Structure and function of a custom anticancer peptide, CB1a

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° to 110°. 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 × 10 5 M −1 at physiological ionic strength at 25 °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.