[67Ga]desferrioxamine--HSA: synthesis of chelon protein conjugates using carbodiimide as a coupling agent

Desferrioxamine-human serum albumin conjugate was prepared at pH 4.7 using a water-soluble carbodiimide and at pH 7.8 using glutaraldehyde. The crude conjugate was purified by dialysis and gel filtration. The efficiency of 67Ga labeling of the purified conjugate was greater than 95%, with good in vitro stability. The specific activity ranged from 5 to 50 microCi/mg. Treatment of the conjugate with urea resulted in a 20--30-fold increase in specific activity, suggesting that a number of chelon groups are unavailable for Ga binding due to non-covalent intramolecular cross-linking.