Therapeutic potential of Notch inhibition in T-cell acute lymphoblastic leukemia: rationale, caveats and promises

T-cell acute lymphoblastic leukemia (T-ALL) is a malignancy that presents with poor prognosis. Treatment relies on the application of aggressive therapies that produce deleterious side-effects, justifying the quest for novel, more efficient and selective molecular targeting agents. Mutations leading to abnormal Notch-1 activity are present in more than half of the T-ALL patients, underscoring the potential therapeutic relevance of targeting Notch-1 inhibition and further reinforcing the need to better comprehend the mechanisms by which Notch-1 drives T cell leukemogenesis. Clinical application of γ-secretase inhibitors to block Notch signaling in T-ALL revealed new challenges that involve improvement of the therapeutic benefit and reduction of intestinal toxicity. Here, we review the latest advances in the development and use of Notch antagonists and summarize the current knowledge on Notch function in T-ALL to understand how it may translate into novel therapeutic strategies that increment the efficiency of Notch inhibition.     

Notch 3沉默对人急性T淋巴细胞白血病细胞增殖与凋亡的影响

目的：探讨Notch 3受体特异性沉默对急性T淋巴细胞白血病的影响。方法：运用survivin启动子介导的RNA干涉方法特异性地封闭急性T淋巴细胞白血病细胞SupT1中Notch 3基因的表达。结果：survivin启动子介导的RNA干涉系统能特异而高效封闭肿瘤细胞内源Notch 3基因的表达,Notch 3基因表达的下调能够使肿瘤细胞的增殖活性降低,凋亡明显增加。结论：Notch 3基因沉默可有效抑制白血病细胞的增殖,并促进其凋亡,为急性T淋巴细胞白血病相关基因功能研究及靶向性治疗探索了一种新策略。     

Notch信号与急性T细胞淋巴瘤白血病关系的研究进展

 Notch信号不仅能调节T细胞分化、发育,参与T细胞淋巴瘤/白血病（Acute T lymphocty lymphoma/leukemia, T-ALL）的发生、发展,还影响造血干、祖细胞生长、分化和自我更新。最常见的Notch1突变为HD区域和PEST区域的突变,活化突变的Notch信号通过PI3K/Akt信号通路、mTOR、NF-κB信号通路等诱导T-ALL的发病与发展。多项研究表明Notch受体不仅能调节T细胞发育,还参与急性髓系白血病（acute myeloid leukemia, AML）和异基因造血干细胞移植（allogeneic hematopoietic stem cell transplantation, allo-HSCT）后移植物抗宿主病（Graft-versus-host Disease, GVHD）的发生,调节造血干、祖细胞生长、分化和自我更新,对造血干细胞移植后造血重建以及造血微环境的动态平衡均发挥重要作用。本文对Notch信号通路与造血系统疾病的关系及其治疗进展作一综述。     

Notch 3沉默对人急性T淋巴细胞白血病细胞增殖与凋亡的影响

目的:探讨Notch 3受体特异性沉默对急性T淋巴细胞白血病的影响。方法:运用survivin启动子介导的RNA干涉方法特异性地封闭急性T淋巴细胞白血病细胞SupT1中Notch 3基因的表达。结果:survivin启动子介导的RNA干涉系统能特异而高效封闭肿瘤细胞内源Notch 3基因的表达,Notch 3基因表达的下调能够使肿瘤细胞的增殖活性降低,凋亡明显增加。结论:Notch 3基因沉默可有效抑制白血病细胞的增殖,并促进其凋亡,为急性T淋巴细胞白血病相关基因功能研究及靶向性治疗探索了一种新策略。     

Epigenetic regulation of PAX5 expression in acute T-cell lymphoblastic leukemia

The analysis of genomic alterations in acute lymphoblastic leukemia (ALL) has provided new insights for prognosis and possible targets of novel therapies. In T-ALL the role of molecular abnormalities has still to be determined. Deregulated promoter hypermethylation of critical genes like PAX5 may have a significant impact on the course of ALL. Samples derived from 75 patients with ALL (B-ALL = 24, T-ALL = 51) and from healthy volunteers were analyzed. PAX5 expression was assessed by micro-array analysis (HG-U133plus 2.0) and correlated with promoter CpG island methylation of PAX5 using a pyrosequencing approach. The analyzed CpG marks in the promoter region of PAX5 were completely and uniformly unmethylated in the control group of healthy individuals. The T-ALL cases featured even higher methylation levels (median: 20%) with a strong variation of values of up to 85% methylation. Analysis of the association of altered methylation levels with gene expression data indicated a differential epigenetic regulation of PAX5 through promoter methylation which may contribute to the pathogenesis of this disease.     

PI3K inhibition synergizes with glucocorticoids but antagonizes with methotrexate in T-cell acute lymphoblastic leukemia

The PI3K pathway is frequently hyperactivated in primary T-cell acute lymphoblastic leukemia (T-ALL) cells. Activation of the PI3K pathway has been suggested as one mechanism of glucocorticoid resistance in T-ALL, and patients harboring mutations in the PI3K negative regulator PTEN may be at increased risk of induction failure and relapse. By gene expression microarray analysis of T-ALL cells treated with the PI3K inhibitor AS605240, we identified Myc as a prominent downstream target of the PI3K pathway. A significant association was found between the AS605240 gene expression signature and that of glucocorticoid resistance and relapse in T-ALL. AS605240 showed anti-leukemic activity and strong synergism with glucocorticoids both in vitro and in a NOD/SCID xenograft model of T-ALL. In contrast, PI3K inhibition showed antagonism with methotrexate and daunorubicin, drugs that preferentially target dividing cells. This antagonistic interaction, however, could be circumvented by the use of correct drug scheduling schemes. Our data indicate the potential benefits and difficulties for the incorporation of PI3K inhibitors in T-ALL therapy.     

Targeting IRAK1 in T-Cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) represents expansion of cells arrested at specific stages of thymic development with the underlying genetic abnormality often determining the stage of maturation arrest. Although their outcome has been improved with current therapy, survival rates remain only around 50% at 5 years and patients may therefore benefit from specific targeted therapy. Interleukin receptor associated kinase 1 (IRAK1) is a ubiquitously expressed serine/threonine kinase that mediates signaling downstream to Toll-like (TLR) and Interleukin-1 Receptors (IL1R). Our data demonstrated that IRAK1 is overexpressed in all subtypes of T-ALL, compared to normal human thymic subpopulations, and is functional in T-ALL cell lines. Genetic knock-down of IRAK1 led to apoptosis, cell cycle disruption, diminished proliferation and reversal of corticosteroid resistance in T-ALL cell lines. However, pharmacological inhibition of IRAK1 using a small molecule inhibitor (IRAK1/4-Inh) only partially reproduced the results of the genetic knock-down. Altogether, our data suggest that IRAK1 is a candidate therapeutic target in T-ALL and highlight the requirement of next generation IRAK1 inhibitors.     

Notch1基因表达对急性T淋巴细胞白血病SupT1细胞增殖、凋亡的影响及其机制

目的探讨Notch信号通路与急性T淋巴细胞白血病发生、发展的关系。方法利用携带Notch1特异性和非特异性shRNA的慢病毒载体包装成的病毒颗粒感染急性T淋巴细胞白血病SupT1细胞,采用CCK．8法检测细胞抑制率;采用流式细胞术检测细胞凋亡率（AnnexinV＋／7-AAD一和AnnexinV＋／7-AAD＋）;采用实时荧光定量PCR法检测Notch1受体基因及下游靶基因的表达水平。结果Notch1干扰组、空白对照组和空载体组96h的细胞增殖抑制率分别为0．902±0．013、0、0．486±0．084,干扰组较空白对照组、空载体组升高（均P〈0．05）;三组细胞早期凋亡率分别为（15．27±0．31）％、（5．57±0．25）％、（5．80±0．20）％,干扰组较空白对照组、空载体组升高（均P〈0．05）;而各组细胞晚期凋亡率无明显变化（均P〉0．05）。干扰组细胞中Notch1受体基因及其下游靶基因Hes1、c-myc、NF-κB在48、72、96h的mRNA相对表达量均较空白对照组及空载体组降低（均P〈0．05）。结论特异性Notch1-shRNA可有效下调Notch1mRNA的表达,并降低其下游靶基因的表达水平。Notch1表达下调可以抑制急性T淋巴细胞白血病SupT1细胞增殖,促进supT1细胞的早期凋亡。     

Targeting Notch1 and proteasome as an effective strategy to suppress T-cell lymphoproliferative neoplasms

The T-cell lymphoproliferative neoplasms (T-LPN) are characterized by a poor clinical outcome. Current therapeutics are mostly non-selective and may induce harmful side effects. It has been reported that NOTCH1 activation mutations frequently associate T-LPN. Because anti-Notch1 based therapies such as γ-secretase inhibitors (GSI) are less efficient and induce considerable side effects, we hypothesized that combining low concentrations of GSI and the proteasome inhibitor bortezomib (BTZ) may provide an effective and tolerable approach to treat T-LPN. Hence, we analyzed the in vitro and in vivo effects of GSI-I and BTZ, alone or in combination, against T-LPN. GSI-I and BTZ synergistically decreased cell viability, proliferation, and colony formation, and induced apoptosis in T-LPN cell lines. Furthermore, combining GSI-I and BTZ decreased the viability of primary T-LPN cells from patients. These effects were accompanied by deregulation of Notch1, AKT, ERK, JNK, p38 MAPK, and NF-κB survival pathways. Moreover, combination treatment inhibited T-LPN tumor growth in nude mice. In all experiments, combining low concentrations of GSI-I and BTZ was superior to using a single agent. Our data support that a synergistic antitumor activity exists between GSI-I and BTZ, and provide a rationale for successful utilization of dual Notch1 and proteasome inhibition to treat T-LPN.     

WDR54 exerts oncogenic roles in T-cell acute lymphoblastic leukemia

WDR54 has been recently identified as a novel oncogene in colorectal and bladder cancers. However, the expression and function of WDR54 in T-cell acute lymphoblastic leukemia (T-ALL) were not reported. In this study, we investigated the expression of WDR54 in T-ALL, as well as its function in T-ALL pathogenesis using cell lines and T-ALL xenograft. Bioinformatics analysis indicated high mRNA expression of WDR54 in T-ALL. We further confirmed that the expression of WDR54 was significantly elevated in T-ALL. Depletion of WDR54 dramatically inhibited cell viability and induced apoptosis and cell cycle arrest at S phase in T-ALL cells in vitro. Moreover, knockdown of WDR54 impeded the process of leukemogenesis in a Jurkat xenograft model in vivo. Mechanistically, the expression of PDPK1, phospho-AKT (p-AKT), total AKT, phospho-ERK (p-ERK), Bcl-2 and Bcl-xL were downregulated, while cleaved caspase-3 and cleaved caspase-9 were upregulated in T-ALL cells with WDR54 knockdown. Additionally, RNA-seq analysis indicated that WDR54 might regulate the expression of some oncogenic genes involved in multiple signaling pathways. Taken together, these findings suggest that WDR54 may be involved in the pathogenesis of T-ALL and serve as a potential therapeutic target for the treatment of T-ALL.     

T细胞淋巴瘤中Notch1基因突变及其蛋白表达的研究

 目的　探讨Notch1蛋白表达及基因突变在T细胞淋巴瘤发病中的作用。方法　采用免疫组织化学和基因测序法检测30例T细胞淋巴瘤组织中Notch1蛋白的表达及Notch1基因26、27号外显子（HD）和34号外显子（PEST）突变情况。另取l0例淋巴结反应增生标本作为对照。结果　30例T细胞淋巴瘤中,21例（70.0 %）Notch1蛋白表达阳性。17例（56.7 %）Notch1基因发生突变,其中,8例突变发生在Notch1基因的HD结构域,6例发生在Notch1基因的PEST结构域,3例在HD和PEST结构域均发生突变。突变方式有插入、片段缺失、无义突变和错义突变。对照组有1例（10.0 %）Notch1蛋白表达阳性,Notch1基因无突变。结论　Notch1蛋白表达可能与Notch1基因突变有关,Notch1蛋白表达和基因突变可能与T细胞淋巴瘤的发生有关。     

Downregulation of Glutamine Synthetase,not glutaminolysis,is responsible for glutamine addiction in Notch1‐driven acute lymphoblastic leukemia

The cellular receptor Notch1 is a central regulator of T‐cell development, and as a consequence, Notch1 pathway appears upregulated in > 65% of the cases of T‐cell acute lymphoblastic leukemia (T‐ALL). However, strategies targeting Notch1 signaling render only modest results in the clinic due to treatment resistance and severe side effects. While many investigations reported the different aspects of tumor cell growth and leukemia progression controlled by Notch1, less is known regarding the modifications of cellular metabolism induced by Notch1 upregulation in T‐ALL. Previously, glutaminolysis inhibition has been proposed to synergize with anti‐Notch therapies in T‐ALL models. In this work, we report that Notch1 upregulation in T‐ALL induced a change in the metabolism of the important amino acid glutamine, preventing glutamine synthesis through the downregulation of glutamine synthetase (GS). Downregulation of GS was responsible for glutamine addiction in Notch1‐driven T‐ALL both in vitro and in vivo. Our results also confirmed an increase in glutaminolysis mediated by Notch1. Increased glutaminolysis resulted in the activation of the mammalian target of rapamycin complex 1 (mTORC1) pathway, a central controller of cell growth. However, glutaminolysis did not play any role in Notch1‐induced glutamine addiction. Finally, the combined treatment targeting mTORC1 and limiting glutamine availability had a synergistic effect to induce apoptosis and to prevent Notch1‐driven leukemia progression. Our results placed glutamine limitation and mTORC1 inhibition as a potential therapy against Notch1‐driven leukemia.

Abbreviations

7‐AAD

7‐Aminoactinomycin D

BPTES

bis‐2‐(5‐phenylacetamido‐1,2,4‐thiadiazol‐2‐yl)ethyl sulfide

DON

diazo‐5‐oxo‐L‐norleucine

ECAR

extracellular acidification rate

GDH

glutamate dehydrogenase

GLS

glutaminase

GS

glutamine synthetase

GSI

γ‐secretase inhibitor

MSO

L‐methionine sulfoximine

mTORC1

mammalian target of rapamycin complex 1

NICD

Notch intracellular domain

PI

propidium iodide

RAP

rapamycin

T‐ALL

T‐cell acute lymphoblastic leukemia

TCA

tricarboxylic acid

αKG

α‐ketoglutarate

     

Inhibition of the MAP2K7-JNK pathway with 5Z-7-oxozeaenol induces apoptosis in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive pediatric leukemia with a worse prognosis than most frequent B-cell ALL due to a high incidence of treatment failures and relapse. Our previous work showed that loss of the pioneer factor KLF4 in a NOTCH1-induced T-ALL mouse model accelerated the development of leukemia through expansion of leukemia-initiating cells and activation of the MAP2K7 pathway. Similarly, epigenetic silencing of the KLF4 gene in children with T-ALL was associated with MAP2K7 activation. Here, we showed the small molecule 5Z-7-oxozeaenol (5Z7O) induces dose-dependent cytotoxicity in a panel of T-ALL cell lines mainly through inhibition of the MAP2K7-JNK pathway, which further validates MAP2K7 as a therapeutic target. Mechanistically, 5Z7O-mediated apoptosis was caused by the downregulation of regulators of the G2/M checkpoint and the inhibition of survival pathways. The anti-leukemic capacity of 5Z7O was evaluated using leukemic cells from two mouse models of T-ALL and patient-derived xenograft cells generated using lymphoblasts from pediatric T-ALL patients. Finally, a combination of 5Z7O with dexamethasone, a drug used in frontline therapy, showed synergistic induction of cytotoxicity. In sum, we report here that MAP2K7 inhibition thwarts survival mechanisms in T-ALL cells and warrants future pre-clinical studies for high-risk and relapsed patients.     

Dual antitumor mechanisms of Notch signaling inhibitor in a T-cell acute lymphoblastic leukemia xenograft model

Constitutive activation of Notch signaling is required for the proliferation of a subgroup of human T-cell acute lymphoblastic leukemias (T-ALL). Previous in vitro studies have demonstrated the therapeutic potential of Notch signaling inhibitors for treating T-ALL. To further examine this possibility, we applied a γ-secretase inhibitor (GSI) to T-ALL xenograft models. Treatment of established subcutaneous tumors with GSI resulted in partial or complete regression of tumors arising from four T-ALL cell lines that were also sensitive to GSI in vitro . To elucidate the mechanism of action, we transduced DND-41 cells with the active form of Notch1 (aN1), which conferred resistance to in vitro GSI treatment. Nevertheless, in vivo treatment with GSI induced a partial but significant regression of subcutaneous tumors that developed from aN1-transduced DND-41 cells, whereas it induced complete regression of tumors that developed from mock-transduced DND-41 cells. These findings indicate that the remarkable efficacy of GSI might be attributable to dual mechanisms, directly via apoptosis of DND-41 cells through the inhibition of cell-autonomous Notch signaling, and indirectly via disturbance of tumor angiogenesis through the inhibition of non-cell-autonomous Notch signaling. ( Cancer Sci 2009; 100: 2444–2450)     

CXCR4 chemokine receptors, histone deacetylase inhibitors and acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a malignancy with the potential to infiltrate the liver, spleen, lymph nodes and brain. The mechanism for selective homing of ALL cells to preferential sites has long been unclear. Recent reports indicate that the chemokine receptor CXCR4 is found on ALL cells and its ligand is highly expressed at sites associated with ALL-induced organ infiltration. This results in chemotaxis, or directed migration of leukemic cells from the bone marrow via the circulation to preferential sites of extramedullary organ infiltration. Because overexpression of CXCR4 on ALL cells is associated with high extramedullary organ infiltration and shorter disease-free survival, numerous pharmacological agents affecting CXCR4 have currently been investigated. The most promising data are available for histone deacetylase inhibitors (HDAIs), which have been shown to be safe and well tolerated in phase I clinical trials. In vitro, HDAIs extensively downregulate CXCR4 protein and mRNA levels. As a result, the ability of CXCR4 ligand to induce cellular migration is impaired. Wider recognition of the role of CXCR4 in ALL and manipulation of this important mechanism may lead to novel approaches in the treatment and outcome of this disease.     

Triple Akt inhibition as a new therapeutic strategy in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive neoplastic disorder in which chemotherapy resistance and refractory relapses occur, with a poorer prognostic outcome.Constitutively active PI3K/Akt/mTOR pathway is a common feature of T-ALL upregulating cell proliferation, survival and drug resistance. This pathway is currently under clinical trials with small molecules inhibitors (SMI).To verify whether a multi-inhibition treatment against Akt protein could enhance the efficacy of individual drug administration and overcome drug resistance as well as to obtain a decrease in single drug concentration, we tested on T-ALL cell lines the effects of combined treatments with three Akt inhibitors with different mode of action, GSK690693, MK-2206 and Perifosine.In cells with hyperactivated Akt, combined administration of the drugs displayed a significant synergistic and cytotoxic effect and affected PI3K/Akt/mTOR pathway at much lower concentration than single drug use. Highest synergistic effect for full inhibition of Akt was also related to the timing of every drug administration. Furthermore the triple treatment had greater efficacy in inducing cell cycle arrest in G₀/G₁ phase and both apoptosis and autophagy.Targeting Akt as a key protein of PI3K/Akt/mTOR pathway with multiple drugs might represent a new and promising pharmacological strategy for treatment of T-ALL patients.     

T-cell acute lymphoblastic leukemia in Israel: clinical and laboratory features

T-cell acute lymphoblastic leukemia (ALL) comprises a third of the cases of childhood ALL in Israel. This high proportion of T-ALL is most probably due to a deficiency in pre-B/common ALL. The T-ALL patients had significantly worse 4-yr survival compared to standard risk or non-T high risk patients. In view of these special epidemiologic and clinical features a study of the immunophenotype of all consecutive cases of T-ALL and T-non Hodgkin's lymphoma (NHL) observed in our medical center was performed. Twenty-eight ALL and 3 NHL patients were studied and their cells characterized using a panel of monoclonal antibodies, TdT reactivity and E-rosette formation. Assays of the activities of adenosine deaminase (ADA) and purine nucleoside phosphorylase (NP) were also performed. Based on the surface antigen expression, the tumor cells could be classified into one of the three known developmental stages of T cells. It was found that the immunophenotype of the T-ALL cases in Israel was similar to that observed in other countries. Considerable heterogeneity of surface antigen expression was found and in a number of cases the phenotype analysis was not easily reconciled with models of T-cell ontogeny. The activities of ADA and NP were correlated with the developmental stage, as defined by the surface antigenic expression. Contrary to observations on normal T-cells, where ADA activity decreases and NP activity increases as T-cells mature and differentiate, this was not found in the malignant T cells. These findings as well as the existence of atypical immunophenotypes suggest that the leukemic T cell has an abnormal gene expression.