Membrane transport of Tc-99m-labeled radiopharmaceuticals. I. Brain uptake by passive transport

The membrane transport properties of twelve Tc-99m complexes were studied by determining each complex's brain uptake index (BUI), extent of protein binding, and octanol-to-saline partition coefficient. The chelating agents used were classified as either N-substituted carbamoylmethyliminodiacetates, substituted oxines, N,N'-diesters of EDTA, or N-substituted derivatives of DTPA. The Tc-99m complexes were found to cross the blood-brain barrier in proportion to their lipophilicity. Of the four types of chelating agents tested, substituted oxines appear to be most suitable for the development of diffusible Tc-99m-labeled compounds for imaging nonexcretory organs