Surface Physical Activity and Hydrophobicity of Designed Helical Peptide Amphiphiles Control Their Bioactivity and...

G(IIKK)₃I-NH₂ has been recently shown to be highly effective at killing bacteria and inhibiting cancer cell growth while remaining benign to normal host mammalian cells. The aim of this work is to evaluate how residue substitutions of Ala (A), Val (V), Glu (E), and Lys (K) for the N-terminal Gly (G) or C-terminal Ile (I) of G(IIKK)₃I-NH₂ affect the physiochemical properties and bioactivity of the variants. All substitutions caused the reduction of peptide hydrophobicity, while N-terminal substitutions had a less noticeable effect on the surface activity and helix-forming ability than C-terminal substitutions. N-terminal variants held potent anticancer activity but exhibited reduced hemolytic activity; these actions were related to the maintenance of their moderate surface pressures (12-16 mN m^-1), while their hydrophobicity was reduced. Thus, N-terminal substitutions enhanced the cell selectivity of the mutants relative to the control peptide G(IIKK)₃I-NH₂. In contrast, C-terminal variants exhibited lower anticancer activity and much lower hemolytic activity except for G(IIKK)₃V-NH₂. These features were correlated well with their lower surface pressures (≤10 mN m^-1) and decreased hydrophobicity. In spite of its very low helical content, the C-terminal variant G(IIKK)₃V-NH₂ still displayed potent anticancer activity while retaining high hemolytic activity as well, again correlating well with its relatively high surface pressure and hydrophobicity. These results together indicated that surface activity governs the anticancer activity of the peptides, but hydrophobicity influences their hemolytic activity. In contrast, helicity appears to be poorly correlated to their bioactivity. This work has demonstrated that N-terminal modifications provide a useful strategy to optimize the anticancer activity of helical anticancer peptides (ACPs) against its potential toxicity to mammalian host cells.