Preparation of the iodine-124 derivative of the Bolton-Hunter reagent ([124I]I-SHPP) and its use for labelling a VEGF antibody as a PET tracer

This study describes the radioiodination of an antibody specific to the vascular endothelial growth factor (VEGF), VG76e, with [I-124]iodine to obtain a novel PET tracer for measurement of angiogenesis. In vitro binding assays showed a significantly higher immunoreactive fraction with the protein labelling reagent N-succinimidyl 3-(4-hydroxy-5-[I-125]iodophenyl) propionate ([I-125]Bolton-Hunter reagent, [I-121]I-SHPP) (34.0 +/- 4.0%) as compared with N-succinimidyl 3-[I-125]iodobenzoate (10.9 +/- 6.4%) or direct radioiodination using [I-125]iodide and IodoGen (3.1 +/- 3.0%). Consequently, the cyclotron-produced positron- emitting [I-124]iodine (T-1/2=4.2 days) was employed to prepare SHPP. Using an improved radioiodination methodology, [I-124]I-SHPP was prepared from sodium [I-124]iodide with IodoGen at pH 6.5. The [I-124]Bolton-Hunter reagent was isolated with 25-58% (n=3) radiochemical yield and 88-95% (n=3) radiochemical purity by the conventional extraction procedure. The conjugate of VG76e with [I-124]I-SHPP was prepared with 17-18% (n=3) labelling efficiency and 98% radiochemical purity. The immunoreactive fraction was determined to be 33.5% (n=2). Copyright (C) 2002 John Wiley Sons, Ltd.