title: Enhanced EGFR inhibition and distinct epitope recognition by EGFR antagonistic mAbs C225 and 425.
abstract: Monoclonal antibodies (mAbs) that inhibit activation of the epidermal growth factor receptor (EGFR) have shown therapeutic potential in select malignancies including breast cancer. Here, we describe that combined use of two such mAbs, C225 (Cetuximab) and 425 (EMD55900), reduced growth and survival of EGFR overexpressing MDA-MB-468 breast cancer cells more effectively than either antibody alone. Similarly, the C225/425 antibody combination more effectively inhibited AKT and MAPK phosphorylation in MDA-MB-468 cells. Surface plasmon resonance, size exclusion chromatography and analytical ultracentrifugation demonstrated that mAbs C225 and 425 simultaneously bind to distinct antigenic epitopes on domain III of the soluble wild-type EGFR. Furthermore, neither mAb competed with the other for binding to cells expressing either wild-type EGFR or a mutant EGFR (EGFRvIII) associated with neoplasia. Mutagenesis experiments revealed that residues S460/G461 in EGFR domain III are essential components of the 425 epitope and clearly distinguish it from the EGF/ TGFalpha binding site and the C225 interaction interface. Collectively, these results support the conclusion that therapeutic EGFR blockade in cancer patients by combined use of mAbs C225 and 425 could provide advantages over the use of the two antibodies as single agents.
authors.affiliation: School of Biomedical Engineering, Science & Health Systems, Drexel University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: Vishal
authors.initials: V
authors.lastname: Kamat
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Donaldson
authors.forename: Csaba
authors.initials: C
authors.lastname: Kari
authors.forename: Marlene R D
authors.initials: MR
authors.lastname: Quadros
authors.forename: Peter I
authors.initials: PI
authors.lastname: Lelkes
authors.forename: Irwin
authors.initials: I
authors.lastname: Chaiken
authors.forename: Simon
authors.initials: S
authors.lastname: Cocklin
authors.forename: John C
authors.initials: JC
authors.lastname: Williams
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Papazoglou
authors.forename: Ulrich
authors.initials: U
authors.lastname: Rodeck
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000494:pharmacology; D061067:Antibodies, Monoclonal, Humanized; D045744:Cell Line, Tumor; D000068818:Cetuximab; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D018604:Epitope Mapping; D000939:Epitopes / Q000737:chemistry; D066246:ErbB Receptors / Q000037:antagonists & inhibitors*; D006801:Humans; D051379:Mice; D008968:Molecular Conformation; D041681:NIH 3T3 Cells; D020032:Tyrphostins / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000939:Epitopes; D020032:Tyrphostins; D066246:ErbB Receptors; C520777:matuzumab; D000068818:Cetuximab