MicroRNA expression profiling in acute myeloid and chronic lymphocytic leukaemias

Implication of microRNAs in Carcinogenesis with Emphasis on Hematological Malignancies and Clinical Translation

MicroRNAs (miRNAs) are evolutionarily conserved small non-coding RNAs, that are involved in the multistep process of carcinogenesis, contributing to all established hallmarks of cancer. In this review, implications of miRNAs in hematological malignancies and their clinical utilization fields are discussed. As components of the complex regulatory network of gene expression, influenced by the tissue microenvironment and epigenetic modifiers, miRNAs are “micromanagers” of all physiological processes including the regulation of hematopoiesis and metabolic pathways. Dysregulated miRNA expression levels contribute to both the initiation and progression of acute leukemias, the metabolic reprogramming of malignantly transformed hematopoietic precursors, and to the development of chemoresistance. Since they are highly stable and can be easily quantified in body fluids and tissue specimens, miRNAs are promising biomarkers for the early detection of hematological malignancies. Besides novel opportunities for differential diagnosis, miRNAs can contribute to advanced chemoresistance prediction and prognostic stratification of acute leukemias. Synthetic oligonucleotides and delivery vehicles aim the therapeutic modulation of miRNA expression levels. However, major challenges such as efficient delivery to specific locations, differences of miRNA expression patterns between pediatric and adult hematological malignancies, and potential side effects of miRNA-based therapies should be considered.

Physiological Fitness and the Pathophysiology of Chronic Lymphocytic Leukemia (CLL)

Chronic lymphocytic leukemia (CLL) is associated with physical dysfunction and low overall fitness that predicts poor survival following the commencement of treatment. However, it remains unknown whether higher fitness provides antioncogenic effects. We identified ten fit (CLL-FIT) and ten less fit (CLL-UNFIT) treatment-naïve CLL patients from 144 patients who completed a set of physical fitness and performance tests. Patient plasma was used to determine its effects on an in vitro 5-day growth/viability of three B-cell cell lines (OSU-CLL, Daudi, and Farage). Plasma exosomal miRNA profiles, circulating lipids, lipoproteins, inflammation levels, and immune cell phenotypes were also assessed. CLL-FIT was associated with fewer viable OSU-CLL cells at Day 1 (p = 0.003), Day 4 (p = 0.001), and Day 5 (p = 0.009). No differences between the groups were observed for Daudi and Farage cells. Of 455 distinct exosomal miRNAs identified, 32 miRNAs were significantly different between the groups. Of these, 14 miRNAs had ≤-1 or ≥1 log2 fold differences. CLL-FIT patients had five exosomal miRNAs with lower expression and nine miRNAs with higher expression. CLL-FIT patients had higher HDL cholesterol, lower inflammation, and lower levels of triglyceride components (all p < 0.05). CLL-FIT patients had lower frequencies of low-differentiated NKG2+/CD158a/b^neg (p = 0.015 and p = 0.014) and higher frequencies of NKG2A^neg/CD158b+ mature NK cells (p = 0.047). The absolute number of lymphocytes, including CD19+/CD5+ CLL-cells, was similar between the groups (p = 0.359). Higher physical fitness in CLL patients is associated with altered CLL-like cell line growth in vitro and with altered circulating and cellular factors indicative of better immune functions and tumor control.

The power of microRNAs as diagnostic and prognostic biomarkers in liquid biopsies

In the last decades, progresses in medical oncology have ameliorated the treatment of patients and their outcome. However, further improvements are still necessary, in particular for certain types of tumors such as pancreatic, gastric, and lung cancer as well as acute myeloid leukemia where early detection and monitoring of the disease are crucial for final patient outcome. Liquid biopsy represents a great advance in the field because it is less invasive, less time-consuming, and safer compared to classical biopsies and it can be useful to monitor the evolution of the disease as well as the response of patients to therapy. Liquid biopsy allows the detection of circulating tumor cells, nucleic acids, and exosomes not only in blood but also in different biological fluids: urine, saliva, pleural effusions, cerebrospinal fluid, and stool. Among the potential biomarkers detectable in liquid biopsies, microRNAs (miRNAs) are gaining more and more attention, since they are easily detectable, quite stable in biological fluids, and show high sensitivity. Many data demonstrate that miRNAs alone or in combination with other biomarkers could improve the diagnostic and prognostic power for many different tumors. Despite this, standardization of methods, sample preparation, and analysis remain challenging and a huge effort should be made to address these issues before miRNA biomarkers can enter the clinic. This review summarizes the main findings in the field of circulating miRNAs in both solid and hematological tumors.

Cancer cells stemness: A doorstep to targeted therapy

Recent advances in research on cancer have led to understand the pathogenesis of cancer and development of new anticancer drugs. Despite of these advancements, many tumors have been found to recur, undergo metastasis and develop resistance to therapy. Accumulated evidences suggest that small population of cancer cells known as cancer stem cells (CSC) are responsible for reconstitution and propagation of the disease. CSCs possess the ability to self-renew, differentiate and proliferate like normal stem cells. CSCs also appear to have resistance to anti-cancer therapies and subsequent relapse. The underlying stemness properties of the CSCs are reliant on multiple molecular targets such as signaling pathways, cell surface molecules, tumor microenvironment, apoptotic pathways, microRNA, stem cell differentiation, and drug resistance markers. Thus an effective therapeutic strategy relies on targeting CSCs to overcome the possible tumor relapse and chemoresistance. The targeted inhibition of these stem cell biomarkers is one of the promising approaches to eliminate cancer stemness. This review article summarizes possible targets of cancer cell stemness for the complete treatment of cancer.

Clinical significance of microRNAs in chronic and acute human leukemia

Small non-coding microRNAs (miRNAs) are epigenetic regulators that target specific cellular mRNA to modulate gene expression patterns and cellular signaling pathways. miRNAs are involved in a wide range of biological processes and are frequently deregulated in human cancers. Numerous miRNAs promote tumorigenesis and cancer progression by enhancing tumor growth, angiogenesis, invasion and immune evasion, while others have tumor suppressive effects (Hayes, et al., Trends Mol Med 20(8): 460-9, 2014; Stahlhut and Slack, Genome Med 5 (12): 111, 2013). The expression profile of cancer miRNAs can be used to predict patient prognosis and clinical response to treatment (Bouchie, Nat Biotechnol 31(7): 577, 2013). The majority of miRNAs are intracellular localized, however circulating miRNAs have been detected in various body fluids and represent new biomarkers of solid and hematologic cancers (Fabris and Calin, Mol Oncol 10(3):503-8, 2016; Allegra, et al., Int J Oncol 41(6): 1897-912, 2012). This review describes the clinical relevance of miRNAs, lncRNAs and snoRNAs in the diagnosis, prognosis and treatment response in patients with chronic lymphocytic leukemia (CLL), chronic myeloid leukemia (CML), acute lymphocytic leukemia (ALL), acute myeloid leukemia (AML) and acute adult T-cell leukemia (ATL).

Targeting leukemia stem cells in vivo with antagomiR-126 nanoparticles in acute myeloid leukemia

Current treatments for acute myeloid leukemia (AML) are designed to target rapidly dividing blast populations with limited success in eradicating the functionally distinct leukemia stem cell (LSC) population, which is postulated to be responsible for disease resistance and relapse. We have previously reported high miR-126 expression levels to be associated with a LSC-gene expression profile. Therefore, we hypothesized that miR-126 contributes to “stemness” and is a viable target for eliminating the LSC in AML. Here we first validate the clinical relevance of miR-126 expression in AML by showing that higher expression of this microRNA (miR) is associated with worse outcome in a large cohort of older (≥60 years) cytogenetically normal AML patients treated with conventional chemotherapy. We then show that miR-126 overexpression characterizes AML LSC-enriched cell subpopulations and contributes to LSC long-term maintenance and self-renewal. Finally, we demonstrate the feasibility of therapeutic targeting of miR-126 in LSCs with novel targeting nanoparticles (NP) containing antagomiR-126 resulting in in vivo reduction of LSCs likely by depletion of the quiescent cell subpopulation. Our findings suggest that by targeting a single miR, i.e., miR-126, it is possible to interfere with LSC activity, thereby opening potentially novel therapeutic approaches to treat AML patients.

MicroRNA-155 hallmarks promising accuracy for the diagnosis of various carcinomas: results from a meta-analysis

Background. Recent studies have shown that microRNAs (miRNAs) have diagnostic values in various cancers. This meta-analysis seeks to summarize the global diagnostic role of miR-155 in patients with a variety of carcinomas. Methods. Eligible studies were retrieved by searching the online databases, and the bivariate meta-analysis model was employed to generate the summary receiver operator characteristic (SROC) curve. Results. A total of 17 studies dealing with various carcinomas were finally included. The results showed that single miR-155 testing allowed for the discrimination between cancer patients and healthy donors with a sensitivity of 0.82 (95% CI: 0.73–0.88) and specificity of 0.77 (95% CI: 0.70–0.83), corresponding to an area under curve (AUC) of 0.85, while a panel comprising expressions of miR-155 yielded a sensitivity of 0.76 (95% CI: 0.68–0.82) and specificity of 0.82 (95% CI: 0.77–0.86) in diagnosing cancers. The subgroup analysis displayed that serum miR-155 test harvested higher accuracy than plasma-based assay (the AUC, sensitivity, and specificity were, resp., 0.87 versus 0.73, 0.78 versus 0.74, and 0.77 versus 0.70). Conclusions. Our data suggest that single miR-155 profiling has a potential to be used as a screening test for various carcinomas, and parallel testing of miR-155 confers an improved specificity compared to single miR-155 analysis.

Microvesicles as mediators of intercellular communication in cancer

The discovery that cancer cells generate large membrane-enclosed packets of epigenetic information, known as microvesicles (MVs), that can be transferred to other cells and influence their behavior (Antonyak et al., Small GTPases 3:219-224, 2012; Cocucci et al., Trends Cell Biol 19:43-51, 2009; Rak, Semin Thromb Hemost 36:888-906, 2010; Skog et al., Nat Cell Biol 10:1470-1476, 2008) has added a unique perspective to the classical paracrine signaling paradigm. This is largely because, in addition to growth factors and cytokines, MVs contain a variety of components that are not usually thought to be released into the extracellular environment by viable cells including plasma membrane-associated proteins, cytosolic- and nuclear-localized proteins, as well as nucleic acids, particularly RNA transcripts and micro-RNAs (Skog et al., Nat Cell Biol 10:1470-1476, 2008; Al-Nedawi et al., Nat Cell Biol 10:619-624, 2008; Antonyak et al., Proc Natl Acad Sci U S A 108:4852-4857, 2011; Balaj et al., Nat Commun 2:180, 2011; Choi et al., J Proteome Res 6:4646-4655, 2007; Del Conde et al., Blood 106:1604-1611, 2005; Gallo et al., PLoS One 7:e30679, 2012; Graner et al., FASEB J 23:1541-1557, 2009; Grange et al., Cancer Res 71:5346-5356, 2011; Hosseini-Beheshti et al., Mol Cell Proteomics 11:863-885, 2012; Martins et al., Curr Opin Oncol 25:66-75, 2013; Noerholm et al., BMC Cancer 12:22, 2012; Zhuang et al., EMBO J 31:3513-3523, 2012). When transferred between cancer cells, MVs have been shown to stimulate signaling events that promote cell growth and survival (Al-Nedawi et al., Nat Cell Biol 10:619-624, 2008). Cancer cell-derived MVs can also be taken up by normal cell types that surround the tumor, an outcome that helps shape the tumor microenvironment, trigger tumor vascularization, and even confer upon normal recipient cells the transformed characteristics of a cancer cell (Antonyak et al., Proc Natl Acad Sci U S A 108:4852-4857, 2011; Martins et al., Curr Opin Oncol 25:66-75, 2013; Al-Nedawi et al., Proc Natl Acad Sci U S A 106:3794-3799, 2009; Ge et al., Cancer Microenviron 5:323-332, 2012). Thus, the production of MVs by cancer cells plays crucial roles in driving the expansion of the primary tumor. However, it is now becoming increasingly clear that MVs are also stable in the circulation of cancer patients, where they can mediate long-range effects and contribute to the formation of the pre-metastatic niche, an essential step in metastasis (Skog et al., Nat Cell Biol 10:1470-1476, 2008; Noerholm et al., BMC Cancer 12:22, 2012; Peinado et al., Nat Med 18:883-891, 2012; Piccin et al., Blood Rev 21:157-171, 2007; van der Vos et al., Cell Mol Neurobiol 31:949-959, 2011). These findings, when taken together with the fact that MVs are being aggressively pursued as diagnostic markers, as well as being considered as potential targets for intervention against cancer (Antonyak et al., Small GTPases 3:219-224, 2012; Hosseini-Beheshti et al., Mol Cell Proteomics 11:863-885, 2012; Martins et al., Curr Opin Oncol 25:66-75, 2013; Ge et al., Cancer Microenviron 5:323-332, 2012; Peinado et al., Nat Med 18:883-891, 2012; Piccin et al., Blood Rev 21:157-171, 2007; Al-Nedawi et al., Cell Cycle 8:2014-2018, 2009; Cocucci and Meldolesi, Curr Biol 21:R940-R941, 2011; D'Souza-Schorey and Clancy, Genes Dev 26:1287-1299, 2012; Shao et al., Nat Med 18:1835-1840, 2012), point to critically important roles for MVs in human cancer progression that can potentially be exploited to develop new targeted approaches for treating this disease.

MicroRNAs and cancer stem cells: the sword and the shield

Emerging chemotherapy drugs and targeted therapies have been widely applied in anticancer treatment and have given oncologists a promising future. Nevertheless, regeneration and recurrence are still huge obstacles on the way to cure cancer. Cancer stem cells (CSCs) are capable of self-renewal, tumor initiation, recurrence, metastasis, therapy resistance, and reside as a subset in many, if not all, cancers. Therefore, therapeutics specifically targeting and killing CSCs are being identified, and may be promising and effective strategies to eliminate cancer. MicroRNAs (miRNAs, miRs), small noncoding RNAs regulating gene expression in a post-transcriptional manner, are dysregulated in most malignancies and are identified as important regulators of CSCs. However, limited knowledge exists for biological and molecular mechanism by which miRNAs regulate CSCs. In this article, we review CSCs, miRNAs and the interactions between miRNA regulation and CSCs, with a specific focus on the molecular mechanisms and clinical applications. This review will help us to know in detail how CSCs are regulated by miRNAs networks and also help to develop more effective and secure miRNA-based clinical therapies.

Molecular-based classification of acute myeloid leukemia and its role in directing rational therapy: personalized medicine for profoundly promiscuous proliferations

Acute myeloid leukemia (AML) is not a single pathologic entity but represents a heterogeneous group of malignancies. This heterogeneity is exemplified by the variable clinical outcomes that are observed in patients with AML, and it is largely the result of diverse mutations within the leukemic cells. These mutations range from relatively large genetic alterations, such as gains, losses, and translocations of chromosomes, to single nucleotide changes. Detection of many of these mutations is required for accurate diagnosis, prognosis, and treatment of patients with AML. As such, many testing modalities have been developed and are currently employed in clinical laboratories to ascertain mutational status at prognostically and therapeutically critical loci. The assays include those that specifically identify large chromosomal alterations, such as conventional metaphase analysis and fluorescence in situ hybridization, and methods that are geared more toward analysis of small mutations, such as PCR with allele-specific oligonucleotide primers. Furthermore, newer tests, including array analysis and next-generation sequencing, which can simultaneously probe numerous molecular aberrancies within tumor cells, are likely to become commonplace in AML diagnostics. Each testing method clearly has advantages and disadvantages, an understanding of which should influence the choice of test in various clinical circumstances. To aid such understanding, this review discusses both genetic mutations in AML and the clinical tests-including their pros and cons-that may be used to probe these abnormalities. Additionally, we highlight the significance of genetic testing by describing cases in which results of genetic testing significantly influence clinical management of patients with AML.

Alteration in miRNA gene expression pattern in acute promyelocytic leukemia cell induced by arsenic trioxide: a possible mechanism to explain arsenic multi-target action

MicroRNAs (miRNAs) are involved in cancer pathogenesis, apoptosis, and cell growth, and these miRNAs are thought to be functional as oncogenes and/or tumor suppressors in the gene regulatory networks. We studied the potential contribution of miRNAs in acute promyelocytic leukemia (APL) cell NB4 during the apoptosis induction by arsenic trioxide (ATO). The apoptotic effects of ATO on the NB4 cell line at a pharmacological dose (2 μM) was verified using cell growth and viability assays, MTT assay, BrdU cell proliferation assay, flow cytometric analysis, and caspase-3 activity assay. miRNAs from untreated and 2 μM ATO-treated NB4 cell line were extracted, purified, and converted to complementary DNAs. Differential expressions of 88 cancer-related miRNAs were analyzed by real-time reverse transcription PCR using miRNA PCR cancer-array system. After normalizing to the average Ct value of three housekeeping genes in the array (U6, SNORD47, and SNORD48), the fold change of miRNAs was calculated in the ATO-treated cells as compared to untreated. Among the 88 cancer-focused miRNAs, 51 miRNAs were found to be differentially expressed more than 2-fold after ATO treatment. Of these, 48 miRNAs were upregulated up to 21.65-fold changes, while three miRNAs were downregulated up to 5.19-fold changes. By screening the literature, a majority of these upregulated miRNAs were found to have tumor and/or metastatic suppressors' functions associated with cell cycle arrest and apoptosis, as well as inhibition of angiogenesis, invasion, and metastasis. Our results demonstrate that ATO, at the relevant concentration, modulate a substantial number of cancer-related miRNAs in APL cell line; most of these are known to function as a tumor and/or metastatic suppressors and have confirmed targets involved in cell cycle arrest and apoptosis. The results of this study support the hypothesis that miRNAs may play a mediatory role in eliciting the multi-target and pleiotropic action of ATO.

MicroRNA-146a and hemopoietic disorders

MicroRNAs (MiRNAs) are a class of small non-coding regulatory RNAs that repress protein expression at the posttranscriptional level and play important roles in hematopoiesis processes. MiR-146a is a miRNA that is thought to regulate physiological and pathophysiological pathways in hematopoietic cells. In this review, we focus on recent progress in analyzing the functional roles of miR-146a in normal hematopoiesis and hematopoietic disease. We suggest that manipulation of miR-146a expression may represent a potential new therapy for several hematopoietic diseases, and may further serve as a biomarker for diagnosis, prevention, and treatment of such disease.

The oncogenic and tumour suppressive roles of microRNAs in cancer and apoptosis

MicroRNAs (miRNAs) are small, non-coding, endogenous RNAs that regulate gene expression at the post-transcriptional level. MiRNAs play important roles in regulating a variety of biological process such as proliferation, differentiation and apoptosis. It has been demonstrated that miRNAs have a crucial function in oncogenesis by regulating cell proliferation and apoptosis as oncogenes or tumour suppressors. As several reports have underlined the possible contribution of miRNAs to promote or evade apoptosis, it seems that the dysregulation of miRNAs involved in apoptosis may provide a mechanism for cancer development. Given emerging evidence that points to oncogenic and tumour suppressive roles of miRNAs in cancer and apoptosis, it is thought that manipulating miRNA expression level may be a potential therapeutic strategy for curing cancer.

Prognostic significance of expression of a single microRNA, miR-181a, in cytogenetically normal acute myeloid leukemia: a Cancer and Leukemia Group B study

PURPOSE

To evaluate the prognostic significance of expression levels of a single microRNA, miR-181a, in the context of established molecular markers in cytogenetically normal acute myeloid leukemia (CN-AML), and to gain insight into the leukemogenic role of miR-181a.

PATIENTS AND METHODS

miR-181a expression was measured in pretreatment marrow using Ohio State University Comprehensive Cancer Center version 3.0 arrays in 187 younger (<60 years) adults with CN-AML. Presence of other molecular prognosticators was assessed centrally. A gene-expression profile associated with miR-181a expression was derived using microarrays and evaluated by Gene-Ontology analysis.

RESULTS

Higher miR-181a expression associated with a higher complete remission (CR) rate (P=.04), longer overall survival (OS; P=.01) and a trend for longer disease-free survival (DFS; P=.09). The impact of miR-181a was most striking in poor molecular risk patients with FLT3-internal tandem duplication (FLT3-ITD) and/or NPM1 wild-type, where higher miR-181a expression associated with a higher CR rate (P=.009), and longer DFS (P<.001) and OS (P<.001). In multivariable analyses, higher miR-181a expression was significantly associated with better outcome, both in the whole patient cohort and in patients with FLT3-ITD and/or NPM1 wild-type. These results were also validated in an independent set of older (≥60 years) patients with CN-AML. A miR-181a-associated gene-expression profile was characterized by enrichment of genes usually involved in innate immunity.

CONCLUSION

To our knowledge, we provide the first evidence that the expression of a single microRNA, miR-181a, is associated with clinical outcome of patients with CN-AML and may refine their molecular risk classification. Targeted treatments that increase endogenous levels of miR-181a might represent novel therapeutic strategies.

The prognostic and functional role of microRNAs in acute myeloid leukemia

Expression of microRNAs, a new class of noncoding RNAs that hybridize to target messenger RNA and regulate their translation into proteins, has been recently demonstrated to be altered in acute myeloid leukemia (AML). Distinctive patterns of increased expression and/or silencing of multiple microRNAs (microRNA signatures) have been associated with specific cytogenetic and molecular subsets of AML. Changes in the expression of several microRNAs altered in AML have been shown to have functional relevance in leukemogenesis, with some microRNAs acting as oncogenes and others as tumor suppressors. Both microRNA signatures and a single microRNA (ie, miR-181a) have been shown to supply prognostic information complementing that gained from cytogenetics, gene mutations, and altered gene expression. Moreover, it has been demonstrated experimentally that antileukemic effects can be achieved by modulating microRNA expression by pharmacologic agents and/or increasing low endogenous levels of microRNAs with tumor suppressor function by synthetic microRNA oligonucleotides, or down-regulating high endogenous levels of leukemogenic microRNAs by antisense oligonucleotides (antagomirs). Therefore, it is reasonable to predict the development of novel microRNA-based therapeutic approaches in AML. We review herein results of current studies analyzing changes of microRNA expression in AML and discuss their potential biologic, diagnostic, and prognostic relevance.

[Molecular evolution and regulatory mechanism of microRNAs]

MicroRNAs, a type of small non-coding RNA specialized in regulation of gene expression, extensively participate in biological development, cell differentiation, apoptosis, and other cellular processes. MiRNAs evolved independently in different strains and generally conserved in the process of evolution. This review summarized the origin, regulation of methylation, and evolutionary conservation of miRNAs. In addition, application of miRNAs in diseases, animals and plants was discussed.

IDH1 and IDH2 gene mutations identify novel molecular subsets within de novo cytogenetically normal acute myeloid leukemia: a Cancer and Leukemia Group B study

PURPOSE To analyze the frequency and associations with prognostic markers and outcome of mutations in IDH genes encoding isocitrate dehydrogenases in adult de novo cytogenetically normal acute myeloid leukemia (CN-AML). PATIENTS AND METHODS Diagnostic bone marrow or blood samples from 358 patients were analyzed for IDH1 and IDH2 mutations by DNA polymerase chain reaction amplification/sequencing. FLT3, NPM1, CEBPA, WT1, and MLL mutational analyses and gene- and microRNA-expression profiling were performed centrally. Results IDH mutations were found in 33% of the patients. IDH1 mutations were detected in 49 patients (14%; 47 with R132). IDH2 mutations, previously unreported in AML, were detected in 69 patients (19%; 13 with R172 and 56 with R140). R172 IDH2 mutations were mutually exclusive with all other prognostic mutations analyzed. Younger age (< 60 years), molecular low-risk (NPM1-mutated/FLT3-internal tandem duplication-negative) IDH1-mutated patients had shorter disease-free survival than molecular low-risk IDH1/IDH2-wild-type (wt) patients (P = .046). R172 IDH2-mutated patients had lower complete remission rates than IDH1/IDH2wt patients (P = .007). Distinctive microarray gene- and microRNA-expression profiles accurately predicted R172 IDH2 mutations. The highest expressed gene and microRNAs in R172 IDH2-mutated patients compared with the IDH1/IDH2wt patients were APP (previously associated with complex karyotype AML) and miR-1 and miR-133 (involved in embryonal stem-cell differentiation), respectively. CONCLUSION IDH1 and IDH2 mutations are recurrent in CN-AML and have an unfavorable impact on outcome. The R172 IDH2 mutations, previously unreported in AML, characterize a novel subset of CN-AML patients lacking other prognostic mutations and associate with unique gene- and microRNA-expression profiles that may lead to the discovery of novel, therapeutically targetable leukemogenic mechanisms.

Differential expression of specific microRNA and their targets in acute myeloid leukemia

Acute myeloid leukemia (AML) the most common acute leukemia in adults is characterized by various cytogenetic and molecular abnormalities. However, the genetic etiology of the disease is not yet fully understood. MicroRNAs (miRNA) are small noncoding RNAs which regulate the expression of target mRNAs both at transcriptional and translational level. In recent years, miRNAs have been identified as a novel mechanism in gene regulation, which show variable expression during myeloid differentiation. We studied miRNA expression of leukemic blasts of 29 cases of newly diagnosed and genetically defined AML using quantitative reverse transcription polymerase chain reaction (RT-PCR) for 365 human miRNA. We showed that miRNA expression profiling reveals distinctive miRNA signatures that correlate with cytogenetic and molecular subtypes of AML. Specific miRNAs with consolidated role on cell proliferation and differentiation such as miR-155, miR-221, let-7, miR-126 and miR-196b appear to be associated with particular subtypes. We observed a significant differentially expressed miRNA profile that characterizes two subgroups of AML with different mechanism of leukemogenesis: core binding factor (CBF) and cytogenetically normal AML with mutations in the genes of NPM1 and FLT3-ITD. We demonstrated, for the first time, the inverse correlation of expression levels between miRNA and their targets in specific AML genetic groups. We suggest that miRNA deregulation may act as complementary hit in the multisteps mechanism of leukemogenesis offering new therapeutic strategies.