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 insulin. 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 tomography (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-bromosuccinimide 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 intravenous 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 radiotracer can now be obtained in useful radioactivities at high effective specific radioactivity and is now being applied to PET studies of its biodistribution in living subjects. Copyright (C) 2001 John Wiley & Sons, Ltd.