Characterization of Chronic Myeloid Leukemia Cell Lines with Acquired Drug Resistance to 6-mercaptopurine and Imatinib
Zhe-Sheng Chen, Department of Pharmaceutical Sciences, College of Pharmacy and Health Sciences
Xing-Xiang Peng, Zhi Shi, Xiao-Cong Huang, Gary D. Kruh, Hsiang-Chun Wu, Smitaben Parmar, Ying Zhou, Ioana Abraham, Medical Science Division, Fox Chase Cancer Center, Philadelphia, PA
The development of refractory disease is often associated with the overexpression of multidrug resistance (MDR) proteins, especially in the hematological malignancies, such as chronic myeloid leukemia (CML), acute myeloid leukemia (AML), and non Hodgkin’s lymphomas (NHL). To investigate the mechanisms of cellular resistance to 6-mercaptopurine (6-MP) and imatinib mesylate, we established a 6-MP resistant cell line, K562-MP5, and an imatinib mesylate resistant cell line K562-imatinib, by step wise selection of the CML cell line K562 cells in drug. Drug sensitivity analysis showed that K562-MP5 cells were about 300-fold resistant to 6-MP and cross-resistant to imatinib mesylate, 6-thioguanine (6-TG) and doxorubicin compared to the parental cells. K562-imatinib cells were about 330-fold resistant to imatinib mesylate and cross-resistant to 6-MP, 6-TG and arabinosylcytosine (AraC) compared to the parental cells. Accumulation of [14C]6-MP in K562-MP5 cells was lower than that in K562 cells, and ATP-dependent efflux of [14C]6-MP in K562-MP5 cells was increased compared to the parental K562 cells. Accumulation of [14C]6-MP in K562-imatinib cells was also lower than that in parental cells and ATP-dependent efflux of [14C]6-MP in K562-imatinib cells was increased compared to the parental cells. Immunoblot analysis demonstrated that both K562-MP5 and K562-imatinib cells overexpressed P-glycoprotein (P-gp), an ATP-binding cassette (ABC) transporter that is able to extrude anticancer drugs out from the cells. However, in the present investigation there were no significant differences in the levels of expression of MRP1, MRP4 and MRP5 in parental K562 cells, K562-MP5 cells and K562-imatinib cells detected by western blotting analysis. These results suggest that overexpression of P-gp is involved in 6-MP and imatinib mesylate resistance in K562 cells. To our knowledge, this is the first report that overexpression of P-gp has been observed in a cell line made resistant to a nucleobase anticancer drug.