Design of a new cell penetrating peptide for DNA, siRNA and mRNA delivery

Background Delivery systems, including peptide‐based ones, that destabilize endosomes in a pH‐dependent manner are increasingly used to deliver cargoes of therapeutic interest, such as nucleic acids and proteins into mammalian cells. Methods The negatively charged amphipathic alpha‐helicoidal forming peptide named HELP (Helical Erythrocyte Lysing Peptide) is a derivative from the bee venom melittin and was shown to have a pH‐dependent activity with the highest lytic activity at pH 5.0 at the same time as becoming inactive when the pH is increased. The present study aimed to determine whether replacement in the HELP peptide of the glutamic acid residues by histidines, for which the protonation state is sensitive to the pH changes that occur during endosomal acidification, can transform this fusogenic peptide into a carrier able to deliver different nucleic acids into mammalian cells. Results The resulting HELP‐4H peptide displays high plasmid DNA, small interfering RNA and mRNA delivery capabilities. Importantly, in contrast to other cationic peptides, its transfection activity was only marginally affected by the presence of serum. Using circular dichroism, we found that acidic pH did not induce significant conformational changes for HELP‐4H. Conclusions In summary, we were able to develop a new cationic histidine rich peptide able to efficiently deliver various nucleic acids into cells. The newly designed cationic amphipathic histidine‐rich peptide HELP‐4H displays high DNA, small interfering and mRNA transfection capabilities. We also found that the transfection activity is poorly affected by the presence of serum and that HELP‐4H adopts an alpha‐helix in a pH‐independent manner.