FRET-Based In-Cell Detection of Highly Selective Supramolecular Complexes of meso-Tetraarylporphyrin with Peptide/BODIPY-Modified Per-O-Methyl-β-Cyclodextrins

Artificial supramolecular systems capable of self-assembly and that precisely function in biological media are in high demand. Herein, we demonstrate a highly specific host-guest-pair system that functions in living cells. A per-O-methyl-beta-cyclodextrin derivative (R8-B-CDMe) bearing both an octaarginine peptide chain and a BODIPY dye was synthesized as a fluorescent intracellular delivery tool. R8-B-CDMe was efficiently taken up by HeLa cells through both endocytosis and direct transmembrane pathways. R8-B-CDMe formed a 2 : 1 inclusion complex with tetrakis(4-sulfonatophenyl)porphyrin (TPPS) as a guest molecule in water, from which fluorescence resonance energy transfer (FRET) from R8-B-CDMe to TPPS was observed. The FRET phenomenon was clearly detected in living cells using confocal microscopy techniques, which revealed that the formed supramolecular R8-B-CDMe/TPPS complex was maintained within the cells. The R8-B-CDMe cytotoxicity assay revealed that the addition of TPPS counteracts the strong cytotoxicity (IC50=16 mu M) of the CD cavity due to complexation within the cells. A series of experiments demonstrated the bio-orthogonality of the supramolecular per-O-methyl-beta-CD/tetraarylporphyrin host-guest pair in living cells.

Automated summary

A highly specific host-guest system capable of functioning in living cells was demonstrated in this study. Fluorescence resonance energy transfer (FRET) phenomenon between the host-guest pair was observed in living cells using confocal microscopy techniques, indicating the stability of the supramolecular complex within the cells. The bio-orthogonality of the host-guest pair in living cells was confirmed through a series of experiments.