Abstract 5652: Activation of FGF2-FGFR1 pathway in EGFR-mutant lung cancer cell line with long-term gefitinib exposure.
Authors: Terai Hideki , Soejima Kenzo , Naoki Katsuhiko , Yasuda Hiroyuki , Satomi Ryosuke , Nakayama Sohei , Yoda Satoshi , Ikemura Shinnosuke , Sato Takashi , Ishioka Kota , Arai Daisuke , Ohgino Keiko , Tani Tetsuo , Kuroda Aoi , Hamamoto Junko , Betsuyaku Tomoko 
Published: August 2014

Abstract
Many of the patients with non-small cell lung cancer (NSCLC) with sensitive epidermal growth factor receptor (EGFR)-mutation who initially responded well to EGFR-tyrosine kinase inhibitors (TKIs) eventually relapse. In spite of many studies over the last few years to elucidate this mechanism of acquired resistance to EGFR-TKIs, approximately 30% of the mechanisms of acquired resistance are still unknown. Recently autocrine signaling of fibroblast growth factors (FGFs) and their receptors (FGFRs) has been demonstrated in NSCLC cell lines. And several studies suggest that the FGF-FGFR autocrine growth pathway could be an important mechanism for intrinsic resistance to EGFR-TKIs in NSCLC cell lines with wild-type EGFR. But until now, no report has clarified the role of FGF-FGFR pathway in acquired resistance to EGFR-TKIs in NSCLC cell lines with sensitive EGFR mutations. We have established a gefitinib-resistant cell line (PC9 GR), by serial exposure of gefitinib to PC9, an originally gefitinib-sensitive lung cancer cell line (PC9 na). We confirmed that these cell lines did not harbor two well-known EGFR-TKI resistance mechanisms, the second mutation in the EGFR gene itself, EGFR T790 and the amplification of the MET oncogene. We collected total RNA from both PC9 na and PC9 GR and examined mRNA expression profile, by using cDNA microarray analysis. We found the expressions of FGFR1 and FGF2 were increased in PC9 GR compared to in PC9 na. The growth of PC9 GR cells was inhibited either by PD173074 (inhibitors of FGFRs) or knocking down of FGFR1 or FGF2 by siRNA in combination with gefitinib. FACS analysis revealed that the combination treatment with PD173074 and gefitinib induced apoptosis more efficiently in PC9 GR cells compared to gefitinib alone. PC9 na cells and PC9 GR cells did not show any change in the proportion of apoptotic cells after treatment with PD173074 alone. To further investigate how FGF2-FGFR1 pathway affects resistance to gefitinib in these cell lines, the downstream targets of EGFR signaling including the MEK-ERK and PI3K-AKT pathways were examined. In PC9 na cells, the phosphorylation of EGFR, ERK, and AKT was efficiently inhibited by gefitinib alone. On the other hand, in PC9 GR cells, the phosphorylation of ERK and AKT was not efficiently inhibited by gefitinib alone. However, the inhibition of phosphorylation of ERK was completely and AKT was less efficiently rescued by gefitinib and PD173074 combination therapy. In conclusion, these data suggest the activation of FGF2-FGFR1 signaling pathway contributes to the gefitinib resistance in PC9 GR. FGF2-FGFR1 pathway will be a therapeutic target for a subset of NSCLC that acquires EGFR-TKI resistance.
Citation Format: Hideki Terai, Kenzo Soejima, Katsuhiko Naoki, Hiroyuki Yasuda, Ryosuke Satomi, Sohei Nakayama, Satoshi Yoda, Shinnosuke Ikemura, Takashi Sato, Kota Ishioka, Daisuke Arai, Keiko Ohgino, Tetsuo Tani, Aoi Kuroda, Junko Hamamoto, Tomoko Betsuyaku. Activation of FGF2-FGFR1 pathway in EGFR-mutant lung cancer cell line with long-term gefitinib exposure. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5652. doi:10.1158/1538-7445.AM2013-5652