A Novel Method to Efficiently Synthesize a Biodegradable Dextran to Use as an Efficient Cationic Nanopolymer Carrier for siRNA Delivery

Unmet Need
In theory, RNA interference (RNAi) can be used to decrease expression of any gene driving a disease or pathology, but has seen limited clinical usage as gene therapy due to technical issues, i.e., small interfering RNA (siRNA) cannot enter cells efficiently due to their weight and charge. As such, a carrier molecule is needed to bring siRNA into the cell. Unfortunately, there is a lack of suitable carriers to deliver siRNA. For example, cationic polymers, polysaccharides and dextran have been considered as potential carriers because siRNA may be attached by electrostatic interactions or covalent conjugation. To date, a number of possible carrier molecule types have demonstrated varying levels of success. An ideal transmission vector for siRNA delivery should protect siRNA from degradation, increase siRNA to the target and facilitate its cellular uptake and subsequent release.
 
Technology Overview
Hopkins researchers discovered a novel method to efficiently synthesize a biodegradable dextran to use as an efficient cationic nanopolymer carrier for siRNA delivery. Small molecules containing amine groups were conjugated to a dextran scaffold through acetal bonds. The dextran carrier is taken up by the cell where acidic conditions in endocytic cellular compartments will cause the acetal bonds to break, releasing its siRNA, imaging or labeling agents (e.g., rhodamine, Cy5.5), from the amine group on the naturally biodegradable dextran carrier.
 
Using this novel synthesis process, Hopkins scientists attached siRNA and labeled dextran amine groups with the two different imaging agents. Data demonstrated that the dextran carrier was taken into the cells by endocytosis, whose acidic environment broke the bonds of the acetal group, releasing the siRNA, rhodamine-labeled amine groups and the Cy5.5-labeled from the dextran platform. The rapid cleavage and release of amine groups minimized the proinflammatory side effects of the positively charged amine groups. Altogether, this novel synthesis methodology demonstrated the ability to modify the dextran scaffold with a variety of functional groups such as imaging reporters and therapeutic moieties, but avoids crosslinking the dextran scaffold.
 
Stage of Development
Hopkins researchers were able to confirm the results by colorimetric assay, NMR spectroscopy and gel permeation chromatography. Fluorescence imaging showed that the dextran siRNA nanoplex entered the cells through endocytosis and was able to effectively deliver cyclooxygenase-2 (COX-2) siRNA. The qRT-PCR assay showed that the COX2 siRNA/dextran nanoplex downregulated COX-2 expression efficiently. COX-2 siRNA/dextran treatment decreased prostaglandin E2 levels significantly. It was also demonstrated that the treatment can accumulate in tumors. qRT-PCR and Western blot assays showed the nanoplex significantly decreased COX-2 expression in mouse tumor tissue.
 
Publications
Chen Z et al. Acid-degradable Dextran as an Image Guided siRNA Carrier for COX-2 Downregulation. Theranostics. 2018; 8(1):1-12.
 

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