Effect of imatinib on the signal transduction cascade regulating telomerase activity in K562 (BCR-ABL–positive) cells sensitive and resistant to imatinib

doi:10.1016/j.exphem.2009.10.005

Experimental Hematology

Volume 38, Issue 1, January 2010, Pages 27-37

https://doi.org/10.1016/j.exphem.2009.10.005 Get rights and content

Objective

Imatinib mesylate (IM) is a tyrosine kinase inhibitor selective for BCR-ABL and indicated for the treatment of chronic myeloid leukemia. It has recently been demonstrated that IM also targets other cellular components. Considering the significant role of telomerase in malignant transformation, we studied the effect of IM on telomerase activity (TA) and regulation in BCR-ABL–positive and –negative cells, sensitive and resistant to IM.

Materials and Methods

Through combining telomeric repeat amplification protocol for detecting TA, reverse transcription polymerase chain reaction and Western blots for detecting RNA and protein levels of telomerase regulating proteins and fluorescence-activated cell sorting analysis, we showed that IM targets telomerase and the signal transduction cascade upstream of it.

Results

IM significantly inhibited TA in BCR-ABL–positive and –negative cells and in chronic myeloid leukemia patients. TA inhibition was also observed in BCR-ABL positive cells resistant to IM at drug concentrations that did not lead to a reduction in BCR-ABL expression. In addition, a reduction in phosphorylated AKT and phosphorylated PDK-1 was also detected following IM incubation.

Conclusions

We demonstrate an inhibitory effect of IM on TA and on the AKT/PDK pathway. Because this effect was observed in cell expressing the BCR-ABL protein as well as cells not expressing it, and in cells sensitive as well as resistant to IM, it is reasonable to assume that the inhibitory effect of IM on TA is not mediated through known IM targets. The results of this study show that cells resistant to IM with regard to its effect on BCR-ABL could still be sensitive to IM treatment regarding other cellular components.

Section snippets

Cells

K562, K562_res (kindly provided by Dr. Esther Rabizadeh), K562_res2 (kindly provided by Prof. Giuseppe Saglio, University of Turin, Italy), Meg-01, HL-60 (kindly provided by Dr. Shay Izraeli, Sheba Medical Center, Israel), and HBL-2 (kindly provided by Prof. Martin Dreyling, University of Munich, Germany) cells were maintained in RPMI-1640 with 10% fetal calf serum, glutamine (2 mM), penicillin and streptomycin (1%). K562_res and K562_res2 cells were constantly maintained with 2 μM and 0.6 μM IM,

Growth inhibition of different cell lines by IM

K562_{res/ res2} cells are constantly maintained with IM. Because it is possible that the presence of IM can obscure our results, these cells were grown in IM-free medium prior to each experiment. The growth inhibitory effect of IM was tested on all cell lines and is presented in Figure 1 (representative results of K562 and K562_res cells) and in Table 1.

Effect of IM on TA

TA of BCR-ABL–positive, IM-sensitive cell lines (K562 and Meg-01) was evaluated following 3 days of exposure to IM. K562 cells showed a

Discussion

Telomere maintenance and TA play an essential role in tumor formation. Consequently, the effect of different drugs on TA is being widely explored [35]. This study demonstrates that IM is capable of inhibiting TA in BCR-ABL–positive cell lines and patients and that this inhibition is reversible. In our study, TA inhibition was detected, for the first time, to a similar extent in cells harboring the BCR-ABL protein, which are resistant to IM. This inhibition was observed at concentrations that

Acknowledgment

This work was performed in partial fulfillment of the requirements for the M.Sc. degree of Rahav Mor-Tzuntz, Sackler Faculty of Medicine, Tel-Aviv University.

Conflict of Interest Disclosure

No financial interest/relationships with financial interest relating to the topic of this article have been declared.

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In conclusion, we provide evidence for transcriptional and post-translational inhibition of telomerase by nilotinib and dasatinib which is not necessarily mediated via known targets of these tyrosine kinase inhibitors.

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Hematological MalignanciesEffect of imatinib on the signal transduction cascade regulating telomerase activity in K562 (BCR-ABL–positive) cells sensitive and resistant to imatinib

Objective

Materials and Methods

Results

Conclusions

Section snippets

Cells

Growth inhibition of different cell lines by IM

Effect of IM on TA

Discussion

Acknowledgment

Conflict of Interest Disclosure

Lancet

Blood

Blood

Leuk Res

Curr Opin Genet Dev

J Biol Chem

Eur J Cancer

Biochem Biophys Res Commun

Exp Hematol

FEBS Lett

Exp Cell Res

Curr Biol

Biochem Pharmacol

J Biol Chem

Blood

Blood

Drug Resist Updat

Blood Cells Mol Dis

Chronic myeloid leukaemia as a model of disease evolution in human cancer

Nat Rev Cancer

Current and emerging treatment options in chronic myeloid leukemia

Cancer

A non-ATP-competitive inhibitor of BCR-ABL overrides imatinib resistance

Proc Natl Acad Sci U S A

Clinical resistance to STI-571 cancer therapy caused by BCR-ABL gene mutation or amplification

Science

Molecular and chromosomal mechanisms of resistance to imatinib (STI571) therapy

Leukemia

Role of alpha1 acid glycoprotein in the in vivo resistance of human BCR-ABL(+) leukemic cells to the abl inhibitor STI571

J Natl Cancer Inst

P-glycoprotein-mediated drug efflux is a resistance mechanism of chronic myelogenous leukemia cells to treatment with imatinib mesylate

Leukemia

Hematological Malignancies
Effect of imatinib on the signal transduction cascade regulating telomerase activity in K562 (BCR-ABL–positive) cells sensitive and resistant to imatinib