Long-term survival after nonintensive chemotherapy in some juvenile myelomonocytic leukemia patients with CBL mutations, and the possible presence of healthy persons with the mutations

Potential value of high-throughput single-cell DNA sequencing of Juvenile myelomonocytic leukemia: report of two cases

Juvenile myelomonocytic leukemia (JMML) is a rare myeloproliferative disease of early childhood that develops due to mutations in the genes of the RAS-signaling pathway. Next-generation high throughput sequencing (NGS) enables identification of various secondary molecular genetic events that can facilitate JMML progression and transformation into secondary acute myeloid leukemia (sAML). The methods of single-cell DNA sequencing (scDNA-seq) enable overcoming limitations of bulk NGS and exploring genetic heterogeneity at the level of individual cells, which can help in a better understanding of the mechanisms leading to JMML progression and provide an opportunity to evaluate the response of leukemia to therapy. In the present work, we applied a two-step droplet microfluidics approach to detect DNA alterations among thousands of single cells and to analyze clonal dynamics in two JMML patients with sAML transformation before and after hematopoietic stem cell transplantation (HSCT). At the time of diagnosis both of our patients harbored only "canonical" mutations in the RAS signaling pathway genes detected by targeted DNA sequencing. Analysis of samples from the time of transformation JMML to sAML revealed additional genetic events that are potential drivers for disease progression in both patients. ScDNA-seq was able to measure of chimerism level and detect a residual tumor clone in the second patient after HSCT (sensitivity of less than 0.1% tumor cells). The data obtained demonstrate the value of scDNA-seq to assess the clonal evolution of JMML to sAML, response to therapy and engraftment monitoring.

Advances in molecular evaluation of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPN) are a group of clonal hematopoietic stem cell disorders with uncontrolled proliferation of one or more hematopoietic cell types, including myeloid, erythroid and megakaryocytic lineages, and minimal defect in maturation. Most MPN are associated with well-defined molecular abnormalities involving genes that encode protein tyrosine kinases that lead to constitutive activation of the downstream signal transduction pathways and confer cells proliferative and survival advantage. Genome-wide sequencing analyses have discovered secondary cooperating mutations that are shared by most of the MPN subtypes as well as other myeloid neoplasms and play a major role in disease progression. Without appropriate management, the natural history of most MPN consists of an initial chronic phase and a terminal blast phase. Molecular aberrations involving protein tyrosine kinases have been used for the diagnosis, classification, detection of minimal/measurable residual disease, and target therapy. We review recent advances in molecular genetic aberrations in MPN with a focus on MPN associated with gene rearrangements or mutations involving tyrosine kinase pathways.

Genomic and Epigenomic Landscape of Juvenile Myelomonocytic Leukemia

Simple Summary

Juvenile myelomonocytic leukemia (JMML) is a rare pediatric myelodysplastic/myeloproliferative neoplasm characterized by the constitutive activation of the RAS pathway. In spite of the recent progresses in the molecular characterization of JMML, this disease is still a clinical challenge due to its heterogeneity, difficult diagnosis, poor prognosis, and the lack of curative treatment options other than hematopoietic stem cell transplantation (HSCT). In this review, we will provide a detailed overview of the genetic and epigenetic alterations occurring in JMML, and discuss their clinical relevance in terms of disease prognosis and risk of relapse after HSCT. We will also present the most recent advances on novel preclinical and clinical therapeutic approaches directed against JMML molecular targets. Finally, we will outline future research perspectives to further explore the oncogenic mechanism driving JMML leukemogenesis and progression, with special attention to the application of single-cell next-generation sequencing technologies.

Abstract

Juvenile myelomonocytic leukemia (JMML) is a rare myelodysplastic/myeloproliferative neoplasm of early childhood. Most of JMML patients experience an aggressive clinical course of the disease and require hematopoietic stem cell transplantation, which is currently the only curative treatment. JMML is characterized by RAS signaling hyperactivation, which is mainly driven by mutations in one of five genes of the RAS pathway, including PTPN11, KRAS, NRAS, NF1, and CBL. These driving mutations define different disease subtypes with specific clinico-biological features. Secondary mutations affecting other genes inside and outside the RAS pathway contribute to JMML pathogenesis and are associated with a poorer prognosis. In addition to these genetic alterations, JMML commonly presents aberrant epigenetic profiles that strongly correlate with the clinical outcome of the patients. This observation led to the recent publication of an international JMML stratification consensus, which defines three JMML clinical groups based on DNA methylation status. Although the characterization of the genomic and epigenomic landscapes in JMML has significantly contributed to better understand the molecular mechanisms driving the disease, our knowledge on JMML origin, cell identity, and intratumor and interpatient heterogeneity is still scarce. The application of new single-cell sequencing technologies will be critical to address these questions in the future.

Role of CBL Mutations in Cancer and Non-Malignant Phenotype

Simple Summary

CBL mutations are progressively being described as involved in different clinical manifestations. Somatic CBL mutations can be found in different type of cancer. The clinical spectrum of germline mutations configures the so-called CBL syndrome, a cancer-predisposing condition that includes multisystemic involvement characterized by variable phenotypic expression and expressivity. In this review we provide an up-to-date review of the clinical manifestation of CBL mutations and of the molecular mechanisms in which CBL exerts its pathogenic role.

Abstract

CBL plays a key role in different cell pathways, mainly related to cancer onset and progression, hematopoietic development and T cell receptor regulation. Somatic CBL mutations have been reported in a variety of malignancies, ranging from acute myeloid leukemia to lung cancer. Growing evidence have defined the clinical spectrum of germline CBL mutations configuring the so-called CBL syndrome; a cancer-predisposing condition that also includes multisystemic involvement characterized by variable phenotypic expression and expressivity. This review provides a comprehensive overview of the molecular mechanisms in which CBL exerts its function and describes the clinical manifestation of CBL mutations in humans.

Morphologic and Immunophenotypic Differences in Juvenile Myelomonocytic Leukemias With CBL and Other Canonical RAS-pathway Gene Mutations: A Single Institutional Experience

The diagnostic criteria for juvenile myelomonocytic leukemia have recently been revised to include clinical findings and RAS-pathway gene mutations per the 2016 World Health Organization Classification of Tumors of Hematopoietic and Lymphoid Tissues. Differing clinical behaviors have been observed in cases with CBL versus other RAS-pathway gene (RAS-p) mutations, notably the patients with CBL mutations can be self-limiting with spontaneous resolution. Additional clinical characteristics and histopathologic findings between these subsets are less well-described. We performed a retrospective search and identified cases with either CBL or RAS-p mutations, as per targeted and/or massively parallel sequencing. Eight patients had sufficient material for review, including cytogenetic studies and peripheral blood, bone marrow aspirate, and/or biopsy with flow cytometry analyses. Three patients showed CBL mutations and lower percentages of hemoglobin F and peripheral blood absolute monocyte counts, lesser degrees of leukocytosis compared with the RAS-p cohort, and normal megakaryocyte morphology and myeloblast immunophenotypes. Two of these patients were managed with observation only and experienced resolution of their disease. The patients with RAS-p mutations had severe thrombocytopenia, moderate to severe anemia, and experienced variable clinical outcomes. Abnormal megakaryocyte morphology and decreased numbers of megakaryocytes were seen in cases with RAS-p mutations. In addition, 3 of 4 cases with flow cytometry data demonstrated aberrant CD7 expression in myeloblasts. Our study is the first to identify morphologic and immunophenotypic differences between juvenile myelomonocytic leukemia cases with CBL or RAS-p mutations, and further supports previous reports of significantly different clinical behaviors between these subsets of patients.

Primary Graft Failure but Treatment Success: A Case of Reversion to Heterozygosity After Allogeneic Hematopoietic Cell Transplantation With Autologous Hematopoietic Recovery in a Child With CBL-related Juvenile Myelomonocytic Leukemia

Juvenile myelomonocytic leukemia (JMML) typically requires allogeneic hematopoietic cell transplantation with full donor chimerism for cure. Certain genetic subtypes, including JMML due to germline mutations in CBL, can have a more indolent course. We describe a young male patient with CBL-related JMML who experienced primary graft failure after allogeneic hematopoietic cell transplantation. Despite autologous recovery, the resulting hematopoietic tissue did not harbor the original homozygous CBL mutations, due to reversion of prior loss of heterozygosity of the 11q chromosomal region. The patient remains disease free without further leukemia-directed therapy.

A child with juvenile myelomonocytic leukemia possessing a concurrent germline CBL mutation and a NF1 variant of uncertain significance: A rare case with a common problem in the era of high-throughput sequencing

Genetic changes in juvenile myelomonocytic leukemia (JMML) determine distinct subtypes, treatments, and outcomes. JMML with germline CBL mutation and somatic NRAS mutation possibly achieves spontaneous remission, but hematopoietic stem cell transplantation is indicated for other subtypes of JMML. We hereby report a child with JMML harboring a germline CBL mutation (c.1111T>C) and an NF1 variant (c.3352A>G) concurrently. After evaluation, we considered that the NF1 variant was not the major contributor. After one year of observation, this case had no signs of disease progression. This case highlights the importance of combining available evidence and clinical findings in caring for patients with unusual genomic variations.

Changes in the World Health Organization 2016 classification of myeloid neoplasms everyone should know

PURPOSE OF REVIEW

This review highlights the main changes in the revised 2016 WHO classification of myeloid neoplasms (published in 2017) that impact diagnosis and ultimately impact management of patients with these diseases.

RECENT FINDINGS

The revision was based on data accumulated since the 2008 WHO classification, much of which relate to new molecular genetic information about these neoplasms. This massive recent influx of data concerning the significance of pathogenic mutations has affected all myeloid neoplasm categories. The new information has been incorporated as part of the diagnostic criteria of many diseases and has led to the creation of new provisional entities defined by genetic features. Germline mutations that predispose to myeloid neoplasms are also emerging as important findings that impact disease classification.

SUMMARY

The growing body of genetic data have not only altered the classification of myeloid neoplasms, but are also impacting patient management. Genetically-defined disease categories have characteristic prognoses and predicted clinical behavior. Some mutations are associated with responsiveness to certain therapies, including those that target relevant oncogenes. The disease categories in the new classification facilitate the application of risk-adapted therapy based on the most recently available data.

A case of splenomegaly in CBL syndrome

INTRODUCTION

We present a child with unexplained splenomegaly to highlight this feature as a presenting sign of the RASopathy CBL syndrome and to draw attention to the power and utility of next generation genomic sequencing for providing rapid diagnosis and critical information to guide care in the pediatric clinical setting.

CLINICAL REPORT

A 7-year-old boy presented with unexplained splenomegaly, attention deficit hyperactivity disorder, mild learning difficulties, easy bruising, mild thrombocytopenia, and subtle dysmorphic features. Extensive haematological testing including a bone marrow biopsy showed mild megaloblastoid erythropoiesis and borderline fibrosis. There were no haematological cytogenetic anomalies or other haematological pathology to explain the splenomegaly. Metabolic testing and chromosomal microarray were unremarkable. Trio whole-exome sequencing (WES) identified a pathogenic de novo heterozygous germline CBL variant (c.1111T > C, p.Y371H), previously reported to cause CBL syndrome and implicated in development of juvenile myelomonocytic leukemia (JMML).

DISCUSSION

CBL syndrome (more formally known as "Noonan-syndrome-like disorder with or without juvenile myelomonocytic leukemia") has overlapping features to Noonan syndrome with significant variability. CBL syndrome and other RASopathy disorders-including Noonan syndrome, neurofibromatosis 1, and Costello syndrome-are important to recognize as these are associated with a cancer-predisposition. CBL syndrome carries a very high risk for JMML, thus accurate diagnosis is of utmost importance. The diagnosis of CBL syndrome in this patient would not have been possible based on clinical features alone. Through WES, a specific genetic diagnosis was made, allowing for an optimized management and surveillance plan, illustrating the power of genomics in clinical practice.

Juvenile Myelomonocytic Leukemia in Turkey: A Retrospective Analysis of Sixty-five Patients

OBJECTIVE

This study aimed to define the status of juvenile myelomonocytic leukemia (JMML) patients in Turkey in terms of time of diagnosis, clinical characteristics, mutational studies, clinical course, and treatment strategies.

MATERIALS AND METHODS

Data including clinical and laboratory characteristics and treatment strategies of JMML patients were collected retrospectively from pediatric hematology-oncology centers in Turkey.

RESULTS

Sixty-five children with JMML diagnosed between 2002 and 2016 in 18 institutions throughout Turkey were enrolled in the study. The median age at diagnosis was 17 months (min-max: 2-117 months). Splenomegaly was present in 92% of patients at the time of diagnosis. The median white blood cell, monocyte, and platelet counts were 32.9x109/L, 5.4x109/L, and 58.3x109/L, respectively. Monosomy 7 was present in 18% of patients. JMML mutational analysis was performed in 32 of 65 patients (49%) and PTPN11 was the most common mutation. Hematopoietic stem cell transplantation (HSCT) could only be performed in 28 patients (44%), the majority being after the year 2012. The most frequent reason for not performing HSCT was the inability to find a suitable donor. The median time from diagnosis to HSCT was 9 months (min-max: 2-63 months). The 5-year cumulative survival rate was 33% and median estimated survival time was 30±17.4 months (95% CI: 0-64.1) for all patients. Survival time was significantly better in the HSCT group (log-rank p=0.019). Older age at diagnosis (>2 years), platelet count of less than 40x109/L, and PTPN11 mutation were the factors significantly associated with shorter survival time.

CONCLUSION

Although there has recently been improvement in terms of definitive diagnosis and HSCT in JMML patients, the overall results are not satisfactory and it is necessary to put more effort into this issue in Turkey.

Diagnosis and treatment of juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML) is a rare myelodysplastic/myeloproliferative disorder that occurs during infancy and early childhood; this disorder is characterized by hypersensitivity of the myeloid progenitor cells to granulocyte-macrophage colony-stimulating factor in vitro. JMML usually involves somatic and/or germline mutations in the genes of the RAS pathway, including PTPN11, NRAS, KRAS, NF1, and CBL, in the leukemic cells. Almost all patients with JMML experience an aggressive clinical course, and hematopoietic stem cell transplantation (HSCT) is the only curative treatment. A certain proportion of patients with somatic NRAS and germline mutations in CBL, however, have spontaneous resolution. A suitable treatment after diagnosis and conditioning regimen prior to HSCT are yet to be determined, but several clinical trials have been initiated throughout the world to develop suitable pre- or post-allogeneic HSCT treatments and new targeted therapies that are less toxic, to improve patient outcome.

Anti-proliferative effects of T cells expressing a ligand-based chimeric antigen receptor against CD116 on CD34(+) cells of juvenile myelomonocytic leukemia

Background

Juvenile myelomonocytic leukemia (JMML) is a fatal, myelodysplastic/myeloproliferative neoplasm of early childhood. Patients with JMML have mutually exclusive genetic abnormalities in granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor (GMR, CD116) signaling pathway. Allogeneic hematopoietic stem cell transplantation is currently the only curative treatment option for JMML; however, disease recurrence is a major cause of treatment failure. We investigated adoptive immunotherapy using GMR-targeted chimeric antigen receptor (CAR) for JMML.

Methods

We constructed a novel CAR capable of binding to GMR via its ligand, GM-CSF, and generated piggyBac transposon-based GMR CAR-modified T cells from three healthy donors and two patients with JMML. We further evaluated the anti-proliferative potential of GMR CAR T cells on leukemic CD34⁺ cells from six patients with JMML (two NRAS mutations, three PTPN11 mutations, and one monosomy 7), and normal CD34⁺ cells.

Results

GMR CAR T cells from healthy donors suppressed the cytokine-dependent growth of MO7e cells, but not the growth of K562 and Daudi cells. Co-culture of healthy GMR CAR T cells with CD34⁺ cells of five patients with JMML at effector to target ratios of 1:1 and 1:4 for 2 days significantly decreased total colony growth, regardless of genetic abnormality. Furthermore, GMR CAR T cells from a non-transplanted patient and a transplanted patient inhibited the proliferation of respective JMML CD34⁺ cells at onset to a degree comparable to healthy GMR CAR T cells. Seven-day co-culture of GMR CAR T cells resulted in a marked suppression of JMML CD34⁺ cell proliferation, particularly CD34⁺CD38⁻ cell proliferation stimulated with stem cell factor and thrombopoietin on AGM-S3 cells. Meanwhile, GMR CAR T cells exerted no effects on normal CD34⁺ cell colony growth.

Conclusions

Ligand-based GMR CAR T cells may have anti-proliferative effects on stem and progenitor cells in JMML.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0256-3) contains supplementary material, which is available to authorized users.

The genomic landscape of juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML) is a myeloproliferative neoplasm (MPN) of childhood with a poor prognosis. Mutations in NF1, NRAS, KRAS, PTPN11 or CBL occur in 85% of patients, yet there are currently no risk stratification algorithms capable of predicting which patients will be refractory to conventional treatment and could therefore be candidates for experimental therapies. In addition, few molecular pathways aside from the RAS-MAPK pathway have been identified that could serve as the basis for such novel therapeutic strategies. We therefore sought to genomically characterize serial samples from patients at diagnosis through relapse and transformation to acute myeloid leukemia to expand knowledge of the mutational spectrum in JMML. We identified recurrent mutations in genes involved in signal transduction, splicing, Polycomb repressive complex 2 (PRC2) and transcription. Notably, the number of somatic alterations present at diagnosis appears to be the major determinant of outcome.

Management of Two Juvenile Myelomonocytic Leukemia Patients According to Clinical and Genetic Features

Juvenile myelomonocytic leukemia (JMML) is a rare clonal myeloproliferative disorder of childhood. Major progress has been achieved in diagnosis and the understanding of the pathogenesis of JMML by identifying the genetic pathologies that occur in patients. Mutations of RAS, NF1, PTPN11, and CBL are found in approximately 80% of JMML patients. Distinct clinical features have been reported to be associated with specific gene mutations. The advent of genomic studies and recent identification of novel genetic mutations in JMML are important not only in diagnosis but also in the management and prognosis of the disease. Herein, we present 2 patients with JMML harboring different mutations, NRAS and c-CBL, respectively, with distinct clinical features and different therapeutic approaches.

RAS diseases in children

RAS genes encode a family of 21 kDa proteins that are an essential hub for a number of survival, proliferation, differentiation and senescence pathways. Signaling of the RAS-GTPases through the RAF-MEK-ERK pathway, the first identified mitogen-associated protein kinase (MAPK) cascade is essential in development. A group of genetic syndromes, named "RASopathies", had been identified which are caused by heterozygosity for germline mutations in genes that encode protein components of the RAS/MAPK pathway. Several of these clinically overlapping disorders, including Noonan syndrome, Noonan-like CBL syndrome, Costello syndrome, cardio-facio-cutaneous (CFC) syndrome, neurofibromatosis type I, and Legius syndrome, predispose to cancer and abnormal myelopoiesis in infancy. This review focuses on juvenile myelomonocytic leukemia (JMML), a malignancy of early childhood characterized by initiating germline and/or somatic mutations in five genes of the RAS/MAPK pathway: PTPN11, CBL, NF-1, KRAS and NRAS. Natural courses of these five subtypes differ, although hematopoietic stem cell transplantation remains the only curative therapy option for most children with JMML. With whole-exome sequencing studies revealing few secondary lesions it will be crucial to better understand the RAS/MAPK signaling network with its crosstalks and feed-back loops to carefully design early clinical trials with novel pharmacological agents in this still puzzling leukemia.

How I treat juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML) is a unique, aggressive hematopoietic disorder of infancy/early childhood caused by excessive proliferation of cells of monocytic and granulocytic lineages. Approximately 90% of patients carry either somatic or germline mutations of PTPN-11, K-RAS, N-RAS, CBL, or NF1 in their leukemic cells. These genetic aberrations are largely mutually exclusive and activate the Ras/mitogen-activated protein kinase pathway. Allogeneic hematopoietic stem cell transplantation (HSCT) remains the therapy of choice for most patients with JMML, curing more than 50% of affected children. We recommend that this option be promptly offered to any child with PTPN-11-, K-RAS-, or NF1-mutated JMML and to the majority of those with N-RAS mutations. Because children with CBL mutations and few of those with N-RAS mutations may have spontaneous resolution of hematologic abnormalities, the decision to proceed to transplantation in these patients must be weighed carefully. Disease recurrence remains the main cause of treatment failure after HSCT. A second allograft is recommended if overt JMML relapse occurs after transplantation. Recently, azacytidine, a hypomethylating agent, was reported to induce hematologic/molecular remissions in some children with JMML, and its role in both reducing leukemia burden before HSCT and in nontransplant settings requires further studies.

Frequent coexistence of RAS mutations in RUNX1-mutated acute myeloid leukemia in Arab Asian children

BACKGROUND

RUNX1 mutation plays an important role in adult leukemic transformation. However, its contribution to the development of childhood leukemia remains unclear. In the present study, we analyzed point mutations of RUNX1 gene in children and adolescents with acute myeloid leukemia (AML) from Iraq and Jordan.

PROCEDURE

Bone marrow and/or peripheral blood samples were collected from 178 patients of Arab Asian ethnicity (aged ≤17 years) newly diagnosed with AML: 145 samples from Iraq and 33 samples from Jordan. Direct DNA sequencing was performed on six genes including RUNX1 gene (exons 3-8).

RESULTS

RUNX1 point mutations were identified in 10 (5.6%) of 178 patients. One patient possessed biallelic mutations of RUNX1 gene. C-terminal area was the predominant site of RUNX1 mutations (eight in C-terminal and two in N-terminal). Patients with RUNX1 mutations were significantly older than those with wild-type of the gene. Additionally, AML M0 subtype was more frequently found in patients with RUNX1 mutations. Both RUNX1 mutations and RAS mutations were identified in 4 of 10 children. Three patients with RUNX1 mutation had FLT3-ITD. On the other hand, 36 (21.4%) and 25 (14.9%) of 168 patients with wild-type of the gene had a RAS mutation and FLT3-ITD, respectively. Eight of 10 patients with RUNX1 mutations died of hematological relapse.

CONCLUSION

The incidence of RUNX1 mutations in Arab Asian children and adolescents with AML was 5.6%. Further studies are required to clarify whether RAS mutations contribute to the development of pediatric AML associated with RUNX1 mutations.

CBL mutations in myeloproliferative neoplasms are also found in the gene's proline-rich domain and in patients with the V617FJAK2

BACKGROUND

Despite the discovery of the p.V617F in JAK2, the molecular pathogenesis of some chronic myeloproliferative neoplasms remains unclear. Although very rare, different studies have identified CBL (Cas-Br-Murine ecotropic retroviral transforming sequence) mutations in V617FJAK2-negative patients, mainly located in the RING finger domain. In order to determine the frequency of CBL mutations in these diseases, we studied different regions of all CBL family genes (CBL, CBLB and CBLC) in a selected group of patients with myeloproliferative neoplasms. We also included V617FJAK2-positive patients to check whether mutations in CBL and JAK2 are mutually exclusive events.

DESIGN AND METHODS

Using denaturing high performance liquid chromatography, we screened for mutations in CBL, CBLB and CBLC in a group of 172 V617FJAK2-negative and 232 V617FJAK2-positive patients with myeloproliferative neoplasms not selected for loss of heterozygosity. The effect on cell proliferation of the mutations detected was analyzed on a 32D(FLT3) cell model.

RESULTS

An initial screening of all coding exons of CBL, CBLB and CBLC in 44 V617FJAK2-negative samples revealed two new CBL mutations (p.C416W in the RING finger domain and p.A678V in the proline-rich domain). Analyses performed on 128 additional V617FJAK2-negative and 232 V617FJAK2-positive samples detected three CBL changes (p.T402HfsX29, p.P417R and p.S675C in two cases) in four V617FJAK2-positive patients. None of these mutations was found in 200 control samples. Cell proliferation assays showed that all of the mutations promoted hypersensitivity to interleukin-3 in 32D(FLT3) cells.

CONCLUSIONS

Although mutations described to date have been found in the RING finger domain and in the linker region of CBL, we found a similar frequency of mutations in the proline-rich domain. In addition, we found CBL mutations in both V617FJAK2-positive (4/232; 1.7%) and negative (2/172; 1.2%) patients and all of them promoted hypersensitivity to interleukin-3.

CBL mutation-related patterns of phosphorylation and sensitivity to tyrosine kinase inhibitors

Recurrent homozygous CBL-inactivating mutations in myeloid malignancies decrease ubiquitin ligase activity that inactivates SRC family kinases (SFK) and receptor tyrosine kinases (RTK). However, the most important SFK and RTK affected by these mutations, and hence, the most important therapeutic targets, have not been clearly characterized. We compared SFK and RTK pathway activity and inhibitors in acute myeloid leukemia cell lines containing homozygous R420Q mutation (GDM-1), heterozygous deletion (MOLM13) and wild-type (WT) CBL (THP1, U937). As expected with CBL loss, GDM-1 displayed high KIT expression and granulocyte-macrophage colony-stimulating factor (GM-CSF) hypersensitivity. Ectopic expression of WT CBL decreased GDM-1 proliferation but not cell lines with WT CBL. GDM-1, but not the other cell lines, was highly sensitive to growth inhibition by dasatinib (dual SFK and RTK inhibitor, LD50 50 nM); there was less or no selective inhibition of GDM-1 growth by sunitinib (RTK inhibitor), imatinib (ABL, KIT inhibitor), or PP2 (SFK inhibitor). Phosphoprotein analysis identified phosphorylation targets uniquely inhibited by dasatinib treatment of GDM-1, including a number of proteins in the KIT and GM-CSF receptor pathways (for example, KIT Tyr721, STAT3 Tyr705). In conclusion, the promiscuous effects of CBL loss on SFK and RTK signaling appear to be best targeted by dual SFK and RTK inhibition.

Recent advances in the pathogenesis and treatment of juvenile myelomonocytic leukaemia

Myeloid neoplasms derive from the pathological clonal expansion of an abnormal stem cell and span a diverse spectrum of phenotypes including acute myeloid leukaemia (AML), myeloproliferative neoplasms (MPN) and myelodysplastic syndromes (MDS). Expansion of myeloid blasts with suppression of normal haematopoiesis is the hallmark of AML, whereas MPN is associated with over-proliferation of one or more lineages that retain the capacity to differentiate, and MDS is characterized by cytopenias and aberrant differentiation. MPD and MDS can progress to AML, which is likely due to the acquisition of cooperative mutations. Juvenile myelomonocytic leukaemia (JMML) is an aggressive myeloid neoplasm of childhood that is clinically characterized by overproduction of monocytic cells that can infiltrate organs, including the spleen, liver, gastrointestinal tract, and lung. JMML is categorized as an overlap MPN/MDS by the World Health Organization and also shares some clinical and molecular features with chronic myelomonocytic leukaemia, a similar disease in adults. While the current standard of care for patients with JMML relies on allogeneic haematopoietic stem cell transplant (HSCT), relapse is the most frequent cause of treatment failure. This review outlines our understanding of the genetic underpinnings of JMML with a recent update on the discovery of novel CBL mutations, as well as a brief review on current therapeutic approaches.