FK506 reverses adriamycin resistance in a multidrug-resistant human leukemia cell line.

We have examined the effect of FK506 on the Adriamycin sensitivity of the multidrug resistant human chronic myelocytic leukemia cell line (K562/ADM). In K562/ADM cells, 1.0 microgram/ml FK506 reversed the resistance of Adriamycin, and increased the IC50 value for Adriamycin up to 17 fold. However, IC50 value for the parent cells (K562) increased only 1.5 fold. By cell cycle analysis, the accumulation in late S-G2M phase was confirmed on K562/ADM cells, treated with 1.0 microgram/ml FK506 and low-dose of Adriamycin. Cyclosporin A (CsA) could also restored the Adriamycin sensitivity in the K562/ADM cells, as previously reported. 1.0 microgram/ml FK506 as well as CsA significantly increased radioactive Adriamycin accumulation in K562/ADM cells and blocked [3H]azidopien photoaffinity labeling of P-glycoprotein. These results suggest that 1.0 microgram/ml FK506 could reverse the Adriamycin resistance in a MDR human leukemia cells through the interaction with P-glycoprotein.