PTPN11 mutations in pediatric patients with acute myeloid leukemia: results from the Children's Cancer Group

Deciphering the structural and dynamic effects of SHP2-E76 mutations: mechanistic insights into oncogenic activation

The tyrosine phosphatase known as SHP2 is a cytoplasmic protein and encodes by proto-oncogene PTPN11. This protein is essential for the regulation of cell growth, differentiation, programed cell death, and survival. This regulation is achieved through the release of intramolecular autoinhibition and the modulation of several signaling pathways, including the signaling cascade of Ras-MAPK. Mutations in SHP2 are frequently associated with human malignancies and neurodevelopmental disorders (NDDs). Specifically, a germline mutation (E76D) in SHP2 is linked to neurodevelopmental disorders, such as Noonan syndrome, while somatic mutations (E76G and E76A) and altered SHP2 expression are implicated in several forms of leukemia. These mutations disrupt the closed conformation, which normally keeps SHP2 in an inactive, auto-inhibited state, thereby enhancing phosphatase activity and activating SHP2, leading to a gain-of-function effect. However, the structural and functional implications of these disease-related mutants are not well elucidated. Therefore, in this study, we investigate the structural mechanisms underlying three distinct gain-of-function SHP2 mutations (E76D, E76G, and E76A) through the application of molecular dynamics (MD) simulations, focusing on how a single amino acid mutation at the same position result in different disease phenotypes, either cause cancer or NDDs. Notably, Patients with Noonan Syndrome have an increased risk of developing cancer, suggesting a potential link between these diseases and their mutations. MD simulation was employed to elucidate this mechanism, examining four distinct states: Apo-state (E76), M1-state (E76D), M2-state (E76G), and M3-state (E76A). The dynamics and conformational changes of SHP2 in both its Apo-state and mutant states (M1, M2, and M3) were compared. Our findings indicate that both cancer-related and NDD-related mutations destabilize the N-SH2 and PTP interface, facilitating SHP2 activation. However, the cancer-associated mutations induce more severe disruption at the N-SH2 and PTP interface than the NDD mutations. Additionally, dynamic analyses revealed that mutations at the interface (M1, M2, and M3) not only alter the native folded conformation of SHP2 but also significantly enhance the C-distance between the N-SH2 and PTP domains. Overall, this study provides a comprehensive understanding of the structural dynamics of SHP2 at the atomic level, revealing how mutations disrupt its auto-inhibition and increase PTP activity, providing valuable insights into the molecular mechanisms driving both cancer and neurodevelopmental disorders.

Targeting Protein Tyrosine Phosphatases to Improve Cancer Immunotherapies

Advances in immunotherapy have brought significant therapeutic benefits to many cancer patients. Nonetheless, many cancer types are refractory to current immunotherapeutic approaches, meaning that further targets are required to increase the number of patients who benefit from these technologies. Protein tyrosine phosphatases (PTPs) have long been recognised to play a vital role in the regulation of cancer cell biology and the immune response. In this review, we summarize the evidence for both the pro-tumorigenic and tumour-suppressor function of non-receptor PTPs in cancer cells and discuss recent data showing that several of these enzymes act as intracellular immune checkpoints that suppress effective tumour immunity. We highlight new data showing that the deletion of inhibitory PTPs is a rational approach to improve the outcomes of adoptive T cell-based cancer immunotherapies and describe recent progress in the development of PTP inhibitors as anti-cancer drugs.

The clinical features and prognostic implications of PTPN11 mutation in adult patients with acute myeloid leukemia in China

BACKGROUND

The clinical significance of protein tyrosine phosphatase nonreceptor type 11 mutation (PTPN11mut ) in acute myeloid leukemia (AML) is underestimated.

METHODS

We collected the data of AML patients with mutated PTPN11 and wild-type PTPN11 (PTPN11wt ) treated at our hospital and analyzed their clinical characteristics and prognosis.

RESULTS

Fifty-nine PTPN11mut and 124 PTPN11wt AML patients were included. PTPN11mut was more common in myelomonocytic and monocytic leukemia, and was more likely to co-mutate with KRAS, KMT2C, NRAS, U2AF1, NOTCH1, IKZF1, and USH2A mutations than PTPN11wt . The overall survival for AML patients with PTPN11mut was significantly shorter than that for those with PTPN11wt (p = 0.03). The negative impact of PTPN11mut on overall survival was pronounced in the "favorable" and "intermediate" groups of ELN2017 risk stratification, as well as in the wild-type NPM1 group (p = 0.01, p = 0.01, and p = 0.04).

CONCLUSION

PTPN11mut is associated with distinct clinical and molecular characteristics, and adverse prognosis in AML patients.

Analysis of the clinical characteristics and prognosis of adult de novo acute myeloid leukemia (none APL) with PTPN11 mutations

We discuss the clinical characteristics and prognostic significance of adult individuals with PTPN11 mutations who have developed acute myeloid leukemia (AML) (none acute promyelocytic leukemia). Next generation sequencing and Sanger sequencing were used to detect 51 gene mutations, and multiplex-PCR was used to detect 41 fusion genes from 232 de novo adult AML patients retrospectively. About 7.76% patients harbored PTPN11 mutations, 20 PTPN11 alterations were identified, all of which were missense mutations in the N-SH2 (n = 16) and PTP (n = 4) domains located in exon 3. Patients with PTPN11 mut had significantly higher platelet counts and hemoglobin levels (p < 0.001), which were mainly detected in M5 (n = 12, 66.67%, p < 0.001) subtype. Patients with MLL-AF6 positive showed a higher frequency of PTPN11 mut (p = 0.018) in the 118 AML cases. PTPN11 mut were accompanied by other mutations, which were NPM1 (44.44%), DNMT3A (38.89%), FLT3 (38.89%), and NRAS (17.2%). PTPN11 mut had a negative impact on the complete remission rate in M5 subtype patients (p < 0.001). However, no statistically significant effect on overall survival (OS) with PTPN11 mut patients in the whole cohort and age group (p > 0.05) was observed. Further analysis revealed no significant difference in OS among NPM1 mut/PTPN11 mut, NPM1 mut/PTPN11 wt, DNMT3A mut/PTPN11 mut, and DNMT3A mut/PTPN11 wt patients (p > 0.05). Multivariate analysis showed the proportion of bone marrow blasts ≥65.4% was a factor significantly affecting OS in PTPN11 mut patients (p = 0.043).

A Direct Comparison, and Prioritisation, of the Immunotherapeutic Targets Expressed by Adult and Paediatric Acute Myeloid Leukaemia Cells: A Systematic Review and Meta-Analysis

Acute myeloid leukaemia (AML) is characterized by impaired myeloid differentiation resulting in an accumulation of immature blasts in the bone marrow and peripheral blood. Although AML can occur at any age, the incidence peaks at age 65. The pathobiology of AML also varies with age with associated differences in incidence, as well as the frequency of cytogenetic change and somatic mutations. In addition, 5-year survival rates in paediatrics are 60-75% but fall to 5-15% in older AML patients. This systematic review aimed to determine whether the altered genes in AML affect the same molecular pathways, indifferent of patient age, and, therefore, whether patients could benefit from the repurposing drugs or the use of the same immunotherapeutic strategies across age boundaries to prevent relapse. Using a PICO framework and PRISMA-P checklist, relevant publications were identified using five literature databases and assessed against an inclusion criteria, leaving 36 articles, and 71 targets for therapy, for further analysis. QUADAS-2 was used to determine the risk of bias and perform a quality control step. We then priority-ranked the list of cancer antigens based on predefined and pre-weighted objective criteria as part of an analytical hierarchy process used for dealing with complex decisions. This organized the antigens according to their potential to act as targets for the immunotherapy of AML, a treatment that offers an opportunity to remove residual leukaemia cells at first remission and improve survival rates. It was found that 80% of the top 20 antigens identified in paediatric AML were also within the 20 highest scoring immunotherapy targets in adult AML. To analyse the relationships between the targets and their link to different molecular pathways, PANTHER and STRING analyses were performed on the 20 highest scoring immunotherapy targets for both adult and paediatric AML. There were many similarities in the PANTHER and STRING results, including the most prominent pathways being angiogenesis and inflammation mediated by chemokine and cytokine signalling pathways. The coincidence of targets suggests that the repurposing of immunotherapy drugs across age boundaries could benefit AML patients, especially when used in combination with conventional therapies. However, due to cost implications, we would recommend that efforts are focused on ways to target the highest scoring antigens, such as WT1, NRAS, IDH1 and TP53, although in the future other candidates may prove successful.

Epigenomic machinery regulating pediatric AML: clonal expansion mechanisms, therapies, and future perspectives

Acute myeloid leukemia (AML) is a heterogeneous disease with a genetic, epigenetic, and transcriptional etiology mainly presenting somatic and germline abnormalities. AML incidence rises with age but can also occur during childhood. Pediatric AML (pAML) accounts for 15-20% of all pediatric leukemias and differs considerably from adult AML. Next-generation sequencing technologies have enabled the research community to "paint" the genomic and epigenomic landscape in order to identify pathology-associated mutations and other prognostic biomarkers in pAML. Although current treatments have improved the prognosis for pAML, chemoresistance, recurrence, and refractory disease remain major challenges. In particular, pAML relapse is commonly caused by leukemia stem cells that resist therapy. Marked patient-to-patient heterogeneity is likely the primary reason why the same treatment is successful for some patients but, at best, only partially effective for others. Accumulating evidence indicates that patient-specific clonal composition impinges significantly on cellular processes, such as gene regulation and metabolism. Although our understanding of metabolism in pAML is still in its infancy, greater insights into these processes and their (epigenetic) modulation may pave the way toward novel treatment options. In this review, we summarize current knowledge on the function of genetic and epigenetic (mis)regulation in pAML, including metabolic features observed in the disease. Specifically, we describe how (epi)genetic machinery can affect chromatin status during hematopoiesis, leading to an altered metabolic profile, and focus on the potential value of targeting epigenetic abnormalities in precision and combination therapy for pAML. We also discuss the possibility of using alternative epidrug-based therapeutic approaches that are already in clinical practice, either alone as adjuvant treatments and/or in combination with other drugs.

Molecular evaluation of gene mutation profiles and copy number variations in pediatric acute myeloid leukemia

BACKGROUND

The objectives of this study were to investigate the mutation profiles of targeted genes and copy number variations (CNVs) in normal cytogenetics (CN) pediatric acute myeloid leukemia (AML).

METHODS

This prospective study was conducted from October 2018 to December 2020. The next-generation sequencing (NGS) and chromosomal microarray analyses (CMA) were performed in pediatric CN-AML patients.

RESULTS

Out of 94 children (aged ≤18 years), 70 patients with AML (24 excluded) underwent conventional karyotyping/cytogenetic analyses. Forty-five (64.3%) of patients had abnormal/ recurrent cytogenetic abnormalities and 25 (35.7%) had normal cytogenetics. Twenty-three out of 25 CN-AML were further processed for gene mutation profile and CNVs using NGS and CMA, respectively. Twenty-two out of 23 (95.7%) patients were detected to have mutations in various genes. The common mutations were: NRAS, NPM1, CEBPA, KRAS, KIT, RUNX1, NOTCH1, WT1, GATA1, GATA2, FLT3, KMT2D, FLT3-TKD, and PHF6. Copy number variations (CNVs) were detected in nine patients (39%), and eight (34.8%) had a long contiguous stretch of homozygosity (LCSH) /loss of heterozygosity (LOH). An LCSH was detected on chromosomes 5, 7, 11, and 19. The gains were more common than losses (8 vs 2). The gains were observed on chromosomes 8, 9, 14, 19, 21, and 22, and the losses were detected on chromosomes 7 and 10. Monosomy was observed in three patients. Three patients (monosomy7, n = 2, and FLT-ITD, n = 1) were reclassified into the high-risk category. Post-induction, complete remission was achieved in all evaluable patients.

CONCLUSION

CN-AML patients have genetic abnormalities that can be detected by more advanced techniques like NGS and CMA. These genetic abnormalities play a role in risk stratification that may remain hidden in otherwise CN-AML.

Whole exome sequencing of pediatric leukemia reveals a novel InDel within FLT-3 gene in AML patient from Mizo tribal population, Northeast India

Background

Leukemia is the most common type of cancer in pediatrics. Genomic mutations contribute towards the molecular mechanism of disease progression and also helps in diagnosis and prognosis. This is the first scientific mutational exploration in whole exome of pediatric leukemia patients from a cancer prone endogamous Mizo tribal population, Northeast India.

Result

Three non-synonymous exonic variants in NOTCH1 (p.V1699E), MUTYH (p.G143E) and PTPN11 (p.S502P) were found to be pathogenic. A novel in-frame insertion-deletion within the juxtamembrane domain of FLT3 (p.Tyr589_Tyr591delinsTrpAlaGlyAsp) was also observed.

Conclusion

These unique variants could have a potential mutational significance and these could be candidate genes in elucidating the possibility of predisposition to cancers within the population. This study merits further investigation for its role in diagnosis and prognosis and also suggests the need for population wide screening to identify unique mutations that might play a key role towards precision medicine.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12863-022-01037-x.

Recent advances in the discovery of protein tyrosine phosphatase SHP2 inhibitors

Src homology 2 domain-containing protein tyrosine phosphatase (SHP2) is a non-receptor protein tyrosine phosphatase encoded by the Ptpn11 gene, which regulates cell growth, differentiation and apoptosis via modulating various signaling pathways, such as the RAS/ERK signaling pathway, and participates in the PD-1/PD-L1 pathway governing immune surveillance. It has been recognized as a breakthrough antitumor therapeutic target. Besides, numerous studies have shown that SHP2 plays an important role in the regulation of inflammatory diseases. However, inhibitors targeting the active site of SHP2 lack drug-likeness due to their low selectivity and poor bioavailability, thus none has advanced to clinical development. Recently, allosteric inhibitors that stabilize the inactive conformation of SHP2 have achieved breakthrough progress, providing the clinical proof for the druggability of SHP2 as an antitumor drug target. This paper reviews the recently reported design and discovery of SHP2 small molecule inhibitors, focused on the structure-activity relationship (SAR) analysis of several representative SHP2 inhibitors, outlining the evolution and therapeutic potential of the small molecule inhibitors targeting SHP2.

Inhibition of SHP2 as an approach to block RAS-driven cancers

The non-receptor protein tyrosine phosphatase SHP2 (encoded by PTPN11) is a critical component of RAS/MAPK signaling by acting upstream of RAS to promote oncogenic signaling and tumor growth. Over three decades, SHP2 was considered "undruggable" because enzymatic active-site inhibitors generally showed off-target inhibition of other proteins and low membrane permeability. More recently, allosteric SHP2 inhibitors with striking inhibitory potency have been developed. These small molecules effectively block the signal transduction between receptor tyrosine kinases (RTKs) and RAS/MAPK signaling and show efficacy in preclinical cancer models. Moreover, clinical evaluation of these allosteric SHP2 inhibitors is ongoing. RAS proteins which harbor transforming properties by gain-of-function mutations are present in various cancer types. While inhibitors of KRASG12C show early clinical promise, resistance remains a challenge and other forms of oncogenic RAS remain to be selectively inhibited. Here, we summarize the role of SHP2 in RAS-driven cancers and the therapeutic potential of allosteric SHP2 inhibitors as a strategy to block RAS-driven cancers.

Impact of PTPN11 mutations on clinical outcome analyzed in 1529 patients with acute myeloid leukemia

The tyrosine-protein phosphatase nonreceptor type 11 (PTPN11) is an important regulator of RAS signaling and frequently affected by mutations in patients with acute myeloid leukemia (AML). Despite the relevance for leukemogenesis and as a potential therapeutic target, the prognostic role is controversial. To investigate the prognostic impact of PTPN11 mutations, we analyzed 1529 adult AML patients using next-generation sequencing. PTPN11 mutations were detected in 106 of 1529 (6.93%) patients (median VAF: 24%) in dominant (36%) and subclonal (64%) configuration. Patients with PTPN11 mutations were associated with concomitant mutations in NPM1 (63%), DNMT3A (37%), and NRAS (21%) and had a higher rate of European LeukemiaNet (ELN) favorable cytogenetics (57.8% vs 39.1%; P < .001) and higher white blood cell counts (P = .007) compared with PTPN11 wild-type patients. In a multivariable analysis, PTPN11 mutations were independently associated with poor overall survival (hazard ratio [HR]: 1.75; P < .001), relapse-free survival (HR: 1.52; P = .013), and a lower rate of complete remission (odds ratio: 0.46; P = .008). Importantly, the deleterious effect of PTPN11 mutations was confined predominantly to the ELN favorable-risk group and patients with subclonal PTPN11 mutations (HR: 2.28; P < .001) but not found with dominant PTPN11 mutations (HR: 1.07; P = .775), presumably because of significant differences within the rate and spectrum of associated comutations. In conclusion, our data suggest an overall poor prognostic impact of PTPN11 mutations in AML, which is significantly modified by the underlying cytogenetics and the clonal context in which they occur.

Mutational landscape of Juvenile Myelomonocytic Leukemia (JMML)-A real-world context

INTRODUCTION

Juvenile myelomonocytic leukemia (JMML) is a rare childhood neoplasm (<5% cases), which has been categorized under myelodysplastic/myeloproliferative neoplasms (MDS/MPN) in the recent classification by the World Health Organization.

METHODS

We developed a 51-gene (151.5kB) low-cost targeted myeloid panel based on single-molecule molecular inversion probes to comprehensively evaluate the genomic profile of Juvenile myelomonocytic leukemia (JMML).

RESULTS

A total of 50 children with clinical and pathological features of JMML were sequenced at high coverage. Among the 50 patients, 44(88%) harbored mutations in one of the RAS/MAPK-pathway genes, most frequently in NRAS (32%), followed by PTPN11 (28%) and NF1 (22%). One-fifth of children had more than one mutation, with 5 cases harboring two RAS pathway mutations. Monosomy 7 was detected in 32% (16) patients, and five of these did not harbor any RAS pathway mutations. Children with monosomy 7 showed shorter overall survival compared with their wild-type counterparts (P = .02).

CONCLUSION

Our study highlights that comprehensive genomic profiling identifies at least one mutation in almost 90% of JMML patients. Performing genomic analysis at baseline might help in triaging children with JMML for allogenic stem cell transplant in resource-constrained settings.

The Clinical impact of PTPN11 mutations in adults with acute myeloid leukemia

While germline and somatic mutations in the gene PTPN11, encoding a phosphatase which regulates the RAS signaling pathway, are well characterized in children with Noonan syndrome and juvenile myelomonocytic leukemia, less is known about their clinical impact in adults with acute myeloid leukemia (AML). To elucidate the effect of PTPN11 mutations (PTPN11^mut) on clinical outcomes, we screened adult patients with AML treated at our institution using targeted next-generation sequencing. Among 1406 consecutive patients, 112 (8%) had PTPN11^mut. These mutations were more commonly associated with the acute myelomonocytic/monocytic leukemia subtype than was wild-type PTPN11, while none were detected in patients with core-binding factor AML. They co-occurred more commonly with NPM1 mutations and FLT3 internal tandem duplications and less commonly with mutations in IDH2 and a complex karyotype. Compared with the wild-type allele, PTPN11^mut was associated with lower complete response rates (54% vs 40%; P = 0.04), and shorter overall survival (median 13.6 vs 8.4 months; P = 0.008). In a multivariate analysis, PTPN11^mut independently increased the risk of death, with a hazard ratio of 1.69 (95% CI, 1.25-2.29; P = 0.0007). In summary, mutations in PTPN11 have a characteristic phenotype in adults with AML and are associated with an adverse prognosis.

ZMYND11-MBTD1 induces leukemogenesis through hijacking NuA4/TIP60 acetyltransferase complex and a PWWP-mediated chromatin association mechanism

Recurring chromosomal translocation t(10;17)(p15;q21) present in a subset of human acute myeloid leukemia (AML) patients creates an aberrant fusion gene termed ZMYND11-MBTD1 (ZM); however, its function remains undetermined. Here, we show that ZM confers primary murine hematopoietic stem/progenitor cells indefinite self-renewal capability ex vivo and causes AML in vivo. Genomics profilings reveal that ZM directly binds to and maintains high expression of pro-leukemic genes including Hoxa, Meis1, Myb, Myc and Sox4. Mechanistically, ZM recruits the NuA4/Tip60 histone acetyltransferase complex to cis-regulatory elements, sustaining an active chromatin state enriched in histone acetylation and devoid of repressive histone marks. Systematic mutagenesis of ZM demonstrates essential requirements of Tip60 interaction and an H3K36me3-binding PWWP (Pro-Trp-Trp-Pro) domain for oncogenesis. Inhibitor of histone acetylation-'reading' bromodomain proteins, which act downstream of ZM, is efficacious in treating ZM-induced AML. Collectively, this study demonstrates AML-causing effects of ZM, examines its gene-regulatory roles, and reports an attractive mechanism-guided therapeutic strategy.

Clinical Utility of Next-Generation Sequencing in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a genetically heterogeneous disease that, even with current advancements in therapy, continues to have a poor prognosis. Recurrent somatic mutations have been identified in a core set of pathogenic genes including FLT3 (25-30% prevalence), NPM1 (25-30%), DNMT3A (25-30%), IDH1/2 (5-15%), and TET2 (5-15%), with direct diagnostic, prognostic, and targeted therapeutic implications. Advances in the understanding of the complex mechanisms of AML leukemogenesis have led to the development and recent US Food and Drug Administration (FDA) approval of several targeted therapies: midostaurin and gilteritinib targeting activated FLT3, and ivosidenib and enasidenib targeting mutated IDH1/2. Several additional drug candidates targeting other recurrently mutated gene pathways in AML are also being actively developed. Furthermore, outside of the realm of predicting responses to targeted therapies, many other mutated genes, which comprise the so-called long tail of oncogenic drivers in AML, have been shown to provide clinically useful diagnostic and prognostic information for AML patients. Many of these recurrently mutated genes have also been shown to be excellent biomarkers for post-treatment minimal residual disease (MRD) monitoring for assessing treatment response and predicting future relapse. In addition, the identification of germline mutations in a set of genes predisposing to myeloid malignancies may directly inform treatment decisions (particularly stem cell transplantation) and impact other family members. Recent advances in sequencing technology have made it practically and economically feasible to evaluate many genes simultaneously using next-generation sequencing (NGS). Mutation screening with NGS panels has been recommended by national and international professional guidelines as the standard of care for AML patients. NGS-based detection of the heterogeneous genes commonly mutated in AML has practical clinical utility for disease diagnosis, prognosis, prediction of targeted therapy response, and MRD monitoring.

Tyrosine phosphatase SHP2 inhibitors in tumor-targeted therapies

Src homology containing protein tyrosine phosphatase 2 (SHP2) represents a noteworthy target for various diseases, serving as a well-known oncogenic phosphatase in cancers. As a result of the low cell permeability and poor bioavailability, the traditional inhibitors targeting the protein tyrosine phosphate catalytic sites are generally suffered from unsatisfactory applied efficacy. Recently, a particularly large number of allosteric inhibitors with striking inhibitory potency on SHP2 have been identified. In particular, few clinical trials conducted have made significant progress on solid tumors by using SHP2 allosteric inhibitors. This review summarizes the development and structure–activity relationship studies of the small-molecule SHP2 inhibitors for tumor therapies, with the purpose of assisting the future development of SHP2 inhibitors with improved selectivity, higher oral bioavailability and better physicochemical properties.

Comprehensive Genomic Analysis of Noonan Syndrome and Acute Myeloid Leukemia in Adults: A Review and Future Directions

Acute myeloid leukemia (AML) in the setting of Noonan syndrome (NS) has been reported before without clear guidelines for treatment or prognosis in these subgroups of patients, most likely due to its rarity and incomplete understanding of the pathogenesis of both diseases. In the current era of next-generation sequencing-based genomic analysis, we can better identify patients with NS with more accurate AML-related prognostic markers. Germline mutations in PTPN11 are the most common cause of NS. Somatic mutations in NPM1 occur frequently in AML. Here, we describe a young adult patient with a novel combined germline PTPN11 and somatic NPM1, IDH1,and BCL6 mutations who presented with fatal AML. In addition, a 50.5-Mb interstitial deletion of 7q21.11-q33 in tumor DNA was detected by chromosomal microarray analysis. While mutations in the transcriptional repressor BCL6 are known to contribute to the pathogenesis of diffuse large B cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL), its novel identification in this patient suggests an expanded role in aggressive AML. The identification of key molecular aberrations including the overexpression of SHP2, which drives leukemogenesis and tumorigenesis, has led to the development of novel investigational targeted SHP2 inhibitors.

KRasG12D expression in the bone marrow vascular niche affects hematopoiesis with inflammatory signals

The bone marrow (BM) niche is an important milieu where hematopoietic stem and progenitor cells (HSPCs) are maintained. Previous studies have indicated that genetic mutations in various components of the niche can affect hematopoiesis and promote hematologic abnormalities, but the impact of abnormal BM endothelial cells (BMECs), a crucial niche component, on hematopoiesis remains incompletely understood. To dissect how genetic alterations in BMECs could affect hematopoiesis, we have employed a novel inducible Tie2-CreERT2 mouse model, with a tdTomato fluorescent reporter, to introduce an oncogenic KRas^G12D mutation specifically in the adult endothelial cells. Tie2-CreERT2;KRas^G12D mice had significantly more leukocytes and myeloid cells in the blood with mostly normal BM HSPC populations and developed splenomegaly. Genotyping polymerase chain reaction revealed KRas^G12D activation in BMECs but not hematopoietic cells, confirming that the phenotype is due to the aberrant BMECs. Competitive transplant assays revealed that BM cells from the KRas^G12D mice contained significantly fewer functional hematopoietic stem cells, and immunofluorescence imaging showed that the hematopoietic stem cells in the mutant mice were localized farther away from BM vasculature and closer to the endosteal area. RNA sequencing analyses found an inflammatory gene network, especially tumor necrosis factor α, as a possible contributor. Together, our results implicate an abnormal endothelial niche in compromising normal hematopoiesis.

Small Molecule Inhibitor that Stabilizes the Autoinhibited Conformation of the Oncogenic Tyrosine Phosphatase SHP2

Genetic mutations in the phosphatase PTPN11 (SHP2) are associated with childhood leukemias. These mutations cause hyperactivation of SHP2 due to the disruption of the autoinhibitory conformation. By targeting the activation-associated protein conformational change, we have identified an SHP2 inhibitor ( E)-1-(1-(5-(3-(2,4-dichlorophenyl)acryloyl)-2-ethoxy-4-hydroxybenzyl)-1,2,5,6-tetrahydropyridin-3-yl)-1 H-benzo[ d]imidazol-2(3 H)-one (LY6, 1) using computer-aided drug design database screening combined with cell-based assays. This compound inhibited SHP2 with an IC₅₀ value of 9.8 μM, 7-fold more selective for SHP2 than the highly related SHP1. Fluorescence titration, thermal shift, and microscale thermophoresis quantitative binding assays confirmed its direct binding to SHP2. This compound was further verified to effectively inhibit SHP2-mediated cell signaling and proliferation. Furthermore, mouse and patient leukemia cells with PTPN11 activating mutations were more sensitive to this inhibitor than wild-type cells. This small molecule SHP2 inhibitor has a potential to serve as a lead compound for further optimization studies to develop novel anti-SHP2 therapeutic agents.

Gain-of-function mutations in the gene encoding the tyrosine phosphatase SHP2 induce hydrocephalus in a catalytically dependent manner

Catalytically activating mutations in Ptpn11, which encodes the protein tyrosine phosphatase SHP2, cause 50% of Noonan syndrome (NS) cases, whereas inactivating mutations in Ptpn11 are responsible for nearly all cases of the similar, but distinct, developmental disorder Noonan syndrome with multiple lentigines (NSML; formerly called LEOPARD syndrome). However, both types of disease mutations are gain-of-function mutations because they cause SHP2 to constitutively adopt an open conformation. We found that the catalytic activity of SHP2 was required for the pathogenic effects of gain-of-function, disease-associated mutations on the development of hydrocephalus in the mouse. Targeted pan-neuronal knockin of a Ptpn11 allele encoding the active SHP2 E76K mutant resulted in hydrocephalus due to aberrant development of ependymal cells and their cilia. These pathogenic effects of the E76K mutation were suppressed by the additional mutation C459S, which abolished the catalytic activity of SHP2. Moreover, ependymal cells in NSML mice bearing the inactive SHP2 mutant Y279C were also unaffected. Mechanistically, the SHP2 E76K mutant induced developmental defects in ependymal cells by enhancing dephosphorylation and inhibition of the transcription activator STAT3. Whereas STAT3 activity was reduced in Ptpn11^E76K/+ cells, the activities of the kinases ERK and AKT were enhanced, and neural cell-specific Stat3 knockout mice also manifested developmental defects in ependymal cells and cilia. These genetic and biochemical data demonstrate a catalytic-dependent role of SHP2 gain-of-function disease mutants in the pathogenesis of hydrocephalus.

Regulatory Mechanisms and Novel Therapeutic Targeting Strategies for Protein Tyrosine Phosphatases

An appropriate level of protein phosphorylation on tyrosine is essential for cells to react to extracellular stimuli and maintain cellular homeostasis. Faulty operation of signal pathways mediated by protein tyrosine phosphorylation causes numerous human diseases, which presents enormous opportunities for therapeutic intervention. While the importance of protein tyrosine kinases in orchestrating the tyrosine phosphorylation networks and in target-based drug discovery has long been recognized, the significance of protein tyrosine phosphatases (PTPs) in cellular signaling and disease biology has historically been underappreciated, due to a large extent to an erroneous assumption that they are largely constitutive and housekeeping enzymes. Here, we provide a comprehensive examination of a number of regulatory mechanisms, including redox modulation, allosteric regulation, and protein oligomerization, that control PTP activity. These regulatory mechanisms are integral to the myriad PTP-mediated biochemical events and reinforce the concept that PTPs are indispensable and specific modulators of cellular signaling. We also discuss how disruption of these PTP regulatory mechanisms can cause human diseases and how these diverse regulatory mechanisms can be exploited for novel therapeutic development.

Functional variation of SHP-2 promoter is associated with preterm birth and delayed myelination and motor development in preterm infants

Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP-2) is a cytoplasmic tyrosine phosphatase that is highly expressed in hematopoietic cells and in the CNS and exerts opposite effects on signal transduction by exerting a neuroprotective or proapoptotic effect. Several mutations of SHP-2 have been found in children with myeloproliferative disorders or malignant leukemia, and some of these can affect brain development. In the present study, we aimed to identify and functionally characterize genetic variations in SHP-2 in 72 preterm and 58 full-term infants and to evaluate the effect of the variations on neurodevelopment in preterm infants. Twelve genetic variations were identified. Among them, two variations in the SHP-2 promoter, g.-317C > T and g.-273G > A, were found to significantly increase promoter activity, and the frequency of g.-273G > A was higher in preterm infants than in full-term infants. Two transcription factors, NF-κB and GABPα, were found to be involved in the transcriptional regulation of SHP-2 by the two above-mentioned variations. In particular, we found that g.-273G > A was significantly associated with delayed myelination and poor motor development in preterm infants. Our results suggest that a functional promoter variation in SHP-2 is associated with spontaneous preterm birth itself as well as white matter myelination and neurodevelopment.

Cooperation of MLL/AF10(OM-LZ) with PTPN11 activating mutation induced monocytic leukemia with a shorter latency in a mouse bone marrow transplantation model

PTPN11 mutation, a RAS signaling pathway mutation, is associated with MLL translocations in acute leukemia. A girl with MLL/AF10 AML was found to carry PTPN11G503A . To study the impact of PTPN11G503A cooperating with MLL/AF10 on leukemogenesis, we established a retroviral transduction/transplantation mouse model. Compared to the MLL/AF10(OM-LZ) leukemia cells harboring PTPN11wt , the cells harboring PTPN11G503A were hypersensitive to GM-CSF and IL3, and more resistant to death upon treatment with daunorubicin but sensitive to cytarabine. The cells harboring PTPN11G503A autonomously differentiated into macrophages (1.8%) in the medium containing IL3. Further studies showed that the cells had an elevated (∼2.9-fold) Csf1 transcription level and secreted more (∼4.5-fold) M-CSF to the medium which can stimulate monocyte/macrophage differentiation of BM cells. Mice transplanted with the cells harboring PTPN11G503A had a higher concentration of M-CSF in plasma. When mixed with the MLL/AF10(OM-LZ) leukemia cells harboring PTPN11wt , the cells harboring PTPN11G503A had an increased competitive engraftment and clonal expansion in the BM and spleen of recipient mice, although no competitive growth advantage was observed in the in vitro co-culturing assays. The mice transplanted with the MLL/AF10(OM-LZ) cells harboring PTPN11wt developed myelomonocytic leukemia, while those transplanted with the cells harboring PTPN11G503A -induced monocytic leukemia in a shorter latency. Our results demonstrated that addition of PTPN11G503A to MLL/AF10 affected cell proliferation, chemo-resistance, differentiation, in vivo BM recruitment/clonal expansion and accelerated disease progression.

Integrating Genomics Into Clinical Pediatric Oncology Using the Molecular Tumor Board at the Memorial Sloan Kettering Cancer Center

BACKGROUND

Pediatric oncologists have begun to leverage tumor genetic profiling to match patients with targeted therapies. At the Memorial Sloan Kettering Cancer Center (MSKCC), we developed the Pediatric Molecular Tumor Board (PMTB) to track, integrate, and interpret clinical genomic profiling and potential targeted therapeutic recommendations.

PROCEDURE

This retrospective case series includes all patients reviewed by the MSKCC PMTB from July 2014 to June 2015. Cases were submitted by treating oncologists and potential treatment recommendations were based upon the modified guidelines of the Oxford Centre for Evidence-Based Medicine.

RESULTS

There were 41 presentations of 39 individual patients during the study period. Gliomas, acute myeloid leukemia, and neuroblastoma were the most commonly reviewed cases. Thirty nine (87%) of the 45 molecular sequencing profiles utilized hybrid-capture targeted genome sequencing. In 30 (73%) of the 41 presentations, the PMTB provided therapeutic recommendations, of which 19 (46%) were implemented. Twenty-one (70%) of the recommendations involved targeted therapies. Three (14%) targeted therapy recommendations had published evidence to support the proposed recommendations (evidence levels 1-2), eight (36%) recommendations had preclinical evidence (level 3), and 11 (50%) recommendations were based upon hypothetical biological rationales (level 4).

CONCLUSIONS

The MSKCC PMTB enabled a clinically relevant interpretation of genomic profiling. Effective use of clinical genomics is anticipated to require new and improved tools to ascribe pathogenic significance and therapeutic actionability. The development of specific rule-driven clinical protocols will be needed for the incorporation and evaluation of genomic and molecular profiling in interventional prospective clinical trials.

Structural and Functional Consequences of Three Cancer-Associated Mutations of the Oncogenic Phosphatase SHP2

The proto-oncogene PTPN11 encodes a cytoplasmic protein tyrosine phosphatase, SHP2, which is required for normal development and sustained activation of the Ras-MAPK signaling pathway. Germline mutations in SHP2 cause developmental disorders, and somatic mutations have been identified in childhood and adult cancers and drive leukemia in mice. Despite our knowledge of the PTPN11 variations associated with pathology, the structural and functional consequences of many disease-associated mutants remain poorly understood. Here, we combine X-ray crystallography, small-angle X-ray scattering, and biochemistry to elucidate structural and mechanistic features of three cancer-associated SHP2 variants harboring single point mutations within the N-SH2:PTP interdomain autoinhibitory interface. Our findings directly compare the impact of each mutation on autoinhibition of the phosphatase and advance the development of structure-guided and mutation-specific SHP2 therapies.

Azacitidine and Sorafenib Therapy in a Pediatric Patient With Refractory Acute Myeloid Leukemia With Monosomy 7 and Somatic PTPN11 Mutation

Monosomy 7 is a well-documented cytogenetic aberration in pediatric acute myeloid leukemia (AML) and may occur in combinations with molecular abnormalities including PTPN11 mutation. PTPN11 mutations contribute to leukemogenesis through upregulation of Ras pathway signaling. We present the case of a 3-year-old female with AML with monosomy 7 and somatic PTPN11 mutation who was refractory to conventional AML chemotherapy but responded to a novel regimen of azacitidine and sorafenib followed by stem cell transplantation. Combination therapy with azacitidine and sorafenib may be an effective therapeutic strategy for patients with AML with Ras pathway abnormalities.

Gain-of-function mutations of Ptpn11 (Shp2) cause aberrant mitosis and increase susceptibility to DNA damage-induced malignancies

Gain-of-function (GOF) mutations of protein tyrosine phosphatase nonreceptor type 11 Ptpn11 (Shp2), a protein tyrosine phosphatase implicated in multiple cell signaling pathways, are associated with childhood leukemias and solid tumors. The underlying mechanisms are not fully understood. Here, we report that Ptpn11 GOF mutations disturb mitosis and cytokinesis, causing chromosomal instability and greatly increased susceptibility to DNA damage-induced malignancies. We find that Shp2 is distributed to the kinetochore, centrosome, spindle midzone, and midbody, all of which are known to play critical roles in chromosome segregation and cytokinesis. Mouse embryonic fibroblasts with Ptpn11 GOF mutations show a compromised mitotic checkpoint. Centrosome amplification and aberrant mitosis with misaligned or lagging chromosomes are significantly increased in Ptpn11-mutated mouse and patient cells. Abnormal cytokinesis is also markedly increased in these cells. Further mechanistic analyses reveal that GOF mutant Shp2 hyperactivates the Polo-like kinase 1 (Plk1) kinase by enhancing c-Src kinase-mediated tyrosine phosphorylation of Plk1. This study provides novel insights into the tumorigenesis associated with Ptpn11 GOF mutations and cautions that DNA-damaging treatments in Noonan syndrome patients with germ-line Ptpn11 GOF mutations could increase the risk of therapy-induced malignancies.

Integrative genetic analysis of mouse and human AML identifies cooperating disease alleles

Hatlen et al. provide an integrative analysis of the mutational landscape of mouse and human AML and identify functionally relevant cooperation between AML1-ETO and PTPN11 D61Y. Based on these findings, they generate a novel mouse model of t(8;21)⁺ AML.

t(8;21) is one of the most frequent chromosomal abnormalities observed in acute myeloid leukemia (AML). However, expression of AML1-ETO is not sufficient to induce transformation in vivo. Consistent with this observation, patients with this translocation harbor additional genetic abnormalities, suggesting a requirement for cooperating mutations. To better define the genetic landscape in AML and distinguish driver from passenger mutations, we compared the mutational profiles of AML1-ETO–driven mouse models of leukemia with the mutational profiles of human AML patients. We identified TET2 and PTPN11 mutations in both mouse and human AML and then demonstrated the ability of Tet2 loss and PTPN11 D61Y to initiate leukemogenesis in concert with expression of AML1-ETO in vivo. This integrative genetic profiling approach allowed us to accurately predict cooperating events in t(8;21)⁺ AML in a robust and unbiased manner, while also revealing functional convergence in mouse and human AML.

Inhibition of SHP2-mediated dephosphorylation of Ras suppresses oncogenesis

Ras is phosphorylated on a conserved tyrosine at position 32 within the switch I region via Src kinase. This phosphorylation inhibits the binding of effector Raf while promoting the engagement of GTPase-activating protein (GAP) and GTP hydrolysis. Here we identify SHP2 as the ubiquitously expressed tyrosine phosphatase that preferentially binds to and dephosphorylates Ras to increase its association with Raf and activate downstream proliferative Ras/ERK/MAPK signalling. In comparison to normal astrocytes, SHP2 activity is elevated in astrocytes isolated from glioblastoma multiforme (GBM)-prone H-Ras(12V) knock-in mice as well as in glioma cell lines and patient-derived GBM specimens exhibiting hyperactive Ras. Pharmacologic inhibition of SHP2 activity attenuates cell proliferation, soft-agar colony formation and orthotopic GBM growth in NOD/SCID mice and decelerates the progression of low-grade astrocytoma to GBM in a spontaneous transgenic glioma mouse model. These results identify SHP2 as a direct activator of Ras and a potential therapeutic target for cancers driven by a previously ‘undruggable' oncogenic or hyperactive Ras.

Aberrant Ras signalling resulting in downstream Mek/Erk pathway activation is found in many cancers. Here, the authors show that the phosphatase SHP2 dephosphorylates Ras resulting in increased Ras activity, and that increased SHP2 activity is found in glioblastomas.

Shp2 and Pten have antagonistic roles in myeloproliferation but cooperate to promote erythropoiesis in mammals

Previous data suggested a negative role of phosphatase and tensin homolog (Pten) and a positive function of SH2-containing tyrosine phosphatase (Shp2)/Ptpn11 in myelopoiesis and leukemogenesis. Herein we demonstrate that ablating Shp2 indeed suppressed the myeloproliferative effect of Pten loss, indicating directly opposing functions between pathways regulated by these two enzymes. Surprisingly, the Shp2 and Pten double-knockout mice suffered lethal anemia, a phenotype that reveals previously unappreciated cooperative roles of Pten and Shp2 in erythropoiesis. The lethal anemia was caused collectively by skewed progenitor differentiation and shortened erythrocyte lifespan. Consistently, treatment of Pten-deficient mice with a specific Shp2 inhibitor suppressed myeloproliferative neoplasm while causing anemia. These results identify concerted actions of Pten and Shp2 in promoting erythropoiesis, while acting antagonistically in myeloproliferative neoplasm development. This study illustrates cell type-specific signal cross-talk in blood cell lineages, and will guide better design of pharmaceuticals for leukemia and other types of cancer in the era of precision medicine.

SHP2 sails from physiology to pathology

Over the two past decades, mutations of the PTPN11 gene, encoding the ubiquitous protein tyrosine phosphatase SHP2 (SH2 domain-containing tyrosine phosphatase 2), have been identified as the causal factor of several developmental diseases (Noonan syndrome (NS), Noonan syndrome with multiple lentigines (NS-ML), and metachondromatosis), and malignancies (juvenile myelomonocytic leukemia). SHP2 plays essential physiological functions in organism development and homeostasis maintenance by regulating fundamental intracellular signaling pathways in response to a wide range of growth factors and hormones, notably the pleiotropic Ras/Mitogen-Activated Protein Kinase (MAPK) and the Phosphoinositide-3 Kinase (PI3K)/AKT cascades. Analysis of the biochemical impacts of PTPN11 mutations first identified both loss-of-function and gain-of-function mutations, as well as more subtle defects, highlighting the major pathophysiological consequences of SHP2 dysregulation. Then, functional genetic studies provided insights into the molecular dysregulations that link SHP2 mutants to the development of specific traits of the diseases, paving the way for the design of specific therapies for affected patients. In this review, we first provide an overview of SHP2's structure and regulation, then describe its molecular roles, notably its functions in modulating the Ras/MAPK and PI3K/AKT signaling pathways, and its physiological roles in organism development and homeostasis. In the second part, we describe the different PTPN11 mutation-associated pathologies and their clinical manifestations, with particular focus on the biochemical and signaling outcomes of NS and NS-ML-associated mutations, and on the recent advances regarding the pathophysiology of these diseases.

Juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML), a rare myeloid malignancy that occurs in young children, is considered a clonal disease originating in pluripotent stem cells of the hematopoietic system. The pathogenesis of JMML involves disruption of signal transduction through the RAS pathway, with resultant selective hypersensitivity of JMML cells to granulocyte-macrophage colony-stimulating factor. Progress has been made in understanding aspects of the molecular basis of JMML. How these molecular mechanisms may lead to targeted therapeutics and improved outcomes remains to be elucidated. Allogeneic hematopoietic stem cell transplant is the only curative option for children with JMML, and it is fraught with frequent relapse and significant toxicity.

Therapeutic potential of targeting the oncogenic SHP2 phosphatase

The Src homology 2 domain containing protein tyrosine phosphatase-2 (SHP2) is an oncogenic phosphatase associated with various kinds of leukemia and solid tumors. Thus, there is substantial interest in developing SHP2 inhibitors as potential anticancer and antileukemia agents. Using a structure-guided and fragment-based library approach, we identified a novel hydroxyindole carboxylic acid-based SHP2 inhibitor 11a-1, with an IC₅₀ value of 200 nM and greater than 5-fold selectivity against 20 mammalian PTPs. Structural and modeling studies reveal that the hydroxyindole carboxylic acid anchors the inhibitor to the SHP2 active site, while interactions of the oxalamide linker and the phenylthiophene tail with residues in the β₅–β₆ loop contribute to 11a-1’s binding potency and selectivity. Evidence suggests that 11a-1 specifically attenuates the SHP2-dependent signaling inside the cell. Moreover, 11a-1 blocks growth factor mediated Erk1/2 and Akt activation and exhibits excellent antiproliferative activity in lung cancer and breast cancer as well as leukemia cell lines.

Identification of cryptotanshinone as an inhibitor of oncogenic protein tyrosine phosphatase SHP2 (PTPN11)

Activating mutations of PTPN11 (encoding the SHP2 phosphatase) are associated with Noonan syndrome, childhood leukemias, and sporadic solid tumors. Virtual screening combined with experimental assays was performed to identify inhibitors of SHP2 from a database of natural products. This effort led to the identification of cryptotanshinone as an inhibitor of SHP2. Cryptotanshinone inhibited SHP2 with an IC50 of 22.50 μM. Fluorescence titration experiments confirmed that it directly bound to SHP2. Enzymatic kinetic analyses showed that cryptotanshinone was a mixed-type and irreversible inhibitor. This drug was further verified for its ability to block SHP2-mediated cell signaling and cellular functions. Furthermore, mouse myeloid progenitors and patient leukemic cells with the activating mutation E76K in PTPN11 were found to be sensitive to this inhibitor. Since cryptotanshinone is used to treat cardiovascular diseases in Asian countries, this drug has a potential to be used directly or to be further developed to treat PTPN11-associated malignancies.

Heterogeneous nuclear ribonucleoprotein Q is a novel substrate of SH2 domain-containing phosphatase-2

SH2 domain-containing phosphatase-2 (SHP2) is a protein-tyrosine phosphatase implicated in activation of cell signalling such as the Ras/extracellular signal-regulated kinase pathway. The substrates of SHP2 and their roles in cell activation are not fully understood. By using the substrate-trapping method with the phosphatase-dead SHP2 mutant, in which C459 was substituted by serine, and the matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometric analysis, we found that heterogeneous nuclear ribonucleoprotein Q (hnRNP Q), a protein implicated in RNA metabolisms, was a novel substrate of SHP2. Tyrosine-phosphorylated hnRNP Q was detected in HL-60, Jurkat and human peripheral blood mononuclear cells, but not mature neutrophils, treated with pervanadate. Tyrosine-phosphorylated hnRNP Q was directly bound to SHP2 in vivo and in vitro, and dephosphorylated by SHP2 in vitro. These findings suggest that hnRNP Q is a novel substrate of SHP2 and the SHP2 activity may be also involved in RNA metabolisms via dephosphorylation of hnRNP Q.

Targeting protein tyrosine phosphatase SHP2 for the treatment of PTPN11-associated malignancies

Activating mutations in PTPN11 (encoding SHP2), a protein tyrosine phosphatase (PTP) that plays an overall positive role in growth factor and cytokine signaling, are directly associated with the pathogenesis of Noonan syndrome and childhood leukemias. Identification of SHP2-selective inhibitors could lead to the development of new drugs that ultimately serve as treatments for PTPN11-associated diseases. As the catalytic core of SHP2 shares extremely high homology to those of SHP1 and other PTPs that play negative roles in cell signaling, to identify selective inhibitors of SHP2 using computer-aided drug design, we targeted a protein surface pocket that is adjacent to the catalytic site, is predicted to be important for binding to phosphopeptide substrates, and has structural features unique to SHP2. From computationally selected candidate compounds, #220-324 effectively inhibited SHP2 activity with an IC50 of 14 μmol/L. Fluorescence titration experiments confirmed its direct binding to SHP2. This active compound was further verified for its ability to inhibit SHP2-mediated cell signaling and cellular function with minimal off-target effects. Furthermore, mouse myeloid progenitors with the activating mutation (E76K) in PTPN11 and patient leukemic cells with the same mutation were more sensitive to this inhibitor than wild-type cells. This study provides evidence that SHP2 is a "druggable" target for the treatment of PTPN11-associated diseases. As the small-molecule SHP2 inhibitor identified has a simple chemical structure, it represents an ideal lead compound for the development of novel anti-SHP2 drugs. Mol Cancer Ther; 12(9); 1738-48. ©2013 AACR.

Activating mutations in protein tyrosine phosphatase Ptpn11 (Shp2) enhance reactive oxygen species production that contributes to myeloproliferative disorder

Gain of function (GOF) mutations in protein tyrosine phosphatase Ptpn11 have been identified in childhood leukemias, and these mutations are sufficient to drive the development of myeloproliferative disorder and malignant leukemias in mice. However, the molecular mechanisms by which Ptpn11 mutations induce these malignancies are not completely understood. Here we report that Ptpn11 GOF mutations cause cytokine hypersensitivity in hematopoietic cells partly by enhancing the production of reactive oxygen species (ROS). GOF mutations D61G or E76K in Ptpn11 increased ROS levels in myeloid progenitors but not in hematopoietic stem cells. Increased ROS enhanced cellular responses to cytokines by promoting cytokine signaling. Treatment with an antioxidant partially corrected cytokine hypersensitivity in Ptpn11 mutant progenitors. Further analyses demonstrated that Ptpn11 mutations increased mitochondrial aerobic metabolism by interacting with a novel substrate in the mitochondria. This study provides new insights into the pathogenic effects of GOF mutations of Ptpn11 and implies that antioxidants may have a therapeutic benefit for the leukemic patients with these mutations.

The protein tyrosine phosphatase, Shp2, positively contributes to FLT3-ITD-induced hematopoietic progenitor hyperproliferation and malignant disease in vivo

Internal tandem duplications (ITDs) in the fms-like tyrosine kinase receptor (FLT3-ITDs) confer a poor prognosis in acute myeloid leukemia (AML). We hypothesized that increased recruitment of the protein tyrosine phosphatase, Shp2, to FLT3-ITDs contributes to FLT3 ligand (FL)-independent hyperproliferation and STAT5 activation. Co-immunoprecipitation demonstrated constitutive association of Shp2 with the FLT3-ITD, N51-FLT3, as well as with STAT5. Knockdown of Shp2 in Baf3/N51-FLT3 cells significantly reduced proliferation while having little effect on WT-FLT3-expressing cells. Consistently, mutation of N51-FLT3 tyrosine 599 to phenylalanine or genetic disruption of Shp2 in N51-FLT3-expressing bone marrow low-density mononuclear cells reduced proliferation and STAT5 activation. In transplants, genetic disruption of Shp2 in vivo yielded increased latency to and reduced severity of FLT3-ITD-induced malignancy. Mechanistically, Shp2 co-localizes with nuclear phospho-STAT5, is present at functional interferon-γ activation sites (GAS) within the BCL2L1 promoter, and positively activates the human BCL2L1 promoter, suggesting that Shp2 works with STAT5 to promote pro-leukemogenic gene expression. Further, using a small molecule Shp2 inhibitor, the proliferation of N51-FLT3-expressing bone marrow progenitors and primary AML samples was reduced in a dose-dependent manner. These findings demonstrate that Shp2 positively contributes to FLT3-ITD-induced leukemia and suggest that Shp2 inhibition may provide a novel therapeutic approach to AML.

Shp2 function in hematopoietic stem cell biology and leukemogenesis

PURPOSE OF REVIEW

The protein tyrosine phosphatase Shp2 is encoded by PTPN11 and positively regulates physiologic hematopoiesis. Mutations of PTPN11 cause the congenital disorder Noonan syndrome and pathologically promote human leukemias. Given the high frequency of PTPN11 mutations in human disease, several animal models have been generated to investigate Shp2 in hematopoietic stem cell (HSC) function and leukemic transformation.

RECENT FINDINGS

Two independent animal models bearing knockout of Shp2 in hematopoietic tissues clearly demonstrate the necessity of Shp2 in HSC repopulating capacity. Reduced HSC quiescence and increased apoptosis accounts for diminished HSC function in the absence of Shp2. The germline mutation Shp2D61G enhances HSC activity and induces myeloproliferative disease (MPD) in vivo by HSC transformation. The somatic mutation Shp2D61Y produces MPD in vivo but fails to induce acute leukemia, whereas somatic Shp2E76K produces MPD in vivo that transforms into full-blown leukemia. HSCs expressing Shp2D61Y do not generate MPD in recipient animals upon transplantation, whereas Shp2E76K-expressing HSCs yield MPD as well as acute leukemia in recipient animals. The mechanisms underlying the unique functions of Shp2D61Y and Shp2E76K in HSC transformation and leukemogenesis continue to be under investigation.

SUMMARY

Further understanding of the physiologic and pathologic role of Shp2 in hematopoiesis and leukemogenesis, respectively, will yield information needed to develop therapeutic strategies targeted to Shp2 in human disease.

Diagnosis and management of acute myeloid leukemia in children and adolescents: recommendations from an international expert panel

Despite major improvements in outcome over the past decades, acute myeloid leukemia (AML) remains a life-threatening malignancy in children, with current survival rates of ∼70%. State-of-the-art recommendations in adult AML have recently been published in this journal by Döhner et al. The primary goal of an international expert panel of the International BFM Study Group AML Committee was to set standards for the management, diagnosis, response assessment, and treatment in childhood AML. This paper aims to discuss differences between childhood and adult AML, and to highlight recommendations that are specific to children. The particular relevance of new diagnostic and prognostic molecular markers in pediatric AML is presented. The general management of pediatric AML, the management of specific pediatric AML cohorts (such as infants) or subtypes of the disease occurring in children (such as Down syndrome related AML), as well as new therapeutic approaches, and the role of supportive care are discussed.

Chronic myelomonocytic leukemia and atypical chronic myeloid leukemia: novel pathogenetic lesions

Chronic myelomonocytic leukemia (CMML) and atypical chronic myeloid leukemia (aCML) are distinct, yet related, entities of myelodysplastic/myeloproliferative neoplasms (MDS/MPN) characterized by morphologic dysplasia with accumulation of monocytes or neutrophils, respectively. Our understanding of the molecular pathogenesis of CMML and aCML has advanced, mainly due to the application of novel technologies such as array-based karyotyping and next-generation sequencing. In addition to previously known recurrent aberrations, somatic uniparental disomy affecting chromosomes 3, 4, 7, and 11 frequently occurs in CMML. Novel somatic mutations of genes, including those associated with proliferation signaling (CBL, RAS, RUNX1, JAK2 (V617F)) and with modification of epigenetic status (TET2, ASXL1, UTX, EZH2) have been found. Various combinations of mutations suggest a multistep pathogenesis and may account for clinical heterogeneity. Most recently, several spliceosome-associated-gene mutations were reported and SRSF2 mutations are frequently detected in CMML. The prognostic and diagnostic significance of these molecular lesions, in particular their value as biomarkers of response or resistance to specific therapies, while uncertain now is likely to be clarified as large systematic studies come to completion.

SHP-2 acts via ROCK to regulate the cardiac actin cytoskeleton

Noonan syndrome is one of the most common causes of human congenital heart disease and is frequently associated with missense mutations in the protein phosphatase SHP-2. Interestingly, patients with acute myelogenous leukemia (AML), acute lymphoblastic leukemia (ALL), juvenile myelomonocytic leukemia (JMML) and LEOPARD syndrome frequently carry a second, somatically introduced subset of missense mutations in SHP-2. To determine the cellular and molecular mechanisms by which SHP-2 regulates heart development and, thus, understand how Noonan-associated mutations affect cardiogenesis, we introduced SHP-2 encoding the most prevalent Noonan syndrome and JMML mutations into Xenopus embryos. Resulting embryos show a direct relationship between a Noonan SHP-2 mutation and its ability to cause cardiac defects in Xenopus; embryos expressing Noonan SHP-2 mutations exhibit morphologically abnormal hearts, whereas those expressing an SHP-2 JMML-associated mutation do not. Our studies indicate that the cardiac defects associated with the introduction of the Noonan-associated SHP-2 mutations are coupled with a delay or arrest of the cardiac cell cycle in M-phase and a failure of cardiomyocyte progenitors to incorporate into the developing heart. We show that these defects are a result of an underlying malformation in the formation and polarity of cardiac actin fibers and F-actin deposition. We show that these defects can be rescued in culture and in embryos through the inhibition of the Rho-associated, coiled-coil-containing protein kinase 1 (ROCK), thus demonstrating a direct relationship between SHP-2(N308D) and ROCK activation in the developing heart.

Molecular targets for the treatment of juvenile myelomonocytic leukemia

Significant advances in our understanding of the genetic defects and the pathogenesis of juvenile myelomonocytic leukemia (JMML) have been achieved in the last several years. The information gathered tremendously helps us in designing molecular targeted therapies for this otherwise fatal disease. Various approaches are being investigated to target defective pathways/molecules in this disease. However, effective therapy is still lacking. Development of specific target-based drugs for JMML remains a big challenge and represents a promising direction in this field.

Bicyclic benzofuran and indole-based salicylic acids as protein tyrosine phosphatase inhibitors

Protein tyrosine phosphatases (PTPs) constitute a large and structurally diverse family of signaling enzymes that control the cellular levels of protein tyrosine phosphorylation. Malfunction of PTP activity has significant implications in many human diseases, and the PTP protein family provides an exciting array of validated diabetes/obesity (PTP1B), oncology (SHP2), autoimmunity (Lyp), and infectious disease (mPTPB) targets. However, despite the fact that PTPs have been garnering attention as novel therapeutic targets, they remain largely an untapped resource. The main challenges facing drug developers by the PTPs are inhibitor specificity and bioavailability. Work over the last ten years has demonstrated that it is feasible to develop potent and selective inhibitors for individual members of the PTP family by tethering together small ligands that can simultaneously occupy both the active site and unique nearby peripheral binding sites. Recent results with the bicyclic salicylic acid pharmacophores indicate that the new chemistry platform may provide a potential solution to overcome the bioavailability issue that has plagued the PTP drug discovery field for many years. Structural analysis of PTP-inhibitor complexes reveals molecular determinants important for the development of more potent and selective PTP inhibitors, thus offering hope in the medicinal chemistry of a largely unexploited protein class with a wealth of attractive drug targets.