Solid-phase synthesis and application of double-fluorescent-labeled lipopeptides, containing a CTL-epitope from the measles fusion protein

: The mechanism which enables lipopeptides to induce cytotoxicity is not known. By preparing fluorescent-labeled lipopeptides one might unravel the mechanism of their entry into the cell and their intracellular pathway. A method of preparing double-fluorescent-labeled peptides by solid-phase chemistry is described. As model peptides we have chosen analogs of the sequence RRYPDAVYL, which occurs in the measles fusion protein (F438–446) and is an epitope for cytotoxic T lymphocytes. The peptides Pal-KTMRKKKRRYPDAVKFLL (7) and Pal-KFLKKKRRYPDAVKTMRL (8), in which Pal is palmitoyl and KTMR and KFL are Ne-carboxytetramethylrhodamine- and Ne-carboxyfluorescein-labeled lysyl residues, respectively, were prepared and obtained in ≈ 30% yield after purification by high-performance liquid chromatography. The fluorescence of fluorescein and tetramethylrhodamine in lipopeptide Pal-KTMRKKKRRYPDAVKFLL (7) was quenched to 98–99% due to intramolecular interaction of the labels. On incubation with trypsin (i.e. cleavage at the KKKRR-site) the fluorescence of both labels was restored. The intracellular routing of lipopeptide Pal-KTMRKKKRRYPDAVKFLL was studied with human melanoma cell line, Mel/J, which was transfected with human leukocyte antigen B*2705. It appeared that the double-fluorescent-labeled lipopeptide was able to induce antigen-specific cytotoxicity. Furthermore, preliminary confocal microscopical studies indicated that this lipopeptide is observed intracellularly.