Structural Engineering of Fluorescent Self-Threaded Peptide Probes for Targeted Cell Imaging(dagger)

Squaraine figure-eight (SF8) molecules are a new class of deep-red fluorescent probes that are well suited for fluorescence cell microscopy due to their very high fluorescence brightness and excellent stability. Three homologous SF8 probes, with peptidyl loops that differ by very minor changes in the peptide sequence, were synthesized and assessed for probe uptake by cancer cells. One of probes included the RGD motif that is recognized by many classes of integrin receptors that reside on the surface of the cancer cells, and it permeated the cells by receptor-mediated endocytosis. In contrast, cell microscopy showed that there was negligible cell uptake of the two homologous SF8 probes indicating differences in probe targeting capability. The synthetic method allows for easy alteration of the peptide sequence; thus, it is straightforward to develop new classes of peptidyl SF8 probes with loop sequences that target other cancer biomarkers.

Automated summary

The new class of deep-red fluorescent probes SF8 exhibit high fluorescence brightness and stability, making them suitable for fluorescence cell microscopy research. By synthesizing and evaluating different SF8 probes for probe uptake by cancer cells, it was found that the probe with the RGD motif permeated the cells through receptor-mediated endocytosis, while the other two homologous SF8 probes showed negligible cell uptake, indicating differences in targeting capability. Additionally, the synthetic method allows for easy alteration of the peptide sequence, enabling the development of new peptidyl SF8 probes targeting other cancer biomarkers.