Pazopanib, a multitarget
tyrosine kinase (TK) inhibitor, has been approved for treatment of
soft tissue sarcoma. Elucidation of the molecular background of
pazopanib resistance should lead to improved clinical outcomes in
sarcomas; accordingly, we investigated this in
synovial sarcoma using a proteomic approach.
Pazopanib sensitivity was examined in four
synovial sarcoma cell lines: SYO-1, HS-SYII, 1273/99, and YaFuSS. The 1273/99 cell line showed significantly higher IC50 values than the others for
pazopanib. Expression levels of 90 TKs in the cell lines were examined by western blotting. Among these, the levels of
PDGFRB, DDR1, AXL, MET, and PYK2 were higher, and those of FGFR1 and VEGFR3 were lower in the 1273/99 cell line than the other cell lines. Gene silencing analysis of the TKs upregulated in 1273/99 cells showed differing effects on cell growth:
PDGFRB, MET, and PYK2 knockdown induced cell growth inhibition, whereas DDR1 and AXL knockdown did not influence cell growth. Using the PamChip
peptide microarray, we found that 18
peptide substrates were highly phosphorylated in the 1273/99 cell line compared with other cell lines. Using the PhosphoNet database, we found that
kinases FGFR3, RET, VEGFR1, EPHA2, EPHA4, TRKA, and SRC phosphorylated these 18
peptide substrates. Moreover, the results for overexpressed and aberrantly activated TKs in
pazopanib-resistant cells showed no overlap. Taken together, our study indicates that identification of comprehensive TK profiles represents an essential approach to determining the molecular background of
pazopanib resistance in
synovial sarcoma.