Blockade of AXL activation overcomes acquired resistance to EGFR tyrosine kinase inhibition in non-small cell lung cancer

BACKGROUND: Despite improved outcomes with the introduction of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) in the treatment of patients with advanced non-small cell lung cancer (NSCLC) whose tumors harbor EGFR-activating mutations, unfortunately most patients eventually develop drug resistance. We and others recently reported that AXL activation confers acquired and intrinsic EGFR TKI resistance and represents a bypass resistance mechanism analogous to MET amplification in a subset of patients. This study aims to better assess the mechanisms whereby specific AXL inhibitors overcome such EGFR TKI resistance in NSCLC. METHODS: AXL inhibitors including MGCD265 (glesatinib), MGCD516 (sitravatinib) and R428 (BGB-324) alone or in combination with erlotinib were used to test the inhibitory effect on EGFR TKI resistant NSCLC cells. Subsequently, the effects of single or combinational treatment on cell cycle and apoptosis were assessed. Then, RNA sequencing study was conducted to evaluate the dynamic gene expression profile changes and consequently based on key cellular pathway alterations studies of migration and EMT were pursued. RESULTS: Administration of AXL inhibitors in combination with erlotinib significantly inhibited the growth of erlotinib-resistant NSCLC cells through potently inducing G2-M cell cycle arrest and enhancing apoptosis, relative to single agent treatment. RNA-sequencing analysis identified that several groups of genes enriched in cell survival inhibition or apoptosis promotion were upregulated, whereas genes enriched in DNA replication and repair, cell cycle and cell division were downregulated in cells treated with the combination of erlotinib and AXL inhibitor. Lastly, in line with pathway alterations indicating impaired migration, experiments showed reduced migration and EMT upon combination therapy. CONCLUSIONS: Our results indicate that effective blockade of the AXL pathway may represent a novel strategy to overcome EGFR TKI resistance for the treatment of biomarker-selected subsets of NSCLC patients.