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

Abstract

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.