PD166866 is a selective FGFR1 tyrosine kinase inhibitor with an IC₅₀ of 52.4 nM. IC50 & Target: IC50: 52.4 nM (hFGFR1 tyrosine kinase)^[1] In Vitro: PD 166866 inhibits human full-length FGFR-1 tyrosine kinase with an IC₅₀ value of 52.4 nM and is characterized as an ATP competitive inhibitor of the FGFR-1. PD 166866 is a potent inhibitor of FGFR autophosphorylation in NIH 3T3 cells expressing endogenous FGFR-1 and in L6 cells overexpressing the human FGFR-1 tyrosine kinase. PD 166866 also inhibits bFGF-induced tyrosine phosphorylation of the 44- and 42-kDa (ERK 1/2) mitogen-activated protein kinase isoforms in L6 cells. Daily exposure of PD 166866 to L6 cells at concentrations from 1 to 100 nM results in a concentration-related inhibition of bFGF-stimulated cell growth for 8 consecutive days with an IC₅₀ value of 24 nM^[1].