Lung cancer remains one of the leading causes for cancer-related death in developed countries. In lung adenocarcinomas, EGFR mutations and EML4-ALK fusions are associated with response to EGFR and ALK inhibition. By contrast, therapeutically exploitable genetic alterations have been lacking in squamous-cell lung cancer. We conducted a systematic search for alterations that are therapeutically amenable and performed high-resolution gene-copy number analyses in a set of 232 lung cancer specimens. We identified frequent and focal FGFR1 amplification in squamous-cell lung cancer (n=155), but not in other lung cancer subtypes, and confirmed its presence in an independent cohort of squamous-cell lung cancer samples employing FISH (22% of cases). Using cell-based screening with the FGFR inhibitor (PD173074) in a large (n=83) panel of lung cancer cell lines, we demonstrated that this compound inhibited growth (p=0.0002) and induced apoptosis (p=0.008) specifically in those lung cancer cells carrying amplified FGFR1. We validated the dependency on FGFR1 of FGFR1-amplified cell lines by knockdown of FGFR1 and by ectopic expression of a resistance allele of FGFR1 (FGFR1V561M), which rescued FGFR1-amplified cells from PD173074-mediated cytotoxicity. Finally we showed that inhibition of FGFR1 with a small molecule led to significant tumor shrinkage in vivo. Focal FGFR1 amplification is common in squamous-cell lung cancer and associated with tumor growth and survival, suggesting that FGFR inhibitors may be a viable therapeutic option in this cohort of patients.

Purpose: ALK rearrangement-positive lung cancers can be effectively treated with ALK inhibitors. However, the magnitude and duration of response is heterogeneous. In addition, acquired resistance limits the efficacy of ALK inhibitors, with most upfront resistance mechanisms being unknown.Experimental Design: By making use of the Ba/F3 cell line model, we analyzed the cytotoxic efficacy of ALK kinase inhibitors as a function of different EML4-ALK fusion variants v1, v2, v3a, and v3b as well as of three artificially designed EML4-ALK deletion constructs and the ALK fusion genes KIF5b-ALK and NPM1-ALK. In addition, the intracellular localization, the sensitivity to HSP90 inhibition and the protein stability of ALK fusion proteins were studied.Results: Different ALK fusion genes and EML4-ALK variants exhibited differential sensitivity to the structurally diverse ALK kinase inhibitors crizotinib and TAE684. In addition, differential sensitivity correlated with differences in protein stability in EML4-ALK-expressing cells. Furthermore, the sensitivity to HSP90 inhibition also varied depending on the ALK fusion partner but differed from ALK inhibitor sensitivity patterns. Finally, combining inhibitors of ALK and HSP90 resulted in synergistic cytotoxicity.Conclusions: Our results might explain some of the heterogeneous responses of ALK-positive tumors to ALK kinase inhibition observed in the clinic. Thus, targeted therapy of ALK-positive lung cancer should take into account the precise ALK genotype. Furthermore, combining ALK and HSP90 inhibitors might enhance tumor shrinkage in EML4-ALK-driven tumors.