Synthesis and evaluation of tricarbonyl 99mTc-Labeled 2-(4-Chloro)phenyl-imidazo[1,2-a] pyridine analogs as novel SPECT imaging radiotracer for TSPO-rich cancer

Ji Young Choi, Rosa Maria Iacobazzi, Mara Perrone, Nicola Margiotta, Annalisa Cutrignelli, Jae Ho Jung, Do Dam Park, Byung Seok Moon, Nunzio Denora, Sang Eun Kim, Byung Chul Lee

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The 18-kDa translocator protein (TSPO) levels are associated with brain, breast, and prostate cancer progression and have emerged as viable targets for cancer therapy and imaging. In order to develop highly selective and active ligands with a high affinity for TSPO, imidazopyridine-based TSPO ligand (CB256, 3) was prepared as the precursor. 99mTc- and Re-CB256 (1 and 2, respectively) were synthesized in high radiochemical yield (74.5% ± 6.4%, decay-corrected, n = 5) and chemical yield (65.6%) by the incorporation of the [99mTc(CO)3(H2O)3]+ and (NEt4)2[Re(CO)3Br3] followed by HPLC separation. Radio-ligand 1 was shown to be stable (>99%) when incubated in human serum for 4 h at 37 °C with a relatively low lipophilicity (logD = 2.15 ± 0.02). The rhenium-185 and -187 complex 2 exhibited a moderate affinity (Ki = 159.3 ± 8.7 nM) for TSPO, whereas its cytotoxicity evaluated on TSPO-rich tumor cell lines was lower than that observed for the precursor. In vitro uptake studies of1 in C6 and U87-MG cells for 60 min was found to be 9.84% ± 0.17% and 7.87% ± 0.23% ID, respectively. Our results indicated that 99mTc-CB256 can be considered as a potential new TSPO-rich cancer SPECT imaging agent and provides the foundation for further in vivo evaluation.

Original languageEnglish
Article number1085
JournalInternational Journal of Molecular Sciences
Issue number7
Publication statusPublished - Jul 1 2016


  • Tc(CO)
  • Translocator protein
  • Tricarbonyltechnetium-99m
  • TSPO
  • TSPO-rich tumors

ASJC Scopus subject areas

  • Catalysis
  • Molecular Biology
  • Spectroscopy
  • Computer Science Applications
  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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