Preparation of no-carrier-added [I-124]A(14)-iodoinsulin as a radiotracer for positron emission tomography

A(14)-Iodoinsulin is a close biochemical and pharmacological mimic of insul in. Human insulin was labelled in its A chain tyrosine-14 residue by direct iodination with the positron-emitter iodine-124 (beta (+) = 25.6%; t(1/2) = 4.15 days) to provide a radiotracer for imaging with positron emission to mography (PET). Several reagents were compared for conversion of cyclotron- produced [I-124]iodide into a reactive species for the labelling reaction. Radiochemical yields from the use of Iodo-Gen (R), Chloramine-T, N-bromosuc cinimide or lactoperoxidase-hydrogen peroxide were similar [35% (n = 1), 33 +/- 9% (n = 10), 32 +/- 11% (n = 25) or 33% (n = 2), respectively]. [I-124 ]A(14)-Iodoinsulin was separated from unreacted insulin and radioactive by- products by tandem reverse phase HPLC and rapidly formulated for intravenou s injection by adsorption on a Sep-Pak (t)C18-Plus (R) cartridge, followed by elution with 10 mM hydrochloric acid-ethanol (1 : 1 v/v, 1 mi). This rad iotracer can now be obtained in useful radioactivities at high effective sp ecific radioactivity and is now being applied to PET studies of its biodist ribution in living subjects. Copyright (C) 2001 John Wiley & Sons, Ltd.