Immunoenzymetric assay of epidermal growth factor receptor. Application to breast tumor samples

An immunoenzymetric assay (IEMA) for the human epidermal growth factor receptor (EGFR) solubilized with nonionic detergent has been developed using two commercially available monoclonal antibodies (MoAb) and tested on breast tumor samples. The first MoAb (R1), immunoadsorbed on a solid phase, is used to immobilize solubilized EGFR. A second MoAb (528) binds to the immobilized EGFR and is revealed with o-phenylenediamine by a peroxidase-linked goat antimouse IgG2a. The detection limit is 2.5 fmol/ml, corresponding to 1-2.5 fmol/mg membrane protein which allows a determination of EGFR from as low as 100-200 micrograms of membrane proteins. The IEMA was linear for serial sample dilutions in a large range of EGFR concentrations. The recovery of increasing quantities of EGFR added to clinical samples ranged from 82 to 107%. We found a high reproducibility (r = 0.97) between two successive assays of 36 breast tumor samples. The EGFR content measured by this method in 50 breast tumor samples correlated (r = 0.95) with the values obtained by a radioligand assay on crude membrane preparations. This sensitive, accurate, reproducible, time and tissue quantity efficient IEMA appears suitable for biological and clinical studies of the role of EGFR in malignant pathology.