title: Functional dissection of the epidermal growth factor receptor epitopes targeted by panitumumab and cetuximab.
abstract: Cetuximab and panitumumab, two antibodies targeting the extracellular domain of the epidermal growth factor receptor (EGFR), are of major clinical importance particularly in the treatment of metastatic colorectal cancer. As patients may acquire resistance-mediating mutations within the extracellular EGFR domain, functional dissection of the exact binding sites of EGFR targeting antibodies may help predict treatment responses. We therefore assessed the epitope recognition of panitumumab by screening phage-displayed random cyclic 7mer and linear 12mer peptide libraries on this antibody. Phage screenings revealed two strong, potentially epitope-mimicking consensus motifs targeted by panitumumab. A computational approach was used to map the sequences back to the potential epitope region on domain III of EGFR. The presumed epitope regions (386)WPEXRT(391) and a biochemically similar though discontinuous region P349-F352-D355 on a neighboring loop of domain III could be confirmed as part of the functionally relevant binding site of panitumumab by site-directed mutational analysis. To more accurately differentiate the panitumumab epitope from the previously characterized cetuximab epitope, binding studies were performed on a broad range of additional mutants. Taken together, this analysis revealed two large, partially overlapping functional epitopes consisting of 17 critical amino acid positions. Four of these positions were selectively targeted by cetuximab (I467, S468, Q408, and H409), whereas another four were selectively recognized by panitumumab (W386, E388, R390, and T391). In view of the clinical significance of extracellular domain mutations, our data may help guide treatment decisions in selected patients receiving EGFR-targeted therapies.
authors.affiliation: Department of Oncology and Hematology with Sections Bone Marrow Transplant and Pneumology, Hubertus Wald Tumorzentrum/University Cancer Center Hamburg, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Mareike
authors.initials: M
authors.lastname: Voigt
authors.forename: Friederike
authors.initials: F
authors.lastname: Braig
authors.forename: Markus
authors.initials: M
authors.lastname: Göthel
authors.forename: Alexander
authors.initials: A
authors.lastname: Schulte
authors.forename: Katrin
authors.initials: K
authors.lastname: Lamszus
authors.forename: Carsten
authors.initials: C
authors.lastname: Bokemeyer
authors.forename: Mascha
authors.initials: M
authors.lastname: Binder
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D061067:Antibodies, Monoclonal, Humanized; D061505:Cell Surface Display Techniques; D000068818:Cetuximab; D018604:Epitope Mapping; D000939:Epitopes / Q000737:chemistry / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D066246:ErbB Receptors / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D018716:Molecular Mimicry / Q000276:immunology; D009154:Mutation; D000077544:Panitumumab; D019151:Peptide Library; D010455:Peptides / Q000276:immunology / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000939:Epitopes; D019151:Peptide Library; D010455:Peptides; D000077544:Panitumumab; D066246:ErbB Receptors; D000068818:Cetuximab