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Integrin αvβ3 is an effective marker of angiogenesis in cancer, and αvβ3-specific imaging can yield important details about this complex physiological process. We utilized the recently reported and highly αvβ3-specific peptide, bicyclic RGD (bcRGD), as the basic structure of an in vivo αvβ3 imaging probe, and synthesized a radioiodinated form of bcRGD, namely [125I]bcRGD, with high radiochemical purity (>99%) and high molar activity (81 GBq/μmol). As expected, [125I]bcRGD exhibited high selectivity for αvβ3 compared with αvβ5 and α5β1 in vitro. [125I]bcRGD showed significantly higher accumulation in U-87MG cells (1.6% dose/mg) with high expression of αvβ3 compared to A549 cells (0.3% dose/mg) with only moderate expression. Furthermore, 30 min after administration to tumor-bearing mice, [125I]bcRGD showed significantly higher accumulation in U-87MG tumors (3.8% ID/g) than in A549 tumors (2.1% ID/g), and the radioactivity accumulation ratios of U-87MG tumor/blood and U-87MG tumor/muscle were 4.0 and 6.0, respectively. These results highlight the promising properties of [123/125I]bcRGD for use as an in vivo αvβ3 imaging probe, as well as the utility of bcRGD as a basic structure of molecular probes for both imaging and therapeutic applications. bcRGD may exhibit broad use in future theranostics applications targeting integrin αvβ3-related diseases.

Integrin α

We examined exendin(9-39), an antagonist of glucagon-like peptide-1 (GLP-1) receptor (GLP-1R), as a potential probe for imaging of pancreatic beta-cells. To evaluate in vitro receptor specificity, binding assay was performed using dispersed mouse islet cells. Binding assay showed competitive inhibition of [(125)I]BH-exendin(9-39) binding by non-radioactive exendin(9-39). To assess in vivo selectivity, the biodistribution was evaluated by intravenous administration of [(125)I]BH-exendin(9-39) to mice. Radioactivity of harvested pancreas reached highest levels at 60 and 120min among organs examined except lung. Pre-administration of excess non-radioactive exendin(9-39) remarkably and specifically blocked the radioactivity of pancreas. After [(125)I]BH-exendin(9-39) injection into transgenic mice with pancreatic beta-cells expressing GFP, fluorescent and radioactive signals of sections of pancreas were evaluated with an image analyzer. Imaging analysis showed that the fluorescent GFP signals and the radioactive signals were correspondingly located. Thus, the GLP-1R antagonist exendin(9-39) may serve as a useful probe for pancreatic beta-cell imaging.