Structure and activity of NS-187. Chemical structures of NS-187 (A) and imatinib (B). K562 cells (C), BaF3/wt cells (D), and BaF3/E255K cells (E) were incubated for 1.5 hours with the indicated concentrations of each compound. Serum-starved NHDF cells (F), NCI-H526 cells (G), and A431 cells (H) were incubated for 1.5 hours with each compound prior to stimulation for 10 minutes with PDGF, SCF, or EGF, respectively. Cells were then lysed and subjected to Western blot analysis with antiphosphotyrosine antibody (C-H), anti–c-Abl antibody (C-E), anti-PDGFR antibody (F), anti–c-Kit antibody (G), or anti-EGFR antibody (H). p indicates phosphorylated.