Antibacterial, antitumor and hemolytic activities of α‐helical antibiotic peptide, P18 and its analogs

Abstract

The alpha-helical antibiotic peptide (P18: KWKLFKKIPKFLHLAKKF-NH2) designed from the cecropin A(1-8)-magainin 2 (1-12) hybrid displayed strong bactericidal and tumoricidal activity without inducing hemolysis. The effect of the Pro9 residue at central position of P18 on cell selectivity was investigated by Pro9 --> Leu or Pro9 --> Ser substitution. Either substitution markedly reduced the antibacterial activity of P18 and increased hemolysis, although it did not significantly affect cytotoxicity against human transformed tumor and normal fibroblast cells. These results suggest that a proline kink in alpha-helical antibiotic peptide P18 serves as a hinge region to facilitate ion channel formation on bacterial cell membranes and thus plays an important role in providing high selectivity against bacterial cells. Furthermore, to investigate the structure-antibiotic activity relationships of P18, a series of N- or C-terminal deletion and substitution analogs of P18 were synthesized. The C-terminal region of P18 was related to its antibiotic activity and alpha-helical conformation on lipid membranes rather than N-terminal one. Higher alpha-helicity of the peptides was involved in the hemolytic and antitumor activity rather than antibacterial activity. Except for [L9]-P18 and [S9]-P18, all the designed peptides containing a Pro residue showed potent antibacterial activity, although they did not induce a cytolytic effect against human erythrocyte and normal fibroblast cells at the concentration required to kill bacteria. In particular, P18 and some analogs (N-1, N-2, N-3, N-3L and N-4L) with potent bactericidal and tumoricidal activity and little or no normal cell toxicity may serve as an attractive candidate for the development of novel anti-infective or antitumor agents.

Peptoids that mimic the structure, function, and mechanism of helical antimicrobial peptides

“…In contrast, the antibacterial activity of selective AMPs depends on (i) high net cationic charge (12)(13)(14)18) (although excessive cationic charge can also lead to hemolytic activity) (18, 19) and (ii) only moderate hydrophobicity (16,19,21,22). Perhaps counterintuitively, a well defined amphipathic structure is not necessary for selective antimicrobial activity (7,16); destabilization of AMP secondary structure often leads to improvements in selectivity (15,20).…”

“…Numerous structure-activity studies of a wide variety of AMPs have delineated the physicochemical characteristics that give rise to selective antibacterial activity or nonselective cytotoxicity. Regardless of structural class (i.e., ␣-helix, ␤-sheet, loop, or extended), nonselective AMPs typically (i) are very hydrophobic, such that their interactions with membranes are governed primarily by the hydrophobic effect (10)(11)(12)(13)(14)(15), and (ii) have a well defined amphipathic structure (4,11,(14)(15)(16)(17). In contrast, the antibacterial activity of selective AMPs depends on (i) high net cationic charge (12)(13)(14)18) (although excessive cationic charge can also lead to hemolytic activity) (18, 19) and (ii) only moderate hydrophobicity (16,19,21,22).…”

“…The precise nature of AMP-membrane interactions remains controversial and actively debated; a variety of mechanisms have been proposed, including the carpet (4), barrel-stave pore (4), toroidal pore (8), and aggregate (9) models. Nevertheless, a considerable number of structure-activity investigations have elucidated how the physicochemical properties of these molecules relate to their biological activities (4,7,(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22).…”

Suppression of Human Prostate Tumor Growth in Mice by a Cytolytic d-, l-Amino Acid Peptide

“…These peptides have a central role in the innate immunity of all of the organisms, including insects, amphibians, and mammals (18). Examples include human defensins (19 -21), cecropins (22), cecropin-magainin hybrids (23,24), magainins (14), peptides conjugated to homing domains (15)(16)(17), propeptides (25), and others (26,27). These peptides preferentially bind and disrupt negatively charged phospholipid membranes, the major component of the bacterial cytoplasmic membrane.…”

First-in-class thyrotropin-releasing hormone (TRH)-based compound binds to a pharmacologically distinct TRH receptor subtype in human brain and is effective in neurodegenerative models

“…Positive and negative controls in this test were TritonX-100 (which gave 100% hemolysis) and phosphate buffered saline (which gave 0% hemolysis). Percent hemolysis was calculated as described by (Shin et al, 2001). …”