Molecular mechanisms for survival regulation of chronic myeloid leukemia stem cells

YBX1 regulates the survival of chronic myeloid leukemia stem cells by modulating m6A-mediated YWHAZ stability

PURPOSE

Chronic myeloid leukemia (CML) is a myeloproliferative disease derived from hematopoietic stem cells (HSCs) that harbor Philadelphia chromosome (Ph chromosome). In clinic, leukemia stem cells (LSCs) in CML are insensitive to the treatment with tyrosine kinase inhibitors, and are responsible for disease relapse. However, the molecular mechanisms for maintaining LSCs survival remain elusive.

METHODS

CML patient-derived cell lines and BCR-ABL-induced CML mouse model were used to explore the role of YBX1 in regulating the survival of CML LSCs. Bone marrow transduction and transplantation, and colony-forming unit assay were used to investigate LSC function. The underlying mechanism of how YBX1 regulates LSCs survival were assessed using flow cytometry, RNA sequencing, western blot, RNA decay assay, co-immunoprecipitation and RNA immunoprecipitation.

RESULTS

Here we show that RNA-binding protein YBX1 plays an important role in regulating survival of CML LSCs. We find that YBX1 expression is significantly increased in CML cells, and confirm that YBX1 is required for maintaining survival of LSCs. Deletion of YBX1 impairs the propagation of CML through blocking cell proliferation and inducing apoptosis of LSCs. Mechanistically, we find that YBX1 regulates expression of apoptotic associated genes. YBX1 cooperates with RNA m⁶A reader IGF2BPs to stabilize YWHAZ transcript in an m⁶A-dependent manner, and loss of YBX1 decreases YWHAZ expression by accelerating mRNA decay. Restoration of YWHAZ efficiently rescues the defects of YBX1-deficient CML cells.

CONCLUSION

Our findings reveal a critical role of YBX1 in maintaining survival of CML LSCs, which provides a rationale for targeting YBX1 in CML treatment.

MiR-125a-3p and MiR-320b Differentially Expressed in Patients with Chronic Myeloid Leukemia Treated with Allogeneic Hematopoietic Stem Cell Transplantation and Imatinib Mesylate

Chronic myeloid leukemia (CML), a hematopoietic neoplasm arising from the fusion of BCR (breakpoint cluster region) gene on chromosome 22 to the ABL (Abelson leukemia virus) gene on chromosome 9 (BCR-ABL1 oncogene), originates from a small population of leukemic stem cells with extensive capacity for self-renewal and an inflammatory microenvironment. Currently, CML treatment is based on tyrosine kinase inhibitors (TKIs). However, allogeneic hematopoietic stem cell transplantation (HSCT-allo) is currently the only effective treatment of CML. The difficulty of finding a compatible donor and high rates of morbidity and mortality limit transplantation treatment. Despite the safety and efficacy of TKIs, patients can develop resistance. Thus, microRNAs (miRNAs) play a prominent role as biomarkers and post-transcriptional regulators of gene expression. The aim of this study was to analyze the miRNA profile in CML patients who achieved cytogenetic remission after treatment with both HSCT-allo and TKI. Expression analyses of the 758 miRNAs were performed using reverse transcription quantitative polymerase chain reaction (RT-qPCR). Bioinformatics tools were used for data analysis. We detected miRNA profiles using their possible target genes and target pathways. MiR-125a-3p stood out among the downregulated miRNAs, showing an interaction network with 52 target genes. MiR-320b was the only upregulated miRNA, with an interaction network of 26 genes. The results are expected to aid future studies of miRNAs, residual leukemic cells, and prognosis in CML.

Sphingosine kinases are involved in the regulation of all-trans retinoic acid sensitivity of K562 chronic myeloid leukemia cells

The efficacy of all-trans retinoic acid (ATRA) for the treatment of chronic myeloid leukemia (CML) has been reported to be limited both as single-drug treatment or in combination with other drugs. Our previous study demonstrated that sphingosine 1-phosphate attenuated the effects of ATRA on human colon cancer cells by blocking the expression of retinoic acid receptor β. The aim of the present study was to investigate whether the ATRA-dependent proliferation inhibition of K562 cells was regulated by sphingosine kinases (SphKs). The results of cell proliferation assay and reverse transcription-PCR demonstrated that ATRA may exert synergistic effects with the SphK1 inhibitor SKI 5C or the pan-SphK inhibitor SKI II to inhibit the proliferation of K562 cells and upregulate the expression levels of the ATRA-inducible enzyme cytochrome P450 26A1 (CYP26A1). Knocking down the expression of SphK1 or SphK2 in K562 cells by small interfering RNA enhanced the inhibitory effects of ATRA and induced the expression of CYP26A1. Crude asterosaponins, which abrogated the expression of SphK2, also enhanced the effects of ATRA on K562 cells. In conclusion, the results of the present study demonstrated that SphKs may be involved in the regulation of the sensitivity of CML cells to ATRA.

Integrative Genomic Analysis Reveals Cancer-Associated Gene Mutations in Chronic Myeloid Leukemia Patients with Resistance or Intolerance to Tyrosine Kinase Inhibitor

Introduction

While the acquisition of mutations in the ABL1 kinase domain (KD) has been identified as a common mechanism behind tyrosine kinase inhibitor (TKI) resistance, recent genetic studies have revealed that patients with TKI resistance or intolerance frequently harbor one or more genetic alterations implicated in myeloid malignancies. This suggests that additional mutations other than ABL1 KD mutations might contribute to disease progression.

Methods

We performed targeted-capture sequencing of 127 known and putative cancer-related genes of 63 patients with CML using next-generation sequencing (NGS), including 42 patients with TKI resistance and 21 with TKI intolerance.

Results

The differences in the number of mutations between groups had no statistical significance. This could be explained in part by not all of the patients having achieved major molecular remission in the early period as expected. Overall, 66 mutations were identified in 96.8% of the patients, most frequently in the KTM2C (31.82%), ABL1 (31.82%), FAT1 (25.76%), and ASXL1 (22.73%) genes. CUX1, KIT, and GATA2 were associated with TKI intolerance, and two of them (CUX1, GATA2) are transcription factors in which mutations were identified in 82.61% of patients with TKI intolerance. ASXL1 mutations were found more frequently in patients with ABL1 KD mutations (38.1% vs 15.21%, P=0.041). Although the number of mutations was low, pairwise interaction between mutated genes showed that ABL1 KD mutations cooccurred with SH2B3 mutations (P<0.05). In Kaplan-Meier analyses, only TET2 mutations were associated with shorter progression-free survival (P=0.026).

Conclusion

Our data suggested that the CUX1, KIT, and GATA2 genes may play important roles in TKI intolerance. ASXL1 and TET2 mutations may be associated with poor patient prognosis. NGS helps improving the clinical risk stratification, which enables the identification of patients with TKI resistance or intolerance in the era of TKI therapy.

RBFOX3 Promotes Gastric Cancer Growth and Progression by Activating HTERT Signaling

Tumor invasion, metastasis, and recrudescence remain a considerable challenge in the treatment of gastric cancer (GC). Herein we first identified that RNA binding protein fox-1 homolog 3 (RBFOX3) was markedly overexpressed in GC tissues and negatively linked to the survival rate of GC patients. RBFOX3 promoted cell division and cell cycle progression in vitro and in vivo. Furthermore, RBFOX3 increased the cell invasion and migration ability. The suppression of GC cell multiplication and invasion, caused by silencing of RBFOX3, was rescued by HTERT overexpression. Additionally, RBFOX3 augmented the resistance of GC cells to 5-fluorouracil by repressing RBFOX3. Mechanistically, the exogenous up-regulation of RBFOX3 triggered promoter activity and HTERT expression, thereby enhancing the division and the development of GC cells. Further co-immunoprecipitation tests revealed that RBFOX3 bound to AP-2β to modulate HTERT expression. In conclusion, our study indicates that a high expression of RBFOX3 promotes GC progression and development and predicts worse prognosis. Collectively, these results indicate that the RBFOX3/AP-2β/HTERT signaling pathway can be therapeutically targeted to prevent and treat GC recurrence and metastasis.

Signaling pathways involved in chronic myeloid leukemia pathogenesis: The importance of targeting Musashi2-Numb signaling to eradicate leukemia stem cells

OBJECTIVES

Chronic myeloid leukemia (CML) is a myeloid clonal proliferation disease defining by the presence of the Philadelphia chromosome that shows the movement of BCR-ABL1. In this study, the critical role of the Musashi2-Numb axis in determining cell fate and relationship of the axis to important signaling pathways such as Hedgehog and Notch that are essential for self-renewal pathways in CML stem cells will be reviewed meticulously.

MATERIALS AND METHODS

In this review, a PubMed search using the keywords of Leukemia, signaling pathways, Musashi2-Numb was performed, and then we summarized different research works .

RESULTS

Although tyrosine kinase inhibitors such as Imatinib significantly kill and remove the cell with BCR-ABL1 translocation, they are unable to target BCR-ABL1 leukemia stem cells. The main problem is stem cells resistance to Imatinib therapy. Therefore, the identification and control of downstream molecules/ signaling route of the BCR-ABL1 that are involved in the survival and self-renewal of leukemia stem cells can be an effective treatment strategy to eliminate leukemia stem cells, which supposed to be cured by Musashi2-Numb signaling pathway.

CONCLUSION

The control of molecules /pathways downstream of the BCR-ABL1 and targeting Musashi2-Numb can be an effective therapeutic strategy for treatment of chronic leukemia stem cells. While Musashi2 is a poor prognostic marker in leukemia, in treatment and strategy, it has significant diagnostic value.

The human Smoothened inhibitor PF-04449913 induces exit from quiescence and loss of multipotent Drosophila hematopoietic progenitor cells

The efficient treatment of hematological malignancies as Acute Myeloid Leukemia, myelofibrosis and Chronic Myeloid Leukemia, requires the elimination of cancer-initiating cells and the prevention of disease relapse through targeting pathways that stimulate generation and maintenance of these cells. In mammals, inhibition of Smoothened, the key mediator of the Hedgehog signaling pathway, reduces Chronic Myeloid Leukemia progression and propagation. These findings make Smo a candidate target to inhibit maintenance of leukemia-initiating cells. In Drosophila melanogaster the same pathway maintains the hematopoietic precursor cells of the lymph gland, the hematopoietic organ that develops in the larva. Using Drosophila as an in vivo model, we investigated the mode of action of PF-04449913, a small-molecule inhibitor of the human Smo protein. Drosophila larvae fed with PF-04449913 showed traits of altered hematopoietic homeostasis. These include the development of melanotic nodules, increase of circulating hemocytes, the size increase of the lymph gland and accelerated differentiation of blood cells likely due to the exit of multi-potent precursors from quiescence. Importantly, the Smo inhibition can lead to the complete loss of hematopoietic precursors. We conclude that PF-04449913 inhibits Drosophila Smo blocking the Hh signaling pathway and causing the loss of hematopoietic precursor cells. Interestingly, this is the effect expected in patients treated with PF-04449913: number decrease of cancer initiating cells in the bone marrow to reduce the risk of leukemia relapse. Altogether our results indicate that Drosophila comprises a model system for the in vivo study of molecules that target evolutionary conserved pathways implicated in human hematological malignancies.

Mechanisms of Resistance to Targeted Therapies in Chronic Myeloid Leukemia

Patients with newly diagnosed chronic myeloid leukemia (CML) usually received as first-line treatment a first- or second-generation tyrosine kinase inhibitor (TKI). Although initial responses are high, therapy fails in up to 40% of patients and initial response is lost within 2 years in approximately 25% of patients. In the last few years, intensive efforts have been spent to explain treatment failure, and different mechanisms of resistance have been identified, ranging from BCR-ABL1 kinase domain mutations to lack of adherence to therapy. In this review, we briefly summarize the clinical efficacy of approved TKIs and describe the main mechanisms of TKI resistance.

Targeting chronic myeloid leukemia stem cells with the hypoxia-inducible factor inhibitor acriflavine

Chronic myeloid leukemia (CML) is a hematopoietic stem cell (HSC)-driven neoplasia characterized by expression of the constitutively active tyrosine kinase BCR/Abl. CML therapy based on tyrosine kinase inhibitors (TKIs) is highly effective in inducing remission but not in targeting leukemia stem cells (LSCs), which sustain minimal residual disease and are responsible for CML relapse following discontinuation of treatment. The identification of molecules capable of targeting LSCs appears therefore of primary importance to aim at CML eradication. LSCs home in bone marrow areas at low oxygen tension, where HSCs are physiologically hosted. This study addresses the effects of pharmacological inhibition of hypoxia-inducible factor-1 (HIF-1), a critical regulator of LSC survival, on the maintenance of CML stem cell potential. We found that the HIF-1 inhibitor acriflavine (ACF) decreased survival and growth of CML cells. These effects were paralleled by decreased expression of c-Myc and stemness-related genes. Using different in vitro stem cell assays, we showed that ACF, but not TKIs, targets the stem cell potential of CML cells, including primary cells explanted from 12 CML patients. Moreover, in a murine CML model, ACF decreased leukemia development and reduced LSC maintenance. Importantly, ACF exhibited significantly less-severe effects on non-CML hematopoietic cells in vitro and in vivo. Thus, we propose ACF, a US Food and Drug Administration (FDA)-approved drug for nononcological use in humans, as a novel therapeutic approach to prevent CML relapse and, in combination with TKIs, enhance induction of remission.

Immunological Analyses of Leukemia Stem Cells

Traditionally, the intracellular localization and expression levels of specific proteins in CML Leukemia stem cells (LSCs) have been evaluated by fluorescence immunohistochemistry (FIHC). More recently, Duolink(®) in situ PLA technology has opened up a new and more quantitative way to evaluate signal transduction, posttranslational modification, and protein-protein interaction at the single-stem-cell level. This novel methodology, which employs two antibody-based probes, has already increased our understanding of the biology of the rare CML LSC population. In the future, the use of this approach may contribute to the development of novel therapeutics aimed at eradicating CML LSCs in CML patients.

Salarin C inhibits the maintenance of chronic myeloid leukemia progenitor cells

We previously showed that incubation of chronic myeloid leukemia (CML) cells in very low oxygen selects a cell subset where the oncogenetic BCR/Abl protein is suppressed and which is thereby refractory to tyrosine kinase inhibitors used for CML therapy. In this study, salarin C, an anticancer macrolide extracted from the Fascaplysinopsis sponge, was tested as for its activity on CML cells, especially after their incubation in atmosphere at 0.1% oxygen. Salarin C induced mitotic cycle arrest, apoptosis and DNA damage. Salarin C also concentration-dependently inhibited the maintenance of stem cell potential in cultures in low oxygen of either CML cell lines or primary cells. Surprisingly, the drug also concentration-dependently enforced the maintenance of BCR/Abl signaling in low oxygen, an effect which was paralleled by the rescue of sensitivity of stem cell potential to IM. These results suggest a potential use of salarin C for the suppression of CML cells refractory to tyrosine kinase inhibitors.

Detecting Autophagy and Autophagy Flux in Chronic Myeloid Leukemia Cells Using a Cyto-ID Fluorescence Spectrophotometric Assay

Autophagy is a catabolic process whereby cellular components are degraded to fuel cells for longer survival during stress. Hence, autophagy plays a vital role in determining cell fate and is central for homeostasis and pathogenesis of many human diseases including chronic myeloid leukemia (CML). It has been well established that autophagy is important for the leukemogenesis as well as drug resistance in CML. Thus, autophagy is an intriguing therapeutic target. However, current approaches that detect autophagy lack reliability and often fail to provide quantitative measurements. To overcome this hurdle and facilitate the development of autophagy-related therapies, we have recently developed an autophagy assay termed as the Cyto-ID fluorescence spectrophotometric assay. This method uses a cationic fluorescence dye, Cyto-ID, which specifically labels autophagic compartments and is detected by a spectrophotometer to permit a large-scale and quantitative analysis. As such, it allows rapid, reliable, and quantitative detection of autophagy and estimation of autophagy flux. In this chapter, we further provide technical details of this method and step-by-step protocols for measuring autophagy or autophagy flux in CML cell lines as well as primary hematopoietic cells.

Dipeptide species regulate p38MAPK-Smad3 signalling to maintain chronic myelogenous leukaemia stem cells

Understanding the specific survival of the rare chronic myelogenous leukaemia (CML) stem cell population could provide a target for therapeutics aimed at eradicating these cells. However, little is known about how survival signalling is regulated in CML stem cells. In this study, we survey global metabolic differences between murine normal haematopoietic stem cells (HSCs) and CML stem cells using metabolomics techniques. Strikingly, we show that CML stem cells accumulate significantly higher levels of certain dipeptide species than normal HSCs. Once internalized, these dipeptide species activate amino-acid signalling via a pathway involving p38MAPK and the stemness transcription factor Smad3, which promotes CML stem cell maintenance. Importantly, pharmacological inhibition of dipeptide uptake inhibits CML stem cell activity in vivo. Our results demonstrate that dipeptide species support CML stem cell maintenance by activating p38MAPK–Smad3 signalling in vivo, and thus point towards a potential therapeutic target for CML treatment.

Chronic myelogenous leukaemia contains a stem cell fraction and targeting this population of cells is an attractive therapeutic strategy. Here, the authors demonstrate that the stem cells take up dipeptides and that inhibiting the dipeptide transporter could reduce the number of these stem cells in mice.

Stem Cell Hierarchy and Clonal Evolution in Acute Lymphoblastic Leukemia

Cancer is characterized by a remarkable intertumoral, intratumoral, and cellular heterogeneity that might be explained by the cancer stem cell (CSC) and/or the clonal evolution models. CSCs have the ability to generate all different cells of a tumor and to reinitiate the disease after remission. In the clonal evolution model, a consecutive accumulation of mutations starting in a single cell results in competitive growth of subclones with divergent fitness in either a linear or a branching succession. Acute lymphoblastic leukemia (ALL) is a highly malignant cancer of the lymphoid system in the bone marrow with a dismal prognosis after relapse. However, stabile phenotypes and functional data of CSCs in ALL, the so-called leukemia-initiating cells (LICs), are highly controversial and the question remains whether there is evidence for their existence. This review discusses the concepts of CSCs and clonal evolution in respect to LICs mainly in B-ALL and sheds light onto the technical controversies in LIC isolation and evaluation. These aspects are important for the development of strategies to eradicate cells with LIC capacity. Common properties of LICs within different subclones need to be defined for future ALL diagnostics, treatment, and disease monitoring to improve the patients' outcome in ALL.

Selective JAK2/ABL dual inhibition therapy effectively eliminates TKI-insensitive CML stem/progenitor cells

Imatinib Mesylate (IM) and other tyrosine kinase inhibitor (TKI) therapies have had a major impact on the treatment of chronic myeloid leukemia (CML). However, TKI monotherapy is not curative, with relapse and persistence of leukemic stem cells (LSCs) remaining a challenge. We have recently identified an AHI-1-BCR-ABL-JAK2 protein complex that contributes to the transforming activity of BCR-ABL and IM-resistance in CML stem/progenitor cells. JAK2 thus emerges as an attractive target for improved therapies, but off-target effects of newly developed JAK2 inhibitors on normal hematopoietic cells remain a concern. We have examined the biological effects of a highly selective, orally bioavailable JAK2 inhibitor, BMS-911543, in combination with TKIs on CD34⁺ treatment-naïve IM-nonresponder cells. Combination therapy reduces JAK2/STAT5 and CRKL activities, induces apoptosis, inhibits proliferation and colony growth, and eliminates CML LSCs in vitro. Importantly, BMS-911543 selectively targets CML stem/progenitor cells while sparing healthy stem/progenitor cells. Oral BMS-911543 combined with the potent TKI dasatinib more effectively eliminates infiltrated leukemic cells in hematopoietic tissues than TKI monotherapy and enhances survival of leukemic mice. Dual targeting BCR-ABL and JAK2 activities in CML stem/progenitor cells may consequently lead to more effective disease eradication, especially in patients at high risk of TKI resistance and disease progression.

Src family kinases and their role in hematological malignancies

The Src family protein tyrosine kinases (SFKs) are non-receptor intracellular kinases that have important roles in both hematopoiesis and leukemogenesis. The derangement of their expression or activation has been demonstrated to contribute to hematological malignancies. This review first examines the mechanisms of SFK overexpression and hyperactivation, emphasizing the dysregulation of the upstream modulators. Subsequently, the role of SFK up-regulation in the initiation, progression and therapy resistance of many hematological malignancies is also analyzed. The presented evidence endeavors to highlight the influence of SFK up-regulation on an extensive number of hematological malignancies and the need to consider them as candidates in targeted anticancer therapy.

Mechanisms of resistance to BCR-ABL TKIs and the therapeutic strategies: A review

BCR-ABL caused by the translocation of t(9,22) with elevated tyrosine-kinase activity could induce leukemia in mice, which established BCR-ABL as the molecular pathogenic event in CML (Chronic myeloid leukemia). In recent years, a variety of tyrosine kinase inhibitors (TKIs) targeting at BCR-ABL specifically and effectively have been developed, which has fundamentally promoted the treatment of CML. However, the efficacy of TKIs was limited by its resistance induced by the development of kinase domain mutations and other mechanisms illustrated. In this review, we summarized BCR-ABL inhibitors approved by Food and Drug Administration (FAD), with the same concerns focus on the resistant mechanisms of BCR-ABL inhibitors and therapeutic resistant strategies.

One more stem cell niche: how the sensitivity of chronic myeloid leukemia cells to imatinib mesylate is modulated within a "hypoxic" environment

This is a review (by no means comprehensive) of how the stem cell niche evolved from an abstract concept to a complex system, implemented with a number of experimental data at the cellular and molecular levels, including metabolic cues, on which we focused in particular. The concept was introduced in 1978 to model bone marrow sites suited to host hematopoietic stem cells (HSCs) and favor their self-renewal, while restraining clonal expansion and commitment to differentiation. Studies of the effects of low oxygen tension on HSC maintenance in vitro led us to hypothesize niches were located within bone marrow areas where oxygen tension is lower than elsewhere. We named these areas hypoxic stem cell niches, although a low oxygen tension is to be considered physiological for the environment where HSCs are maintained. HSCs were later shown to have the option of cycling in low oxygen, which steers this cycling to the maintenance of stem cell potential. Cell subsets capable of withstanding incubation in very low oxygen were also detected within leukemia cell populations, including chronic myeloid leukemia (CML). The oncogenetic Bcr/Abl protein is completely suppressed in these subsets, whereas Bcr/Abl messenger ribonucleic acid is not, indicating that CML cells resistant to low oxygen are independent of Bcr/Abl for persistence in culture but remain genetically leukemic. Accordingly, leukemia stem cells of CML selected in low oxygen are refractory to the Bcr/Abl inhibitor imatinib mesylate. Bcr/Abl protein suppression turned out to be actually determined when glucose shortage complicated the effects of low oxygen, indicating that ischemia-like conditions are the driving force of leukemia stem cell refractoriness to imatinib mesylate. These studies pointed to “ischemic” stem cell niches as a novel scenario for the maintenance of minimal residual disease of CML. A possible functional relationship of the “ischemic” with the “hypoxic” stem cell niche is discussed.

Surface proteomic analysis of differentiated versus stem-like osteosarcoma human cells

Cancer stem cell characterization represents a breakthrough in cancer research. Despite evidence showing the existence and the role of cancer stem cells in osteosarcoma (OS) onset and progression, little is known about their specific surface phenotype. To address this issue, we carried out a cytometric analysis with an antibody-array comprising 245 membrane proteins comparing the stem and differentiated OS cells. As experimental model, we chose the stem-like cell line 3aminobenzamide-OS and its parental, differentiated, cell line MG63. We identified 50 differentially expressed, 23 homogeneously expressed, and 172 not expressed proteins in the two cell line models, thus defining a surface protein signature specific for each of them. Furthermore, we selected ERK1/2 (p44/42 mitogen-activated protein kinases) as a potential pathway correlated with processes that characterize tumorigenic potential and stemness of 3aminobenzamide-OS cells.

Emerging therapeutic strategies for targeting chronic myeloid leukemia stem cells

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder. Current targeted therapies designed to inhibit the tyrosine kinase activity of the BCR-ABL oncoprotein have made a significant breakthrough in the treatment of CML patients. However, CML remains a chronic disease that a patient must manage for life. Although tyrosine kinase inhibitors (TKI) therapy has completely transformed the prognosis of CML, it has made the therapeutic management more complex. The interruption of TKI treatment results in early disease progression because it does not eliminate quiescent CML stem cells which remain a potential reservoir for disease relapse. This highlights the need to develop new therapeutic strategies for CML to achieve a permanent cure, and to allow TKI interruption. This review summarizes recent research done on alternative targeted therapies with a particular focus on some important signaling pathways (such as Alox5, Hedgehog, Wnt/b-catenin, autophagy, and PML) that have the potential to target CML stem cells and potentially provide cure for CML.