Combined effect of cabozantinib and gefitinib in crizotinib‐resistant lung tumors harboring ROS 1 fusions

The ROS 1 tyrosine kinase inhibitor ( TKI ) crizotinib has shown dramatic effects in patients with non‐small cell lung cancer ( NSCLC ) harboring ROS1 fusion genes. However, patients inevitably develop resistance to this agent. Therefore, a new treatment strategy is required for lung tumors with ROS1 fusion genes. In the present study, lung cancer cell lines, HCC 78 harboring SLC 34A2‐ ROS 1 and ABC ‐20 harboring CD 74‐ ROS 1 , were used as cell line‐based resistance models. Crizotinib‐resistant HCC 78R cells were established from HCC 78. We comprehensively screened the resistant cells using a phosphor‐receptor tyrosine kinase array and RNA sequence analysis by next‐generation sequencing. HCC 78R cells showed upregulation of HB ‐ EGF and activation of epidermal growth factor receptor ( EGFR ) phosphorylation and the EGFR signaling pathway. Recombinant HB ‐ EGF or EGF rendered HCC 78 cells or ABC ‐20 cells resistant to crizotinib. RNA sequence analysis by next‐generation sequencing revealed the upregulation of AXL in HCC 78R cells. HCC 78R cells showed marked sensitivity to EGFR ‐ TKI or anti‐ EGFR antibody treatment in vitro. Combinations of an AXL inhibitor, cabozantinib or gilteritinib, and an EGFR ‐ TKI were more effective against HCC 78R cells than monotherapy with an EGFR ‐ TKI or AXL inhibitor. The combination of cabozantinib and gefitinib effectively inhibited the growth of HCC 78R tumors in an in vivo xenograft model of NOG mice. The results of this study indicated that HB ‐ EGF / EGFR and AXL play roles in crizotinib resistance in lung cancers harboring ROS1 fusions. The combination of cabozantinib and EGFR ‐ TKI may represent a useful alternative treatment strategy for patients with advanced NSCLC harboring ROS1 fusion genes.