TUMOR-SPECIFIC ANTIEPIDERMAL GROWTH-FACTOR RECEPTOR VARIANT-III MONOCLONAL-ANTIBODIES - USE OF THE TYRAMINE-CELLOBIOSE RADIOIODINATION METHOD ENHANCES CELLULAR RETENTION AND UPTAKE IN TUMOR XENOGRAFTS

Amplification and rearrangement of the epidermal growth factor recepto r (EGFR) gene are characteristics of many types of tumors. One class o f EGFR mutations, EGFRvIII, is characterized by an in-frame deletion r esulting in a truncated external domain of the receptor. EGFR-vIII was first identified in a subset of gliomas and has since been found in s ome non-small cell lung carcinomas and breast carcinomas, mAbs specifi c for this variant form of EGFR but unreactive with the wild-type EGFR have been reported from our laboratory, This study further characteri zes three of these antibodies, We determined, via radiolabeling techni ques and immunofluorescence microscopy, that, after cell binding in vi tro, the anti-EGFRvIII-specific mAbs internalize at 37 degrees C. Furt hermore, subsequent to internalization, the antibodies were processed intracellularly, presumably by lysosomal degradation. We also examined the use of an alternative radiolabeling procedure that uses nonmetabo lizable radioiodinated tyramine cellobiose, Our results show that the tyramine cellobiose labeling method allo rvs for greater tumor cell re tention of radiolabel in vitro (76% for tyramine cellobiose and 27% fo r Iodo-Gen after 24 h), Paired-label biodistribution studies in athymi c mice indicate that anti-EGFRvIII mAb L8A4 localizes specifically to EGFRvIII-expressing tumor xenografts with a maximum of 34.3 +/- 7.6% i njected dose/g when labeled using tyramine cellobiose compared with a maximum of 14.9 +/- 4.3% injected dose/g using Iodo-Gen; similar resul ts were obtained with mAb H10. These results suggest that the anti-EGF RvIII mAbs may serve as potential carriers for radioconjugate- and imm unotoxin-based therapies for tumors expressing EGFRvIII.