PET of insulinoma using ¹⁸F-FBEM-EM3106B, a new GLP-1 analogue

Mol Pharm. 2011 Oct 3;8(5):1775-82. doi: 10.1021/mp200141x. Epub 2011 Aug 19.

Abstract

Derived from endocrine pancreatic beta cells, insulinomas express glucagon-like peptide-1 (GLP-1) receptor with high density and incidence. In this study, we labeled a novel GLP-1 analogue, EM3106B, with (18)F and performed PET imaging to visualize insulinoma tumors in an animal model. A GLP-1 analogue that contains multiple lactam bridges, EM3106B, was labeled with (18)F through a maleimide-based prosthetic group, N-2-(4-(18)F-fluorobenzamido)ethylmaleimide ((18)F-FBEM). The newly developed radiotracer was characterized by cell based receptor-binding assay, cell uptake and efflux assay. The stability in serum was evaluated by radio-HPLC analysis. In vivo PET imaging was performed in nude mice bearing subcutaneous INS-1 insulinoma tumors and MDA-MB-435 tumors of melanoma origin. Ex vivo biodistribution study was performed to confirm the PET imaging data. EM3106B showed high binding affinity (IC(50) = 1.38 nM) and high cell uptake (5.25 ± 0.61% after 120 min incubation). (18)F-FBEM conjugation of EM3106B resulted in high labeling yield (24.9 ± 2.4%) and high specific activity (>75 GBq/μmol at the end of bombardment). EM3106B specifically bound and was internalized by GLP-1R positive INS-1 cells. After intravenous injection of 3.7 MBq (100 μCi) of (18)F-FBEM-EM3106B, the INS-1 tumors were clearly visible with high contrast in relation to the contralateral background on PET images, and tumor uptake of (18)F-FBEM-EM3106B was determined to be 28.5 ± 4.7 and 25.4 ± 4.1% ID/g at 60 and 120 min, respectively. (18)F-FBEM-EM3106B showed low uptake in MB-MDA-435 tumors with low level of GLP-1R expression. Direct tissue sampling biodistribution experiment confirmed high tracer uptake in INS-1 tumors and receptor specificity in both INS-1 tumor and pancreas. In conclusion, (18)F-FBEM-EM3106B exhibited GLP-1R-receptor-specific targeting properties in insulinomas. The favorable characteristics of (18)F-FBEM-EM3106B, such as high specific activity and high tumor uptake, and high tumor to nontarget uptake, demonstrate that it is a promising tracer for clinical insulinoma imaging.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport
  • Cell Line, Tumor
  • Contrast Media* / chemistry
  • Contrast Media* / metabolism
  • Contrast Media* / pharmacokinetics
  • Drug Stability
  • Female
  • Glucagon-Like Peptide 1 / analogs & derivatives*
  • Glucagon-Like Peptide 1 / chemistry
  • Glucagon-Like Peptide 1 / metabolism
  • Glucagon-Like Peptide 1 / pharmacokinetics
  • Glucagon-Like Peptide-1 Receptor
  • Humans
  • Insulinoma / diagnosis*
  • Insulinoma / metabolism
  • Insulinoma / pathology
  • Islets of Langerhans / metabolism
  • Islets of Langerhans / pathology
  • Lactams* / chemistry
  • Lactams* / metabolism
  • Lactams* / pharmacokinetics
  • Maleimides / chemistry*
  • Maleimides / metabolism
  • Maleimides / pharmacokinetics
  • Mice
  • Mice, Nude
  • Molecular Imaging / methods*
  • Neoplasm Proteins / metabolism
  • Peptide Fragments / chemistry
  • Peptide Fragments / metabolism
  • Peptide Fragments / pharmacokinetics
  • Peptides / chemistry*
  • Peptides / metabolism
  • Peptides / pharmacokinetics
  • Positron-Emission Tomography
  • Receptors, Glucagon / agonists
  • Receptors, Glucagon / metabolism
  • Tissue Distribution
  • Whole Body Imaging

Substances

  • Contrast Media
  • GLP1R protein, human
  • Glp1r protein, mouse
  • Glucagon-Like Peptide-1 Receptor
  • Lactams
  • Maleimides
  • N-(2-(4-18F-fluorobenzamido)ethyl)maleimide
  • N-2-(4-fluorobenzamido)ethylmaleimide-EM 3106B
  • Neoplasm Proteins
  • Peptide Fragments
  • Peptides
  • Receptors, Glucagon
  • glucagon-like peptide 1 (7-36)
  • Glucagon-Like Peptide 1