Crosstalk of Nucleic Acid Mimics with Lipid Membranes: A Multifaceted Computational and Experimental Study

Nucleic acid mimics (NAMs) have demonstrated high potential as antibacterial drugs. However, very few studies have assessed their possible diffusion across the bacterial envelope. In this work, we studied NAMs' diffusion in lipid bilayer systems that mimic the bacterial outer membrane using molecular dynamics (MD) simulations. Additionally, we examined the interactions of a NAM sequence with lipid membranes and ascertained the partition constants (K_p) through MD and spectroscopic investigations. The NAM sequences were composed of locked nucleic acid (LNA) and 2'-O-methyl (2'-OMe) residues, whereas the membrane models were composed of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (POPG) phospholipids. The parametrization protocol followed was validated against literature data and demonstrated the reliability of our approach for simulating NAM sequences. Investigation into the interaction of the sequences with zwitterionic and anionic membranes revealed a preference for hydrogen bond formation with the anionic model over the zwitterionic one. Additionally, potential of mean force (PMF) calculations unveiled a lower free energy barrier for translocation across the zwitterionic bilayer model. Contrarily, the partition constants derived suggested a slightly higher partitioning within the anionic membrane, emphasizing a nuanced interplay of factors. Finally, spectroscopic partition measurements with liposomes presented challenges in quantifying the partition of NAMs due to minimal signal variations. However, a tendency for quenching in anionic vesicles suggested a potential, albeit small, partitioning effect that warrants further investigation. In summary, our study revealed that NAMs will not, in principle, be able to cross an intact bacterial outer membrane by passive diffusion.