IC50 of inhibition of p185BCR-ABL kinase. 32Dp185 cells were incubated for 1.5 hours in the presence of the indicated concentration of inhibitor. Cells were lysed and equal amounts of lysate were analyzed by immunoblotting with antiphosphotyrosine (A) or anti-ABL antibodies (B). The migration of BCR-ABL is marked with an arrow on the left of the panel. These gels were scanned using a laser densitometer. No significant differences in the amount of ABL protein were noted on the ABL immunoblot. The scanned data from the antiphosphotyrosine immunoblot were used to calculate the IC50, defined as a 50% reduction of the intensity of the BCR-ABL phosphotyrosine band. The data shown are representative of two separate experiments and similar values were obtained for the IC50s.