LABELING OF HUMAN SERUM-ALBUMIN WITH TC-99M USING SN(II) CITRATE

Labelling of human serum albumin (HSA) with 99m Tc, at neutral pH, using Sn(II) citrate as reducing agent is described. At pH 7.4, more than 98% binding efficiency for 99m Tc‐HSA is achieved. 99mTc‐Sn‐citrate with high protein binding capacity is first formed as an intermediate complex and in the presence of albumin, a more stable 99mTc‐HSA complex is formed. 99mTc‐HSA complex is formed by ligand exchange and 30 min reaction time is sufficient for the complex formation of 99mTc‐HSA. Biodistribution in normal mice at 30 min obtained for 99mTc‐HSA prepared by Sn(II) citrate showed 30.3% injected dose in blood compared to 32.9–34.5% for 99mTc‐HSA prepared by Sn(II)Cl2. The presence of citrate stabilizes Sn(II) ions towards oxidation and hydrolysis. The addition of ascorbic acid did not increase the percent yield of 99mTc‐HSA and has adverse effect on its biological distribution. Copyright © 1990 John Wiley & Sons, Ltd.