DNA induced dimerization of a sulfhydryl surfactant in transfection agents studied by ESR spectroscopy

Synthetic vectors for gene delivery offer a wide variety of functional derivatization, which can be exploited to increase targeting and transfection efficacy. In this field, redox-sensitive agents based on the thiol/disulfide (-SH/-SS-) equilibrium are a class of promising transfectants. Here the thiol group content in lipoplexes formed by a triazine-based sulfhydryl surfactant (SH14) and a plasmid (pGEFP-N1) was probed by Electron Spin Resonance (ESR) of appropriately tailored nitroxides. By modelling the time decay of ESR intensity, details on the process of lipoplex formation were obtained. It was found that the concentration of available -SH groups depended on the contact time between SH14 and DNA, suggesting that lipoplex formation entailed disulfide bridge formation among SH14 molecules. This finding represents the first experimental evidence that the -SH/-SS- equilibrium plays a role in lipoplex formation when DNA is complexed by sulfhydryl-based transfecting agents, which may have profound influence on their mechanism of action.