Kinase Assay:Kinase Inhibition Assays Kinase activities of KDR and PDGFRα are measured as the percent of ATP consumed following the kinase reaction using luciferaseluciferin-coupled chemiluminescence. Kinase reactions are initiated by combining test compound (XL 999), ATP, kinases and substrates in a 20 mL volume using 384-well microtiter plates. For KDR , the final reaction mixture contained 3 mM ATP, 1.6 mM poly(Glu, Tyr) 4:1 and 1.5 nM KDR of residues D807-V1356 with an N-terminal GST tag. For PDGFRα , the final reaction mixture contained 2 mM ATP, 10 mM MBP and 14 nM PDGFRα of residues Q551-L1089 with an N-terminal GST tag. The reaction mixture is incubated at room temperature for 4 h ( KDR ) or 2 h PDGFRα before a 20 mL aliquot of Kinase Glo is added and luminescence signal is measured using a Victor2 plate reader. Total ATP consumption is limited below 50%.