152P - Epidermal Growth Factor Receptor Signaling Conferred Acquired Crizotinib Resistance to a Non-Small Cell Lung Cancer Cell Line Harboring the Slc34A2-Ros1 Fusion Gene

Abstract

ABSTRACT Aim: The ROS1 inhibitor crizotinib produces a remarkable response in patients with non-small cell lung cancer (NSCLC) harboring the ROS1 fusion gene (J Clin Oncol 2013 abstr 8032); however, acquired crizotinib resistance is inevitable, but the mechanism is unclear. Methods: HCC78 cells harboring the SLC34A2-ROS1 gene alteration were used to model acquired crizotinib resistance to explore alternative molecular mechanisms. The resistant cell line (HCC78R) was established from HCC78 cells after continuous exposure to crizotinib for 4 months in vitro. Results: The 50% inhibitory concentration (IC50) of crizotinib in HCC78R cells (4085.9 nM) was 47-fold larger than the IC50 in parental HCC78 cells (85.8 nM) (p = 0.0145). The expression of ROS1 protein was decreased significantly in HCC78R cells, as compared to HCC78 cells. Crizotinib inhibited the phosphorylation of AKT or ERK and downstream ROS1 signaling in HCC78 cells, but did not inhibit this in HCC78R. A receptor tyrosine kinas array showed that there was no increased tyrosine kinase activation in HCC78R cells, as compared to HCC78 cells. Interestingly, however, the phosphorylation of EGFR was maintained under 2,000 nM crizotinib exposure in HCC78R cells, but inhibited in parental HCC78 cells. Therefore, we hypothesize that the EGFR signaling pathway plays a role in HCC78R cells. Expectedly, HCC78R cells were very sensitive to EGFR-TKI in a cell proliferation assay (IC50: 117 nM vs. > 10,000 nM for HCC78R vs. HCC78 cells). Consistently, the addition of EGF to the culture medium rendered the parental HCC78 cells resistant to crizotinib. No activation of EGFR mutations were found in HCC78R cells. Finally, foretinib, a multi-kinase inhibitor of ROS1 and EGFR, effectively inhibited the proliferation of both HCC78R and HCC78 cells. Conclusions: These studies suggest that EGFR signaling plays a role in crizotinib resistance in lung cancer cells harboring ROS1 fusion genes. Disclosure: All authors have declared no conflicts of interest.