Building a Simple Platform for Tailoring Peptide Surface Chemistry to Enhance Cellular Uptake of Polymer-Coated Gold Nanoparticles

Nanotherapeutic delivery requires particulate systems composed of only a few components yet featuring multiple capabilities to reach the clinic. In this study, we built a platform based on selective reactions (solid-phase peptide synthesis, peptide coupling chemistry, and click chemistry) to enhance cellular uptake of gold nanoparticles (AuNPs) by anchoring cell-penetrating peptides (CPPs) at the outermost layer of the constructs. Model amphipathic peptide (MAP), trans-acting activator of transcription (TAT), hexarginine (R₆), and arginine monomer (Arg) were attached to the surface of AuNPs synthesized directly by using branched polyethylenimine (BPEI) polyelectrolyte. From a different perspective, a water-soluble CGSWQWRR sequence capable of promoting the reduction of auric species and steric stabilization of gold colloids was also synthesized. The structure and dynamics of particles were characterized using imaging, scattering, and spectroscopy techniques, and their biological performance was evaluated by assessing cell viability and cellular uptake. The nanoconstructs were noncytotoxic up to 1.0 ppm in the case of CPP-BPEI@AuNPs (5.2 nm metallic core) or up to 10 ppm for CGSWQWRR@AuNPs (30 nm metallic core). Those featuring CPPs at the surface were internalized faster and to a higher extent (∼40% in 4 h) compared to the precursor (∼20% in 4 h). The highest cellular uptake was found for CGSWQWRR@AuNPs (∼75% in 4 h), which mediated the membrane-wrapping process more effectively and was prepared by the easiest protocol (one-pot, two-reactant, no workup reaction in aqueous media). The findings of this study simplify nanoparticle manufacturing, thereby reducing the gap between chemical synthesis and clinical applications.