99m Tc-labelled chelates for nuclear medicine application

The quality control of 99mTc-labelled chelates is difficult due to partial hydrolysis of 99mTc as the central atom, autoxidation and formation of polynuclear complexes of Tc(IV) at concentrations above 10*sp-7*M, and the tendency of Tc(V) to participate in disproportionation reactions. Electrophoretic separation with ligandconcentration and pH similar to kit conditions may give good information about the quality of the kits and of the most likely structures of the chelates present. Evidence is presented for the formation of the following chelates under kit conditions: HIDA: [99mTc(III)(L)*sb3*]*sp3-*, DTPA: [99mTc(III)(L)]*sp2-*. For 99mTc- tris-chelates (of HIDA and MDP) a rapid transformation into the corresponding bis-chelates during dilution or i.v. injection may take place, as demonstrated for 99mTc (HIDA). For 99mTc-bis-chelates of DMSA with Tc(IV) and Tc(V) a rapid transformation into mono- chelates takes place in vivo. The reactive chelate [Tc(IV)H*sb2*O(OH)*sb3*(HL)]*sp2-* is bound to plasma proteins and retained in kidney tubuli cells. For many kit preparations it is necessary to carry out in vivo distribution studies in order to verify the oxidation state of 99mTc. (Auth.)