Overproduction of BCR-ABL induces apoptosis in imatinib mesylate-resistant cell lines

Combination therapy using TGF-β1 and STI-571 can induce apoptosis in BCR-ABL oncogene-expressing cells

The BCR-ABL oncogene is a tyrosine kinase gene that is over-expressed in CML. It inhibits the TGF-β1 signaling pathway. Due to resistance of cells to the tyrosine kinase inhibitor, STI-571, the combined effect of STI-571 and TGF-β1 on K562 cells was studied in the present research. Results revealed that the TGF-β1 cell signaling pathway, which is activated in K562 cells treated with TGF-β1, activates collective cell signaling pathways involved in survival and apoptosis. It is noteworthy that treating K562 cells with STI-571 triggered apoptotic pathways, accompanied by a reduction in proteins such as Bcl-xL, Bcl-2, p-AKT, p-Stat5, p-FOXO3, and Mcl-1 and an increase in the pro-apoptotic proteins PARP cleavage, and p27, leading to an increase in sub-G1 phase-arrested and Annexin-positive cells. Interestingly, the proliferation behavior of TGF-β1-induced cells was changed with the combination therapy, and STI-571-induced apoptosis was also prompted by this combination. Thus, combination treatment appears to promote sub-G1 cell cycle arrest compared to individually treated cells. Furthermore, it strongly triggered apoptotic signaling. In conclusion, TGF-β1 did not negatively impact the effect of STI-571, based on positive annexin cells, and AKT protein phosphorylation remains effective in apoptosis.

Excess of NPM-ALK oncogenic signaling promotes cellular apoptosis and drug dependency

Most of the anaplastic large-cell lymphoma (ALCL) cases carry the t(2;5; p23;q35) that produces the fusion protein NPM-ALK (nucleophosmin-anaplastic lymphoma kinase). NPM-ALK-deregulated kinase activity drives several pathways that support malignant transformation of lymphoma cells. We found that in ALK-rearranged ALCL cell lines, NPM-ALK was distributed in equal amounts between the cytoplasm and the nucleus. Only the cytoplasmic portion was catalytically active in both cell lines and primary ALCL, whereas the nuclear portion was inactive because of heterodimerization with NPM1. Thus, about 50% of the NPM-ALK is not active and sequestered as NPM-ALK/NPM1 heterodimers in the nucleus. Overexpression or relocalization of NPM-ALK to the cytoplasm by NPM genetic knockout or knockdown caused ERK1/2 (extracellular signal-regulated protein kinases 1 and 2) increased phosphorylation and cell death through the engagement of an ATM/Chk2- and γH2AX (phosphorylated H2A histone family member X)-mediated DNA-damage response. Remarkably, human NPM-ALK-amplified cell lines resistant to ALK tyrosine kinase inhibitors (TKIs) underwent apoptosis upon drug withdrawal as a consequence of ERK1/2 hyperactivation. Altogether, these findings indicate that an excess of NPM-ALK activation and signaling induces apoptosis via oncogenic stress responses. A 'drug holiday' where the ALK TKI treatment is suspended could represent a therapeutic option in cells that become resistant by NPM-ALK amplification.

UV Differentially Induces Oxidative Stress, DNA Damage and Apoptosis in BCR-ABL1-Positive Cells Sensitive and Resistant to Imatinib

Chronic myeloid leukemia (CML) cells express the active BCR-ABL1 protein, which has been targeted by imatinib in CML therapy, but resistance to this drug is an emerging problem. BCR-ABL1 induces endogenous oxidative stress promoting genomic instability and imatinib resistance. In the present work, we investigated the extent of oxidative stress, DNA damage, apoptosis and expression of apoptosis-related genes in BCR-ABL1 cells sensitive and resistant to imatinib. The resistance resulted either from the Y253H mutation in the BCR-ABL1 gene or incubation in increasing concentrations of imatinib (AR). UV irradiation at a dose rate of 0.12 J/(m²·s) induced more DNA damage detected by the T4 pyrimidine dimers glycosylase and hOGG1, recognizing oxidative modifications to DNA bases in imatinib-resistant than -sensitive cells. The resistant cells displayed also higher susceptibility to UV-induced apoptosis. These cells had lower native mitochondrial membrane potential than imatinib-sensitive cells, but UV-irradiation reversed that relationship. We observed a significant lowering of the expression of the succinate dehydrogenase (SDHB) gene, encoding a component of the complex II of the mitochondrial respiratory chain, which is involved in apoptosis sensing. Although detailed mechanism of imatinib resistance in AR cells in unknown, we detected the presence of the Y253H mutation in a fraction of these cells. In conclusion, imatinib-resistant cells may display a different extent of genome instability than their imatinib-sensitive counterparts, which may follow their different reactions to both endogenous and exogenous DNA-damaging factors, including DNA repair and apoptosis.

Variable behavior of iPSCs derived from CML patients for response to TKI and hematopoietic differentiation

Chronic myeloid leukemia disease (CML) found effective therapy by treating patients with tyrosine kinase inhibitors (TKI), which suppress the BCR-ABL1 oncogene activity. However, the majority of patients achieving remission with TKI still have molecular evidences of disease persistence. Various mechanisms have been proposed to explain the disease persistence and recurrence. One of the hypotheses is that the primitive leukemic stem cells (LSCs) can survive in the presence of TKI. Understanding the mechanisms leading to TKI resistance of the LSCs in CML is a critical issue but is limited by availability of cells from patients. We generated induced pluripotent stem cells (iPSCs) derived from CD34⁺ blood cells isolated from CML patients (CML-iPSCs) as a model for studying LSCs survival in the presence of TKI and the mechanisms supporting TKI resistance. Interestingly, CML-iPSCs resisted to TKI treatment and their survival did not depend on BCR-ABL1, as for primitive LSCs. Induction of hematopoietic differentiation of CML-iPSC clones was reduced compared to normal clones. Hematopoietic progenitors obtained from iPSCs partially recovered TKI sensitivity. Notably, different CML-iPSCs obtained from the same CML patients were heterogeneous, in terms of BCR-ABL1 level and proliferation. Thus, several clones of CML-iPSCs are a powerful model to decipher all the mechanisms leading to LSC survival following TKI therapy and are a promising tool for testing new therapeutic agents.

Oncogenic stress induced by acute hyper-activation of Bcr-Abl leads to cell death upon induction of excessive aerobic glycolysis

In response to deregulated oncogene activation, mammalian cells activate disposal programs such as programmed cell death. To investigate the mechanisms behind this oncogenic stress response we used Bcr-Abl over-expressing cells cultivated in presence of imatinib. Imatinib deprivation led to rapid induction of Bcr-Abl activity and over-stimulation of PI3K/Akt-, Ras/MAPK-, and JAK/STAT pathways. This resulted in a delayed necrosis-like cell death starting not before 48 hours after imatinib withdrawal. Cell death was preceded by enhanced glycolysis, glutaminolysis, and amino acid metabolism leading to elevated ATP and protein levels. This enhanced metabolism could be linked to induction of cell death as inhibition of glycolysis or glutaminolysis was sufficient to sustain cell viability. Therefore, these data provide first evidence that metabolic changes induced by Bcr-Abl hyper-activation are important mediators of oncogenic stress-induced cell death.

During the first 30 hours after imatinib deprivation, Bcr-Abl hyper-activation did not affect proliferation but resulted in cellular swelling, vacuolization, and induction of eIF2α phosphorylation, CHOP expression, as well as alternative splicing of XPB, indicating endoplasmic reticulum stress response. Cell death was dependent on p38 and RIP1 signaling, whereas classical death effectors of ER stress, namely CHOP-BIM were antagonized by concomitant up-regulation of Bcl-xL.

Screening of 1,120 compounds for their potential effects on oncogenic stress-induced cell death uncovered that corticosteroids antagonize cell death upon Bcr-Abl hyper-activation by normalizing cellular metabolism. This protective effect is further demonstrated by the finding that corticosteroids rendered lymphocytes permissive to the transforming activity of Bcr-Abl. As corticosteroids are used together with imatinib for treatment of Bcr-Abl positive acute lymphoblastic leukemia these data could have important implications for the design of combination therapy protocols.

In conclusion, excessive induction of Warburg type metabolic alterations can cause cell death. Our data indicate that these metabolic changes are major mediators of oncogenic stress induced by Bcr-Abl.

Metabolic characteristics of imatinib resistance in chronic myeloid leukaemia cells

BACKGROUND AND PURPOSE

Early detection of resistance development is crucial for imatinib-based treatment in chronic myeloid leukaemia (CML) patients. We aimed to distinguish metabolic markers of cell resistance to imatinib.

EXPERIMENTAL APPROACH

Two human imatinib-sensitive CML cell lines: LAMA84-s and K562-s, and their resistant counterparts: LAMA84-r and K562-r (both resistant to 1 microM imatinib), and K562-R (5 microM) were analysed by nuclear magnetic resonance spectroscopy to assess global metabolic profiling, including energy state, glucose and phospholipid metabolism.

KEY RESULTS

We found, by Western blotting and flow cytometry, that the levels of Bcr-Abl tyrosine kinase and multi-drug resistance p-glycoprotein were inconsistent among resistant clones. On the other hand, phospholipid metabolism and lactate production were highly predictive for cell response to imatinib. As previously reported, sensitive cells showed significantly decreased glycolytic activity (lactate) and phospholipid synthesis (phosphocholine) as well as increased phospholipid catabolism (glycerophosphocholine) after 24 h of 1 microM imatinib treatment, which correlated with inhibition of cell proliferation and induction of apoptosis. In contrast to their sensitive counterparts, the K562-r, K562-R and LAMA84-r maintained increased phospholipid synthesis and glycolytic lactate production in the presence of 1 microM (K562-r and LAMA84-r) and 5 microM (K562-R) imatinib.

CONCLUSIONS AND IMPLICATIONS

Specific metabolic markers for early detection of imatinib resistance, including increased glycolytic activity and phospholipid turnover, can be identified in resistant clones. Once validated in human isolated leukocytes, they may be used to monitor the responsiveness of CML patients to treatment.

Characteristics of dasatinib- and imatinib-resistant chronic myelogenous leukemia cells

PURPOSE

Although dual src-family kinase/BCR/ABL inhibitor, dasatinib (BMS-354825), provides therapeutic advantages to imatinib-resistant cells, the mechanism of dasatinib resistance was not fully known.

EXPERIMENTAL DESIGN

We used TF-1 BCR/ABL cells, by introducing the BCR/ABL gene into a leukemia cell line, TF-1 and K562, and established dasatinib- (BMS-R) and imatinib-resistant (IM-R) cells. We characterized chronic myelogenous leukemia drug-resistant cells and examined intracellular signaling.

RESULTS

The IC(50) of dasatinib was 0.75 nmol/L (TF-1 BCR/ABL), 1 nmol/L (K562), 7.5 nmol/L (TF-1 BCR/ABL IM-R), 10 nmol/L (K562 IM-R), 15 micromol/L (TF-1 BCR/ABL BMS-R), and 25 micromol/L (K562 BMS-R). The number of BCR/ABL copies in resistant cell lines was the same as the parental cell line by fluorescence in situ hybridization analysis. There was no mutation in Abl kinase. We found that protein levels of BCR/ABL were reduced in dasatinib-resistant cell lines. BCR/ABL protein was increased by treatment of an ubiquitin inhibitor. The Src kinase, Lck, as well as mitogen-activated protein kinase and Akt were activated, but p21(WAF), phosphatase and tensin homologue was reduced in K562 BMS-R cells. Removal of dasatinib from the culture medium of K562 BMS-R cells led to apoptosis, and activated caspase 3 and poly (ADP-ribose) polymerase.

CONCLUSION

These results suggest that the expression and protein activation signatures identified in this study provide insight into the mechanism of resistance to dasatinib and imatinib and may be of therapeutic chronic myelogenous leukemia value clinically.

Intermittent dosage of imatinib mesylate in CML patients with a history of significant hematologic toxicity after standard dosing

Hematologic toxicity is reported as one of the most important problems connected with imatinib mesylate (IM) treatment in patients with chronic myelogenous leukemia (CML). Withholding the drug or application of growth factors is recommended in this situation. This study introduced a novel approach using intermittent dosage of IM in order to avoid prolonged interruptions in therapy, to allow spontaneous recovery in blood count and, simultaneously, to achieve intermittently therapeutic plasma drug levels. A retrospective analysis of intermittent therapy (iT) in 12 patients with CML is presented. All patients had intermediate-to-high prognostic scores. Two patients had history of autologous stem cell transplantation. Initial standard therapy with IM was indicated for resistance to interferon (eight subjects) and for accelerated phase in four cases (one of them cytogenetic) and lasted for 1 - 6 months. iT with 300 - 600 mg of IM 1 - 5 times a week was started after significant hematologic toxicity occurred. In three patients treated 3 - 5 times a week, hematologic recovery allowed reintroduction of full dose after 3 - 7 (mean 4.6) months. In three patients, one-to-three doses per week were sufficient to maintain the cytogenetic response for a mean of 30.6 months (range 29 - 33). Six patients tolerated more frequent dosage of 4 - 5 times a week for a mean of 17.8 months (range 3 - 28). Five patients improved their cytogenetic response during iT, while hematologic progression occurred in one patient. Development of a cytogenetic abnormality in a Ph-negative clone was observed in one patient. Overall, two complete and five major cytogenetic responses were achieved. The sensitivity of Bcr/Abl kinase to inhibition by IM was proved in seven patients tested by Crkl phosphorylation assay. Measurement of plasma IM concentrations in three subjects showed concentrations fully compatible with the dosage applied suggesting normal intestinal absorption. iT with IM is a feasible and safe strategy for short-time 'bridging' management of patients with significant hematologic toxicity after standard daily dosing. Long-term iT with IM does not seem to compromise the cytogenetic response in patients with sensitivity of Bcr/Abl kinase to IM and should be considered as a plausible treatment option in patients with persistent signs of myelotoxicity.