Establishment of an arsenic trioxide-resistant human leukemia cell line that shows multidrug resistance.

We have established an arsenic trioxide (As2O3)-resistant cell line (K562/AS-3) derived from the human leukemia cell line K562. K562/AS-3 was sequentially cultured with increasing concentrations of As2O3 up to 3.5 microM and then cloned by the limiting dilution method. K562/AS-3 was found to be about 7-fold more resistant to As2O3 than the parent cells (IC50=12.9 microM for K562/AS-3 and 1.8 microM for K562), and also showed cross resistance to VP-16 and vincristine. The multidrug resistance-associated protein (MRP1) gene was found to be overexpressed, but the MDR gene was not detected. MRP1 function was evaluated by measuring calcein acetoxymethyl ester (calcein-AM) efflux, and by verifying its inhibition by MK571, a potent MRP inhibitor. In addition, an increase of the total intracellular glutathione content was found in K562/AS-3. The resistance of K562/AS-3 to As2O3 was reversed by the addition of MK571, but not by verapamil. K562/AS-3 may be useful for studying the mechanism of the anticancer effect of As2O3 and how to overcome As2O3-resistance.