Panitumumab and cetuximab epitope mapping and in vitro activity

14536 Background: Panitumumab, a fully human monoclonal antibody against epidermal growth factor receptor (EGFR), has anti- tumor activity as monotherapy in both preclinical models and clinical trials. The objective of this study was to identify the epitope on EGFR for panitumumab and compare it to that of cetuximab, a chimeric anti-EGFR Ab. Methods: The extracellular domain of EGFR (amino acids 1–618) and domains I, II, III, IV individually were expressed to determine the domain on EGFR that was necessary for panitumumab binding. Chromatography was used to compare the binding affinity of panitumumab vs cetuximab. By flow cytometry and amino acid replacement scanning, the critical residues involved in panitumumab and cetuximab binding for EGFR were determined. Using diffraction data from the panitumumab Fab’2 and published data for cetuximab, crystal structure models of EGFR and the residues determined to be critical for panitumumab or cetuximab binding were built. To evaluate in vitro activity, A549 NSCL...