Preparation of ^<99m>Tc radiopharmaceuticals using macroreticular Sn (II) complex

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Stannous chloride (SnCl_2) has the disadvantages of being easily hydrolyzed and oxidized, but it is included in most commercial kits as an appropriate reducing agent in the preparation of ^<99m>Tc radiopharmaceuticals. The replacement of SnCl_2 by the insoluble macromolecular Sn (II) (R-Sn) complex was proposed as a way to resolve some of the problems caused by a large excess of SnCl_2 Macroreticular chelating ion exchange resins having an adsorption ability for Sn (II) were investigated for the development of R-Sn complex. Among them, a chelating resin containing aminophosphonic acid groups showed a high capacity for Sn (II) , which bound strongly to the resin by chelation. The use of the R-Sn complex was expected to minimize Sn (II) comtamination of the ^<99m>Tc labeling solution and be effectively used as a reducing agent for ^<99m>Tc labeling of proteins containing sulfhydryl groups. So, the R-Sn complex was applied to the direct ^<99m>Tc labeling of human immunoglobulin (IgG) to minimize the influence of Sn (II). ^<99m>Tc labeling was achieved at greater than 90% yield simply by the short-term mixing of IgGa containing>2 -SH groups per IgG molecule, ^<99m>Tc pertechnetate, and the R-Sn complex in pH 7 solution. The ^<99m>Tc-IgGa obtained by this labeling method has high stability based on the thiol-specific binding of ^<99m>Tc without transchelation from another weakly bound ^<99m>Tc-complex.