99mTc-labeling experiments on CCK4 by a direct method

Tc-99m-labeling studies have been performed on CCK, fragment of cholecystokinin, starting from Tc-99m-pertechnetate, by using tin(II)pyrophosphate or tin(II)gluconate as reducing agents, together with NaBH4 acting as a stabilizing agent of tin(II). Gluconate has been used as exchange ligand in the carrier added experiments and in the syntheses of Tc-99-CCK4 and Re-CCK4 complexes to be able to reproduce at macroscopic level the same chemical reactions occurring at non carrier added conditions. 99mTc-labeling yields higher than 95% have been achieved depending on Sn(II) concentration, CCK4/gluconate ratio, reaction time and applied temperature. The species produced with Tc-99m, Tc-99, and cold rhenium nuclides have been compared by means of HPLC measurements, which showed similar retention times and thus probably the same species in the three situations. (C) 2001 Elsevier Science Inc. All rights reserved.