Albumin-mediated delivery of siRNA

Research output: Book/anthology/dissertation/reportPh.D. thesisResearch

  • Konrad Bienk
The recent development of protein, peptide and nucleotide therapeutics is an important step towards the successful treatment of many severe diseases caused by altered gene expression. Small interfering RNA (siRNA) can be used for regulation of cellular gene expression to revert pathologic states in autoimmune disorders, neurodegenerative disorders and cancer by specific gene silencing. The effective delivery of the therapeutic to target cells and tissues is currently a great challenge for successful siRNA therapy. In the bloodstream, free siRNA is rapidly cleared by renal excretion or degraded by serum nucleases. Development of protective carriers for active transport of siRNA is a promising strategy to utilize the potential of siRNA therapeutics. Synthetic carriers have been used but are recognized as foreign and susceptible to capture by the mononuclear phagocytic system and invoking an immune response. The human body, however, possesses several natural transport mechanisms for active transport of molecules. Amongst these is albumin, which is the most abundant plasma protein and has a circulatory half-life of ~21 days, partially due to engagement and recycling by the neonatal Fc receptor (FcRn). Albumin is present in plasma and most tissues, and transports fatty acids, bile salts, steroid hormones and other insoluble molecules. Exploitation of albumins interaction with the FcRn has been utilized by Novozymes Biopharma to modulate the circulatory half-life of albumin. Single amino acid substitutions have been used to create a range of albumin variants with FcRn affinity both
lower and higher than that of wild-type albumin. The aim of this project is to develop a siRNA carrier system utilizing albumin as a natural delivery
vehicle. Cholesteryl functionalized siRNA was designed to facilitate binding towards albumin. The binding affinity was shown to be dependent on position and number of modifications, and experiments suggested Fatty Acid site 5 as the binding site for the cholesteryl siRNA. In vitro experiments showed reduced serum degradation, increased stability of albumin/siRNA complexes for up to 72 hours in serum and reduced TNFα response towards albumin/siRNA complexes compared to naked siRNA in peripheral blood mononuclear cells (PBMCs). It was also demonstrated that albumin can help efficient annealing of highly hydrophobic siRNA. Furthermore, it was shown that, by preferentially modifying the SS, cholesteryl modifications do not compromise the ability of the siRNA to silence genes.
siRNA half-life and biodistribution studies revealed an increase in half-life from 12 minutes for naked,
to 45 and 72 minutes for single and double cholesteryl modified siRNA respectively, after formulation
with albumin. Furthermore, the experiments revealed a preferential accumulation of the 2-
cholesteryl siRNA in the liver after 6 hours. The finding of accumulation in the liver was utilized in
vivo to illustrate liver specific Factor VII silencing of ~30%, mediated only by albumin as a delivery
vehicle. This proof of concept silencing showed that siRNA can be used for therapeutic purposes
without the use of non-biocompatible polymer or lipid materials. This work, therefore, provides a
novel technology platform for the safe delivery of siRNA therapeutics.
Original languageEnglish
Number of pages127
Publication statusPublished - Oct 2015

    Research areas

  • albumin, siRNA, drug delivery, half-life extension

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