title: 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.affiliation: Department of Nuclear Medicine, Xijing Hospital, The Fourth Military Medical University, Xi'an, 710032, Shaanxi, China.
authors.forename: Guoquan
authors.initials: G
authors.lastname: Li
authors.forename: Yan
authors.initials: Y
authors.lastname: Xing
authors.forename: Jing
authors.initials: J
authors.lastname: Wang
authors.forename: Peter S
authors.initials: PS
authors.lastname: Conti
authors.forename: Kai
authors.initials: K
authors.lastname: Chen
mesh_terms: D000818:Animals; D002232:Carbocyanines; D045744:Cell Line, Tumor; D005456:Fluorescent Dyes; D006801:Humans; D061986:MCF-7 Cells; D051379:Mice; D018613:Microscopy, Confocal; D009842:Oligopeptides; D019265:Spectroscopy, Near-Infrared / Q000379:methods
chemical_list: C098793:CY5.5 cyanine dye; D002232:Carbocyanines; D005456:Fluorescent Dyes; C526428:NGR peptide; D009842:Oligopeptides