Objective To investigate the anti-tumor effect of ZM-66 on multidrug-resistant leukemic cell line K562/ADM. Methods The K562/ADM cells were treated with varying concentrations (0

1

2

4×10-3 mmol/L) of ZM-66 or etoposide for 24 hours. The proliferation was detected by Sulforhodamine B Sodium Salt (SRB) assay and apoptosis was detected by flow cytometry analysis and fluorescent staining. In addition

the expression levels of p53 and bax genes in K562/ADM cells were detected by RT-PCR analysis. The level of P-glycoprotein (P-gp)

P53 and Bax protein in K562/ADM cells were detected by Western blot assay. Results SRB assay demonstrated that etoposide had little inhibitory effect on K562/ADM cells

whereas ZM-66 (1

2

4×10

-3

mmol/L) had significantly inhibitory effect on K562/ADM cells (all P

<

0.01). The acridine orange/propidium iodide dual staining showed that there were typical condensation of chromatin and nuclear fragmentation nuclei with red color in ZM-66 treated cells. Flow cytometric analysis showed that there was a significantly increase of apoptotic cells in K562/ADM cells after treated with ZM-66. RT-PCR showed that the p53 and bax mRNA expression levels in K562/ADM cells treated with ZM-66 at 1

2

4×10

-3

mmol/L were higher than those in the cell without treatment. Western blot showed that the P53 and Bax protein expression levels in K562/ADM cells treated with ZM-66 at 2

4×10

-3

mmol/L were higher than those in the cell without treatment. But the P-gp protein expression level in K562/ADM cells treated with ZM-66 at 2

4×10

-3

mmol/L was gradually lower than those in the cell without treatment. Conclusion ZM-66 is able to induce cell death by apoptosis in vitro

as a result of the reverse of the apoptosis resistance in drug-resistant K562/ADM cells by modulating expression of key factors associated with apoptosis induction.