Up-Regulated FGFR1 Expression as a Mediator of Intrinsic TKI Resistance in EGFR-Mutated NSCLC

Non-small cell lung carcinoma patients with epidermal growth factor receptor (EGFR) mutations are offered EGFR tyrosine kinase inhibitors (TKI) as first line treatment, but 20–40% of these patients do not respond. High expression of alternative receptor tyrosine kinases, such as Fibroblast growth factor receptor 1 (FGFR1), potentially mediates intrinsic EGFR TKI resistance. To study this in molecular detail, we used CRISPR-dCas9 Synergistic Activation Mediator (SAM) for up-regulation of FGFR1 in physiological relevant levels in the EGFR mutated NSCLC cell lines HCC827 and PC9 thereby generating HCC827(gFGFR1) and PC9(gFGFR1). The sensitivity to the TKI erlotinib was investigated in vitro and in a BALBc nu/nu mouse xenograft model. FGFR1 up-regulation decreased TKI-sensitivity in both NSCLC cell lines in the presence of the ligand fibroblast growth factor 2 (FGF2). Xenografts were established with PC9(gFGFR1) cells and it was demonstrated that there was no significant difference in tumor size between TKI- and vehicle-treated PC9(gFGFR1) tumors. This supports decreased TKI-sensitivity in NSCLC cells with FGFR1 up-regulation. Our study points to FGFR1 signaling being an intrinsic resistance mechanism abolishing TKI response in EGFR mutated NSCLC.