Berbamine exhibits potent antitumor effects on imatinib-resistant CML cells in vitro and in vivo.

AIM: The aim of this study was to explore the effects and mechanism of berbamine on imatinib-resistant BCR-ABL-positive human leukemia K562 (K562-r) cells in vitro and in vivo.

METHODS

Cell viability was measured by MTT assay, and apoptotic morphology changes were detected by fluorescence microscopy. The apoptosis rate was measured by flow cytometric assay. mdr-1 mRNA levels were determined by RT-PCR. Bcl-2 family proteins, cytochrome c(cyt C), poly (ADP-ribose) polymerase (PARP), and P-glycoprotein were detected by Western blot. BALB/c nu/nu mice were injected with K562-r cells subcutaneously. Tumor-bearing mice were treated intravenously with berbamine.

RESULTS

MTT tests revealed that berbamine significantly inhibited K562-r cell proliferation and increased the chemo-sensitivity of K562-r cells to imatinib. The apoptosis rate was significantly increased following treatment with 21.2 micromol/L berbamine; formation of typical apoptotic blebs was apparent, as observed by fluorescence microscopy. Expression levels of mdr-1 mRNA and P-gp protein were high in untreated K562-r cells and significantly down-regulated by berbamine treatment. Berbamine-treated K562-r cells also exhibited down-regulated expression of the anti-apoptotic proteins Bcl-2 and Bcl-x(L), up-regulated expression of the apoptotic proteins Bax and cytoplasmic cyt C, and stimulated proteolytic cleavage of PARP. In addition, berbamine also suppressed the growth of K562-r xenotransplanted tumors in vivo.

CONCLUSION

Berbamine inhibited proliferation of K562-r cells both in vitro and in vivo. Berbamine-induced apoptosis in K562-r cells appeared to occur through a mechanism involving Bcl-2 family proteins, as well as mdr-1 mRNA and P-gp protein. Berbamine in combination with imatinib restored the chemo-sensitivity of K562-r cells to imatinib. Our findings suggest that berbamine may be useful in treating imatinib-resistant CML patients.