Dose-response curves obtained by MTT assays for various imatinib-sensitive and -resistant cell lines after 3 days of continuous exposure to imatinib. In vitro resistance to imatinib in cell lines is either conferred by Bcr-Abl overexpression (AR230-r1, Baf/BCR-ABL-r1)²⁹  or engineered expression of Bcr-Abl with various point mutations in Ba/F3p210 cells (Ba/F3p210^{Y253F/M351T/T315I}).²⁸  The different resistant lines represent graded levels of resistance to imatinib with low (Ba/F3p210^M351T), intermediate (AR230-r1, Baf/BCR-ABL-r1, Ba/F3p210^Y253F), and complete (Ba/F3p210^T315I) resistance as compared with sensitive counterparts (AR230-s, Baf/BCR-ABL-s). Plotted is the percentage of growth inhibition (y-axis) through exposure to imatinib at increasing doses (x-axis). Single data points are mean values of at least 3 independent experiments.