Protein-based drug delivery carrier has been one of the most employed modalities in biopharmaceuticals. In this study, we have compared avidin and its two analogues, neutravidin and streptavidin, as nanocarriers for the delivery of biotin-labeled siRNA with the help of biotinylated cholesterol (targeting ligand) and protamine (condensing agent). These proteins have similar binding affinity to biotin but substantial difference in their physical and chemical characteristics. Here, we have shown how these characteristics affect the size, cellular uptake, and activity of the avidin-based siRNA nanocomplex. In contrast to avidin and streptavidin nanocomplexes, neutravidin-based nanocomplex shows very low endosome entrapment and high cytoplasmic localization at extended times. High amount of the siRNA released in the cytoplasm by neutravidin-based nanocomplex at extended times (24 h) results in extensive and sustained PCBP2 gene silencing activity in HSC-T6 rat hepatic stellate cells. Neutravidin-based nanocomplex shows significantly low exocytosis in comparison to the streptavidin-based nanocomplex. Avidin-, neutravidin-, and streptavidin-based nanocomplexes are similar in size and had no significant cytotoxicity in transfected HSC-T6 cells or inflammatory cytokine induction in a whole blood assay. Compared to free siRNA, the neutravidin-based siRNA nanocomplex exhibits higher accumulation at 2 h in the liver of the rats with CCl4-induced liver fibrosis. Neutravidin has therefore been shown to be the most promising avidin analogue for the delivery of siRNA.
Keywords: avidin; biotin; conjugation; disulfide bond; liver fibrosis; nanocomplex; neutravidin; siRNA; streptavidin.