Radioiodination, quality assessment, in vitro and in vivo stability of iodine-125 nofetumomab

Abstract

Iodine-125 radiolabeled monoclonal antibody (MAb) preparations used for radioimmunoguided surgery should be prepared in a manner to insure a stable, efficacious and safe product is used in clinical studies. A number of MAbs have been radioiodinated and used for radioimmunoguided surgery procedures including B72.3 and CC49. Individual MAbs and their fragments differ in their physico-chemical response to conditions of radiolabeling, effects of radiolysis, storage and general handling conditions. A radiolabeling and stability study was completed to evaluate the radiochemical purity and immunoreactivity of NR-LU-10 Fab (nofetumomab) radiolabeled with I-125 at three different specific activities using the IODO-GEN® method. Ratios of 2:1, 1:1, 0.4:1 and 0.2:1(mCi/mg) were used to determine the effects of increasing specific activity on the in vitro stability in a range of potential patient dosages. The radiochemical purity and immunoreactivity of each lot of radiolabeled nofetumomab were determined on days 0, 8, 15, 22, 29 and 36 after radiolabeling using standard tests of instant thin layer chromatography (ITLC), high performance liquid chromatography (HPLC) and whole cell binding assay of immunoreactivity. These standard tests indicated the radiochemical purity on the day of radioiodination was high for all specific activity levels (98–99% for ITLC and >98% for HPLC). Preparations at all specific activities showed a slight decrease in radiochemical purity over time with the amount of unbound I-125 increasing or remaining unchanged. The immunoreactivity net bound showed excellent binding with values ranging from 65–75%. The data indicate I-125 nofetumomab undergoes in vitro physico-chemical changes over time. However, the changes in radio-chemical purity and immunoreactivity were minimal and should prove to be clinically insignificant. © 1998 John Wiley & Sons, Ltd.