Non-Amplified FGFR1 is a Growth Driver in Malignant Pleural Mesothelioma

Molecular Cancer Research 2014 June 15. [Epub ahead of print] [Link]

Bohm D, Gozgit JM, Heasley LE, Hinz TK, Hoffman H, Kleczko EK, Marek LA, Nemenoff RA, Olszewski KA, Perner S, von Massenhausen A, Warth A, Weiser-Evans MC.


Malignant pleural mesothelioma (MPM) is associated with asbestos exposure and is a cancer that has not been significantly impacted by small molecule-based targeted therapeutics. Previously, we demonstrated the existence of functional subsets of lung cancer and head and neck squamous cell carcinoma (HNSCC) cell lines in which fibroblast growth factor receptor (FGFR) autocrine signaling functions as a non-mutated growth pathway. In a panel of pleural mesothelioma cell lines, FGFR1 and FGF2 were co-expressed in 3 of 7 cell lines and were significantly associated with sensitivity to the FGFR-active tyrosine kinase inhibitor (TKI), ponatinib, both in vitro and in vivo using orthotopically propagated xenografts. Furthermore, RNAi-mediated silencing confirmed the requirement for FGFR1 in specific mesothelioma cells and sensitivity to the FGF ligand trap, FP-1039, validated the requirement for autocrine FGFs. None of the FGFR1-dependent mesothelioma cells exhibited increased FGFR1 gene copy number, based on a FISH assay, indicating that increased FGFR1 transcript and protein expression were not mediated by gene amplification. Elevated FGFR1 mRNA was detected in a subset of primary MPM clinical specimens and like MPM cells, none harbored increased FGFR1 gene copy number. These results indicate that autocrine signaling through FGFR1 represents a targetable therapeutic pathway in MPM and that biomarkers distinct from increased FGFR1 gene copy number such as FGFR1 mRNA would be required to identify MPM patients bearing tumors driven by FGFR1 activity. Implications: FGFR1 is a viable therapeutic target in a subset of malignant pleural mesotheliomas, but FGFR TKI-responsive tumors will need to be selected by a biomarker distinct from increased FGFR1 gene copy number, possibly FGFR1 mRNA or protein levels.