Wnt信号通路与慢性粒细胞白血病

 慢性粒细胞白血病作为血液系统的恶性增殖性肿瘤，其主要发病机制为BCR-ABL1融合基因形成，因此针对BCR-ABL1基因的靶向药物TKI为其治疗带来了希望，但TKI无法完全消除CML患者体内的LSCs，CML患者容易出现TKI药物耐药及治疗后复发。随着Wnt信号通路在实体瘤中的应用，大量研究发现Wnt信号通路同样在CML中起到重要作用，我们就Wnt信号通路对CML的影响作一综述。     

Expansion of Bcr-Abl-positive leukemic stem cells is dependent on Hedgehog pathway activation

Resistance of Bcr-Abl-positive leukemic stem cells (LSCs) to imatinib treatment in patients with chronic myeloid leukemia (CML) can cause relapse of disease and might be the origin for emerging drug-resistant clones. In this study, we identified Smo as a drug target in Bcr-Abl-positive LSCs. We show that Hedgehog signaling is activated in LSCs through upregulation of Smo. While Smo(-/-) does not impact long-term reconstitution of regular hematopoiesis, the development of retransplantable Bcr-Abl-positive leukemias was abolished in the absence of Smo expression. Pharmacological Smo inhibition reduced LSCs in vivo and enhanced time to relapse after end of treatment. Our results indicate that Smo inhibition might be an effective treatment strategy to reduce the LSC pool in CML.     

IL-6 controls leukemic multipotent progenitor cell fate and contributes to chronic myelogenous leukemia development

Using a mouse model recapitulating the main features of human chronic myelogenous leukemia (CML), we uncover the hierarchy of leukemic stem and progenitor cells contributing to disease pathogenesis. We refine the characterization of CML leukemic stem cells (LSCs) to the most immature long-term hematopoietic stem cells (LT-HSCs) and identify some important molecular deregulations underlying their aberrant behavior. We find that CML multipotent progenitors (MPPs) exhibit an aberrant B-lymphoid potential but are redirected toward the myeloid lineage by the action of the proinflammatory cytokine IL-6. We show that BCR/ABL activity controls Il-6 expression thereby establishing a paracrine feedback loop that sustains CML development. These results describe how proinflammatory tumor environment affects leukemic progenitor cell fate and contributes to CML pathogenesis.     

Genetic Mechanisms of Chronic Myeloid Leukemia Blastic Transformation

The BCR-ABL1 oncogenic tyrosine kinase can transform pluripotent hematopoietic stem cells and initiate chronic myeloid leukemia in chronic phase (CML-CP), a myeloproliferative disorder characterized by excessive accumulation of mature myeloid cells. Patients in CML-CP usually respond to treatment with ABL1 tyrosine kinase inhibitors (TKIs) such as imatinib, though some patients who respond initially may become resistant later. CML-CP leukemia stem cells (LSCs) are intrinsically insensitive to TKIs and thus survive in the long term. These LSCs or their progeny may at some stage acquire additional genetic changes that cause the leukemia to transform further, from CML-CP to a more advanced phase, which has been subclassified as either accelerated phase (CML-AP) or blastic phase (CML-BP). CML-BP is characterized by a major clonal expansion of immature progenitors, which have either myeloid or lymphoid features. CML-BP responds poorly to treatment and is usually fatal. This review discusses the role of genomic instability leading to blastic transformation of CML and proposes some novel therapeutic approaches.     

Novel combination treatments targeting chronic myeloid leukemia stem cells

Chronic myeloid leukemia (CML) is currently considered incurable in most patients. Stem cell transplantation, an accepted curative option for which extensive experience has been gained, is limited by high morbidity and mortality rates, particularly in older patients. Tyrosine kinase inhibitors targeting BCR-ABL are widely used and induce remission in a high proportion of patients, but resistance and incomplete response to these agents portends eventual relapse and disease progression. Although BCR-ABL inhibitors eradicate most CML cells, they are largely ineffective against the reservoir of quiescent leukemic stem cells (LSCs). Thus a strong medical need exists for therapies that effectively eradicate LSCs and is currently a focus of extensive research. To date, evidence obtained from in vitro studies, animal models, and clinical CML specimens suggests that an effective approach may be to partner existing BCR-ABL inhibitors with compounds targeting key stem cell molecular effectors, including Wnt/β-catenin, hedgehog pathway components, histone deacetylase (HDAC), transforming growth factor-β (TGF-β), Janus kinase 2, promyelocytic leukemia protein, and arachidonate 5-lipoxygenase (ALOX5). Novel combinations may sensitize LSCs to BCR-ABL inhibitors, thereby overcoming resistance and creating the possibility of improving disease outcome beyond the current standard of care.     

Pushing the limits of targeted therapy in chronic myeloid leukaemia

Tyrosine kinase inhibitor (TKI) therapy targeting the BCR-ABL1 kinase is effective against chronic myeloid leukaemia (CML), but is not curative for most patients. Minimal residual disease (MRD) is thought to reside in TKI-insensitive leukaemia stem cells (LSCs) that are not fully addicted to BCR-ABL1. Recent conceptual advances in both CML biology and therapeutic intervention have increased the potential for the elimination of CML cells, including LSCs, through simultaneous inhibition of BCR-ABL1 and other newly identified, crucial targets.     

Identification and characterization of leukemia stem cells in murine MLL-AF9 acute myeloid leukemia

Using a mouse model of human acute myeloid leukemia (AML) induced by the MLL-AF9 oncogene, we demonstrate that colony-forming cells (CFCs) in the bone marrow and spleen of leukemic mice are also leukemia stem cells (LSCs). These self-renewing cells (1) are frequent, accounting for 25%-30% of myeloid lineage cells at late-stage disease; (2) generate a phenotypic, morphologic, and functional leukemia cell hierarchy; (3) express mature myeloid lineage-specific antigens; and (4) exhibit altered microenvironmental interactions by comparison with the oncogene-immortalized CFCs that initiated the disease. Therefore, the LSCs responsible for sustaining, expanding, and regenerating MLL-AF9 AML are downstream myeloid lineage cells, which have acquired an aberrant Hox-associated self-renewal program as well as other biologic features of hematopoietic stem cells.     

抗CD123抗体靶向治疗急性髓系白血病

白血病干细胞（leukemic stem cells,LSCs）被认为是白血病发生、发展、耐药、复发的根源,如何彻底根除LSCs已成为白血病治疗研究的一个重要方向。CD123是LSCs表面相对特异的抗原,针对其研发的靶向抗体治疗药物可有效杀伤急性髓系白血病（acute myeloid leukemia,AML）的LSCs,本文对抗CD123抗体靶向治疗AML的最新进展做一综述。     

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.     

Leukemia stem cells

Leukemia stem cells (LSCs) might originate from malignant transformation of normal hematopoietic stem cells (HSCs), or alternatively, of progenitors in which the acquired mutations have re-installed a dysregulated self-renewal program. LSCs are on top of a hierarchy and generate leukemia cells with more differentiated characteristics. While most leukemia cells are initially sensitive to chemo- and radiotherapy, LSCs are resistant and are considered to be the basis for disease relapse after initial response. Albeit important knowledge on LSC biology has been gained from xenogeneic transplantation models introducing human leukemia cells into immune deficient mouse models, the prospective identification and isolation of human LSC candidates has remained elusive and their prognostic and therapeutic significance controversial. This review focuses on the identification, enrichment and characterization of human LSC derived from patients with acute myeloid leukemia (AML). Experimental data demonstrating the clinical significance of estimating LSC burden and strategies to eliminate LSC will be summarized. For long-term cure of AML, it is of importance to define LSC candidates and to understand their tumor biology compared to normal HSCs. Such comparative studies might provide novel markers for the identification of LSC and for the development of treatment strategies that might be able to eradicate them.     

Acute myelogenous leukemia stem cells: From Bench to Bedside

Despite reaching remission with traditional chemotherapy, most adult patients with acute myeloid leukemia (AML) will relapse and die of their disease. Numerous studies have identified a rare subset of leukemia cells that evade traditional chemotherapy and are capable of self-renewal and initiating leukemia. These cells are thought to be responsible for relapse and are termed leukemia stem cells (LSCs). This article will review the current LSC translational research and focus on new approaches to detect LSC burden and its prognostic implications, as well as the identification and development of therapeutic agents active against LSCs.     

Myelodysplasia presenting as granulocytic sarcoma of mediastinum causing superior vena cava syndrome

Granulocytic sarcomas (GS) are extramedullary tumor masses of immature myeloid cells, most frequently associated with hematological disorders including acute myeloid leukemia (AML), chronic myelogenous leukemia (CML), and myelodysplastic syndrome (MDS). Recent interest has centered upon the possible biologic properties that enable theses myeloid cells to adhere to tissues and establish a tumor mass. GS presenting as a mediastinal mass is relatively infrequent, and more uncommon is presentation with the superior vena cava syndrome. We present one such case and review some of the available literature.     

ASXL1 mutation correction by CRISPR/Cas9 restores gene function in leukemia cells and increases survival in mouse xenografts

Recurrent somatic mutations of the epigenetic modifier and tumor suppressor ASXL1 are common in myeloid malignancies, including chronic myeloid leukemia (CML), and are associated with poor clinical outcome. CRISPR/Cas9 has recently emerged as a powerful and versatile genome editing tool for genome engineering in various species. We have used the CRISPR/Cas9 system to correct the ASXL1 homozygous nonsense mutation present in the CML cell line KBM5, which lacks ASXL1 protein expression. CRISPR/Cas9-mediated ASXL1 homozygous correction resulted in protein re-expression with restored normal function, including down-regulation of Polycomb repressive complex 2 target genes. Significantly reduced cell growth and increased myeloid differentiation were observed in ASXL1 mutation-corrected cells, providing new insights into the role of ASXL1 in human myeloid cell differentiation. Mice xenografted with mutation-corrected KBM5 cells showed significantly longer survival than uncorrected xenografts. These results show that the sole correction of a driver mutation in leukemia cells increases survival in vivo in mice. This study provides proof-of-concept for driver gene mutation correction via CRISPR/Cas9 technology in human leukemia cells and presents a strategy to illuminate the impact of oncogenic mutations on cellular function and survival.     

TIM-3 in normal and malignant hematopoiesis: Structure,function, and signaling pathways

Acute myeloid leukemia (AML) is hierarchically organized by self-renewing leukemic stem cells (LSCs). LSCs originate from hematopoietic stem cells (HSCs) by acquiring multistep leukemogenic events. To specifically eradicate LSCs, while keeping normal HSCs intact, the discrimination of LSCs from HSCs is important. We have identified T-cell immunoglobulin and mucin-domain containing-3 (TIM-3) as an LSC-specific surface molecule in human myeloid malignancies and demonstrated its essential function in maintaining the self-renewal ability of LSCs. TIM-3 has been intensively investigated as a “coinhibitory” or “immune checkpoint” molecule of T cells. However, little is known about its distinct function in T cells and myeloid malignancies. In this review, we discuss the structure of TIM-3 and its function in normal blood cells and LSCs, emphasizing the specific signaling pathways involved, as well as the therapeutic applications of TIM-3 molecules in human myeloid malignancies.     

Multidrug resistance protein 4/ ATP binding cassette transporter 4: a new potential therapeutic target for acute myeloid leukemia

Less than a third of adults patients with acute myeloid leukemia (AML) are cured by current treatments, emphasizing the need for new approaches to therapy. We previously demonstrated that besides playing a role in drug-resistant leukemia cell lines, multidrug resistance protein 4 (MRP4/ABCC4) regulates leukemia cell proliferation and differentiation through the endogenous MRP4/ABCC4 substrate, cAMP. Here, we studied the role of MRP4/ABCC4 in tumor progression in a mouse xenograft model and in leukemic stem cells (LSCs) differentiation. We found a decrease in the mitotic index and an increase in the apoptotic index associated with the inhibition of tumor growth when mice were treated with rolipram (PDE4 inhibitor) and/or probenecid (MRPs inhibitor). Genetic silencing and pharmacologic inhibition of MRP4 reduced tumor growth. Furthermore, MRP4 knockdown induced cell cycle arrest and apoptosis in vivo. Interestingly, when LSC population was isolated, we observed that increased cAMP levels and MRP4/ABCC4 blockade resulted in LSCs differentiation. Taken together, our findings show that MRP4/ABCC4 has a relevant role in tumor growth and apoptosis and in the eradication of LSCs, providing the basis for a novel promising target in AML therapy.     

Why do chronic myelogenous leukemia stem cells survive allogeneic stem cell transplantation or imatinib: does it really matter?

It is generally accepted that allogeneic stem cell transplantation can 'cure' chronic myelogenous leukemia (CML), although occasional patients relapse more than 10 years after the transplant procedure. Such cures presumably result from the combined effects of leukemia stem cells (LSCs) of the conditioning regimen and the graft-vs.-leukemia (GvL) effect mediated by donor-derived T lymphocytes. The advent of imatinib has revolutionized the management of patients with CML, but much evidence suggests that it does not eradicate all LSCs, which theoretically remain a potential source of relapse to chronic phase or advanced phase disease. Moreover, sub-clones of Philadelphia-positive cells bearing mutations that code for amino-acid substitutions in the Bcr-Abl kinase domain can be identified in patients receiving treatment with imatinib and are associated with varying degrees of resistance to this agent. In the present review, we postulate that LSCs, similar to their normal counterparts, may alternate between cycling and quiescent modes. In the cycling mode, they may express Bcr-Abl protein and be susceptible to the acquisition of additional mutations, whereas, in the quiescent mode, they may express little or no Bcr-Abl oncoprotein, cannot acquire additional mutations and are unaffected by imatinib. Thus, a patient who starts treatment early in the natural history of CML, and who responds to imatinib clinically, may not have had the opportunity to acquire additional mutations in LSCs. In this case, the persistence long-term of quiescent 'non-mutated' LSCs despite imatinib treatment might be consistent with freedom from relapse to chronic or advanced phase disease, provided that they remain vulnerable to imatinib when they are recruited into cycle. Conversely, when imatinib resistant Philadelphia-positive sub-clones predominate, this is likely to be due to the recruitment to hematopoiesis of quiescent stem cells that had been in cycle before administration of imatinib and that had acquired additional mutations; in such cases, the best approach to eradication of residual LSCs might be to target expressed proteins thought to be targets for the GvL effect.