Abstract 2191: Multiple imaging reporter labeled acid-degradable dextran nanopolymer as a COX-2 siRNA carrier for COX-2 specific downregulation

Cyclooxygenase-2 (COX-2) as a target has attracted interest for multiple degenerative diseases and cancers. COX-2 siRNA provides specific and effective down-regulation of COX-2. However, because artificial cationic polymers can induce proinflammatory signals that increase COX-2 expression, there are few if any reports about the use of artificial cationic polymers as siRNA carrier to downregulate COX-2 in cancer cells. Here we developed a method to efficiently synthesize a multiple imaging reporter labeled biodegradable dextran to use as an efficient cationic polymer carrier for COX-2 siRNA delivery. Amine function groups were conjugated to the dextran platform through acetal bonds. Acetal bonds were broken at acidic conditions that occur in cancer and endocytosis compartments. Rhodamine was labeled to the amine groups to detect degradation and removal of these groups from the cell, while the dextran scaffold was labeled with Cy5.5. The rapid cleavage and release of amine groups minimized the proinflammatory side effects of the positively charged amine groups.Colorimetric assay of Cy5.5 and rhodamine in different pH buffer indicated that the amine group was cleaved at pH 5.5 buffer but was stable in pH 7.4 buffer. Fluorescence imaging showed that the dextran siRNA nanoplex entered the cells through endocytosis that provided acidic conditions for the breaking of the amine group. For the first time, the intracellular breaking of acetal bonds was clearly visualized by multiple imaging reporters. Because the rapid cleavage and release of amine groups minimized the proinflammatory side-effects, quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay indicated that this dextran COX-2 siRNA nanoplex could downregulate COX-2 expression efficiently. Prostaglandin E2 level decreased significantly with COX-2 siRNA/dextran treatment. In vivo imaging demonstrated that the COX-2 siRNA/dextran nanoplex accumulated in MDA-MB-231 tumors. QRT-PCR and western blot assays of COX-2 levels in tumor tissue demonstrated that this nanoplex significantly downregulated COX-2 expression in vivo efficiently and within 24h. This dextran nanopolymer can be used as a safe, reproducible, and biocompatible siRNA carrier to effectively reduce COX-2 expression in cancer cells and tumors. Citation Format: Zhihang Chen, Balaji Krishnamachary, Marie-France Penet, Zaver M. Bhujwalla. Multiple imaging reporter labeled acid-degradable dextran nanopolymer as a COX-2 siRNA carrier for COX-2 specific downregulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2191. doi:10.1158/1538-7445.AM2017-2191