RADIOIODINATION, QUALITY ASSESSMENT, IN-VITRO AND IN-VIVO STABILITY OF I-125 NOFETUMOMAB

Iodine-125 radiolabeled monoclonal antibody (MAb) preparations used fo r radioimmunoguided surgery should be prepared in a manner to insure a stable, efficacious and safe product is used in clinical studies. A n umber 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 con ditions. A radiolabeling and stability study was completed to evaluate the radiochemical purity and immunoreactivity of NR-LU-10 Fab (nofetu momab) radiolabeled with I-125 at three different specific activities using the IODO-GEN(R) 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. Th e radiochemical purity end immunoreactivity of each lot of radiolabele d nofetumomab were determined on days 0, 8, 15, 22, 29 and 36 after ra diolabeling using standard tests of instant thin layer chromatography (ITLC), high performance liquid chromatography (HPLC) and whole cell b inding assay of immunoreactivity. These standard tests indicated the r adiochemical purity on the day of radioiodination was high for all spe cific activity levels (98-99% for ITLC and >98% for HPLC). Preparation s at ali specific activities showed a slight decrease in radiochemical purity over time with the amount of unbound I-125 increasing or remai ning unchanged. The immunoreactivity net bound showed excellent bindin g with values ranging from 65-75%. The data indicate I-125 nofetumomab undergoes in vitro physico-chemical changes over time. However, the c hanges in radio-chemical purity and immunoreactivity were minimal and should prove to be clinically insignificant.