• Ahnah Song, Tae Min Kim, Dong-Wan Kim, Soyeon Kim, Bhumsuk Keam, Se-Hoon Lee, and Dae Seog Heo.
• Cancer Research Institute, Seoul National University College of Medicine, Seoul, Republic of Korea.
• Clin Cancer Res. 2015 May 15; 21 (10): 2379-87.

PurposeAlthough ROS1-rearranged non-small cell lung cancer (NSCLC) is sensitive to crizotinib, development of resistance is inevitable. Here, we identified molecular alterations in crizotinib-resistant tumors from two NSCLC patients with the CD74-ROS1 rearrangement, and in HCC78 cells harboring SLC34A2-ROS1 that showed resistance to crizotinib (HCC78CR cells).Experimental DesignROS1 kinase domain mutations were examined in fresh tumor tissues from two NSCLC patients and HCC78CR1-3 cells by direct sequencing. Ba/F3 cells expressing ROS1 secondary mutations were constructed to evaluate resistance to crizotinib. An upregulated pathway was identified using phospho-receptor tyrosine kinase array, EGFR signaling antibody array, and RNA sequencing (RNA-seq). Cell proliferation and ROS1 downstream signaling pathways were compared between HCC78 and HCC78CR1-3 cells.ResultsThe ROS1 G2032R mutation was identified in crizotinib-resistant tumors from one patient. Furthermore, HCC78CR1 and CR2 cells harbored a novel ROS1 L2155S mutation (73.3% and 76.2%, respectively). ROS1 G2032R and L2155S mutations conferred resistance to crizotinib in Ba/F3 cells. Evidence of epithelial-to-mesenchymal transition with downregulated E-cadherin and upregulated vimentin was observed in HCC78CR1-2 cells and in the other patient. RNA-seq and EGFR signaling antibody array revealed that the EGFR pathway was significantly upregulated in HCC78CR3 versus HCC78 cells. Cells with the ROS1 mutation and upregulated EGFR were sensitive to foretinib, an inhibitor of c-MET, VEGFR2, and ROS1 and irreversible EGFR tyrosine kinase inhibitors plus crizotinib, respectively.ConclusionsMolecular changes associated with acquired crizotinib resistance in ROS1-rearranged NSCLC are heterogeneous, including ROS1 tyrosine kinase mutations, EGFR activation, and epithelial-to-mesenchymal transition.©2015 American Association for Cancer Research.

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