Chemical details on nucleolipid supramolecular architecture: molecular modeling and physicochemical studies

Nucleolipids are currently under investigation as vectors for oligonucleotides (ON) delivery thanks to their supramolecular organization properties and their ability to develop specific interactions (i.e., stacking and potential Watson and Crick hydrogen bonds) for lipoplexes formation. To investigate the factors that govern the interaction events at a molecular level and optimize nucleolipid chemical structures, physicochemical experiments (tensiometry, AFM, BAM, and ellipsometry) combined with molecular dynamics simulation were performed on a series of zwitterionic nucleolipids (PUPC, DPUPC, PAPC) featuring a phosphocholine chain (PC). After construction and initial equilibration, simulations of pure nucleolipid bilayers were run for 100 ns at constant temperature and pressure, and their properties were compared to experimental data and to natural dipalmitoylphosphatidylcholine (DPPC) bilayers. Nucleolipid-based membranes are significantly more ordered and compact than DPPC bilayers mainly due to the presence of many intermolecular interactions between nucleoside polar heads. The hydrophilic phosphocholine moieties connected to the 5' hydroxyls are located above the bilayers, penalizing nucleic bases accessibility for further interactions with ON. Hence, a neutral nucleolipid (PUOH) without hydrophilic phosphocholine was inserted in the membranes. Simulations and experimental analysis of nucleolipid membranes in interaction with a single strand RNA structure indicate that PUOH interacts with ON in the subphase. This study demonstrates that molecular modeling can be used to determine the interactions between oligonucleotide and nucleolipids.