A lactoferrin-derived peptide with cationic residues concentrated in a region of its helical structure induces necrotic cell death in a leukemic cell line (HL-60).

Model studies have shown that peptides derived from the N-terminal region of bovine lactoferrin (Lf-B) exhibit antitumor activity against certain cell lines. This activity is due primarily to the peptides' apoptogenic effect. Several reports indicate that cationic residues clustered in two regions of the peptide sequence can be shuffled into one region and thereby increase cytotoxic activity, although the mechanism of this enhanced cytotoxic effect has not been clarified. In this paper, we considered several parameters that determine the mode of cell death after exposure to a native Lf-B derived peptide (Pep1, residues 17-34), and a modified peptide (mPep1) wherein the cationic residues of Pep1 are clustered in a single region of its helical structure. We found that the cytotoxic activity of mPep1 was about 9.6 fold-higher than that of Pep1 against HL-60 cells, as determined by the 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethonyphenol)-2-(4-sulfophenyl)-2 H-tetrazolium (MTS) assay. In investigating the expression of phosphatidylserine, we observed that the native peptide (Pep1) caused both apoptotic cell death and necrotic cell death, depending on the concentration of the peptide. In contrast, the action of mPep1 was exclusively characteristic of necrotic cell death. This observation was further confirmed by agarose gel electrophoresis, in which clear ladder-like DNA bands were observed from cells exposed to Pep1, whereas DNA from cells treated with mPep1 produced a smeared pattern. We extended the study by investigating the release of mitochondrial cytochrome c into the cytosol, and the activation of caspase-3; both peptides caused the release of cytochrome c into the cytosol, and the activation of caspase-3.These results suggest that Pep1 may kill cancer cells by activating an apoptosis-inducing pathway, whereas mPep1 causes necrotic cell death by destroying cellular membrane structure notwithstanding sharing some cellular events with apoptotic cell death.