Multifunctional self-assembled cationic peptide nanostructures efficiently carry plasmid DNA in vitro and exhibit antimicrobial activity with minimal toxicity.

In this study, a modified dehydropeptide, Boc-FΔF-εAhx-OH, was conjugated with an aminoglycoside antibiotic, neomycin, to construct a multifunctional conjugate, Pep-Neo. The amphiphilic conjugate (Pep-Neo) was able to self-assemble into cationic nanostructures in an aqueous solution at low concentrations. Nanostructure formation was evidenced by TEM and dynamic light scattering analyses. The average hydrodynamic diameter of the self-assembled Pep-Neo nanostructures was found to be ∼279 nm with a zeta potential of +28 mV. The formation of nanostructures with a hydrophobic core and cationic hydrophilic shell resulted in an increased local concentration of cationic charge (ca. in 50% aqueous methanol, i.e. disassembled structure, zeta potential decreased to +17.6 mV), leading to efficient interactions with negatively charged plasmid DNA (pDNA). The size and zeta potential of the resulting Pep-Neo/pDNA complex were found to be ∼154 nm and +19.4 mV, respectively. Having been characterized by physicochemical techniques, the complex was evaluated for its toxicity and ability to deliver nucleic acid therapeutics. The flow cytometry results on MCF-7 cells revealed that Pep-Neo/pDNA complex transfected ∼27% cells at a w/w ratio of 66.6 while the standard transfection reagent, Lipofectamine, could transfect only ∼15% cells. MTT and hemolysis assays showed the non-toxic nature of the projected conjugate at various concentrations. Further, these nanostructures were shown to encapsulate hydrophobic drugs in the core. Finally, Pep-Neo nanostructures showed efficient antibacterial activity against different strains of Gram-positive and -negative bacteria. Interestingly, unlike neomycin, which is highly effective against Gram-negative bacteria, these nanostructures showed considerably high efficiency against Gram-positive strains, highlighting the promising potential of these nanostructures for various biomedical applications.