Gold-peptide nanoconjugate cellular uptake is modulated by serum proteins

Gold nanoparticles (Au NPs, 20 nm) were conjugated with two different cysteine-terminated peptides. Radio-ligand binding studies were conducted to characterize Au NP-peptide binding, suggesting both covalent and noncovalent interactions. The interactions of serum proteins with Au NP-peptide nanoconjugates were determined using gel electrophoresis and dynamic light scattering. Serum proteins rapidly bound the nanoconjugates (15 minutes). The cellular uptake of free peptides and nanoconjugates into mouse myogenic (Sol8) cells was investigated in the absence or presence of serum. In the absence of serum, peptides presented as nanoconjugates showed significantly higher intracellular fluorescence signals compared to those in the presence of serum (P < 0.05), suggesting that serum proteins inhibit Au NP-mediated peptide delivery. The cellular uptake of nanoconjugates was also confirmed using transmission electron microscopy. These data suggest that Au NP-peptide nanoconjugates are a useful platform for intracellular delivery of therapeutics. However, a deeper understanding of the mechanisms regulating their uptake and intracellular trafficking is needed.