The PEG-Fluorochrome Shielding Approach for Targeted Probe Design

Abstract

We provide a new approach for fluorescent probe design termed “PEG-fluorochrome shielding”, where PEGylation enhances quantum yields while blocking troublesome interactions between fluorochromes and biomolecules. To demonstrate PEG-fluorochrome shielding, fluorochrome-bearing peptide probes were synthesized, three without PEG and three with a 5 kDa PEG functional group. <i>In vitro</i>, PEG blocked the interactions of fluorochrome-labeled peptide probes with each other (absorption spectra, self-quenching) and reduced nonspecific interactions with cells (by FACS). <i>In vivo</i>, PEG blocked interactions with biomolecules that lead to probe retention (by surface fluorescence). Integrin targeting <i>in vivo</i> was obtained as the differential uptake of an ¹¹¹In-labeled, fluorochrome-shielded, integrin-binding RGD probe and a control RAD. Using PEG to block fluorochrome-mediated interactions, rather than synthesizing <i>de novo</i> fluorochromes, can yield new approaches for the design of actively or passively targeted near-infrared fluorescent probes