In vitro evaluation of iodine-125-labeled monoclonal antibody (MAb 425) in human high-grade glioma cells

Human high-grade glioma cell lines (A1207, U-87MG, U-373MG, and F39) with high levels of epidermal growth factor receptor (EGF-R) expression were incubated for 2-48 h with 1 μCi/ml of the EGF-R-specific ¹²⁵I-MAb 425 and measured for surface-bound, cytoplasmic, and nuclear radioactivity. The A1207 and U-373MG cell lines showed the highest surface-bound radioactivity with 215.9 ± 8.7 nCi (30 h) and 287.8 ± 23.2 nCi (24 h)/10⁶ cells, respectively, whereas the U-87MG and the F39 cell lines bound significantly less antibody (48.8 ± 5.4 nCi [48 h] and 31.1 ± 0.7 nCi [24 h]). Surface- bound antibody was efficiently internalized into the cytoplasm. The U-373MG, U-87MG, and A1207 cell lines achieved 19.8% ± 2.1 internalization of the surface-bound antibody in contrast to >40% for the F39 cell line. Only the A 1207 cell line showed significant nuclear radioactivity. There was no correlation between the reported EGF-R number and amount of antibody bound or internalized. We conclude that binding and uptake of the ¹²⁵I-MAb 425 is specific for human glioma cells and shows saturation kinetics independent of receptor density.