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Dasatinib Cellular Uptake and Efflux in Chronic Myeloid Leukemia Cells: Therapeutic Implications

Authors' Affiliations: ¹ Division of Haematology, Institute of Medical and Veterinary Science and ² Faculty of Health Science, Department of Medicine, University of Adelaide, Adelaide, South Australia, Australia

Requests for reprints: Timothy P. Hughes, Division of Haematology, Institute of Medical and Veterinary Science, Frome Road, Adelaide, South Australia 5000, Australia. Phone: 61-8-82223330; Fax: 61-8-82223139; E-mail: Timothy.hughes{at}imvs.sa.gov.au.

Purpose: The organic cation transporter OCT-1 mediates active transport of imatinib. We recently showed that low OCT-1 activity is a major contributor to suboptimal response in chronic myeloid leukemia (CML) patients treated with imatinib. The relevance of OCT-1 activity and efflux pumps in determining intracellular uptake and retention (IUR) of dasatinib was assessed.

Experimental Design: The effect of OCT inhibitors on [¹⁴C]dasatinib and [¹⁴C]imatinib IUR was compared using peripheral blood mononuclear cells from newly diagnosed CML patients. The role of efflux transporters was studied using ABCB1- and ABCG2-overexpressing cell lines and relevant inhibitors.

Results: Unlike imatinib, there was no significant difference in the dasatinib IUR at 37°C and 4°C (P = 0.8), and OCT-1 inhibitors including prazosin did not reduce dasatinib IUR significantly. In CML mononuclear cells, prazosin inhibitable IUR was significantly higher for imatinib than dasatinib (6.38 versus 1.48 ng/200,000 cells; P = 0.002; n = 11). Patients with high OCT-1 activity based on their imatinib uptake had IC₅₀^dasatinib values equivalent to patients with low OCT-1 activity. Dasatinib IUR was significantly lower in ABCB1-overexpressing cell lines compared with parental cell lines (P < 0.05). PSC833 (ABCB1 inhibitor) significantly increased the dasatinib IUR (P < 0.05) and reduced IC₅₀^dasatinib (from 100 to 8 nmol/L) in K562-DOX cell line. The ABCG2 inhibitor Ko143 significantly increased dasatinib IUR in ABCG2-overexpressing cell lines and reduced IC₅₀^dasatinib.

Conclusion: Unlike imatinib, dasatinib cellular uptake is not significantly affected by OCT-1 activity, so that expression and function of OCT-1 is unlikely to affect response to dasatinib. Dasatinib is a substrate of both efflux proteins, ABCB1 and ABCG2.

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