Efficient and Tumor Targeted siRNA Delivery by Polyethylenimine-graft-polycaprolactone-block-poly(ethylene glycol)-folate (PEI–PCL–PEG–Fol)

Abstract

Efficient delivery of functional nucleic acids into specific cells or tissues is still a challenge for gene therapy and largely depends on targeted delivery strategies. The folate receptor (FR) is known to be overexpressed extracellularly on a variety of human cancers and is therefore an outstanding gate for tumor-targeted Trojan horse-like delivery of therapeutics. In this study, an amphiphilic and biodegradable ternary copolymer conjugated with folate as ligand, polyethylenimine-graft-polycaprolactone-block-poly(ethylene glycol)-folate (PEI-PCL-PEG-Fol) was synthesized and evaluated for targeted siRNA delivery via folate-FR recognition. The amphiphilic character of similar polymers was shown previously to support endosomal release of endocytosed nanocarriers and to promote formation of long circulating micelles. The obtained PEI-PCL-PEG-Fol exhibited less cytotoxicity in comparison with the corresponding ternary copolymer without folate (PEI-PCL-PEG) and with unmodified PEI25kDa. Stable micelle-like polyplexes with hydrodynamic diameters about 100 nm were found to have a zeta potential of +8.6 mV, which was lower than that of micelleplexes without folate-conjugation (+13-16 mV). Nonetheless, increased cellular uptake and in vitro gene knockdown of PEI-PCL-PEG-Fol/siRNA micelleplexes were observed in SKOV-3 cells, an FR overexpressing cell line, in comparison with the nonfolate-conjugated ones. Moreover, PEI-PCL-PEG-Fol/siRNA micelleplexes exhibited excellent stability in vivo during the analysis of 120 min and a longer circulation half life than hyPEI25kDa/siRNA polyplexes. Most interestingly, the targeted delivery system yielded 17% deposition of the i.v. injected siRNA per gram in the tumor after 24 h due to the effective folate targeting and the prolonged circulation.

Revisiting the value of competition assays in folate receptor-mediated drug delivery

“…Therefore, SKOV-3 cells were utilized in all in vitro experiments to be consistent with previously published results. (21, 22)…”

“…al., while their polyplexes were shown to be able to be inhibited with low excess amounts of FA added to the system, these micelles demonstrated within this manuscript carry more FA on the surface. (21) This discrepancy can therefore be explained by the difference in valency which determines the affinity and avidity with the receptor and the ability of these multivalent nanoparticles to be displaced by a monovalent ligand or not. Similar observations have been reported not only in vitro , but even in vivo .…”

“…(17-20) Additionally, when this PEI-PCL-PEG platform was further modified with a folic acid targeting moiety, the self-assembling nanoparticles can selectively target and deliver siRNA to cancer cells which over-express FRα. (21, 22)…”

Tumoral gene silencing by receptor-targeted combinatorial siRNA polyplexes

“…In recent years, great efforts have been made in the development of various siRNA carriers. Polymeric materials [5][6][7][8][9][10][11][12][13][14][15][16][17], liposomes [18,19], inorganic platforms [20] and hybrid systems [21][22][23][24] all showed their potential [25]. However, systemic delivery of siRNA directed to the tumor site remains a major limitation.…”

In vitro and in vivo delivery of siRNA via VIPER polymer system to lung cells

“…siRNA has long been proposed as a highly selective approach of disease treatment due to its ability to potentially knock down any gene of interest involved in disease development or progression, [11] and is therefore an attractive alternative to conventional cancer therapy. [12] Although plasmid DNA and siRNA are both comprised of synthetic nucleic acids, the two molecules differ greatly.…”