P2.13-21 MET Addiction Can be Circumvented Through EGFR Inhibition Via AXL in MET-Amplified Primary Resistant EGFR-Mutant NSCLCX.

Abstract

Primary resistance to EGFR-TKI is observed in approximately 10% of patients with activating EGFR mutations. In a patient harboring L858R mutation and high cMET amplification (MET copy number 7.3, CEP7 ratio 3.4) who progressed after just 4 weeks of erlotinib (ERL), significant tumor regression was achieved with MET inhibition alone (Crizotinib, CRZ). We confirmed this phenotype in the corresponding patient-derived cell line model (A482) and identified EGFR-AXL interaction as a mechanism that can circumvent clonal cMET addiction. We generated patient-derived cell lines from the patient’s baseline neck excision biopsy (A482) and evaluated the effect of mono and combination therapy (ERL, CRZ, ERL-CRZ) on A482, including viability (CellTiter-Glo Luminescent Assay, Promega), colony forming (Crystal Violet Assay), downstream signaling (Western blots) and adaptive pathways (Human Phosho-Receptor Tyrosine Kinase Array Kit, RandD systems). AXL was identified as a key mediator of resistance and subsequently subjected to further functional validation. Finally, we examined the prevalence of this clinical phenomenon in a retrospective series of MET amplified EGFR-mutant NSCLC. Cell viability assays confirmed the patient-derived cell line to be more sensitive to CRZ as compared to ERL alone or with combination CRZ-ERL. Upregulation of AXL, RET and FGFR3 expression were identified as adaptive changes 24 hours upon ERL exposure. A targeted pharmacologic screen revealed A482 to be exquisitely sensitive to combination EGFR and AXL inhibition. Immunoprecipitation revealed a direct interaction between EGFR and AXL, which upon treatment with ERL resulted in attenuation of cMET addiction. Co-existing cMET amplification with demonstrated suboptimal response to EGFR TKI was found in 3% of EGFR-mutant NSCLC in a retrospective series of patients. Targeting the EGFR-AXL axis through EGFR inhibition alone can lead to paradoxical MET pathway activation, while the combination of EGFR and AXL inhibition can circumvent downstream signaling in MET amplified EGFR-mutant NSCLC. AXL expression levels can potentially identify patients in whom combination or monotherapy with MET inhibitors may be most beneficial. Our data highlights the challenge in interpreting genomic alterations alone; and how cellular context can lead to differential sensitivities to EGFR and MET inhibitors alone and/or in combination in MET amplified EGFR-mutant NSCLC.