Methylation status of the p15 and p16 genes in paediatric myelodysplastic syndrome and juvenile myelomonocytic leukaemia

The effect of decitabine-combined minimally myelosuppressive regimen bridged allo-HSCT on the outcomes of pediatric MDS from 10 years' experience of a single center

Background

Myelodysplastic syndrome (MDS) is a rare disease in children and the treatment option before the allogeneic hematopoietic stem cell transplantation (allo-HSCT) is rarely reported. Our main objective was to report our single-center experience with the DNA-hypomethylating agent, decitabine-combined minimally myelosuppressive regimen (DAC + MMR) bridged allo-HSCT in children with MDS.

Methods

Twenty-eight children with de novo MDS who underwent allo-HSCT between 2011 and 2020 were enrolled. Patients were divided into subgroups (refractory cytopenia of childhood [RCC] and advanced MDS [aMDS]) and treated by HSCT alone or pre-transplant combination treatment based on risk stratification. The patients’ clinical characteristics, treatment strategies and outcomes were retrospectively evaluated.

Results

Twenty patients with aMDS had received pre-transplant treatment (three were treated with decitabine alone, thirteen with DAC + MMR, and four with acute myeloid leukemia type [AML-type] induction therapy). DAC + MMR was well tolerated and the most common adverse events were myelosuppression and gastrointestinal reaction. DAC + MMR had shown an improved marrow complete remission (mCR) compared with AML-type chemotherapy (13/13, 100% versus 2/4, 50%, P = 0.044). The median follow-up for total cohort was 53.0 months (range, 2.3-127.0 months) and the 4-year overall survival (OS) was 71.4 ± 8.5%. In the subgroup of aMDS, pretreatment of DAC + MMR resulted in a much better survival rate than AML-type chemotherapy (84.6 ± 10.0% versus 0.0 ± 0.0%, P < 0.001).

Conclusions

The DAC + MMR bridged allo-HSCT may be recommended as a novel and effective approach.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-022-03376-1.

International Consensus Definition of DNA Methylation Subgroups in Juvenile Myelomonocytic Leukemia

PURPOSE

Known clinical and genetic markers have limitations in predicting disease course and outcome in juvenile myelomonocytic leukemia (JMML). DNA methylation patterns in JMML have correlated with outcome across multiple studies, suggesting it as a biomarker to improve patient stratification. However, standardized approaches to classify JMML on the basis of DNA methylation patterns are lacking. We, therefore, sought to define an international consensus for DNA methylation subgroups in JMML and develop classification methods for clinical implementation.

EXPERIMENTAL DESIGN

Published DNA methylation data from 255 patients with JMML were used to develop and internally validate a classifier model. Accuracy across platforms (EPIC-arrays and MethylSeq) was tested using a technical validation cohort (32 patients). The suitability of both methods for single-patient classification was demonstrated using an independent cohort (47 patients).

RESULTS

Analysis of pooled, published data established three DNA methylation subgroups as a de facto standard. Unfavorable prognostic parameters (PTPN11 mutation, elevated fetal hemoglobin, and older age) were significantly enriched in the high methylation (HM) subgroup. A classifier was then developed that predicted subgroups with 98% accuracy across different technological platforms. Applying the classifier to an independent validation cohort confirmed an association of HM with secondary mutations, high relapse incidence, and inferior overall survival (OS), while the low methylation subgroup was associated with a favorable disease course. Multivariable analysis established DNA methylation subgroups as the only significant factor predicting OS.

CONCLUSIONS

This study provides an international consensus definition for DNA methylation subgroups in JMML. We developed and validated methods which will facilitate the design of risk-stratified clinical trials in JMML.

Role of p15(INK4B) Methylation in Patients With Myelodysplastic Syndromes: A Systematic Meta-Analysis

BACKGROUND

Tumor suppressor gene cyclin-dependent kinase inhibitor 2B (p15(INK4B)) methylation has been frequently reported in myelodysplastic syndromes (MDS). However, the association between p15(INK4B) methylation and MDS remains elusive. Thus, this meta-analysis was first conducted to evaluate the clinical significance of p15(INK4B) methylation in MDS.

MATERIALS AND METHODS

Eligible studies were identified via an online electronic databases search. The overall odds ratios (ORs) or hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated.

RESULTS

Twenty-eight studies published between 1997 and 2017 were identified, including 1205 MDS patients and 243 nontumor controls. No evidence of heterogeneity was found in our study. p15(INK4B) methylation was significantly elevated in MDS compared with nontumor controls (OR, 10.37; P < .001). In addition, p15(INK4B) methylation was significantly higher in advanced MDS than in early MDS (OR, 4.70; P < .001) and was linked to an unfavorable overall survival (multivariate analysis: HR, 1.78; 95% CI, 1.23-2.71). Subgroup analyses on the basis of ethnicity and detection method showed that the results remained significant in different subgroups (all Ps < .05).

CONCLUSION

Our findings suggest that p15(INK4B) methylation might play an important role in the development, progression, and poor prognosis of MDS. More prospective studies with larger study populations are needed.

Gene mutations do not operate in a vacuum: the increasing importance of epigenetics in juvenile myelomonocytic leukemia

Juvenile myelomonocytic leukemia (JMML) stands out among malignant neoplasms of childhood in several ways. First, JMML is a model condition to elucidate the relevance of deregulated Ras signal transduction in human cancer. Second, the identification of Ras pathway mutations in JMML has informed the field of germline cancer predisposition and advanced the understanding of molecular mechanisms underlying the progression from predisposition to neoplasia. Third and not least, genomic DNA methylation was discovered to play a salient role in the classification and prognostication of the disease. This article discusses the evolution of epigenetic research on JMML over the past years and reviews the relevance of aberrant DNA methylation in the diagnosis, concept, and clinical decision-making of JMML.

Developing DNA methylation-based prognostic biomarkers of acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous clonal neoplasm characterized by complex genomic alterations. The incidence of AML increases with age, and most cases experience serious illness and poor prognosis. To explore the relationship between abnormal DNA methylation and the occurrence and development of AML based on the Gene Expression Database (GEO), this study extracted data related to methylation in AML and identified a methylated CpG site that was significantly different in terms of expression and distribution between the primary cells of AML patients, and hematopoietic stem/progenitor cells from normal bone marrow. To further investigate the differences caused by the dysfunction of methylation sites, bioinformatics analysis was used to screen methylation-related biomarkers, and the potential prognostic genes were selected by univariate and multivariate Cox proportional hazards regressions. Finally, five independent prognostic indicators were identified. In addition, these results provide new insight into the molecular mechanisms of methylation.

Panobinostat inhibits the proliferation of CD34+ CD38- cells under stimulation of hematopoietic growth factors on AGM-S3 cells in juvenile myelomonocytic leukemia

BACKGROUND

Encouraging responses to histone deacetylase inhibitors have been reported for hematologic malignancies. Here, we report effects of panobinostat and 5-azacytidine on the proliferation of juvenile myelomonocytic leukemia (JMML) CD34⁺ cells.

PROCEDURE

We previously reported that stimulation of JMML CD34⁺ cells with stem cell factor and thrombopoietin on irradiated murine AGM-S3 cells led to substantial expansion of JMML CD34⁺ cells that contained leukemic stem cells capable of transplantation into immunodeficient mice. Using this culture system, we evaluated effects of panobinostat and 5-azacytidine on the proliferation of JMML CD34⁺ cells.

RESULTS

Panobinostat dose dependently reduced the numbers of day 7 CD34⁺ cells generated under stimulation of hematopoietic growth factors on AGM-S3 cells in all eight patients with JMML. These patients possessed various genetic and/or karyotypic abnormalities. CD34⁺ CD38^- cells were substantially more sensitive to panobinostat at 10 and 20 nM than CD34⁺ CD38⁺ cells. Panobinostat, however, failed to influence the ability of AGM-S3 cells to stimulate JMML CD34⁺ cell production. In contrast to HL60 cells, apoptosis and cell cycle arrest in panobinostat-mediated inhibition were at low levels in JMML. The inhibitor also suppressed the factor-dependent proliferation of normal CD34⁺ cells on AGM-S3 cells. Meanwhile, no substantial inhibitory effects of 5-azacytidine on the growth of JMML CD34⁺ cells were observed.

CONCLUSIONS

These results demonstrate that panobinostat directly suppresses the growth of JMML CD34⁺ cells, in particular CD34⁺ CD38^- cells, regardless of the genetic abnormality type, suggesting that it is a useful antileukemic drug to target JMML stem cells at a pretransplant stage.

DNA-hypomethylating agents as epigenetic therapy before and after allogeneic hematopoietic stem cell transplantation in myelodysplastic syndromes and juvenile myelomonocytic leukemia

Myelodysplastic syndrome (MDS) is a clonal bone marrow disorder, typically of older adults, which is characterized by ineffective hematopoiesis, peripheral blood cytopenias and risk of progression to acute myeloid leukemia. Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative neoplasm occurring in young children. The common denominator of these malignant myeloid disorders is the limited benefit of conventional chemotherapy and a particular responsiveness to epigenetic therapy with the DNA-hypomethylating agents 5-azacytidine (azacitidine) or decitabine. However, hypomethylating therapy does not eradicate the malignant clone in MDS or JMML and allogeneic hematopoietic stem cell transplantation (HSCT) remains the only curative treatment option. An emerging concept with intriguing potential is the combination of hypomethylating therapy and HSCT. Possible advantages include disease control with good tolerability during donor search and HSCT preparation, improved antitumoral alloimmunity, and reduced risk of relapse even with non-myeloablative regimens. Herein we review the current role of pre- and post-transplant therapy with hypomethylating agents in MDS and JMML.

Response to treatment with azacitidine in children with advanced myelodysplastic syndrome prior to hematopoietic stem cell transplantation

Advanced myelodysplastic syndrome harbors a high risk of progression to acute myeloid leukemia and poor prognosis. In children, there is no established treatment to prevent or delay progression to leukemia prior to hematopoietic stem cell transplantation. Azacitidine is a hypomethylating agent, which was shown to slow progression to leukemia in adults with myelodysplastic syndrome. There is little data on the efficacy of azacitidine in children. We reviewed 22 pediatric patients with advanced myelodysplastic syndrome from a single center, diagnosed between January 2000 and December 2015. Of those, eight patients received off-label azacitidine before hematopoietic stem cell transplantation. A total of 31 cycles were administered and modification or delay occurred in four of them due to cytopenias, infection, nausea/vomiting, and transient renal impairment. Bone marrow blast percentages in azacitidine-treated patients decreased significantly from a median of 15% (range 9-31%) at the start of treatment to 5.5% (0-12%, P=0.02) before hematopoietic stem cell transplantation. Following azacitidine treatment, four patients (50%) achieved marrow remission, and none progressed. In contrast, three untreated patients (21.4%) had progressive disease characterized by >50% increase in blast counts or progression to leukemia. Azacitidine-treated patients had significantly increased 4-year event-free survival (P=0.04); predicted 4-year overall survival was 100% versus 69.3% in untreated patients (P=0.1). In summary, azacitidine treatment prior to hematopoietic stem cell transplantation was well tolerated in pediatric patients with advanced myelodysplastic syndrome, led to partial or complete bone marrow response in seven of eight patients (87.5%), and correlated with superior event-free survival in this cohort.

Epigenetic silencing of AKAP12 in juvenile myelomonocytic leukemia

A-kinase anchor protein 12 (AKAP12) is a regulator of protein kinase A and protein kinase C signaling, acting downstream of RAS. Epigenetic silencing of AKAP12 has been demonstrated in different cancer entities and this has been linked to the process of tumorigenesis. Here, we used quantitative high-resolution DNA methylation measurement by MassARRAY to investigate epigenetic regulation of all three AKAP12 promoters (i.e., α, β, and γ) within a large cohort of juvenile myelomonocytic leukemia (JMML) patient samples. The AKAP12α promoter shows DNA hypermethylation in JMML samples, which is associated with decreased AKAP12α expression. Promoter methylation of AKAP12α correlates with older age at diagnosis, elevated levels of fetal hemoglobin and poor prognosis. In silico screening for transcription factor binding motifs around the sites of most pronounced methylation changes in the AKAP12α promoter revealed highly significant scores for GATA-2/-1 sequence motifs. Both transcription factors are known to be involved in the haematopoietic differentiation process. Methylation of a reporter construct containing this region resulted in strong suppression of AKAP12 promoter activity, suggesting that DNA methylation might be involved in the aberrant silencing of the AKAP12 promoter in JMML. Exposure to DNMT- and HDAC-inhibitors reactivates AKAP12α expression in vitro, which could potentially be a mechanism underlying clinical treatment responses upon demethylating therapy. Together, these data provide evidence for epigenetic silencing of AKAP12α in JMML and further emphasize the importance of dysregulated RAS signaling in JMML pathogenesis.

Aberrant DNA Methylation Is Associated with a Poor Outcome in Juvenile Myelomonocytic Leukemia

Juvenile myelomonocytic leukemia (JMML), an overlap of myelodysplastic / myeloproliferative neoplasm, is an intractable pediatric myeloid neoplasm. Epigenetic regulation of transcription, particularly by CpG methylation, plays an important role in tumor progression, mainly by repressing tumor-suppressor genes. To clarify the clinical importance of aberrant DNA methylation, we studied the hypermethylation status of 16 target genes in the genomes of 92 patients with JMML by bisulfite conversion and the pryosequencing technique. Among 16 candidate genes, BMP4, CALCA, CDKN2A, and RARB exhibited significant hypermethylation in 72% (67/92) of patients. Based on the number of hypermethylated genes, patients were stratified into three cohorts based on an aberrant methylation score (AMS) of 0, 1–2, or 3–4. In the AMS 0 cohort, the 5-year overall survival (OS) and transplantation-free survival (TFS) were good (69% and 76%, respectively). In the AMS 1–2 cohort, the 5-year OS was comparable to that in the AMS 0 cohort (68%), whereas TFS was poor (6%). In the AMS 3–4 cohort, 5-year OS and TFS were markedly low (8% and 0%, respectively). Epigenetic analysis provides helpful information for clinicians to select treatment strategies for patients with JMML. For patients with AMS 3–4 in whom hematopoietic stem cell transplantation does not improve the prognosis, alternative therapies, including DNA methyltransferase inhibitors and new molecular-targeting agents, should be established as treatment options.

TET2 expression level and 5-hydroxymethylcytosine are decreased in refractory cytopenia of childhood

Myelodysplastic syndromes (MDS) are myeloid malignancies characterized by ineffective hematopoiesis, dysplasia, peripheral cytopenia and increased risk of progression to acute myeloid leukemia. Refractory cytopenia of childhood (RCC) is the most common subtype of pediatric MDS and has overlapping clinical features with viral infections and autoimmune disorders. Mutations in TET2 gene are found in about 20-25% of adult MDS and are associated with a decrease in 5-hydroxymethylcytosine (5-hmC) content. TET2 deregulation and its malignant potential were reported in adult but not in pediatric MDS. We evaluated the gene expression and the presence of mutations in TET2 gene in 19 patients with RCC. TET2 expression level was correlated with 5-hmC amount in DNA and possible regulatory epigenetic mechanisms. One out of 19 pediatric patients with RCC was a carrier of a TET2 mutation. TET2 expression and 5-hmC levels were decreased in patients when compared to a disease-free group. Lower expression was not associated to the presence of mutation or with the status of promoter methylation, but a significant correlation with microRNA-22 expression was found. These findings suggested that TET2 downregulation and low levels of 5-hmC are inversely related to miR-22 expression. The existence of a regulatory loop between microRNA-22 and TET2 may play a role in MDS pathogenesis.

RASA4 undergoes DNA hypermethylation in resistant juvenile myelomonocytic leukemia

Aberrant DNA methylation at specific genetic loci is a key molecular feature of juvenile myelomonocytic leukemia (JMML) with poor prognosis. Using quantitative high-resolution mass spectrometry, we identified RASA4 isoform 2, which maps to chromosome 7 and encodes a member of the GAP1 family of GTPase-activating proteins for small G proteins, as a recurrent target of isoform-specific DNA hypermethylation in JMML (51% of 125 patients analyzed). RASA4 isoform 2 promoter methylation correlated with clinical parameters predicting poor prognosis (older age, elevated fetal hemoglobin), with higher risk of relapse after hematopoietic stem cell transplantation, and with PTPN11 mutation. The level of isoform 2 methylation increased in relapsed cases after transplantation. Interestingly, most JMML cases with monosomy 7 exhibited hypermethylation on the remaining RASA4 allele. The results corroborate the significance of epigenetic modifications in the phenotype of aggressive JMML.

Quantitative comparison of CDKN2B methylation in pediatric and adult myelodysplastic syndromes

BACKGROUND/AIMS

Transcriptional repression of tumor suppressor genes is determined by the quantity of promoter hypermethylation. We analyzed the methylation quantity of CDKN2B in pediatric myelodysplastic syndromes (MDS).

METHODS

Quantitative measurement of CDKN2B methylation was performed in 25 pediatric MDS patients and 12 controls using pyrosequencing, and the result was compared with those from 74 adult MDS cases and 31 adult controls. The association between CDKN2B methylation quantity and factors related to prognosis including bone marrow blast percentage and karyotype was analyzed.

RESULTS

Pediatric MDS patients showed a higher methylation level (MtL) of CDKN2B than pediatric controls (2.94 vs. 1.62; p = 0.031) but a lower level than adult MDS patients (8.76; p < 0.001). MtL was higher in pediatric MDS cases with >5% blasts than in pediatric controls (3.78 vs. 1.62; p = 0.052). Pediatric MDS cases with abnormal karyotype showed a higher MtL than pediatric controls (5.95 vs. 1.62; p = 0.045).

CONCLUSIONS

We confirmed that methylation of CDKN2B is associated with the pathogenesis and prognosis in pediatric MDS. The difference in MtLs between pediatric and adult MDS might be related to the physiological hypermethylation of tumor suppressor genes in aging.

Genetic and epigenetic similarities and differences between childhood and adult AML

BACKGROUND

The biology of acute myeloid leukemia (AML) is complex and includes both genetic and epigenetic aberrations. We addressed the combined consequences of promoter hypermethylation of p15, CDH1, ER, MDR1, and RARB2 and mutation of NPM1, CEBPA, FLT3, and WT1 in a Danish cohort of 70 pediatric and 383 adult AML patients.

PROCEDURE

Mutation analysis was done by fragment analysis followed by sequencing or by sequencing alone. Methylation status was determined using methylation-sensitive melting curve analysis (MS-MCA) after initial bisulfite modification.

RESULTS

Among pediatric AMLs, we found promoter hypermethylation in p15 (47%), CDH1 (64%), ER (62%), MDR1 (8%), and RARB2 (22%) and mutations in NPM1 (11%), CEBPA (3%), FLT3ITD (4%), FLT3D835 (7%), and WT1 (7%). Promoter hypermethylation was significantly more frequent in core binding factor leukemias (CBF) compared to AMLs with abnormalities involving 11q23 (P = 0.024). Compared to adult AML we found a significant difference in p15 (47% vs. 73%, P < 0.001) and RARB2 (22% vs. 42%, P = 0.003) methylation, as well as in NPM1 (11% vs. 31%, P = 0.001) and FLT3ITD (4% vs. 26%, P < 0.001) mutation.

CONCLUSION

Age-related differences exist in the frequency of mutations and it appears that promoter hypermethylation occurs in a non-random pattern in childhood AML accompanying specific genetic aberrations, and might represent an important step in the leukemogenic transformation.

Aberrant DNA methylation characterizes juvenile myelomonocytic leukemia with poor outcome

Aberrant DNA methylation contributes to the malignant phenotype in virtually all types of cancer, including myeloid leukemia. We hypothesized that CpG island hypermethylation also occurs in juvenile myelomonocytic leukemia (JMML) and investigated whether it is associated with clinical, hematologic, or prognostic features. Based on quantitative measurements of DNA methylation in 127 JMML cases using mass spectrometry (MassARRAY), we identified 4 gene CpG islands with frequent hypermethylation: BMP4 (36% of patients), CALCA (54%), CDKN2B (22%), and RARB (13%). Hypermethylation was significantly associated with poor prognosis: when the methylation data were transformed into prognostic scores using a LASSO Cox regression model, the 5-year overall survival was 0.41 for patients in the top tertile of scores versus 0.72 in the lowest score tertile (P = .002). Among patients given allogeneic hematopoietic stem cell transplantation, the 5-year cumulative incidence of relapse was 0.52 in the highest versus 0.10 in the lowest score tertile (P = .007). In multivariate models, DNA methylation retained prognostic value independently of other clinical risk factors. Longitudinal analyses indicated that some cases acquired a more extensively methylated phenotype at relapse. In conclusion, our data suggest that a high-methylation phenotype characterizes an aggressive biologic variant of JMML and is an important molecular predictor of outcome.

Epigenetic alterations of p15(INK4B) and p16(INK4A) genes in pediatric primary myelodysplastic syndrome

We studied the methylation status of the p15(INK4B) and p16(INK4A) genes in 47 pediatric patients with primary MDS, its correlation with subtype, and the role of p15(INK4B) and p16(INK4A) in the evolution of MDS toward AML. Aberrant methylation of the p15(INK4B) gene was detected in 15 of 47 patients (32%), whereas only four patients demonstrated methylation of the p16(INK4A) gene (8%). The frequency of p15(INK4B) methylation was significantly higher in RAEB and RAEB-t subtypes (p<0.003). Aberrant methylation of the p16(INK4A) gene was also more frequent in the subtypes that characterize advanced stages of the disease (p<0.05). Evolution of disease was verified in 17 (36%) of the 47 patients. The association of p15(INK4B) and p16(INK4A) methylation status with evolution of disease was clearly significant (p<0.008 and p<0.05, respectively). These results suggest that methylation of the p15(INK4B) and p16(INK4A) genes is an epigenetic biomarker of pediatric disease evolution.

Analysis of histone modification around the CpG island region of the p15 gene in acute myeloblastic leukemia

Seven of 11 patients with acute myeloblastic leukemia (AML) had allele(s) in which more than half of 27 CpG sites in the p15 gene were methylated. The p15 CpG island region was surrounded with both the acetylated histone H3 (AcH3) and dimethylated histone H3-lysine 9 (MeH3K9) in bone marrow cells of AML patients, whereas with AcH3 alone in normal marrow cells. The p15 CpG islands of DNA immunoprecipitated with anti-AcH3 antibody and anti-MeH3K9 antibody were not always unmethylated and methylated, respectively, in the patients. These results suggest perturbed modifications of histone H3 around the p15 CpG island region in AML.

Myelodysplastic and myeloproliferative disorders in children

PURPOSE OF REVIEW

Myelodysplastic and myeloproliferative disorders are clonal myeloid malignancies characterized by the triad of a growth advantage of clonal cells, disturbed differentiation and increased apoptosis. The rarity of these disorders in children and the lack of a widely accepted classification have contributed to the paucity of reports on these malignancies in the pediatric literature. A number of significant advances have been achieved in recent years. The present review will focus on diagnostics and therapy.

RECENT FINDINGS

International consensus has been achieved on classifying these disorders into three main groups; myelodysplastic syndrome (MDS), myeloid leukemia of Down syndrome (ML-DS) and juvenile myelomonocytic leukemia (JMML). In the last few years we have witnessed important advances, especially regarding the therapy of these disorders, and we have gained insights into the molecular pathogenesis of ML-DS and JMML.

SUMMARY

Classification of myelodysplastic and myeloproliferative disorders has been facilitated. Chemotherapy regimens for ML-DS have been reduced, resulting in fewer toxic deaths and improved survival. The results of stem-cell transplantation for MDS and JMML have improved. Insight into the molecular mechanisms involved may open new therapeutic avenues.

Aberrant methylation in pediatric myelodysplastic syndrome

BACKGROUND

Aberrant methylation of gene promoter region is responsible for inappropriate gene silencing, and it has been associated to initiation and progression of cancer. Aberrant promoter methylation is frequently observed in adult patients with myelodysplastic syndrome (MDS), but in pediatric patients it has been poorly investigated.

METHODS

We examined the promoter methylation status of 13 genes in bone marrow cells collected at diagnosis of 21 pediatric patients with MDS (subtype RAEB or RAEB-t). For this analysis, we performed sodium bisulfite treatment of genomic DNA, followed by methylation specific PCR (MSP).

RESULTS

In pediatric MDS samples, we observed two genes frequently methylated: CALCA was methylated in 85.7% (18/21) of the analyzed samples and CDKN2B in 50% (6/12).

CONCLUSIONS

Our findings indicate that CALCA and CDKN2B are frequently methylated in pediatric MDS. It suggests that aberrant methylation in pediatric MDS seems to be similar to adult MDS, thus pediatric patients could be also benefited with treatment using demethylating agents.

Diversity and functional consequences of germline and somatic PTPN11 mutations in human disease

Germline mutations in PTPN11, the gene encoding the protein tyrosine phosphatase SHP-2, cause Noonan syndrome (NS) and the clinically related LEOPARD syndrome (LS), whereas somatic mutations in the same gene contribute to leukemogenesis. On the basis of our previously gathered genetic and biochemical data, we proposed a model that splits NS- and leukemia-associated PTPN11 mutations into two major classes of activating lesions with differential perturbing effects on development and hematopoiesis. To test this model, we investigated further the diversity of germline and somatic PTPN11 mutations, delineated the association of those mutations with disease, characterized biochemically a panel of mutant SHP-2 proteins recurring in NS, LS, and leukemia, and performed molecular dynamics simulations to determine the structural effects of selected mutations. Our results document a strict correlation between the identity of the lesion and disease and demonstrate that NS-causative mutations have less potency for promoting SHP-2 gain of function than do leukemia-associated ones. Furthermore, we show that the recurrent LS-causing Y279C and T468M amino acid substitutions engender loss of SHP-2 catalytic activity, identifying a previously unrecognized behavior for this class of missense PTPN11 mutations.

Molecularly targeted therapies in myelodysplastic syndromes and acute myeloid leukemias

Although there has been significant progress in acute myeloid leukemia (AML) treatment in younger adults during the last decade, standard induction therapy still fails to induce remission in up to 40% of AML patients. Additionally, relapses are common in 50-70% of patients who achieve a complete remission, and only 20-30% of patients enjoy long-term disease-free survival. The natural history of myelodysplastic syndrome (MDS) is variable, with about half of the patients dying from cytopenic complications, and an additional 20-30% transforming to AML. The advanced age of the majority of MDS patients limits the therapeutic strategies often to supportive care. To address these shortcomings, much effort has been directed toward the development of novel treatment strategies that target the evolution and proliferation of malignant clones. Presented here is an overview of molecularly targeted therapies currently being tested in AML and MDS patients, with a focus on FMS-like tyrosine kinase 3 inhibitors, farnesyltransferase inhibitors, antiangiogenesis agents, DNA hypomethylation agents, and histone deacetylase inhibitors.