Structure-activity Relationships And Synergistic Activities Of Antimicrobial Peptides With Different Structural Features

So far, Several antimicrobial peptides (CAPs) are in clinical trial,. exhibited the highest activity against varieties of tumor cells, the Gram-negative, the Gram-positive bacteria and the fungi. But, there are multiple barriers to overcome, First most of antimicrobial peptides are mainly for topical use, because in the presence of complex fluids such as plasma, serum, saliva and sputum, they display a significant reduction in their antibacterial potency. In addition, there are many problems specific for antimicrobial peptides such as low therapeutic indices in vivo, short circulating half-life due to protease digestion and rapid kidney clearance and certain cytotoxicity. so designing the antimicrobial peptides with potent activity against varieties of tumor cells and low hemolytic activity are our target.In order to investigate the influence of the Leucine, Lysine, Ahx, especially the Proline residues on the synergistic activities and antitumor activities, we designed and synthesized five peptides with 25-amino acid by connecting the MP and Anoplin (AM-1, AM-2, AM-3, AM-4 and AM-5), the Leucine, Lysine, Ahx and Proline residues as the linkers. These antimicrobial peptides different in hydrophobic, amphiphilic, a-helix content, extension in space and charge, So as to select the antimicrobial peptides with potent anti-tumor activities and lower hemolysis. Their sequences are in follow: MP:Ile-Asn-Leu-Lys-Ala-Leu-Ala-Ala-Leu-Ala-Lys-Lys-Ile-Leu-NH2 Anoplin:Gly-Leu-Leu-Lys-Arg-Ile-Lys-Thr-Leu-Leu-NH2 AM-1:Gly-Leu-Leu-Lys-Arg-Ile-Lys-Thr-Leu-Leu-Lys-Ile-Asn-Leu-Lys-Ala-Leu-Ala-Ala-Leu-Ala-Lys-Lys-Ile-Leu-NH2 AM-2:Gly-Leu-Leu-Lys-Arg-Ile-Lys-Thr-Leu-Leu-Pro-Ile-Asn-Leu-Lys-AIa-Leu-Ala-Ala-Leu-Ala-Lys-Lys-Ile-Leu-NH2 AM-3:Gly-Leu-Leu-Lys-Arg-Ile-Lys-Thr-Leu-Leu-Ahx-Ile-Asn-Leu-Lys-Ala-Leu-Ala-Ala-Leu-Ala-Lys-Lys-Ile-Leu-NH2 AM-4:Ile-Asn-Leu-Lys-Ala-Leu-Ala-Ala-Leu-Ala-Lys-Lys-Ile-Leu-Pro-Gly-Leu-Leu-Lys-Arg-Ile-Lys-Thr-Leu-Leu-NH2 AM-5:Gly-Leu-Leu-Lys-Arg-Ile-Lys-Thr-Leu-Leu-Leu-Ile-Asn-Leu-Lys-Ala-Leu-Ala-Ala-Leu-Ala-Lys-Lys-Ile-Leu-NH2The results indicates that, compared with MP and Anoplin, AM-1, AM-2, AM-3, AM-4 and AM-5 not only have exhibited the higher activity against tumor cells such as HEPG-2, Hela and MDA in vitro, their IC50 are all lower than MP and Anoplin, but also have selective toxicity to normal cells (NIH-3T3). In addition, the hemolytic activity of the five peptides are stronger than MP and Anoplin, which may be depended on the insertion of proline residues in the center of peptide chain and increase of the the charge and the hydrophobic. Compared with AM-5, AM-2 has the higher activity against tumor cells and lower hemolytic activity, So the insertion of proline in the center of peptide chain may be a feasible strategy to improve the antitumor activities, selective activities and synergistic activities.The relationship between anti-tumor activity and selective toxicity of antimicrobial peptides, we have not yet understood. Although some of the antimicrobial peptides in the hemolytic activity and selective toxicity are unsatisfactory, but as examples of success and failure, these give us the valuable experience benfits for us to design the better target peptides.