Overcoming AXL Activation and EpithelialMesenchymal Transition is Critical in Conquering ALK-positive NonSmall Cell Lung Cancer

Anaplastic lymphoma kinase tyrosine kinase inhibitors (ALK-TKIs) induce a dramatic response in nonsmall cell lung cancer (NSCLC) patients with the ALK fusion gene. However, acquired resistance to ALK-TKIs in lung cancer cells remains an inevitable problem: ALK secondary mutations and bypass pathways have been reported as major resistance mechanisms. In this study, we aimed to discover a novel mechanism of acquired resistance to ALK-TKIs and a strategy to conquer ALK-positive lung cancer. We established three types of ALK-TKI (crizotinib, alectinib and ceritinib)resistant H2228 non-small cell lung cancer cell lines by high exposure and stepwise methods. We found these cells showed a loss of ALK signaling, overexpressed AXL with epithelialmesenchymal transition (EMT), and had cancer stem celllike properties. Similarly, we demonstrated that TGF-1 treated H2228 cells also showed AXL overexpression with EMT features and ALK-TKIresistance. The AXL inhibitor, R428, or HSP90 inhibitor, ganetespib, were effective in reversing ALK-TKIresistance and EMT changes in both ALK-TKIresistant and TGF-1exposed H2228 cells. Progression-free survival of ALK-positive NSCLC patients with AXL overexpression was shorter than that of patients who underwent crizotinib therapy and showed low AXL expression. Thus, we found ALK signaling-independent AXL overexpression and EMT features were commonly involved in intrinsic and acquired resistance to first and second generation ALK-TKIs. This suggests AXL and HSP90 inhibitors may be promising therapeutic drugs to overcome tumor cells in ALK-positive NSCLC patients.

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