Studies On Anticancer Activity Of Alpha-helical Peptides Against Different Tumor Cells

In the present study, the 26-residue amphipathicα-helical antitumor peptide V13K Ac-KWKSFLKTFKSAKKTVLHTALKAISS-amide (peptide P) was utilized as the framework to study the effects of peptide hydrophobicity of cationic anticancer peptides. Hydrophobicity was systematically decreased or increased by replacing leucine residues with less hydrophobic alanine residues or replacing alanine residues with more hydrophobic leucine residues on the nonpolar face of the helix, respectively. Hydrophobicity of the nonpolar face of the amphipathic helix was demonstrated to correlate with peptide helicity (measured by circular dichroism spectroscopy) and self-associating ability (measured by reversed-phase high-performance liquid chromatography temperature profiling) in aqueous environments. Higher hydrophobicity was correlated with stronger hemolytic activity. Peptide self association (i.e., the ability to dimerize) in aqueous solutions is a very important parameter to understand anticancer activity. If the self association ability of a peptide is too strong in aqueous media, it could affect the ability of the peptide to dissociate, interact with the cell surface and penetrate into the cytoplasmic membrane to kill cancer cells. The circular dichroism (CD) spectra revealed that the peptides had negligible helical structure in aqueous solution and could be induced into highα-helical structure in a mimic of membrane environment. Both of the helical structure ability of the peptides in aqueous solution and mimic of membrane environment are correlated with the peptide hydrophobicity, which is indicated that the peptides were induced into helical structure when reached the membrane surface, and then partitioned into the hydrophobic component of the membrane lipid.The 26-residue amphipathicα-helical cationic antitumor peptide V13K (peptide P) with high antimicrobial activity of broad spectrum, and negligible hemolytic activity. In the present study, we research the anticancer activity of peptide P and its analogs. To investigate whether peptide P and its analogs induce a loss of cell survival, we evaluated cellular viability by MTT, a water soluble tetrazolium salt which is cleaved by dehydrogenase activity in the mitochondria of metabolically viable cells to produce a dark-blue formazan product. Data from different concentrations of peptide P and its analogs. The biophysical properties have shown effect on anticancer activity. The anticancer activity of the peptide analogs, as shown in Fig 12 - Fig 15 and Table 8, was determined on various cancer cell lines. The geometric mean IC50s for eight cancer cell lines were calculated (Table 8) to provide an overall evaluation of the anticancer activity of the peptide analogs with differentα-helical structure for 36 h. The results of the present study demonstrated that amphipathicα-helical cationic antitumor peptide V13K (peptide P) and its analogs significantly inhibited proliferation of tumor cell, including human cervix carcinoma cells (HeLa), human melanoma cells (A375), human colorectal carcinoma cells (SW1116), human breast adenocarcinoma cells (MCF-7), human lung carcinoma cells (H1299), human rhabdomyosarcoma cells (RD), human lung carcinoma cells (A549), and mouse melanoma cells (B16). The Ala-substituted peptides showed lower anticancer activity than that of the parent peptide P; in contrast, the Leu-substituted peptides exhibited greater anticancer activity with IC50 from (4.6-5.6μM). In vitro, the implantation of human HeLa in mice was done as described experiment previously. Introduction of the peptide P and its analogs in tumors resulted in a significant decrease in HeLa cancer tumor volume in a xenograft mice model. Peptide V13K (peptide P) and its analogs may have the potential to overcome multi-drug resistance activity by increasing the permeability of cancer cells, thus providing opportunities to develop new drugs for chemotherapeutic use.The reasons of the selectivity against cancer cells may be due to that many cancer cell membranes, compared to normal cell membranes characterized by zwitterionic phospholipids as red blood cells, have more anionic phospholipids in their outer leaflet, and together with O-glycosylated mucin. The electrostatic interaction between cationic anticancer peptides and negatively charged cancer cell surface and membrane components contributes to the selectivity for cancer cells. The reduced interaction between cationic peptides and neutral charged zwitterionic normal cell membrane avoids cytotoxicity to healthy eukaryotic cells by anticancer peptides. Several models and mechanisms were developed for cell death by anticancer activity of the peptides, such as pore formation of barrel-stave model, the detergent-like membrane destabilisation model, and cell penetration model, etc. The antitumor mechanism of the peptide P and its analogs needed to be studied further. Theα-helical structure of the peptides makes an important role in the different action models.