Composite liposome-PEI/nucleic acid lipopolyplexes for safe and efficient gene delivery and gene knockdown

Cytotoxicity is a major drawback impeding the therapeutic use of gene delivery and gene down-regulation vehicles. Apart from cytotoxicity, rapid degradation and low cellular uptake are other major factors affecting therapeutic use. Considering the above factors, formulation and development of PEI (Polyethylenimine) based, liposome encapsulated delivery vehicles with improved transfection efficiency and low cytotoxicity which can be used for gene delivery and gene knockdown. DOPE (1,2-Dioleoyl-sn-glycero-3-phosphoethanolamine), DPPC (Dipalmitoylphosphatidylcholine) and cholesterol have been considered as lipids of choice bearing in mind various factors such as rigidness and surface charge which greatly influence the formation of liposomes, polyplex encapsulation and transfection efficiency. For the condensation of plasmid DNA (pDNA) and short interfering RNA (siRNA), branched PEI 25kDa (bPEI) and deacylated linear PEI 22kDa (lPEI) were employed. lPEI and siRNA polyplexes encapsulated within DOPE/DPPC/Cholesterol (DDC) liposomes exhibited higher luc (luciferase) gene knockdown in vitro compared to the controls. They also showed superior transfection efficiencies compared to polyplexes in experiments using pCMV-luc (luciferase reporter plasmid) and pEGFP-N1 (Green Fluorescence protein reporter plasmid). This can partly be attributed to the improved integrity imparted by the liposomal layer which was confirmed by complex stability and integrity assays. Cytotoxicity and coagulation time assays of DDC-lPEI based lipopolyplexes showed decreased cytotoxic potential and negligible influence on coagulation respectively for compared to polyplexes, thus rendering them suitable for gene therapy.