Development of Cell-Penetration PG-Surfactants and Its Application in External Peptide Delivery to Cytosol

Recently, development of techniques to deliver pharmacologically active biomacromolecules such as peptides and proteins to cytosol has gained much interest. Here, we applied the peptide gemini (PG)-surfactants to a novel platform to design cell penetration lipopeptides (CP-PGs), which can deliver exogenous peptides and proteins to cytosol. Among the number of candidate CP-PGs having different peptide sequences at the X-, Y-, and Z-positions, we focused on those having two C12 alkyl chains appended to the side chain of two Cys residues, the betaine sequence -Asp-Lys-Asp-Lys- between the alkylated Cys residues (i.e., at the X-position), and having different cationic peptide sequences of oligo-Lys or oligo-Arg at the Y- and/or Z-positions. With respect to cytotoxicity for mammalian cells such as NIH3T3 cells upon 1 h exposure, those having (Lys)₃ (K-DKDKC and DKCK-K) showed lower cytotoxicity (IC₅₀ = 241 and 198 μM) among those having oligo-Lys, (Lys) (n = 1, 3, 5; IC₅₀ = 88-197 μM). Similar lower cytotoxicity was also observed for the CP-PG having two (Lys)₃ at both N- and C-terminal sides (K-DKDKC-K) (IC₅₀ = 225 μM). In contrast, the CP-PG having (Arg)₃ at the N-terminal side (R-DKDKC) showed higher cytotoxicity (IC₅₀ = 88 μM). Carrier abilities of the CP-PGs for exogenous peptides were evaluated using the proapoptotic domain (PAD) peptide, which induces apoptosis by disturbing mitochondrial membranes after delivery into cytosol. As a result, the CP-PGs of K-DKDKC, DKCK-K, K-DKDKC-K, DKCK-K, and R-DKDKC exhibited micromolar range carrier ability (the necessary half concentration to induce cell death (EC₅₀) by delivering PAD peptide to cytosol was 10, 6.2, 8.5, 5.8, and 11.5 μM, respectively). Especially, the carrier abilities of DKCK-K and DKCK-K were superior to the well-established cell penetration Arg-rich R8 peptide (EC₅₀ = 6.8 μM). Together, our results indicate that the PG-surfactant molecular framework could be a potential new platform to design efficient cell penetration carrier materials.