title: The development and in-vivo behavior of tin containing radiopharmaceuticals--I. Chemistry, preparation, and biodistribution in small animals.
abstract: Tin is an essential ingredient of most technetium-99m radiopharmaceutical preparations but its in-vivo distribution and long-term fate are not well understood. Tin-117m (t1/2 14d; gamma 159 keV, 86%) is an ideal tracer for studying biological behavior of tin compounds as well as for developing clinically-useful radiopharmaceuticals. This work describes the preparation and in-vivo distribution in mice of a number of tin-117m labeled compounds with commonly used ligands. High bone uptake of most compounds studied as well as the unexpectedly high bone uptake of Sn4+-DTPA indicates a high bone affinity of tin bound to chemically diverse ligands. Various compounds show subtle but significant differences in blood clearance, excretion, and soft-tissue uptake. Differences among Sn2+ and Sn4+ compounds with the same ligand are particularly noteworthy. For stannic chelates, higher bone uptake, faster blood clearance, and reduced soft-tissue concentration were observed. It appears that tin compounds bind to bone predominantly through the tin atom and that the differences in biodistribution depend on factors such as the net charge on the complex, the oxidation state of tin, and hydrolytic and kinetic stabilities of the complexes. The results indicate that the favorable half-life and decay characteristics of tin-117m in various stannic compounds, especially stannic-DTPA, make it potentially useful as an agent for skeletal scintigraphy and radiotherapy of bone tumors.
mesh_terms: D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D007202:Indicators and Reagents; D007700:Kinetics; D051379:Mice; D011868:Radioisotopes; D013667:Technetium; D014001:Tin; D014018:Tissue Distribution
chemical_list: D007202:Indicators and Reagents; D011868:Radioisotopes; D013667:Technetium; D014001:Tin