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In vivo imaging of GLP-1R with a targeted bimodal PET/fluorescence imaging agent.

Brand C, Abdel-Atti D, Zhang Y, Carlin S, Clardy SM, Keliher EJ, Weber WA, Lewis JS, Reiner T - Bioconjug. Chem. (2014)

Bottom Line: The bimodal imaging agent (64)Cu-E4-Fl was synthesized in good radiochemical yield and specific activity (RCY = 36%, specific activity: 141 μCi/μg, >98% radiochemical purity).The agent showed good performance in vivo and ex vivo, visualizing small xenografts (<2 mm) with PET and pancreatic β-cell mass by phosphor autoradiography.We believe that our procedure could become relevant as a protocol for the development of bimodal imaging agents.

View Article: PubMed Central - PubMed

Affiliation: Radiochemistry and Imaging Sciences Service and §Molecular Imaging and Therapy Service, Department of Radiology, ∥Molecular Pharmacology and Chemistry Program, and ⊥Center for Molecular Imaging and Nanotechnology, Memorial Sloan Kettering Cancer Center , New York, New York 10065, United States.

ABSTRACT
Accurate visualization and quantification of β-cell mass is critical for the improved understanding, diagnosis, and treatment of both type 1 diabetes (T1D) and insulinoma. Here, we describe the synthesis of a bimodal imaging probe (PET/fluorescence) for imaging GLP-1R expression in the pancreas and in pancreatic islet cell tumors. The conjugation of a bimodal imaging tag containing a near-infrared fluorescent dye, and the copper chelator sarcophagine to the GLP-1R targeting peptide exendin-4 provided the basis for the bimodal imaging probe. Conjugation was performed via a novel sequential one-pot synthetic procedure including (64)Cu radiolabeling and copper-catalyzed click-conjugation. The bimodal imaging agent (64)Cu-E4-Fl was synthesized in good radiochemical yield and specific activity (RCY = 36%, specific activity: 141 μCi/μg, >98% radiochemical purity). The agent showed good performance in vivo and ex vivo, visualizing small xenografts (<2 mm) with PET and pancreatic β-cell mass by phosphor autoradiography. Using the fluorescent properties of the probe, we were able to detect individual pancreatic islets, confirming specific binding to GLP-1R and surpassing the sensitivity of the radioactive label. The use of bimodal PET/fluorescent imaging probes is promising for preoperative imaging and fluorescence-assisted analysis of patient tissues. We believe that our procedure could become relevant as a protocol for the development of bimodal imaging agents.

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Related in: MedlinePlus

Fluorescence histologyof a 10 μm pancreas section 1 h postinjectionof Hoechst cell nuclear stain (top left) and 64Cu-E4-Sar-Fl(bottom left) into transgenic mice with β-cell specific expressionof GFP (top right). Green and red signal accumulations demonstrateislets of Langerhans. All images were acquired with an objective of20×. Scale bar: 100 μm for all images.
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fig3: Fluorescence histologyof a 10 μm pancreas section 1 h postinjectionof Hoechst cell nuclear stain (top left) and 64Cu-E4-Sar-Fl(bottom left) into transgenic mice with β-cell specific expressionof GFP (top right). Green and red signal accumulations demonstrateislets of Langerhans. All images were acquired with an objective of20×. Scale bar: 100 μm for all images.

Mentions: Similar to in vitro binding, ex vivo histology confirmedthe selectivityof Cu-E4-Fl 6 to GLP-1R (Figure 3). One of the goals of developing GLP-1R targeting imaging agentsis to use them as a β-cell targeting agent for delineating isletsof Langerhans from exocrine pancreas. To show that 64Cu-E4-Flis selective for GLP-1R in vivo, we injected the imaging agent inMIP-GFP mice and let the agent circulate for 1 h, before nuclear cellstain was injected, the mice sacrificed, and pancreata harvested forhistology. The GLP-1R targeted 64Cu-E4-Fl probe showeda strong fluorescent signal in the 650 nm channel, colocalizing withthe islets of Langerhans, as indicated by GFP fluorescence and similarto other GLP-1R imaging probes.11,12


In vivo imaging of GLP-1R with a targeted bimodal PET/fluorescence imaging agent.

Brand C, Abdel-Atti D, Zhang Y, Carlin S, Clardy SM, Keliher EJ, Weber WA, Lewis JS, Reiner T - Bioconjug. Chem. (2014)

Fluorescence histologyof a 10 μm pancreas section 1 h postinjectionof Hoechst cell nuclear stain (top left) and 64Cu-E4-Sar-Fl(bottom left) into transgenic mice with β-cell specific expressionof GFP (top right). Green and red signal accumulations demonstrateislets of Langerhans. All images were acquired with an objective of20×. Scale bar: 100 μm for all images.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4215873&req=5

fig3: Fluorescence histologyof a 10 μm pancreas section 1 h postinjectionof Hoechst cell nuclear stain (top left) and 64Cu-E4-Sar-Fl(bottom left) into transgenic mice with β-cell specific expressionof GFP (top right). Green and red signal accumulations demonstrateislets of Langerhans. All images were acquired with an objective of20×. Scale bar: 100 μm for all images.
Mentions: Similar to in vitro binding, ex vivo histology confirmedthe selectivityof Cu-E4-Fl 6 to GLP-1R (Figure 3). One of the goals of developing GLP-1R targeting imaging agentsis to use them as a β-cell targeting agent for delineating isletsof Langerhans from exocrine pancreas. To show that 64Cu-E4-Flis selective for GLP-1R in vivo, we injected the imaging agent inMIP-GFP mice and let the agent circulate for 1 h, before nuclear cellstain was injected, the mice sacrificed, and pancreata harvested forhistology. The GLP-1R targeted 64Cu-E4-Fl probe showeda strong fluorescent signal in the 650 nm channel, colocalizing withthe islets of Langerhans, as indicated by GFP fluorescence and similarto other GLP-1R imaging probes.11,12

Bottom Line: The bimodal imaging agent (64)Cu-E4-Fl was synthesized in good radiochemical yield and specific activity (RCY = 36%, specific activity: 141 μCi/μg, >98% radiochemical purity).The agent showed good performance in vivo and ex vivo, visualizing small xenografts (<2 mm) with PET and pancreatic β-cell mass by phosphor autoradiography.We believe that our procedure could become relevant as a protocol for the development of bimodal imaging agents.

View Article: PubMed Central - PubMed

Affiliation: Radiochemistry and Imaging Sciences Service and §Molecular Imaging and Therapy Service, Department of Radiology, ∥Molecular Pharmacology and Chemistry Program, and ⊥Center for Molecular Imaging and Nanotechnology, Memorial Sloan Kettering Cancer Center , New York, New York 10065, United States.

ABSTRACT
Accurate visualization and quantification of β-cell mass is critical for the improved understanding, diagnosis, and treatment of both type 1 diabetes (T1D) and insulinoma. Here, we describe the synthesis of a bimodal imaging probe (PET/fluorescence) for imaging GLP-1R expression in the pancreas and in pancreatic islet cell tumors. The conjugation of a bimodal imaging tag containing a near-infrared fluorescent dye, and the copper chelator sarcophagine to the GLP-1R targeting peptide exendin-4 provided the basis for the bimodal imaging probe. Conjugation was performed via a novel sequential one-pot synthetic procedure including (64)Cu radiolabeling and copper-catalyzed click-conjugation. The bimodal imaging agent (64)Cu-E4-Fl was synthesized in good radiochemical yield and specific activity (RCY = 36%, specific activity: 141 μCi/μg, >98% radiochemical purity). The agent showed good performance in vivo and ex vivo, visualizing small xenografts (<2 mm) with PET and pancreatic β-cell mass by phosphor autoradiography. Using the fluorescent properties of the probe, we were able to detect individual pancreatic islets, confirming specific binding to GLP-1R and surpassing the sensitivity of the radioactive label. The use of bimodal PET/fluorescent imaging probes is promising for preoperative imaging and fluorescence-assisted analysis of patient tissues. We believe that our procedure could become relevant as a protocol for the development of bimodal imaging agents.

Show MeSH
Related in: MedlinePlus