Combined activity of imatinib and As₂O₃ or decitabine in colony-forming assays of primary CML cells with defined mechanisms of resistance to imatinib. Growth of CFU-GMs and BFU-Es was assessed after continuous exposure to combined treatment for 14 days. Cells were grown in the presence of 0 μM (♦) or 0.5 μM (□) imatinib with increasing doses of the combined agent (x-axis); 0.5 μM was selected because this represents dose escalation under our assay conditions.¹⁹  Mechanisms of resistance to imatinib have been determined by cytogenetic and FISH analysis and sequencing of the Abl kinase domain. Results of resistance testing are given next to patient number (M351T or BCR-ABL amplification). Data points represent means of duplicate experiments.