GEMINI BISPYRIDINIUM SURFACTANTS AS NONVIRAL VECTORS FOR GENE-DELIVERY

The interaction with model membrane, the formation of DNA nanoparticles and the transfection ability of a homologous series of bispyridinium diexadecyl cationic gemini surfactants, differing for the length of the alkyl spacer bridging the two pyridinium polar heads in 1,1’ position (P16-n with n =3, 4, 8, 12), has been studied by means of differential scanning calorimetry (DSC), atomic force microscopy ( AFM), electrophoresis mobility shift assay (EMSA) and transient transfection assays measurements. The results here presented show that their performance in gene delivery is strictly related to their structure in solution. For the first time the different transfection activity of the compounds can be explained by referring to their thermodynamic properties in solution, previously studied. The compound with spacer formed by four carbon atoms, showing unexpected enthalpic properties vs. concentration in solution, is the only one giving rise to a transfection activity comparable to that of the commercial reagent, when formulated with L-α-dioleylphosphatidylethanolamine (DOPE). We suggest that P16-4 behaves like molecular tongs able to grip basic group near each other, so allowing the formation of compact and near spherical DNA particles. The compound with the longest spacer gives rise to loosely condensed structures by forming a sort of bows, not able to give rise to transfection notwithstanding the double positive charge of the molecule. On the other hand, DSC measurements on synthetic membranes show that the compounds with the shortest spacer (3 and 4 methylene groups) practically do not interact with the 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) membrane, while the compounds P16-8 and, particularly, P16-12 induce the formation of surfactant-rich and surfactant-poor domains in the membrane, without showing any peculiarity for the compound P16-4. This could suggest that the mechanisms involved in the interaction with model membrane and in gene delivery are substantially different and could strike a blow for an endocytosis mechanism for the internalization in the cell of the DNA nanoparticles.