Differential induction of antibody-dependent cellular cytotoxicity (ADCC) against human EGFR-expressing NSCLC cell lines by necitumumab, cetuximab, and panitumumab.

Abstract

e21075 Background: Necitumumab, cetuximab and panitumumab are monoclonal antibodies specific for human epidermal growth factor receptor (EGFR). They act as functional antagonists by blocking ligand binding (EGF and TGFa) to EGFR and inhibit EGFR activation and downstream signaling in tumor cells. Necitumumab and cetuximab are IgG1 molecules and panitumumab is an IgG2 molecule. Methods: In the present study, we analyzed the binding of all three antibodies to EGFR, human Fc receptors and C1q. We also examined the ability to elicit antibody-dependent cellular cytotoxicity (ADCC) in vitro using non-small cell lung cancer (NSCLC) cells expressing various levels of EGFR. Fc-receptor and C1q binding activity was evaluated by ELISA. ADCC was evaluated with a reporter gene based assay using Jurkat cells or human peripheral blood mononuclear cells (PBMC) from normal donors as effector cells. Results: Necitumumab and cetuximab exhibited similar binding to FcgRIa, FcgRIIa, FcgRIIIa and C1q, whereas no binding activity was observed for panitumumab. Necitumumab and cetuximab induced potent ADCC against NSCLC tumor cells at a concentration as low as 1.0 nM. Interestingly, the extent of ADCC induced by cetuximab and necitumumab correlated with the level of EGFR expression on the cell surface. Panitumumab did not elicit ADCC against EGFR expressing tumor cells, even though panitumumab binding to EGFR was similar to that of necitumumab and cetuximab. Conclusions: Both necitumumab and cetuximab, but not panitumumab, target effector cells to EGFR-expressing NSCLC cells to elicit ADCC, with a magnitude that correlates with EGFR expression level. C1q binding studies suggest the relative abilities of EGFR antibodies to fix complement will parallel results with ADCC.