Investigation of an 18F-labelled Imidazopyridotriazine for Molecular Imaging of Cyclic Nucleotide Phosphodiesterase 2A

Molecules. 2018 Mar 2;23(3):556. doi: 10.3390/molecules23030556.

Abstract

Specific radioligands for in vivo visualization and quantification of cyclic nucleotide phosphodiesterase 2A (PDE2A) by positron emission tomography (PET) are increasingly gaining interest in brain research. Herein we describe the synthesis, the 18F-labelling as well as the biological evaluation of our latest PDE2A (radio-)ligand 9-(5-Butoxy-2-fluorophenyl)-2-(2-([18F])fluoroethoxy)-7-methylimidazo[5,1-c]pyrido[2,3-e][1,2,4]triazine (([18F])TA5). It is the most potent PDE2A ligand out of our series of imidazopyridotriazine-based derivatives so far (IC50 hPDE2A = 3.0 nM; IC50 hPDE10A > 1000 nM). Radiolabelling was performed in a one-step procedure starting from the corresponding tosylate precursor. In vitro autoradiography on rat and pig brain slices displayed a homogenous and non-specific binding of the radioligand. Investigation of stability in vivo by reversed-phase HPLC (RP-HPLC) and micellar liquid chromatography (MLC) analyses of plasma and brain samples obtained from mice revealed a high fraction of one main radiometabolite. Hence, we concluded that [18F]TA5 is not appropriate for molecular imaging of PDE2A neither in vitro nor in vivo. Our ongoing work is focusing on further structurally modified compounds with enhanced metabolic stability.

Keywords: PDE2A radioligands; Phosphodiesterase 2A (PDE2A); metabolic stability; micellar liquid chromatography (MLC); neuroimaging; positron emission tomography (PET); secondary messengers.

MeSH terms

  • Animals
  • Autoradiography / methods
  • Brain / enzymology*
  • Brain / ultrastructure
  • Chromatography, Liquid / methods
  • Cyclic Nucleotide Phosphodiesterases, Type 2 / analysis*
  • Cyclic Nucleotide Phosphodiesterases, Type 2 / metabolism
  • Fluorine Radioisotopes
  • Imidazoles / chemistry*
  • Mice
  • Microtomy
  • Molecular Imaging / methods*
  • Neuroimaging / methods*
  • Positron-Emission Tomography / methods
  • Protein Binding
  • Pyridines / chemistry*
  • Radiopharmaceuticals / chemistry
  • Rats
  • Staining and Labeling / methods
  • Swine
  • Tissue Culture Techniques

Substances

  • Fluorine Radioisotopes
  • Imidazoles
  • Pyridines
  • Radiopharmaceuticals
  • Cyclic Nucleotide Phosphodiesterases, Type 2
  • Pde2a protein, rat