Rational Approach To Select Small Peptide Molecular Probes Labeled with Fluorescent Cyanine Dyes for in Vivo Optical Imaging

摘要

We demonstrate that the structure of carbocyanine dyes, which arencommonly used to label small peptides for molecular imaging and not the boundnpeptide, controls the rate of extravasation from blood vessels to tissue. Bynexamining several near-infrared (NIR) carbocyanine fluorophores, we demon-nstrate a quantitative correlation between the binding of a dye to albumin, amodelnplasma protein, and the rate of extravasation of the probe into tissue. Binding ofnthe dyes was measured by fluorescence quenching of the tryptophans in albuminnand was found to be inversely proportional to the rate of extravasation. The ratenof extravasation, determined by kurtosis from longitudinal imaging studies usingnrodent ear models, provided a basis for quantitative measurements. Structure-nactivity studies aimed at evaluating a representative library of NIR fluorescent cyanine probes showed that hydrophilic dyes withnbinding constants several orders of magnitude lower than their hydrophobic counterparts have much faster extravasation rate,nestablishing a foundation for rational probe design. The correlation provides a guideline for dye selection in optical imaging and anmethod to verify if a certain dye is optimal for a specific molecular imaging application.