Cetuximab is a chimeric (mouse/human) IgG1 antibody that binds EGFR subdomain III, blocking ligand binding and enabling Fc-mediated ADCC. It is produced in murine SP2/0 cells and carries α-1,3-galactose (α-Gal) glycan epitopes, which can cause hypersensitivity reactions in patients with pre-existing anti-α-Gal IgE. Panitumumab is a fully human IgG2 antibody that also binds subdomain III but lacks ADCC activity (IgG2 Fc) and is produced in CHO cells without α-Gal. Both require KRAS/NRAS wild-type status in CRC patients — downstream RAS mutations render EGFR blockade ineffective.

The most common activating EGFR mutations in NSCLC are exon 19 deletions (~45%) and L858R point mutation in exon 21 (~40%) — both are sensitive to TKI therapy. Exon 20 insertions (~10%) are generally TKI-resistant but targetable by Amivantamab (bispecific antibody). The T790M gatekeeper mutation (exon 20) is the dominant resistance mechanism to 1st/2nd-generation TKIs, overcome by Osimertinib. C797S is an emerging resistance mechanism to Osimertinib. For research, we offer wild-type and mutant EGFR ECD proteins, and anti-EGFR antibodies suitable for detecting both wild-type and mutant receptor by WB and IHC.

EGFRvIII (variant III) is a deletion mutant lacking exons 2-7 (267 amino acids from the extracellular domain), creating a constitutively active receptor that cannot bind ligand. EGFRvIII is found in ~30% of glioblastomas and a subset of HNSCC. Its tumor-specific expression (absent on normal tissues) makes it an attractive target for CAR-T therapy, ADCs, and tumor-specific vaccines (Rindopepimut). Anti-EGFRvIII antibodies that recognize the unique junction epitope do not cross-react with wild-type EGFR.

Cetuximab is produced in murine SP2/0 cells that add α-1,3-galactose (α-Gal) residues to the Fc glycans — a non-human glycan structure. Patients with pre-existing anti-α-Gal IgE antibodies (common in certain geographic regions due to tick bites/α-Gal syndrome) can develop severe anaphylaxis. Cetuximab biosimilar development must carefully characterize α-Gal content and demonstrate comparable levels to the reference product. Some biosimilar manufacturers produce Cetuximab in CHO cells (which lack the α-Gal transferase), but this creates a glycan profile different from the reference, complicating regulatory comparability.

Both Cetuximab and Panitumumab bind EGFR subdomain III (the ligand-binding domain), with partially overlapping but non-identical epitopes. They directly compete with EGF and TGF-α for receptor binding, preventing ligand-induced dimerization and signaling. This is distinct from HER2-targeting antibodies: Trastuzumab binds subdomain IV and Pertuzumab binds subdomain II. For epitope mapping of novel anti-EGFR candidates, individual EGFR subdomain proteins and competitive binding assays with Cetuximab/Panitumumab can determine epitope overlap.