3044 Background: The epidermal growth factor receptor (EGFR) serves as a molecular target for novel cancer therapeutic approaches. Two groups of anti-EGFR agents are clinically most advanced: tyrosine kinase inhibitors (TKI) and EGFR antibodies. Recently, somatic mutations in the EGFR kinase domain were identified in tumors from lung cancer patients, which affected EGFR signaling and which correlated with responses to TKI therapy. Since interference with tumor cell signaling is also considered an important mechanism of action for therapeutic antibodies, we investigated the influence of these intracellular EGFR mutations on cell killing by EGFR antibodies, in comparison to TKI. Methods: For this purpose, we established an EGF-responsive, non-transformed cell line model for the three most common lung cancer-derived intracellular EGFR mutations L858R, G719S and delE746-A750. EGFR phosphorylation status was analyzed by Western Blots. MTT assays were performed to compare TKI gefitinib and erlotinib with antibodies C225 and 2F8 in their capacity to inhibit cell growth of wild type and mutated EGFR-transfectants. Impact of intracellular EGFR mutations on immune cell-mediated killing by EGFR antibodies was measured in classical 3 hours 51-chromium-release assays. Results: Mutated EGFR transfected cells were growth factor- responsive, and significantly more sensitive to both gefitinib and erlotinib than wild type (WT) EGFR expressing cells. However, anti-tumor effector functions of both EGFR-directed IgG1 antibodies—chimeric C225 and fully human 2F8—were not affected by the mutations. Conclusions: Intracellular mutations of EGFR may, therefore, be less relevant for EGFR antibodies than for TKI. No significant financial relationships to disclose.
Coexistence of KRAS mutation with mutant but not wild-type EGFR predicts response to tyrosine-kinase inhibitors in human lung cancer
