Cyclodextrin-Based Peptide Self-Assemblies (Spds) That Enhance Peptide-Based Fluorescence Imaging and Antimicrobial Efficacy

Abstract

As a result of their high specificity for their corresponding biological targets, peptides have shown significant potential in a range of diagnostic and therapeutic applications. However, their widespread use has been limited by their minimal cell permeability and stability in biological milieus. We describe here a hepta-dicyanomethylene-4<i>H</i>-pyran appended β-cyclodextrin (<b>DCM</b>_<b>7</b><b>-β-CD</b>) that acts as a delivery enhancing "host" for 1-bromonaphthalene-modified peptides, as demonstrated with peptide probes <b>P1-P4</b>. Interaction between the fluorescent peptides <b>P1-P3</b> and <b>DCM</b>_<b>7</b><b>-β-CD</b> results in the hierarchical formation of unique supramolecular architectures, which we term supramolecular-peptide-dots (<b>Spds</b>). Each <b>Spd</b> (<b>Spd-1</b>, <b>Spd-2</b>, and <b>Spd-3</b>) was found to facilitate the intracellular delivery of the constituent fluorescent probes (<b>P1-P3</b>), thus allowing spatiotemporal imaging of an apoptosis biomarker (caspase-3) and mitosis. <b>Spd-4</b>, incorporating the antimicrobial peptide <b>P4</b>, was found to provide an enhanced therapeutic benefit against both Gram-positive and Gram-negative bacteria relative to <b>P4</b> alone. In addition, a fluorescent <b>Spd-4</b> was prepared, which revealed greater bacterial cellular uptake compared to the peptide alone (<b>P4-FITC</b>) in <i>E. coli</i>. (ATCC 25922) and <i>S. aureus</i> (ATCC 25923). This latter observation supports the suggestion that the <b>Spd</b> platform reported here has the ability to facilitate the delivery of a therapeutic peptide and provides an easy-to-implement strategy for enhancing the antimicrobial efficacy of known therapeutic peptides. The present findings thus serve to highlight a new and effective supramolecular delivery approach that is potentially generalizable to overcome limitations associated with functional peptides.