PD 173074 inhibited the kinase activity of FGFR1 with an IC50 of 25 nM in vitro, while inhibiting Src, the receptors for insulin, epidermal growth factor (EGF) and PDGF, and several serine/threonine kinases with 1000-fold or higher IC50 values. PD 173074 was an ATP-competitive inhibitor of FGFR1, with a Ki of around 40 nM. PD 173074 inhibited autophosphorylation of FGFR1 and VEGFR2 in a dose-dependent manner with IC50s in the range of 1-5 nM and 100-200 nM, respectively.