The evolution of 99mTc-NGA as a clinically useful receptor-binding radiopharmaceutical

Technetium-99m-labeled benzoyl-mercaptoacetylglycylglycyl-glycine-mannosyl-dextran ([99mTc]MAG3-mannosyl-dextran) is a receptor-binding radiotracer that binds to mannosebinding protein, a receptor expressed by recticuloendothelial tissue. This agent is composed of a 10.5-kilodalton molecule of dextran and multiple units of mannose, and benzoylmercaptoacetylglycylglycyl-glycine (BzMAG3). The tetraflorophenol-activated ester of BzMAG3 and the imidate of thiomannose were used to covalently attach BzMAG3 and mannose to an amino-terminated conjugate of dextran. This yielded a 19-kilodalton macromolecule consisting of 3 BzMAG3 and 21 mannose units per dextran. Dynamic light scattering was used to measure a mean diameter of 5.5 nanometers for BzMAG3-mannosyldextran and 0.28 microns for filtered Tc-99m sulfur colloid. A preliminary sentinel node detection study employing right fore and hind footpad injections of [99mTc]MAG3-mannosyldextran and left fore and hind footpad injections of filtered Tc-99m sulfur colloid demonstrated greater sentinel lymph node uptake by the receptor-binding agent.