Nanomedicines for Systemic Delivery of RNAi Therapeutics - RNA Interference from Biology to Therapeutics - page 133

Antibody-protamine fusion carriers (Fig. 6.2e ) are a promising approach for
systemic siRNA delivery. Protamines are relatively small (5-8 kDa) and highly
basic proteins composed of 55-79% arginine residues [ 66 ] . Positively charged
protamine interacts with the negatively charged siRNAs to stabilise, neutralise and
condense the siRNAs. ErbB2-protamine fusion protein in complex with siRNA
significantly inhibited growth of breast cancer cells [ 67 ] .
Different formulations of targeted cationic liposomes served for selective target-
ing of hepatic stellate cells, which are the major cell population involved in the
formation of scar tissue in response to liver damage such as fibrosis or solid tumours.
Stellate cells express receptors for retinol binding protein, which efficiently uptake
vitamin A. Taking advantage of this physiological condition, injection of cationic
liposomes coupled to vitamin A and complexed with siRNA to a murine key
fibrogenesis factor (gp46) into cirrhotic mice silenced the speci fi c gene in mouse liver
and resolved fi brosis [ 68 ] . 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP)
liposomes encapsulating HER2-siRNA and containing endosomolytic histidine-
lysine peptides and a single-chain antibody fragment targeting transferrin receptors
coupled to the liposomes' surface have been targeted to tumour xenograft and inhib-
ited its growth [ 69 ] (Fig. 6.2h ). Anisamide-PEG-Liposomes-Polycation-DNA (anis-
amide-PEG-LPDs) are unilamellar cationic liposomes coated with PEG-linked
anisamide (a small-molecule compound that binds to sigma receptors) on their sur-
face, and protamine-condensed mixture of siRNA and a carrier calf thymus DNA in
the core. Encapsulating EGFR-siRNA, anisamide-PEG-LPDs injected intrave-
nously into tumour-bearing mice have been shown to increase sensitivity to chemo-
therapy [ 70 ]. These particles induced a significant increase in serum cytokine levels
that limits the potential for clinical translation. However, it is important to note that
cytokine response is not always deleterious with therapy and there are cases when
immune activation could enhance the therapeutic effects [ 71 ] .

6.4.3 Targeted Nanomedicines for Leukocytes

Utilising siRNAs to manipulate gene expression in leucocytes holds great promise
for drug discovery, as well as for facilitating the development of new therapeutic
platforms for leucocyte-implicated diseases such as inflammation, blood cancers
and leucocyte-tropic viral infections. However, due to their resistance to conven-
tional transfection methods and the fact that they are dispersed throughout the body,
systemic delivery to leucocytes remains a challenge, although several promising
approaches have been documented from 2007.
Kortylewski et al. [ 72 ] used siRNA synthetically linked to a CpG oligonucle-
otide agonist of toll-like receptor (TLR) 9 for targeting myeloid cells and B cells
(both are key components of tumour microenvironment) that express this receptor.
These particles simultaneously silenced STAT3 by siRNA and activated TLRs
responses by their agonists. Consequently, they effectively shifted the tumour
microenvironment from pro-oncogenic to anti-oncogenic (by causing activation of
tumour-associated immune cells and potent anti-tumour immune responses).