Near-infrared fluorescence imaging of CD13 receptor expression using a novel Cy5.5-labeled dimeric NGR peptide.

Abstract

In this study, we synthesized a novel Cy5.5-labeled dimeric NGR peptide (Cy5.5-NGR2) via bioorthogonal click chemistry, and evaluated the utility of Cy5.5-NGR2 for near-infrared fluorescence imaging of CD13 receptor expression in vivo. The dimeric NGR peptide (NGR2) was conjugated with an alkyne-containing PEG unit followed by mixing with an azide-terminated Cy5.5 fluorophore (Cy5.5-N3) to afford Cy5.5-NGR2. The probe was subject to in vitro and in vivo evaluations. The bioorthogonal click chemistry provided a rapid conjugation of the alkyne-containing NGR2 with Cy5.5-N3 in a quantitative yield within 15 min. The laser confocal microscopy revealed that binding of Cy5.5-NGR2 to CD13 receptor is target-specific as demonstrated in CD13-positive HT-1080 cells, CD13-negative MCF-7 cells, and a blocking study in HT-1080 cells. For in vivo optical imaging, Cy5.5-NGR2 exhibited rapid HT-1080 tumor targeting at 0.5 h postinjection (pi), and highest tumor-to-background contrast at 2 h pi. The CD13-specific tumor accumulation of Cy5.5-NGR2 was accomplished by a blocking study with unlabeled NGR peptide in HT-1080 tumor bearing mice. The tumor-to-muscle ratio of Cy5.5-NGR2 at 2 h pi reached 2.65 ± 0.13 in the non-blocking group vs. 1.05 ± 0.06 in the blocking group. The results from ex vivo imaging were consistent with the in vivo findings. We concluded that Cy5.5-NGR2 constructed by bioorthogonal click chemistry is a promising molecular probe, not only allowing the NIR optical imaging of CD13 overexpressed tumors, but also having the potential to facilitate noninvasive monitoring of CD13-targeted tumor therapy.

• Authors: Guoquan Li, Yan Xing, Jing Wang, Peter S Conti, Kai Chen
• Journal: Amino acids (Amino Acids) Vol. 46 Issue 6 Pg. 1547-56 (Jun 2014) ISSN: 1438-2199 [Electronic] Austria
• PMID: 24652439 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• CY5.5 cyanine dye
• Carbocyanines
• Fluorescent Dyes
• NGR peptide
• Oligopeptides

Topics

• Animals
• Carbocyanines
• Cell Line, Tumor
• Fluorescent Dyes
• Humans
• MCF-7 Cells
• Mice
• Microscopy, Confocal
• Oligopeptides
• Spectroscopy, Near-Infrared (methods)