Figure 1.

HL-60 cells acquire multidrug resistance. HL-60 cells resistant to 10–40 mg/l ADM were treated with various chemotherapeutic drugs. Inhibitory rate and IC₅₀ values were determined by MTT assay. HL-60 cells resistant to 40 mg/l ADM were defined as HL-60/RS cells. (A) HL-60 cells became increasingly resistant to ADM at increasing concentrations of ADM and increasing exposure times. (B) ADM-resistant HL-60 cells were cross-resistant to other chemotherapeutic drugs, including cisplatin, daunorubicin, cytarabine, vincristine and etoposide, but not 5-fluorouracil. (C) HL-60/RS cells acquired high As₂O₃ resistance. *P<0.05, **P<0.01 compared with HL-60 cells. IC₅₀, half-maximal inhibitory concentration; ADM, doxorubicin; conc., concentration; 5-FU, 5-fluorouracil.