BCR-ABL In Chronic Myeloid Leukemia Research Articles

Abstract 1829: Brusatol overcomes tyrosine kinase inhibitors resistance in myeloid leukemia cells by inhibiting translation of fast turnover protein cyclin D1 and Mcl-1

Abstract Myeloid leukemia is characterized with fast proliferation and apoptosis evasion, which are controlled by mutant or activated tyrosine kinase signalings. Tyrosine kinase inhibitors (TKI) targeting BCR-ABL in chronic myeloid leukemia (CML) and FLT3-ITD in acute myeloid leukemia (AML) significantly improved the therapy, but not cure, due to the general resistance. Overactivated mTOR protein translation pathway is believed to be one of the mechanisms causing resistance and that targeting protein translation should be one effective approach to overcome resistance. Brusatol is a quassinoid extracted from the fruit of Brucea javanica and an inhibitor of protein translation. We tested its antiproliferation and apoptosis induction in a variety of AML and CML cell lines as well as in TKI resistant cell lines. Brusatol effectively inhibits the growth of seven leukemia cell lines with GI50 values less than 20 nM. Brusatol induces apoptosis in AML cell lines and induces G0/G1 phase arrest in CML cell lines. Brusatol decreases the levels of fast turnover protein cyclin D1 and Mcl-1. In FLT3-ITD inhibitor sorafenib resistant MOLM-13/Sor cell line brusatol exhibits similar growth inhibition and apoptosis induction with the parental MOLM-13 cells, associated with inhibition of Mcl-1 and FLT3-ITD proteins. In BCR-ABL inhibitor imatinib resistant K562/STI cell line brusatol is effective as in parental K562 cells, associated with inhibition of cyclin D1 and BCR-ABL proteins. Brusatol at 2 mg/kg effectively inhibit tumor growth of K562 xenografts without causing toxicity to normal organs. These data indicate that brusatol inhibits oncogenic protein translation and has potential to be used to treat TKI resistant leukemia. Citation Format: Huiming Hua, Ying Yang, Guangfuxin Lin, Jingyi Zhang, Samuel Waxman, Yongkui Jing. Brusatol overcomes tyrosine kinase inhibitors resistance in myeloid leukemia cells by inhibiting translation of fast turnover protein cyclin D1 and Mcl-1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1829.

Abstract 1602: Co-targeting mitochondria and nucleotide metabolism in T315I-BCR-ABL myeloid leukemia for therapy

Abstract T315I mutation of Bcr-Abl in chronic myeloid leukemia (CML) leads to therapeutic resistance. It is known that Bcr-Abl transformation causes ROS-induced DNA damage, which can be exploited for anti-nucleotide treatment. We developed a small compound, JMF4073, which inhibits pyrimidylate kinases. Intriguingly, treatment of JMF4073 selectively eliminated WT-, but not T315I-, Bcr-Abl-transformed cells. We found that the higher level of cellular glutathione(GSH) in T315I-Bcr-Abl cells confers replication fork progression and sustains dTTP pool, leading to JMF4073 insusceptibility. Blocking mitochondrial pyruvate carrier (MPC) by UK-5099 reduced GSH and induced DNA replication stress in T315I-Bcr-Abl cells, thus increasing JMF4073 sensitivity in vitro and in vivo. We also observed the increases in glutamine flux to GSH production in T315I-Bcr-Abl cells, and reductive carboxylation of glutamate metabolism, together with mitochondrial dysfunction. The proteomic assay revealed the deficiencies in respiration complex I, II, and IV proteins in T315I-Bcr-Abl cells. Most interestingly, calcineurin inhibition remarkably elevated mitochondrial oxidative stress to cause cytotoxicity specifically in T315I-Bcr-Abl cells. Our results demonstrate the metabolic shift by T315I mutation of Bcr-Abl CML and provide the therapeutic options by co-targeting mitochondria and pyrimidylate kinases. Citation Format: Chang-Yu Huang, Yin-Hsuan Chung, Sheng-Yang Wu, Hsin-Yang Wang, Chih-Yu Lin, Tsung-Jung Yang, Jim-Ming Fang, Yu-Ju Chen, Chun-Mei Hu, Zee-Fen Chang. Co-targeting mitochondria and nucleotide metabolism in T315I-BCR-ABL myeloid leukemia for therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1602.

Pharmacotherapeutic Options for Philadelphia Chromosome-Positive CML

Chronic myeloid leukemia (CML) is a myeloproliferative disorder of hematopoietic stem cells. Identifying the leading mutation in BCR-ABL that causes CML made it possible to develop a targeted approach against this vastly disseminating disease. The active tyrosine kinase protein of BCR-ABL was effectively blocked with an identified tyrosine kinase inhibitor (TKI), imatinib. Imatinib became the first targeted therapy licensed for patients with chronic-phase CML and its introduction was associated with substantial improvements in response and survival compared with previous therapies. However, drug resistance towards imatinib therapy soon emerged and hence limited the complete eradication of CML in patients receiving imatinib. This is primarily due to the mutations within the ABL kinase domain, and to a lesser degree, due to residual disease after treatment. Nilotinib and dasatinib were soon introduced and showed improved clinical outcomes in patients intolerant and resistant to imatinib treatment. However, the T315I mutant overcame these agents along with imatinib, rendering the treatment ineffective. Exploring the kinase domain of the BCR-ABL protein and identifying key components involved in the signal transduction pathways is crucial towards understanding the disease and developing better strategic approaches towards combating it. In this review, we broadly discuss the current treatment options available against Philadelphia chromosome (Ph) positive BCR-ABL CML.

S100A8 may govern hyper-inflammation in severe COVID-19.

The coronavirus disease 2019 (COVID‐19) pandemic threatens human species with mortality rate of roughly 2%. We can hardly predict the time of herd immunity against and end of COVID‐19 with or without success of vaccine. One way to overcome the situation is to define what delineates disease severity and serves as a molecular target. The most successful analogy is found in BCR‐ABL in chronic myeloid leukemia, which is the golden biomarker, and simultaneously, the most effective molecular target. We hypothesize that S100 calcium‐binding protein A8 (S100A8) is one such molecule. The underlying evidence includes accumulating clinical information that S100A8 is upregulated in severe forms of COVID‐19, pathological similarities of the affected lungs between COVID‐19 and S100A8‐induced acute respiratory distress syndrome (ARDS) model, homeostatic inflammation theory in which S100A8 is an endogenous ligand for endotoxin sensor Toll‐like receptor 4/Myeloid differentiation protein‐2 (TLR4/MD‐2) and mediates hyper‐inflammation even after elimination of endotoxin‐producing extrinsic pathogens, analogous findings between COVID‐19‐associated ARDS and pre‐metastatic lungs such as S100A8 upregulation, pulmonary recruitment of myeloid cells, increased vascular permeability, and activation coagulation cascade. A successful treatment in an animal COVID‐19 model is given with a reagent capable of abrogating interaction between S100A8/S100A9 and TLR4. In this paper, we try to verify our hypothesis that S100A8 governs COVID‐19‐associated ARDS.

Inhibitors Targeting STAT5 Signaling in Myeloid Leukemias: New Tetrahydroquinoline Derivatives with Improved Antileukemic Potential.

Signal transducers and activators of transcription 5A and 5B (STAT5A and STAT5B) are two closely related STAT family members that are crucial downstream effectors of tyrosine kinase oncoproteins such as FLT3-ITD in acute myeloid leukemia (AML) and BCR-ABL in chronic myeloid leukemia (CML). We recently developed and reported the synthesis of a first molecule called 17 f that selectively inhibits STAT5 signaling in myeloid leukemia cells and overcomes their resistance to chemotherapeutic agents. To improve the antileukemic effect of 17 f, we synthesized ten analogs of this molecule and analyzed their impact on cell growth, survival, chemoresistance and STAT5 signaling. Two compounds, 7 a and 7 a', were identified as having similar or higher antileukemic effects in various AML and CML cell lines. Both molecules were found to be more effective than 17 f at inhibiting STAT5 activity/expression and suppressing the chemoresistance of CML.

Abstract 1278: Elucidating the mechanistic role of ERG in prostate cancer

Abstract Introduction: The transcription factor ERG is important for the development of angiogenesis, blood vessel integrity, and maintenance of hematopoietic stem cells. However, aberrant overexpression of ERG has been shown to be associated with various cancers. For example, ERG is recurrently involved in a translocation with TMPRSS2, which shifts it under AR regulation, and is thus subjected to overexpression in about 50% of prostate cancers in Caucasian males. While the clinical prognostic value of the TMPRSS2:ERG fusion is still debated, mechanistic studies of ERG-positive prostate cancers have demonstrated that ERG promotes cell invasion and metastasis. However, the molecular and cellular mechanisms of oncogenic ERG function in prostate cancer remain largely unclear. Methods/Results: To more comprehensively study the molecular and phenotypic roles of the TMPRSS2:ERG fusion product in prostate cancer, we developed an inducible ERG overexpression model in multiple cell lines as well as a CRISPR-Cas9-mediated TMPRSS2:ERG fusion translocation model. Using these models, we first performed RNA-seq and observed that ERG overexpression induced a global transcriptional program that increased the expression of genes related to epithelial-mesenchymal transition and decreased the expression of genes related to cell-cycle promotion. Further, using Boyden Chamber Assays as well as IncuCyte, we showed that overexpression of ERG promoted cell invasion but suppressed cell proliferation. We then used flow cytometric analysis to show that cells overexpressing ERG undergo a prolonged S phase. Interestingly, ERG antagonization through peptidomimetic inhibition partially rescued the proliferation rates of these ERG-overexpressing cells. Finally, using genome-wide CRISPR/Cas9 screening and NGS of the integrated sgRNA expression cassettes in the inducible ERG model, we identified panels of genes mediating ERG functions. Discussion: Unlike oncogenic kinases such as BCR-ABL in Chronic Myeloid Leukemia, transcription factors such as ERG have been more challenging to directly target in cancer. Thus, elucidation of the mechanisms of ERG-mediated transcriptional reprogramming, ERG binding partners, as well as the regulation of ERG, may result in the development of new strategies to target ERG by selectively antagonizing ERG oncogenic functions. Using our models, we are able to gain a better understanding of the role of ERG in cancer development and progression and thus provide insight for the development of new strategies for the prevention, detection, and treatment of prostate cancer. Citation Format: Caleb Cheng, Lanbo Xiao, Jean Tien, Cynthia Wang, Jesse Cheng, Eileen Shiau, Xiaoju Wang, Arul M. Chinnaiyan. Elucidating the mechanistic role of ERG in prostate cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1278.

Therapeutic inhibition of Fc\u03b3RIIb signaling targets leukemic stem cells in chronic myeloid leukemia

Despite the successes achieved with molecular targeted inhibition of the oncogenic driver Bcr-Abl in chronic myeloid leukemia (CML), the majority of patients still require lifelong tyrosine kinase inhibitor (TKI) therapy. This is primarily caused by resisting leukemic stem cells (LSCs), which prevent achievement of treatment-free remission in all patients. Here we describe the ITIM (immunoreceptor tyrosine-based inhibition motif)-containing Fc gamma receptor IIb (FcγRIIb, CD32b) for being critical in LSC resistance and show that targeting FcγRIIb downstream signaling, by using a Food and Drug Administration-approved BTK inhibitor, provides a successful therapeutic approach. First, we identified FcγRIIb upregulation in primary CML stem cells. FcγRIIb depletion caused reduced serial re-plaiting efficiency and cell proliferation in malignant cells. FcγRIIb targeting in both a transgenic and retroviral CML mouse model provided in vivo evidence for successful LSC reduction. Subsequently, we identified BTK as a main downstream mediator and targeting the Bcr-Abl-FcγRIIb-BTK axis in primary CML CD34+ cells using ibrutinib, in combination with standard TKI therapy, significantly increased apoptosis in quiescent CML stem cells thereby contributing to the eradication of LSCs.. As a potential curative therapeutic approach, we therefore suggest combining Bcr-Abl TKI therapy along with BTK inhibition.

Therapeutic Challenges in Chronic Myeloid Leukemia: A Case-Based Discussion

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by a reciprocal translocation between the long arms of chromosomes 9 and 22 that results in expression of the oncoprotein BCR-ABL1. An optimal response to tyrosine kinase inhibitors (TKIs) requires a BCR-ABL transcript level ≤ 10% at 3 months, ≤ 1% at 6 months, ≤ 0.1% at 1 year, and ≤ 0.01% onwards. Complex scenarios like P190 BCR-ABL CML, unusual BCR-ABL transcripts, primary refractory CML, and detection of TKI-resistance mutations during treatment frequently pose a therapeutic challenge. In this article we present some of these clinical scenarios using a case-based approach. J Med Cases. 2020;11(7):215-220 doi: https://doi.org/10.14740/jmc3510

Therapeutic Challenges in Chronic Myeloid Leukemia: A Case-Based Discussion

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by a reciprocal translocation between the long arms of chromosomes 9 and 22 that results in expression of the oncoprotein BCR-ABL1. An optimal response to tyrosine kinase inhibitors (TKIs) requires a BCR-ABL transcript level ≤ 10% at 3 months, ≤ 1% at 6 months, ≤ 0.1% at 1 year, and ≤ 0.01% onwards. Complex scenarios like P190BCR-ABL CML, unusual BCR-ABL transcripts, primary refractory CML, and detection of TKI-resistance mutations during treatment frequently pose a therapeutic challenge. In this article we present some of these clinical scenarios using a case-based approach.

A Novel Inhibitor of STAT5 Signaling Overcomes Chemotherapy Resistance in Myeloid Leukemia Cells.

Signal transducers and activators of transcription 5A and 5B (STAT5A and STAT5B) are crucial downstream effectors of tyrosine kinase oncogenes (TKO) such as BCR-ABL in chronic myeloid leukemia (CML) and FLT3-ITD in acute myeloid leukemia (AML). Both proteins have been shown to promote the resistance of CML cells to tyrosine kinase inhibitors (TKI) such as imatinib mesylate (IM). We recently synthesized and discovered a new inhibitor (17f) with promising antileukemic activity. 17f selectively inhibits STAT5 signaling in CML and AML cells by interfering with the phosphorylation and transcriptional activity of these proteins. In this study, the effects of 17f were evaluated on CML and AML cell lines that respectively acquired resistance to IM and cytarabine (Ara-C), a conventional therapeutic agent used in AML treatment. We showed that 17f strongly inhibits the growth and survival of resistant CML and AML cells when associated with IM or Ara-C. We also obtained evidence that 17f inhibits STAT5B but not STAT5A protein expression in resistant CML and AML cells. Furthermore, we demonstrated that 17f also targets oncogenic STAT5B N642H mutant in transformed hematopoietic cells.

USP10 modulates the SKP2/Bcr-Abl axis via stabilizing SKP2 in chronic myeloid leukemia

Constitutive activation of tyrosine kinase Bcr-Abl is the leading cause of the development and progression of chronic myeloid leukemia (CML). Currently, the application of tyrosine kinase inhibitors (TKIs) targeting the Bcr-Abl is the primary therapy for CML patients. However, acquired resistance to TKIs that develops overtime in the long-term administration renders TKIs ineffective to patients with advanced CML. Therefore, increasing studies focus on the amplified expression or activation of Bcr-Abl which is proposed to contribute to the advanced phase. Here, we show that S-phase kinase-associated protein 2 (SKP2) acts as a co-regulator of Bcr-Abl by mediating its K63-linked ubiquitination and activation. Further investigations show that USP10 as a novel deubiquitinase of SKP2 amplifies the activation of Bcr-Abl via mediating deubiquitination and stabilization of SKP2 in CML cells. Moreover, inhibition of USP10 significantly suppresses the proliferation of both imatinib-sensitive and imatinib-resistant CML cells, which likely depends on SKP2 status. This findings are confirmed in primary CML cells because these cells are over-expressed with USP10 and SKP2 and are sensitive to a USP10 inhibitor. Taken together, the present study not only provides a novel insight into the amplified activation of Bcr-Abl in CML, but also demonstrates that targeting the USP10/SKP2/Bcr-Abl axis is a potential strategy to overcome imatinib resistance in CML patients.

Antitumor efficacy of arsenic/interferon in preclinical models of chronic myeloid leukemia resistant to tyrosine kinase inhibitors.

Tyrosine kinase inhibitors (TKIs) are the standard treatment for chronic myeloid leukemia (CML). Despite their clinical success, TKIs are faced with challenges such as treatment resistance, which may be driven by kinase domain mutations, and frequent disease relapse upon the cessation of treatment. The combination of arsenic trioxide (ATO) and interferon-α (IFN) was previously demonstrated to inhibit proliferation and induce apoptosis in CML cell lines, prolong the survival of primary wild-type CML mice, and dramatically decrease the activity of leukemia-initiating cells (LICs). The ATO/IFN combination was tested in vitro on imatinib (IMN)-resistant K562-R and Ar230-R cells. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays were used to evaluate proliferation and apoptosis, respectively. The acridine orange assay was used to assess autophagy, and quantitative reverse transcription-polymerase chain reaction was used to assess the involvement of the hedgehog (Hh) pathway. In vivo, a retroviral transduction/transplantation T315I BCR-ABL CML mouse model was used to assay the effect of the treatment on survival, tumor burden (histopathology and blood counts), and LIC activity (secondary transplantation). In vitro, ATO/IFN synergized to inhibit proliferation and induce apoptosis of IMN-resistant cells with variant modes of resistance. Furthermore, the preclinical effects of ATO/IFN were associated with induction of autophagy along with inhibition of the Hh pathway. Most remarkably, ATO/IFN significantly prolonged the survival of primary T315I-CML mice and displayed a dramatic impairment of disease engraftment in secondary mice, which reflected decreased LIC activity. Collectively, the ATO/IFN strategy has been demonstrated to have the potential to lead to durable remissions in TKI-resistant CML preclinical models and to overcome various TKI-specific mechanisms of resistance.

Experimental and integrative analyses identify an ETS1 network downstream of BCR-ABL in chronic myeloid leukemia (CML)

The BCR-ABL oncogene, the hallmark of chronic myeloid leukemia (CML), has been shown to activate several signaling pathways in leukemic cells. The natural history of this disease has been radically modified by tyrosine kinase inhibitors (TKIs). However, resistance to several lines of TKI therapies and progression to blast crisis (BC) remain significant concerns. To identify novel signaling pathways induced by BCR-ABL, we performed a transcriptome analysis in a BCR-ABL-expressing UT-7 cell line. More than 2000 genes differentially expressed between BCR-ABL-expressing and parental UT-7 cells were identified and ETS1 was found to be the most upregulated. ETS1 protein expression was also shown to be highly increased in UT-7 cells expressing BCR-ABL either constitutively or under the control of TET-inducible promoters. ETS1 expression is tyrosine-kinase dependent because it was reduced by TKIs. A significant increase of ETS1 messenger RNA (mRNA) expression was observed in blood cells from CML patients at diagnosis compared with healthy controls. Integration of publicly available chromatin immunoprecipitation sequencing and transcriptomic data with our results allowed us to identify potential ETS1 targets, some of which are involved in the progression of CML. The messenger RNA expression of two of these genes (DNM3 and LIMS1) was found to be associated with the absence of major cytogenetic response after 1 year of imatinib therapy. The present work demonstrates for the first time the involvement of the ETS1 transcriptional program in the experimental UT-7 model and a large cohort of CML patients.

Ponatinib exerts anti-angiogenic effects in the zebrafish and human umbilical vein endothelial cells via blocking VEGFR signaling pathway.

Angiogenesis is a hallmark for cancer development because it is essential for cancer growth and provides the route for cancer cell migration (metastasis). Understanding the mechanism of angiogenesis and developing drugs that target the process has therefore been a major focus for research on cancer therapy. In this study, we screened 114 FDA-approved anti-cancer drugs for their effects on angiogenesis in the zebrafish. Among those with positive effects, we chose to focus on Ponatinib (AP24534; Iclusig®) for further investigation. Ponatinib is an inhibitor of the tyrosine kinase BCR-ABL in chronic myeloid leukemia (CML), and its clinical trial has been approved by FDA for the treatment of the disease. In recent clinical trials, however, some side effects have been reported for Ponatinib, mostly on blood vessel disorders, raising the possibility that this drug may influence angiogenesis. In this study, we demonstrated that Ponatinib was able to suppress the formation of intersegmental vessels (ISV) and subintestinal vessels (SIV) in the zebrafish larvae. The anti-angiogenic effect of Ponatinib was further validated by other bioassays in human umbilical vein endothelial cells (HUVECs), including cell proliferation and migration, tube formation, and wound healing. Further experiments showed that Ponatinib inhibited VEGF-induced VEGFR2 phosphorylation and its downstream signaling pathways including Akt/eNOS/NO pathway and MAPK pathways (ERK and p38MAPK). Taken together, these results suggest that inhibition of VEGF signaling at its receptor level and downstream pathways may likely be responsible for the antiangiogenic activity of Ponatinib.

BCR-ABL Tyrosine Kinase Inhibitors: Which Mechanism(s) May Explain the Risk of Thrombosis?

Imatinib, the first-in-class BCR-ABL tyrosine kinase inhibitor (TKI), had been a revolution for the treatment of chronic myeloid leukemia (CML) and had greatly enhanced patient survival. Second- (dasatinib, nilotinib, and bosutinib) and third-generation (ponatinib) TKIs have been developed to be effective against BCR-ABL mutations making imatinib less effective. However, these treatments have been associated with arterial occlusive events. This review gathers clinical data and experiments about the pathophysiology of these arterial occlusive events with BCR-ABL TKIs. Imatinib is associated with very low rates of thrombosis, suggesting a potentially protecting cardiovascular effect of this treatment in patients with BCR-ABL CML. This protective effect might be mediated by decreased platelet secretion and activation, decreased leukocyte recruitment, and anti-inflammatory or antifibrotic effects. Clinical data have guided mechanistic studies toward alteration of platelet functions and atherosclerosis development, which might be secondary to metabolism impairment. Dasatinib, nilotinib, and ponatinib affect endothelial cells and might induce atherogenesis through increased vascular permeability. Nilotinib also impairs platelet functions and induces hyperglycemia and dyslipidemia that might contribute to atherosclerosis development. Description of the pathophysiology of arterial thrombotic events is necessary to implement risk minimization strategies.

Hypomethylation-mediated H19 overexpression increases the risk of disease evolution through the association with BCR-ABL transcript in chronic myeloid leukemia.

Previous study has revealed that H19 expression is required for efficient tumor growth induced by BCR-ABL in chronic myeloid leukemia (CML). Herein, we further determined H19 expression and its clinical implication in patients with CML. H19 expression and methylation were detected by real-time quantitative PCR and real-time quantitative methylation-specific PCR, and then clinical implication of H19 expression was further analyzed. H19 expression was significantly up-regulated in CML patients (p < 0.001). H19 expression with an area under receiver operating characteristic curve value of 0.824 might serve as a promising biomarker in distinguishing CML patients from controls. The patients with high H19 expression had a tendency of higher white blood cells and BCR-ABL transcript than those with low H19 expression. H19 overexpression occurred with the higher frequency in blast crisis stage (11/11, 100%), lower in accelerated phase (3/5, 60%), and chronic phase (42/62, 66%) stages. Moreover, paired patients during disease progression with increased BCR-ABL transcript also showed a significant upregulation of H19 expression. Meanwhile, H19 expression was decreased in follow-up patients who achieved complete molecular remission after tyrosine kinase inhibitors-based therapy. Epigenetic studies showed that H19 differentially methylated region/imprinting control region (DMR/ICR) was hypomethylated and associated with H19 expression in CML patients. Moreover, demethylation of H19 DMR/ICR reactivated H19 expression in K562 cells. Collectively, H19 overexpression, a frequent event in CML, was associated with higher BCR-ABL transcript involving in disease progression. Moreover, H19 DMR/ICR hypomethylation in CML may be one of the mechanisms mediating H19 overexpression.

SHC004-221A1, a novel tyrosine kinase, potently inhibits T315I mutant BCR-ABL in chronic myeloid leukemia

Although judicious use of tyrosine kinase inhibitors that target BCR-ABL constitutes an effective strategy for the control of chronic myeloid leukemia (CML), drug resistance is observed due to kinase domain mutations, among which a major one is BCR-ABLT315I. In this study, we identified SHC004-221A1 as a potent inhibitor of T315I and other BCR-ABL mutants. Biochemical assays demonstrated that SHC004-221A1 has an inhibitory effect on all selected BCR-ABL mutants. In vitro studies showed that SHC004-221A1 inhibited the proliferation of tumor cell lines carrying native and T315I mutant BCR-ABL. Signaling pathway analysis revealed that SHC004-221A1 inhibited the phosphorylation of STAT5 and CrkL, which contributed to the apoptosis of CML cells. In vivo studies indicated that SHC004-221A1 suppressed BCR-ALBT315I-driven tumor growth in mice. Taken together, the results of this study suggested that SHC004-221A1 may be a promising BCR-ABLT315I inhibitor for the treatment of CML.

Comprehensive Analysis of the Structural, Biochemical and Signaling Differences of the p210 and p185 Isoforms of Bcr-Abl in CML and B-ALL

Distinct chromosomal translocation breakpoints result in the expression of two major isoforms of Bcr-Abl - p210 and p185 - from the Philadelphia (Ph)-chromosome. While p210 is the molecular hallmark of Chronic Myeloid Leukemia (CML), in Ph-positive B-cell Acute Lymphoblastic Leukemia (B-ALL), ~1/3 of the patients express p210 and ~2/3 express p185. In mouse models, under certain experimental conditions, expression of p185 causes disease with a shorter latency and more B-ALL than CML-like leukemias as did p210. Ph-positive B-ALL patients show a poorer response and frequent resistance to tyrosine kinase inhibitor (TKI) therapy as compared to CML patients. Specific intrinsic differences in p185 and p210 Bcr-Abl signaling have long been hypothesized, but have never been studied in a comparative, unbiased and comprehensive manner. We have now:(i) Mapped the differences in the p210 and p185 protein interaction network: We performed an unbiased proteomics analysis of the composition of the endogenous p210 and p185 protein complexes in murine cell lines using SILAC (stable isotope labeling with amino acids in cell culture) quantification. The interactome analysis confirmed previously reported p210 interactors in human CML cells and identified unexpectedly many interactors that preferentially associate with either p185 or p210, including an endocytosis-regulating complex (enriched in p185) and a phosphatase complex (enriched in p210). Several differential interactors were validated in a panel of nine human CML and B-ALL cell lines.(ii) Performed a comprehensive phospho-proteomics study in p210 and p185 cell lines: Using phospho-tyrosine, as well as general phospho-peptide enrichment strategies coupled to SILAC quantification, we mapped >800 phosphorylation sites and identified differentially activated signaling by p210 and p185, including differential activation of the STAT5 and STAT3 transcription factors, SRC kinases and ERK1/2 signaling. These findings were validated in a panel of nine human CML and B-ALL cell lines.(iii) Determined the atomic structures of the Dbl-homology (DH) and pleckstrin homology (PH) domains of p210: The DH-PH domain unit of p210 is the only structural difference to p185 and has remained the only structurally uncharacterized region of Bcr-Abl. We solved different structures of these domains by NMR spectroscopy, X-ray crystallography, as well as Small-Angle X-ray scattering, alone and in complex with an engineered monobody inhibitor targeting the DH domain. While the DH-PH structural motif is found in Rho guanine nucleotide exchange factors (Rho GEF), our results have not provided evidence that the p210 DH-PH domain acts as a Rho GEF or binds Rho GTPases, in contrast to previous reports. On the other hand, we found the PH domain to be important for specific membrane binding of p210 and we determined the binding specificity of the PH domain to certain phospho-inositide lipids.Our results provide the first systematic insight showing critical differences in protein-protein interactions, signaling and structure of p210 and p185 Bcr-Abl. This will contribute to a better understanding of Bcr-Abl dependent signaling, mechanisms of oncogenic transformation, resulting disease pathobiology and responses to TKIs. DisclosuresHantschel:Ariad Pharmaceuticals: Honoraria.

Cantharidin Overcomes Imatinib Resistance by Depleting BCR-ABL in Chronic Myeloid Leukemia.

Cantharidin (CTD) is an active compound isolated from the traditional Chinese medicine blister beetle and displayed anticancer properties against various types of cancer cells. However, little is known about its effect on human chronic myeloid leukemia (CML) cells, including imatinib-resistant CML cells. The objective of this study was to investigate whether CTD could overcome imatinib resistance in imatinib-resistant CML cells and to explore the possible underlying mechanisms associated with the effect. Our results showed that CTD strongly inhibited the growth of both imatinib-sensitive and imatinib-resistant CML cells. CTD induced cell cycle arrest at mitotic phase and triggered DNA damage in CML cells. The ATM/ATR inhibitor CGK733 abrogated CTD-induced mitotic arrest but promoted the cytotoxic effects of CTD. In addition, we demonstrated that CTD downregulated the expression of the BCR-ABL protein and suppressed its downstream signal transduction. Real-time quantitative PCR revealed that CTD inhibited BCR-ABL at transcriptional level. Knockdown of BCR-ABL increased the cell-killing effects of CTD in K562 cells. These findings indicated that CTD overcomes imatinib resistance through depletion of BCR-ABL. Taken together, CTD is an important new candidate agent for CML therapy.

Oncogenic STAT5 signaling promotes oxidative stress in chronic myeloid leukemia cells by repressing antioxidant defenses.

STAT5 transcription factors are frequently activated in hematopoietic neoplasms and are targets of various tyrosine kinase oncogenes. Evidences for a crosstalk between STAT5 and reactive oxygen species (ROS) metabolism have recently emerged but mechanisms involved in STAT5-mediated regulation of ROS still remain elusive. We demonstrate that sustained activation of STAT5 induced by Bcr-Abl in chronic myeloid leukemia (CML) cells promotes ROS production by repressing expression of two antioxidant enzymes, catalase and glutaredoxin-1(Glrx1). Downregulation of catalase and Glrx1 expression was also observed in primary cells from CML patients. Catalase was shown not only to reduce ROS levels but also, to induce quiescence in Bcr-Abl-positive leukemia cells. Furthermore, reduction of STAT5 phosphorylation and upregulation of catalase and Glrx1 were also evidenced in leukemia cells co-cultured with bone marrow stromal cells to mimic a leukemic niche. This caused downregulation of ROS levels and enhancement of leukemic cell quiescence. These data support a role of persistent STAT5 signaling in the regulation of ROS production in myeloid leukemias and highlight the repression of antioxidant defenses as an important regulatory mechanism.