The Molecular Basis of Leukemia

Cancer fusion transcripts with human non-coding RNAs

Cancer chimeric, or fusion, transcripts are thought to most frequently appear due to chromosomal aberrations that combine moieties of unrelated normal genes. When being expressed, this results in chimeric RNAs having upstream and downstream parts relatively to the breakpoint position for the 5'- and 3'-fusion components, respectively. As many other types of cancer mutations, fusion genes can be of either driver or passenger type. The driver fusions may have pivotal roles in malignisation by regulating survival, growth, and proliferation of tumor cells, whereas the passenger fusions most likely have no specific function in cancer. The majority of research on fusion gene formation events is concentrated on identifying fusion proteins through chimeric transcripts. However, contemporary studies evidence that fusion events involving non-coding RNA (ncRNA) genes may also have strong oncogenic potential. In this review we highlight most frequent classes of ncRNAs fusions and summarize current understanding of their functional roles. In many cases, cancer ncRNA fusion can result in altered concentration of the non-coding RNA itself, or it can promote protein expression from the protein-coding fusion moiety. Differential splicing, in turn, can enrich the repertoire of cancer chimeric transcripts, e.g. as observed for the fusions of circular RNAs and long non-coding RNAs. These and other ncRNA fusions are being increasingly recognized as cancer biomarkers and even potential therapeutic targets. Finally, we discuss the use of ncRNA fusion genes in the context of cancer detection and therapy.

Leukemia cancer cells and immune cells derived-exosomes: Possible roles in leukemia progression and therapy

Exosomes have a significant impact on tumor survival, proliferation, metastasis, and recurrence. They also open up new therapeutic options and aid in the pathological identification and diagnosis of cancers. Exosomes have been shown in numerous studies to be essential for facilitating cell-to-cell communication. In B-cell hematological malignancies, the proteins and RNAs that are encased by circulating exosomes are thought to represent prospective sources for therapeutic drugs as well as biomarkers for diagnosis and prognosis. Additionally, exosomes can offer a "snapshot" of the tumor and the metastatic environment at any given point in time. In this review study, we concluded that leukemia-derived exosomes could be utilized as prognostic, diagnostic, and therapeutic biomarkers for individuals suffering from leukemia. Moreover, clinical studies have demonstrated that immune cells like dendritic cells create exosomes, which have the ability to activate the immune system against leukemia.

The dark side of stemness - the role of hematopoietic stem cells in development of blood malignancies

Hematopoietic stem cells (HSCs) produce all blood cells throughout the life of the organism. However, the high self-renewal and longevity of HSCs predispose them to accumulate mutations. The acquired mutations drive preleukemic clonal hematopoiesis, which is frequent among elderly people. The preleukemic state, although often asymptomatic, increases the risk of blood cancers. Nevertheless, the direct role of preleukemic HSCs is well-evidenced in adult myeloid leukemia (AML), while their contribution to other hematopoietic malignancies remains less understood. Here, we review the evidence supporting the role of preleukemic HSCs in different types of blood cancers, as well as present the alternative models of malignant evolution. Finally, we discuss the clinical importance of preleukemic HSCs in choosing the therapeutic strategies and provide the perspective on further studies on biology of preleukemic HSCs.

Vitamin D and potential effects on cancers: a review

Cancer is characterized by the abnormal and uncontrollable division and growth of cells that can infiltrate tissues and alter normal physiological function, which will become crucial and life-threatening if left untreated. Cancer can be a result of genetics, such as mutations or environmental causes, including smoking, lack of physical activity, as well as nutritional imbalance in the body. Vitamin D is one of the foremost nutrients that play a crucial role in a variety of biochemical pathways, and it is an important key factor in several diseases. Vitamin D is an essential nutrient for preventing malignancies and a complementary treatment for cancer through direct and indirect biochemical pathways. In this article, we summarized the correlation between vitamin D and various cancers using an extensive search on PubMed, Google Scholar, and Scopus. This paper reviews the role of vitamin D in different types of cancer.

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.

Deregulated Gene Expression Profiles and Regulatory Networks in Adult and Pediatric RUNX1/RUNX1T1-Positive AML Patients

Acute myeloid leukemia (AML) is a heterogeneous and complex disease concerning molecular aberrations and prognosis. RUNX1/RUNX1T1 is a fusion oncogene that results from the chromosomal translocation t(8;21) and plays a crucial role in AML. However, its impact on the transcriptomic profile of different age groups of AML patients is not completely understood. Here, we investigated the deregulated gene expression (DEG) profiles in adult and pediatric RUNX1/RUNX1T1-positive AML patients, and compared their functions and regulatory networks. We retrospectively analyzed gene expression data from two independent Gene Expression Omnibus (GEO) datasets (GSE37642 and GSE75461) and computed their differentially expressed genes and upstream regulators, using limma, GEO2Enrichr, and X2K. For validation purposes, we used the TCGA-LAML (adult) and TARGET-AML (pediatric) patient cohorts. We also analyzed the protein–protein interaction (PPI) networks, as well as those composed of transcription factors (TF), intermediate proteins, and kinases foreseen to regulate the top deregulated genes in each group. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways enrichment analyses were further performed for the DEGs in each dataset. We found that the top upregulated genes in (both adult and pediatric) RUNX1/RUNX1T1-positive AML patients are enriched in extracellular matrix organization, the cell projection membrane, filopodium membrane, and supramolecular fiber. Our data corroborate that RUNX1/RUNX1T1 reprograms a large transcriptional network to establish and maintain leukemia via intricate PPI interactions and kinase-driven phosphorylation events.

The Omnipresence of DYRK1A in Human Diseases

The increasing population will challenge healthcare, particularly because the worldwide population has never been older. Therapeutic solutions to age-related disease will be increasingly critical. Kinases are key regulators of human health and represent promising therapeutic targets for novel drug candidates. The dual-specificity tyrosine-regulated kinase (DYRKs) family is of particular interest and, among them, DYRK1A has been implicated ubiquitously in varied human diseases. Herein, we focus on the characteristics of DYRK1A, its regulation and functional role in different human diseases, which leads us to an overview of future research on this protein of promising therapeutic potential.

Analysis of rare driving events in pediatric acute myeloid leukemia

Elucidating genetic aberrations in pediatric acute myeloid leukemia (AML) provides insight in biology and may impact on risk-group stratification and clinical outcome. This study aimed to detect such aberrations in a selected series of samples without known (cyto)genetic aberration using molecular profiling. A cohort of 161 patients was selected from various study groups: DCOG, BFM, SJCRH, NOPHO and AEIOP. Samples were analyzed using RNA sequencing (n=152), whole exome (n=135) and/or whole genome sequencing (n=100). In 70 of 156 patients (45%), of whom RNA sequencing or whole genome sequencing was available, rearrangements were detected, 22 of which were novel; five involving ERG rearrangements and four NPM1 rearrangements. ERG rearrangements showed self-renewal capacity in vitro, and a distinct gene expression pattern. Gene set enrichment analysis of this cluster showed upregulation of gene sets derived from Ewing sarcoma, which was confirmed comparing gene expression profiles of AML and Ewing sarcoma. Furthermore, NPM1-rearranged cases showed cytoplasmic NPM1 localization and revealed HOXA/B gene overexpression, as described for NPM1 mutated cases. Single-gene mutations as identified in adult AML were rare. Patients had a median of 24 coding mutations (range, 7-159). Novel recurrent mutations were detected in UBTF (n=10), a regulator of RNA transcription. In 75% of patients an aberration with a prognostic impact could be detected. Therefore, we suggest these techniques need to become standard of care in diagnostics.

A review of the mutagenic potential of N-ethyl-N-nitrosourea (ENU) to induce hematological malignancies

This review is intended to summarize the existing literature on the mutagenicity of N-ethyl-N-nitrosourea (ENU) in inducing hematological malignancies, including acute myeloid leukemia (AML) in mice. Blood or hematological malignancies are the most common malignant disorders seen in people of all age groups. Driven by a number of genetic alterations, leukemia rule out the normal proliferation and differentiation of hematopoietic stem cells (HSCs) and their progenitors in the bone marrow (BM) and severely affects blood functions. Out of all hematological malignancies, AML is the most aggressive type, with a high incidence and mortality rate. AML is found as either de novo or secondary therapeutic AML (t-AML). t-AML is a serious adverse consequence of alkylator chemotherapy to the cancer patient and alone constitutes about 10%-20% of all reported AML cases. Cancer patients who received alkylator chemotherapy are at an elevated risk of developing t-AML. ENU has a long history of use as a potent carcinogen that induces blood malignancies in mice and rats that are pathologically similar to human AML and t-AML. ENU, once entered into the body, circulates all over the body tissues and reaches BM. It creates an overall state of suppression within the BM by damaging the marrow cells, alkylating the DNA, and forming DNA adducts within the early and late hematopoietic stem and progenitor cells. The BM holds a weak DNA repair mechanism due to low alkyltransferase, and poly [ADP-ribose] polymerase (PARP) enzyme content often fails to obliterate those adducts, acting as a catalyst to bring genetic abnormalities, including point gene mutations as well as chromosomal alterations, for example, translocation and inversion. Taking advantage of ENU-induced immune-suppressed state and weak immune surveillance, these mutations remain viable and slowly give rise to transformed HSCs. This review also highlights the carcinogenic nature of ENU and the complex relation between the ENU's overall toxicity in the induction of hematological malignancies.

Synergy of Venetoclax and 8-Chloro-Adenosine in AML: The Interplay of rRNA Inhibition and Fatty Acid Metabolism

It is known that 8-chloro-adenosine (8-Cl-Ado) is a novel RNA-directed nucleoside analog that targets leukemic stem cells (LSCs). In a phase I clinical trial with 8-Cl-Ado in patients with refractory or relapsed (R/R) AML, we observed encouraging but short-lived clinical responses, likely due to intrinsic mechanisms of LSC resistance. LSC homeostasis depends on amino acid-driven and/or fatty acid oxidation (FAO)-driven oxidative phosphorylation (OXPHOS) for survival. We recently reported that 8-Cl-Ado and the BCL-2-selective inhibitor venetoclax (VEN) synergistically inhibit FAO and OXPHOS in LSCs, thereby suppressing acute myeloid leukemia (AML) growth in vitro and in vivo. Herein, we report that 8-Cl-Ado inhibits ribosomal RNA (rRNA) synthesis through the downregulation of transcription initiation factor TIF-IA that is associated with increasing levels of p53. Paradoxically, 8-Cl-Ado-induced p53 increased FAO and OXPHOS, thereby self-limiting the activity of 8-Cl-Ado on LSCs. Since VEN inhibits amino acid-driven OXPHOS, the addition of VEN significantly enhanced the activity of 8-Cl-Ado by counteracting the self-limiting effect of p53 on FAO and OXPHOS. Overall, our results indicate that VEN and 8-Cl-Ado can cooperate in targeting rRNA synthesis and OXPHOS and in decreasing the survival of the LSC-enriched cell population, suggesting the VEN/8-Cl-Ado regimen as a promising therapeutic approach for patients with R/R AML.

Put in a “Ca2+ll” to Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a clonal disorder characterized by genetic aberrations in myeloid primitive cells (blasts) which lead to their defective maturation/function and their proliferation in the bone marrow (BM) and blood of affected individuals. Current intensive chemotherapy protocols result in complete remission in 50% to 80% of AML patients depending on their age and the AML type involved. While alterations in calcium signaling have been extensively studied in solid tumors, little is known about the role of calcium in most hematologic malignancies, including AML. Our purpose with this review is to raise awareness about this issue and to present (i) the role of calcium signaling in AML cell proliferation and differentiation and in the quiescence of hematopoietic stem cells; (ii) the interplay between mitochondria, metabolism, and oxidative stress; (iii) the effect of the BM microenvironment on AML cell fate; and finally (iv) the mechanism by which chemotherapeutic treatments modify calcium homeostasis in AML cells.

Mutation profile of acute myeloid leukaemia in a Chinese cohort by targeted next-generation sequencing

Background

Acute myeloid leukaemia (AML) results from the clonal expansion of blast cells of myeloid origin driven by genomic defects. The advances in next‐generation sequencing (NGS) have allowed the identification of many mutated genes important in the pathogenesis of AML.

Aims

In this study, we aimed to assess the mutation types and frequency in a Chinese cohort presenting with de novo AML cohort using a targeted NGS strategy.

Methods

In total, we studied samples from 87 adult patients with de novo AML who had no prior history of cytotoxic chemotherapy. Samples were evaluated using a 120‐gene targeted NGS panel to assess the mutation profile.

Results

Of the 87 AML patients, there were 60 (69%) with a normal karyotype. 89.7% of patients had variants, with an average of 1.9 mutations per patient (range: 0–5 mutations per patient). DNMT3A variants were the most common, being detected in 33 patients (37.9%). NPM1 (34.5%), IDH1/2 (24.1%) and FLT3‐ITD (20.7%) mutations was the next most common. Of the patients with DNMT3A mutations, 24.2% also had mutations NPM1 and FLT3‐ITD and 6.1% NPM1, FLT3‐ITD and IDH mutations.

Conclusion

Both DNMT3A and NPM1 mutations were more common than in other Chinese and Western AML cohorts that have been studied. DNMT3A mutations tended to co‐occur with NPM1 and FLT3‐ITD mutations and were most commonly seen with a normal karyotype.

Targeting the metabolic vulnerability of acute myeloid leukemia blasts with a combination of venetoclax and 8-chloro-adenosine

Background

BCL‐2 inhibition through venetoclax (VEN) targets acute myeloid leukemia (AML) blast cells and leukemic stem cells (LSCs). Although VEN-containing regimens yield 60–70% clinical response rates, the vast majority of patients inevitably suffer disease relapse, likely because of the persistence of drug-resistant LSCs. We previously reported preclinical activity of the ribonucleoside analog 8-chloro-adenosine (8-Cl-Ado) against AML blast cells and LSCs. Moreover, our ongoing phase I clinical trial of 8-Cl-Ado in patients with refractory/relapsed AML demonstrates encouraging clinical benefit. Of note, LSCs uniquely depend on amino acid-driven and/or fatty acid oxidation (FAO)-driven oxidative phosphorylation (OXPHOS) for survival. VEN inhibits OXPHOS in LSCs, which eventually may escape the antileukemic activity of this drug. FAO is activated in LSCs isolated from patients with relapsed AML.

Methods

Using AML cell lines and LSC-enriched blast cells from pre-treatment AML patients, we evaluated the effects of 8-Cl-Ado, VEN and the 8-Cl-Ado/VEN combination on fatty acid metabolism, glycolysis and OXPHOS using liquid scintillation counting, a Seahorse XF Analyzer and gene set enrichment analysis (GSEA). Western blotting was used to validate results from GSEA. HPLC was used to measure intracellular accumulation of 8-Cl-ATP, the cytotoxic metabolite of 8-Cl-Ado. To quantify drug synergy, we created combination index plots using CompuSyn software. The log-rank Kaplan–Meier survival test was used to compare the survival distributions of the different treatment groups in a xenograft mouse model of AML.

Results

We here report that VEN and 8-Cl-Ado synergistically inhibited in vitro growth of AML cells. Furthermore, immunodeficient mice engrafted with MV4-11-Luc AML cells and treated with the combination of VEN plus 8-Cl-Ado had a significantly longer survival than mice treated with either drugs alone (p ≤ 0.006). We show here that 8-Cl-Ado in the LSC-enriched population suppressed FAO by downregulating gene expression of proteins involved in this pathway and significantly inhibited the oxygen consumption rate (OCR), an indicator of OXPHOS. By combining 8-Cl-Ado with VEN, we observed complete inhibition of OCR, suggesting this drug combination cooperates in targeting OXPHOS and the metabolic homeostasis of AML cells.

Conclusion

Taken together, the results suggest that 8-Cl-Ado enhances the antileukemic activity of VEN and that this combination represents a promising therapeutic regimen for treatment of AML.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13045-021-01076-4.

The RUNX1/RUNX1T1 network: translating insights into therapeutic options

RUNX1/RUNX1T1 is the most common fusion gene found in acute myeloid leukemia. Seminal contributions by many different research groups have revealed a complex regulatory network promoting leukemic self-renewal and propagation. Perturbation of RUNX1/RUNX1T1 levels and its DNA binding affects chromatin accessibility and transcription factor occupation at multiple gene loci associated with changes in gene expression levels. Exploration of this transcriptional program by targeted RNAi screens uncovered a crucial role of RUNX1/RUNX1T1 in cell cycle progression by regulating CCND2. This dependency results in a high vulnerability toward inhibitors of CDK4 and CDK6 and suggests new avenues for therapeutic intervention against acute myeloid leukemia.

Determinants and role of chromatin organization in acute leukemia

DNA is compacted into higher order structures that have major implications in gene regulation. These structures allow for long-range interactions of DNA elements, such as the association of promoters with their cognate enhancers. In recent years, mutations in genes that control these structures, including the cohesin-complex and the insulator-binding protein CTCF, have been found in a spectrum of hematologic disorders, and especially in acute leukemias. Cohesin and CTCF are critical for mediating looping and establishing boundaries within chromatin. Cells that harbor mutations in these genes display aberrant chromatin architecture and resulting differences in gene expression that contribute to leukemia initiation and progression. Here, we provide detailed discussion of the nature of 3D interactions and the way that they are disrupted in acute leukemia. Continued research in this area will provide new insights into the mechanisms of leukemogenesis and may shed light on novel treatment strategies.

Synthesis and evaluation of etoposide and podophyllotoxin analogs against topoisomerase IIα and HCT-116 cells

Etoposide is a widely-used anticancer agent that targets human type II topoisomerases. Evidence suggests that metabolism of etoposide in myeloid progenitor cells is associated with translocations involved in leukemia development. Previous studies suggest halogenation at the C-2' position of etoposide reduces metabolism. Halogens were introduced into the C-2' position by electrophilic aromatic halogenation onto etoposide (ETOP, 1), podophyllotoxin (PPT, 2), and 4-dimethylepipodophyllotoxin (DMEP, 3), and to bridge the gap of knowledge regarding the activity of these metabolically stable analogs. Five halogenated analogs (6-10) were synthesized. Analogs 8-10 displayed variable ability to inhibit DNA relaxation. Analog 9 was the only analog to show concentration-dependent enhancement of Top2-mediated DNA cleavage. Dose response assay results indicated that 8 and 10 were most effective at decreasing the viability of HCT-116 and A549 cancer cell lines in culture. Flow cytometry with 8 and 10 in HCT-116 cells provide evidence of sub-G1 cell populations indicative of apoptosis. Taken together, these results indicate C-2' halogenation of etoposide and its precursors, although metabolically stable, decreases overall activity relative to etoposide.

Preleukemic stem cells: leave it or not?

Acute myeloid leukemia (AML) has been shown to undergo multiple acquired mutations in hematopoietic cell lineages over years before becoming clinically apparent. The early stage of AML (before it becomes clinically recognizable) may be characterized by acquisition of some, but not all, leukemia-related somatic mutations in hematopoietic stem cells (HSCs). The physiological roles of these mutations remain puzzling. These HSCs have been termed as preleukemic HSCs. However, those frequent acquired somatic mutations are also found in healthy aging adults, namely, “age-related clonal hematopoiesis.” Multiple studies have demonstrated that the preleukemic HSCs survive through chemotherapy and then contribute to the relapse and the development of de novo AML. Whether preleukemic HSCs should be targeted or whether a preventive therapy should be considered for those individuals remains to be determined. This article aims to shed light on this special subject and to discuss the roles of preleukemic HSCs in leukemogenesis.

Inhibitory effects of SEL201 in acute myeloid leukemia

MAPK interacting kinase (MNK), a downstream effector of mitogen-activated protein kinase (MAPK) pathways, activates eukaryotic translation initiation factor 4E (eIF4E) and plays a key role in the mRNA translation of mitogenic and antiapoptotic genes in acute myeloid leukemia (AML) cells. We examined the antileukemic properties of a novel MNK inhibitor, SEL201. Our studies provide evidence that SEL201 suppresses eIF4E phosphorylation on Ser209 in AML cell lines and in primary patient-derived AML cells. Such effects lead to growth inhibitory effects and leukemic cell apoptosis, as well as suppression of leukemic progenitor colony formation. Combination of SEL201 with 5'-azacytidine or rapamycin results in synergistic inhibition of AML cell growth. Collectively, these results suggest that SEL201 has significant antileukemic activity and further underscore the relevance of the MNK pathway in leukemogenesis.

An ERG Enhancer-Based Reporter Identifies Leukemia Cells with Elevated Leukemogenic Potential Driven by ERG-USP9X Feed-Forward Regulation

Acute leukemia is a rapidly progressing blood cancer with low survival rates. Unfavorable prognosis is attributed to insufficiently characterized subpopulations of leukemia stem cells (LSC) that drive chemoresistance and leukemia relapse. Here we utilized a genetic reporter that assesses stemness to enrich and functionally characterize LSCs. We observed heterogeneous activity of the ERG+85 enhancer-based fluorescent reporter in human leukemias. Cells with high reporter activity (tagBFP^High) exhibited elevated expression of stemness and chemoresistance genes and demonstrated increased clonogenicity and resistance to chemo- and radiotherapy as compared with their tagBFP^Neg counterparts. The tagBFP^High fraction was capable of regenerating the original cellular heterogeneity and demonstrated increased invasive ability. Moreover, the tagBFP^High fraction was enriched for leukemia-initiating cells in a xenograft assay. We identified the ubiquitin hydrolase USP9X as a novel ERG transcriptional target that sustains ERG+85-positive cells by controlling ERG ubiquitination. Therapeutic targeting of USP9X led to preferential inhibition of the ERG-dependent leukemias. Collectively, these results characterize human leukemia cell functional heterogeneity and suggest that targeting ERG via USP9X inhibition may be a potential treatment strategy in patients with leukemia. SIGNIFICANCE: This study couples a novel experimental tool with state-of-the-art approaches to delineate molecular mechanisms underlying stem cell-related characteristics in leukemia cells.

Building upon the success of CART19: chimeric antigen receptor T cells for hematologic malignancies

Chimeric antigen receptor T cell (CART) therapy has dramatically changed the therapeutic prospects for B cell malignancies. Over the last decade CD19-redirected CART have demonstrated the ability to induce deep, long-lasting remissions and possibly cure patients with relapsing B cell neoplasms. Such impressive results with CART19 fostered efforts to expand this technology to other incurable malignancies that naturally do not express CD19, such as acute myeloid leukemia (AML), Hodgkin lymphoma (HL) and multiple myeloma (MM). However, to reach this goal, several hurdles have to be overcome, in particular: (i) the apparent lack of suitable targets as effective as CD19; (ii) the immunosuppressive tumor microenvironment; (iii) intra-tumoral heterogeneity and antigen-negative relapses. Therefore, new strategies that allow safer and more potent CART platforms are under development and may provide grounds for new exciting breakthroughs in the field.

Turning Stem Cells Bad: Generation of Clinically Relevant Models of Human Acute Myeloid Leukemia through Gene Delivery- or Genome Editing-Based Approaches

Acute myeloid leukemia (AML), the most common acute leukemia in the adult, is believed to arise as a consequence of multiple molecular events that confer on primitive hematopoietic progenitors unlimited self-renewal potential and cause defective differentiation. A number of genetic aberrations, among which a variety of gene fusions, have been implicated in the development of a transformed phenotype through the generation of dysfunctional molecules that disrupt key regulatory mechanisms controlling survival, proliferation, and differentiation in normal stem and progenitor cells. Such genetic aberrations can be recreated experimentally to a large extent, to render normal hematopoietic stem cells "bad", analogous to the leukemic stem cells. Here, we wish to provide a brief outline of the complementary experimental approaches, largely based on gene delivery and more recently on gene editing, employed over the last two decades to gain insights into the molecular mechanisms underlying AML development and progression and on the prospects that their applications offer for the discovery and validation of innovative therapies.

NPM1 and FLT3 mutations in acute myeloid leukemia with normal karyotype: Indian perspective

BACKGROUND

FLT3-ITD and NPM1 mutations are considered to be the major determinants of the patient response to therapy and outcome. The primary aim of this study was to establish the correlation between these molecular mutations and the clinico-hematologic parameters as well as the prognostic outcome of the Indian acute myeloid leukemia (AML) patients.

MATERIALS AND METHODS

This prospective study involved newly diagnosed nonpromyelocytic AML patients who had undergone complete diagnostic workup, including immunophenotyping, conventional cytogenetics and molecular analysis for NPM1 and FLT3-ITD mutation by reverse transcriptase polymerase chain reaction at presentation.

RESULTS

Overall, the prevalence of NPM1 and FLT3-ITD mutations was found to be 14.4% and 10.8%, respectively. Among patients with normal karyotype, leukocytosis was significantly associated with NPM1+ group than the NPM1- group (P = 0.0019) and more severe degree of anemia was observed in the FLT3-ITD+ patients than the other groups (P = 0.025). No significant correlation was found in terms of age at presentation (P = 0.56), sex ratio (P = 0.467), median platelet count (P = 0.27), and blast percentage between NPM1+ and FLT3-ITD+ groups. Complete remission (CR) rates were better in the NPM1+/FLT3-ITD- group than the other three groups. Unlike most other studies, improved CR rates as well as disease-free survival were observed in the NPM-/FLT3-ITD- group than the FLT3-ITD+ groups although not reaching statistically significant levels.

CONCLUSION

Some differences in the clinical behavior of the Indian AML patients in comparison to that of the West in the presence of NPM1 and FLT3-ITD suggests that comprehensive studies are required to confirm the definitive role of these mutations among AML patients, especially with normal karyotype.

Acute myeloid leukaemia at an early age: Reviewing the interaction between pesticide exposure and KMT2A-rearrangement

Acute myeloid leukaemia (AML) in early childhood is characterised by a high frequency of recurrent genomic aberrations associated with distinct myeloid subtypes, clinical outcomes and pathogenesis. Genomic instability is the first step of pathogenic mechanism in early childhood AML. A sum of adverse events is necessary to the development of infant AML (i-AML), which includes latency of biochemical-molecular and cellular effects. Inherited genetic susceptibility associated with exposures to biotransformation substances can modulate the risk of DNA damage and it is a very important piece in the pathogenic puzzle. In this review, we have aimed to explore the chain of events in the time-points of the natural history of i-AML, which includes maternal exposures during pregnancy, the speculations about the formation of somatic mutations during foetal life and the secondary genomic aberrations associated with i-AML. The modulation of risk conferred by xenobiotic metabolism´s genes variants is the bottom line of the pathogenic process. Since we have conducted observational and molecular investigations in early childhood leukaemia, the data focused here is based on Brazilian findings with summarised results of our experience with epidemiological and molecular studies in early-age leukaemia.

Mitotic Gene Bookmarking: An Epigenetic Mechanism for Coordination of Lineage Commitment, Cell Identity and Cell Growth

Epigenetic control of gene expression contributes to dynamic responsiveness of cellular processes that include cell cycle, cell growth and differentiation. Mitotic gene bookmarking, retention of sequence-specific transcription factors at target gene loci, including the RUNX regulatory proteins, provide a novel dimension to epigenetic regulation that sustains cellular identity in progeny cells following cell division. Runx transcription factor retention during mitosis coordinates physiological control of cell growth and differentiation in a broad spectrum of biological conditions, and is associated with compromised gene expression in pathologies that include cancer.

RUNX1-ETO Leukemia

AML1-ETO leukemia is the most common cytogenetic subtype of acute myeloid leukemia, defined by the presence of t(8;21). Remarkable progress has been achieved in understanding the molecular pathogenesis of AML1-ETO leukemia. Proteomic surveies have shown that AML-ETO forms a stable complex with several transcription factors, including E proteins. Genome-wide transcriptome and ChIP-seq analyses have revealed the genes directly regulated by AML1-ETO, such as CEBPA. Several lines of evidence suggest that AML1-ETO suppresses endogenous DNA repair in cells to promote mutagenesis, which facilitates acquisition of cooperating secondary events. Furthermore, it has become increasingly apparent that a delicate balance of AML1-ETO and native AML1 is important to sustain the malignant cell phenotype. Translation of these findings into the clinical setting is just beginning.

LncRNAs downregulated in childhood acute lymphoblastic leukemia modulate apoptosis, cell migration, and DNA damage response

Childhood acute lymphoblastic leukemia (cALL) accounts for 25% of pediatric cancers and is one of the leading causes of disease-related death in children. Although long non-coding RNAs (lncRNAs) have been implicated in cALL etiology, progression, and treatment response, little is known about their exact functional role. We had previously sequenced the whole transcriptome of 56 cALL patients and identified lncRNA transcripts specifically silenced in tumoral cells. Here we investigated the impact of restoring the expression of three of these (RP11-624C23.1, RP11-203E8, and RP11-446E9) in leukemic cell lines had dramatic impact on cancer hallmark cellular phenotypes such as apoptosis, cell proliferation and migration, and DNA damage response. Interestingly, both RP11-624C23.1 and RP11-203E8 had very similar impacts on DNA damage response, specifically displaying lower γ-H2A.X and higher apoptosis levels than control cells in response to genotoxic stress. These results indicate that silencing RP11-624C23.1 or RP11-203E8 could provide a selective advantage to leukemic cells by increasing resistance to genotoxic stress, possibly by modulating the DDR pathway. Since genotoxic agents are fundamental parts of antineoplastic treatment, further investigation of the mechanisms these lncRNAs impact would provide novel and interesting avenues for overcoming treatment resistance.

Dysregulation of haematopoietic stem cell regulatory programs in acute myeloid leukaemia

Haematopoietic stem cells (HSC) are situated at the apex of the haematopoietic differentiation hierarchy, ensuring the life-long supply of mature haematopoietic cells and forming a reservoir to replenish the haematopoietic system in case of emergency such as acute blood loss. To maintain a balanced production of all mature lineages and at the same time secure a stem cell reservoir, intricate regulatory programs have evolved to control multi-lineage differentiation and self-renewal in haematopoietic stem and progenitor cells (HSPCs). Leukaemogenic mutations commonly disrupt these regulatory programs causing a block in differentiation with simultaneous enhancement of proliferation. Here, we briefly summarize key aspects of HSPC regulatory programs, and then focus on their disruption by leukaemogenic fusion genes containing the mixed lineage leukaemia (MLL) gene. Using MLL as an example, we explore important questions of wider significance that are still under debate, including the importance of cell of origin, to what extent leukaemia oncogenes impose specific regulatory programs and the relevance of leukaemia stem cells for disease development and prognosis. Finally, we suggest that disruption of stem cell regulatory programs is likely to play an important role in many other pathologies including ageing-associated regenerative failure.

β-catenin induces expression of prohibitin gene in acute leukemic cells

Prohibitin (PHB) is a multifunctional protein conserved in eukaryotic systems and shows various expression levels in tumor cells. However, regulation of PHB is not clearly understood. Here, we focused on the regulation of PHB expression by Wnt signaling, one of dominant regulatory signals in various leukemic cells. High mRNA levels of PHB were found in half of clinical leukemia samples. PHB expression was increased by inhibition of the MAPK pathway and decreased by activation of EGF signal. Although cell proliferating signals downregulated the transcription of PHB, treatment with lithium chloride, an analog of the Wnt signal, induced PHB level in various cell types. We identified the TCF-4/LEF-1 binding motif, CATCTG, in the promoter region of PHB by site-directed mutagenesis and ChIP assay. This β-catenin-mediated activation of PHB expression was independent of c‑MYC activation, a product of Wnt signaling. These data indicate that PHB is a direct target of β-catenin and the increased level of PHB in leukemia can be regulated by Wnt signaling.

KPT-8602, a second-generation inhibitor of XPO1-mediated nuclear export, is well tolerated and highly active against AML blasts and leukemia-initiating cells

Acute myeloid leukemia (AML) is a clonal hematologic malignant disease of developing myeloid cells that have acquired aberrant survival, uncontrolled proliferation and a block in normal hematopoietic cell differentiation. Standard chemotherapy often induces remissions in AML patients, but the disease frequently relapses due to incomplete targeting of leukemia-initiating cells (LICs), emphasizing the need for novel effective treatments. Exportin 1 (XPO1)-mediated nuclear export, which is inhibited by the drug selinexor, is an attractive new therapeutic target in AML. Selinexor has shown impressive activity in Phase I/II clinical trials for AML. Here we report the anti-leukemic efficacy and tolerability of KPT-8602, a second-generation XPO1 inhibitor. KPT-8602 demonstrates substantially reduced brain penetration compared to selinexor, with resultant attenuation of the central nervous system mediated side effects of anorexia and weight loss. Due to its improved tolerability profile, KPT-8602 can be given daily compared to the two or three times weekly regimen of selinexor, and exhibits greater anti-leukemic efficacy against both leukemic blasts and LICs in AML patient-derived xenograft models. Importantly, normal hematopoietic stem and progenitor cell (HSPC) frequency is not significantly reduced by KPT-8602, providing a therapeutic window for elimination of relapse-driving LICs while sparing normal HSPCs. These findings strongly endorse clinical testing of KPT-8602 in patients with relapsed and refractory AML.

LIN28B Activation by PRL-3 Promotes Leukemogenesis and a Stem Cell-like Transcriptional Program in AML

PRL-3 (PTP4A3), a metastasis-associated phosphatase, is also upregulated in patients with acute myeloid leukemia (AML) and is associated with poor prognosis, but the underlying molecular mechanism is unknown. Here, constitutive expression of PRL-3 in human AML cells sustains leukemogenesis in vitro and in vivo Furthermore, PRL-3 phosphatase activity dependently upregulates LIN28B, a stem cell reprogramming factor, which in turn represses the let-7 mRNA family, inducing a stem cell-like transcriptional program. Notably, elevated levels of LIN28B protein independently associate with worse survival in AML patients. Thus, these results establish a novel signaling axis involving PRL-3/LIN28B/let-7, which confers stem cell-like properties to leukemia cells that is important for leukemogenesis.Implications: The current study offers a rationale for targeting PRL-3 as a therapeutic approach for a subset of AML patients with poor prognosis. Mol Cancer Res; 15(3); 294-303. ©2016 AACR.

Significant Role of Segmental Duplications and SIDD Sites in Chromosomal Translocations of Hematological Malignancies: A Multi-parametric Bioinformatic Analysis

Recurrent non-random chromosomal translocations are hallmark characteristics of leukemogenesis, and however, molecular mechanisms underlying these rearrangements are less explored. The fundamental question is, why and how chromosomes break and reunite so precisely in the genome. Meticulous understanding of mechanism leading to chromosomal rearrangement can be achieved by characterizing breakpoints. To address this hypothesis, a novel multi-parametric computational approach for characterization of major leukemic translocations within and around breakpoint region was performed. To best of our knowledge, this bioinformatic analysis is unique in finding the presence of segmental duplications (SDs) flanking breakpoints of all major leukemic translocation. Breakpoint islands (BpIs) were analyzed for stress-induced duplex destabilization (SIDD) sites along with other complex genomic architecture and physicochemical properties. Our study distinctly emphasizes on the probable correlative role of SDs, SIDD sites and various genomic features in the occurrence of breakpoints. Further, it also highlights potential features which may be playing a crucial role in causing double-strand breaks, leading to translocation.

IDH1/2 but not DNMT3A mutations are suitable targets for minimal residual disease monitoring in acute myeloid leukemia patients: a study by the Acute Leukemia French Association

Acute myeloid leukemia (AML) is a heterogeneous disease. Even within the same NPM1-mutated genetic subgroup, some patients harbor additional mutations in FLT3, IDH1/2, DNMT3A or TET2. Recent studies have shown the prognostic significance of minimal residual disease (MRD) in AML but it remains to be determined which molecular markers are the most suitable for MRD monitoring. Recent advances in next-generation sequencing (NGS) have provided the opportunity to use multiple molecular markers. In this study, we used NGS technology to assess MRD in 31 AML patients enrolled in the ALFA-0701 trial and harboring NPM1 mutations associated to IDH1/2 or DNMT3A mutations. NPM1 mutation-based MRD monitoring was performed by RTqPCR. IDH1/2 and DNMT3A mutations were quantified by NGS using an Ion Torrent Proton instrument with high coverage (2 million reads per sample). The monitoringof IDH1/2 mutations showed that these mutations were reliable MRD markers that allowed the prediction of relapse in the majority of patients. Moreover, IDH1/2 mutation status predicted relapse or disease evolution in 100% of cases if we included the patient who developed myelodysplastic syndrome. In contrast, DNMT3A mutations were not correlated to the disease status, as we found that a preleukemic clone with DNMT3A mutation persisted in 40% of the patients who were in complete remission, reflecting the persistence of clonal hematopoiesis.

Progress and Prospects in Pediatric Leukemia

Pediatric leukemia is the single most common malignancy affecting children, representing up to 30% of all pediatric cancers. Dramatic improvements in survival for acute lymphoblastic leukemia (ALL) have taken place over the past 4 decades with outcomes approaching 90% in the latest studies. However, progress has been slower for myeloid leukemia and certain subgroups like infant ALL, adolescent/young adult ALL, and relapsed ALL. Recent advances include recognition of molecularly defined subgroups, which has ushered in precision medicine approaches. We discuss the current understanding of the biology of the various childhood leukemias, recent advances in research, and future challenges in this field.

Dual targeting of eIF4E by blocking MNK and mTOR pathways in leukemia

Dysregulation of mRNA translation leads to aberrant activation of cellular pathways that promote expansion and survival of leukemic clones. A key element of the initiation translation complex is eIF4E (eukaryotic translation initiation factor 4E). The mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) pathways play important roles in the regulation of eIF4E expression and downstream functional outcomes. Mitogen-activated protein kinase interacting protein kinases (Mnks) control translation by phosphorylation of eIF4E, whereas the mTOR kinase phosphorylates/de-activates the eIF4E inhibitor, 4E-BP1, to release translational repression. Both pathways are often abnormally activated in leukemia cells and promote cell survival events by controlling expression of oncogenic proteins. Targeting these pathways may provide approaches to avoid aberrant proliferation and neoplastic transformation.

Activity of a selective inhibitor of nuclear export, selinexor (KPT-330), against AML-initiating cells engrafted into immunosuppressed NSG mice

Currently available combination chemotherapy for acute myeloid leukemia (AML) often fails to result in long-term remissions, emphasizing the need for novel therapeutic strategies. We reasoned that targeted inhibition of a prominent nuclear exporter, XPO1/CRM1, could eradicate self-renewing leukemia-initiating cells (LICs) whose survival depends on timely XPO1-mediated transport of specific protein and RNA cargoes. Using an immunosuppressed mouse model bearing primary patient-derived AML cells, we demonstrate that selinexor (KPT-330), an oral antagonist of XPO1 that is currently in clinical trials, has strong activity against primary AML cells while sparing normal stem and progenitor cells. Importantly, limiting dilution transplantation assays showed that this cytotoxic activity is not limited to the rapidly proliferating bulk population of leukemic cells but extends to the LICs, whose inherent drug resistance and unrestricted self-renewal capacity has been implicated in the difficulty of curing AML patients with conventional chemotherapy alone.

Effects of diallyl trisulfide on induction of apoptotic death in murine leukemia WEHI-3 cells in vitro and alterations of the immune responses in normal and leukemic mice in vivo

Diallyl trisulfide (DATS), a chemopreventive dietary constituent and extracted from garlic, has been shown to against cultured many types of human cancer cell liens but the fate of apoptosis in murine leukemia cells in vitro and immune responses in leukemic mice remain elusive. Herein, we clarified the actions of DATS on growth inhibition of murine leukemia WEHI-3 cells in vitro and used WEHI-3 cells to generate leukemic mice in vivo, following to investigate the effects of DATS in animal model. In in vitro study, DATS induced apoptosis of WEHI-3 cells through the G0/G1 phase arrest and induction of caspase-3 activation. In in vivo study DATS decreased the weight of spleen of leukemia mice but did not affect the spleen weight of normal mice. DATS promoted the immune responses such as promotions of the macrophage phagocytosis and NK cell activities in WEHI-3 leukemic and normal mice. However, DATS only promotes NK cell activities in normal mice. DATS increases the surface markers of CD11b and Mac-3 in leukemia mice but only promoted CD3 in normal mice. In conclusion, the present study indicates that DATS induces cell death through induction of apoptosis in mice leukemia WHEI-3 cells. DATS also promotes immune responses in leukemia and normal mice in vivo.

UBASH3B/Sts-1-CBL axis regulates myeloid proliferation in human preleukemia induced by AML1-ETO

The t(8;21) rearrangement, which creates the AML1-ETO fusion protein, represents the most common chromosomal translocation in acute myeloid leukemia (AML). Clinical data suggest that CBL mutations are a frequent event in t(8;21) AML, but the role of CBL in AML1-ETO-induced leukemia has not been investigated. In this study, we demonstrate that CBL mutations collaborate with AML1-ETO to expand human CD34+ cells both in vitro and in a xenograft model. CBL depletion by shRNA also promotes the growth of AML1-ETO cells, demonstrating the inhibitory function of endogenous CBL in t(8;21) AML. Mechanistically, loss of CBL function confers hyper-responsiveness to thrombopoietin and enhances STAT5/AKT/ERK/Src signaling in AML1-ETO cells. Interestingly, we found the protein tyrosine phosphatase UBASH3B/Sts-1, which is known to inhibit CBL function, is upregulated by AML1-ETO through transcriptional and miR-9-mediated regulation. UBASH3B/Sts-1 depletion induces an aberrant pattern of CBL phosphorylation and impairs proliferation in AML1-ETO cells. The growth inhibition caused by UBASH3B/Sts-1 depletion can be rescued by ectopic expression of CBL mutants, suggesting that UBASH3B/Sts-1 supports the growth of AML1-ETO cells partly through modulation of CBL function. Our study reveals a role of CBL in restricting myeloid proliferation of human AML1-ETO-induced leukemia, and identifies UBASH3B/Sts-1 as a potential target for pharmaceutical intervention.

Targeting BTK for the treatment of FLT3-ITD mutated acute myeloid leukemia

Approximately 20% of patients with acute myeloid leukaemia (AML) have a mutation in FMS-like-tyrosine-kinase-3 (FLT3). FLT3 is a trans-membrane receptor with a tyrosine kinase domain which, when activated, initiates a cascade of phosphorylated proteins including the SRC family of kinases. Recently our group and others have shown that pharmacologic inhibition and genetic knockdown of Bruton's tyrosine kinase (BTK) blocks AML blast proliferation, leukaemic cell adhesion to bone marrow stromal cells as well as migration of AML blasts. The anti-proliferative effects of BTK inhibition in human AML are mediated via inhibition of downstream NF-κB pro-survival signalling however the upstream drivers of BTK activation in human AML have yet to be fully characterised. Here we place the FLT3-ITD upstream of BTK in AML and show that the BTK inhibitor ibrutinib inhibits the survival and proliferation of FLT3-ITD primary AML blasts and AML cell lines. Furthermore ibrutinib inhibits the activation of downstream kinases including MAPK, AKT and STAT5. In addition we show that BTK RNAi inhibits proliferation of FLT3-ITD AML cells. Finally we report that ibrutinib reverses the cyto-protective role of BMSC on FLT3-ITD AML survival. These results argue for the evaluation of ibrutinib in patients with FLT3-ITD mutated AML.

Inhibition of bromodomain and extra-terminal proteins (BET) as a potential therapeutic approach in haematological malignancies: emerging preclinical and clinical evidence

Post-translational modifications of the nucleosomal histone proteins orchestrate chromatin organization and gene expression in normal and cancer cells. Among them, the acetylation of N-terminal histone tails represents the fundamental epigenetic mark of open structure chromatin and active gene transcription. The bromodomain and extra-terminal (BET) proteins are epigenetic readers which utilize tandem bromodomains (BRD) modules to recognize and dock themselves on the acetylated lysine tails. The BET proteins act as scaffolds for the recruitment of transcription factors and chromatin organizers required in transcription initiation and elongation. The recent discovery of small molecules capable of blocking their lysine-binding pocket is the first paradigm of successful pharmacological inhibition of epigenetic readers. JQ1 is a prototype benzodiazepine molecule and a specific BET inhibitor with antineoplastic activity both in solid tumours and haematological malignancies. The quinolone I-BET151 and the suitable for clinical development I-BET762 benzodiazepine were introduced in parallel with JQ1 and have also shown potent antitumour activity in preclinical studies. I-BET762 is currently being tested in early phase clinical trials, along with a rapidly growing list of other BET inhibitors. Unlike older epigenetic therapies, the study of BET inhibitors has offered substantial, context-specific, mechanistic insights of their antitumour activity, which will facilitate optimal therapeutic targeting in future. Here, we review the development of this novel class of epigenetic drugs, the biology of BET protein inhibition, the emerging evidence from preclinical work and early phase clinical studies and we discuss their potential role in the treatment of haematological malignancies.

Targeting cell cycle regulators in hematologic malignancies

Hematologic malignancies represent the fourth most frequently diagnosed cancer in economically developed countries. In hematologic malignancies normal hematopoiesis is interrupted by uncontrolled growth of a genetically altered stem or progenitor cell (HSPC) that maintains its ability of self-renewal. Cyclin-dependent kinases (CDKs) not only regulate the mammalian cell cycle, but also influence other vital cellular processes, such as stem cell renewal, differentiation, transcription, epigenetic regulation, apoptosis, and DNA repair. Chromosomal translocations, amplification, overexpression and altered CDK activities have been described in different types of human cancer, which have made them attractive targets for pharmacological inhibition. Mouse models deficient for one or more CDKs have significantly contributed to our current understanding of the physiological functions of CDKs, as well as their roles in human cancer. The present review focuses on selected cell cycle kinases with recent emerging key functions in hematopoiesis and in hematopoietic malignancies, such as CDK6 and its role in MLL-rearranged leukemia and acute lymphocytic leukemia, CDK1 and its regulator WEE-1 in acute myeloid leukemia (AML), and cyclin C/CDK8/CDK19 complexes in T-cell acute lymphocytic leukemia. The knowledge gained from gene knockout experiments in mice of these kinases is also summarized. An overview of compounds targeting these kinases, which are currently in clinical development in various solid tumors and hematopoietic malignances, is presented. These include the CDK4/CDK6 inhibitors (palbociclib, LEE011, LY2835219), pan-CDK inhibitors that target CDK1 (dinaciclib, flavopiridol, AT7519, TG02, P276-00, terampeprocol and RGB 286638) as well as the WEE-1 kinase inhibitor, MK-1775. The advantage of combination therapy of cell cycle inhibitors with conventional chemotherapeutic agents used in the treatment of AML, such as cytarabine, is discussed.

The efficacy of the ribonucleotide reductase inhibitor Didox in preclinical models of AML

Acute Myeloid Leukemia (AML) is an aggressive malignancy which leads to marrow failure, and ultimately death. There is a desperate need for new therapeutics for these patients. Ribonucleotide reductase (RR) is the rate limiting enzyme in DNA synthesis. Didox (3,4-Dihydroxybenzohydroxamic acid) is a novel RR inhibitor noted to be more potent than hydroxyurea. In this report we detail the activity and toxicity of Didox in preclinical models of AML. RR was present in all AML cell lines and primary patient samples tested. Didox was active against all human and murine AML lines tested with IC₅₀ values in the low micromolar range (mean IC₅₀ 37 µM [range 25.89–52.70 µM]). It was active against primary patient samples at concentrations that did not affect normal hematopoietic stem cells (HSCs). Didox exposure resulted in DNA damage and p53 induction culminating in apoptosis. In syngeneic, therapy-resistant AML models, single agent Didox treatment resulted in a significant reduction in leukemia burden and a survival benefit. Didox was well tolerated, as marrow from treated animals was morphologically indistinguishable from controls. Didox exposure at levels that impaired leukemia growth did not inhibit normal HSC engraftment. In summary, Didox was well tolerated and effective against preclinical models of AML.

Engineering human tumour-associated chromosomal translocations with the RNA-guided CRISPR-Cas9 system

Cancer-related human chromosomal translocations are generated through the illegitimate joining of two non-homologous chromosomes affected by double-strand breaks (DSB). Effective methodologies to reproduce precise reciprocal tumour-associated chromosomal translocations are required to gain insight into the initiation of leukaemia and sarcomas. Here we present a strategy for generating cancer-related human chromosomal translocations in vitro based on the ability of the RNA-guided CRISPR-Cas9 system to induce DSBs at defined positions. Using this approach we generate human cell lines and primary cells bearing chromosomal translocations resembling those described in acute myeloid leukaemia and Ewing's sarcoma at high frequencies. FISH and molecular analysis at the mRNA and protein levels of the fusion genes involved in these engineered cells reveal the reliability and accuracy of the CRISPR-Cas9 approach, providing a powerful tool for cancer studies.

MicroRNAs as biomarkers in leukemia

Current diagnostic and prognostic markers still exhibit biological limitation and seeking novel molecular biomarkers is crucial for early clinical diagnosis and in the development of novel strategies for leukemia therapy. Emerging evidence showed that dysregulated microRNAs (miRNAs) play important roles in cancer including leukemia. In this review, we summarized recent progress on the role of miRNAs in leukemia, mainly focusing on recent findings that suggest the potential of miRNAs as biomarkers for diagnosis and prognosis. Notably, the circulating miRNAs were also discussed for the fact that they can be detected in body fluids, and thus represent a novel source of promising biomarkers that may be applied to clinical settings.