A comprehensive study in triblock copolymer membrane interaction

Poloxamers are triblock copolymers made of poly(ethylene glycol)-(poly(propylene glycol))-poly(ethylene glycol). They have been shown to enhance gene transfer in the muscle, and co-administration of polymers and DNA appeared to be crucial to obtain this effect. It is questionable then if some interaction occurs between polymers and DNA. Polymer interaction with membranes represents a second crucial point due to the central hydrophobic part of the triblock copolymers. Besides, the question of the polymer spanning or adsorbing to the surface has not been solved by now. We addressed these issues by means of sensitive techniques that allowed working in diluted conditions and gaining in comprehension of gene transfection. By means of simultaneous time-correlated single-photon counting and fluorescence correlation spectroscopy, we have shown that the diffusion time of a single DNA molecule and PicoGreen lifetime was not altered in the presence of the triblock copolymer L64. Polypropylene (glycol) interactions with dodecylphosphocholine micelles were shown to occur at a deep level by (1)H NMR using doxyl probes located at the head or the lipid extremity of the micelles. The polypropylene (glycol) also interacted with lipid bilayers in a manner dependent on the cholesterol content, as shown by differential scanning calorimetry using liposomes. This interaction destabilised the membrane and allowed the release of small molecules. Finally, molecular dynamic simulation of the copolymer L64 in the presence of dodecylphosphocholine showed that the hydrophobic core of the polymer formed an extremely tight cluster, whose dimensions excluded the possibility of polymer spanning across the lipidic micelles. The simulation positively correlated with the destabilising effect observed on the liposomal membrane models.