MEK inhibition is a promising therapeutic strategy for MLL-rearranged infant acute lymphoblastic leukemia patients carrying RAS mutations

Glucocorticoid Therapy in Acute Lymphoblastic Leukemia: Navigating Short-Term and Long-Term Effects and Optimal Regimen Selection

PURPOSE OF REVIEW

Glucocorticoids are a mainstay in acute lymphoblastic leukemia treatment and lack of early response is predictive for overall disease prognosis. Given the vital position of glucocorticoids and well known long and short-term side effects associated with differing glucocorticoids, we aim to highlight the wide breadth of historical and more contemporary data to describe the current landscape of glucocorticoid use in this arena.

RECENT FINDINGS

Emerging studies aim to overcome issues such as steroid resistance and to optimize the antileukemic effects of glucocorticoids while aiming to mitigate the risks and side effects associated with their exposure. Glucocorticoids have and likely always will be a fundamental component of acute lymphoblastic leukemia treatment and understanding how to navigate short- and long-term effects and how to optimize regimens is at the heart of continued treatment success.

Advances in molecular characterization of pediatric acute megakaryoblastic leukemia not associated with Down syndrome; impact on therapy development

Acute megakaryoblastic leukemia (AMKL) is a rare subtype of acute myeloid leukemia (AML) in which leukemic blasts have megakaryocytic features. AMKL makes up 4%-15% of newly diagnosed pediatric AML, typically affecting young children (less than 2 years old). AMKL associated with Down syndrome (DS) shows GATA1 mutations and has a favorable prognosis. In contrast, AMKL in children without DS is often associated with recurrent and mutually exclusive chimeric fusion genes and has an unfavorable prognosis. This review mainly summarizes the unique features of pediatric non-DS AMKL and highlights the development of novel therapies for high-risk patients. Due to the rarity of pediatric AMKL, large-scale multi-center studies are needed to progress molecular characterization of this disease. Better disease models are also required to test leukemogenic mechanisms and emerging therapies.

Potential clinical use of azacitidine and MEK inhibitor combination therapy in PTPN11-mutated juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML) is a rare myeloproliferative neoplasm of childhood. The molecular hallmark of JMML is hyperactivation of the Ras/MAPK pathway with the most common cause being mutations in the gene PTPN11, encoding the protein tyrosine phosphatase SHP2. Current strategies for treating JMML include using the hypomethylating agent, 5-azacitidine (5-Aza) or MEK inhibitors trametinib and PD0325901 (PD-901), but none of these are curative as monotherapy. Utilizing an Shp2E76K/+ murine model of JMML, we show that the combination of 5-Aza and PD-901 modulates several hematologic abnormalities often seen in JMML patients, in part by reducing the burden of leukemic hematopoietic stem and progenitor cells (HSC/Ps). The reduced JMML features in drug-treated mice were associated with a decrease in p-MEK and p-ERK levels in Shp2E76K/+ mice treated with the combination of 5-Aza and PD-901. RNA-sequencing analysis revealed a reduction in several RAS and MAPK signaling-related genes. Additionally, a decrease in the expression of genes associated with inflammation and myeloid leukemia was also observed in Shp2E76K/+ mice treated with the combination of the two drugs. Finally, we report two patients with JMML and PTPN11 mutations treated with 5-Aza, trametinib, and chemotherapy who experienced a clinical response because of the combination treatment.

Updates in infant acute lymphoblastic leukemia and the potential for targeted therapy

Outcomes for infants diagnosed under 1 year of age with KMT2A-rearranged acute lymphoblastic leukemia (ALL) have remained stagnant over the past 20 years. Successive treatment protocols have previously focused on intensification of conventional chemotherapy, but increased treatment-related toxicity and chemoresistance have led to a plateau in survival. We have now entered an era of immunotherapy with integration of agents, such as blinatumomab or chimeric antigen receptor T-cell therapy, into the standard chemotherapy backbone, showing significant promise for improving the dismal outcomes for this disease. There remains much optimism for the future as a wealth of preclinical studies have identified additional novel targeted agents, such as venetoclax or menin inhibitors, ready for incorporation into treatment, providing further ammunition to combat this aggressive disease. In contrast, infants with KMT2A-germline ALL have demonstrated excellent survival outcomes with current therapy, but there remains a high burden of treatment-related morbidity. Greater understanding of the underlying blast genetics for infants with KMT2A-germline ALL and incorporation of immunotherapeutic approaches may enable a reduction in the intensity of chemotherapy while maintaining the excellent outcomes.

Activation of the mitogen-activated protein kinase-extracellular signal-regulated kinase pathway in childhood B-cell acute lymphoblastic leukemia

RAS mutations are frequently observed in childhood B-cell acute lymphoblastic leukemia (B-ALL) and previous studies have yielded conflicting results as to whether they are associated with a poor outcome. We and others have demonstrated that the mitogen-activated protein kinase-extracellular signal-regulated kinase (MAPK) pathway can be activated through epigenetic mechanisms in the absence of RAS pathway mutations. Herein, we examined whether MAPK activation, as determined by measuring phosphorylated extracellular signal-regulated kinase (pERK) levels in 80 diagnostic patient samples using phosphoflow cytometry, could be used as a prognostic biomarker for pediatric B-ALL. The mean fluorescence intensity of pERK (MFI) was measured at baseline and after exogenous stimulation with or without pretreatment with the mitogen-activated protein kinase kinase (MEK) inhibitor trametinib. Activation levels (MFI stimulated/MFI baseline) ranged from 0.76 to 4.40 (median = 1.26), and inhibition indexes (MFI stimulated/MFI trametinib stimulated) ranged from 0.439 to 5.640 (median = 1.30), with no significant difference between patients with wildtype versus mutant RAS for either. Logistic regression demonstrated that neither MAPK activation levels nor RAS mutation status at diagnosis alone or in combination was prognostic of outcome. However, 35% of RAS wildtype samples showed MAPK inhibition indexes greater than the median, thus raising the possibility that therapeutic strategies to inhibit MAPK activation may not be restricted to patients whose blasts display Ras pathway defects.

The first Japanese biobank of patient-derived pediatric acute lymphoblastic leukemia xenograft models

A lack of practical resources in Japan has limited preclinical discovery and testing of therapies for pediatric relapsed and refractory acute lymphoblastic leukemia (ALL), which has poor outcomes. Here, we established 57 patient-derived xenografts (PDXs) in NOD.Cg-Prkdc^scid ll2rg^tm1Sug /ShiJic (NOG) mice and created a biobank by preserving PDX cells including 3 extramedullary relapsed ALL PDXs. We demonstrated that our PDX mice and PDX cells mimicked the biological features of relapsed ALL and that PDX models reproduced treatment-mediated clonal selection. Our PDX biobank is a useful scientific resource for capturing drug sensitivity features of pediatric patients with ALL, providing an essential tool for the development of targeted therapies.

Advanced Molecular Characterisation in Relapsed and Refractory Paediatric Acute Leukaemia, the Key for Personalised Medicine

Relapsed and refractory (R/r) disease in paediatric acute leukaemia remains the first reason for treatment failure. Advances in molecular characterisation can ameliorate the identification of genetic biomarkers treatment strategies for this disease, especially in high-risk patients. The purpose of this study was to analyse a cohort of R/r children diagnosed with acute lymphoblastic (ALL) or myeloid (AML) leukaemia in order to offer them a targeted treatment if available. Advanced molecular characterisation of 26 patients diagnosed with R/r disease was performed using NGS, MLPA, and RT-qPCR. The clinical relevance of the identified alterations was discussed in a multidisciplinary molecular tumour board (MTB). A total of 18 (69.2%) patients were diagnosed with B-ALL, 4 (15.4%) with T-ALL, 3 (11.5%) with AML and 1 patient (3.8%) with a mixed-phenotype acute leukaemia (MPL). Most of the patients had relapsed disease (88%) at the time of sample collection. A total of 17 patients (65.4%) were found to be carriers of a druggable molecular alteration, 8 of whom (47%) received targeted therapy, 7 (87.5%) of them in addition to hematopoietic stem cell transplantation (HSCT). Treatment response and disease control were achieved in 4 patients (50%). In conclusion, advanced molecular characterisation and MTB can improve treatment and outcome in paediatric R/r acute leukaemias.

Overcoming Steroid Resistance in Pediatric Acute Lymphoblastic Leukemia-The State-of-the-Art Knowledge and Future Prospects

Acute lymphoblastic leukemia (ALL) is the most common malignancy among children. Despite the enormous progress in ALL therapy, resulting in achieving a 5-year survival rate of up to 90%, the ambitious goal of reaching a 100% survival rate is still being pursued. A typical ALL treatment includes three phases: remission induction and consolidation and maintenance, preceded by a prednisone prephase. Poor prednisone response (PPR) is defined as the presence of ≥1.0 × 10⁹ blasts/L in the peripheral blood on day eight of therapy and results in significantly frequent relapses and worse outcomes. Hence, identifying risk factors of steroid resistance and finding methods of overcoming that resistance may significantly improve patients' outcomes. A mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK-ERK) pathway seems to be a particularly attractive target, as its activation leads to steroid resistance via a phosphorylating Bcl-2-interacting mediator of cell death (BIM), which is crucial in the steroid-induced cell death. Several mutations causing activation of MAPK-ERK were discovered, notably the interleukin-7 receptor (IL-7R) pathway mutations in T-cell ALL and rat sarcoma virus (Ras) pathway mutations in precursor B-cell ALL. MAPK-ERK pathway inhibitors were demonstrated to enhance the results of dexamethasone therapy in preclinical ALL studies. This report summarizes steroids' mechanism of action, resistance to treatment, and prospects of steroids therapy in pediatric ALL.

Reactive Oxygen Species in Acute Lymphoblastic Leukaemia: Reducing Radicals to Refine Responses

Acute lymphoblastic leukaemia (ALL) is the most common cancer diagnosed in children and adolescents. Approximately 70% of patients survive >5-years following diagnosis, however, for those that fail upfront therapies, survival is poor. Reactive oxygen species (ROS) are elevated in a range of cancers and are emerging as significant contributors to the leukaemogenesis of ALL. ROS modulate the function of signalling proteins through oxidation of cysteine residues, as well as promote genomic instability by damaging DNA, to promote chemotherapy resistance. Current therapeutic approaches exploit the pro-oxidant intracellular environment of malignant B and T lymphoblasts to cause irreversible DNA damage and cell death, however these strategies impact normal haematopoiesis and lead to long lasting side-effects. Therapies suppressing ROS production, especially those targeting ROS producing enzymes such as the NADPH oxidases (NOXs), are emerging alternatives to treat cancers and may be exploited to improve the ALL treatment. Here, we discuss the roles that ROS play in normal haematopoiesis and in ALL. We explore the molecular mechanisms underpinning overproduction of ROS in ALL, and their roles in disease progression and drug resistance. Finally, we examine strategies to target ROS production, with a specific focus on the NOX enzymes, to improve the treatment of ALL.

Adult Acute Myeloid Leukemia with the KMT2A-Mixed Lineage Leukemia T10 Fusion: An Analysis of 10 Cases Showed Common Features and Frequent Mutations in the RAS Signaling Pathway

Mixed lineage leukemia (MLL) T10 is a relatively rare partner for the KMT2A lysine (K)-specific methyltransferase 2A gene. The common features and coexisting mutations of acute myeloid leukemia (AML) patients with KMT2A-MLLT10 remain unknown. In this study, 10 adult AML patients with KMT2A-MLLT10 fusions were picked up from 496 AML patients by using RT-polymerase chain reaction (PCR) and/or fluorescence in situ hybridization, and then screened for mutations in the 49 genes panel with next-generation sequencing and PCR, followed by direct Sanger sequencing. Of the 10 unique individuals identified, 6 were male and 4 were female (M:F ratio, 1.5:1) with ages ranging from 19 to 52 years (median 39.5 years). Most (90%, 9/10) patients with KMT2A-MLLT10 were accompanied by additional mutations. Twelve mutated genes were detected, averaging 2.1 mutations per patient (range, 0-4). The most frequently mutated gene was NRAS (n = 5). Clinical and laboratory data pointed to common features: French American British-M5 subtype (n = 7), a high rate of relapse, and biomarkers CD33 (n = 10), CD117 (n = 9), CD13 (n = 8), and CD64 (n = 8). Overall, most patients harbored at least one mutation. A high incidence of mutations affecting the RAS signaling pathway or RAS regulating components was found in 50% (5/10) patients. The overall survival is about 12.0 months. Allogeneic-hematopoietic stem cell transplantation trends to improve survival in selected patients.

A Combined Antitumor Strategy Mediated by a New Targeted Nanosystem to Hepatocellular Carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the main causes of cancer-related death. Sorafenib, which is the first-line therapy for this disease, is associated with reduced therapeutic efficacy that could potentially be overcome by combination with selumetinib. In this context, the main goal of this work was to develop a new nanosystem, composed of a polymeric core coated by a lipid bilayer containing the targeting ligand GalNAc, to specifically and efficiently co-deliver both drugs into HCC cells, in order to significantly increase their therapeutic efficacy.

METHODS

The physicochemical characterization of hybrid nanosystems (HNP) and their components was performed by dynamic light scattering, zeta potential, matrix-assisted laser desorption ionization - time of flight mass spectroscopy, and transmission electron microscopy. Cellular binding, uptake and specificity of HNP were evaluated through flow cytometry and confocal microscopy. The therapeutic activity was evaluated namely through: cell viability by the Alamar Blue assay; cell death by flow cytometry using FITC-Annexin V; caspases activity by luminescence; mitochondrial membrane potential by flow cytometry; and molecular target levels by Western blot.

RESULTS

The obtained data show that these hybrid nanosystems present high stability and loading capacity of both drugs, and suitable physicochemical properties, namely in terms of size and surface charge. Moreover, the generated formulation allows to circumvent drug resistance and presents high specificity, promoting great cell death levels in HCC cells, but not in non-tumor cells. This potentiation of the antitumor effect of co-loaded drugs was carried out by an increased programmed cell death, being associated with a strong reduction in the mitochondrial membrane potential, a significant increase in the activity of caspases 3/7 and caspase 9, and much greater number of annexin V-positive cells.

CONCLUSION

The developed formulation resulted in a high and synergistic antitumor effect, revealing a translational potential to improve therapeutic approaches against HCC.

Redox Control in Acute Lymphoblastic Leukemia: From Physiology to Pathology and Therapeutic Opportunities

Acute lymphoblastic leukemia (ALL) is a hematological malignancy originating from B- or T-lymphoid progenitor cells. Recent studies have shown that redox dysregulation caused by overproduction of reactive oxygen species (ROS) has an important role in the development and progression of leukemia. The application of pro-oxidant therapy, which targets redox dysregulation, has achieved satisfactory results in alleviating the conditions of and improving the survival rate for patients with ALL. However, drug resistance and side effects are two major challenges that must be addressed in pro-oxidant therapy. Oxidative stress can activate a variety of antioxidant mechanisms to help leukemia cells escape the damage caused by pro-oxidant drugs and develop drug resistance. Hematopoietic stem cells (HSCs) are extremely sensitive to oxidative stress due to their low levels of differentiation, and the use of pro-oxidant drugs inevitably causes damage to HSCs and may even cause severe bone marrow suppression. In this article, we reviewed research progress regarding the generation and regulation of ROS in normal HSCs and ALL cells as well as the impact of ROS on the biological behavior and fate of cells. An in-depth understanding of the regulatory mechanisms of redox homeostasis in normal and malignant HSCs is conducive to the formulation of rational targeted treatment plans to effectively reduce oxidative damage to normal HSCs while eradicating ALL cells.

Clinical diagnostics and treatment strategies for Philadelphia chromosome-like acute lymphoblastic leukemia

Philadelphia chromosome-like B-cell acute lymphoblastic leukemia (Ph-like ALL) accounts for 15% to 30% of B-cell acute lymphoblastic leukemia in older children, adolescents, and adults and is associated with high rates of conventional treatment failure and relapse. Current clinical trials are assessing the efficacy of the addition of tyrosine kinase inhibitors (TKIs) to chemotherapy for children and adults with Ph-like ALL harboring ABL class translocations or CRLF2 rearrangements and other JAK pathway alterations. However, real-time diagnosis of patients can be quite challenging given the genetic heterogeneity of this disease and the often cytogenetically cryptic nature of Ph-like ALL-associated alterations. In this review, we discuss the complex biologic and clinical features of Ph-like ALL across the age spectrum, available diagnostic testing modalities, and current clinical treatment strategies for these high-risk patients. We further propose a practical and step-wise approach to Ph-like ALL genetic testing to facilitate the identification and allocation of patients to appropriate clinical trials of TKI-based therapies or commercially available drugs. Although the majority of patients with Ph-like ALL can be successfully identified via current clinical assays by the end of induction chemotherapy, increasing diagnostic efficiency and sensitivity and decreasing time to test resulting will facilitate earlier therapeutic intervention and may improve clinical outcomes for these high-risk patients.

Combinatorial efficacy of entospletinib and chemotherapy in patient-derived xenograft models of infant acute lymphoblastic leukemia

Survival of infants with KMT2A-rearranged acute lymphoblastic leukemia (ALL) remains dismal despite intensive chemotherapy. We observed constitutive phosphorylation of spleen tyrosine kinase (SYK) and associated signaling proteins in infant ALL patient-derived xenograft (PDX) model specimens and hypothesized that the SYK inhibitor entospletinib would inhibit signaling and cell growth in vitro and leukemia proliferation in vivo. We further predicted that combined entospletinib and chemotherapy could augment anti-leukemia effects. Basal kinase signaling activation and HOXA9/MEIS1 expression differed among KMT2Arearranged (KMT2A-AFF1 [n=4], KMT2A-MLLT3 [n=1], KMT2A-MLLT1 [n=4]) and non-KMT2A-rearranged [n=3] ALL specimens and stratified by genetic subgroup. Incubation of KMT2A-rearranged ALL cells in vitro with entospletinib inhibited methylcellulose colony formation and SYK pathway signaling in a dose-dependent manner. In vivo inhibition of leukemia proliferation with entospletinib monotherapy was observed in RAS-wild-type KMT2A-AFF1, KMT2A-MLLT3, and KMT2A-MLLT1 ALL PDX models with enhanced activity in combination with vincristine chemotherapy in several models. Surprisingly, entospletinib did not decrease leukemia burden in two KMT2A-AFF1 PDX models with NRAS or KRAS mutations, suggesting potential RAS-mediated resistance to SYK inhibition. As hypothesized, superior inhibition of ALL proliferation was observed in KMT2A-AFF1 PDX models treated with entospletinib and the MEK inhibitor selumetinib versus vehicle or inhibitor monotherapies (P<0.05). In summary, constitutive activation of SYK and associated signaling occurs in KMT2A-rearranged ALL with in vitro and in vivo sensitivity to entospletinib. Combination therapy with vincristine or selumetinib further enhanced treatment effects of SYK inhibition. Clinical study of entospletinib and chemotherapy or other kinase inhibitors in patients with KMT2A-rearranged leukemias may be warranted.

Targeting critical kinases and anti-apoptotic molecules overcomes steroid resistance in MLL-rearranged leukaemia

BACKGROUND

Acute lymphoblastic leukaemia with mixed lineage leukaemia gene rearrangement (MLL-ALL) frequently affects infants and is associated with a poor prognosis. Primary refractory and relapsed disease due to resistance to glucocorticoids (GCs) remains a substantial hurdle to improving clinical outcomes. In this study, we aimed to overcome GC resistance of MLL-ALL.

METHODS

Using leukaemia patient specimens, we performed bioinformatic analyses to identify target genes/pathways. To test inhibition of target pathways in vivo, we created pre-clinical therapeutic mouse patient-derived xenograft (PDX)-models by transplanting human MLL-ALL leukaemia initiating cells (LIC) into immune-deficient NSG mice. Finally, we conducted B-cell lymphoma-2 (BCL-2) homology domain 3 (BH3) profiling to identify BH3 peptides responsible for treatment resistance in MLL-leukaemia.

FINDINGS

Src family kinases (SFKs) and Fms-like tyrosine kinase 3 (FLT3) signaling pathway were over-represented in MLL-ALL cells. PDX-models of infant MLL- ALL recapitulated GC-resistance in vivo but RK-20449, an inhibitor of SFKs and FLT3 eliminated human MLL-ALL cells in vivo, overcoming GC-resistance. Further, we identified BCL-2 dependence as a mechanism of treatment resistance in MLL-ALL through BH3 profiling. Furthermore, MLL-ALL cells resistant to RK-20449 treatment were dependent on the anti-apoptotic BCL-2 protein for their survival. Combined inhibition of SFKs/FLT3 by RK-20449 and of BCL-2 by ABT-199 led to substantial elimination of MLL-ALL cells in vitro and in vivo. Triple treatment combining GCs, RK-20449 and ABT-199 resulted in complete elimination of MLL-ALL cells in vivo.

INTERPRETATION

SFKs/FLT3 signaling pathways are promising targets for treatment of treatment-resistant MLL-ALL. Combined inhibition of these kinase pathways and anti-apoptotic BCL-2 successfully eliminated highly resistant MLL-ALL and demonstrated a new treatment strategy for treatment-resistant poor-outcome MLL-ALL.

FUNDING

This study was supported by RIKEN (RIKEN President's Discretionary Grant) for FI, Japan Agency for Medical Research and Development (the Basic Science and Platform Technology Program for Innovative Biological Medicine for FI and by NIH CA034196 for LDS. The funders had no role in the study design, data collection, data analysis, interpretation nor writing of the report.

Targeting the Ras pathway in pediatric hematologic malignancies

PURPOSE OF REVIEW

Ras pathway mutations are one of the most common type of alterations in pediatric hematologic malignancies and are frequently associated with adverse outcomes. Despite ongoing efforts to use targeted treatments, there remain no Food and Drug Administration (FDA)-approved medications specifically for children with Ras pathway-mutated leukemia. This review will summarize the role of Ras pathway mutations in pediatric leukemia, discuss the current state of Ras pathway inhibitors and highlight the most promising agents currently being evaluated in clinical trials.

RECENT FINDINGS

Efficacy using RAF and MEK inhibitors has been demonstrated across multiple solid and brain tumors, and these are now considered standard-of-care for certain tumor types in adults and children. Clinical trials are now testing these medications for the first time in pediatric hematologic disorders, such as acute lymphoblastic leukemia, juvenile myelomonocytic leukemia, and histiocytic disorders. Novel inhibitors of the Ras pathway, including direct RAS inhibitors, are also being tested in clinical trials across a spectrum of pediatric and adult malignancies.

SUMMARY

Activation of the Ras pathway is a common finding in pediatric hematologic neoplasms. Implementation of precision medicine with a goal of improving outcomes for these patients will require testing of Ras pathway inhibitors in combination with other drugs in the context of current and future clinical trials.

T-cell Acute Lymphoblastic Leukemia: A Roadmap to Targeted Therapies

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy characterized by aberrant proliferation of immature thymocytes. Despite an overall survival of 80% in the pediatric setting, 20% of patients with T-ALL ultimately die from relapsed or refractory disease. Therefore, there is an urgent need for novel therapies. Molecular genetic analyses and sequencing studies have led to the identification of recurrent T-ALL genetic drivers. This review summarizes the main genetic drivers and targetable lesions of T-ALL and gives a comprehensive overview of the novel treatments for patients with T-ALL that are currently under clinical investigation or that are emerging from preclinical research.

SIGNIFICANCE

T-ALL is driven by oncogenic transcription factors that act along with secondary acquired mutations. These lesions, together with active signaling pathways, may be targeted by therapeutic agents. Bridging research and clinical practice can accelerate the testing of novel treatments in clinical trials, offering an opportunity for patients with poor outcome.

MLL-Rearranged Acute Lymphoblastic Leukemia

PURPOSE OF REVIEW

Rearrangements of the histone lysine [K]-MethylTransferase 2A gene (KMT2A) gene on chromosome 11q23, formerly known as the mixed-lineage leukemia (MLL) gene, are found in 10% and 5% of adult and children ALL cases, respectively. The most common translocated genes are AFF1 (formerly AF4), MLLT3 (formerly AF9), and MLLT1 (formerly ENL). The bimodal incidence of MLL-r-ALL usually peaks in infants in their first 2 years of life and then declines thereafter during the pediatric/young adult phase until it increases again with age. MLL-rearranged ALL (MLL-r-ALL) is characterized by hyperleukocytosis, aggressive behavior with early relapse, relatively high incidence of central nervous system (CNS) involvement, and poor prognosis.

RECENT FINDINGS

MLL-r-ALL cells are characterized by relative resistance to corticosteroids (due to Src kinase-induced phosphorylation of annexin A2) and L-asparaginase therapy, but they are sensitive to cytarabine chemotherapy (due to increased levels of hENT1 expression). Potential therapeutic targets include FLT3 inhibitors, MEK inhibitors, HDAC inhibitors, BCL-2 inhibitors, MCL-1 inhibitors, proteasome inhibitors, hypomethylating agents, Dot1L inhibitors, and CDK inhibitors. In this review, we discuss MLL-r-ALL focusing on clinical presentation, risk stratification, drug resistance, and treatment strategies, including potential novel therapeutic targets.

Decitabine mildly attenuates MLL-rearranged acute lymphoblastic leukemia in vivo, and represents a poor chemo-sensitizer

MLL-rearranged acute lymphoblastic leukemia (ALL) represents a highly aggressive ALL subtype, characterized by aberrant DNA methylation patterns. DNA methyltransferase inhibitors, such as decitabine have previously been demonstrated to be effective in eradicating MLL-rearranged ALL cells in vitro. Here, we assessed the in vivo anti-leukemic potential of low-dose DNA methyltransferase inhibitor decitabine using a xenograft mouse model of human MLL-rearranged ALL. Furthermore, we explored whether prolonged exposure to low-dose decitabine could chemo-sensitize MLL-rearranged ALL cells toward conventional chemotherapy as well as other known epigenetic-based and anti-neoplastic compounds. Our data reveal that decitabine prolonged survival in xenograft mice of MLL-rearranged ALL by 8.5 days (P = .0181), but eventually was insufficient to prevent leukemia out-growth, based on the examination of the MLLAF4 cell line SEM. Furthermore, we observe that prolonged pretreatment of low-dose decitabine mildly sensitized toward the conventional drugs prednisolone, vincristine, daunorubicin, asparaginase, and cytarabine in a panel of MLL-rearranged cell lines. Additionally, we assessed synergistic effects of decitabine with other epigenetic-based or anticancer drugs using high-throughput drug library screens. Validation of the top hits, including histone deacetylase inhibitor panobinostat, BCL2 inhibitor Venetoclax, MEK inhibitor pimasertib, and receptor tyrosine kinase foretinib, revealed additive and moderate synergistic effects for the combination of each drug together with decitabine in a cell line-dependent manner.

MLLT10 rearranged acute leukemia: Incidence, prognosis, and possible therapeutic strategies

Rearrangements of the MLLT10 gene occur in acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL), most commonly T-lineage ALL (T-ALL), in patients of all ages. MLLT10 rearranged (MLLT10r) acute leukemia presents a complex diagnostic and therapeutic challenge due to frequent presentation of immature or mixed phenotype, and a lack of consensus regarding optimal therapy. Cases of MLLT10r AML or T-ALL bearing immature phenotype are at high risk of poor outcome, but the underlying molecular mechanisms and sensitivity to targeted therapies remain poorly characterized. This review addresses the incidence and prognostic significance of MLLT10r in acute leukemia, and how the aberrant gene expression profile of this disease can inform potential targeted therapeutic strategies. Understanding the underlying genomics of MLLT10r acute leukemia, both clinically and molecularly, will improve prognostic stratification and accelerate the development of targeted therapeutic strategies, to improve patient outcomes.

Pathogenesis of pediatric B-cell acute lymphoblastic leukemia: Molecular pathways and disease treatments

B-cell acute lymphoblastic lymphoma (B-ALL) is a disease found mainly in children and in young adults. B-ALL is characterized by the rapid proliferation of poorly differentiated lymphoid progenitor cells inside the bone marrow. In the United States, ~4,000 of these patients are diagnosed each year, accounting for ~30% of childhood cancer types. The tumorigenesis of the disease involves a number of abnormal gene expressions (including TEL-AML1, BCR-ABL-1, RAS and PI3K) leading to dysregulated cell cycle. Risk factors of B-ALL are the history of parvovirus B 19 infection, high birth weight and exposure to environmental toxins. These risk factors can induce abnormal DNA methylation and DNA damages. Treatment procedures are divided into three phases: Induction, consolidation and maintenance. The goal of treatment is complete remission without relapses. Apart from traditional treatments, newly developed approaches include gene targeting therapy, with the aim of wiping out leukemic cells through the inhibition of mitogen-activated protein kinases and via c-Myb inhibition enhancing sensitivity to chemotherapy. To evaluate the efficacy of ongoing treatments, several indicators are currently used. The indicators include the expression levels of microRNAs (miRs) miR-146a, miR-155, miR-181a and miR-195, and soluble interleukin 2 receptor. Multiple drug resistance and levels of glutathione reductase can affect treatment efficacy through the increased efflux of anti-cancer drugs and weakening the effect of chemotherapy through the reduction of intracellular reactive oxygen species. The present review appraised recent studies on B-ALL regarding its pathogenesis, risk factors, treatments, treatment evaluation and causes of disease relapse. Understanding the mechanisms of B-ALL initiation and causes of treatment failure can help physicians improve disease management and reduce relapses.

KMT2A rearranged acute lymphoblastic leukaemia: Unravelling the genomic complexity and heterogeneity of this high-risk disease

KMT2A rearranged (KMT2Ar) acute lymphoblastic leukaemia (ALL) is a high-risk genomic subtype, with long-term survival rates of less than 60% across all age groups. These cases present a complex clinical challenge, with a high incidence in infants, high-risk clinical features and propensity for aggressive relapse. KMT2A rearrangements are highly pathogenic leukaemic drivers, reflected by the high incidence of KMT2Ar ALL in infants, who carry few leukaemia-associated cooperative mutations. However, transgenic murine models of KMT2Ar ALL typically exhibit long latency and mature or mixed phenotype, and fail to recapitulate the aggressive disease observed clinically. Next-generation sequencing has revealed that KMT2Ar ALL also occurs in adolescents and adults, and potentially cooperative genomic lesions such as PI3K-RAS pathway variants are present in KMT2Ar patients of all ages. This review addresses the aetiology of KMT2Ar ALL, with a focus on the cell of origin and mutational landscape, and how genomic profiling of KMT2Ar ALL patients in the era of next-generation sequencing demonstrates that KMT2Ar ALL is a complex heterogenous disease. Ultimately, understanding the underlying biology of KMT2Ar ALL will be important in improving long-term outcomes for these high-risk patients.

Inhibition of MEK and ATR is effective in a B-cell acute lymphoblastic leukemia model driven by Mll-Af4 and activated Ras

Infant B-cell acute lymphoblastic leukemias (B-ALLs) that harbor MLL-AF4 rearrangements are associated with a poor prognosis. One important obstacle to progress for this patient population is the lack of immunocompetent models that faithfully recapitulate the short latency and aggressiveness of this disease. Recent whole-genome sequencing of MLL-AF4 B-ALL samples revealed a high frequency of activating RAS mutations; however, single-agent targeting of downstream effectors of the RAS pathway in these mutated MLL-r B-ALLs has demonstrated limited and nondurable antileukemic effects. Here, we demonstrate that the expression of activating mutant N-Ras ^G12D cooperates with Mll-Af4 to generate a highly aggressive serially transplantable B-ALL in mice. We used our novel mouse model to test the sensitivity of Mll-Af4/N-Ras ^G12D leukemia to small molecule inhibitors and found potent and synergistic preclinical efficacy of dual targeting of the Mek and Atr pathways in mouse- and patient-derived xenografts with both mutations in vivo, suggesting this combination as an attractive therapeutic opportunity that might be used to treat patients with these mutations. Our studies indicate that this mouse model of Mll-Af4/N-Ras B-ALL is a powerful tool to explore the molecular and genetic pathogenesis of this disease subtype, as well as a preclinical discovery platform for novel therapeutic strategies.

Targeting steroid resistance in T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is characterized by a variable response to steroids during induction and/or consolidation therapy. Notably, recent work suggested that these differences in glucocorticoid sensitivity might, at least in part, be mediated by hyperactivation of specific oncogenic pathways such as RAS/MEK/ERK, PI3K/AKT and IL7R/JAK/STAT. In this review, we elaborate on putative associations between aberrant signaling, therapy resistance, incidence of relapse and clinical outcome in human T-ALL. Furthermore, we emphasize that this potential association with clinical parameters might also be mediated by the tumor microenvironment as a result of increased sensitivity of leukemic T-cells towards cytokine induced signaling pathway activation. With this in mind, we provide an overview of small molecule inhibitors that might have clinical potential for the treatment of human T-ALL in the near future as a result of their ability to overcome steroid resistance thereby potentially increasing survival rates in this aggressive hematological neoplasm.

Outcome of Infants Younger Than 1 Year With Acute Lymphoblastic Leukemia Treated With the Interfant-06 Protocol: Results From an International Phase III Randomized Study

PURPOSE

Infant acute lymphoblastic leukemia (ALL) is characterized by KMT2A (MLL) gene rearrangements and coexpression of myeloid markers. The Interfant-06 study, comprising 18 national and international study groups, tested whether myeloid-style consolidation chemotherapy is superior to lymphoid style, the role of stem-cell transplantation (SCT), and which factors had independent prognostic value.

MATERIALS AND METHODS

Three risk groups were defined: low risk (LR): KMT2A germline; high risk (HR): KMT2A-rearranged and older than 6 months with WBC count 300 × 10⁹/L or more or a poor prednisone response; and medium risk (MR): all other KMT2A-rearranged cases. Patients in the MR and HR groups were randomly assigned to receive the lymphoid course low-dose cytosine arabinoside [araC], 6-mercaptopurine, cyclophosphamide (IB) or experimental myeloid courses, namely araC, daunorubicin, etoposide (ADE) and mitoxantrone, araC, etoposide (MAE).

RESULTS

A total of 651 infants were included, with 6-year event-free survival (EFS) and overall survival of 46.1% (SE, 2.1) and 58.2% (SE, 2.0). In West European/North American groups, 6-year EFS and overall survival were 49.4% (SE, 2.5) and 62.1% (SE, 2.4), which were 10% to 12% higher than in other countries. The 6-year probability of disease-free survival was comparable for the randomized arms (ADE+MAE 39.3% [SE 4.0; n = 169] v IB 36.8% [SE, 3.9; n = 161]; log-rank P = .47). The 6-year EFS rate of patients in the HR group was 20.9% (SE, 3.4) with the intention to undergo SCT; only 46% of them received SCT, because many had early events. KMT2A rearrangement was the strongest prognostic factor for EFS, followed by age, WBC count, and prednisone response.

CONCLUSION

Early intensification with postinduction myeloid-type chemotherapy courses did not significantly improve outcome for infant ALL compared with the lymphoid-type course IB. Outcome for infant ALL in Interfant-06 did not improve compared with that in Interfant-99.

The Impact of PI3-kinase/RAS Pathway Cooperating Mutations in the Evolution of KMT2A-rearranged Leukemia

Leukemia is an evolutionary disease and evolves by the accrual of mutations within a clone. Those mutations that are systematically found in all the patients affected by a certain leukemia are called "drivers" as they are necessary to drive the development of leukemia. Those ones that accumulate over time but are different from patient to patient and, therefore, are not essential for leukemia development are called "passengers." The first studies highlighting a potential cooperating role of phosphatidylinositol 3-kinase (PI3K)/RAS pathway mutations in the phenotype of KMT2A-rearranged leukemia was published 20 years ago. The recent development in more sensitive sequencing technologies has contributed to clarify the contribution of these mutations to the evolution of KMT2A-rearranged leukemia and suggested that these mutations might confer clonal fitness and enhance the evolvability of KMT2A-leukemic cells. This is of particular interest since this pathway can be targeted offering potential novel therapeutic strategies to KMT2A-leukemic patients. This review summarizes the recent progress on our understanding of the role of PI3K/RAS pathway mutations in initiation, maintenance, and relapse of KMT2A-rearranged leukemia.

Binimetinib, a novel MEK1/2 inhibitor, exerts anti-leukemic effects under inactive status of PI3Kinase/Akt pathway

A MEK1/2 inhibitor, binimetinib is promising as a therapeutic agent for malignant melanoma with N-RAS mutation. We examined in vitro effects of binimetinib on 10 human myeloid/lymphoid leukemia cell lines, and found that three of five cell lines with N-RAS mutation and one of five without N-RAS mutation were responsive to treatment with binimetinib. Binimetinib inhibited cell growth mainly by inducing G₁ arrest and this action mechanism was assisted by gene set enrichment analysis. To identify signaling pathways associated with binimetinib response, we examined the status of MAP kinase/ERK and PI3Kinase/Akt pathways. The basal levels of phosphorylated ERK and Akt varied between the cell lines, and the amounts of phosphorylated ERK and Akt appeared to be reciprocal of each other. Interestingly, most of the binimetinib-resistant cell lines revealed strong Akt phosphorylation compared with binimetinib-sensitive ones. The effect of binimetinib may not be predicted by the presence/absence of N-RAS mutation, but rather by Akt phosphorylation status. Moreover, combination of binimetinib with a PI3K/Akt inhibitor showed additive growth-suppressive effects. These results suggest that binimetinib shows potential anti-leukemic effects and the basal level of phosphorylated Akt might serve as a biomarker predictive of therapeutic effect.

Glucocorticoid-resistant B cell acute lymphoblastic leukemia displays receptor tyrosine kinase activation

The response of childhood acute lymphoblastic leukemia (ALL) to dexamethasone predicts the long-term remission outcome. To explore the mechanisms of dexamethasone resistance in B cell ALL (B-ALL), we generated dexamethasone-resistant clones by prolonged treatment with dexamethasone. Using RNA-sequencing and high-throughput screening, we found that dexamethasone-resistant cells are dependent on receptor tyrosine kinases. Further analysis with phosphokinase arrays showed that the type III receptor tyrosine kinase FLT3 is constitutively active in resistant cells. Targeted next-generation and Sanger sequencing identified an internal tandem duplication mutation and a point mutation (R845G) in FLT3 in dexamethasone-resistant cells, which were not present in the corresponding sensitive clones. Finally, we showed that resistant cells displayed sensitivity to second-generation FLT3 inhibitors both in vitro and in vivo. Collectively, our data suggest that long-term dexamethasone treatment selects cells with a distinct genetic background, in this case oncogenic FLT3, and therefore therapies targeting FLT3 might be useful for the treatment of relapsed B-ALL patients.

How I treat infant leukemia

Leukemia in infants is rare but generates tremendous interest due to its aggressive clinical presentation in a uniquely vulnerable host, its poor response to current therapies, and its fascinating biology. Increasingly, these biological insights are pointing the way toward novel therapeutic approaches. Using representative clinical case presentations, we review the key clinical, pathologic, and epidemiologic features of infant leukemia, including the high frequency of KMT2A gene rearrangements. We describe the current approach to risk-stratified treatment of infant leukemia in the major international cooperative groups. We highlight recent discoveries that elucidate the molecular biology of infant leukemia and suggest novel targeted therapeutic strategies, including modulation of aberrant epigenetic programs, inhibition of signaling pathways, and immunotherapeutics. Finally, we underscore the need for increased global collaboration to translate these discoveries into improved outcomes.

Successful implementation of genomically based treatment of chemotherapy refractory peripheral T-cell lymphoma (PTCL)

BACKGROUND

The treatment of peripheral T-cell lymphoma (PTCL) after failure of standard therapy represents a significant clinical challenge as the best approach has not been defined. The outcomes of patients with peripheral T-cell lymphoma (PTCL) after relapse, in the absence of hematopoietic stem-cell transplantation, are poor with median overall survival is less than six months. Thus, relapsed/refractory PTCL presents an area of unmet medical need.

CASE PRESENTATION

Herein, we report an 84-year old woman with stage IV PTCL with extensive involvement of the bowel and abdominal pain. She was treated with cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) chemotherapy which was complicated by prolonged pancytopenia, without response. Disease progression was manifested by small bowel obstruction, for which she received palliative radiation therapy, further complicated by cardiac arrhythmia and sepsis. In the meantime, clinical-grade next generation sequencing of a lymph node (406 gene panel) showed six genomic alterations: NRAS Q61R, PTEN Q17*, CREBBP R768*, EP300 R1529*, SETD2 loss exons 19-21, along with an intermediate tumor mutational burden. Tissue PD-L1 staining was low positive by immunohistochemistry. The patient was discussed in Molecular Tumor Board with consensus opinion favoring a combination of the MEK inhibitor trametinib (for the NRAS alteration) and the checkpoint inhibitor nivolumab for the elevated mutational burden and PD-L1 positivity. Her abdominal pain resolved and she achieved a complete remission ongoing at 5+ months. Side effects at five months included only low-grade rash and peripheral edema.

CONCLUSIONS

Our observations suggest that matching patients with hematologic malignancies with customized combinations based on genomic sequencing warrants further study as a way to achieve and/or deepen responses, including in patients who are elderly and/or have refractory disease and significant disease-related complications.

De novo activating mutations drive clonal evolution and enhance clonal fitness in KMT2A-rearranged leukemia

Activating signaling mutations are common in acute leukemia with KMT2A (previously MLL) rearrangements (KMT2A-R). These mutations are often subclonal and their biological impact remains unclear. Using a retroviral acute myeloid mouse leukemia model, we demonstrate that FLT3^ITD, FLT3^N676K, and NRAS^G12D accelerate KMT2A-MLLT3 leukemia onset. Further, also subclonal FLT3^N676K mutations accelerate disease, possibly by providing stimulatory factors. Herein, we show that one such factor, MIF, promotes survival of mouse KMT2A-MLLT3 leukemia initiating cells. We identify acquired de novo mutations in Braf, Cbl, Kras, and Ptpn11 in KMT2A-MLLT3 leukemia cells that favored clonal expansion. During clonal evolution, we observe serial genetic changes at the Kras^G12D locus, consistent with a strong selective advantage of additional Kras^G12D. KMT2A-MLLT3 leukemias with signaling mutations enforce Myc and Myb transcriptional modules. Our results provide new insight into the biology of KMT2A-R leukemia with subclonal signaling mutations and highlight the importance of activated signaling as a contributing driver.

In acute leukemia with KMT2A rearrangements (KMT2A-R), activating signaling mutations are common. Here, the authors use a retroviral acute myeloid mouse leukemia model to show that subclonal de novo activating mutations drive clonal evolution in acute leukemia with KMT2A-R and enhance clonal fitness.

The role of RAS mutations in MLL-rearranged leukaemia: A path to intervention?

Childhood acute lymphoblastic leukaemia (ALL) with MLL rearrangement (MLL-r) is an aggressive disease still associated with a high mortality rate. Recent investigations have identified co-operating mutations in the RAS pathway and although the functional consequences of these mutations are not yet fully understood, aberrant regulation of RAS pathway signalling at both transcriptional and protein levels is observed. Studies investigating the efficacy of specific inhibitors of this pathway, e.g. MEK-inhibitors, have also achieved encouraging results. In this context, this mini-review summarizes the available data surrounding MLL-r infant ALL with RAS mutation in relation to other well-known features of this intriguing disease.

B lymphoblastic leukemia/lymphoma: new insights into genetics, molecular aberrations, subclassification and targeted therapy

B lymphoblastic leukemia/lymphoma (B-ALL) is a clonal hematopoietic stem cell neoplasm derived from B-cell progenitors, which mostly occurs in children and adolescents and is regarded as one of top leading causes of death related to malignancies in this population. Despite the majority of patients with B-ALL have fairly good response to conventional chemotherapeutic interventions followed by hematopoietic stem cell transplant for the last decades, a subpopulation of patients show chemo-resistance and a high relapse rate. Adult B-ALL exhibits similar clinical course but worse prognosis in comparison to younger individuals. Ample evidences have shown that the clinical behavior, response rate and clinical outcome of B-ALL rely largely on its genetic and molecular profiles, such as the presence of BCR-ABL1 fusion gene which is an independent negative prognostic predictor. New B-ALL subtypes have been recognized with recurrent genetic abnormalities, including B-ALL with intrachromosomal amplification of chromosome 21 (iAMP21), B-ALL with translocations involving tyrosine kinases or cytokine receptors (“BCR-ABL1-like ALL”). Genome-wide genetic profiling studies on B-ALL have extended our understanding of genomic landscape of B-ALL, and genetic mutations involved in various key pathways have been illustrated. These include CRLF2 and PAX5 alterations, TP53, CREBBP and ERG mutations, characteristic genetic aberrations in BCR-ABL1-like B-ALL and others. The review further provides new insights into clinical implication of the genetic aberrations in regard to targeted therapy development.

MLL-Rearranged Leukemias-An Update on Science and Clinical Approaches

The mixed-lineage leukemia 1 (MLL1) gene (now renamed Lysine [K]-specific MethylTransferase 2A or KMT2A) on chromosome 11q23 is disrupted in a unique group of acute leukemias. More than 80 different partner genes in these fusions have been described, although the majority of leukemias result from MLL1 fusions with one of about six common partner genes. Approximately 10% of all leukemias harbor MLL1 translocations. Of these, two patient populations comprise the majority of cases: patients younger than 1 year of age at diagnosis (primarily acute lymphoblastic leukemias) and young- to-middle-aged adults (primarily acute myeloid leukemias). A much rarer subgroup of patients with MLL1 rearrangements develop leukemia that is attributable to prior treatment with certain chemotherapeutic agents-so-called therapy-related leukemias. In general, outcomes for all of these patients remain poor when compared to patients with non-MLL1 rearranged leukemias. In this review, we will discuss the normal biological roles of MLL1 and its fusion partners, how these roles are hypothesized to be dysregulated in the context of MLL1 rearrangements, and the clinical manifestations of this group of leukemias. We will go on to discuss the progress in clinical management and promising new avenues of research, which may lead to more effective targeted therapies for affected patients.