Abstract
Despite widespread expression of epidermal growth factor (EGF) receptors (EGFRs) and EGF family ligands in non-small-cell lung cancer (NSCLC), EGFR-specific tyrosine kinase inhibitors (TKIs) such as gefitinib exhibit limited activity in this cancer. We propose that autocrine growth signaling pathways distinct from EGFR are active in NSCLC cells. To this end, gene expression profiling revealed frequent coexpression of specific fibroblast growth factors (FGFs) and FGF receptors (FGFRs) in NSCLC cell lines. It is noteworthy that FGF2 and FGF9 as well as FGFR1 IIIc and/or FGFR2 IIIc mRNA and protein are frequently coexpressed in NSCLC cell lines, especially those that are insensitive to gefitinib. Specific silencing of FGF2 reduced anchorage-independent growth of two independent NSCLC cell lines that secrete FGF2 and coexpress FGFR1 IIIc and/or FGFR2 IIIc. Moreover, a TKI [(±)-1-(anti-3-hydroxy-cyclopentyl)-3-(4-methoxy-phenyl)-7-phenylamino-3,4-dihydro-1H-pyrimido-[4,5-d]pyrimidin-2-one (RO4383596)] that targets FGFRs inhibited basal FRS2 and extracellular signal-regulated kinase phosphorylation, two measures of FGFR activity, as well as proliferation and anchorage-independent growth of NSCLC cell lines that coexpress FGF2 or FGF9 and FGFRs. By contrast, RO4383596 influenced neither signal transduction nor growth of NSCLC cell lines lacking FGF2, FGF9, FGFR1, or FGFR2 expression. Thus, FGF2, FGF9 and their respective high-affinity FGFRs comprise a growth factor autocrine loop that is active in a subset of gefitinib-insensitive NSCLC cell lines.
Footnotes
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The studies were supported by National Institutes of Health grants R01-CA116527, R01-CA127105, P30-CA046934, and P50-CA58187 and a Cancer League of Colorado grant (to L.E.H.).
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ABBREVIATIONS: EGFR, epidermal growth factor receptor; EGF, epidermal growth factor; TKI, tyrosine kinase inhibitor; NSCLC, non-small-cell lung cancer; FGF, fibroblast growth factor; FGFR, fibroblast growth factor receptor; Ig, immunoglobulin; HITES, RPMI-1640 containing hydrocortisone/insulin/transferrin/estradiol/Na3SeO3/bovine serum albumin; PCR, polymerase chain reaction; RT-PCR, real-time polymerase chain reaction; RO4383596; (±)-1-(anti-3-hydroxy-cyclopentyl)-3-(4-methoxy-phenyl)-7-phenylamino-3,4-dihydro-1H-pyrimido[4,5-d]pyrimidin-2-one; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; ELISA, enzyme-linked immunosorbent assay; ERK, extracellular signal regulated kinase; PAGE, polyacrylamide gel electrophoresis; VEGFR, vascular endothelial growth factor receptor; PDGFR, platelet-derived growth factor receptor; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GFP, green fluorescent protein; VEGF, vascular endothelial growth factor; IGF, insulin-like growth factor; FRS2, FGF receptor substrate 2.
- Received June 7, 2008.
- Accepted October 9, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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