Mechanisms of cellular resistance to imatinib in human chronic myeloid leukemia cells

Abstract

A major advancement in the treatment of chronic myeloid leukemia (CML) has been the development of imatinib, which has shown striking activity in the chronic phase and the accelerated phase, but less so in the blast phase of the disease. Despite high rates of hematologic and cytogenetic responses to therapy, the emergence of resistance to imatinib has been recognized as a major problem in the treatment of patients with CML. Various cellular mechanisms may be involved in the nature of cellular resistance. Increased amount of target, alteration in structure of target proteins, decreased drug uptake and increased detoxification are well-known mechanisms of resistance. On the other hand, in some cases, even if anticancer drugs reach their sites of action, bypassing drug efflux system of the cells, some cells still may survive via the dysregulation of apoptotic signalling. In this study, mechanisms of resistance to imatinib-induced apoptosis in human Meg-01 CML cells were examined. Continuous exposure of cells to step-wise increasing concentrations of imatinib resulted in the selection of 200- and 1000 nM imatinib-resistant sub-lines referred to as Meg-01/IMA-0,2 and Meg-01/IMA-1, respectively. MTT cell proliferation, cell cycle analyses and trypan blue dye exclusion analyses showed that Meg-01/IMA-1 cells were resistant to imatinib-induced apoptosis as compared to parental sensitive cells. There was an increased expression of BCR/ABL, Bcl-2 and an increase in mitochondrial membrane potential (MMP) detected in resistant cells comparing to parental sensitive cells. There was no mutation detected in imatinib binding site of ABL kinase region. Various diverse mechanisms have been reported for their involvement in the multidrug resistance. In this study, it has been shown that the degree of BCR/ABL expression appears to be directly proportional to the levels of imatinib resistance. In addition, there have been BCR/ABL-independent mechanisms reported for deriving resistance against imatinib. Our results revealed that besides BCR/ABL overexpression, imatinib resistance also depends on the inhibition of apoptosis as a result of up-regulation of anti-apoptotic stimuli and down-regulation of pro-apoptotic stimuli through MMP but does not depend on any mutation on imatinib binding site of ABL kinase.

The importance of protein profiling in the diagnosis and treatment of hematologic malignancies

“…The main driving force of leukemogenesis in CML is reciprocal translocation between chromosomes 9 and 22, which produces a fusion protein (BCR-ABL) having constitutive tyrosine kinase activity, and, in turn, induces cell growth [35]. BCR-ABL is one of the most prominent proteins in leukemic cells and its overexpression is linked to chemotherapeutic drug resistance [36]. With the increased knowledge about this fusion protein, highly specific drugs were developed and considerable cytogenetic responses were delineated [37][38][39].…”

Combination of Fludarabine and Imatinib Induces Apoptosis Synergistically Through Loss of Mitochondrial Membrane Potential and Increases in Caspase-3 Enzyme Activity in Human K562 Chronic Myleloid Leukemia Cells

“…IC50 values (dose of the drugs in which 50% of the cells can survive) of fludarabine and imatinib were determined by XTT as described previously (15). Briefly, 2 × 10 4 cells were maintained in 96-well plates with 200 µL growth medium in the absence or presence of increased doses of fludarabine and imatinib.…”

Roles of ceramide synthase and ceramide clearence genes in nilotinib-induced cell death in chronic myeloidleukemia cells

“…Different mechanisms were suggested for imatinib resistance [9,10] such as mutations in the ATP binding site of BCR-ABL [11], decreased availability of the drug either by binding to plasma proteins or by overexpression of transporter proteins such as P-glycoprotein on the plasma membrane [12], or overexpression of BCR-ABL. Furthermore, also BCR-ABL independent resistance mechanisms were suggested, such as aberrations in ceramide generating and clearance genes [9]. Nilotinib, an analog of imatinib, has higher selectivity to BCR-ABL as compared to imatinib.…”