Lyn kinase-dependent regulation of miR181 and myeloid cell leukemia-1 expression: implications for drug resistance in myelogenous leukemia

Profiling of miRNAs and their interfering targets in peripheral blood mononuclear cells from patients with chronic myeloid leukaemia

Introduction

MicroRNAs may be implicated in the acquisition of drug resistance in chronic myeloid leukemia as they regulate the expression of not only BCR-ABL1 but also genes associated with the activation of drug transfer proteins or essential signaling pathways.

Methods

To understand the impact of specifically expressed miRNAs in chronic myeloid leukemia and their target genes, we collected peripheral blood mononuclear cells (PBMC) from patients diagnosed with chronic myeloid leukemia (CML) and healthy donors to determine whole miRNA expression by small RNA sequencing and screened out 31 differentially expressed microRNAs (DE-miRNAs) with high expression. With the utilization of miRNA set enrichment analysis tools, we present here a comprehensive analysis of the relevance of DE-miRNAs to disease and biological function. Furthermore, the literature-based miRNA-target gene database was used to analyze the overall target genes of the DE-miRNAs and to define their associated biological responses. We further integrated DE-miRNA target genes to identify CML miRNA targeted gene signature singscore (CMTGSS) and used gene-set enrichment analysis (GSEA) to analyze the correlation between CMTGSS and Hallmark gene-sets in PBMC samples from clinical CML patients. Finally, the association of CMTGSS stratification with multiple CML cell lineage gene sets was validated in PBMC samples from CML patients using GSEA.

Results

Although individual miRNAs have been reported to have varying degrees of impact on CML, overall, our results show that abnormally upregulated miRNAs are associated with apoptosis and aberrantly downregulated miRNAs are associated with cell cycle. The clinical database shows that our defined DE-miRNAs are associated with the prognosis of CML patients. CMTGSS-based stratification analysis presented a tendency for miRNAs to affect cell differentiation in the blood microenvironment.

Conclusion

Collectively, this study defined differentially expressed miRNAs by miRNA sequencing from clinical samples and comprehensively analyzed the biological functions of the differential miRNAs in association with the target genes. The analysis of the enrichment of specific myeloid differentiated cells and immune cells also suggests the magnitude and potential targets of differentially expressed miRNAs in the clinical setting. It helps us to make links between the different results obtained from the multi-faceted studies to provide more potential research directions.

Therapeutic advancements in targeting BCL-2 family proteins by epigenetic regulators, natural, and synthetic agents in cancer

Cancer is amongst the deadliest and most disruptive disorders, having a much higher death rate than other diseases worldwide. Human cancer rates continue to rise, thereby posing the most significant concerns for medical health professionals. In the last two decades, researchers have gone past several milestones in tackling cancer while gaining insight into the role of apoptosis in cancer or targeting various biomarker tools for prognosis and diagnosis. Apoptosis which is still a topic full of complexities, can be controlled considerably by B-cell lymphoma 2 (BCL-2) and its family members. Therefore, targeting proteins of this family to prevent tumorigenesis, is essential to focus on the pharmacological features of the anti-apoptotic and pro-apoptotic members, which will help to develop and manage this disorder. This review deals with the advancements of various epigenetic regulators to target BCL-2 family proteins, including the mechanism of several microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Similarly, a rise in natural and synthetic molecules' research over the last two decades has allowed us to acquire insights into understanding and managing the transcriptional alterations that have led to apoptosis and treating various neoplastic diseases. Furthermore, several inhibitors targeting anti-apoptotic proteins and inducers or activators targeting pro-apoptotic proteins in preclinical and clinical stages have been summarized. Overall, agonistic and antagonistic mechanisms of BCL-2 family proteins conciliated by epigenetic regulators, natural and synthetic agents have proven to be an excellent choice in developing cancer therapeutics.

Understanding MCL1: from cellular function and regulation to pharmacological inhibition

Myeloid cell leukemia-1 (MCL1), an antiapoptotic member of the BCL2 family characterized by a short half-life, functions as a rapid sensor that regulates cell death and other relevant processes that include cell cycle progression and mitochondrial homeostasis. In cancer, MCL1 overexpression contributes to cell survival and resistance to diverse chemotherapeutic agents; for this reason, several MCL1 inhibitors are currently under preclinical and clinical development for cancer treatment. However, the nonapoptotic functions of MCL1 may influence their therapeutic potential. Overall, the complexity of MCL1 regulation and function represent challenges to the clinical application of MCL1 inhibitors. We now summarize the current knowledge regarding MCL1 structure, regulation, and function that could impact the clinical success of MCL1 inhibitors.

miR-181c regulates MCL1 and cell survival in GATA2 deficient cells

GATA2 is a transcription factor critical for hematopoiesis. Germline mutations in GATA binding protein 2 (GATA2) led to haploinsufficiency, severe cytopenias of multiple cell lineages, susceptibility to infections and strong propensity to develop myelodysplastic syndrome, and acute myeloid leukemia. Mechanisms of progressive cytopenias remain unclear. MicroRNA (miRNA) represents a unique mechanism of post-transcriptional gene regulation. In this study, miRNA profiles were evaluated and eight miRNAs were found to be differentially expressed (≥2-fold, P ≤ 0.05) in patient-derived cell lines (N = 13) in comparison to controls (N = 10). miR-9, miR-181a-2-3p, miR-181c, miR-181c-3p, miR-486-3p, and miR-582 showed increased expression, whereas miR-223 and miR-424-3p showed decreased expression. Cell death assays indicated that miR-181c potently induces cell death in lymphoid (Ly-8 and SP-53) and myeloid (HL-60) cell lines. miR-181c was predicted to target myeloid cell leukemia (MCL)1, which was confirmed by transfection assays, resulting in significantly reduced MCL1 mRNA and decreased live cell numbers. Bone marrow analysis of 34 GATA2 patients showed significantly decreased cellularity, CD34-positive cells, monocytes, dendritic cells, NK cells, B cells, and B cell precursors in comparison to healthy controls (N = 29; P < 0.001 for each), which was accompanied by decreased levels of MCL1 (P < 0.05). GATA2 expression led to significant repression of miR-181c expression in transfection experiments. Conversely, knockdown of GATA2 led to increased miR-181c expression. These findings indicate that miR-181c expression is increased and MCL1 levels decreased in GATA2 deficiency cells, and that GATA2 represses miR-181c transcription. Increased miR-181c may contribute to elevated cell death and cytopenia in GATA2 deficiency potentially through down-regulation of MCL1.

Human and herpesvirus microRNAs in periodontal disease

Periodontitis is a multi-etiologic infection characterized clinically by pathologic loss of the periodontal ligament and alveolar bone. Herpesviruses and specific bacterial species are major periodontal pathogens that cooperate synergistically in producing severe periodontitis. Cellular immunity against herpesviruses and humoral immunity against bacteria are key periodontal host defenses. Genetic, epigenetic, and environmental factors are modifiers of periodontal disease severity. MicroRNAs are a class of noncoding, gene expression-based, posttranscriptional regulatory RNAs of great importance for maintaining tissue homeostasis. Aberrant expression of microRNAs has been associated with several medical diseases. Periodontal tissue cells and herpesviruses elaborate several microRNAs that are of current research interest. This review attempts to conceptualize the role of periodontal microRNAs in the pathogenesis of periodontitis. The diagnostic potential of salivary microRNAs is also addressed. Employment of microRNA technology in periodontics represents an interesting new preventive and therapeutic possibility.

Combinatorial Strategies to Target Molecular and Signaling Pathways to Disarm Cancer Stem Cells

Cancer is an urgent public health issue with a very huge number of cases all over the world expected to increase by 2040. Despite improved diagnosis and therapeutic protocols, it remains the main leading cause of death in the world. Cancer stem cells (CSCs) constitute a tumor subpopulation defined by ability to self-renewal and to generate the heterogeneous and differentiated cell lineages that form the tumor bulk. These cells represent a major concern in cancer treatment due to resistance to conventional protocols of radiotherapy, chemotherapy and molecular targeted therapy. In fact, although partial or complete tumor regression can be achieved in patients, these responses are often followed by cancer relapse due to the expansion of CSCs population. The aberrant activation of developmental and oncogenic signaling pathways plays a relevant role in promoting CSCs therapy resistance. Although several targeted approaches relying on monotherapy have been developed to affect these pathways, they have shown limited efficacy. Therefore, an urgent need to design alternative combinatorial strategies to replace conventional regimens exists. This review summarizes the preclinical studies which provide a proof of concept of therapeutic efficacy of combinatorial approaches targeting the CSCs.

Vitamin D modulation and microRNAs in gastric cancer: prognostic and therapeutic role

Gastric adenocarcinoma arises after a complex interaction between the host and environmental factors. Tumor location and TNM are the tools that currently guide treatment decisions. Surgery is the only curative treatment, but relapse is common. After relapse or advanced staged disease survival is poor and systemic treatment has modestly improved survival. An association between sun exposure, vitamin D status and gastric cancer (GC) incidence and mortality has been reported. The molecular differences of the histological subtypes and the new molecular classifications account for the great heterogeneity of this disease and are the basis for the discovery of new therapeutic targets. New prognostic and predictive factors are essential and microRNAs (miRNAs) are endogenous small non-coding RNA molecules with a great potential for diagnosis, prognosis and treatment of cancer. There are hundreds of miRNAs with altered expression in tumor gastric tissue when compared to normal gastric tissue. Many of these miRNAs are associated with clinicopathological variables and survival in patients with GC. Furthermore, the expression of some of these miRNAs with prognostic importance in CG is influenced by vitamin D and others are mediators of some of the actions of this vitamin. This review aims to update the evidence on several miRNAs with prognostic value and therapeutic potential in GC, whose expression may be influenced by vitamin D or may regulate vitamin D signaling.

miR-181d/RBP2/NF-κB p65 Feedback Regulation Promotes Chronic Myeloid Leukemia Blast Crisis

Background

Chronic myeloid leukemia (CML) is a malignant clonal proliferative disease. Once it progresses into the phase of blast crisis (CML-BP), the curative effect is poor, and the fatality rate is extremely high. Therefore, it is urgent to explore the molecular mechanisms of blast crisis and identify new therapeutic targets.

Methods

The expression levels of miR-181d, RBP2 and NF-κB p65 were assessed in 42 newly diagnosed CML-CP patients and 15 CML-BP patients. Quantitative real-time PCR, Western blots, and cell proliferation assay were used to characterize the changes induced by overexpression or inhibition of miR-181d, RBP2 or p65. Luciferase reporter assay and ChIP assay was conducted to establish functional association between miR-181d, RBP2 and p65. Inhibition of miR-181d expression and its consequences in tumor growth was demonstrated in vivo models.

Results

We found that miR-181d was overexpressed in CML-BP, which promoted leukemia cell proliferation. Histone demethylase RBP2 was identified as a direct target of miR-181d which downregulated RBP2 expression. Moreover, RBP2 inhibited transcriptional expression of NF-κB subunit, p65 by binding to its promoter and demethylating the tri/dimethylated H3K4 region in the p65 promoter locus. In turn, p65 directly bound to miR-181d promoter and upregulated its expression. Therefore, RBP2 inhibition resulting from miR-181d overexpression led to p65 upregulation which further forwarded miR-181d expression. This miR-181d/RBP2/p65 feedback regulation caused sustained NF-κB activation, which contributed to the development of CML-BP.

Conclusions

Taken together, the miR-181d/RBP2/p65 feedback regulation promoted CML-BP and miR-181d may serve as a potential therapeutic target of CML-BP.

miRNAs mediated drug resistance in hematological malignancies

Despite improvements in the therapeutic approaches for hematological malignancies in the last decades, refractory disease still occurs, and cancer drug resistance still remains a major hurdle in the clinical management of these cancer patients. The investigation of this problem has been extensive and different mechanism and molecules have been associated with drug resistance. MicroRNAs (miRNAs) have been described as having an important action in the emergence of cancer, including hematological tumors, and as being major players in their progression, aggressiveness and response to treatments. Moreover, miRNAs have been strongly associated with cancer drug resistance and with the modulation of the sensitivity of cancer cells to a wide array of anticancer drugs. Furthermore, this role has also been reported for miRNAs packaged into extracellular vesicles (EVs-miRNAs), which in turn have been described as essential for the horizontal transfer of drug resistance to sensitive cells. Several studies have been suggesting the use of miRNAs as biomarkers for drug response and clinical outcome prediction, as well as promising therapeutic tools in hematological diseases. Indeed, the combination of miRNA-based therapeutic tools with conventional drugs contributes to overcome drug resistance. This review addresses the role of miRNAs in the pathogenesis of hematological malignances, namely multiple myeloma, leukemias and lymphomas, highlighting their important action (either in their cell-free circulating form or within circulating EVs) in drug resistance and their potential clinical applications.

Gga-miR-181a modulates ANP32A expression and inhibits MDCC-MSB-1 cell

Marek's disease (MD), a highly contagious T cell lymphoid neoplasia disease of chickens, causes huge economic losses to the poultry industry. It is the only one tumor disease which can be prevented by vaccine in chickens; therefore, MD is considered to be an excellent model to study the pathogenesis of virus-induced cancer. Recently, abundant evidences have verified that miRNAs are regulators in the process of neoplastic transformation. In our previous study on miRNome analysis of MDV-induced lymphoma in chicken, we found that gga-miR-181a was downregulated drastically in MDV-infected spleens. To further investigate the role of gga-miR-181a in MDV-induced lymphomagenesis, we performed cell migration assay, and the results suggested that gga-miR-181a suppressed the migration of MDV-transformed lymphoid cell (MSB-1). Subsequently, luciferase reporter gene assay revealed that acidic nuclear phosphoprotein 32A (ANP32A) was a functional target gene of gga-miR181a. Real-time PCR and western blot assay showed that the mRNA and protein levels of ANP32A were downregulated in gga-miR-181a mimic group at 48-h and 96-h post-transfection, respectively, indicating that ANP32A was modulated by gga-miR-181a. All the results suggested that gga-miR-181a was an inhibitor in MSB-1 cell migration. ANP32A was a direct target gene of gga-miR-181a and they were implicated in MD lymphoma tumorigenesis.

Comparison of microRNA Expression Profile in Chronic Myeloid Leukemia Patients Newly Diagnosed and Treated by Allogeneic Hematopoietic Stem Cell Transplantation

Chronic myeloid leukemia (CML) results from a translocation between chromosomes 9 and 22, which generates the Philadelphia chromosome. This forms BCR/ABL1, an active tyrosine kinase protein that promotes cell growth and replication. Despite great progress in CML treatment in the form of tyrosine kinase inhibitors, allogeneic-hematopoietic stem cell transplantation (allo-HSCT) is currently used as an important treatment alternative for patients resistant to these inhibitors. Studies have shown that unregulated expression of microRNAs, which act as oncogenes or tumor suppressors, is associated with human cancers. This contributes to tumor formation and development by stimulating proliferation, angiogenesis, and invasion. Research has demonstrated the potential of microRNAs as biomarkers for cancer diagnosis, prognosis, and therapeutic targets. In the present study, we compared the circulating microRNA expression profiles of 14 newly diagnosed patients with chronic phase-CML and 14 Philadelphia chromosome-negative patients after allo-HSCT. For each patient, we tested 758 microRNAs by reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis. The global expression profile of microRNAs revealed 16 upregulated and 30 downregulated microRNAs. Target genes were analyzed, and key pathways were extracted and compared. Bioinformatics tools were used to analyze data. Among the downregulated miRNA target genes, some genes related to cell proliferation pathways were identified. These results reveal the comprehensive microRNA profile of CML patients and the main pathways related to the target genes of these miRNAs in cytogenetic remission after allo-HSCT. These results provide new resources for exploring stem cell transplantation-based CML treatment strategies.

Diamond Blackfan anemia is mediated by hyperactive Nemo-like kinase

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome associated with ribosomal gene mutations that lead to ribosomal insufficiency. DBA is characterized by anemia, congenital anomalies, and cancer predisposition. Treatment for DBA is associated with significant morbidity. Here, we report the identification of Nemo-like kinase (NLK) as a potential target for DBA therapy. To identify new DBA targets, we screen for small molecules that increase erythroid expansion in mouse models of DBA. This screen identified a compound that inhibits NLK. Chemical and genetic inhibition of NLK increases erythroid expansion in mouse and human progenitors, including bone marrow cells from DBA patients. In DBA models and patient samples, aberrant NLK activation is initiated at the Megakaryocyte/Erythroid Progenitor (MEP) stage of differentiation and is not observed in non-erythroid hematopoietic lineages or healthy erythroblasts. We propose that NLK mediates aberrant erythropoiesis in DBA and is a potential target for therapy.

Diamond Blackfan Anemia (DBA) is a congenital bone marrow failure syndrome that is associated with anemia. Here, the authors examine the role of Nemo-like kinase (NLK) in erythroid cells in the pathogenesis of DBA and as a potential target for therapy.

Lyn regulates creatine uptake in an imatinib-resistant CML cell line

BACKGROUND

Imatinib mesylate (imatinib) is the first-line treatment for newly diagnosed chronic myeloid leukemia (CML) due to its remarkable hematologic and cytogenetic responses. We previously demonstrated that the imatinib-resistant CML cells (Myl-R) contained elevated Lyn activity and intracellular creatine pools compared to imatinib-sensitive Myl cells.

METHODS

Stable isotope metabolic labeling, media creatine depletion, and Na⁺/K⁺-ATPase inhibitor experiments were performed to investigate the origin of creatine pools in Myl-R cells. Inhibition and shRNA knockdown were performed to investigate the specific role of Lyn in regulating the Na⁺/K⁺-ATPase and creatine uptake.

RESULTS

Inhibition of the Na⁺/K⁺-ATPase pump (ouabain, digitoxin), depletion of extracellular creatine or inhibition of Lyn kinase (ponatinib, dasatinib), demonstrated that enhanced creatine accumulation in Myl-R cells was dependent on uptake from the growth media. Creatine uptake was independent of the Na⁺/creatine symporter (SLC6A8) expression or de novo synthesis. Western blot analyses showed that phosphorylation of the Na⁺/K⁺-ATPase on Tyr 10 (Y10), a known regulatory phosphorylation site, correlated with Lyn activity. Overexpression of Lyn in HEK293 cells increased Y10 phosphorylation (pY10) of the Na⁺/K⁺-ATPase, whereas Lyn inhibition or shRNA knockdown reduced Na⁺/K⁺-ATPase pY10 and decreased creatine accumulation in Myl-R cells. Consistent with enhanced uptake in Myl-R cells, cyclocreatine (Ccr), a cytotoxic creatine analog, caused significant loss of viability in Myl-R compared to Myl cells.

CONCLUSIONS

These data suggest that Lyn can affect creatine uptake through Lyn-dependent phosphorylation and regulation of the Na⁺/K⁺-ATPase pump activity.

GENERAL SIGNIFICANCE

These studies identify kinase regulation of the Na⁺/K⁺-ATPase as pivotal in regulating creatine uptake and energy metabolism in cells.

Molecular Comparison of Imatinib-Naïve and Resistant Gastrointestinal Stromal Tumors: Differentially Expressed microRNAs and mRNAs

Despite the success of imatinib in advanced gastrointestinal stromal tumor (GIST) patients, 50% of the patients experience resistance within two years of treatment underscoring the need to get better insight into the mechanisms conferring imatinib resistance. Here the microRNA and mRNA expression profiles in primary (imatinib-naïve) and imatinib-resistant GIST were examined. Fifty-three GIST samples harboring primary KIT mutations (exon 9; n = 11/exon 11; n = 41/exon 17; n = 1) and comprising imatinib-naïve (IM-n) (n = 33) and imatinib-resistant (IM-r) (n = 20) tumors, were analyzed. The microRNA expression profiles were determined and from a subset (IM-n, n = 14; IM-r, n = 15) the mRNA expression profile was established. Ingenuity pathway analyses were used to unravel biochemical pathways and gene networks in IM-r GIST. Thirty-five differentially expressed miRNAs between IM-n and IM-r GIST samples were identified. Additionally, miRNAs distinguished IM-r samples with and without secondary KIT mutations. Furthermore 352 aberrantly expressed genes were found in IM-r samples. Pathway and network analyses revealed an association of differentially expressed genes with cell cycle progression and cellular proliferation, thereby implicating genes and pathways involved in imatinib resistance in GIST. Differentially expressed miRNAs and mRNAs between IM-n and IM-r GIST were identified. Bioinformatic analyses provided insight into the genes and biochemical pathways involved in imatinib-resistance and highlighted key genes that may be putative treatment targets.

Biological Aspects of mTOR in Leukemia

The mammalian target of rapamycin (mTOR) is a central processor of intra- and extracellular signals, regulating many fundamental cellular processes such as metabolism, growth, proliferation, and survival. Strong evidences have indicated that mTOR dysregulation is deeply implicated in leukemogenesis. This has led to growing interest in the development of modulators of its activity for leukemia treatment. This review intends to provide an outline of the principal biological and molecular functions of mTOR. We summarize the current understanding of how mTOR interacts with microRNAs, with components of cell metabolism, and with controllers of apoptotic machinery. Lastly, from a clinical/translational perspective, we recapitulate the therapeutic results in leukemia, obtained by using mTOR inhibitors as single agents and in combination with other compounds.

MicroRNAs and immunity in periodontal health and disease

MicroRNAs (miRNAs) are critical regulators of the host immune and inflammatory response against bacterial pathogens. In the present review, we discuss target genes, target gene functions, the potential regulatory role of miRNAs in periodontal tissues, and the potential role of miRNAs as biomarkers and therapeutics. In periodontal disease, miRNAs exert control over all aspects of innate and adaptive immunity, including the functions of neutrophils, macrophages, dendritic cells and T and B cells. Previous human studies have highlighted some key miRNAs that are dysregulated in periodontitis patients. In the present study, we mapped the major miRNAs that were altered in our reproducible periodontitis mouse model relative to control animals. The miRNAs that were upregulated as a result of periodontal disease in both human and mouse studies included miR-15a, miR-29b, miR-125a, miR-146a, miR-148/148a and miR-223, whereas miR-92 was downregulated. The association of individual miRNAs with unique aspects of periodontal disease and their stability in gingival crevicular fluid underscores their potential as markers for periodontal disease progression or healthy restitution. Moreover, miRNA therapeutics hold great promise for the future of periodontal therapy because of their ability to modulate the immune response to infection when applied in conjunction with synthetic antagomirs and/or relatively straightforward delivery strategies.

Post-Transcriptional Regulation of Anti-Apoptotic BCL2 Family Members

Anti-apoptotic B cell lymphoma 2 (BCL2) family members (BCL2, MCL1, BCLxL, BCLW, and BFL1) are key players in the regulation of intrinsic apoptosis. Dysregulation of these proteins not only impairs normal development, but also contributes to tumor progression and resistance to various anti-cancer therapies. Therefore, cells maintain strict control over the expression of anti-apoptotic BCL2 family members using multiple mechanisms. Over the past two decades, the importance of post-transcriptional regulation of mRNA in controlling gene expression and its impact on normal homeostasis and disease have begun to be appreciated. In this review, we discuss the RNA binding proteins (RBPs) and microRNAs (miRNAs) that mediate post-transcriptional regulation of the anti-apoptotic BCL2 family members. We describe their roles and impact on alternative splicing, mRNA turnover, and mRNA subcellular localization. We also point out the importance of future studies in characterizing the crosstalk between RBPs and miRNAs in regulating anti-apoptotic BCL2 family member expression and ultimately apoptosis.

Determining expression of miRNAs that potentially regulate STAT5A and 5B in dasatinib-sensitive K562 cells

In the era of tyrosine kinase inhibitors, resistance still constitutes a problem in chronic myeloid leukemia (CML) patients; thus, new pathway-specific inhibitors like miRNAs have become important in the treatment of refractory patients. There are no satisfying data regarding the miRNAs and anti-miRNA treatment targeting STAT5A and 5B. In this study, we first researched the effect of dasatinib on apoptosis in the CML cell line K562. The expressions of miRNAs possibly targeting both STAT5A and 5B were then determined. The down- and upregulation of the miRNAs were compared using the ΔΔCT method. At the last stage of the study, we used a new primer probe in order to validate the results. The level of hsa-miR-940 was decreased 4.4 times and the levels of hsa-miR-527 and hsa-miR-518a-5p were increased 12.1 and 8 times, respectively, in the dasatinib-treated group when compared to the control group. We detected similar results in the validation step. As a conclusion, we determined the expression profiles of miRNAs targeting STAT5A and 5B that had an important role in the pathogenesis of CML. The data obtained could lead to determining new therapeutic targets for CML patients.

Epigenetic dysregulation in chronic myeloid leukaemia: A myriad of mechanisms and therapeutic options

The onset of global epigenetic changes in chromatin that drive tumor proliferation and heterogeneity is a hallmark of many forms of cancer. Identifying the epigenetic mechanisms that govern these changes and developing therapeutic approaches to modulate them, is a well-established avenue pursued in translational cancer medicine. Chronic myeloid leukemia (CML) arises clonally when a hematopoietic stem cell (HSC) acquires the capacity to produce the constitutively active tyrosine kinase BCR-ABL1 fusion protein which drives tumor development. Treatment with tyrosine kinase inhibitors (TKI) that target BCR-ABL1 has been transformative in CML management but it does not lead to cure in the vast majority of patients. Thus novel therapeutic approaches are required and these must target changes to biological pathways that are aberrant in CML - including those that occur when epigenetic mechanisms are altered. These changes may be due to alterations in DNA or histones, their biochemical modifications and requisite 'writer' proteins, or to dysregulation of various types of non-coding RNAs that collectively function as modulators of transcriptional control and DNA integrity. Here, we review the evidence for subverted epigenetic mechanisms in CML and how these impact on a diverse set of biological pathways, on disease progression, prognosis and drug resistance. We will also discuss recent progress towards developing epigenetic therapies that show promise to improve CML patient care and may lead to improved cure rates.

Combined targeting of STAT3 and STAT5: a novel approach to overcome drug resistance in chronic myeloid leukemia

In chronic myeloid leukemia, resistance against BCR-ABL1 tyrosine kinase inhibitors can develop because of BCR-ABL1 mutations, activation of additional pro-oncogenic pathways, and stem cell resistance. Drug combinations covering a broad range of targets may overcome resistance. CDDO-Me (bardoxolone methyl) is a drug that inhibits the survival of leukemic cells by targeting different pro-survival molecules, including STAT3. We found that CDDO-Me inhibits proliferation and survival of tyrosine kinase inhibitor-resistant BCR-ABL1⁺ cell lines and primary leukemic cells, including cells harboring BCR-ABL1^T315I or T315I⁺ compound mutations. Furthermore, CDDO-Me was found to block growth and survival of CD34⁺/CD38⁻ leukemic stem cells (LSC). Moreover, CDDO-Me was found to produce synergistic growth-inhibitory effects when combined with BCR-ABL1 tyrosine kinase inhibitors. These drug-combinations were found to block multiple signaling cascades and molecules, including STAT3 and STAT5. Furthermore, combined targeting of STAT3 and STAT5 by shRNA and STAT5-targeting drugs also resulted in synergistic growth-inhibition, pointing to a new efficient concept of combinatorial STAT3 and STAT5 inhibition. However, CDDO-Me was also found to increase the expression of heme-oxygenase-1, a heat-shock-protein that triggers drug resistance and cell survival. We therefore combined CDDO-Me with the heme-oxygenase-1 inhibitor SMA-ZnPP, which also resulted in synergistic growth-inhibitory effects. Moreover, SMA-ZnPP was found to sensitize BCR-ABL1⁺ cells against the combination ‘CDDO-Me+ tyrosine kinase inhibitor’. Together, combined targeting of STAT3, STAT5, and heme-oxygenase-1 overcomes resistance in BCR-ABL1⁺ cells, including stem cells and highly resistant sub-clones expressing BCR-ABL1^T315I or T315I-compound mutations. Whether such drug-combinations are effective in tyrosine kinase inhibitor-resistant patients with chronic myeloid leukemia remains to be elucidated.

MicroRNA-181 inhibits proliferation and promotes apoptosis of chondrocytes in osteoarthritis by targeting PTEN

Objective: To investigate the effects of microRNA-181 (miR-181) on the proliferation and apoptosis of chondrocytes in osteoarthritis (OA) by targeting PTEN. Methods: The chondrocytes in logarithmic growth phase were selected and divided into 6 test groups: the normal, blank, negative control, miR-181 mimic, miR-181 inhibitor, and miR-181 inhibitor + PTEN-siRNA groups. Reverse transcription qPCR was used to detect the expressions of miR-181 and PTEN mRNA. MTT assay and flow cytometry were performed to detect cell proliferation and apoptosis. The protein expressions of PARP and caspase-3 and the activity of MMP-2 and MMP-9 were detected by Western blotting and gelatin zymography assay. Results: The miR-181 mimic group showed increased miR-181 expression and decreased PTEN expression compared with the other 5 groups. Also, by comparison with the other 5 groups, the cell proliferation rate declined and the rate of cell apoptosis was elevated in the miR-181 mimic group. The MiR-181 mimic group showed remarkably increased protein expression of caspase-3 and PARP compared with the other 5 groups. The activity of MMP-2 and MMP-9 was higher in the miR-181 mimic group than the other 5 groups. Conclusion: MiR-181 could up-regulate the expressions of caspase-3, PARP, MMP-2, and MMP-9, and thereby inhibit cell proliferation and promote apoptosis of chondrocytes in OA by targeting PTEN.

BIRC6 mediates imatinib resistance independently of Mcl-1

Baculoviral IAP repeat containing 6 (BIRC6) is a member of the inhibitors of apoptosis proteins (IAPs), a family of functionally and structurally related proteins that inhibit apoptosis. BIRC6 has been implicated in drug resistance in several different human cancers, however mechanisms regulating BIRC6 have not been extensively explored. Our phosphoproteomic analysis of an imatinib-resistant chronic myelogenous leukemia (CML) cell line (MYL-R) identified increased amounts of a BIRC6 peptide phosphorylated at S480, S482, and S486 compared to imatinib-sensitive CML cells (MYL). Thus we investigated the role of BIRC6 in mediating imatinib resistance and compared it to the well-characterized anti-apoptotic protein, Mcl-1. Both BIRC6 and Mcl-1 were elevated in MYL-R compared to MYL cells. Lentiviral shRNA knockdown of BIRC6 in MYL-R cells increased imatinib-stimulated caspase activation and resulted in a ~20-25-fold increase in imatinib sensitivity, without affecting Mcl-1. Treating MYL-R cells with CDK9 inhibitors decreased BIRC6 mRNA, but not BIRC6 protein levels. By contrast, while CDK9 inhibitors reduced Mcl-1 mRNA and protein, they did not affect imatinib sensitivity. Since the Src family kinase Lyn is highly expressed and active in MYL-R cells, we tested the effects of Lyn inhibition on BIRC6 and Mcl-1. RNAi-mediated knockdown or inhibition of Lyn (dasatinib/ponatinib) reduced BIRC6 protein stability and increased caspase activation. Inhibition of Lyn also increased formation of an N-terminal BIRC6 fragment in parallel with reduced amount of the BIRC6 phosphopeptide, suggesting that Lyn may regulate BIRC6 phosphorylation and stability. In summary, our data show that BIRC6 stability is dependent on Lyn, and that BIRC6 mediates imatinib sensitivity independently of Mcl-1 or CDK9. Hence, BIRC6 may be a novel target for the treatment of drug-resistant CML where Mcl-1 or CDK9 inhibitors have failed.

Induction of K562 Cell Apoptosis by As4S4 via Down-Regulating miR181

Background

Chronic myelogenous leukemia (CML) has unsatisfactory treatment efficacy at present. As the major component of red orpiment, tetra-arsenic tetra-sulfide (As₄S₄) has been recently used in treating leukemia, but with unclear mechanism targeting CML. MicroRNA (miR) is a group of endogenous non-coding RNAs regulating pathogenesis. MiR181 has been shown to exert important roles in tumor progression. The relationship between miR181 and As₄S₄ in inducing K562 cell apoptosis, however, is still unclear.

Material/Methods

CML cell line K562 was cultured in vitro in a control group and in groups receiving various dosages (20 μM and 40 μM) of As₄S₄. MTT assay was employed to detect the effect on K562 cell survival. MiR181 expression was quantified by real-time PCR. MTT assay and assay kit were used to determine K562 cell survival and caspase 3 expression. Cell apoptosis was assessed by flow cytometry. Bcl-2 expression was determined by real-time PCR and Western blotting.

Results

As₄S₄ significantly suppressed proliferation of K562 cells (p<0.05) and decreased miR181 expression, and increased caspase3 activity compared to the control group. It can induce K562 cell apoptosis via remarkably down-regulating mRNA and protein expressions of Bcl-2 (p<0.05).

Conclusions

As₄S₄ can facilitate K562 cell apoptosis via down-regulating miR181, inhibiting Bcl02 expression, and enhancing apoptotic protein caspase3 activity.

miRNAs in chronic myeloid leukemia: small molecules, essential function

Chronic myeloid leukemia (CML) is a myeloproliferative disorder associated with clonal expansion of cancerous bone marrow stem cells. Tyrosine kinase inhibitors (TKIs) targeting Bcr-Abl oncoprotein are the first-line therapy for most CML patients, however, some are unresponsive to it or develop resistance. Recently, microRNAs (miRNAs) have been implicated in the progression of CML and the development of TKI resistance based on their important regulatory function in cell homeostasis. MicroRNAs are small noncoding RNAs that post-transcriptionally regulate gene expression. Since microRNAs can function either as oncogenes or tumor suppressor genes in leukemogenesis, the potential of using them as therapeutic targets by inhibiting or amplifying their activity, opens up new opportunities for leukemia therapy. In this review, we focus on recent studies on the important roles of microRNAs in the pathogenesis of CML and their relevance as biomarkers for diagnosis, monitoring disease progression, and treatment response.

MicroRNAs and Gastrointestinal Stromal Tumor

Gastrointestinal stromal tumor (GIST) is the most commonly diagnosed mesenchymal tumor in the gastrointestinal tract. This tumor type is driven by gain-of-function mutations in receptor tyrosine kinases (such as KIT, PDGFRA, and BRAF) or loss-of-function mutations in succinate dehydrogenase complex subunit genes (SDHx). Molecular studies on GIST have improved our understanding of the biology of the disease and have led to the use of targeted therapy approach, such as imatinib for KIT/PDGFRA-mutated GIST. Recently, microRNAs have emerged as important regulators of KIT expression, cancer cell behavior, and imatinib response in GIST. This chapter aims to provide an overview on current understanding of the biological roles of microRNAs in GIST and possible implications in prognosis and therapeutic response.

MiR-203 downregulation is responsible for chemoresistance in human glioblastoma by promoting epithelial-mesenchymal transition via SNAI2

Epithelial-mesenchymal transition (EMT) has been recognized as a key element of cell migration, invasion, and drug resistance in several types of cancer. In this study, our aim was to clarify microRNAs (miRNAs)-related mechanisms underlying EMT followed by acquired resistance to chemotherapy in glioblastoma (GBM). We used multiple methods to achieve our goal including microarray analysis, qRT-PCR, western blotting analysis, loss/gain-of-function analysis, luciferase assays, drug sensitivity assays, wound-healing assay and invasion assay. We found that miR-203 expression was significantly lower in imatinib-resistant GBM cells (U251AR, U87AR) that underwent EMT than in their parental cells (U251, U87). Ectopic expression of miR-203 with miRNA mimics effectively reversed EMT in U251AR and U87AR cells, and sensitized them to chemotherapy, whereas inhibition of miR-203 in the sensitive lines with antisense oligonucleotides induced EMT and conferred chemoresistance. SNAI2 was identified as a direct target gene of miR-203. The knockdown of SNAI2 by short hairpin RNA (shRNA) inhibited EMT and drug resistance. In GBM patients, miR-203 expression was inversely related to SNAI2 expression, and those tumors with low expression of miR-203 experienced poorer clinical outcomes. Our findings indicate that re-expression of miR-203 or targeting SNAI2 might serve as potential therapeutic approaches to overcome chemotherapy resistance in GBM.

The roles of microRNAs in the pathogenesis and drug resistance of chronic myelogenous leukemia (Review)

Chronic myeloid leukemia (CML) is characterized by the accumulation of Philadelphia chromosome-positive (Ph+) myeloid cells. Ph+ cells occur via a reciprocal translocation between the long arms of chromosomes 9 and 22 resulting in constitutively active BCR-ABL fusion protein. Tyrosine kinase inhibitors (TKIs) are used against the kinase activity of BCR-ABL protein for the effective treatment of CML. However, the development of drug resistance, caused by different genetic mechanisms, is the major issue in the clinical application of TKIs. These mechanisms include changes in expression levels of microRNAs (miRNAs). miRNAs are short non-coding regulatory RNAs that control gene expression and play an important role in cancer development and progression. In the present review, we highlight the roles of miRNAs both in the progression and chemotherapy-resistance of CML. Our understanding of these mechanisms may lead to the use of this knowledge not only in the treatment of patients with CML, but also in other type of cancers.

microRNAs as pharmacogenomic biomarkers for drug efficacy and drug safety assessment

Much evidence has documented that microRNAs (miRNAs) play an important role in the modulation of interindividual variability in the production of drug metabolizing enzymes and transporters (DMETs) and nuclear receptors (NRs) through multidirectional interactions involving environmental stimuli/stressors, the expression of miRNA molecules and genetic polymorphisms. MiRNA expression has been reported to be affected by drugs and miRNAs themselves may affect drug metabolism and toxicity. In cancer research, miRNA biomarkers have been identified to mediate intrinsic and acquired resistance to cancer therapies. In drug safety assessment, miRNAs have been found associated with cardiotoxicity, hepatotoxicity and nephrotoxicity. This review article summarizes published studies to show that miRNAs can serve as early biomarkers for the evaluation of drug efficacy and drug safety.

MicroRNAs in Myeloid Hematological Malignancies

MicroRNAs are 19-24 nucleotides noncoding RNAs which silence modulate the expression of target genes by binding to the messenger RNAs. Myeloid malignancies include a broad spectrum of acute and chronic disorders originating from from the clonal transformation of a hematopoietic stem cell. Specific genetic abnormalities may define myeloid malignancies, such as translocation t(9;22) that represent the hallmark of chronic myeloid leukemia. Although next-generation sequencing pro-vided new insights in the genetic characterization and pathogenesis of myeloid neoplasms, the molecular mechanisms underlying myeloid neoplasms are lacking in most cases. Recently, several studies have demonstrated that the expression levels of specific miRNAs may vary among patients with myeloid malignancies compared with healthy individuals and partially unveiled how miRNAs participate in the leukemic transformation process. Finally, in vitro experiments and pre-clinical model provided preliminary data of the safety and efficacy of miRNA inhibitory molecules, opening new avenue in the treatment of myeloid hematological malignancies.

Analogs, formulations and derivatives of imatinib: a patent review

INTRODUCTION

The Bcr-Abl inhibitor imatinib was approved in 2001 for chronic myeloid leukemia therapy, and dramatically changed the lives of patients affected by this disease. Since it also inhibits platelet derived growth factor receptor (PDGFR) and c-Kit, imatinib is used for various other tumors caused by abnormalities of one or both these two enzymes.

AREAS COVERED

This review presents an overview on imatinib formulations and derivatives, synthetic methodologies and therapeutic uses that have appeared in the patent literature since 2008.

EXPERT OPINION

Innovative imatinib formulations, such as nanoparticles containing the drug, will improve its bioavailability. Moreover, oral solutions or high imatinib content tablets or capsules will improve patient compliance. Some solid formulations and innovative syntheses that have appeared in the last few years will reduce the cost of the drug, offering big advantages for poor countries. Some recently patented efficacious imatinib derivatives are in preclinical studies and could enter clinical trials in the next few years. Overall, Bcr-Abl inhibitors constitute a very appealing research field that can be expected to expand further.

MiR181c inhibits ovarian cancer metastasis and progression by targeting PRKCD expression

MicroRNAs (miRNAs) regulate many important cancer related gene expression in the posttranscriptional process. Dysregulated expression of miRNAs has been observed in numerous human cancers including ovarian cancer. In this study, we found that the expression of the miR-181c was significantly decreased in ovarian cancer tissue and in tissues with lymph node metastasis when compared with their control samples, respectively. Moreover, among pathological stages, the expression of miR-181c was significantly decreased in the tissues with IV stage compared with other stages. In vitro, miR-181c significantly inhibited the proliferation, metastasis of A2780 cell line, and induced G1 phase arrest. Through bioinformatics prediction, protein kinase C delta (PRKCD) was identified as a target gene of miR-181c. Western blot results showed that PRKCD was increased in ovarian cancer tissue, in tissues with lymph node metastasis and IV stage of ovarian cancer pathological samples. After knocking down PRKCD, the cell cycle of A2780 cells was also arrested in G1 phase. The proliferation and the metastasis of A2780 cells were reduced. The dual luciferase reporter experiments showed that miR-181c regulated the expression of PRKCD by combining with its 3'UTR. These results indicate that miR-181c inhibits ovarian cancer metastasis and progression by targeting PRKCD expression.

miRNAs as Biomarkers in Chronic Myelogenous Leukemia

Chronic myelogenous leukemia (CML) is a myeloproliferative neoplasm that is frequently characterized by the constitutive expression of the oncogenic protein BCR-ABL tyrosine kinase. Tyrosine kinase inhibitors (TKIs) targeting breakpoint cluster region-ABL are the first-line therapy for most CML patients and have drastically improved the prognosis of CML. However, some CML patients are unresponsive to TKI treatment, and a notable proportion of initially responsive patients develop drug resistance. Several molecular pathways have been correlated with resistance to TKI treatment, however, the exact mechanism of developing drug resistance remains ambiguous. Recently, microRNAs (miRNAs) have been implicated in the progression of CML and the development of resistance to TKI treatment based on their important regulatory function in cell homeostasis, and the deregulation observed in the initiation and progression of many leukemia subtypes. In this review, we summarize some of the major discoveries regarding miRNAs in CML, and their relevance as biomarkers for diagnosis, disease progression, and drug sensitivity.

miR-181b as a therapeutic agent for chronic lymphocytic leukemia in the Eµ-TCL1 mouse model

The involvement of microRNAs (miRNAs) in chronic lymphocytic leukemia (CLL) pathogenesis suggests the possibility of anti-CLL therapeutic approaches based on miRNAs. Here, we used the Eµ-TCL1 transgenic mouse model, which reproduces leukemia with a similar course and distinct immunophenotype as human B-CLL, to test miR-181b as a therapeutic agent.In vitro enforced expression of miR-181b mimics induced significant apoptotic effects in human B-cell lines (RAJI, EHEB), as well as in mouse Eµ-TCL1 leukemic splenocytes. Molecular analyses revealed that miR-181b not only affected the expression of TCL1, Bcl2 and Mcl1 anti-apoptotic proteins, but also reduced the levels of Akt and phospho-Erk1/2. Notably, a siRNA anti-TCL1 could similarly down-modulate TCL1, but exhibited a reduced or absent activity in other relevant proteins, as well as a reduced effect on cell apoptosis and viability. In vivo studies demonstrated the capability of miR-181b to reduce leukemic cell expansion and to increase survival of treated mice.These data indicate that miR-181b exerts a broad range of actions, affecting proliferative, survival and apoptotic pathways, both in mice and human cells, and can potentially be used to reduce expansion of B-CLL leukemic cells.

The implication of cancer progenitor cells and the role of epigenetics in the development of novel therapeutic strategies for chronic myeloid leukemia

SIGNIFICANCE

Chronic myeloid leukemia (CML) involves the malignant transformation of hematopoietic stem cells, defined largely by the Philadelphia chromosome and expression of the breakpoint cluster region-Abelson (BCR-ABL) oncoprotein. Pharmacological tyrosine kinase inhibitors (TKIs), including imatinib mesylate, have overcome limitations in conventional treatment for the improved clinical management of CML.

RECENT ADVANCES

Accumulated evidence has led to the identification of a subpopulation of quiescent leukemia progenitor cells with stem-like self renewal properties that may initiate leukemogenesis, which are also shown to be present in residual disease due to their insensitivity to tyrosine kinase inhibition.

CRITICAL ISSUES

The characterization of quiescent leukemia progenitor cells as a unique cell population in CML pathogenesis has become critical with the complete elucidation of mechanisms involved in their survival independent of BCR-ABL that is important in the development of novel anticancer strategies. Understanding of these functional pathways in CML progenitor cells will allow for their selective therapeutic targeting. In addition, disease pathogenesis and drug responsiveness is also thought to be modulated by epigenetic regulatory mechanisms such as DNA methylation, histone acetylation, and microRNA expression, with a capacity to control CML-associated gene transcription.

FUTURE DIRECTIONS

A number of compounds in combination with TKIs are under preclinical and clinical investigation to assess their synergistic potential in targeting leukemic progenitor cells and/or the epigenome in CML. Despite the collective promise, further research is required in order to refine understanding, and, ultimately, advance antileukemic therapeutic strategies.

MicroRNA-181c targets Bcl-2 and regulates mitochondrial morphology in myocardial cells

Apoptosis is an important mechanism for the development of heart failure. Mitochondria are central to the execution of apoptosis in the intrinsic pathway. The main regulator of mitochondrial pathway of apoptosis is Bcl-2 family which includes pro- and anti-apoptotic proteins. MicroRNAs are small noncoding RNA molecules that regulate gene expression by inhibiting mRNA translation and/or inducing mRNA degradation. It has been proposed that microRNAs play critical roles in the cardiovascular physiology and pathogenesis of cardiovascular diseases. Our previous study has found that microRNA-181c, a miRNA expressed in the myocardial cells, plays an important role in the development of heart failure. With bioinformatics analysis, we predicted that miR-181c could target the 3' untranslated region of Bcl-2, one of the anti-apoptotic members of the Bcl-2 family. Thus, we have suggested that miR-181c was involved in regulation of Bcl-2. In this study, we investigated this hypothesis using the Dual-Luciferase Reporter Assay System. Cultured myocardial cells were transfected with the mimic or inhibitor of miR-181c. We found that the level of miR-181c was inversely correlated with the Bcl-2 protein level and that transfection of myocardial cells with the mimic or inhibitor of miR-181c resulted in significant changes in the levels of caspases, Bcl-2 and cytochrome C in these cells. The increased level of Bcl-2 caused by the decrease in miR-181c protected mitochondrial morphology from the tumour necrosis factor alpha-induced apoptosis.

Selective miRNA expression profile in chronic myeloid leukemia K562 cell-derived exosomes

BACKGROUND

Chronic myeloid leukemia (CML) is a myeloproliferative disorder of hematopoietic stem cell scarrying the Philadelphia (Ph) chromosome and an oncogenic BCR-ABL1 fusion gene. The tyrosine kinase inhibitor (TKI) of BCR-ABL1 kinase is a treatment of choice for control of CML.

OBJECTIVE

Recent studies have demonstrated that miRNAs within exosomes from cancer cells play crucial roles in initiation and progression. This study was performed to assess miRNAs within exosomes of K562 cells.

METHODS

miRNA microarray analysis of K562 cells and K562 cell-derived exosomes was conducted with the 6th generation miRCURYTM LNA Array (v.16.0). Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were also carried out. GO terms and signaling pathways were categorized into 66 classes (including homophilic cell adhesion, negative regulation of apoptotic process, cell adhesion) and 26 signaling pathways (such as Wnt).

RESULTS

In exosomes, 49 miRNAs were up regulated as compared to K562 cells, and two of them were further confirmed by quantitative real-time PCR. There are differentially expressed miRNAs between K562 cell derived-exosomes and K562 cells.

CONCLUSION

Selectively expressed miRNAs in exosomes may promote the development of CML via effects on interactions (e.g. adhesion) of CML cells with their microenvironment.

MicroRNA-181 expression regulates specific post-transcriptional level of SAMHD1 expression in vitro

SAM domain and HD domain 1 (SAMHD1) is a newly discovered human immunodeficiency virus (HIV)-1 host restriction factor with high expression in HIV-1-non-permissive cells and low expression in HIV-1-permissive cells. The regulatory mechanism of SAMHD1 expression is still unclear. We examined the relationship between the expression levels of SAMHD1 mRNA and protein and microRNA-181 (miR-181) level in different cell lines. MiR-181 level was negatively correlated with SAMHD1 expression level. By examining the impact of miR-181 on SAMHD1 3' untranslated region (UTR) reporter luciferase activity and on SAMHD1 mRNA and argonaute RISC catalytic component 2 (AGO2) binding, we found that miR-181 acted directly on the SAMHD1 3' UTR and regulated SAMHD1 mRNA levels after transcription. MiR-181 over-expression significantly reduced the level of SAMHD1 expression in THP-1 cells; miR-181 inhibition up-regulated SAMHD1 expression in THP-1 and Jurkat cells. Our results suggest that miR-181 regulates the level of post-transcriptional SAMHD1 expression negatively by directly binding to the 3' UTR in SAMHD1.

Overexpression of miR-125a in myelodysplastic syndrome CD34+ cells modulates NF-κB activation and enhances erythroid differentiation arrest

Myelodysplastic syndromes (MDS) are characterized by impaired proliferation and differentiation of hematopoietic stem cells. The participation of toll-like receptor (TLR)-mediated signaling in MDS is well documented. Increased TLR signaling leads to the constitutive activation of NF-κB, which mediates inflammation, cell proliferation and apoptosis. In addition, the TLR pathway induces the expression of miRNAs which participate in the fine-tuning of the inflammatory response. miRNAs also regulate other biological processes, including hematopoiesis. miR-125a and miR-125b are known modulators of hematopoiesis and are abnormally expressed in several hematologic malignancies. However, little is known about their role in MDS. NF-κB-activating ability has been described for both miRNAs. We studied the role of miR-125a/miR-125b in MDS and their relationship with TLR signaling and hematopoietic differentiation. Our results indicate that miR-125a is significantly overexpressed in MDS patients and correlates negatively with patient survival. Expression of miR-99b, which is clustered with miR-125a, is also directly correlated with prognosis of MDS. Both miR-125a and miR-99b activated NF-κB in vitro; however, we observed a negative correlation between miR-99b expression and the levels of TLR2, TLR7 and two downstream genes, suggesting that NF-κB activation by the miRNA cluster occurs in the absence of TLR signaling. We also show that TLR7 is negatively correlated with patient survival in MDS. In addition, our data suggest that miR-125a may act as an NF-κB inhibitor upon TLR stimulation. These results indicate that miR-125a is involved in the fine-tuning of NF-κB activity and that its effects may depend on the status of the TLR pathway. Furthermore, we observed that miR-125a inhibits erythroid differentiation in leukemia and MDS cell lines. Therefore, this miRNA could serve as a prognostic marker and a potential therapeutic target in MDS.

Emergence of polyclonal FLT3 tyrosine kinase domain mutations during sequential therapy with sorafenib and sunitinib in FLT3-ITD-positive acute myeloid leukemia

PURPOSE

To evaluate the clinical activity of sequential therapy with sorafenib and sunitinib in FMS-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD)-positive acute myelogenous leukemia (AML) and monitor the emergence of secondary FLT3 tyrosine kinase domain (TKD) mutations during treatment.

EXPERIMENTAL DESIGN

Six children with relapsed/refractory AML were treated with sorafenib in combination with clofarabine and cytarabine, followed by single-agent sorafenib if not a candidate for transplantation. Sunitinib was initiated after sorafenib relapse. Bone marrow samples were obtained for assessment of FLT3 TKD mutations by deep amplicon sequencing. The phase of secondary mutations with ITD alleles was assessed by cloning and sequencing of FLT3 exons 14 through 20. Identified mutations were modeled in Ba/F3 cells, and the effect of kinase inhibitors on FLT3 signaling and cell viability was assessed.

RESULTS

Four patients achieved complete remission, but 3 receiving maintenance therapy with sorafenib relapsed after 14 to 37 weeks. Sunitinib reduced circulating blasts in two patients and marrow blasts in one. Two patients did not respond to sorafenib combination therapy or sunitinib. FLT3 mutations at residues D835 and F691 were observed in sorafenib resistance samples on both ITD-positive and -negative alleles. Deep sequencing revealed low-level mutations and their evolution during sorafenib treatment. Sunitinib suppressed leukemic clones with D835H and F691L mutations, but not D835Y. Cells expressing sorafenib-resistant FLT3 mutations were sensitive to sunitinib in vitro.

CONCLUSIONS

Sunitinib has activity in patients that are resistant to sorafenib and harbor secondary FLT3 TKD mutations. The use of sensitive methods to monitor FLT3 mutations during therapy may allow individualized treatment with the currently available kinase inhibitors.

microRNAs: innovative targets for cerebral ischemia and stroke

Stroke is one of the leading causes of death and disability worldwide. Because stroke is a multifactorial disease with a short therapeutic window many clinical stroke trials have failed and the only currently approved therapy is thrombolysis. MicroRNAs (miRNA) are endogenously expressed noncoding short single-stranded RNAs that play a role in the regulation of gene expression at the post-transcriptional level, via degradation or translational inhibition of their target mRNAs. The study of miRNAs is rapidly growing and recent studies have revealed a significant role of miRNAs in ischemic disease. miRNAs are especially important candidates for stroke therapeutics because of their ability to simultaneously regulate many target genes and since to date targeting single genes for therapeutic intervention has not yet succeeded in the clinic. Although there are already quite a few review articles about miRNA in ischemic heart disease, much less is currently known about miRNAs in cerebral ischemia. This review summarizes current knowledge about miRNAs and cerebral ischemia, focusing on the role of miRNAs in ischemia, both changes in expression and identification of potential targets, as well as the potential of miRNAs as biomarkers and therapeutic targets in cerebral ischemia.

Lyn facilitates glioblastoma cell survival under conditions of nutrient deprivation by promoting autophagy

Members of the Src family kinases (SFK) can modulate diverse cellular processes, including division, death and survival, but their role in autophagy has been minimally explored. Here, we investigated the roles of Lyn, a SFK, in promoting the survival of human glioblastoma tumor (GBM) cells in vitro and in vivo using lentiviral vector-mediated expression of constitutively-active Lyn (CA-Lyn) or dominant-negative Lyn (DN-Lyn). Expression of either CA-Lyn or DN-Lyn had no effect on the survival of U87 GBM cells grown under nutrient-rich conditions. In contrast, under nutrient-deprived conditions (absence of supplementation with L-glutamine, which is essential for growth of GBM cells, and FBS) CA-Lyn expression enhanced survival and promoted autophagy as well as inhibiting cell death and promoting proliferation. Expression of DN-Lyn promoted cell death. In the nutrient-deprived GBM cells, CA-Lyn expression enhanced AMPK activity and reduced the levels of pS6 kinase whereas DN-Lyn enhanced the levels of pS6 kinase. Similar results were obtained in vitro using another cultured GBM cell line and primary glioma stem cells. On propagation of the transduced GBM cells in the brains of nude mice, the CA-Lyn xenografts formed larger tumors than control cells and autophagosomes were detectable in the tumor cells. The DN-Lyn xenografts formed smaller tumors and contained more apoptotic cells. Our findings suggest that on nutrient deprivation in vitro Lyn acts to enhance the survival of GBM cells by promoting autophagy and proliferation as well as inhibiting cell death, and Lyn promotes the same effects in vivo in xenograft tumors. As the levels of Lyn protein or its activity are elevated in several cancers these findings may be of broad relevance to cancer biology.

Down-regulation of miR-181c in imatinib-resistant chronic myeloid leukemia

The association of microRNA alterations with progression and treatment outcome has been revealed in different types of cancers. To find miRNAs involved in imatinib response we performed miRNA microarray followed by RT-qPCR verification of 9 available diagnostic bone marrow core biopsies from 9 CML patients including 4 imatinib-resistant and 5 imatinib-responder patients. Only one differentially expressed miRNA, miR-181c, was found when the imatinib-resistant group was compared with imatinib-responders. Significant down-regulation of miR-181c in imatinib-resistant versus imatinib-responders was confirmed by qRT-PCR. Some miR-181c target genes such as PBX3, HSP90B1, NMT2 and RAD21 have been associated with drug response.

Application of multiplexed kinase inhibitor beads to study kinome adaptations in drug-resistant leukemia

Protein kinases play key roles in oncogenic signaling and are a major focus in the development of targeted cancer therapies. Imatinib, a BCR-Abl tyrosine kinase inhibitor, is a successful front-line treatment for chronic myelogenous leukemia (CML). However, resistance to imatinib may be acquired by BCR-Abl mutations or hyperactivation of Src family kinases such as Lyn. We have used multiplexed kinase inhibitor beads (MIBs) and quantitative mass spectrometry (MS) to compare kinase expression and activity in an imatinib-resistant (MYL-R) and -sensitive (MYL) cell model of CML. Using MIB/MS, expression and activity changes of over 150 kinases were quantitatively measured from various protein kinase families. Statistical analysis of experimental replicates assigned significance to 35 of these kinases, referred to as the MYL-R kinome profile. MIB/MS and immunoblotting confirmed the over-expression and activation of Lyn in MYL-R cells and identified additional kinases with increased (MEK, ERK, IKKα, PKCβ, NEK9) or decreased (Abl, Kit, JNK, ATM, Yes) abundance or activity. Inhibiting Lyn with dasatinib or by shRNA-mediated knockdown reduced the phosphorylation of MEK and IKKα. Because MYL-R cells showed elevated NF-κB signaling relative to MYL cells, as demonstrated by increased IκBα and IL-6 mRNA expression, we tested the effects of an IKK inhibitor (BAY 65-1942). MIB/MS and immunoblotting revealed that BAY 65-1942 increased MEK/ERK signaling and that this increase was prevented by co-treatment with a MEK inhibitor (AZD6244). Furthermore, the combined inhibition of MEK and IKKα resulted in reduced IL-6 mRNA expression, synergistic loss of cell viability and increased apoptosis. Thus, MIB/MS analysis identified MEK and IKKα as important downstream targets of Lyn, suggesting that co-targeting these kinases may provide a unique strategy to inhibit Lyn-dependent imatinib-resistant CML. These results demonstrate the utility of MIB/MS as a tool to identify dysregulated kinases and to interrogate kinome dynamics as cells respond to targeted kinase inhibition.

MicroRNAs in myeloid malignancies

MicroRNAs (miRNAs) are key to the pathogenesis of human malignancies and increasingly recognized as potential biomarkers and therapeutic targets. Haematological malignancies, being the earliest human malignancies linked to aberrant miRNA expression, have consistently underpinned our understanding of the role that miRNAs play in cancer development. Here, we review the expanding roles attributed to miRNAs in the pathogenesis of different types of myeloid malignancies and highlight key findings.