Drug combination studies: imatinib and nilotinib against imatinib-sensitive, BCR-ABL–expressing cell lines. Proliferation studies showing 3-day treatments of (A) K562 cells, (B) 32D.p210 cells, and (C) KU812 cells with nilotinib, imatinib, or a combination of nilotinib and imatinib. (D, i) Normal murine bone marrow colony assay. Colony count following 12 days of treatment. (ii) Normal human bone marrow colony assay. Colony count following 19 days of treatment. Error bars indicate SEM.