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 [124I]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-[125I]iodophenyl) propionate ([125I]Bolton-Hunter reagent, [125I]I-SHPP) (34.0 ± 4.0%) as compared with N-succinimidyl 3-[125I]iodobenzoate (10.9 ± 6.4%) or direct radioiodination using [125I]iodide and IodoGen (3.1 ± 3.0%). Consequently, the cyclotron-produced positron-emitting [124I]iodine (T1/2 = 4.2 days) was employed to prepare [124I]I-SHPP. Using an improved radioiodination methodology, [124I]I-SHPP was prepared from sodium [124I] iodide with IodoGen at pH 6.5. The [124I]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 [124I]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 © 2002 John Wiley & Sons, Ltd.