Evaluation of gallium-68 tris(2-mercaptobenzyl) amine: A complex with brain and myocardial uptake

Cathy S. Cutler, M. Cecilia Giron, David E. Reichert, Abraham Z. Snyder, Pilar Herrero, Carolyn J. Anderson, Duncan A. Quarless, Stephen A. Koch, Michael J. Welch

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Previous research into development of a gallium-radiolabeled agent that crosses the blood-brain barrier has met with limited success. In this study, we focused our attention on a Ga(III) complex of a 4-coordinate amine trithiolate tripod ligand, tris(2-mercaptobenzyl) amine (S3N). The Ga(III) S3N complex is small, neutral, and lipophilic, meeting the requirements for a potential brain imaging agent. The Ga-68 complex was easily formed with a radiochemical purity of >95%. In vitro stability of the Ga-S3N complex, determined in rat serum incubated at 37°C, was greater than 95% intact at 2 h by silica gel and reversed-phase radio-thin layer chromatography. Biodistribution studies conducted in female Sprague-Dawley rats showed the complex cleared rapidly from the blood with initial high liver uptake followed by rapid washout. Significant uptake was observed in the brain, with brain:blood ratios increasing from 0.11 at 2 min postinjection to 3.8 at 60 min postinjection. Uptake was also observed in the heart going from a heart:blood ratio of 2.3 at 2 min postinjection to 11 at 60 rain postinjection. Molecular mechanics were used to determine the coordination number, and demonstrated that the Ga(III) complex prefers to be 4-coordinate. Imaging studies with 68Ga-S3N in a Nemestrina macaque showed significant brain uptake, similar to other lipophilic agents. The extraction of 68Ga- S3N into the brains of both rodents and primates, higher than any 68Ga agent reported in the literature, suggests that this compound may have potential as a brain imaging agent for positron emission tomography.

Original languageEnglish
Pages (from-to)305-316
Number of pages12
JournalNuclear Medicine and Biology
Issue number3
StatePublished - Apr 1999


  • Brain imaging agent
  • Ga(III)
  • Ga-SN
  • Heart imaging agent
  • Imaging


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