[¹¹C]NS9531, [¹¹C]NS9762 and [¹¹C]NS6417, specific SERT tracers: pre-clinical evaluation in pigs and optimization of synthesis conditions using [¹¹C]methyl triflate

Johan Hygum Dam, Dirk Bender, Dan Peters, Kjell Någren

Research output: Contribution to journalJournal articleResearchpeer-review


Introduction: NS9531, NS9762 and NS6417 are nitroquinolinyl-diazabicyclo-alkane derivatives that have been developed as inhibitors of serotonin reuptake transporters (SERT) by NeuroSearch A/S. Methods: IC50 was measured on the up-take of serotonin, dopamine and noradrenaline in synaptosomes prepared from selected rat brain regions. For the pre-clinical evaluation in pigs, [ 11C]NS9531, [ 11C]NS9762 and [ 11C]NS6417 were prepared by N-methylation using [ 11C]methyl iodide. These syntheses were later on optimized regarding: 1) choice of labelled precursor; 2) HPLC purification conditions; and 3) formulation using SPE columns. The synthesis protocols were then fully automated on a GE FX c Pro. Preclinical evaluation was performed by PET studies in landrace pigs before and after treatment with citalopram. Results: IC50 measurements showed that all three compounds have low nanomolar affinity for SERT, and micromolar affinity for DAT and NET. The radiochemical yield (r.y.) of all three ligands from [ 11C]methyl iodide was higher than 30%. From [ 11C]methyl triflate, the r.y. of [ 11C]NS9531 and [ 11C]NS9762 were higher than 80% whereas the r.y. of [ 11C]NS6417 was 65%. Residual precursor amounts in final products could be significantly reduced by the use of [ 11C]methyl triflate, <0.2μg compared with <10μg, calculated for a 300MBq injection at 20minutes EOS. The optimized conditions gave 2.5-4.5GBq of products with a specific radioactivity of 20-70MBq/nmol, residual acetonitrile 15-30ppm, and pH6.5-7.1. All three compounds showed a rapid and comparable high pig brain uptake of about 3%, producing PET images of good contrast, and uptake was reduced after pre-administration with citalopram. Conclusion: The three 11C labelled PET tracers could be prepared in medium to high yield and high purity. IC50 measurements showed that the three NS compounds were highly selective, high affinity SERT inhibitors. PET studies in pig showed high brain uptake that could be blocked by citalopram pre-treatment.

Original languageEnglish
JournalNuclear Medicine and Biology
Issue number1
Pages (from-to)42-51
Publication statusPublished - Jan 2016


  • Preclinical evaluation
  • SERT
  • SPE formulation
  • [ C]NS6417
  • [ C]NS9531
  • [ C]NS9762
  • Radioactive Tracers
  • Chemistry Techniques, Synthetic
  • Serotonin Plasma Membrane Transport Proteins/metabolism
  • Nitroquinolines/chemical synthesis
  • Rats
  • Positron-Emission Tomography
  • Chemistry, Pharmaceutical
  • Animals
  • Swine
  • Isotope Labeling
  • Female
  • Radiopharmaceuticals/chemical synthesis
  • Hydrocarbons, Iodinated/chemistry
  • Mesylates/chemistry
  • Carbon Radioisotopes
  • Quality Control

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