Chirality switching within an anionic cell-penetrating peptide inhibits translocation without affecting preferential entry.

Multiple substitution of d- for l-amino acids decreases the intracellular uptake of cationic cell penetrating peptides (CPP) in a cell line-dependent manner. We show here that a single d-amino acid substitution can decrease the overall uptake of the anionic, amphipathic CPP, p28, into cancer and histologically matched normal cell lines, while not altering the preferential uptake of p28 into cancer cells. The decrease appears dependent on the position of the d-substitution within the peptide and the ability of the substituted d-amino acid to alter chirality. We also suggest that when d-substitution alters the ratio of α-helix to β-sheet content of an anionic CPP, its translocation across the cell membrane is altered, reducing overall entry. These observations may have a significant effect on the design of future d-substituted analogues of cell penetrating peptides.