FBXW7 and NOTCH1 mutations in childhood T cell acute lymphoblastic leukaemia and T cell non-Hodgkin lymphoma

Pediatric relapsed or refractory leukemia: new pharmacotherapeutic developments and future directions

Over the past 50 years, numerous advances in treatment have produced dramatic increases in the cure rates of pediatric leukemias. Despite this progress, the majority of children with relapsed leukemia are not expected to survive. With current chemotherapy regimens, approximately 15 % of children with acute lymphoblastic leukemia and 45 % of children with acute myeloid leukemia will have refractory disease or experience a relapse. Advances in the treatment of pediatric relapsed leukemia have not mirrored the successes of upfront therapy, and newer treatments are desperately needed in order to improve survival in these challenging patients. Recent improvements in our knowledge of cancer biology have revealed an extensive number of targets that have the potential to be exploited for anticancer therapy. These advances have led to the development of a number of new treatments that are now being explored in children with relapsed or refractory leukemia. Novel agents seek to exploit the same molecular aberrations that contribute to leukemia development and resistance to therapy. Newer classes of drugs, including monoclonal antibodies, tyrosine kinase inhibitors and epigenetic modifiers are transforming the treatment of patients who are not cured with conventional therapies. As the side effects of many new agents are distinct from those seen with conventional chemotherapy, these treatments are often explored in combination with each other or combined with conventional treatment regimens. This review discusses the biological rationale for the most promising new agents and the results of recent studies conducted in pediatric patients with relapsed leukemia.

The challenge of targeting notch in hematologic malignancies

Notch signaling can play oncogenic and tumor suppressor roles depending on cell type. Hematologic malignancies encompass a wide range of transformed cells, and consequently the roles of Notch are diverse in these diseases. For example Notch is a potent T-cell oncogene, with >50% of T-cell acute lymphoblastic leukemia (T-ALL) cases carry activating mutations in the Notch1 receptor. Targeting Notch signaling in T-ALL with gamma-secretase inhibitors, which prevent Notch receptor activation, has shown pre-clinical activity, and is under evaluation clinically. In contrast, Notch signaling inhibits acute myeloblastic leukemia growth and survival, and although targeting Notch signaling in AML with Notch activators appears to have pre-clinical activity, no Notch agonists are clinically available at this time. As such, despite accumulating evidence about the biology of Notch signaling in different hematologic cancers, which provide compelling clinical promise, we are only beginning to target this pathway clinically, either on or off. In this review, we will summarize the evidence for oncogenic and tumor suppressor roles of Notch in a wide range of leukemias and lymphomas, and describe therapeutic opportunities for now and the future.

Lymphoblastic lymphoma in childhood and adolescence

Lymphoblastic lymphoma (LBL) are thought to derive from immature precursor T-cells or B-cells. LBL are the second most common subtype of Non-Hodgkin Lymphoma (NHL) in children and adolescents. LBL are closely related to acute lymphoblastic leukemia (ALL), the most common type of cancer in children. Using ALL-type treatment regimen to treat children with LBL was an important development in the treatment of LBL. During the last decades, several systematic clinical trials contributed to the controlled optimization of treatment. Today event-free survival (EFS) can be achieved for 75-90% of patients. However, acute and long-term toxicity, the lack of prognostic parameters and the poor outcome for patients who suffer from refractory or relapsed LBL remain highly relevant subjects for improvement. To date, the pathogenesis of LBL is poorly understood. Learning more about the biology and pathogenesis of LBL might pave the way for targeted treatment to improve survival especially in relapsed and refractory patients.

Disseminated lymphoblastic lymphoma in children and adolescents: results of the COG A5971 trial: a report from the Children's Oncology Group

The Children's Oncology Group's A5971 trial examined central nervous system (CNS) prophylaxis and early intensification in paediatric patients diagnosed with CNS-negative Stage III and IV lymphoblastic lymphoma. Using a 2 × 2 factorial design, the study randomized patients to Children's Cancer Group (CCG) modified Berlin-Frankfurt-Muenster (BFM) acute lymphoblastic leukaemia (ALL) regimen with intensified intrathecal (IT) methotrexate (MTX) (Arm A1) or an adapted non-Hodgkin lymphoma/BFM-95 therapy with high dose MTX in interim maintenance but no IT-MTX in maintenance (Arm B1). Each cohort was randomized ± intensification (cyclophosphamide/anthracycline) (Arms A2/B2). For the 254 randomized patients, there was no difference in 5-year event-free survival (EFS) for the four arms: Arm A1, 80% [95% confidence interval (CI) 67-89%] and Arm A2, 81% (95% CI 69-89%); Arm B1, 80% (95% CI 68-88%) and Arm B2, 84% (95% CI 72-91%). The cumulative incidence of CNS relapse was 1·2%. Age <10 years and institutional imaging response at 2 weeks was associated with improved outcomes (P < 0·001 and P = 0·014 for overall survival). CNS positive patients (n = 12) did poorly [5-year EFS of 63% (95% CI 29-85%)]. For CNS-negative patients, there was no difference in outcome based on CNS prophylaxis (IT-MTX versus HD-MTX) or with intensification.

The NOTCH signaling pathway: role in the pathogenesis of T-cell acute lymphoblastic leukemia and implication for therapy

T-cell acute lymphoblastic leukemia/lymphoma (T-ALL) is characterized by aberrant activation of NOTCH1 in over 60% of T-ALL cases. The high prevalence of activating NOTCH1 mutations highlights the critical role of NOTCH signaling in the pathogenesis of this disease and has prompted the development of therapeutic approaches targeting the NOTCH signaling pathway. Small molecule gamma secretase inhibitors (GSIs) can effectively inhibit oncogenic NOTCH1 and are in clinical testing for the treatment of T-ALL. Treatment with GSIs and glucocorticoids are strongly synergistic and may overcome the gastrointestinal toxicity associated with systemic inhibition of the NOTCH pathway. In addition, emerging new anti-NOTCH1 therapies include selective inhibition of NOTCH1 with anti-NOTCH1 antibodies and stapled peptides targeting the NOTCH transcriptional complex in the nucleus.

Incidence and prognostic relevance of genetic variations in T-cell lymphoblastic lymphoma in childhood and adolescence

Probability of event-free survival (pEFS) in pediatric T-cell lymphoblastic lymphoma is about 80%, whereas survival in relapsed patients is very poor. No stratification criteria have been established so far. Recently, activating NOTCH1 mutations were reported to be associated with favorable prognosis, and loss of heterozygosity at chromosome 6q (LOH6q) was reported to be associated with increased relapse risk. The current project was intended to evaluate the prognostic effect of these markers. Mutations in hot spots of NOTCH1 and FBXW7 were analyzed in 116 patients. Concerning LOH6q status, 118 patients were investigated, using microsatellite marker analysis, in addition to an earlier reported cohort of 99 available patients. Ninety-two cases were evaluable for both analyses. All patients were treated with T-cell lymphoblastic lymphoma-Berlin-Frankfurt-Münster group (BFM)-type treatment. LOH6q was observed in 12% of patients (25/217) and associated with unfavorable prognosis (pEFS 27% ± 9% vs 86% ± 3%; P < .0001). In 60% (70/116) of the patients, NOTCH1 mutations were detected and associated with favorable prognosis (pEFS 84% ± 5% vs 66% ± 7%; P = .021). Interestingly, NOTCH1 mutations were rarely observed in patients with LOH in 6q16. Both prognostic markers will be used as stratification criteria in coming Non-Hodgkin Lymphoma-BFM trials.

Gene mutation profiles and prognostic implications in Korean patients with T-lymphoblastic leukemia

Genetic alterations implicated in the leukemogenesis of T cell acute lymphoblastic leukemia (T-ALL) have been identified in recent years. In this study, we investigated gene mutation profiles and prognostic implications in a series of Korean T-ALL patients. The study patients were 29 Korean patients with T-ALL; 13 adults (45 %) and 16 children (55 %; male-to-female ratio, 25:4). Clinical, hematologic, and cytogenetic findings were reviewed. We performed mutation analyses for NOTCH1, FBXW7, PHF6, and IL7R genes and survival analyses according to the mutational status. Gene mutations were identified in 66 % of the patients in our series (19/29). Eighteen patients (62 %) had NOTCH1/FBXW7 mutations. Sixteen patients (55 %) had NOTCH1 mutations including nine novel mutations, and eight patients (28 %) had known FBXW7 mutations. Eight patients (28 %; six males and two females) had PHF6 mutations including four novel mutations. Three patients (10 %) had IL7R mutations, which were all novel in-frame insertion or deletion-insertions. The gene mutation profile combined with cytogenetics and FISH study for the p16 gene detected genetic aberrations in 90 % of patients (26/29). There was no significant difference in the frequency of gene mutations between the pediatric and adult patients with T-ALL. Survival analyses suggested a favorable prognostic implication of NOTCH1 mutations in adult T-ALL. Gene mutation studies for NOTCH1, FBXW7, PHF6, and IL7R could detect genetic alterations in a majority of Korean T-ALL patients with novel mutations. We observed similar mutation profiles between adult and pediatric T-ALL, and a favorable prognostic implication of NOTCH1 mutations in adult T-ALL.

NOTCH1 activation clinically antagonizes the unfavorable effect of PTEN inactivation in BFM-treated children with precursor T-cell acute lymphoblastic leukemia

Despite improvements in treatment results for pediatric T-cell acute lymphoblastic leukemia, approximately 20% of patients relapse with dismal prognosis. PTEN inactivation and NOTCH1 activation are known frequent leukemogenic events but their effect on outcome is still controversial. We analyzed the effect of PTEN inactivation and its interaction with NOTCH1 activation on treatment response and long-term outcome in 301 ALL-BFM treated children with T-cell acute lymphoblastic leukemia. We identified PTEN mutations in 52 of 301 (17.3%) of patients. In univariate analyses this was significantly associated with increased resistance to induction chemotherapy and a trend towards poor long-term outcome. By contrast, patients with inactivating PTEN and activating NOTCH1 mutations showed marked sensitivity to induction treatment and excellent long-term outcome, which was similar to patients with NOTCH1 mutations only, and more favorable than in patients with PTEN mutations only. Notably, in the subgroup of patients with a prednisone- and minimal residual disease (MRD)-response based medium risk profile, PTEN-mutations without co-existing NOTCH1-mutations represented an MRD-independent highly significant high-risk biomarker. Mutations of PTEN highly significantly indicate a poor prognosis in T-ALL patients who have been stratified to the medium risk group of the BFM-protocol. This effect is clinically neutralized by NOTCH1 mutations. Although these results have not yet been explained by an obvious molecular mechanism, they contribute to the development of new molecularly defined stratification algorithms. Furthermore, these data have unexpected potential implications for the development of NOTCH1 inhibitors in the treatment of T-cell acute lymphoblastic leukemia in general, and in those with a combination of PTEN and NOTCH1 mutations in particular.

Impact of NOTCH1/FBXW7 mutations on outcome in pediatric T-cell acute lymphoblastic leukemia patients treated on the MRC UKALL 2003 trial

Activating mutations in the NOTCH1 pathway are frequent in pediatric T-cell acute lymphoblastic leukemia (T-ALL) but their role in refining risk stratification is unclear. We screened 162 pediatric T-ALL patients treated on the MRC UKALL2003 trial for NOTCH1/FBXW7 gene mutations and related genotype to response to therapy and long-term outcome. Overall, 35% were wild-type (WT) for both genes (NOTCH1(WT)FBXW7(WT)), 38% single NOTCH1 mutant (NOTCH1(Single)FBXW7(WT)), 3% just FBXW7 mutant (NOTCH1(WT)FBXW7(MUT)) and 24% either double NOTCH1 mutant (NOTCH1(Double)FBXW7(WT)) or mutant in both genes (NOTCH1(MUT)FBXW7(MUT)), hereafter called as NOTCH1±FBXW7(Double). There was no difference between groups in early response to therapy, but NOTCH1±FBXW7(Double) patients were more likely to be associated with negative minimal residual disease (MRD) post-induction than NOTCH1(WT)FBXW7(WT) patients (71% versus 40%, P=0.004). Outcome improved according to the number of mutations, overall survival at 5 years 82%, 88% and 100% for NOTCH1(WT)FBXW7(WT), NOTCH1(Single)FBXW7(WT) and NOTCH1±FBXW7(Double) patients, respectively (log-rank P for trend=0.005). Although 14 NOTCH1±FBXW7(Double) patients were classified as high risk (slow response and/or MRD positive), only two had disease progression and all remain alive. Patients with double NOTCH1 and/or FBXW7 mutations have a very good outcome and should not be considered for more intensive therapy in first remission, even if slow early responders or MRD positive after induction therapy.

FBXW7 regulates glucocorticoid response in T-cell acute lymphoblastic leukaemia by targeting the glucocorticoid receptor for degradation

Loss of function mutation in FBXW7, an E3 ubiquitin ligase, is associated with good prognosis and early glucocorticoid treatment response in childhood T-cell acute lymphoblastic leukemia (T-ALL) by unknown mechanisms. Here, we show that FBXW7 targets the glucocorticoid receptor α (GRα) for ubiquitylation and proteasomal degradation in a manner dependent on glycogen synthase kinase 3 β-mediated phsophorylation. FBXW7 inactivation caused elevated GRα levels, and enhanced the transcriptional response to glucocorticoids. There was significant enhancement of GR transcriptional responses in FBXW7-deficient cell lines and primary T-ALL samples, in particular, for those pro-apoptotic regulatory proteins, BIM and PUMA. Reduced FBXW7 expression or function promoted glucocorticoid sensitivity, but not sensitivity to other chemotherapeutic agents used in T-ALL. Moreover, this was a general feature of different cancer cell types. Taken together, our work defines GRα as a novel FBXW7 substrate and demonstrates that favorable patient prognosis in T-ALL is associated with FBXW7 mutations due to enhanced GRα levels and steroid sensitivity. These findings suggest that inactivation of FBXW7, a putative tumor suppressor protein, may create a synthetic lethal state in the presence of specific anticancer therapies.

PI3K/mTOR inhibition upregulates NOTCH-MYC signalling leading to an impaired cytotoxic response

PI3K, mTOR and NOTCH pathways are frequently dysregulated in T-cell acute lymphoblastic leukaemia (T-ALL). Blockade of PI3K and mTOR with the dual inhibitor PI-103 decreased proliferation in all 15 T-ALL cell lines tested, inducing cell death in three. Combined PI3K/mTOR/NOTCH inhibition (with a γ-secretase inhibitor (GSI)) led to enhanced cell-cycle arrest and to subsequent cell death in 7/11 remaining NOTCH mutant cell lines. Commitment to cell death occurred within 48-72 h and was maximal when PI3K, mTOR and NOTCH activities were inhibited. PI-103 addition led to upregulation of c-MYC, which was blocked by coincubation with a GSI, indicating that PI3K/mTOR inhibition resulted in activation of the NOTCH-MYC pathway. Microarray studies showed a global increase in NOTCH target gene expression upon PI3K/mTOR inhibition. NOTCH-MYC-induced resistance to PI3K/mTOR inhibition was supported by synergistic cell death induction by PI-103 and a small molecule c-MYC inhibitor, and by reduction of the cytotoxic effect of PI-103+GSI by c-MYC overexpression. These results show that drugs targeting PI3K/mTOR can upregulate NOTCH-MYC activity, have implications for the use of PI3K inhibitors for the treatment of other malignancies with activated NOTCH, and provide a rational basis for the use of drug combinations that target both the pathways.

BCL11B, FLT3, NOTCH1 and FBXW7 mutation status in T-cell acute lymphoblastic leukemia patients

T-cell acute lymphoblastic leukemia is a heterogeneous malignancy originating from developing lymphocyte precursors likely due to mutations in genes regulating thymocyte differentiation. Here, we characterized mutation status of BCL11B and FLT3 genes, presumably involved in T-ALL, together with FBXW7 and NOTCH1 as known players in T-ALL in 65 pediatric T-cell acute lymphoblastic leukemia patients. We also aimed at the assessment of prognostic value of NOTCH1 and FBXW7 mutations in ALL-IC BFM 2002 protocol. FLT3 and BCL11B mutations were detected in 3% and 2% of patients, respectively. FBXW7 mutations were observed in 8% of patients, while NOTCH1 was mutated in 40%. No correlation was found between NOTCH1 and FBXW7 mutations and traditionally used clinical factors or molecular features. In total we have detected nine mutations, which have not been previously described by others. Eight of them were found in NOTCH1 and one in BCL11B gene. Observed frequencies of NOTCH1 and FBXW7 are in line with previous reports, thus confirming postulated participation of these two genes in T-ALL pathomechanism. Moreover, we report on mutation frequency of FLT3 and BCL11B, not extensively studied in T-ALL so far. Finally, we suggest a putative role of BLC11B as an oncogene in T-ALL pathogenesis.

Elevated TRIB2 with NOTCH1 activation in paediatric/adult T-ALL

TRIB2 is a potent oncogene, elevated in a subset of human acute myeloid leukaemias (AML) with a mixed myeloid/lymphoid phenotype and NOTCH1 mutations. Although rare in AML, activating NOTCH1 mutations occur in 50% of all T cell acute lymphoblastic leukaemias (T-ALL). TRIB2 is a NOTCH1 target gene that functions in the degradation of key proteins and modulation of MAPK signalling pathways, implicated in haematopoietic cell survival and proliferation. This study showed that TRIB2 expression level is highest in the lymphoid compartment of normal haematopoietic cells, specifically in T cells. Analysis of TRIB2 expression across 16 different subtypes of human leukaemia demonstrated that TRIB2 expression was higher in ALL phenotypes versus all other phenotypes including AML, chronic lymphocytic leukaemia (CLL), myelodysplastic syndrome (MDS) and chronic myeloid leukaemia (CML). A T cell profile was distinguished by high TRIB2 expression in normal and malignant haematopoiesis. High TRIB2 expression was seen in T-ALL with normal karyotype and correlated with NOTCH signalling pathways. High TRIB2 expression correlated with NOTCH1/FBXW7 mutations in a paediatric T-ALL cohort, strongly linking NOTCH1 activation and high TRIB2 expression in paediatric T-ALL. The relationship between TRIB2 and T cell signalling pathways uniquely identifies leukaemia subtypes and will be useful in the advancement of our understanding of T cell and ALL biology.

Clinical impact of NOTCH1 and/or FBXW7 mutations, FLASH deletion, and TCR status in pediatric T-cell lymphoblastic lymphoma

PURPOSE

Pediatric T-cell lymphoblastic lymphomas (T-LBL) are commonly treated on T-cell acute lymphoblastic leukemia (T-ALL) -derived protocols. Therapeutic stratification based on response to the prephase treatment and on minimal residual disease assessment is well established in T-ALL but is not easy to extrapolate to T-LBL. The identification of molecular prognostic markers at diagnosis in T-LBL could provide an alternative for early therapeutic stratification. Our study determines the frequency and prognostic value of NOTCH1/FBXW7 mutations (N/F(mut)), FLASH deletion at chromosome 6q, and TCR rearrangements in a prospective cohort of pediatric T-LBL.

PATIENTS AND METHODS

Pathologic samples were obtained at diagnosis for 54 patients treated according to the EuroLB02 protocol in France. N/F(mut) were identified by direct sequencing and allelic dosage was used to detect FLASH and TCRγ deletions, which were interpreted in conjunction with TCRγ, TCRβ, and TCRδ rearrangements.

RESULTS

N/F(mut) were found in 55% of T-LBL patients, in whom they were associated with improved event-free survival (P < .01) and overall survival (P < .01). FLASH monoallelic deletions were observed in 18% of patients; they were predominantly N/F wild-type (six of nine) and tended to be of inferior prognosis (P = .09). Absence of biallelic TCRγ deletion (ABD) was seen in 7%, all of which were N/F(mut) and identified a poor prognosis group (P = .02). On multivariate analysis of N/F(mut), TCRγ ABD, and FLASH deletion, only N/F(mut) was an independent factor for good prognosis.

CONCLUSION

Mutational status of NOTCH1/FBXW7 represents a promising marker for early therapeutic stratification in pediatric T-LBL.

The significance of PTEN and AKT aberrations in pediatric T-cell acute lymphoblastic leukemia

BACKGROUND

PI3K/AKT pathway mutations are found in T-cell acute lymphoblastic leukemia, but their overall impact and associations with other genetic aberrations is unknown. PTEN mutations have been proposed as secondary mutations that follow NOTCH1-activating mutations and cause cellular resistance to γ-secretase inhibitors.

DESIGN AND METHODS

The impact of PTEN, PI3K and AKT aberrations was studied in a genetically well-characterized pediatric T-cell leukemia patient cohort (n=146) treated on DCOG or COALL protocols.

RESULTS

PTEN and AKT E17K aberrations were detected in 13% and 2% of patients, respectively. Defective PTEN-splicing was identified in incidental cases. Patients without PTEN protein but lacking exon-, splice-, promoter mutations or promoter hypermethylation were present. PTEN/AKT mutations were especially abundant in TAL- or LMO-rearranged leukemia but nearly absent in TLX3-rearranged patients (P=0.03), the opposite to that observed for NOTCH1-activating mutations. Most PTEN/AKT mutant patients either lacked NOTCH1-activating mutations (P=0.006) or had weak NOTCH1-activating mutations (P=0.011), and consequently expressed low intracellular NOTCH1, cMYC and MUSASHI levels. T-cell leukemia patients without PTEN/AKT and NOTCH1-activating mutations fared well, with a cumulative incidence of relapse of only 8% versus 35% for PTEN/AKT and/or NOTCH1-activated patients (P=0.005).

CONCLUSIONS

PI3K/AKT pathway aberrations are present in 18% of pediatric T-cell acute lymphoblastic leukemia patients. Absence of strong NOTCH1-activating mutations in these cases may explain cellular insensitivity to γ-secretase inhibitors.

[T-cell pediatric acute lymphoblastic leukemia: analysis of survival and prognostic factors in 4 consecutive protocols of the Spanish cooperative study group SHOP]

BACKGROUND AND OBJECTIVES

Acute lymphoblastic leukemia (ALL) is the most frequent cancer in childhood, with cure rates of 80-85%. In T-cell ALL (15% of ALL), prognostic factors are ill defined. We aimed to describe the event-free survival (EFS) and analyze clinical prognostic factors in a series of pediatric T-ALL of 4 consecutive clinical trials.

PATIENTS AND METHODS

Children with T-ALL aged 1-18 years treated in 37 institutions in Spain were enrolled in 4 consecutive trials from February-1989 to November-2009.

RESULTS

A total of 218 T-ALL patients out of 1,652 pediatric ALL were evaluable during the study period (SHOP/ALL-89: 35, ALL-94: 63, ALL-99: 62, ALL-2005: 58). There were 164 boys (75%). Median age (years) was 7.8 range (1.3-18.6). Median leukocytes (10(9)/L) was 78.2, range 0.8-930. Fifteen (6.8%) children had central nervous system (CNS) involvement at diagnosis. Regarding response to induction treatment, 150 (75%) patients had less than 5% blasts on day-14 bone marrow and 199 achieved complete remission at the end of induction. Overall survival (OS) at 60 months for SHOP/ALL-89, ALL-94, ALL-99 was 48 (8), 49 (6), 70 (6) %, respectively, and at 48 months for SHOP/ALL-2005 (ongoing protocol) was 74 (8) %. Median follow-up (months) was 206, 152, 74 and 17 respectively. Analysis of prognostic factors revealed no statistical differences regarding sex or age. Leukocyte count over 200×10(9)/l (P=.024), CNS infiltration at diagnosis (P<.006) and treatment response had prognostic significance (end-induction complete remission) (P=.0000), day 14-bone marrow (P=.005).

CONCLUSIONS

Results for the SHOP/ALL-89 and ALL-94 protocols were inferior to other contemporary protocols but there has been an improvement in survival in the 2 last trials. In line with other T-ALL series, response to treatment had the strongest prognostic impact.

Beyond the 2008 World Health Organization classification: the role of the hematopathology laboratory in the diagnosis and management of acute lymphoblastic leukemia

The diagnosis of acute lymphoblastic leukemia (ALL) is made by evaluating morphology and immunophenotype. However, appropriate risk stratification and decisions regarding the intensity of therapy are influenced by additional clinical and laboratory testing that reflect the biology of the disease. Recent years have seen tremendous progress in uncovering genetic lesions that influence the biology of ALL. In recognition of these advances, the 2008 WHO classification incorporated the category of B-lymphoblastic leukemia/lymphoma with recurrent genetic abnormalities into the classification of precursor lymphoid neoplasms. Based on the knowledge available at the time, genetic lesions associated with distinct clinical features, immunophenotype, prognosis, or other unique biological characteristics were included in this category. Not surprisingly, significant novel genetic lesions that profoundly affect the biology of ALL have since been identified and will have a major impact on risk stratification and may ultimately be incorporated into future classification schemes. After establishing an initial diagnosis and treatment regimen, hematopathologists must also evaluate for minimal residual disease (MRD) to determine the need for additional intervention because MRD remains the most useful clinical indicator of disease progression and response to treatment. Doing so requires familiarity with not only morphology, but also flow cytometry and molecular genetics. Although not all of these applications are handled directly by the hematopathologist, it is our strong belief that meaningful involvement in patient care dictates that hematopathologists appreciate all aspects of ALL diagnosis and disease monitoring. This review covers the salient aspects of recent advances in the biology of ALL and evaluation of MRD, placing emphasis on how this information may ultimately be used to improve risk stratification and, as a result, patient outcomes.

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.

The indicative effect of Notch1 expression for the prognosis of T-cell acute lymphocytic leukemia: a systematic review

To explore the relationship of Notch1 mutation in T-ALL with the survival rate of T-ALL patients. The PubMed database, the Cochrane Library, conference proceedings, EMBASE databases, and references of published trials and review articles were searched. Two reviewers independently assessed the quality of the trials and extracted data. Hazard ratios (HRs) for event-free survival (EFS) were pooled by STATA package. Seven trials involving 964 patients with T-ALL were ultimately analyzed. Seven hundred and eleven patients were children (age <18 years), 253 patients were adults (age ≥18 years). The pooled HR showed that Notch1 mutated group could not prolong EFS than Notch1 WT group both in children and adult patients. Although constitutively activated forms of the NOTCH1 receptor are potent inducers of T-ALL, our results suggest that Notch1 mutation could not become an indicator for EFS in T-ALL.

Impact of complex NOTCH1 mutations on survival in paediatric T-cell leukaemia

Background

Molecular alterations occur frequently in T-ALL and the potential impact of those abnormalities on outcome is still controversial. The current study aimed to test whether NOTCH1 mutations and additional molecular abnormalities would impact T-ALL outcome in a series of 138 T-ALL paediatric cases.

Methods

T-ALL subtypes, status of SIL-TAL1 fusion, ectopic expression of TLX3, and mutations in FBXW7, KRAS, PTEN and NOTCH1 were assessed as overall survival (OS) and event-free survival (EFS) prognostic factors. OS and EFS were determined using the Kaplan-Meier method and compared using the log-rank test.

Results

The frequencies of mutations were 43.5% for NOTCH1, while FBXW7, KRAS and PTEN exhibited frequencies of 19.1%, 9.5% and 9.4%, respectively. In 78.3% of cases, the coexistence of NOTCH1 mutations and other molecular alterations was observed. In multivariate analysis no statistical association was revealed between NOTCH1 mutations and any other variable analyzed. The mean length of the follow-up was 68.4 months and the OS was 50.7%. SIL-TAL1 was identified as an adverse prognostic factor. NOTCH1 mutation status was not associated with outcome, while the presence of NOTCH1 complex mutations (indels) were associated with a longer overall survival (p = 0.031) than point mutations.

Conclusion

NOTCH1 mutations alone or in combination with FBXW7 did not impact T-ALL prognosis. Nevertheless, complex NOTCH1 mutations appear to have a positive impact on OS and the SIL-TAL1 fusion was validated as a negative prognostic marker in our series of T-ALL.

Recent advances on NOTCH signaling in T-ALL

NOTCH1 receptor signaling plays a central role in T-cell lineage specification and in supporting the growth and proliferation of immature T-cell progenitors in the thymus during lymphoid development. In T-cell acute lymphoblastic leukemia (T-ALL), a tumor resulting from the malignant transformation of T-cell progenitors, aberrant and constitutively active NOTCH1 signaling triggered by activating mutations in the NOTCH1 gene contributes to oncogenic transformation and is a hallmark of this disease. Most notably, small molecule γ-secretase inhibitors (GSIs) can effectively block NOTCH1 signaling in T-ALL, and could be exploited as a targeted therapy in this disease. In addition, a number of emerging anti-NOTCH therapeutic strategies including anti-NOTCH1 inhibitory antibodies, small peptide inhibitors of NOTCH signaling and combination therapies with GSIs and glucocorticoids, have recently been proposed. Finally, the identification of NOTCH1 mutations in solid tumors and chronic lymphocytic leukemias has increased even further the clinical relevance of NOTCH signaling as a therapeutic target in human cancer. Here we review our current understanding of NOTCH1-induced transformation, the mechanisms of action of oncogenic NOTCH1 in T-ALL and the therapeutic and prognostic implications of NOTCH1 mutations in T-ALL.

T-cell acute lymphoblastic leukaemia: recent molecular biology findings

For many years, T-cell acute lymphoblastic leukaemia (T-ALL) has been considered and treated as a single malignancy, but divergent outcomes in T-ALL patients receiving uniform treatment protocols encouraged intensive research on the molecular biology of this disease. Recent findings in the field demonstrate that T-ALL is much more heterogeneous than originally believed and extremely diverse outcomes of patients require refinement of T-ALL classification, leading to subtype-specific adjustment of treatment. Many different biological features of T-ALL blast cells have recently been found to contribute to disease development and patient outcome and their analysis could potentially be introduced into improved diagnostics and classification of the disease. This review focuses on five key issues of T-ALL biology: chromosome aberrations, gene expression profiles, gene mutations, DNA methylation patterns, and immunoglobulin/T cell receptor (Ig/TCR) gene rearrangements. Additionally, molecular monitoring of minimal residual disease, by far the most reliable independent prognostic factor in T-ALL, has been highlighted in the context of Ig/TCR gene rearrangements. Translation of this biological information into better prognostic classification and more effective treatment should lead to improvement of outcome in T-ALL patients.

Current views on the role of Notch signaling and the pathogenesis of human leukemia

The Notch signaling pathway is highly conserved from Drosophila to humans and plays an important role in the regulation of cellular proliferation, differentiation and apoptosis.Constitutive activation of Notch signaling has been shown to result in excessive cellular proliferation and a wide range of malignancies, including leukemia, glioblastoma and lung and breast cancers. Notch can also act as a tumor suppressor, and its inactivation has been associated with an increased risk of spontaneous squamous cell carcinoma. This minireview focuses on recent advances related to the mechanisms and roles of activated Notch1, Notch2, Notch3 and Notch4 signaling in human lymphocytic leukemia, myeloid leukemia and B cell lymphoma, as well as their significance, and recent advances in Notch-targeted therapies.

Notch-ing from T-cell to B-cell lymphoid malignancies

Notch receptors are transmembrane proteins critically determining cell fate and maintenance of progenitor cells in many developmental systems. Notch signaling is involved in stem cell self-renewal and regulates the main functions of cell life at different levels of development: cell proliferation, differentiation and apoptosis. By virtue of its involvement in the regulation of cell physiology, it is not surprising that a deregulation of the Notch pathway leads to the development of different tumors. In this review, we critically discuss the latest findings concerning Notch roles in hematologic oncology, with a special focus on T-cell acute lymphoblastic leukemia and B-cell malignancies. We also describe the molecular mediators of Notch-driven oncogenic effects and the current pharmacological approaches targeting Notch signaling.

T-cell lymphoblastic lymphoma shows differences and similarities with T-cell acute lymphoblastic leukemia by genomic and gene expression analyses

T-cell acute lymphoblastic leukemia (T-ALL) and lymphoma (T-LBL) share common morphological and immunophenotypic features and are treated with similar therapeutic approaches. Nonetheless, they show distinct clinical presentations, suggesting that they may represent two different biological entities. To investigate the genetic characteristics of T-LBL and T-ALL, we used genomic and transcriptional profiling approaches. Genome-wide gene expression profiling, performed on 20 T-LBL and 10 T-ALL diagnostic specimens, revealed that the two malignancies shared a large fraction of their transcriptional profile while a subset of genes appeared to be differentially expressed in T-LBL versus T-ALL. This signature included genes involved in chemotactic responses and angiogenesis, which may play a role in tumor cell localization. Genome-wide copy number alteration analysis was performed on a subset of the samples analyzed by gene expression profiling and detected 41 recurrently altered genetic loci. Although most aberrations were found in both entities, several were selectively identified in T-LBL or T-ALL. In addition, NOTCH1 mutational status was found to correlate with a subset of genetic aberrations. Taken together, these results suggest that T-LBL and T-ALL are indeed two distinct diseases with unique transcriptional and genetic characteristics.

Posttranscriptional deregulation of MYC via PTEN constitutes a major alternative pathway of MYC activation in T-cell acute lymphoblastic leukemia

Cumulative evidence indicates that MYC, one of the major downstream effectors of NOTCH1, is a critical component of T-cell acute lymphoblastic leukemia (T-ALL) oncogenesis and a potential candidate for targeted therapy. However, MYC is a complex oncogene, involving both fine protein dosage and cell-context dependency, and detailed understanding of MYC-mediated oncogenesis in T-ALL is still lacking. To better understand how MYC is interspersed in the complex T-ALL oncogenic networks, we performed a thorough molecular and biochemical analysis of MYC activation in a comprehensive collection of primary adult and pediatric patient samples. We find that MYC expression is highly variable, and that high MYC expression levels can be generated in a large number of cases in absence of NOTCH1/FBXW7 mutations, suggesting the occurrence of multiple activation pathways in addition to NOTCH1. Furthermore, we show that posttranscriptional deregulation of MYC constitutes a major alternative pathway of MYC activation in T-ALL, operating partly via the PI3K/AKT axis through down-regulation of PTEN, and that NOTCH1(m) might play a dual transcriptional and posttranscriptional role in this process. Altogether, our data lend further support to the significance of therapeutic targeting of MYC and/or the PTEN/AKT pathways, both in GSI-resistant and identified NOTCH1-independent/MYC-mediated T-ALL patients.

Fbxw7β resides in the endoplasmic reticulum membrane and protects cells from oxidative stress

Oxidative stress has been implicated in cancer initiation and progression. Fbxw7 (also known as Fbw7, SEL-10, hCdc4, or hAgo) is the F-box protein subunit of an Skp1-Cul1-F-box (SCF)-type ubiquitin ligase complex that plays a central role in the degradation of oncoproteins such as c-Myc, c-Jun, Notch, and cyclin E. Fbxw7 is therefore thought to function as a tumor suppressor, and indeed the Fbxw7 gene is frequently mutated in many human malignancies. The Fbxw7 gene locus encodes three protein isoforms: Fbxw7α, Fbxw7β, and Fbxw7γ. Whereas Fbxw7α and Fbxw7γ are resident in the nucleus, Fbxw7β shows a cytoplasmic distribution suggestive of localization to the endoplasmic reticulum (ER). The specific function of Fbxw7β has remained unknown, however. We now show that Fbxw7β contains a putative transmembrane domain near its NH(2) -terminus, and topological analysis revealed that Fbxw7β is inserted in the ER membrane. Fbxw7β assembled with Skp1, Cul1, and Rbx1 to form an SCF complex, although the efficiency of this process appeared lower than that for Fbxw7α or Fbxw7γ. To explore the physiological role of Fbxw7β, we generated mice specifically lacking this isoform of Fbxw7. Although these animals did not exhibit any apparent abnormalities in development, primary cultures of neurons prepared from the mutant mice were more vulnerable to oxidative stress than were those prepared from wild-type mice. Conversely, overexpression of Fbxw7β rendered cells resistant to oxidative stress, without affecting sensitivity to ER stress or other apoptosis-inducing agents. Our results thus suggest that Fbxw7β contributes to the protection of cells from oxidative stress.

NOTCH1 mutation in a female with myeloid/NK cell precursor acute leukemia

A 6-year-old Japanese female was diagnosed as having myeloid/NK cell precursor acute leukemia (MNKL) using immunocytochemical analysis. The patient was treated by cord blood transplantation from an HLA 1-locus mismatched unrelated donor after chemotherapy comprising cytosine arabinoside, idarubicin, etoposide, and L-asparaginase. We detected a nonsense mutation, C7412A, resulting in S2471X, where X is a terminal codon, in the PEST domain of NOTCH1 in this patient. The presence of the NOTCH1 activating mutation in MNKL might suggest a possible role in the leukemogenesis of MNKL.

Inactivation of FBXW7/hCDC4-β expression by promoter hypermethylation is associated with favorable prognosis in primary breast cancer

INTRODUCTION

Mutational inactivation of the FBXW7/hCDC4 tumor suppressor gene (TSG) is common in many cancer types, but infrequent in breast cancers. This study investigates the presence and impact of FBXW7/hCDC4 promoter methylation in breast cancer.

METHODS

FBXW7/hCDC4-β expression and promoter methylation was assessed in 161 tumors from two independent breast cancer cohorts. Associations between methylation status and clinicopathologic characteristics were assessed by Fisher's exact test. Survival was analyzed using the Kaplan-Meier method in addition to modeling the risk by use of a multivariate proportional hazard (Cox) model adjusting for possible confounders of survival.

RESULTS

Methylation of the promoter and loss of mRNA expression was found both in cell lines and primary tumors (43% and 51%, respectively). Using Cox modeling, a trend was found towards decreased hazard ratio (HR) for death in women with methylation of FBXW7/hCDC4-β in both cohorts (HR 0.53 (95% CI 0.23 to 1.23) and HR 0.50 (95% CI 0.23 to 1.08), respectively), despite an association between methylation and high-grade tumors (P = 0.017). Interestingly, in subgroups of patients whose tumors are p53 mutated or lymph-node positive, promoter methylation identified patients with significantly improved survival (P = 0.048 and P = 0.017, respectively).

CONCLUSIONS

We demonstrate an alternative mechanism for inactivation of the TSG FBXW7/hCDC4, namely promoter specific methylation. Importantly, in breast cancer, methylation of FBXW7/hCDC4-β is related to favorable prognosis despite its association with poorly differentiated tumors. Future work may define whether FBXW7/hCDC4 methylation is a biomarker of the response to chemotherapy and a target for epigenetic modulation therapy.

Notch signalling in T-cell lymphoblastic leukaemia/lymphoma and other haematological malignancies

Notch receptors participate in a highly conserved signalling pathway that regulates normal development and tissue homeostasis in a context- and dose-dependent manner. Deregulated Notch signalling has been implicated in many diseases, but the clearest example of a pathogenic role is found in T-cell lymphoblastic leukaemia/lymphoma (T-LL), in which the majority of human and murine tumours have acquired mutations that lead to aberrant increases in Notch1 signalling. Remarkably, it appears that the selective pressure for Notch mutations is virtually unique among cancers to T-LL, presumably reflecting a special context-dependent role for Notch in normal T-cell progenitors. Nevertheless, there are some recent reports suggesting that Notch signalling has subtle, yet important roles in other forms of haematological malignancy as well. Here, we review the role of Notch signalling in various blood cancers, focusing on T-LL with an eye towards targeted therapeutics.

Molecular pathogenesis and targeted therapies for NOTCH1-induced T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic tumor resulting from the malignant transformation of immature T-cell progenitors. Originally associated with a dismal prognosis, the outcome of T-ALL patients has improved remarkably over the last two decades as a result of the introduction of intensified chemotherapy protocols. However, these treatments are associated with significant acute and long-term toxicities, and the treatment of patients presenting with primary resistant disease or those relapsing after a transient response remains challenging. T-ALL is a genetically heterogeneous disease in which numerous chromosomal and genetic alterations cooperate to promote the aberrant proliferation and survival of leukemic lymphoblasts. However, the identification of activating mutations in the NOTCH1 gene in over 50% of T-ALL cases has come to define aberrant NOTCH signaling as a central player in this disease. Therefore, the NOTCH pathway represents an important potential therapeutic target. In this review, we will update our current understanding of the molecular basis of T-ALL, with a particular focus on the role of the NOTCH1 oncogene and the development of anti-NOTCH1 targeted therapies for the treatment of this disease.

T-lymphoblastic lymphoma cells express high levels of BCL2, S1P1, and ICAM1, leading to a blockade of tumor cell intravasation

The molecular events underlying the progression of T-lymphoblastic lymphoma (T-LBL) to acute T-lymphoblastic leukemia (T-ALL) remain elusive. In our zebrafish model, concomitant overexpression of bcl-2 with Myc accelerated T-LBL onset while inhibiting progression to T-ALL. The T-LBL cells failed to invade the vasculature and showed evidence of increased homotypic cell-cell adhesion and autophagy. Further analysis using clinical biopsy specimens revealed autophagy and increased levels of BCL2, S1P1, and ICAM1 in human T-LBL compared with T-ALL. Inhibition of S1P1 signaling in T-LBL cells led to decreased homotypic adhesion in vitro and increased tumor cell intravasation in vivo. Thus, blockade of intravasation and hematologic dissemination in T-LBL is due to elevated S1P1 signaling, increased expression of ICAM1, and augmented homotypic cell-cell adhesion.

The favorable effect of activating NOTCH1 receptor mutations on long-term outcome in T-ALL patients treated on the ALL-BFM 2000 protocol can be separated from FBXW7 loss of function

Precursor T-cell acute lymphoblastic leukemia (T-ALL) remains an important challenge in pediatric oncology. Because of the particularly poor prognosis of relapses, it is vital to identify molecular risk factors allowing early and effective treatment stratification. Activating NOTCH1 mutations signify a favorable prognosis in patients treated on ALL–BFM protocols. We have now tested if NOTCH pathway activation at different steps has similar clinical effects and if multiple mutations in this pathway function synergistically. Analysis of a validation set of 151 T-ALL patients and of the total cohort of 301 patients confirms the low relapse rate generally and the overall favorable effect of activating NOTCH1 mutations. Subgroup analysis shows that the NOTCH1 effect in ALL–BFM is restricted to patients with rapid early treatment response. Inactivation of the ubiquitin ligase FBXW7 is associated with rapid early treatment response and synergizes with NOTCH1 receptor activation. However, the effect of FBXW7 inactivation is separable from NOTCH1 activation by not synergizing with NOTCH1 mutations in predicting favorable long-term outcome, which can probably be explained by the interaction of FBXW7 with other clients. Finally, the comparison with other European protocols suggests that the NOTCH effect is treatment dependent generally and may depend on the intensity of central nervous system-directed therapy specifically.

NOTCH1 and/or FBXW7 mutations predict for initial good prednisone response but not for improved outcome in pediatric T-cell acute lymphoblastic leukemia patients treated on DCOG or COALL protocols

Aberrant activation of the NOTCH1 pathway by inactivating and activating mutations in NOTCH1 or FBXW7 is a frequent phenomenon in T-cell acute lymphoblastic leukemia (T-ALL). We retrospectively investigated the relevance of NOTCH1/FBXW7 mutations for pediatric T-ALL patients enrolled on Dutch Childhood Oncology Group (DCOG) ALL7/8 or ALL9 or the German Co-Operative Study Group for Childhood Acute Lymphoblastic Leukemia study (COALL-97) protocols. NOTCH1-activating mutations were identified in 63% of patients. NOTCH1 mutations affected the heterodimerization, the juxtamembrane and/or the PEST domains, but not the RBP-J-κ-associated module, the ankyrin repeats or the transactivation domain. Reverse-phase protein microarray data confirmed that NOTCH1 and FBXW7 mutations resulted in increased intracellular NOTCH1 levels in primary T-ALL biopsies. Based on microarray expression analysis, NOTCH1/FBXW7 mutations were associated with activation of NOTCH1 direct target genes including HES1, DTX1, NOTCH3, PTCRA but not cMYC. NOTCH1/FBXW7 mutations were associated with TLX3 rearrangements, but were less frequently identified in TAL1- or LMO2-rearranged cases. NOTCH1-activating mutations were less frequently associated with mature T-cell developmental stage. Mutations were associated with a good initial in vivo prednisone response, but were not associated with a superior outcome in the DCOG and COALL cohorts. Comparing our data with other studies, we conclude that the prognostic significance for NOTCH1/FBXW7 mutations is not consistent and may depend on the treatment protocol given.

Gene expression profiling identifies a subset of adult T-cell acute lymphoblastic leukemia with myeloid-like gene features and over-expression of miR-223

BACKGROUND

Until recently, few molecular aberrations were recognized in acute lymphoblastic leukemia of T-cell origin; novel lesions have recently been identified and a certain degree of overlap between acute myeloid leukemia and T-cell acute lymphoblastic leukemia has been suggested. To identify novel T-cell acute lymphoblastic leukemia entities, gene expression profiling was performed and clinico-biological features were studied.

DESIGN AND METHODS

Sixty-nine untreated adults with T-cell acute lymphoblastic leukemia were evaluated by oligonucleotide arrays: unsupervised and supervised analyses were performed. The up-regulation of myeloid genes and miR-223 expression were validated by quantitative polymerase chain reaction analysis.

RESULTS

Using unsupervised clustering, we identified five subgroups. Of these, one branch included seven patients whose gene expression profile resembled that of acute myeloid leukemia. These cases were characterized by over-expression of a large set of myeloid-related genes for surface antigens, transcription factors and granule proteins. Real-time quantitative polymerase chain reaction analysis confirmed over-expression of MPO, CEBPA, CEBPB, GRN and IL8. We, therefore, evaluated the expression levels of miR-223, involved in myeloid differentiation: these cases had significantly higher levels of miR-223 than had the other cases of T-cell acute lymphoblastic leukemia, with values comparable to those observed in acute myeloid leukemia. Finally, these patients appear to have an unfavorable clinical course.

CONCLUSIONS

Using gene profiling we identified a subset of adult T-cell acute lymphoblastic leukemia, accounting for 10% of the cases analyzed, which displays myeloid features. These cases were not recognized by standard approaches, underlining the importance of gene profiling in identifying novel acute leukemia subsets. The recognition of this subgroup may have clinical, prognostic and therapeutic implications.

Paediatric lymphoblastic T-cell leukaemia and lymphoma: one or two diseases?

There is ongoing discussion on whether paediatric acute T-cell lymphoblastic leukaemia (T-ALL) and paediatric lymphoblastic T-cell lymphoma (T-LBL) are two distinct entities or whether they represent two variant manifestations of one and the same disease and the distinction is arbitrary. Both show overlapping clinical, morphological and immunophenotypic features. Many clinical trials use the amount of blast infiltration of the bone marrow as the sole criterion to distinguish between T-ALL and T-LBL. The current World Health Organization classification designates both malignancies as T lymphoblastic leukaemia/lymphoma. However, subtle immunophenotypic, molecular and cytogenetic differences suggest that T-ALL and T-LBL might be biologically different in certain aspects. The current review summarizes and discusses the recent advances and understanding of the molecular profile of paediatric T-ALL and T-LBL.

The role of NOTCH1 signaling in T-ALL

The identification of activating mutations in NOTCH1 in over 50% of T-cell acute lymphoblastic leukemias (T-ALL) has generated major interest in the elucidation of the mechanisms of transformation downstream of oncogenic NOTCH and in the targeting of the NOTCH signaling pathway in this disease. Small molecule gamma-secretase inhibitors (GSIs) block NOTCH1 signaling in T-ALL lymphoblasts, yet the clinical development of GSIs has been held back by the development of gastrointestinal toxicity and their weak antileukemic effects against human T-ALL. However, new therapeutic strategies aiming to optimize the use of anti-NOTCH1 therapies for T-ALL, including combination therapies with molecularly targeted drugs and glucocorticoids, have started to emerge as a result of improved understanding of the molecular mechanisms that mediate the effects of GSIs in leukemic cells and the intestinal epithelium. This review focuses on the molecular basis of NOTCH1-induced transformation, the mechanisms of action of oncogenic NOTCH1 and clinical significance of NOTCH1 mutations in T-ALL.