Combined therapy with mutant-selective EGFR inhibitor and Met kinase inhibitor for overcoming erlotinib resistance in EGFR-mutant lung cancer.

Although the EGF receptor tyrosine kinase inhibitors (EGFR-TKI) erlotinib and gefitinib have shown dramatic effects against EGFR mutant lung cancer, patients become resistant by various mechanisms, including gatekeeper EGFR-T790M mutation, Met amplification, and HGF overexpression, thereafter relapsing. Thus, it is urgent to develop novel agents to overcome EGFR-TKI resistance. We have tested the effects of the mutant-selective EGFR-TKI WZ4002 and the mutant-selective Met-TKI E7050 on 3 EGFR mutant lung cancer cell lines resistant to erlotinib by different mechanisms: PC-9/HGF cells with an exon 19 deletion, H1975 with an L858R mutation, and HCC827ER with an exon 19 deletion, with acquired resistance to erlotinib because of HGF gene transfection, gatekeeper T790M mutation, and Met amplification, respectively. WZ4002 inhibited the growth of H1975 cells with a gatekeeper T790M mutation, but did not inhibit the growth of HCC827ER and PC-9/HGF cells. HGF triggered the resistance of H1975 cells to WZ4002, whereas E7050 sensitized HCC827ER, PC-9/HGF, and HGF-treated H1975 cells to WZ4002, inhibiting EGFR and Met phosphorylation and their downstream molecules. Combined treatment potently inhibited the growth of tumors induced in severe-combined immunodeficient mice by H1975, HCC827ER, and PC-9/HGF cells, without any marked adverse events. These therapeutic effects were associated with the inhibition of EGFR and Met phosphorylation in vivo. The combination of a mutant-selective EGFR-TKI and a Met-TKI was effective in suppressing the growth of erlotinib-resistant tumors caused by gatekeeper T790M mutation, Met amplification, and HGF overexpression. Further evaluations in clinical trials are warranted.