Several natural
antimicrobial peptides including
cecropins,
magainins and melittins have been found to kill
cancer cells. However, their efficacy may not be adequate for their development as
anticancer agents. In this study, we used a natural
antimicrobial peptide,
cecropin B (CB), as a template to generate a novel anticancer
peptide.
Cecropin B is an amphipathic and polycationic
peptide derived from the hemolymph of Hyalophora cecropia with well-known antimicrobial and cytolytic properties. The signature pattern of
cecropins is W-x-(0,2)-[KDN]-x-{L}-K-[KRE]-[LI]-E-[RKN] (PROSITE: PS00268), and this signature sequence is located at N-terminus of CB. CB1a was constructed by repeating the N-terminal ten
amino acids of CB three times and including a hinge near C-terminus. The circular dichroism spectra showed that CB1a is unstructured in aqueous
solution, but adopt a helical conformation in membrane-like environment. The
solution structure of CB1a in a polar
solvent was also studied by NMR. CB1a formed a helix-hinge-helix in 20% HFIP
solution, and it was found the bent angle between two helical segments was induced ranging from 60 degrees to 110 degrees . A
heparin-binding motif is located in the central part of helix 1. Isothermal titration calorimetry reveals the association constant of CB1a bound to
low molecular weight heparin is 1.66 x 10(5)M(-1) at physiological ionic strength at 25 degrees C. Binding of CB1a to
heparin produces a large conformational change toward a more structural state. CB1a demonstrated promising activity against several
cancer cells but low toxicity against non-
cancer cells. The IC(50) of CB1a on
leukemia and stomach
carcinoma cells were in the range of 2-8-fold lower than those of CB. Besides, CB1a exhibited low hemolytic activity against human red blood cells. Due to these properties, CB1a has the potential to become a promising
anticancer agent.