period and compared to the growth of tumors in control groups (PBS-treated and Luc siRNA-treated). HuR expression in resected tumors was measured by immunoblot analysis. The HuR siRNA oligo was highly efficient and specific. siRNA HuR transfection caused over a 96% reduction in HuR mRNA compared to control cells as detected by qPCR when RNA was extracted from pancreatic cancer cells after 48 hrs post-transfection. Accordingly, the amount of HuR protein was markedly decreased as accessed by immunoblot assays. Reduction in HuR expression caused a dramatic decrease in anchorage-independent growth in soft agar. In the pre-clinical studies, MiaPaca2 xenografts treated with HuR siRNA had a 1.6-fold increase in tumor volume after 4 intratumoral injections as compared to 2.8- and 3-fold increases in Luc siRNA- and PBS-treated control tumors, respectively. Statistical comparisons of growth between Luc siRNA and HuR siRNA treated mice include a p value of 0.009 at day 3; and a p value of 0.031 at day 17. HuR protein expression from the tumors treated with HuR siRNA-nanotherapy was significantly diminished compared to the control groups. Of note, mice treated with HuR siRNA were healthy and no noticeable toxicity was detected. In vitro, HuR reduction in pancreatic tumor cells caused a marked decrease in anchorage-independent growth in soft agar. Nanoparticle delivery of HuR siRNA to xenografts dramatically decreased the amount of HuR protein in tumors and significantly suppressed tumor growth. These are the first proof-of-principle data that silencing HuR in pancreatic tumors, even as a monotherapeutic strategy, may be a promising therapeutic approach.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-231. doi:10.1158/1538-7445.AM2011-LB-231