Molecular typing of adult acute myeloid leukaemia: significance of translocations, tandem duplications, methylation, and selective gene expression profiling

Investigating the Expression Pattern of the SETMAR Gene Transcript Variants in Childhood Acute Leukemia: Revisiting an Old Gene

BACKGROUND

The chimeric enzyme SETMAR (or Metnase) has been associated with several DNA processes, including DNA damage repair through the non-homologous joining pathway and suppression of chromosomal translocation in mouse fibroblasts. SETMAR overexpression has been reported in certain cancers suggesting that it might contribute to the establishment or progression of these cancers. In leukemia, the SETMAR gene transcript variants have not been widely studied. Therefore, this study aimed to quantify 3 predominant SETMAR variants in 2 types of childhood acute leukemia, acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL).

METHODS

In this study, using reverse transcription-quantitative polymerase chain reaction (RT-qPCR), the relative expression of 3 SETMAR transcript variants (Var 1, Var 2, and Var A) were evaluated in the bone marrow samples collected from 30 newly diagnosed patients with AML, 65 newly diagnosed patients with ALL, and 15 healthy individuals.

RESULTS

The expression of SETMAR variants 1 and A were significantly higher in AML patients compared with controls ( P =0.02, and P =0.009, respectively). Variant A expression was significantly higher in ALL compared with controls ( P =0.003). When comparing the expression in translocation-positive and negative subgroups, the expression of variant 1 was significantly higher in translocation-positive ALL patients ( P =0.03). The variants' distribution patterns differed concerning translocation status ( P =0.041), as variants 1 and A were dominant in the translocation-positive ALL group, and variant 2 was more prevalent in translocation-negative ones.

CONCLUSIONS

According to the results, SETMAR showed increased expression in pediatric acute leukemia's bone marrow samples, indicating a role for this molecule in leukemia pathogenesis. As this is the first report of SETMAR expression in pediatric leukemias, further studies are needed to investigate the causality of this association.

A molecular study of pediatric pilomyxoid and pilocytic astrocytomas: Genome-wide copy number screening, retrospective analysis of clinicopathological features and long-term clinical outcome

Background

Pilocytic Astrocytoma (PA) is the most common pediatric brain tumors. PAs are slow-growing tumors with high survival rates. However, a distinct subgroup of tumors defined as pilomyxoid astrocytoma (PMA) presents unique histological characteristics and have more aggressive clinical course. The studies on genetics of PMA are scarce.

Methods

In this study, we report one of the largest cohort of pediatric patients with pilomyxoid (PMA) and pilocytic astrocytomas (PA) in Saudi population providing a comprehensive clinical picture, retrospective analysis with long-term follow-up, genome-wide copy number changes, and clinical outcome of these pediatric tumors. We examined and compared genome-wide copy number aberrations (CNAs) and the clinical outcome of the patients with PA and PMA.

Results

The median progression free survival for the whole cohort was 156 months and it was 111 months for the PMA, however, not statistically significantly different between the groups (log-rank test, P = 0.726). We have identified 41 CNAs (34 gains and 7 losses) in all tested patients. Our study yielded the previously reported KIAA1549-BRAF Fusion gene in over 88% of the tested patients (89% and 80% in PMA and PA, respectively). Besides the fusion gene, twelve patients had additional genomic CNAs. Furthermore, pathway and gene network analyses of genes in the fusion region revealed alterations in retinoic acid mediated apoptosis and MAPK signaling pathways and key hub genes that may potentially be involved in tumor growth and progression, including BRAF, LUC7L2, MKRN1, RICTOR, TP53, HIPK2, HNF4A, POU5F, and SOX4.

Conclusion

Our study is the first report of a large cohort of patients with PMA and PA in the Saudi population that provides detailed clinical features, genomic copy number changes, and outcome of these pediatric tumors and may help better diagnosis and characterization of PMA.

Update on drug transporter proteins in acute myeloid leukemia: Pathological implication and clinical setting

Acute myeloid leukemia (AML) is one of the most common hematological neoplasia causing death worldwide. The long-term overall survival is unsatisfactory due to many factors including older age, genetic heterogeneity and molecular characteristics comprising additional mutations, and resistance to chemotherapeutic drugs. The expression of ABCB1/P-glycoprotein, ABCC1/MRP1, ABCG2/BCRP and LRP transporter proteins is considered the major reason for multidrug resistance (MDR) in AML, however conflicting data have been reported. Here, we review the main issues about drug transporter proteins in AML clinical scenario, and highlight the clinicopathological significance of MDR phenotype associated with ABCB1 polymorphisms and FLT3 mutation.

Dihydroartemisinin-induced apoptosis in human acute monocytic leukemia cells

Dihydroartemisinin (DHA) is a derivative of artemisinin. The present study aimed to investigate whether DHA induces apoptosis in the THP-1 human acute monocytic leukemia cell line (AMoL), and to identify the relative molecular mechanisms. The results of the present study demonstrated that the viability of THP-1 cells were inhibited by DHA in a dose- and time-dependent manner, which was accompanied by morphological characteristics associated with apoptosis. After 24 h of 200 µM DHA treatment, the proportion of apoptotic cells was significantly increased compared with the untreated controls (P<0.01). In addition, DHA downregulated the levels of B-cell lymphoma (Bcl)-2, protein kinase B (Akt)1, Akt2 and Akt3 gene expression, and increased the expression of the Bcl-2-associated X protein apoptosis regulator. The protein expression of phospho-Akt and phospho-extracellular signal-regulated kinase (ERK) was also decreased, and the protein expression level of cleaved caspase-3 was increased following treatment with DHA. Therefore, DHA may induce apoptosis in the AMoL THP-1 cell line via currently unknown underlying molecular mechanisms, including the downregulation of ERK and Akt, and the activation of caspase-3.

Prior hypomethylating agent use lacks impact on clinical outcome in patients with secondary acute myeloid leukemia arising from myelodysplastic syndromes treated with standard induction chemotherapy

Patients with secondary acute myeloid leukemia (sAML) arising from prior myelodysplastic syndromes have poor prognosis. Anthracycline plus cytarabine (7 + 3) is a standard treatment option for patients who are fit for intensive therapy. In the present study, 22 of 96 sAML patients (23 %) were treated with 7 + 3 and achieved median overall survival (OS) of 9.8 months. Hypomethylating agents (HMA) were given for MDS in 6/22 (28 %) of the patients. When evaluating the prior HMA group, CR/CRi was 50 % for those with prior HMA exposure and 63 % for those without HMA exposure (P = 0.6). Median OS was 14 months for prior HMA exposure vs 10 months for no prior HMA (P = 0.9). The outcome of sAML patients who were treated with 7 + 3 continues to be poor. No statistical significant difference was found between response rates and mOS between prior HMA exposure or not. Additional larger studies are needed to confirm our results.

Epigenetic aberrations in acute myeloid leukemia: Early key events during leukemogenesis

As a result of the introduction of new sequencing technologies, the molecular landscape of acute myeloid leukemia (AML) is rapidly evolving. From karyotyping, which detects only large genomic aberrations of metaphase chromosomes, we have moved into an era when sequencing of each base pair allows us to define the AML genome at highest resolution. This has revealed a new complex landscape of genetic aberrations where addition of mutations in epigenetic regulators has been one of the most important contributions to the understanding of the pathogenesis of AML. These findings, together with new insights into epigenetic mechanisms, have placed dysregulated epigenetic mechanisms at the forefront of AML development. Not only have several new mutations in genes directly involved in epigenetic regulatory mechanisms been discovered, but also previously well-known gene fusions have been found to exert aberrant effects through epigenetic mechanisms. In addition, mutations in epigenetic regulators such as DNMT3A, TET2, and ASXL1 have recently been found to be the earliest known events during AML evolution and to be present as preleukemic lesions before the onset of AML. In this article, we review epigenetic changes in AML also in relation to what is known about their mechanism of action and their prognostic role.

Delineation of known and new transcript variants of the SETMAR (Metnase) gene and the expression profile in hematologic neoplasms

SET domain and mariner transposase fusion gene (SETMAR), also known as Metnase, has previously been shown to suppress the formation of chromosomal translocation in mouse fibroblasts. Despite the fact that hematologic malignancies are often characterized by chromosomal rearrangements, no studies have hitherto investigated the expression pattern of the gene in these disorders. We hypothesized that a high expression of SETMAR protected the cells from chromosomal rearrangements; thus, we examined the mRNA expression of SETMAR transcript variants in hematologic patients. We identified six transcript variants (var1, var2, var5, varA, varB, varC), of which three had not been reported previously. Expression levels were quantified by transcript-specific quantitative polymerase chain reaction in 15 healthy individuals, 70 acute myeloid leukemia (AML) patients (translocation positive, n= 30 [AML(TPos)], translocation negative, n = 40 [AML(TNeg)]), seven patients with mantle cell lymphoma (t [11,14] positive), and 13 patients with chronic myeloid leukemia (t [9,22] positive). All variants were significantly overexpressed in both subgroups of AML compared with healthy individuals (var1 and var2: p < 0.00001 for both AML subgroups, varA and varB: p = 0.0002, var5: p = 0.0008, and varC: p = 0.0001 for AML(TNeg); varA: p = 0.0048, varB and var5: p = 0.0001, varC: p = 0.0017). When comparing the expression in AML(TNeg) and AML(TPos), we found a significantly increased expression of the full length SETMAR in AML(TNeg) (var1: p = 0.047), suggesting a protective effect of high SETMAR expression on formation of chromosomal translocations. In conclusion, we have found known and novel SETMAR splice variants to be significantly increased in AML. To our knowledge, this is the first study that describes an expression profile of SETMAR in subgroups of hematologic malignancies, which can be linked to the incidence of chromosomal rearrangements.

FLT3-ITD and MLL-PTD influence the expression of MDR-1, MRP-1, and BCRP mRNA but not LRP mRNA assessed with RQ-PCR method in adult acute myeloid leukemia

Fms-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) and mixed-lineage leukemia gene-partial tandem duplication (MLL-PTD) are aberrations associated with leukemia which indicate unsatisfactory prognosis. Downstream regulatory targets of FLT3-ITD and MLL-PTD are not well defined. We have analyzed the expression of MDR-1, multidrug resistant protein-1 (MRP-1), breast cancer resistance protein (BCRP), and lung resistance protein (LRP) messenger RNA (mRNA) in relation to the mutational status of FLT3-ITD and MLL-PTD in 185 acute myeloid leukemia (AML) adult patients. The real-time quantitative polymerase chain reaction method was performed to assess the expression of the MDR-1, MRP-1, BCRP, and LRP mRNA, and the results were presented as coefficients calculated using an intermediate method according to Pfaffl's rule. Significantly higher expressions of MDR-1 mRNA were found in patients who did not harbor FLT3-ITD (0.20 vs. 0.05; p = 0.0001) and MRP-1 mRNA in patients with this mutation (0.96 vs. 0.70; p = 0.002) and of BCRP mRNA in patients with MLL-PTD (0.61 vs. 0.38; p = 0.03). In univariate analysis, the high expression of MDR-1 mRNA (≥0.1317) negatively influenced the outcome of induction therapy (p = 0.05), whereas the high expression of BCRP mRNA (≥1.1487) was associated with a high relapse rate (RR) (p = 0.013). We found that the high expression of MDR-1 (≥0.1317), MRP-1 (≥0.8409), and BCRP mRNA (≥1.1487) significantly influenced disease-free survival (DFS; p = 0.059, 0.032, and 0.009, respectively) and overall survival (0.048, 0.014, and 0.059, respectively). Moreover, a high expression of BCRP mRNA (≥1.1487) proved to be an independent prognostic factor for RR (p = 0.01) and DFS (p = 0.002) in multivariate analysis. The significant correlation between the expression of MDR-1, MRP-1, and BCRP mRNA and FLT3-ITD or MLL-PTD in AML patients requires further investigation.

The evolving landscape in the therapy of acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous clonal disorder of myeloid precursors arrested in their maturation, creating a diverse disease entity with a wide range of responses to historically standard treatment approaches. While significant progress has been made in characterizing and individualizing the disease at diagnosis to optimally inform those affected, progress in treatment to reduce relapse and induce remission has been limited thus far. In addition to a brief summary of the factors that shape prognostication at diagnosis, this review attempts to expand on the current therapies under investigation that have shown promise in treating AML, including hypomethylating agents, gemtuzumab ozogamicin, FLT3 tyrosine kinase inhibitors, antisense oligonucleotides, and other novel therapies, including aurora kinases, mTOR and PI3 kinase inhibitors, PIM kinase inhibitors, HDAC inhibitors, and IDH targeted therapies. With these, and undoubtedly many others in the future, it is the hope that by combining more accurate prognostication with more effective therapies, patients will begin to have a different, and more complete, outlook on their disease that allows for safer and more successful treatment strategies.

Mitochondrial cytochrome c oxidase subunit II variations predict adverse prognosis in cytogenetically normal acute myeloid leukaemia

Alterations in the two catalytic genes cytochrome c oxidase subunits I and II (COI and COII) have recently been suggested to have an adverse impact on prognosis in patients with acute myeloid leukaemia (AML). In order to explore this in further detail, we sequenced these two mitochondrial genes in diagnostic bone marrow or blood samples in 235 patients with AML. In 37 (16%) patients, a non-synonymous variation in either COI or COII could be demonstrated. No patients harboured both COI and COII non-synonymous variations. Twenty-four (10%) patients had non-synonymous variations in COI, whereas 13 (6%) patients had non-synonymous variations in COII. The COI and COII are essential subunits of cytochrome c oxidase that is the terminal enzyme in the oxidative phosphorylation complexes. In terms of disease course, we observed that in patients with a normal cytogenetic analysis at disease presentation (CN-AML) treated with curative intent, the presence of a non-synonymous variation in the COII was an adverse prognostic marker for both overall survival and disease-free survival (DFS) in both univariate (DFS; hazard ratio (HR) 4.4, P = 0.006) and multivariate analyses (DFS; HR 7.2, P = 0.001). This is the first demonstration of a mitochondrial aberration playing an adverse prognostic role in adult AML, and we argue that its role as a potentially novel adverse prognostic marker in the subset of CN-AML should be explored further.

Epigenetic biomarker development

Epigenetic mechanisms control gene expression in a way that is stably propagated over multiple cell divisions, but which is also flexible enough to respond to environmental influences. This intermediate position between stability and plasticity renders epigenetic information highly useful for monitoring cellular states in the context of personalized medicine. Epigenetic alterations have also been identified as causal events for common diseases such as cancer and autoimmune disorders. The goal of epigenetic biomarker development is to design experimental assays that produce relevant information for diagnosis, prognosis and therapy optimization in routine clinical treatment and drug discovery. Here, I outline a systematic approach to epigenetic biomarker development and highlight key bioinformatic tools that facilitate discovery, optimization and validation of novel biomarkers.

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.

Strikingly different molecular relapse kinetics in NPM1c, PML-RARA, RUNX1-RUNX1T1, and CBFB-MYH11 acute myeloid leukemias

Early relapse detection in acute myeloid leukemia is possible using standardized real-time quantitative polymerase chain reaction (RQ-PCR) protocols. However, optimal sampling intervals have not been defined and are likely to vary according to the underlying molecular lesion. In 74 patients experiencing hematologic relapse and harboring aberrations amenable to RQ-PCR (mutated NPM1 [designated NPM1c], PML-RARA, RUNX1-RUNX1T1, and CBFB-MYH11), we observed strikingly different relapse kinetics. The median doubling time of the CBFB-MYH11 leukemic clone was significantly longer (36 days) than that of clones harboring other markers (RUNX1-RUNX1T1, 14 days; PML-RARA, 12 days; and NPM1c, 11 days; P < .001). Furthermore, we used a mathematical model to determine frequency of relapse detection and median time from detection of minimal residual disease to hematologic relapse as a function of sampling interval length. For example, to obtain a relapse detection fraction of 90% and a median time of 60 days, blood sampling every sixth month should be performed for CBFB-MYH11 leukemias. By contrast, in NPM1c(+)/FLT3-ITD(-), NPM1c(+)/FLT3-ITD(+), RUNX1-RUNX1T1, and PML-RARA leukemias, bone marrow sampling is necessary every sixth, fourth, and fourth and second month, respectively. These data carry important implications for the development of optimal RQ-PCR monitoring schedules suitable for evaluation of minimal residual disease-directed therapies in future clinical trials.

Different clinical importance of FLT3 internal tandem duplications in AML according to FAB classification: possible existence of distinct leukemogenesis involving monocyte differentiation pathway

Impact of FLT3 receptor tyrosine kinase activation via internal tandem duplication (ITD) of the juxtamembrane region on outcome of acute myeloid leukemia (AML) is still controversial. Recent researches reveal a role of FLT3 in monocyte differentiation in hematopoiesis. We analyzed the clinical impact of FLT3 alterations in adult AML patients excluding acute promyelocytic leukemia (APL) who received induction chemotherapy according to morphologic classification. Retrospective review of medical records from three centers in Korea between 1997 and 2007 was performed. Polymerase chain reaction was performed on genomic DNA derived from blood samples of patients before induction chemotherapy for FLT3-ITD detection. We assessed overall survival (OS), first disease-free survival (1-DFS), and response to induction chemotherapy. One hundred eighty-four patients (median age 49.1 years, range 16.0-76.5) with AML excluding APL received induction chemotherapy from three centers. FLT3-ITD was detected in 22 patients. One hundred forty-one patients were below age 60. One hundred seventy-nine patients received induction chemotherapy with cytarabine and idarubicin (AId) regimen. One hundred nineteen patients achieved complete remission (CR) after first induction chemotherapy. FLT3-ITD was not related to achievement of CR. 1-DFS was longer in patients without FLT3-ITD (median 1-DFS 16.5 vs. 8.5 months, p = 0.025). 1-DFS was not different according to FLT3-ITD status in nonmonocyte lineage leukemia (p = 0.355), while 1-DFS was shorter in monocyte lineage leukemia for FLT3-ITD positive patients (20.9 vs. 2.4 months, p < 0.001). FLT3-ITD had no impact on OS except for monocyte lineage, where OS was significantly shorter in FLT3-ITD positive group (39.4 vs. 6.0 months, p = 0.026). Moreover FLT3-ITD was stronger prognostic factors in monocyte lineage AML than risk stratification based on cytogenetics. Status of FLT3-ITD should be analyzed differently in AML patients according to morphologic profile. FLT3-ITD is a predictive and prognostic marker only in monocyte lineage patients. This result suggests an existence of distinct subset of monocyte lineage AML with leukemogenesis involving FLT3 activating pathway.

Epigenetic mechanisms in AML - a target for therapy

Epigenetics refers to a stable, mitotically perpetuated regulatory mechanism of gene expression without an alteration of the coding sequence. Epigenetic mechanism include DNA methylation and histone tail modifications. Epigenetic regulation is part of physiologic development and becomes abnormal in neoplasia, where silencing of critical genes by DNA methylation or histone deacetylation can contribute to leukemogenesis as an alternative to deletion or loss-of-function mutation. In acute myelogenous leukemia (AML), aberrant DNA methylation can be observed in multiple functionally relevant genes such as p15, p 73, E-cadherin, ID 4, RARbeta2. Abnormal activities of histone tail-modifying enzymes have also been seen in AML, frequently as a direct result of chromosomal translocations. It is now clear that these epigenetic changes play a significant role in development and progression of AML, and thus constitute important targets of therapy. The aim of targeting epigenetic effector protein or "epigenetic therapy" is to reverse epigenetic silencing and reactive various genes to induce a therapeutic effect such as differentiation, growth arrest, or apoptosis. Recent clinical studies have shown the relative safety and efficacy of such epigenetic therapies.

Drug delivery in acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia was among the first malignancies to be cured by drug therapy alone, but overall survival rates remain unsatisfactory and have changed little over the past 20 years. Conventional chemotherapeutic regimens, which almost invariably include cytarabine and anthracyclines, are untargeted, and more specific therapies are needed.

OBJECTIVE

We have chosen acute myeloid leukemia as a disease prototype to review established and novel targeted approaches in leukemia treatment.

METHODS

Our selection of the reviewed literature focused on drug delivery aspects.

CONCLUSION

While the toxicity profile of chemotherapeutics has been improved by liposomal formulations and antibody conjugation for leukemia-directed uptake, their efficacy has probably not changed significantly. Drugs with an alternative mode of action, including kinase inhibitors, hold great promise. Further improvements may result from the characterization of novel acute myeloid leukemia (AML) cell surface receptors and of leukemic stem cells, as well as from the design of leukemia-targeted gene therapy vectors.

Preferential hypermethylation of the Dickkopf-1 promoter in core-binding factor leukaemia

The Dickkopf-1 (DKK1) gene product is an extracellular Wnt inhibitor. Hypermethylation of the DKK1 promoter results in transcriptional silencing and may play an important role in cancer development. Here, we investigated hypermethylation of the DKK1 promoter in patients with acute myeloid leukaemia (AML), especially core-binding factor (CBF) leukaemia. The methylation status of DKK1 was analysed using methylation-specific polymerase chain reaction in 47 patients with AML. DKK1 methylation was found in 14 (29.8%) patients, and more frequently in those with CBF leukaemia (6 of 12 patients), than in those with acute promyelocytic leukaemia (APL) (0 of 6 patients) (P = 0.03). In contrast, Wnt inhibitory factor-1 methylation was found in APL (4 of 6 patients) but not in CBF leukaemia (0 of 12 patients) (P = 0.001). Multivariate analyses suggested that DKK1 methylation was a risk factor for poorer overall survival. Sequential analysis using four paired samples obtained at diagnosis and relapse suggested that DKK1 methylation was involved in the progression of leukaemia. Therefore, DKK1 methylation may be involved in leukaemogenesis, especially in CBF leukaemia, and may be a useful prognostic marker in AML.

The MLL partial tandem duplication in acute myeloid leukaemia

Mixed lineage leukaemia gene-partial tandem duplications (MLL-PTD) characterise acute myeloid leukaemia (AML) with trisomy 11 and AML with a normal karyotype. MLL-PTD confer a worse prognosis with shortened overall and event free survival in childhood and adult AML. In spite of these clinical observations, the leukaemogenic mechanism has, so far, not been determined. This review summarises clinical studies on MLL-PTD positive AML and recent experimental findings on the putative leukaemogenic role of MLL-PTD.

Phosphoinositide 3-kinase/Akt signaling pathway and its therapeutical implications for human acute myeloid leukemia

The phosphoinositide 3-kinase (PI3K)/Akt signaling pathway is crucial to many aspects of cell growth, survival and apoptosis, and its constitutive activation has been implicated in the both the pathogenesis and the progression of a wide variety of neoplasias. Hence, this pathway is an attractive target for the development of novel anticancer strategies. Recent studies showed that PI3K/Akt signaling is frequently activated in acute myeloid leukemia (AML) patient blasts and strongly contributes to proliferation, survival and drug resistance of these cells. Upregulation of the PI3K/Akt network in AML may be due to several reasons, including FLT3, Ras or c-Kit mutations. Small molecules designed to selectively target key components of this signal transduction cascade induce apoptosis and/or markedly increase conventional drug sensitivity of AML blasts in vitro. Thus, inhibitory molecules are currently being developed for clinical use either as single agents or in combination with conventional therapies. However, the PI3K/Akt pathway is important for many physiological cellular functions and, in particular, for insulin signaling, so that its blockade in vivo might cause severe systemic side effects. In this review, we summarize the existing knowledge about PI3K/Akt signaling in AML cells and we examine the rationale for targeting this fundamental signal transduction network by means of selective pharmacological inhibitors.

Promoter hypermethylation of the retinoic acid receptor beta2 gene is frequent in acute myeloid leukaemia and associated with the presence of CBFbeta-MYH11 fusion transcripts

Silencing of the putative tumour suppressor gene retinoic acid receptor beta2 (RARbeta2) caused by aberrant promoter hypermethylation has been identified in several solid tumours. In order to evaluate the extent of RARbeta2 hypermethylation and transcription in acute myeloid leukaemia (AML) at diagnosis, 320 patients were investigated by bisulphite-denaturing gradient gel electrophoresis and mRNA transcription levels were analysed in 61 of these by quantitative real-time polymerase chain reaction. The results were compared with demographic- and molecular data from the patients. While RARbeta2 was unmethylated in 10/10 bone marrow and 7/7 blood samples from healthy individuals, the gene was hypermethylated in 43% of the AML patients. The RARbeta2 degree of promoter methylation differed between and within individuals, and the mRNA transcription levels of the gene varied inter-individually by a factor of 4000. A significant inverse correlation between promoter hypermethylation and gene expression could be established (t-test, P = 0.019). Comparison of methylation data with a series of other molecular alterations in the same patient materials revealed a correlation between hypermethylation of the RARbeta2 promoter and the presence of CBF-MYH11 fusion transcripts (P < 0.01). Our data suggest that RARbeta2 promoter methylation is frequent in AML and may co-operate with the expression of CBF-MYH11 fusion transcripts in leukaemogenesis.

FMS-like tyrosine kinase 3 in normal hematopoiesis and acute myeloid leukemia

Ligand-mediated activation of the FMS-like tyrosine kinase 3 (FLT3) receptor is important for normal proliferation of primitive hematopoietic cells. However, activating mutations in FLT3 induce ligand-independent downstream signaling that promotes oncogenesis through pathways involved in proliferation, differentiation, and survival. FLT3 mutations are identified as the most frequent genetic abnormality in acute myeloid leukemia and are also observed in other leukemias. Multiple small-molecule inhibitors are under development to target aberrant FLT3 activity that confers a poor prognosis in patients.