Biological activity in vitro of anti-epidermal growth factor receptor monoclonal antibodies with different affinities

Epidermal growth factor receptor (EGFR) is frequently overexpressed in epithelial tumors and is associated with a poor prognosis. An increasing interest in developing anti-EGFR therapies has resulted in the evaluation of monoclonal antibodies with the capacity to bind to the EGFR, inhibiting EGFR-dependent cellular transformation. A differential toxicity and therapeutic effect in vivo are associated with the affinity and isotype of the molecule. In this study, we examined the biological activities of three monoclonal antibodies (MAbs) -- Ior egf/r3 (mouse IgG2a, 10(-9) M), Nimotuzumab (humanized IgG1, 10(-9) M), and Cetuximab (human/mouse chimeric IgG1, 10(-10) M) -- considering inhibition of cell proliferation, apoptosis, and complement-mediated cell death in squamous cell carcinoma A431 in vitro. All the antibodies bound to the EGFR on these cells, inhibiting the receptor phosphorylation, as measured by flow cytometry, inmunocytochemistry, and Western blot. Exposure to the different antibodies inhibited cell proliferation in culture in a range from 50 to 80% compared to controls. Furthermore, similar capabilities to induce either complement-mediated cytotoxicity (ranging between 70 and 90%) or a two-fold increase in the rate of apoptotic cells were found when tumor cells were exposed to the antibodies. These results suggest that the affinity between specific anti-EGFR antibodies and its receptor could affect, but not determine their biological activity at least in those cell lines that exhibit high sensitivity to withheld EGFR. Our findings also confirm previous evidences that blocking EGFR in A431 cells by means of antibodies significantly changes tumor cell biology by promoting apoptosis while decreasing tumor cell proliferation.