Emodin Inhibits Resistance to Imatinib by Downregulation of Bcr-Abl and STAT5 and Allosteric Inhibition in Chronic Myeloid Leukemia Cells.

Imatinib-resistance is a significant concern for Bcr-Abl-positive chronic myelogenous leukemia (CML) treatment. Emodin, the predominant compound of traditional medicine rhubarb, was reported to inhibit the multidrug resistance by downregulating P-glycoprotein of K562/ADM cells with overexpression of P-glycoprotein in our previous studies. In the present study, we found that emodin can be a potential inhibitor for the imatinib-resistance in K562/G01 cells which are the imatinib-resistant subcellular line of human chronic myelogenous leukemia cells with overexpression of breakpoint cluster region-abelson (Bcr-Abl) oncoprotein. Emodin greatly enhanced cell sensitivity to imatinib, suppressed resistant cell proliferation and increased potentiated apoptosis induced by imatinib in K562/G01 cells. After treatment of emodin and imatinib together, the levels of p-Bcr-Abl and Bcr-Abl were significantly downregulated. Moreover, Bcr-Abl important downstream target, STAT5 and its phosphorylation were affected. Furthermore, the expression of Bcr-Abl and signal transducers and activators of transcription 5 (STAT5) related molecules, including c-MYC, MCL-1, poly(ADP-ribose)polymerase (PARP), Bcl-2 and caspase-3, were changed. Emodin also decreased Src expression and its phosphorylation. More importantly, emodin simultaneously targeted both the ATP-binding and allosteric sites on Bcr-Abl by molecular docking, with higher affinity with the myristoyl-binding site for enhanced Bcr-Abl kinase inhibition. Overall, these data indicated emodin might be an effective therapeutic agent for inhibiting resistance to imatinib in CML treatment.

Polyphyllin D induces apoptosis and differentiation in K562 human leukemia cells.

Polyphyllin D, a compound derived from Paris polyphylla rhizoma, demonstrated strong anticancer activities in a previous study. Our results demonstrated that polyphyllin D exerts a growth inhibitory effect by inducing apoptosis and differentiation in the human erythroleukemia cell line K562. Polyphyllin D induced apoptosis via the mitochondrial apoptotic pathway, as evidenced by the decreased Bcl-2 and Bcr/Abl expression levels, the disruption of MMP and increased Bax, cytochrome c and cleaved-caspase-3 levels. At a low dose, polyphyllin D increased CD14 expression on the surface of K562 cells and induced cells to differentiate into monocytes or mature macrophages. These data suggest that polyphyllin D has the potential to be a potent therapeutic agent for treating human chronic myelogenous leukemia.

The antiproliferation effect of berbamine on k562 resistant cells by inhibiting NF-kappaB pathway.

Imatinib mesylate is effective against Ph chromosome-positive leukemia; however, resistance has been reported. High expression of bcr-abl in mRNA and protein levels, and other alterations were found in patients who experienced imatinib treatment failures and thus it is important to design alternative treatment strategies. The aim of this study was to evaluate the in vitro effect of berbamine, on imatinib-resistant chronic myelogenous leukemia (CML) K562 (K562-r) cells, and explore the mechanisms. The growth of K562-r cells was examined using the 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Morphological analysis and DNA agarose electrophoresis were used to detect apoptosis in K562-r cells, and the extent of the cells in the sub-G1 cell cycle phase was measured using flow cytometry. The expression levels of BCR-ABL, phospho-BCR-ABL, and nuclear factor kappaB (NF-kappaB), IkappaBalpha, phospho-IkappaBalpha, IkappaB kinases alpha(IKKalpha), and Survivin were determined by Western blot. bcr-abl mRNA expression was determined by RT-PCR. MTT assays indicated that berbamine significantly inhibited the proliferation of K562-r cells. Cells with characteristics of apoptosis were confirmed by morphology examination and DNA agarose electrophoresis and percentage of apoptosis were increased after treatment with berbamine. The results also showed that berbamine was able to down-regulate BCR-ABL and phospho-BCR-ABL proteins by affecting bcr-abl mRNA expression and decrease expression of nuclear NF-kappaB, phospho-IkappaBalpha, IKKalpha, and Survivin. Collectively, berbamine could inhibit the proliferation of K562-r cells and induce apoptosis. The mechanisms may be related at least in part, to inhibit BCR-ABL and its downstream NF-kappaB signaling. Berbamine may provide an alternative candidate for the treatment of patients with CML resistant to imatinib therapy.

Inhibition of abl oncogene tyrosine kinase induces erythroid differentiation of human myelogenous leukemia K562 cells.

The human chronic myelogenous leukemia cell line K562 expresses a structurally altered c-abl protein with tyrosine kinase activity. Erythroid differentiation of K562 cells was induced by tyrosine kinase inhibitors, but not by other kinase inhibitors. Treatment of K562 cells with 5'd(TACTGGCCGCTG-AAGGGC)3', complementary to the second exon (codons 2 to 7) of c-abl mRNA, inhibited cell growth and induced benzidine-positive cells in a dose-dependent manner. However, exposure to the sense oligomer did not induce erythroid differentiation of the cells. These results suggest that inhibition of abl tyrosine kinase activity is closely related to induction of erythroid differentiation of K562 cells. A multidrug-resistant subline (K562R) was induced to undergo erythroid differentiation by tyrosine kinase inhibitors such as genistein or herbimycin A as effectively as the parent K562 cells were. Therefore, tyrosine kinase inhibitors might be useful as cancer chemotherapeutic agents against some multidrug-resistant leukemias having abnormally high activity of oncogene tyrosine kinase(s).