Synthesis and PET imaging of the benzodiazepine receptor tracer [N-methyl-11C]iomazenil

Ronald M. Baldwin, Andrew G. Horti, J. Douglas Bremner, Morgan D. Stratton, Robert F. Dannals, Hayden T. Ravert, Yolanda Zea-Ponce, Chin K. Ng, Holley M. Dey, Robert Soufer, Dennis S. Charney, Samuel M. Mazza, Richard B. Sparks, James B. Stubbs, Robert B. Innis

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The central benzodiazepine receptor tracer [N-methyl-11C]iomazenil (Ro 16-0154) was synthesized by alkylation of the desmethyl precursor noriomazenil with [11C]methyl iodide. The [11C]CH3I (prepared by reduction of [11C]CO2 with LiAlH4 followed by reaction with HI) was reacted with noriomazenil in N,N-dimethylformamide and Bu4N+OH- for 1 min at 80 °C and purified by HPLC (C18, 34% CH3CN/H2O, 7 mL/min). The product was obtained with synthesis time 35 ± 5 min (mean ± SD, n = 7), radiochemical yield (EOB) 36 ± 16%, radiochemical purity 99 ± 1%, and specific activity 5100 ± 2800 mCi/μmol. Absorbed radiation doses were calculated from previously acquired human biodistribution data. The urinary bladder wall received the highest dose (0.099 mGy/MBq) for 4.8 h voiding interval and the effective dose equivalent was 0.015 mSv/MBq. After i.v. injection of [11C]iomazenil in an adult baboon or healthy human volunteer, radioactivity accumulated in the cortex with time-activity curves in agreement with results obtained with [11C]flumazenil PET and [123I]iomazenil SPECT studies. The count rate was sufficient to obtain quantitative images up to 2 h post-injection with a 14mCi injection. These results suggest that [11C]iomazenil will be a useful agent for measuring benzodiazepine receptors in vivo by positron emission tomography.

Original languageEnglish (US)
Pages (from-to)659-665
Number of pages7
JournalNuclear Medicine and Biology
Issue number5
StatePublished - Jul 1995

ASJC Scopus subject areas

  • Molecular Medicine
  • Radiology Nuclear Medicine and imaging
  • Cancer Research

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    Baldwin, R. M., Horti, A. G., Bremner, J. D., Stratton, M. D., Dannals, R. F., Ravert, H. T., Zea-Ponce, Y., Ng, C. K., Dey, H. M., Soufer, R., Charney, D. S., Mazza, S. M., Sparks, R. B., Stubbs, J. B., & Innis, R. B. (1995). Synthesis and PET imaging of the benzodiazepine receptor tracer [N-methyl-11C]iomazenil. Nuclear Medicine and Biology, 22(5), 659-665.