The roles of fatty acid modification in the activity of anticancer peptide of R-lycosin-I.

We previously reported that R-lycosin-I, modified by amino acid substitution from lycosin-I, was a peptide with anticancer activity and a linear amphipathic alpha-helix conformation and that it can induce cancer cell apoptosis and inhibit cell proliferation. However, the anticancer activity of R-lycosin-I was not highly improved. In order to further improve the anticancer activity of R-lycosin-I, fatty acids with different chain lengths from 12 to 20 carbons were introduced to the N-terminal of R-lycosin-I to yield five lipopeptides (R-C-12, R-C-14, R-C-16, R-C-18, R-C-20). The physicochemical properties of the five lipopeptides were determined by hydrodynamic size, zeta-potential, and circular dichroism spectroscopy, respectively. Then, the cytotoxic activity of these lipopeptides in A549 cells was evaluated with serum-containing and serum-free media, respectively, showing their anticancer activities were all increased through fatty-acid modification. This may be a result of the increased hydrophobicity and the enhanced interaction with the cancer cell membrane. The cytotoxic activity of R-C-16 was 3-4-fold higher than that of the original R-lycosin-I and also was the strongest among all five lipopeptides, whether in serum or serum free conditions. Compared with R-lycosin-I, the lactate dehydrogenase (LDH) leakage assay and scanning electron microscopy (SEM) indicated that R-C-16 had a weakly destructive effect on the cancer cell membrane, but it might cause apoptosis to exert an anticancer activity. Finally, the impacts of fatty-acid length on the physicochemical properties and the anticancer potential of peptide were discussed. Our data consolidate work on fatty-acid-modified anticancer peptides.