Effect of Poly(ethylene glycol) Spacer on Peptide-Decorated Hepatocellular Carcinoma-Targeted Lipoplexes In Vitro

Hepatocellular carcinoma (HCC) is a leading cause of cancer related deaths and is particularly prevalent in regions where Hepatitis B is highly endemic. Classical treatment options are largely limited to surgical measures and transcatheter chemoembolization. However biopanning of phage display libraries has identified very selective HCC-targeting peptides, which may be tethered to cationic liposomes for non-viral delivery of therapeutic DNA to affected cells thus providing a foundation for the development of new gene therapy treatment approaches. In this investigation, a cysteinylated HCC-tropic peptide has been linked directly to cationic liposomes, containing the cytofectin 3β-[N-(N',N'-dimethlaminopropylamino)-carbamoyl]-cholestero (Chol-T) and dioleolphosphatidyl ethanolamine, via a novel membrane-embedded maleimido cholesteryl derivative 3-[N-(hydrazino-y-maleimidobutyryl)-carbamoyl] cholesterol (Chol-Mal), or with an intervening poly(ethylene glycol) spacer element. The effect that inclusion of the hydrophilic polymer has on targeted lipoplex-mediated gene delivery in the human HCC cell line HepG2 has been investigated. Results show that both systems bind DNA and transfect this cell line with equal efficiency, while transgene expression levels in human embryo kidney cells HEK293 were low and comparable to those achieved in competition assays in HepG2 cells and by lipoplexes decorated with scrambled peptides. Although inclusion of poly(ethylene glycol) in formulations should be considered for in vivo studies, we show here that it offers no advantage in this application in vitro.