Molecular characterization and clinical outcome of B-cell precursor acute lymphoblastic leukemia with IG-MYC rearrangement.

Rarely, immunophenotypically immature B-cell precursor acute lymphoblastic leukemia (BCP-ALL) carries an immunoglobulin- MYC rearrangement (IG-MYC-r). This can result in diagnostic confusion with Burkitt lymphoma/leukemia and use of individualized treatment schedules of unproven efficacy. Here we compare the molecular characteristics of these conditions and investigate historic clinical outcome data. We identified 90 cases registered in a national BCP-ALL clinical trial/registry. When present, diagnostic material underwent cytogenetic, exome, methylome and transcriptome analyses. The outcomes analyzed were 3-year event-free survival and overall survival. IG-MYC-r was identified in diverse cytogenetic backgrounds, co-existing with either established BCP-ALL-specific abnormalities (high hyperdiploidy, n=3; KMT2A-rearrangement, n=6; iAMP21, n=1; BCR-ABL1, n=1); BCL2/BCL6-rearrangements (n=15); or, most commonly, as the only defining feature (n=64). Within this final group, precursor-like V(D)J breakpoints predominated (8/9) and KRAS mutations were common (5/11). DNA methylation identified a cluster of V(D)J-rearranged cases, clearly distinct from Burkitt leukemia/lymphoma. Children with IG-MYC-r within that subgroup had a 3-year event-free survival of 47% and overall survival of 60%, representing a high-risk BCP-ALL. To develop effective management strategies this group of patients must be allowed access to contemporary, minimal residual disease-adapted, prospective clinical trial protocols.

Phase II-like murine trial identifies synergy between dexamethasone and dasatinib in T-cell acute lymphoblastic leukemia.

T-cell Acute Lymphoblastic Leukemia (T-ALL) is frequently characterized by glucocorticoid (GC) resistance, which is associated with inferior outcomes, thus highlighting the need for novel therapeutic approaches for GC resistant T-ALL. The pTCR/TCR signaling pathways play a critical role in cell fate decisions during physiological thymocyte development, with an interplay between TCR and glucocorticoid receptor (GR) signaling determining the T-lymphocyte selection process. We performed an shRNA screen in vitro and in vivo in T-ALL cell lines and patient derived xenograft (PDX) samples to identify vulnerabilities in the pTCR/TCR pathway and identified a critical role for the kinase LCK in cell proliferation. LCK knockdown or inhibition with dasatinib (DAS) caused cell cycle arrest. Combination of DAS with dexamethasone (DEX) resulted in significant drug synergy leading to cell death. The efficacy of this drug combination was underscored in a randomized phase II-like murine trial, recapitulating an early phase human clinical trial. T-ALL expansion in immunocompromised mice was significantly impaired using this drug combination, relative to mice receiving control vehicle or single drug treatment, highlighting the immediate clinical relevance of this drug combination for high risk T-ALL patients. Our results thus provide a strategy to improve the efficacy of current chemotherapy platforms and circumvent GC resistance.

Glucocorticoids and selumetinib are highly synergistic in RAS pathway-mutated childhood acute lymphoblastic leukemia through upregulation of BIM.

New drugs are needed for the treatment of relapsed acute lymphoblastic leukemia and preclinical evaluation of the MEK inhibitor, selumetinib, has shown that this drug has excellent activity in those leukemias with RAS pathway mutations. The proapoptotic protein, BIM is pivotal in the induction of cell death by both selumetinib and glucocorticoids, suggesting the potential for synergy. Thus, combination indices for dexamethasone and selumetinib were determined in RAS pathway-mutated acute lymphoblastic leukemia primagraft cells in vitro and were indicative of strong synergism (combination index <0.2; n=5). Associated pharmacodynamic assays were consistent with the hypothesis that the drug combination enhanced BIM upregulation over that achieved by a single drug alone. Dosing of dexamethasone and selumetinib singly and in combination in mice engrafted with primary-derived RAS pathway-mutated leukemia cells resulted in a marked reduction in spleen size which was significantly greater with the drug combination. Assessment of the central nervous system leukemia burden showed a significant reduction in the drug-treated mice, with no detectable leukemia in those treated with the drug combination. These data suggest that a selumetinib-dexamethasone combination may be highly effective in RAS pathway-mutated acute lymphoblastic leukemia. An international phase I/II clinical trial of dexamethasone and selumetinib (Seludex trial) is underway in children with multiply relapsed/refractory disease.

Allogeneic hematopoietic cell transplantation in Farber disease.

BACKGROUND: Farber disease (FD) is a rare, lysosomal storage disorder caused by deficient acid ceramidase activity. FD has long been considered a fatal disorder with death in the first three decades of life resulting either from respiratory insufficiency as a consequence of airway involvement or from progressive neurodegeneration because of nervous system involvement. Peripheral symptoms associated with FD, including inflammatory joint disease, have been described to improve relatively rapidly after hematopoietic cell transplantation (HCT). AIMS: To evaluate the disease-specific status and limitations in the long-term follow-up after HCT, investigate genotype/phenotype correlations and the benefit of allogeneic HCT in FD patients with nervous system involvement. PATIENTS AND METHODS: Transplant- and disease-related information of ten FD patients was obtained by using a questionnaire, physicians' letters and additional telephone surveys. ASAH1 gene mutations were identified to search for genotype/phenotype correlations. RESULTS: After mainly busulfan-based preparative regimens, all patients engrafted with one late graft loss. The inflammatory symptoms resolved completely in all patients. Abnormal neurologic findings were present pre-transplant in 4/10 patients, post-transplant in 6/10 patients. Mutational analyses revealed new mutations in the ASAH1 gene and a broad diversity of phenotypes without a genotype/phenotype correlation. With a median follow-up of 10.4 years, overall survival was 80% with two transplant-related deaths. CONCLUSION: Allogeneic HCT leads to complete and persistent resolution of the inflammatory aspects in FD patients. It appears to have no beneficial effect on progression of nervous system involvement. New mutations in the acid ceramidase gene were identified. A genotype/phenotype correlation could not be established.

The ability to cross the blood-cerebrospinal fluid barrier is a generic property of acute lymphoblastic leukemia blasts.

Prevention of central nervous system (CNS) relapse is critical for cure of childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Despite this, mechanisms of CNS infiltration are poorly understood, and the timing, frequency, and properties of BCP-ALL blasts entering the CNS compartment are unknown. We investigated the CNS-engrafting potential of BCP-ALL cells xenotransplanted into immunodeficient NOD.Cg- ITALIC! Prkdc (ITALIC! scid) ITALIC! Il2rg (ITALIC! tm1Wjl)/SzJ mice. CNS engraftment was seen in 23 of 29 diagnostic samples (79%): 2 of 2 from patients with overt CNS disease and 21 of 27 from patients thought to be CNS negative by diagnostic lumbar puncture. Histologic findings mimic human pathology and demonstrate that leukemic cells transit the blood-cerebrospinal fluid barrier situated close to the dural sinuses, the site of recently discovered CNS lymphatics. Retrieval of blasts from the CNS showed no evidence for chemokine receptor-mediated selective trafficking. The high frequency of infiltration and lack of selective trafficking led us to postulate that CNS tropism is a generic property of leukemic cells. To test this, we performed serial dilution experiments which showed CNS engraftment in 5 of 6 mice after transplant of as few as 10 leukemic cells. Clonal tracking techniques confirmed the polyclonal nature of CNS-infiltrating cells, with multiple clones engrafting in both the CNS and periphery. Overall, these findings suggest that subclinical seeding of the CNS is likely to be present in most BCP-ALL patients at original diagnosis, and efforts to prevent CNS relapse should concentrate on effective eradication of disease from this site rather than targeting entry mechanisms.

Accelerating drug development in pediatric cancer: a novel Phase I study design of venetoclax in relapsed/refractory malignancies.

Venetoclax is a highly selective, potent BCL-2 inhibitor that is approved for some patients previously treated for chronic lymphocytic leukemia, and has shown promising activity in adult studies across several hematologic malignancies. Preclinical studies have demonstrated venetoclax activity in pediatric patient-derived xenograft models and cell lines; however, clinical studies in pediatric patients have yet to be conducted. The prognosis is poor for children with most relapsed/refractory malignancies, and limited treatment options result in unmet clinical need. Herein, we describe the rationale and design of the first study of venetoclax in pediatric patients with relapsed/refractory malignancies: a Phase I trial investigating the safety and pharmacokinetics of venetoclax monotherapy followed by the addition of chemotherapy (Trial registration: EudraCT 2017-000439-14; NCT03236857).

From class waivers to precision medicine in paediatric oncology.

New drugs are crucially needed for children with cancer. The European Paediatric Regulation facilitates paediatric class waivers for drugs developed for diseases only occurring in adults. In this Review, we retrospectively searched oncology drugs that were class waivered between June, 2012, and June, 2015. 147 oncology class waivers were confirmed for 89 drugs. Mechanisms of action were then assessed as potential paediatric therapeutic targets by both a literature search and an expert review. 48 (54%) of the 89 class-waivered drugs had a mechanisms of action warranting paediatric development. Two (2%) class-waivered drugs were considered not relevant and 16 (18%) required further data. In light of these results, we propose five initiatives: an aggregated database of paediatric biological tumour drug targets; molecular profiling of all paediatric tumours at diagnosis and relapse; a joint academic-pharmaceutical industry preclinical platform to help analyse the activity of new drugs (Innovative Therapy for Children with Cancer Paediatric Preclinical Proof-of-Concept Platform); paediatric strategy forums; and the suppression of article 11b of the European Paediatric Regulation, which allows product-specific waivers on the grounds that the associated condition does not occur in children. These initiatives and a mechanism of action-based approach to drug development will accelerate the delivery of new therapeutic drugs for front-line therapy for those children who have unmet medical needs.

A population pharmacokinetic model of AT9283 in adults and children to predict the maximum tolerated dose in children with leukaemia.

AIMS: AT9283 is used to treat patients with solid tumours and patients with leukaemia. However, the maximum tolerated dose (MTD) for children with leukaemia remains unknown due to early termination of the Phase I trial. The aim of this study was to develop a population model of AT9283 to describe the pharmacokinetics in adults and children and to estimate the MTD in children with leukaemia. METHODS: Data from Phase I dose-escalation studies in adults and children were used to build a population pharmacokinetic model (NONMEM v7.3). Potential covariates investigated included body weight, body surface area (BSA), glomerular filtration rate (GFR), age and sex. Model-derived area under the concentration-time curve was used to investigate the relationship between dose and exposure in adults and children. RESULTS: The plasma concentrations of AT9283 (n = 1770) from 92 patients (53 adults, 39 children) were used to build a two-compartment model with all pharmacokinetic parameters scaled using body weight. Renal function (GFR), but not BSA, was a significant covariate for the clearance of AT9283. In children with leukaemia (median weight 16 kg), a flat dose of 500 mg 72 h-1 provided similar drug exposures at the MTD as the adult population. The estimated MTD for children with leukaemia, therefore, is 30 mg kg-1  72 h-1 . CONCLUSION: For adults, GFR was a significant predictor of clearance, whilst body-weight based dosing was more useful than BSA in determining the drug exposure in children. The MTD was estimated to be 30 mg kg-1  72 h-1 children with leukaemia.

Ras pathway mutations are prevalent in relapsed childhood acute lymphoblastic leukemia and confer sensitivity to MEK inhibition.

For most children who relapse with acute lymphoblastic leukemia (ALL), the prognosis is poor, and there is a need for novel therapies to improve outcome. We screened samples from children with B-lineage ALL entered into the ALL-REZ BFM 2002 clinical trial (www.clinicaltrials.gov, #NCT00114348) for somatic mutations activating the Ras pathway (KRAS, NRAS, FLT3, and PTPN11) and showed mutation to be highly prevalent (76 from 206). Clinically, they were associated with high-risk features including early relapse, central nervous system (CNS) involvement, and specifically for NRAS/KRAS mutations, chemoresistance. KRAS mutations were associated with a reduced overall survival. Mutation screening of the matched diagnostic samples found many to be wild type (WT); however, by using more sensitive allelic-specific assays, low-level mutated subpopulations were found in many cases, suggesting that they survived up-front therapy and subsequently emerged at relapse. Preclinical evaluation of the mitogen-activated protein kinase kinase 1/2 inhibitor selumetinib (AZD6244, ARRY-142886) showed significant differential sensitivity in Ras pathway-mutated ALL compared with WT cells both in vitro and in an orthotopic xenograft model engrafted with primary ALL; in the latter, reduced RAS-mutated CNS leukemia. Given these data, clinical evaluation of selumetinib may be warranted for Ras pathway-mutated relapsed ALL.

CD19: A multifunctional immunological target molecule and its implications for Blineage acute lymphoblastic leukemia.

Over the last 20-30 years CD19 has gained attention as a potential target in the therapy of B-cell malignancies. In particular, targeting CD19 with the bispecific T-cell engager (BiTE) antibody Blinatumomab and T-cells modified by chimeric antigen receptors (CAR) has shown promising efficacy in early phase clinical trials for adults and children with precursor B-cell ALL (BCP-ALL). This review will discuss the rationale behind targeting CD19 in BCP-ALL and its potential importance in BCP-ALL signaling pathways.

Casitas B lymphoma mutations in childhood acute lymphoblastic leukemia.

Casitas B-lineage lymphoma (CBL) proteins are RING finger ubiquitin E3 ligases that attenuate the signaling of receptor tyrosine kinases and are mutated in a number of myeloid disorders. In this study, mutational screening of the linker-RING domains of CBL and CBLB was performed by denaturing high performance liquid chromatography in a cohort of diagnostic (n = 180) or relapse (n = 46) samples from children with acute lymphoblastic leukemia. Somatic mutations were identified in three children, giving an overall incidence of 1.7% and involved small deletions affecting the intron/exon boundaries of exon 8, leading to skipping of exon 8 and abolishing E3 ligase function. Mutated primary samples were associated with constitutive activation of the RAS pathway and sensitivity to MEK inhibitors was shown. Thus, mutation of CBL is an alternative route to activate the RAS pathway and may identify children who are candidates for MEK inhibitor clinical trials.

Novel Adaption of the SARC-F Score to Classify Pediatric Hemato-Oncology Patients with Functional Sarcopenia.

Sarcopenia in pediatric hemato-oncology patients is undesirable because of the consequences it may have for treatment continuation and outcome, physical abilities and participation in daily life. An easy-to-use screening tool for sarcopenia will facilitate the identification of children at risk who need interventions to prevent serious physical deterioration. In the elderly, the use of the SARC-F score as a case-finding tool for sarcopenia is recommended. The aim of this cross-sectional study was to investigate the accuracy of the pediatric SARC-F (PED-SARC-F) for identifying sarcopenia in pediatric hemato-oncology patients, including the determination of a cut-off point for clinical use. Patients 3−20 years of age, under active treatment or within 12 months after treatment cessation were eligible. Patients had a physiotherapy assessment including a PED-SARC-F (0−10) and measurements of muscle strength (handheld dynamometry), physical performance (various tests) and/or muscle mass (bio-impedance analysis), as part of the standard of care. Spearman's correlation coefficient (rs) between the PED-SARC-F and physiotherapy outcomes were calculated. Structural sarcopenia was defined as low appendicular skeletal muscle mass (ASMM) in combination with low muscle strength and/or low physical performance. Functional sarcopenia indicated low muscle strength combined with low physical performance. Multiple logistic regression models were estimated to study the associations between the PED-SARC-F and structural/functional sarcopenia. To evaluate which cut-off point provides the most accurate classification, the area under the receiver operating characteristic curve (AUCs), sensitivity and specificity per point were calculated. In total, 215 assessments were included, 62% were performed in boys and the median age was 12.9 years (interquartile range: 8.5−15.8). The PED-SARC-F scores correlated moderately with the measurements of muscle strength (rs = −0.37 to −0.47, p < 0.001) and physical performance (rs = −0.45 to −0.66, p < 0.001), and weakly with ASMM (rs = −0.27, p < 0.001). The PED-SARC-F had an AUC of 0.90 (95% confidence interval (CI) = 0.84−0.95) for functional sarcopenia and 0.79 (95% CI = 0.68−0.90) for structural sarcopenia. A cut-off point of ≥5 had the highest specificity of 96% and a sensitivity of 74%. In conclusion, we adapted the SARC-F to a pediatric version, confirmed its excellent diagnostic accuracy for identifying functional sarcopenia and defined a clinically useful cut-off point in pediatric hemato-oncology patients.

Have we made progress in taking care of adolescents and young adults with cancer? Results of a European multi-professional survey.

BACKGROUND: It is well documented that traditional health care models do not meet the specific needs of Adolescents and Young Adults (AYA) cancer patients. METHODS: We explore a map of the development of age-specific AYA cancer care across Europe, from the perspective of healthcare professionals with an interest in AYA care, in order to understand the specific challenges and map progress over time. An on-line survey was developed by international professional cancer organisations. RESULTS: We had 377 respondents from 60 countries. The majority of respondents were physicians 298 (79%), a minority of survey respondents (39, 10.4%) work exclusively with AYA patients, most respondents declared substantial and routine clinical service collaborations to provide care and treatment to AYA with cancer. Policy for the multidisciplinary management of AYA cancer patients commonly appears in Europe now, and was reported by 234 (78.52%) respondents. Specific professional training for AYA cancer care is not uniformly available. CONCLUSION: There is considerable opportunity for many organisations to work together in raising the profile of AYA cancer related issues, in providing education and in encouraging research and collaboration.

The role of matched sibling donor allogeneic stem cell transplantation in pediatric high-risk acute myeloid leukemia: results from the AML-BFM 98 study.

BACKGROUND: The role of allogeneic stem cell transplantation in post-remission management of children with high-risk acute myeloid leukemia remains controversial. In the multi-center AML-BFM 98 study we prospectively evaluated the impact of allogeneic stem cell transplantation in children with high-risk acute myeloid leukemia in first complete remission. DESIGN AND METHODS: HLA-typed patients with high-risk acute myeloid leukemia, who achieved first complete remission (n = 247), were included in this analysis. All patients received double induction and consolidation. Based on the availability of a matched-sibling donor, patients were allocated by genetic chance to allogeneic stem cell transplantation (n = 61) or chemotherapy-only (i.e. intensification and maintenance therapy; n = 186). The main analysis was done on an intention-to-treat basis according to this allocation. RESULTS: Intention-to-treat analysis did not show a significantly different 5-year disease-free survival (49 ± 6% versus 45 ± 4%, P(log rank) = 0.44) or overall survival (68 ± 6% versus 57 ± 4%, P(log rank) = 0.17) between the matched-sibling donor and no-matched-sibling donor groups, whereas late adverse effects occurred more frequently after allogeneic stem cell transplantation (72.5% versus 31.8%, P(Fischer)<0.01). These results were confirmed by as-treated analysis corrected for the time until transplantation (5-year overall survival: 72 ± 8% versus 60 ± 4%, P(Mantel-Byar) 0.21). Subgroup analysis demonstrated improved survival rates for patients with 11q23 aberrations allocated to allogeneic stem cell transplantation (5-year overall survival: 94 ± 6% versus 52 ± 7%, P(log-rank) = 0.01; n = 18 versus 49) in contrast to patients without 11q23 aberrations (5-year overall survival: 58 ± 8% versus 55 ± 5%, P(log-rank) = 0.66). CONCLUSIONS: Our analyses defined a genetic subgroup of children with high-risk acute myeloid leukemia who benefited from allogeneic stem cell transplantation in the prospective multi-center AML-BFM 98 study. For the remainder of the pediatric high-risk acute myeloid leukemia patients the prognosis was not improved by allogeneic stem cell transplantation, which was, however, associated with a higher rate of late sequelae.

Selumetinib in combination with dexamethasone for the treatment of relapsed/refractory RAS-pathway mutated paediatric and adult acute lymphoblastic leukaemia (SeluDex): study protocol for an international, parallel-group, dose-finding with expansion phase I/II trial.

INTRODUCTION: Event-free survival rates at 15 years for paediatric patients with relapsed/refractory acute lymphoblastic leukaemia (ALL) are 30%-50%, with 5-year survival for adult patients only 20%. Many patients with newly diagnosed and relapsed ALL harbour somatic RAS-signalling activation mutations. Induction therapy for ALL involves steroids, with preclinical data suggesting the combination of dexamethasone with the MEK1/2 inhibitor, selumetinib (ARRY-142886) has a synergistic anticancer effect. METHODS AND ANALYSIS: The SeluDex trial is an international, parallel-group, dose-finding with expansion, phase I/II trial to assess the selumetinib/dexamethasone combination in adult and paediatric patients with relapsed/refractory, RAS pathway mutant ALL. The Cancer Research UK Clinical Trials Unit at University of Birmingham is the UK Coordinating Centre, with national hubs in Copenhagen, Denmark; Monza, Italy; Münster, Germany; Paris, France; and Utrecht, Netherlands. Patients with morphologically proven relapsed/refractory or progressive B-cell precursor or T-cell ALL, with demonstrated RAS pathway activating mutations are eligible. Adult patients are >18 years old, ECOG <2 and paediatric <18 years old, Lansky play scale ≥60% or Karnofsky score ≥60%. Phase I primary objective is the recommended phase II dose of selumetinib as defined by occurrence/non-occurrence of dose limiting toxicities using the continual reassessment method; phase II will evaluate preliminary antileukaemic activity of the combination, as defined by morphological response 28 days post-treatment using a Bayesian approach. Target recruitment is between 26 and 42 patients (minimum 13 and maximum 21 per group), depending the number of phase I patients included in phase II. ETHICS AND DISSEMINATION: Medical ethical committees of all the participating countries have approved the study protocol; initial (UK) ethics approval (17/YH/0123) was granted by Yorkshire & The Humber-Leeds West Research Ethics Committee. Participants are required to provide written informed consent/assent. Results will be disseminated through national and international presentations and peer-reviewed publications. TRIAL REGISTRATION NUMBER: ISRCTN92323261.

Targeted inhibitors and antibody immunotherapies: Novel therapies for paediatric leukaemia and lymphoma.

Despite improved outcomes achieved in the last decades for children with newly diagnosed leukaemia and lymphoma, treatment of patients with refractory/relapsed disease remains a challenge. The cure rate is still unsatisfactory and often achieved at the cost of significant morbidity. Exploring treatment with novel agents should offer less toxic therapeutic options, without compromising efficacy. Bispecific and antibody-drug conjugates targeting CD19 and CD22 (blinatumomab and inotuzumab ozogamicin) play an important role in the treatment of relapsed and refractory B-cell precursor acute lymphoblastic leukaemia (BCP-ALL); antibodies targeting CD123 and CD38 are also under investigation for acute myeloid leukaemia (AML) and T-ALL, respectively. Targeted therapy with small molecules is of primary importance for specific genetic subtypes, such as BCR-ABL-positive ALL, FLT3-ITD AML and anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma. KMT2A-directed targeted therapy with menin inhibitors holds promise to be of relevance in KMT2A-rearranged leukaemias, known to have dismal prognosis. Target inhibition in cellular pathways such as BCL-2, RAS, MEK, Bruton's tyrosine kinase, JAK-STAT or CDK4/CDK6 inhibition may be suitable for different diseases with common mutated pathways. Nevertheless, development and approval of new agents for paediatric cancers lags behind adult therapeutic options. New regulations were implemented to accelerate drug development for children. Considering the number of oncology medicinal products available for adults and the rarity of paediatric cancers, prioritisation based on scientific evidence and medical need, as well as international collaboration, is critical. Herein, we review the current status of drug development for children with leukaemia and lymphoma, excluding cellular therapy despite its well-known significance.

hiPSC-derived bone marrow milieu identifies a clinically actionable driver of niche-mediated treatment resistance in leukemia.

Leukemia cells re-program their microenvironment to augment blast proliferation and enhance treatment resistance. Means of clinically targeting such niche-driven treatment resistance remain ambiguous. We develop human induced pluripotent stem cell (hiPSC)-engineered niches to reveal druggable cancer-niche dependencies. We reveal that mesenchymal (iMSC) and vascular niche-like (iANG) hiPSC-derived cells support ex vivo proliferation of patient-derived leukemia cells, affect dormancy, and mediate treatment resistance. iMSCs protect dormant and cycling blasts against dexamethasone, while iANGs protect only dormant blasts. Leukemia proliferation and protection from dexamethasone-induced apoptosis is dependent on cancer-niche interactions mediated by CDH2. Consequently, we test CDH2 antagonist ADH-1 (previously in Phase I/II trials for solid tumors) in a very aggressive patient-derived xenograft leukemia mouse model. ADH-1 shows high in vivo efficacy; ADH-1/dexamethasone combination is superior to dexamethasone alone, with no ADH-1-conferred additional toxicity. These findings provide a proof-of-concept starting point to develop improved, potentially safer therapeutics targeting niche-mediated cancer dependencies in blood cancers.

MAPK-ERK is a central pathway in T-cell acute lymphoblastic leukemia that drives steroid resistance.

(Patho-)physiological activation of the IL7-receptor (IL7R) signaling contributes to steroid resistance in pediatric T-cell acute lymphoblastic leukemia (T-ALL). Here, we show that activating IL7R pathway mutations and physiological IL7R signaling activate MAPK-ERK signaling, which provokes steroid resistance by phosphorylation of BIM. By mass spectrometry, we demonstrate that phosphorylated BIM is impaired in binding to BCL2, BCLXL and MCL1, shifting the apoptotic balance toward survival. Treatment with MEK inhibitors abolishes this inactivating phosphorylation of BIM and restores its interaction with anti-apoptotic BCL2-protein family members. Importantly, the MEK inhibitor selumetinib synergizes with steroids in both IL7-dependent and IL7-independent steroid resistant pediatric T-ALL PDX samples. Despite the anti-MAPK-ERK activity of ruxolitinib in IL7-induced signaling and JAK1 mutant cells, ruxolitinib only synergizes with steroid treatment in IL7-dependent steroid resistant PDX samples but not in IL7-independent steroid resistant PDX samples. Our study highlights the central role for MAPK-ERK signaling in steroid resistance in T-ALL patients, and demonstrates the broader application of MEK inhibitors over ruxolitinib to resensitize steroid-resistant T-ALL cells. These findings strongly support the enrollment of T-ALL patients in the current phase I/II SeluDex trial (NCT03705507) and contributes to the optimization and stratification of newly designed T-ALL treatment regimens.

Flow minimal residual disease monitoring of candidate leukemic stem cells defined by the immunophenotype, CD34+CD38lowCD19+ in B-lineage childhood acute lymphoblastic leukemia.

Flow cytometric minimal residual disease (MRD) monitoring could become more powerful if directed towards the disease-maintaining leukemic stem cell (LSC) compartment. Using a cohort of 48 children with B-lineage acute lymphoblastic leukemia (ALL), we sought the newly proposed candidate-LSC population, CD34(+)CD38(low)CD19(+), at presentation and in end of induction bone marrow samples. We identified the candidate LSC population in 60% of diagnostic samples and its presence correlated with expression of CD38, relative to that of normal B-cell progenitors. In addition, the candidate LSC was not detectable in all MRD positive samples. The absence of the population in 40% of diagnostic and 40% of MRD positive samples does not support the use of this phenotype as a generic biomarker to track LSCs and suggests that this phenotype may be an artifact of CD38 underexpression rather than a biologically distinct LSC population. ClinicalTrials.gov Identifier: NCT00222612.

The Oncogenic Transcription Factor RUNX1/ETO Corrupts Cell Cycle Regulation to Drive Leukemic Transformation.

Oncogenic transcription factors such as the leukemic fusion protein RUNX1/ETO, which drives t(8;21) acute myeloid leukemia (AML), constitute cancer-specific but highly challenging therapeutic targets. We used epigenomic profiling data for an RNAi screen to interrogate the transcriptional network maintaining t(8;21) AML. This strategy identified Cyclin D2 (CCND2) as a crucial transmitter of RUNX1/ETO-driven leukemic propagation. RUNX1/ETO cooperates with AP-1 to drive CCND2 expression. Knockdown or pharmacological inhibition of CCND2 by an approved drug significantly impairs leukemic expansion of patient-derived AML cells and engraftment in immunodeficient murine hosts. Our data demonstrate that RUNX1/ETO maintains leukemia by promoting cell cycle progression and identifies G1 CCND-CDK complexes as promising therapeutic targets for treatment of RUNX1/ETO-driven AML.