Abstract 2954: MAP-kinase pathway activation facilitates survival of persistent FGFR1-amplified lung cancer cells upon FGFR inhibition

One recurrent alteration of squamous cell lung cancer is the amplified region of the 8p12-p11 locus. The tyrosine kinase fibroblast growth factor receptor 1 (FGFR1) seems to be one of the most prominent targets of this amplification. Thus, small molecules inhibiting FGFRs have been employed to treat FGFR1-amplified squamous cell lung cancer. However, only about 16% of such FGFR1-amplified tumors respond to single agent inhibitor therapy. Several tumors exhibited insufficient tumor shrinkage, compatible with the existence of persistence of inhibitor-resistant tumor cells in the tumor. To investigate the mechanism of FGFR-inhibitor persistence we studied the lung cancer cell lines DMS114 and H1581. Both cell lines demonstrate GI50 values in the nanomolar range upon three different FGFR-inhibitors. However, both cell lines exhibit sustained cell viability within 0.5 to 5 μM inhibitor treatment, indicating a subpopulation of persistent cells. We therefore isolated these persistent cells by treating with a high dose of FGFR inhibitors. After 8 to 12 weeks the cells were completely resistant against all FGFR inhibitors tested. Genetic identity with the original cell line was confirmed by fingerprinting. We found that while parental cell lines showed depleted pERK signals, persistent cells were marked by a constant pERK level upon treatment. In H1581 cells, reactivation of the mitogen-activated protein kinase (MAPK) pathway was demonstrated by an active RAS-pulldown assay. Whole exome sequencing (WES) revealed high and focal NRAS amplification and DUSP6 depletion, leading to MAPK-pathway reactivation. Furthermore, retroviral overexpression of wild type RAS-isoforms induced FGFR-inhibitor resistance in parental H1581 cells. In DMS114 we observed MET and IGF-1R activation as possible mechanisms of persistence. Furthermore, co-inhibition of FGFR and MEK was a highly effective combination therapy to treat FGFR-inhibitor persistent cells. This study associates the MAPK-pathway as a key pathway for FGFR-dependent cell lines. Furthermore, these results suggest a beneficial FGFR / MEK combination treatment to avoid the outgrowth of FGFR-inhibitor persistent cells. Citation Format: Florian Malchers, Meryem Seda Ercanoglu, Roman Kurt Thomas. MAP-kinase pathway activation facilitates survival of persistent FGFR1-amplified lung cancer cells upon FGFR inhibition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2954.