Preparation of no‐carrier‐added [ 124 I]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 (β + =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 [ 124 I]iodide into a reactive species for the labelling reaction. Radiochemical yields from the use of Iodo‐Gen ® , 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]. [ 124 I]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 ® cartridge, followed by elution with 10 mM hydrochloric acid–ethanol (1:1 v/v, 1 ml). 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 © 2001 John Wiley & Sons, Ltd.