title: IgG isotype, glycosylation, and EGFR expression determine the induction of antibody-dependent cellular cytotoxicity in vitro by cetuximab.
abstract: OBJECTIVE
  To evaluate the antibody-dependent cellular cytotoxicity (ADCC) of cetuximab, an anti-epidermal growth factor receptor (EGFR) IgG1 antibody, in vitro.
  
  
  METHODS
  Binding to human Fc receptors was measured by ELISA. ADCC against a panel of tumor cell lines was evaluated using peripheral blood mononuclear cells or NK cells as effectors and lactate dehydrogenase release as a marker of cell killing. Cetuximab was compared with two glycan variants of cetuximab and with panitumumab, an anti-EGFR IgG2.
  
  
  RESULTS
  Cetuximab bound with high affinity to FcγRI (EC50 = 0.13 nM) and FcγRIIIa (EC50 = 6 nM) and effectively induced ADCC across multiple tumor cell lines. Panitumumab and aglycosylated cetuximab did not bind to FcγRI or FcγRIIIa nor have ADCC activity even at high effector-target cell ratios, even though the EGFR-binding affinity of cetuximab and panitumumab were shown to be comparable (KD = 87 pM and 83 pM, respectively). The extent of cetuximab-elicited ADCC was associated with the level of EGFR expression on tumor cells.
  
  
  CONCLUSIONS
  Cetuximab elicits effective ADCC activity against a wide range of tumor cells in vitro. This activity is dependent on antibody glycosylation and IgG1 isotype as well as tumor-cell EGFR expression. These findings suggest that ADCC may contribute to the antitumor activity of cetuximab.
authors.affiliation: Department of Immunology, ImClone Systems, New York, NY 10014, USA.
authors.forename: Dipa
authors.initials: D
authors.lastname: Patel
authors.forename: Xuemei
authors.initials: X
authors.lastname: Guo
authors.forename: Stanley
authors.initials: S
authors.lastname: Ng
authors.forename: Maxine
authors.initials: M
authors.lastname: Melchior
authors.forename: Paul
authors.initials: P
authors.lastname: Balderes
authors.forename: Douglas
authors.initials: D
authors.lastname: Burtrum
authors.forename: Kris
authors.initials: K
authors.lastname: Persaud
authors.forename: Xenia
authors.initials: X
authors.lastname: Luna
authors.forename: Dale L
authors.initials: DL
authors.lastname: Ludwig
authors.forename: Xiaoqiang
authors.initials: X
authors.lastname: Kang
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000378:metabolism; D061067:Antibodies, Monoclonal, Humanized; D000920:Antibody-Dependent Cell Cytotoxicity; D000970:Antineoplastic Agents / Q000276:immunology* / Q000378:metabolism; D045744:Cell Line, Tumor; D000068818:Cetuximab; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D066246:ErbB Receptors / Q000276:immunology / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology*; D007132:Immunoglobulin Isotypes; D007694:Killer Cells, Natural / Q000276:immunology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000276:immunology; D000077544:Panitumumab
chemical_list: D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D007074:Immunoglobulin G; D007132:Immunoglobulin Isotypes; D000077544:Panitumumab; D007770:L-Lactate Dehydrogenase; D066246:ErbB Receptors; D000068818:Cetuximab