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Characteristics of Dasatinib- and Imatinib-Resistant Chronic Myelogenous Leukemia Cells

Authors' Affiliation: First Department of Internal Medicine, Tokyo Medical University, Tokyo, Japan

Requests for reprints: Seiichi Okabe, First Department of Internal Medicine, Tokyo Medical University, 6-7-1 Nishi-shinjuku, Shinjuku-ku, Tokyo, 160-0023 Japan. Phone: 81-3-3342-6111; Fax: 81-3-5381-6651; E-mail: okabe{at}tokyo-med.ac.jp.

Purpose: Although dual src-family kinase/BCR/ABL inhibitor, dasatinib (BMS-354825), provides therapeutic advantages to imatinib-resistant cells, the mechanism of dasatinib resistance was not fully known.

Experimental Design: We used TF-1 BCR/ABL cells, by introducing the BCR/ABL gene into a leukemia cell line, TF-1 and K562, and established dasatinib- (BMS-R) and imatinib-resistant (IM-R) cells. We characterized chronic myelogenous leukemia drug-resistant cells and examined intracellular signaling.

Results: The IC₅₀ of dasatinib was 0.75 nmol/L (TF-1 BCR/ABL), 1 nmol/L (K562), 7.5 nmol/L (TF-1 BCR/ABL IM-R), 10 nmol/L (K562 IM-R), 15 µmol/L (TF-1 BCR/ABL BMS-R), and 25 µmol/L (K562 BMS-R). The number of BCR/ABL copies in resistant cell lines was the same as the parental cell line by fluorescence in situ hybridization analysis. There was no mutation in Abl kinase. We found that protein levels of BCR/ABL were reduced in dasatinib-resistant cell lines. BCR/ABL protein was increased by treatment of an ubiquitin inhibitor. The Src kinase, Lck, as well as mitogen-activated protein kinase and Akt were activated, but p21^WAF, phosphatase and tensin homologue was reduced in K562 BMS-R cells. Removal of dasatinib from the culture medium of K562 BMS-R cells led to apoptosis, and activated caspase 3 and poly (ADP-ribose) polymerase.

Conclusion: These results suggest that the expression and protein activation signatures identified in this study provide insight into the mechanism of resistance to dasatinib and imatinib and may be of therapeutic chronic myelogenous leukemia value clinically.