Synthesis and in vitro stability of <SUP>123</SUP>I-labelled annexin V: a potential agent for spect imaging of apoptotic cells

Human recombinant annexin V was radiolabelled with iodine-123 by electrophilic substitution of the containing tyrosine residues using carrier-free sodium iodide-123 as the isotope source. The synthesis of ¹²³H-labelled annexin V was performed using IodoBeads as oxidative solid phase iodinating agent and reaction parameters were optimized and evaluated. Purification by straight-phase HPLC gave [¹²³I]annexin V in a maximum yield of approximately 70% with a radiochemical purity of more than 95% and a specific activity of about 10 MBq/μg of protein. Furthermore, in vitro stability experiments indicated that [¹²³I]-annexin V was stable for at least 8 hours in an aqueous phosphate buffer solution. In plasma however it decreased more rapidly. The biological activity of [¹²³I]-annexin V remained intact in comparison with FITC labelled annexin V as confirmed by in vitro binding experiments with apoptotic cells. Copyright © 2000 John Wiley & Sons, Ltd.