DNA–METAFECTENE™ PRO complexation: a physical chemistry study

Complexes formed between cationic liposomes and DNA (also known as lipoplexes or genosomes) have proven, for years now, to be a suitable option for gene delivery to cells, transfection, however, some aspects regarding the liposome–DNA interaction mechanism and complex stability remain still unclear. This work aims to improve the understanding of the poorly defined mechanisms and structural conformation associated with the interaction of METAFECTENE™ PRO (MEP), a commercial liposomal transfection reagent, with poly-anion DNA at mass ratios around the mass ratio recommended for transfection (L/D ≅ 700). A physical chemistry characterization was conducted at a pH of 6.5 and at a temperature of 25 °C by means of dynamic light scattering (DLS), electrophoretic mobility (ζ-potential), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Five parameters important for transfection were determined for the lipoplexes: (i) the hydrodynamic radius, RH, (ii) the stability with time, (iii) the mass ratio of at which both moieties start to interact, (L/D)i, (iv) the overall charge, and (v) the morphology. Results in ensemble point to a “beads on a string” conformation, with the lipoplex formation occurring well below isoneutrality from (L/D)i ≅ 600. The lipoplexes were found to be stable within at least seven days presenting an average RH of 135 nm.