Noninvasive Imaging of Islet Transplants with 111In-Exendin-3 SPECT/CT

J Nucl Med. 2016 May;57(5):799-804. doi: 10.2967/jnumed.115.166330. Epub 2016 Jan 21.


Islet transplantation is a promising treatment for type 1 diabetic patients. However, there is acute as well as chronic loss of islets after transplantation. A noninvasive imaging method that could monitor islet mass might help to improve transplantation outcomes. In this study, islets were visualized after transplantation in a rat model with a dedicated small-animal SPECT scanner by targeting the glucagonlike peptide-1 receptor (GLP-1R), specifically expressed on β-cells, with (111)In-labeled exendin-3.

Methods: Targeting of (111)In-exendin-3 to GLP-1R was tested in vitro on isolated islets of WAG/Rij rats. For in vivo evaluation, 400 or 800 islets were transplanted into the calf muscle of WAG/Rij rats (6-8 wk old). Four weeks after transplantation, SPECT/CT images were acquired 1 h after injection of (111)In-labeled exendin-3. After SPECT acquisition, the muscles containing the transplant were analyzed immunohistochemically and autoradiographically.

Results: The binding assay, performed on isolated islets, showed a linear correlation between the number of islets and (111)In-exendin-3 accumulation (Pearson r = 0.98). In vivo, a 1.70 ± 0.44-fold difference in tracer uptake between 400 and 800 transplanted islets was observed. Ex vivo analysis of the islet transplant showed colocalization of tracer accumulation on autoradiography, with insulin-positive cells and GLP-1R expression on immunohistochemistry.

Conclusion: (111)In-exendin-3 accumulates specifically in the β-cells after islet transplantation and is a promising tracer for noninvasive monitoring of the islet mass.

Keywords: GLP-1R; SPECT; exendin-3; islet imaging; islet transplantation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Female
  • Glucagon-Like Peptide-1 Receptor / metabolism
  • Indium Radioisotopes*
  • Islets of Langerhans Transplantation*
  • Peptides* / metabolism
  • Peptides* / pharmacokinetics
  • Rats
  • Single Photon Emission Computed Tomography Computed Tomography / methods*
  • Tissue Distribution


  • Glucagon-Like Peptide-1 Receptor
  • Indium Radioisotopes
  • Peptides
  • exendin 3