Dual Chemical Modification of a Polytheonamide Mimic: Rational Design and Synthesis of Ion-Channel-Forming 48-mer Peptides with Potent Cytotoxicity.

Abstract

Polytheonamide B (1) is a natural peptide that displays potent cytotoxicity against P388 mouse leukemia cells (IC50 =0.098 nm). Linear 48-mer 1 is known to form monovalent cation channels on binding to lipid bilayers. We previously developed a fully synthetic route to 1, and then achieved the design and synthesis of a structurally simplified analogue of 1, namely, dansylated polytheonamide mimic 2. Although the synthetically more accessible 2 was found to emulate the channel function of 1, its cytotoxicity was decreased 120-fold. Herein, the chemical preparation and biological evaluation of seven analogues 3-9 of 2 are reported. Compounds 3-9 were modified at their N terminus and/or the side chain of residue 44 of 2 to alter their physicochemical properties. The total synthesis of 3-9 was accomplished in a unified fashion by a combination of solid-phase and solution-phase chemistry. Systematic evaluation of the hydrophobicities, single-channel currents, ion-exchange activities, and cytotoxicities of 3-9 revealed that their hydrophobicities are correlated with the total magnitude of ion exchange and determine their cytotoxic potency. Consequently, the most hydrophobic analogue 9 exhibited the lowest IC50 value, which is comparable to that of 1. Therefore, these results clarified that the bioactivity of the polytheonamide-based peptides can be rationally controlled by changing their hydrophobicity at the N and C termini of the 48-amino-acid sequence.