T790M-selective EGFR-TKI combined with dasatinib as an optimal strategy for overcoming EGFR-TKI resistance in T790M-positive non-small cell lung cancer

T790M mutation-selective epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have demonstrated clinical benefits in non-small cell lung cancer (NSCLC) patients harboring T790M mutation, which is the major cause of resistance to EGFR-TKI. However, their efficacy is limited, possibly due to the emergence of apoptosis resistance in T790M-positive NSCLC. We previously identified Src family kinases as co-oncogenic drivers along with T790M and found that the Src inhibitor dasatinib combined with an irreversible or a preclinical T790M-selective EGFR-TKI enhanced anti-tumor activity in T790M-positive cells. In the current study, we evaluated the efficacy of dasatinib combined with the clinically relevant T790M-selective EGFR-TKI or osimertinib in EGFR mutation-positive NSCLC with or without T790M mutation. A cell viability assay revealed that dasatinib had synergistic effects with these TKIs in T790M-positive cells, and simultaneously inhibited Src, Akt, and Erk, which remained activated upon single-agent treatment. Dasatinib also increased the rate of apoptosis in T790M-positive cells induced by T790M-selective EGFR-TKIs, as determined by the annexin-V binding assay; this was associated with downregulation of the anti-apoptotic Bcl-2 family member Bcl-xL, a finding that was confirmed in mice bearing T790M-positive xenografts. Our results suggest that Bcl-xL plays a key role in the apoptosis resistance of T790M-positive NSCLC, and that dasatinib combined with clinically relevant T790M-selective EGFR-TKIs is potentially effective in overcoming resistance to first-generation EGFR-TKIs in NSCLC patients with acquired T790M.

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