Imatinib-resistant Chronic Myelogenous Leukemia Cells Research Articles

Hydroxychavicol sensitizes imatinib-resistant chronic myelogenous leukemia cells to TRAIL-induced apoptosis by ROS-mediated IAP downregulation: Erratum.

Hydroxychavicol sensitizes imatinib-resistant chronic myelogenous leukemia cells to TRAIL-induced apoptosis by ROS-mediated IAP downregulation: Erratum.

BCR-ABL triggers a glucose-dependent survival program during leukemogenesis through the suppression of TXNIP

sImatinib is highly effective in the treatment of chronic myelogenous leukemia (CML), but the primary and acquired imatinib resistance remains the big hurdle. Molecular mechanisms for CML resistance to tyrosine kinase inhibitors, beyond point mutations in BCR-ABL kinase domain, still need to be addressed. Here, we demonstrated that thioredoxin-interacting protein (TXNIP) is a novel BCR-ABL target gene. Suppression of TXNIP was responsible for BCR-ABL triggered glucose metabolic reprogramming and mitochondrial homeostasis. Mechanistically, Miz-1/P300 complex transactivates TXNIP through the recognition of TXNIP core promoter region, responding to the c-Myc suppression by either imatinib or BCR-ABL knockdown. TXNIP restoration sensitizes CML cells to imatinib treatment and compromises imatinib resistant CML cell survival, predominantly through the blockage of both glycolysis and glucose oxidation which results in the mitochondrial dysfunction and ATP production. In particular, TXNIP suppresses expressions of the key glycolytic enzyme, hexokinase 2 (HK2), and lactate dehydrogenase A (LDHA), potentially through Fbw7-dependent c-Myc degradation. In accordance, BCR-ABL suppression of TXNIP provided a novel survival pathway for the transformation of mouse bone marrow cells. Knockout of TXNIP accelerated BCR-ABL transformation, whereas TXNIP overexpression suppressed this transformation. Combination of drug inducing TXNIP expression with imatinib synergistically kills CML cells from patients and further extends the survival of CML mice. Thus, the activation of TXNIP represents an effective strategy for CML treatment to overcome resistance.

JKST6, a novel multikinase modulator of the BCR-ABL1/STAT5 signaling pathway that potentiates direct BCR-ABL1 inhibition and overcomes imatinib resistance in chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is a hematological malignancy that highly depends on the BCR-ABL1/STAT5 signaling pathway for cell survival. First-line treatments for CML consist of tyrosine kinase inhibitors that efficiently target BCR-ABL1 activity. However, drug resistance and intolerance are still therapeutic limitations in Ph+ cells. Therefore, the development of new anti-CML drugs that exhibit alternative mechanisms to overcome these limitations is a desirable goal. In this work, the antitumoral activity of JKST6, a naphthoquinone-pyrone hybrid, was assessed in imatinib-sensitive and imatinib-resistant human CML cells. Live-cell imaging analysis revealed JKST6 potent antiproliferative activity in 2D and 3D CML cultures. JKST6 provoked cell increase in the subG1 phase along with a reduction in the G0/G1 phase and altered the expression of key proteins involved in the control of mitosis and DNA damage. Rapid increases in Annexin V staining and activation/cleavage of caspases 8, 9 and 3 were observed after JKST6 treatment in CML cells. Of interest, JKST6 inhibited BCR-ABL1/STAT5 signaling through oncokinase downregulation that was preceded by rapid polyubiquitination. In addition, JKST6 caused a transient increase in JNK and AKT phosphorylation, whereas the phosphorylation of P38-MAPK and Src was reduced. Combinatory treatment unveiled synergistic effects between imatinib and JKST6. Notably, JKST6 maintained its antitumor efficacy in BCR-ABL1-T315I-positive cells and CML cells that overexpress BCR-ABL and even restored imatinib efficacy after a short exposure time. These findings, together with the observed low toxicity of JKST6, reveal a novel multikinase modulator that might overcome the limitations of BCR-ABL1 inhibitors in CML therapy.

Screening and identification of key genes in imatinib-resistant chronic myelogenous leukemia cells: a bioinformatics study

ABSTRACT Background Chronic myelogenous leukemia (CML) is one of the most common cancers in the world. Imatinib is one of the most effective therapeutic strategies to inhibit the BCR-ABL tyrosine Kinase in patients with CML, but resistance is increasingly encountered. Material and Methods Microarray data GSE7114, GSE92624 and GSE97562 were downloaded and analyzed from Gene Expression Omnibus (GEO) to identify the candidate genes in the imatinib-resistant CML cells. The differentially expressed genes (DEGs) were appraised, and the protein–protein interaction (PPI) network was created by using STRING and Cytoscape. Results We screened a total of 217 DEGs, including 151 upregulated genes and 66 downregulated genes. The enriched functions and pathways of genes include insulin-like growth factor I binding, cysteine-type endopeptidase inhibitor activity involved in apoptotic process, cell adhesion, positive regulation of nitric oxide biosynthetic process and hematopoietic cell lineage. Nine hub genes were appraised and Gene Ontology enrichment analysis revealed that these genes are mainly enriched in cell cycle, peptidase inhibitor activity and cell division. Several genes such as BIRC5, CCNE2 and MCM4 were identified in survival analysis and these genes alteration are significantly associated with worse overall survival and disease-free survival. Conclusions These genes have the potential to become surrogate markers for a clinical evaluation of imatinib-resistant CML patients. Our results provide potential target genes for diagnosis and treatment of imatinib-resistant CML patients.

Identification and development of non-cytotoxic cell death modulators: Impact of sartans and derivatives on PPARγ activation and on growth of imatinib-resistant chronic myelogenous leukemia cells

4’-((2-Propyl-1H-benzo[d]imidazol-1-yl)methyl)-[1,1′-biphenyl]-2-carboxylic acid derived from telmisartan was identified as lead for the design of cell death modulators. In this study, we evaluated the efficacy of telmisartan itself and other sartans in combination with imatinib against K562-resistant cells. The findings were directly used to further optimize the lead structure. Telmisartan and candesartan cilexetil represented the most effective sartans, thus the influence of carboxyl/methyl carboxylate groups at positions 7 (compounds 6, 7) or 4 (compounds 12–14) at the benzimidazole core was studied. Additionally, according to the results of a former structure-activity study, telmisartan was transformed to the related amide (1). Telmisartan amide 1, as well as the esters 6 and 12 markedly sensitized the resistant CML cells to imatinib treatment. Correlation with their potency to activate PPARγ is not given. Candesartan cilexetil, telmisartan and 1 showed the profile of partial agonists at PPARγ with EC50 values of 4.2, 4.3 and 9.1 μM, respectively, while 6 and 12 caused only marginal intrinsic activation at 10 μM (Amax = 22% and 13%). However, the repression of the STAT5 phosphorylation relates with the possibility to sensitize K562-resistant CML cells to imatinib treatment. It is worth mentioning that all compounds were per se non-cytotoxic at relevant concentrations.

Andrographolide and its potent derivative exhibit anticancer effects against imatinib-resistant chronic myeloid leukemia cells by downregulating the Bcr-Abl oncoprotein

Chronic myelogenous leukemia (CML) is clinically treated with imatinib, which inhibits the kinase activity of the Bcr-Abl oncoprotein. However, imatinib resistance remains a common clinical issue. Andrographolide, the major compound of the medicinal plant Andrographis paniculata, was reported to exhibit anticancer activity. In this study, we explored the therapeutic potential of andrographolide and its derivative, NCTU-322, against both imatinib-sensitive and imatinib-resistant human CML cell lines. Both andrographolide and NCTU-322 downregulated the Bcr-Abl oncoprotein in imatinib-resistant CML cells through an Hsp90-dependent mechanism similar to that observed in imatinib-sensitive CML cells. In addition, NCTU-322 had stronger effects than andrographolide on downregulation of Bcr-Abl oncoprotein, induction of Hsp90 cleavage and cytotoxicity of CML cells. Notably, andrographolide and NCTU-322 could induce differentiation, mitotic arrest and apoptosis of both imatinib-sensitive and imatinib-resistant CML cells. Finally, the anticancer activity of NCTU-322 against imatinib-resistant CML cells was demonstrated in vivo. In summary, our data demonstrated that andrographolide and NCTU-322 inhibit Bcr-abl function via a mechanism different from that of imatinib, and they induced multiple anticancer effects in both imatinib-sensitive and resistant CML cells. Our findings demonstrate that andrographolide and NCTU-322 are potential therapeutic agents again CML.

Hydroxychavicol sensitizes imatinib-resistant chronic myelogenous leukemia cells to TRAIL-induced apoptosis by ROS-mediated IAP downregulation.

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a member of cytokine superfamily, induces apoptosis in a number of tumor cells through the activation of extrinsic apoptotic pathway but shows little or no cytotoxicity toward normal cells. However some tumor cells are inherently resistant to TRAIL-mediated apoptosis, which needs to be addressed to establish TRAIL as a potential chemotherapeutic drug. In this study, our aim was to manipulate TRAIL-apoptosis pathway by hydroxychavicol (HCH), a polyphenol from Piper betel leaf, for the induction of apoptosis in TRAIL resistant chronic myeloid leukemia cell. When imatinib-resistant K562 cells were treated with HCH, it made these K562 cells sensitive to TRAIL. It was observed that HCH downregulated antiapoptotic proteins XIAP and FLIP, whereas the expression of TRAIL receptors, DR4 and DR5, remains unchanged. Moreover, we observed that reactive oxygen species or ROS played a crucial role in the downregulation of FLIP and XIAP because ROS scavenger significantly reversed the decrease of XIAP, and FLIP. Ubiquitin-proteasome pathway was observed to play a crucial role in the downregulation of XIAP and FLIP, as proteasomal inhibitor MG132 significantly reversed the downregulation of XIAP and FLIP. In conclusion, this study demonstrates the combinatorial treatment of TRAIL and HCH as promising alternative therapeutic approach to treat the imatinib-resistant leukemia, which are also resistant to TRAIL.

ZNF224 is a transcriptional repressor of AXL in chronic myeloid leukemia cells

ZNF224 is a KRAB-zinc finger transcription factor that exerts a key tumor suppressive role in chronic myelogenous leukemia.In this study, we identify the receptor tyrosine kinase Axl as a novel target of ZNF224 transcriptional repression activity. Axl overexpression is found in many types of cancer and is frequently associated with drug resistance. Interestingly, we also found that sensitivity to imatinib can be partly restored in imatinib-resistant chronic myelogenous leukemia cells by ZNF224 overexpression and the resulting suppression of Axl expression.These results, in accordance with our previous findings, support the role of ZNF224 in imatinib responsiveness and shed new insights into potential therapeutic use of ZNF224 in imatinib-resistant chronic myelogenous leukemia.

Role of ZNF224 in c-Myc repression and imatinib responsiveness in chronic myeloid leukemia.

The transcription factor ZNF224 plays a key proapoptotic role in chronic myelogenous leukemia (CML), by modulating Wilms Tumor protein 1 (WT1) dependent apoptotic genes transcription. Recently, we demonstrated that Bcr-Abl signaling represses ZNF224 expression in Bcr-Abl positive CML cell lines and in CML patients. Interestingly, Imatinib and second-generation tyrosine kinase inhibitors specifically increase ZNF224 expression.On the other hand, Bcr-Abl positively modulates, via JAK2 activation, the expression of the c-Myc oncogene, which is required for Bcr-Abl oncogenic transformation in CML. Consequently, JAK2 inhibitors represent promising molecular therapeutic tools in CML.In this work, we demonstrate that ZNF224 is a novel transcriptional repressor of c-Myc in CML. We also show that ZNF224 induction by Imatinib and AG490, a specific JAK2 inhibitor, is responsible for the transcriptional repression of c-MYC, thus highlighting the crucial role of the ZNF224/c-Myc axis in Imatinib responsiveness.Interestingly, we also report that ZNF224 is induced by AG490 in Imatinib-resistant CML cells, leading to c-Myc repression and apoptosis induction. These findings suggest that the development of molecular tools able to induce ZNF224 expression could provide promising means to bypass Imatinib resistance in CML.

The role of long noncoding RNA HOTAIR in the acquired multidrug resistance to imatinib in chronic myeloid leukemia cells

ABSTRACTObjectives: Imatinib, a breakpoint cluster region-Abelson murine leukemia tyrosine kinase inhibitor, has revolutionized the treatment of chronic myelogenous leukemia (CML). However, the development of multidrug resistance (MDR) limits the clinical application of imatinib. In this study, we aimed to investigate the mechanisms of long noncoding RNA (lncRNA) HOTAIR in CML resistance to imatinib.Methods: Thirty-four CML patients were divided into multidrug resistance protein 1 (MRP1)-low and MRP1-high groups according to the median expression. Real-time PCR (qPCR) was used to detect the expression of lncRNA HOTAIR in CML patients, and MTT assay and flow cytometry assay were employed to detect the biological function of silencing lncRNA HOTAIR on the cell survival rate and apoptotic rate. An imatinib-resistant human CML cell line K562 (K562-R) was established, and western blot was used to detect the impact of lncRNA HOTAIR on the activation of PI3K/Akt signaling pathway.Results: Our results showed that lncRNA HOTAIR was greatly upregulated in the MRP1-high patients as well as in the K562-imatinib-resistant cells compared with control. Knockdown of HOTAIR expression downregulated the MRP1 expression levels in the K562-imatinib cells and resulted in higher sensitivity to the imatinib treatment. In addition, the activation of PI3K/Akt was greatly attenuated when HOTAIR was knocked down in K562-imatinib cells.Discussions: These data suggest that the knockdown of HOTAIR may play a crucial role in improving acquired resistance to imatinib in CML K562-R cells via PI3K/Akt pathway.Conclusions: LncRNA HOTAIR modulates CML cell MDR in a PI3K/Akt-dependent way.

Natural-Based Indirubins Display Potent Cytotoxicity toward Wild-Type and T315I-Resistant Leukemia Cell Lines.

Drug resistance in chronic myelogenous leukemia (CML) requires the development of new CML chemotherapeutic drugs. Indirubin, a well-known mutikinase inhibitor, is the major active component of "Danggui Longhui Wan", a Chinese traditional medicine used for the treatment of CML symptoms. An in-house collection of indirubin derivatives was screened at 1 μM on wild-type and imatinib-resistant T315I mutant CML cells. Herein are reported that only 15 analogues of the natural 6-bromoindirubin displayed potent cytotoxicity in the submicromolar range. Kinase assays in vitro show that eight out of the 15 active molecules strongly inhibited both c-Src and Abl oncogenic kinases in the nanomolar range. Most importantly, these eight molecules blocked the activity of T315I mutant Abl kinase at the submicromolar level and with analogue 22 exhibiting inhibitory activity at the low nanomolar range. Docking calculations suggested that active indirubins might inhibit T315I Abl kinase through an unprecedented binding to both active and Src-like inactive conformations. Analogue 22 is the first derivative of a natural product identified as an inhibitor of wild-type and imatinib-resistant T315I mutant Abl kinases.

Effect of A Novel Emodin Derivative on Chronic Myelogenous Leukemia K562 Cells and Imatinib-resistant K562/G01 Cells

To explore the effect of a novel emodin derivative E19 on proliferation inhibition and apoptosis induction of human chronic myelogenous leukemia (CML) cell line K562 and imatinib-resistant CML cell line (K562/G01), and to clarify the involved mechanisms. MTT and colony formation test were used to detect the cell proliferation. Apoptotic induction effects were examined by DAPI staining method and DNA ladder assay. Western blot was performed to detect the changes of P210(Bcr-Abl) protein. The emodin derivative E19 could efficiently inhibit proliferation and induce apoptosis in K562 and K562/G01 cells. IC50 of K562 cells and IC50 of K562/G01 cells were (1.20 ± 0.19) µmol/L and (1.22 ± 0.16) µmol/L, respectively. DNA fragmentation in K562 cells and K562/G01 cells confirmed that the E19 induced apoptosis in dose-dependent manner. Western blot showed that emodin derivative inhibited phosphorylation of P210 protein in K562 cells and K562/G01 cells and down-regulated the expression level of P210 in dose- and time-dependent manners. The emodin derivative E19 can efficiently inhibit growth and induce apoptosis of K562 cells and K562/G01 cells, while the inhibition of phosphorylation of P210 protein and down-regulation of P210 protein expression may be involved in these processes.

Dual inhibition of Bcr-Abl and Hsp90 by C086 potently inhibits the proliferation of imatinib-resistant CML cells.

Although tyrosine kinase inhibitors (TKI) such as imatinib provide an effective treatment against Bcr-Abl kinase activity in the mature cells of patients with chronic myelogenous leukemia (CML), TKIs probably cannot eradicate the leukemia stem cell (LSC) population. Therefore, alternative therapies are required to target both mature CML cells with wild-type (WT) or mutant Bcr-Abl and LSCs. To investigate the effect of C086, a derivative of curcumin, on imatinib-resistant cells, we explored its underlying mechanisms of Bcr-Abl kinase and heat shock protein 90 (Hsp90) function inhibition. Biochemical assays were used to test ABL kinase activity; fluorescence measurements using recombinant NHsp90, Hsp90 ATPase assay, immunoprecipitation, and immunoblotting were applied to examine Hsp90 function. Colony-forming unit, long-term culture-initiating cells (LTC-IC), and flow cytometry were used to test CML progenitor and stem cells. Biochemical assays with purified recombinant Abl kinase confirmed that C086 can directly inhibit the kinase activity of Abl, including WT and the Q252H, Y253F, and T315I mutations. Furthermore, we identified C086 as a novel Hsp90 inhibitor with the capacity to disrupt the Hsp90 chaperone function in CML cells. Consequently, it inhibited the growth of both imatinib-sensitive and -resistant CML cells. Interestingly, C086 has the capacity to inhibit LTC-ICs and to induce apoptosis in both CD34(+)CD38(+) and CD34(+)CD38(-) cells in vitro. Moreover, C086 could decrease the number of CD45(+), CD45(+)CD34(+)CD38(+), and CD45(+)CD34(+)CD38(-) cells in CML NOD-SCID mice. Dual suppression of Abl kinase activity and Hsp90 chaperone function by C086 provides a new therapeutic strategy for treating Bcr-Abl-induced leukemia resistant to TKIs.

SAHA and S116836, a novel tyrosine kinase inhibitor, synergistically induce apoptosis in imatinib-resistant chronic myelogenous leukemia cells

Limited treatment options are available for chronic myelogenous leukemia (CML) patients who develop imatinib mesylate (IM) resistance. Here we proposed a novel combination regimen, a co-administration of S116836, a novel small molecule multi-targeted tyrosine kinase inhibitor that was synthesized by rational design, and histone deacetylases inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA), to overcome IM resistance in CML. S116836 at low concentrations used in the present study mildly downregulates auto-tyrosine phosphorylation of Bcr-Abl. SAHA, an FDA-approved HDACi drug, at 1 μM has modest anti-tumor activity in treating CML. However, we found a synergistic interaction between SAHA and S116836 in Bcr-Abl-positive CML cells that were sensitive or resistant to IM. Exposure of KBM5 and KBM5-T315I cells to minimal or non-toxic concentrations of SAHA and S116836 synergistically reduced cell viability and induced cell death. Co-treatment with SAHA and S116838 repressed the expressions of anti-apoptosis proteins, such as Mcl-1 and XIAP, but promoted Bim expression and mitochondrial damage. Of importance, treatment with both drugs significantly reduced cell viability of primary human CML cells, as compared with either agent alone. Taken together, our findings suggest that SAHA exerts synergistically with S116836 at a non-toxic concentration to promote apoptosis in the CML, including those resistant to imatinib or dasatinib.

Suppression of Survivin Induced by a BCR-ABL/JAK2/STAT3 Pathway Sensitizes Imatinib-Resistant CML Cells to Different Cytotoxic Drugs

The BCR-ABL oncoprotein of chronic myelogenous leukemia (CML) displays exclusive cytoplasmic localization and constitutive tyrosine kinase activity leading to the activation of different pathways that favor cell proliferation and survival. BCR-ABL induces survivin expression at both the mRNA and protein level, thus inhibiting the apoptotic machinery of CML cells and contributing to the expansion of the leukemic clone. We report that, in human CML cell lines, BCR-ABL-mediated upregulation of survivin involves the JAK2/STAT3 pathway since silencing of either protein caused a consistent reduction in survivin expression. Cell lines unresponsive to imatinib mesylate (IM) because of BCR-ABL gene amplification were not resensitized to the drug after survivin downregulation. However, cells insensitive to IM because of point mutations in the BCR-ABL kinase domain were highly responsive to hydroxyurea (HU) after survivin silencing. To address the possible clinical applications of our results, we used shepherdin, a cell-permeable peptidomimetic compound that downregulates survivin expression by preventing its interaction with Hsp90. Incubation with shepherdin of immortalized cell lines both sensitive and resistant to IM enhanced cell death induced by HU and doxorubicin. Similarly, the combination of shepherdin with first- and second-generation tyrosine kinase inhibitors reduced the colony-forming potential of human progenitors derived from both patients with IM-sensitive and IM-resistant CML. These results suggest that strategies aimed at reducing survivin levels may represent a potential therapeutic option for patients with CML unresponsive to IM.

Synergistic killing effect of imatinib and simvastatin on imatinib-resistant chronic myelogenous leukemia cells

The antiproliferative effect of simvastatin on tumor cells has been speculated to be by intracellular signal inhibition through 3-hydroxy-3-methylglutaryl acetyl coenzyme A reductase. We examined the killing effect of simvastatin on imatinib-sensitive and resistant chronic myelogenous leukemia (CML) cells (three kinds of CML cell lines representative of each hematopoietic lineage: K562, KCL22, and LAMA84) and T315I and E255K site-directed mutant cells (Ba/F3). The in-vivo effect of simvastatin was determined in K562-xenografted nude mice. Cotreatment with imatinib and simvastatin in imatinib-resistant CML cells showed a synergistic killing effect in K562-R, KCL22-R, LAMA84-R, and E255K mutant cells, but only an additive effect in the T315I mutant cell, although a single treatment of simvastatin strongly inhibited T315I mutant cells. Mechanisms of killing were an induction of apoptosis and cell cycle arrest, through inhibition of tyrosine phosphorylation, and activated STAT5 and STAT3. Simvastatin suppressed the growth of K562-transplanted tumors, and cotreatment with imatinib was more effective in reducing tumor size. Simvastatin also killed primary CD34 cells from patients with CML more efficiently, compared with CD34 CML cells. Our study shows a synergic effect of imatinib and simvastatin both in imatinib-sensitive and imatinib-resistant cells, but more effective synergism in resistant cells. On the basis of these findings, we suggest that a combination of simvastatin and imatinib may be a potential candidate for the treatment of imatinib-resistant CML.

All tyrosine kinase inhibitor-resistant chronic myelogenous cells are highly sensitive to Ponatinib

The advent of tyrosine kinase inhibitor (TKI) therapy has considerably improved the survival of patients suffering chronic myelogenous leukemia (CML). Indeed, inhibition of BCR-ABL by imatinib, dasatinib or nilotinib triggers durable responses in most patients suffering from this disease. Moreover, resistance to imatinib due to kinase domain mutations can be generally circumvented using dasatinib or nilotinib, but the multi-resistant T315I mutation that is insensitive to these TKIs, remains to date a major clinical problem. In this line, ponatinib (AP24534) has emerged as a promising therapeutic option in patients with all kinds of BCR-ABL mutations, especially the T315I one. However and surprisingly, the effect of ponatinib has not been extensively studied on imatinib-resistant CML cell lines. Therefore, in the present study, we used several CML cell lines with different mechanisms of resistance to TKI to evaluate the effect of ponatinib on cell viability, apoptosis and signaling. Our results show that ponatinib is highly effective on both sensitive and resistant CML cell lines, whatever the mode of resistance and also on BaF3 murine B cells carrying native BCR-ABL or T315I mutation. We conclude that ponatinib could be effectively used for all types of TKI-resistant patients.

Indirubin derivatives induce apoptosis of chronic myelogenous leukemia cells involving inhibition of Stat5 signaling

Indirubin is the major active anti-tumor component of a traditional Chinese herbal medicine used for treatment of chronic myelogenous leukemia (CML). While previous studies indicate that indirubin is a promising therapeutic agent for CML, the molecular mechanism of action of indirubin is not fully understood. We report here that indirubin derivatives (IRDs) potently inhibit Signal Transducer and Activator of Transcription 5 (Stat5) protein in CML cells. Compound E804, which is the most potent in this series of IRDs, blocked Stat5 signaling in human K562 CML cells, imatinib-resistant human KCL-22 CML cells expressing the T315I mutant Bcr-Abl (KCL-22M), and CD34-positive primary CML cells from patients. Autophosphorylation of Src family kinases (SFKs) was strongly inhibited in K562 and KCL-22M cells at 5 μM E804, and in primary CML cells at 10 μM E804, although higher concentrations partially inhibited autophosphorylation of Bcr-Abl. Previous studies indicate that SFKs cooperate with Bcr-Abl to activate downstream Stat5 signaling. Activation of Stat5 was strongly blocked by E804 in CML cells. E804 down-regulated expression of Stat5 target proteins Bcl-xL and Mcl-1, associated with induction of apoptosis. In sum, our findings identify IRDs as potent inhibitors of the SFK/Stat5 signaling pathway downstream of Bcr-Abl, leading to apoptosis of K562, KCL-22M and primary CML cells. IRDs represent a promising structural class for development of new therapeutics for wild type or T315I mutant Bcr-Abl-positive CML patients.

Overexpression of P-glycoprotein induces acquired resistance to imatinib in chronic myelogenous leukemia cells

Imatinib, a breakpoint cluster region (BCR)-Abelson murine leukemia (ABL) tyrosine kinase inhibitor (TKI), has revolutionized the treatment of chronic myelogenous leukemia (CML). However, development of multidrug resistance (MDR) limits the use of imatinib. In the present study, we aimed to investigate the mechanisms of cellular resistance to imatinib in CML. Therefore, we established an imatinib-resistant human CML cell line (K562-imatinib) through a stepwise selection process. While characterizing the phenotype of these cells, we found that K562-imatinib cells were 124.6-fold more resistant to imatinib than parental K562 cells. In addition, these cells were cross-resistant to second- and third-generation BCR-ABL TKIs. Western blot analysis and reverse transcription-polymerase chain reaction(RT-PCR) demonstrated that P-glycoprotein (P-gp) and MDR1 mRNA levels were increased in K562-imatinib cells. In addition, accumulation of [14C]6-mercaptopurine (6-MP) was decreased, whereas the ATP-dependent efflux of [14C] 6-MP and [3H]methotrexate transport were increased in K562-imatinib cells. These data suggest that the overexpression of P-gp may play a crucial role in acquired resistance to imatinib in CML K562-imatinib cells.

Lyn Kinase-Dependent Regulation of miR181 and Myeloid Cell Leukemia-1 Expression: Implications for Drug Resistance in Myelogenous Leukemia

Imatinib, a BCR-Abl inhibitor, is a successful front-line treatment for chronic myelogenous leukemia (CML). Despite the success of imatinib, multiple mechanisms of resistance remain a problem, including overexpression of Lyn kinase (Lyn) and Bcl-2 family antiapoptotic proteins. Profiling micro-RNA (miRNA) expression in a model of Lyn-mediated imatinib-resistant CML (MYL-R) identified approximately 30 miRNAs whose expression differed >2-fold compared with drug-sensitive MYL cells. In particular, the expression of the miR181 family (a-d) was significantly reduced (∼11- to 25-fold) in MYL-R cells. Incubation of MYL-R cells with a Lyn inhibitor (dasatinib) or nucleofection with Lyn-targeting short interfering RNA increased miR181b and miR181d expression. A similar Lyn-dependent regulation of miR181b and miR181d was observed in imatinib-resistant K562 CML cells. Sequence analysis of potential targets for miR181 regulation predicted myeloid cell leukemia-1 (Mcl-1), a Bcl-2 family member whose expression is increased in MYL-R cells and drug-resistant leukemias. Inhibition of Lyn or rescue of miR181b expression reduced Mcl-1 expression in the MYL-R cells. To further investigate the mechanism of Mcl-1 repression by miR181, a luciferase reporter construct incorporating the Mcl-1 3'-untranslated region was tested. Overexpression of miR181b reduced luciferase activity, whereas these effects were ablated by the mutation of the seed region of the miR181 target site. Finally, stimulation of Lyn expression by 1,25-dihydroxyvitamin D(3) treatment in HL-60 cells, a cell model of acute myelogenous leukemia, decreased miR181b expression and increased Mcl-1 expression. In summary, our results suggest that Lyn-dependent regulation of miR181 is a novel mechanism of regulating Mcl-1 expression and cell survival.