Amplification and rearrangement of the
epidermal growth factor receptor (EGFR) gene are characteristics of many types of
tumors. One class of EGFR mutations,
EGFRvIII, is characterized by an in-frame deletion resulting in a truncated external domain of the receptor.
EGFRvIII was first identified in a subset of
gliomas and has since been found in some
non-small cell lung carcinomas and
breast carcinomas. mAbs specific for this variant form of EGFR but unreactive with the wild-type EGFR have been reported from our laboratory. This study further characterizes three of these
antibodies. We determined, via radiolabeling techniques and immunofluorescence microscopy, that, after cell binding in vitro, the anti-
EGFRvIII-specific mAbs internalize at 37 degrees C. Furthermore, subsequent to internalization, the
antibodies were processed intracellularly, presumably by lysosomal degradation. We also examined the use of an alternative radiolabeling procedure that uses nonmetabolizable radio-iodinated
tyramine cellobiose. Our results show that the
tyramine cellobiose labeling method allows for greater
tumor cell retention of radiolabel in vitro (76% for
tyramine cellobiose and 27% for
Iodo-Gen after 24 h). Paired-label biodistribution studies in athymic mice indicate that anti-
EGFRvIII mAb L8A4 localizes specifically to
EGFRvIII-expressing
tumor xenografts with a maximum of 34.3 +/- 7.6% injected dose/g when labeled using
tyramine cellobiose compared with a maximum of 14.9 +/- 4.3% injected dose/g using
Iodo-Gen; similar results were obtained with mAb H10. These results suggest that the anti-
EGFRvIII mAbs may serve as potential carriers for radioconjugate- and
immunotoxin-based
therapies for
tumors expressing
EGFRvIII.