Abstract 1406: Evoking potent RNAi response using novel 2′-OMe-phosphorodithioated modified siRNAs

Abstract

Abstract Improving small interfering RNA (siRNA) efficacy in target cell populations remains a critical challenge to bringing siRNA therapy into the clinic. There is currently an unmet need to develop a reliable strategy to globally enhance siRNA stability and potency. Here, we report a novel chemical modification, consisting of phosphorodithioate (PS2) and 2′-O-Methyl (2′-OMe) MePS2 on a single nucleotide, that significantly enhances potency and resistance to nuclease degradation for a variety of siRNA sequences. We show a 3.5-fold improvement in gene silencing in tumors following systemic delivery of MePS2-modified siRNAs using DOPC nanoliposomes compared to unmodified counterparts. We found that this enhanced potency stems from an unforeseen increase in loading of siRNAs to the RNA-induced silencing complex (RISC), likely due to the unique interaction between 2′-OMe and PS2 moieties. We subsequently demonstrate the therapeutic utility of MePS2 siRNAs in orthotopic mouse models of chemoresistant ovarian cancer, focusing on targeting GRAM domain containing 1B (GRAMD1B), a protein whose role in taxane resistance is first reported here. Efficient silencing of GRAMD1B (>80%) was achieved in tumors following systemic delivery of these MePS2-modified siRNAs and a synergistic anti-tumor effect was observed when combined with paclitaxel treatment. Given that limited success has been achieved thus far toward broadly enhancing siRNA potency with chemically modified siRNAs, our finding represents an important step forward in bringing siRNA therapeutics into the clinic. Citation Format: Sherry Wu, Xianbin Yang, Martin Egli, Kshipra Ghaupure, Hiroto Hatakeyama, Michael McGuire, Rajesha Rupaimoole, Takahito Miyake, Morgan Taylor, Sunila Pradeep, Archana Nagaraja, Malgorzata Sierant, Richa Singhania, Cristian Rodriguez-Aguayo, Nigel McMillan, Gabriel Lopez-Berestein, Prahlad Ram, Barbara Nawrot, Anil K. Sood. Evoking potent RNAi response using novel 2′-OMe-phosphorodithioated modified siRNAs. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1406. doi:10.1158/1538-7445.AM2014-1406