PD-161570 is a selective FGFR inhibitor (IC50 values are 40, 262 and 3700 nM for FGFR, PDGFR and EGFR respectively). PD 161570 had about 5- and 100-fold greater selectivity toward the FGF-1 receptor (IC50 = 40 nM) compared with the PDGFbeta receptor (IC50 = 262 nM) or EGF receptor (IC50 = 3.7 microM) tyrosine kinases, respectively. In addition, PD 161570 suppressed constitutive phosphorylation of the FGF-1 receptor in both human ovarian carcinoma cells (A121(p)) and Sf9 insect cells overexpressing the human FGF-1 receptor and blocked the growth of A121(p) cells in culture. The results demonstrate a novel synthetic inhibitor with nanomolar potency and specificity towards the FGF-1 receptor tyrosine kinase.