The fibroblast growth factor- fibroblast growth factor receptor (FGF-FGFR) signaling pathway plays a role in cell proliferation, migration, survival, and angiogenesis. Because approximately 10% of gastric cancers show amplification of FGFR2, inhibition of FGFR2 activation has been regarded as one of therapeutic targets. AZD4547, a selective inhibitor of the FGFR1-3 tyrosine kinases, was developed to inhibit FGFR signaling, however, its efficacy is limited by emergency of the acquired resistance. We tried to clarify a resistance mechanism against the FGFR inhibitor.
The cell line resistant against the AZD4547 was established using SNU-16 (SNU16R), a FGFR2 amplified gastric cancer cell line, by culturing with increasing concentration of the AZD4547. The expression level of FGFR or phosphorylated FGFR (pFGFR) and downstream signaling molecules was determined by Western blot. Cell viability was measured with MTT assay. Relative level of tyrosine phosphorylation of receptor tyrosine kinases (RTKs) was evaluated with proteome profilerTM array by human phosphor-RTK kit (R&D Systems).
Loss of expression of FGFR2 and pFGFR2 was confirmed in the SNU16R cell line by Western blotting. The viability of SNU16R cell line was shown to be increased than that of the parent cell line after incubation with AZD 4547. Change of the FGFR2 downstream signaling pathways was addressed, and upregulated expression level of phosphorylated mammalian target of rapamycin (mTOR) was found. Overexpression of downstream targets of mTOR, such as phosphorylated 4E-BP1 and S6K was also confirmed. The SNU15R and parent SNU16 cell lines were incubated with everolimus or AZD 4547, and inhibition of activated mTOR was observed with everolimus but not with AZD 4547 by Western blotting and MTT assay. Because PI3K and Akt were not activated, an alternative signaling pathway was sought and the phosphorylated level of EphB3 was found to be elevated.
Activation of mTOR is one of mechanisms of acquiring resistance against AZD 4547 in FGFR2 amplified gastric cancer cells. Targeting mTOR could overcome the resistance by inhibition of activation of mTOR.
Clinical trial identification
Legal entity responsible for the study
Korea University Guro Hospital
S.Y. Lee, Y. Jeong, Y. Na, J.L. Kim, D.H. Lee, S.C. Oh: This research was funded by AstraZeneca. All experiments were performed independently from AstraZeneca.