Inclusion of the helper lipid dioleoyl-phosphatidylethanolamine in solid lipid nanoparticles inhibits their transfection efficiency

Solid lipid nanoparticles (SLNs) are a promising system for the delivery of lipophilic and hydrophilic drugs. They consist of a solid lipid core that is stabilized by a layer of surfactants. By the incorporation of cationic lipids in the formulation, positively charged SLNs can be generated, that are suitable carriers for nucleic acids (DNA, siRNA). Considering the beneficial effect of helper lipids on the transfection efficiency with cationic liposomes, the effect of the helper lipid 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) on transfection with cationic lipid-containing solid lipid nanoparticles was investigated in PC3 prostate cancer cells. The inclusion of DOPE in SLN formulations, instead of promoted, strongly inhibited SLN transfection efficiency, by frustrating the accommodation of DNA by the particles, as was revealed by biochemical analysis. SLNs devoid of DOPE maintained a homogenous size distribution of similar to 150 nm following lipoplex assembly and cellular delivery, and showed transfection efficiency comparable to that of Lipofectamine 2000 (R) (LF2k). Moreover, the SLNs maintain their high transfection efficiency after lyophilization and long-term storage (1-2 years), an important asset for biomedical applications. There is even the possibility to lyophilize the SLN carrier together with its DNA cargo, which represents an interesting pharmaceutical advantage of the SLN formulations over LF2k. These results reflect marked differences between the physicochemical properties of cationic liposomes and SLNs, the latter requiring more critical lipid-depending properties for effective 'packaging' of DNA but displaying a higher storage stability than cationic lipid based carriers like LF2k.