Elephantopus mollis Kunth extracts induce antiproliferation and apoptosis in human lung cancer and myeloid leukemia cells

ETHNOPHARMACOLOGICAL RELEVANCE

Elephantopus mollis Kunth (EM), which belongs to Asteraceae family, has been used as a folk medicine with diverse therapeutic properties. Previous studies reported that crude extracts of this plant could inhibit several cancer cell lines, including breast carcinoma MCF-7, liver carcinoma HepG2, colorectal carcinoma DLD-1, lung carcinoma NCI-H23, etc. AIM: In this study, the anticancer activity and associated molecular mechanism of EM which is distributed in Vietnam were investigated.

MATERIALS AND METHODS

The cytotoxicity of various EM extracts was evaluated on different cell lines by MTT assay. In addition, the effects of EM extracts on cell growth, cell morphology, nuclear morphology, caspase-3 activation, and mRNA expression levels of apoptosis-related genes were also examined.

RESULTS

Our results demonstrated that ethyl acetate extract (EM-EA) caused proliferative inhibition and apoptotic induction towards A549 lung cancer cells (IC₅₀ = 18.66 μg/ml, SI = 5.8) and HL60 leukemia cells (IC₅₀ = 7.45 μg/ml, SI = 14.5) while petroleum ether extract (EM-PE) showed high toxicity to HL60 cell line (IC₅₀ = 11.14 μg/ml, SI = 6.7). Notably, Raji lymphoma cells were also affected by these extracts (IC₅₀ < 20 μg/ml, SI > 4), which has not been reported yet. Furthermore, mechanisms of EM extracts were elucidated. The significant downregulation of PCNA mRNA level induced by EM-EA/PE extracts contributed to the cell-growth restraint. EM-EA extract might activate apoptosis in A549 cells through both extrinsic and intrinsic signaling pathways by causing a 1.55-fold increase in BID, 3.65-fold increase in BAK and 3.11-fold decrease in BCL-2 expression level. Meanwhile, with EM-EA-extract treatment, HL60 cells might encounter P53-dependent apoptotic deaths.

CONCLUSIONS

The combination of antiproliferation and apoptosis activation contributed to the high efficacy of EM extracts. These findings not only proved the anticancer potential of EM but also provided further insights into the mechanisms of EM extracts.

SWATH-Proteomics of Ibrutinib's Action in Myeloid Leukemia Initiating Mutated G-CSFR Signaling

PURPOSE

To evaluate cellular protein changes in response to treatment with an approved drug, ibrutinib, in cells expressing normal or mutated granulocyte-colony stimulating factor receptor (G-CSFR). G-CSFR mutations are associated with some hematological malignancies. Previous studies show the efficacy of ibrutinib (a Bruton's tyrosine kinase inhibitor) in mutated G-CSFR leukemia models but do not address broader signaling mechanisms.

EXPERIMENTAL DESIGN

A label-free quantitative proteomics workflow to evaluate the cellular effects of ibrutinib treatment is established. This includes three biological replicates of normal and mutated G-CSFR expressed in a mouse progenitor cell (32D cell line) with and without ibrutinib treatment.

RESULTS

The proteomics dataset shows about 1000 unique proteins quantified with nearly 400 significant changes (p value < 0.05), suggesting a highly dynamic network of cellular signaling in response to ibrutinib. Importantly, the dataset is very robust with coefficients of variation for quantitation at 13.0-20.4% resulting in dramatic patterns of protein differences among the groups.

CONCLUSIONS AND CLINICAL RELEVANCE

This robust dataset is available for further mining, hypothesis generation, and testing. A detailed understanding of the restructuring of the proteomics signaling cascades by ibrutinib in leukemia biology will provide new avenues to explore its use for other related malignancies.

Targeting RSPO3-LGR4 Signaling for Leukemia Stem Cell Eradication in Acute Myeloid Leukemia

Signals driving aberrant self-renewal in the heterogeneous leukemia stem cell (LSC) pool determine aggressiveness of acute myeloid leukemia (AML). We report that a positive modulator of canonical WNT signaling pathway, RSPO-LGR4, upregulates key self-renewal genes and is essential for LSC self-renewal in a subset of AML. RSPO2/3 serve as stem cell growth factors to block differentiation and promote proliferation of primary AML patient blasts. RSPO receptor, LGR4, is epigenetically upregulated and works through cooperation with HOXA9, a poor prognostic predictor. Blocking the RSPO3-LGR4 interaction by clinical-grade anti-RSPO3 antibody (OMP-131R10/rosmantuzumab) impairs self-renewal and induces differentiation in AML patient-derived xenografts but does not affect normal hematopoietic stem cells, providing a therapeutic opportunity for HOXA9-dependent leukemia.

Effect of methoxy stilbenes-analogs of resveratrol-on the viability and induction of cell cycle arrest and apoptosis in human myeloid leukemia cells

The present study aimed to evaluate the cytotoxicity and its mechanism of five synthetic methoxy stilbenes, namely 3,4,4ʹ-trimethoxy, 3,4,2ʹ-trimethoxy, 3,4,2ʹ,4ʹ-tetramethoxy, 3,4,2ʹ,6ʹ-tetramethoxy, and 3,4,2ʹ,4ʹ,6ʹ-pentamethoxy-trans-stilbenes (MS), in comparison with resveratrol (RSV). Human promyelocytic (HL-60) and monocytic leukemia (THP-1) cells were treated with the tested compounds for 24 h, and cytotoxicity, cell cycle distribution, and apoptosis were evaluated. Significant differences were found in the susceptibility of these cell lines to all stilbenes, including RSV. The THP-1 cells were more resistant to cytotoxic activity of these compounds than HL-60 cells. Among the tested stilbenes, 3,4,4ʹ-tri-MS and 3,4,2ʹ,4ʹ-tetra-MS exhibited higher cytotoxicity toward both cell lines than RSV and the other methoxy stilbenes. This activity might be related to cell cycle arrest at the G2/M phase and induction of apoptosis. In this regard, 3,4,4ʹ-tri-MS and 3,4,2ʹ,4ʹ-tetra-MS at highest concentrations increased the p53 protein level particularly in HL-60 cells. Moreover, treatment with these derivatives increased the ratio of the proapoptotic Bax protein to the antiapoptotic Bcl-xl protein, suggesting the induction of apoptosis through the intrinsic mitochondrial pathway in both cell lines. Further studies are required to fully elucidate the mechanism of these activities.

Mechanistic insights into chromatin targeting by leukemic NUP98-PHF23 fusion

Chromosomal NUP98-PHF23 translocation is associated with an aggressive form of acute myeloid leukemia (AML) and poor survival rate. Here, we report the molecular mechanisms by which NUP98-PHF23 recognizes the histone mark H3K4me3 and is inhibited by small molecule compounds, including disulfiram that directly targets the PHD finger of PHF23 (PHF23PHD). Our data support a critical role for the PHD fingers of NUP98-PHF23, and related NUP98-KDM5A and NUP98-BPTF fusions in driving leukemogenesis, and demonstrate that blocking this interaction in NUP98-PHF23 expressing AML cells leads to cell death through necrotic and late apoptosis pathways. An overlap of NUP98-KDM5A oncoprotein binding sites and H3K4me3-positive loci at the Hoxa/b gene clusters and Meis1 in ChIP-seq, together with NMR analysis of the H3K4me3-binding sites of the PHD fingers from PHF23, KDM5A and BPTF, suggests a common PHD finger-dependent mechanism that promotes leukemogenesis by this type of NUP98 fusions. Our findings highlight the direct correlation between the abilities of NUP98-PHD finger fusion chimeras to associate with H3K4me3-enriched chromatin and leukemic transformation.

The Bone's Role in Myeloid Neoplasia

The interaction of hematopoietic stem and progenitor cells with their direct neighboring cells in the bone marrow (the so called hematopoietic niche) evolves as a key principle for understanding physiological and malignant hematopoiesis. Significant progress in this matter has recently been achieved making use of emerging high-throughput techniques that allow characterization of the bone marrow microenvironment at single cell resolution. This review aims to discuss these single cell findings in the light of other conventional niche studies that together define the current notion of the niche's implication in i) normal hematopoiesis, ii) myeloid neoplasms and iii) disease-driving pathways that can be exploited to establish novel therapeutic strategies in the future.

β3-Adrenoreceptor Blockade Reduces Hypoxic Myeloid Leukemic Cells Survival and Chemoresistance

β-adrenergic signaling is known to be involved in cancer progression; in particular, beta3-adrenoreceptor (β3-AR) is associated with different tumor conditions. Currently, there are few data concerning β3-AR in myeloid malignancies. Here, we evaluated β3-AR in myeloid leukemia cell lines and the effect of β3-AR antagonist SR59230A. In addition, we investigated the potential role of β3-AR blockade in doxorubicin resistance. Using flow cytometry, we assessed cell death in different in vitro myeloid leukemia cell lines (K562, KCL22, HEL, HL60) treated with SR59230A in hypoxia and normoxia; furthermore, we analyzed β3-AR expression. We used healthy bone marrow cells (BMCs), peripheral blood mononuclear cells (PBMCs) and cord blood as control samples. Finally, we evaluated the effect of SR59230A plus doxorubicin on K562 and K562/DOX cell lines; K562/DOX cells are resistant to doxorubicin and show P-glycoprotein (P-gp) overexpression. We found that SR59230A increased cancer cell lines apoptosis especially in hypoxia, resulting in selective activity for cancer cells; moreover, β3-AR expression was higher in malignancies, particularly under hypoxic condition. Finally, we observed that SR59230A plus doxorubicin increased doxorubicin resistance reversion mainly in hypoxia, probably acting on P-gp. Together, these data point to β3-AR as a new target and β3-AR blockade as a potential approach in myeloid leukemias.

Cytotoxicity, fluorescence tagging and gene-expression study of CuInS/ZnS QDS - meso (hydroxyphenyl) porphyrin conjugate against human monocytic leukemia cells

The toxicity of heavy metals present in binary semiconductor nanoparticles also known as quantum dots (QDs) has hindered their wide applications hence the advent of non-toxic ternary quantum dots. These new group of quantum dots have been shown to possess some therapeutic action against cancer cell lines but not significant enough to be referred to as an ideal therapeutic agent. In this report, we address this problem by conjugating red emitting CuInS/ZnS QDs to a 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin -photosensitizer for improved bioactivities. The glutathione capped CuInS/ZnS QDs were synthesized in an aqueous medium using a kitchen pressure cooker at different Cu: In ratios (1:4 and 1:8) and at varied temperatures (95 °C, 190 °C and 235 °C). Optical properties show that the as-synthesized CuInS/ZnS QDs become red-shifted compared to the core (CuInS) after passivation with emission in the red region while the cytotoxicity study revealed excellent cell viability against normal kidney fibroblasts (BHK21). The highly fluorescent, water-soluble QDs were conjugated to 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (mTHPP) via esterification reactions at room temperature. The resultant water-soluble conjugate was then used for the cytotoxicity, fluorescent imaging and gene expression study against human monocytic leukemia cells (THP-1). Our result showed that the conjugate possessed high cytotoxicity against THP-1 cells with enhanced localized cell uptake compared to the bare QDs. In addition, the gene expression study revealed that the conjugate induced inflammation compared to the QDs as NFKB gene was over-expressed upon cell inflammation while the singlet oxygen (1O2) study showed the conjugate possessed large amount of 1O2, three times than the bare porphyrin. Thus, the as-synthesized conjugate looks promising as a therapeutic agent for cancer therapy.

NKL homeobox gene activities in normal and malignant myeloid cells

Recently, we have documented a hematopoietic NKL-code mapping physiological expression patterns of NKL homeobox genes in early hematopoiesis and in lymphopoiesis, which spotlights genes deregulated in lymphoid malignancies. Here, we enlarge this map to include normal NKL homeobox gene expressions in myelopoiesis by analyzing public expression profiling data and primary samples from developing and mature myeloid cells. We thus uncovered differential activities of six NKL homeobox genes, namely DLX2, HHEX, HLX, HMX1, NKX3-1 and VENTX. We further examined public expression profiling data of 251 acute myeloid leukemia (AML) and 183 myelodysplastic syndrome (MDS) patients, thereby identifying 24 deregulated genes. These results revealed frequent deregulation of NKL homeobox genes in myeloid malignancies. For detailed analysis we focused on NKL homeobox gene NANOG, which acts as a stem cell factor and is correspondingly expressed alone in hematopoietic progenitor cells. We detected aberrant expression of NANOG in a small subset of AML patients and in AML cell line NOMO-1, which served as a model. Karyotyping and genomic profiling discounted rearrangements of the NANOG locus at 12p13. But gene expression analyses of AML patients and AML cell lines after knockdown and overexpression of NANOG revealed regulators and target genes. Accordingly, NKL homeobox genes HHEX, DLX5 and DLX6, stem cell factors STAT3 and TET2, and the NOTCH-pathway were located upstream of NANOG while NKL homeobox genes HLX and VENTX, transcription factors KLF4 and MYB, and anti-apoptosis-factor MIR17HG represented target genes. In conclusion, we have extended the NKL-code to the myeloid lineage and thus identified several NKL homeobox genes deregulated in AML and MDS. These data indicate a common oncogenic role of NKL homeobox genes in both lymphoid and myeloid malignancies. For misexpressed NANOG we identified an aberrant regulatory network, which contributes to the understanding of the oncogenic activity of NKL homeobox genes.

Targeting the arginine metabolic brake enhances immunotherapy for leukaemia

Therapeutic approaches which aim to target Acute Myeloid Leukaemia through enhancement of patients' immune responses have demonstrated limited efficacy to date, despite encouraging preclinical data. Examination of AML patients treated with azacitidine (AZA) and vorinostat (VOR) in a Phase II trial, demonstrated an increase in the expression of Cancer-Testis Antigens (MAGE, RAGE, LAGE, SSX2 and TRAG3) on blasts and that these can be recognised by circulating antigen-specific T cells. Although the T cells have the potential to be activated by these unmasked antigens, the low arginine microenvironment created by AML blast Arginase II activity acts a metabolic brake leading to T cell exhaustion. T cells exhibit impaired proliferation, reduced IFN-γ release and PD-1 up-regulation in response to antigen stimulation under low arginine conditions. Inhibition of arginine metabolism enhanced the proliferation and cytotoxicity of anti-NY-ESO T cells against AZA/VOR treated AML blasts, and can boost anti-CD33 Chimeric Antigen Receptor-T cell cytotoxicity. Therefore, measurement of plasma arginine concentrations in combination with therapeutic targeting of arginase activity in AML blasts could be a key adjunct to immunotherapy.

PRL-3 exerts oncogenic functions in myeloid leukemia cells via aberrant dephosphorylation of stathmin and activation of STAT3 signaling

PRL-3, an oncogenic dual-specificity phosphatase, is overexpressed in 50% of acute myeloid leukemia patients. Stathmin has been identified as a downstream target of PRL-3 in colorectal cancer. However, the correlation between PRL-3 and stathmin in myeloid leukemia is unclear. In this study, we revealed the positive correlation between PRL-3 and stathmin in myeloid leukemia. Knockdown of the PRL-3 gene by shRNA reduced the expression of downstream stathmin, suppressed cell proliferation, induced G2/M arrest and cell apoptosis, and inhibited migration and invasion in myeloid leukemia cells. Moreover, our study was the first to provide evidence that silencing PRL-3 increased the phosphorylation level in Ser16, Ser25, Ser38, and Ser63 of stathmin, and in turn inhibited the STAT3 and STAT5 signaling in myeloid leukemia cells. This evidence points to a promoted role for PRL-3 in the progression of myeloid leukemia, and PRL-3 could be a possible new treatment target.

A Proposed Kinetic Model for the Diagnostic and Prognostic Value of WT1 and p53 in Acute Myeloid Leukemia

BACKGROUND

Wilms tumor (WT1) and p53 proteins were identified in the pathogenesis of several malignancies, including hematological malignancies. As a result of their interaction and diverse context-specific functions, this study aimed to emphasize the diagnostic and prognostic impacts of WT1 and p53 expression in acute myeloid leukemia (AML).

METHODS

Twelve bone marrow (BM) biopsies were obtained from AML patients who were diagnosed in accordance with the French-American-British diagnostic criteria. For comparative purposes, nine normal BM biopsies were included. The expression rate of WT1 and p53 were determined by an immunohistochemistry assay.

RESULTS

A significantly higher (p < 0.005) and strongly correlated ( = 0.855, p = 0.001) expression rates of WT1 and p53 were observed in the BM of AML patients in comparison to control BM. Furthermore, relapsed AML patients had significantly higher expression of WT1, but not p53, when compared to newly diagnosed patients. In regard of patient's responsiveness to chemotherapy, no significant difference was reported between good and poor responders. However, the relative ratio of p53 to WT1 expression was evidently correlated to the responsiveness groups (p < 0.05), where the ratio was observed to be significantly higher among poor responders. Poor responders were characterized by a statistically significant and dominant p53 expression (p53/WT1 > 1.0) while both good responding patients and control subjects had a dominant WT1 expression (p53/WT1 < 1.0).

CONCLUSIONS

The enhanced expression levels of WT1 and p53 proteins in the BM of AML patients is supportive of their intermediate role in the pathogenesis of the disease. WT1 expression rate may encompass a negative prognostic value of the disease. Furthermore, the ratio of p53/WT expression may serve as a hallmark of the patient's responsiveness to chemotherapy, where a dominant WT1 expression may reveal good responsiveness to chemotherapy. Herein, we are proposing a kinetic model where the p53/WT1 ratio might be useful as a laboratory approach to evaluate the prognostic value of AML including the patient's responsiveness to chemotherapeutic regimen.

Immunotherapy-Based Targeting and Elimination of Leukemic Stem Cells in AML and CML

The concept of leukemic stem cells (LSC) has been developed with the idea to explain the clonal hierarchies and architectures in leukemia, and the more or less curative anti-neoplastic effects of various targeted drugs. It is now widely accepted that curative therapies must have the potential to eliminate or completely suppress LSC, as only these cells can restore and propagate the malignancy for unlimited time periods. Since LSC represent a minor cell fraction in the leukemic clone, little is known about their properties and target expression profiles. Over the past few years, several cell-specific immunotherapy concepts have been developed, including new generations of cell-targeting antibodies, antibody-toxin conjugates, bispecific antibodies, and CAR-T cell-based strategies. Whereas such concepts have been translated and may improve outcomes of therapy in certain lymphoid neoplasms and a few other malignancies, only little is known about immunological targets that are clinically relevant and can be employed to establish such therapies in myeloid neoplasms. In the current article, we provide an overview of the immunologically relevant molecular targets expressed on LSC in patients with acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). In addition, we discuss the current status of antibody-based therapies in these malignancies, their mode of action, and successful examples from the field.

Energy metabolism and drug response in myeloid leukaemic stem cells

Despite significant advances in the treatment of myeloid malignancies, many patients become resistant to therapy and ultimately succumb to their disease. Accumulating evidence over the past several years has suggested that the inadequacy of many leukaemia therapies results from their failure to target the leukaemic stem cell (LSC). For this reason, the LSC population currently represents the most critical target in the treatment of myeloid malignancies. However, while LSCs are ideal targets in the treatment of these diseases, they are also the most difficult population to target. This is due to both their heterogeneity within the LSC population, and also their phenotypic similarities with normal haematopoietic stem cells. This review will highlight the current landscape surrounding LSC biology in myeloid malignancies, with a focus on altered energy metabolism, and how that knowledge is being translated into clinical advances for the treatment of chronic and acute myeloid leukaemia and myelodysplastic syndromes.

MicroRNA-16 Regulates Myeloblastosis Oncogene Expression to Affect Differentiation of Acute Leukemia Cells

BACKGROUND

This study was designed to evaluate the effects of micro-RNA-16 (miR-16)-regulated expression of myeloblastosis oncogene (MYB) on the differentiation of acute leukemia cells, the expressions of miR-16 and MYB mRNA, and protein in differently differentiated leukemia cells were detected by real-time PCR and western blot.

METHODS

1,25-Dihydroxyvitamin D3 (1,25 D3) induced monocytic differentiation of HL60 cells, and the resulting changes in miR-16 and MYB expressions were detected. Morphology of the cells induced by 1,25 D3, after being transfection with miR-16 mimics, was observed by Wright-Giemsa staining. The expression of mononuclear cell surface marker CD14 was detected by flow cytometry.

RESULTS

Minimum miR-16 was expressed in early-differentiation KG-1a cells, while late-differentiation U937 and THP-1 cells had higher expressions (p < 0.01). The expressions of MYB changed oppositely. During the monocytic differentiation of HL60 cells, miR-16 expression showed a time-dependent increase, but MYB expression gradually decreased. Overexpression of miR-16 in HL60 cells promoted 1,25 D3-induced morphological changes and CD14 expression (p < 0.05).

CONCLUSIONS

MR-16 facilitated the monocytic differentiation of leukemia HL60 cells by negatively regulating MYB expression.

A Novel MCL1 Inhibitor Combined with Venetoclax Rescues Venetoclax-Resistant Acute Myelogenous Leukemia

Suppression of apoptosis by expression of antiapoptotic BCL2 family members is a hallmark of acute myeloblastic leukemia (AML). Induced myeloid leukemia cell differentiation protein (MCL1), an antiapoptotic BCL2 family member, is commonly upregulated in AML cells and is often a primary mode of resistance to treatment with the BCL2 inhibitor venetoclax. Here, we describe VU661013, a novel, potent, selective MCL1 inhibitor that destabilizes BIM/MCL1 association, leads to apoptosis in AML, and is active in venetoclax-resistant cells and patient-derived xenografts. In addition, VU661013 was safely combined with venetoclax for synergy in murine models of AML. Importantly, BH3 profiling of patient samples and drug-sensitivity testing ex vivo accurately predicted cellular responses to selective inhibitors of MCL1 or BCL2 and showed benefit of the combination. Taken together, these data suggest a strategy of rationally using BCL2 and MCL1 inhibitors in sequence or in combination in AML clinical trials. SIGNIFICANCE: Targeting antiapoptotic proteins in AML is a key therapeutic strategy, and MCL1 is a critical antiapoptotic oncoprotein. Armed with novel MCL1 inhibitors and the potent BCL2 inhibitor venetoclax, it may be possible to selectively induce apoptosis by combining or thoughtfully sequencing these inhibitors based on a rational evaluation of AML.See related commentary by Leber et al., p. 1511.This article is highlighted in the In This Issue feature, p. 1494.

Preclinical pharmacokinetics and pharmacodynamics of DCLL9718A: An antibody-drug conjugate for the treatment of acute myeloid leukemia

Few treatment options are available for acute myeloid leukemia (AML) patients. DCLL9718A is an antibody-drug conjugate that targets C-type lectin-like molecule-1 (CLL-1). This receptor is prevalent on monocytes, neutrophils, and AML blast cells, and unlike CD33, is not expressed on hematopoietic stem cells, thus providing possible hematopoietic recovery. DCLL9718A comprises an anti-CLL-1 IgG1 antibody (MCLL0517A) linked to a pyrrolobenzodiazepine (PBD) dimer payload, via a cleavable disulfide-labile linker. Here, we characterize the in vitro and in vivo stability, the pharmacokinetics (PK) and pharmacodynamics (PD) of DCLL9718A and MCLL0517A in rodents and cynomolgus monkeys. Three key PK analytes were measured in these studies: total antibody, antibody-conjugated PBD dimer and unconjugated PBD dimer. In vitro, DCLL9718A, was stable with most (> 80%) of the PBD dimer payload remaining conjugated to the antibody over 96 hours. This was recapitulated in vivo with antibody-conjugated PBD dimer clearance estimates similar to DCLL9718A total antibody clearance. Both DCLL9718A and MCLL0517A showed linear PK in the non-binding rodent species, and non-linear PK in cynomolgus monkeys, a binding species. The PK data indicated minimal impact of conjugation on the disposition of DCLL9718A total antibody. Finally, in cynomolgus monkey, MCLL0517A showed target engagement at all doses tested (0.5 and 20 mg/kg) as measured by receptor occupancy, and DCLL9718A (at doses of 0.05, 0.1 and 0.2 mg/kg) showed strong PD activity as evidenced by notable reduction in monocytes and neutrophils.

Insulin Substrate Receptor (IRS) proteins in normal and malignant hematopoiesis

The insulin receptor substrate (IRS) proteins are a family of cytoplasmic proteins that integrate and coordinate the transmission of signals from the extracellular to the intracellular environment via transmembrane receptors, thus regulating cell growth, metabolism, survival and proliferation. The PI3K/AKT/mTOR and MAPK signaling pathways are the best-characterized downstream signaling pathways activated by IRS signaling (canonical pathways). However, novel signaling axes involving IRS proteins (noncanonical pathways) have recently been identified in solid tumor and hematologic neoplasm models. Insulin receptor substrate-1 (IRS1) and insulin receptor substrate-2 (IRS2) are the best-characterized IRS proteins in hematologic-related processes. IRS2 binds to important cellular receptors involved in normal hematopoiesis (EPOR, MPL and IGF1R). Moreover, the identification of IRS1/ABL1 and IRS2/JAK2V617F interactions and their functional consequences has opened a new frontier for investigating the roles of the IRS protein family in malignant hematopoiesis. Insulin receptor substrate-4 (IRS4) is absent in normal hematopoietic tissues but may be expressed under abnormal conditions. Moreover, insulin receptor substrate-5 (DOK4) and insulin receptor substrate-6 (DOK5) are linked to lymphocyte regulation. An improved understanding of the signaling pathways mediated by IRS proteins in hematopoiesis-related processes, along with the increased development of agonists and antagonists of these signaling axes, may generate new therapeutic approaches for hematological diseases. The scope of this review is to recapitulate and review the evidence for the functions of IRS proteins in normal and malignant hematopoiesis.

Epigenetic Modifiers in Myeloid Malignancies: The Role of Histone Deacetylase Inhibitors

Myeloid hematological malignancies are clonal bone marrow neoplasms, comprising of acute myeloid leukemia (AML), the myelodysplastic syndromes (MDS), chronic myelomonocytic leukemia (CMML), the myeloproliferative neoplasms (MPN) and systemic mastocytosis (SM). The field of epigenetic regulation of normal and malignant hematopoiesis is rapidly growing. In recent years, heterozygous somatic mutations in genes encoding epigenetic regulators have been found in all subtypes of myeloid malignancies, supporting the rationale for treatment with epigenetic modifiers. Histone deacetylase inhibitors (HDACi) are epigenetic modifiers that, in vitro, have been shown to induce growth arrest, apoptotic or autophagic cell death, and terminal differentiation of myeloid tumor cells. These effects were observed both at the bulk tumor level and in the most immature CD34⁺38⁻ cell compartments containing the leukemic stem cells. Thus, there is a strong rationale supporting HDACi therapy in myeloid malignancies. However, despite initial promising results in phase I trials, HDACi in monotherapy as well as in combination with other drugs, have failed to improve responses or survival. This review provides an overview of the rationale for HDACi in myeloid malignancies, clinical results and speculations on why clinical trials have thus far not met the expectations, and how this may be improved in the future.

EVI1 carboxy-terminal phosphorylation is ATM-mediated and sustains transcriptional modulation and self-renewal via enhanced CtBP1 association

The transcriptional regulator EVI1 has an essential role in early hematopoiesis and development. However, aberrantly high expression of EVI1 has potent oncogenic properties and confers poor prognosis and chemo-resistance in leukemia and solid tumors. To investigate to what extent EVI1 function might be regulated by post-translational modifications we carried out mass spectrometry- and antibody-based analyses and uncovered an ATM-mediated double phosphorylation of EVI1 at the carboxy-terminal S858/S860 SQS motif. In the presence of genotoxic stress EVI1-WT (SQS), but not site mutated EVI1-AQA was able to maintain transcriptional patterns and transformation potency, while under standard conditions carboxy-terminal mutation had no effect. Maintenance of hematopoietic progenitor cell clonogenic potential was profoundly impaired with EVI1-AQA compared with EVI1-WT, in particular in the presence of genotoxic stress. Exploring mechanistic events underlying these observations, we showed that after genotoxic stress EVI1-WT, but not EVI1-AQA increased its level of association with its functionally essential interaction partner CtBP1, implying a role for ATM in regulating EVI1 protein interactions via phosphorylation. This aspect of EVI1 regulation is therapeutically relevant, as chemotherapy-induced genotoxicity might detrimentally sustain EVI1 function via stress response mediated phosphorylation, and ATM-inhibition might be of specific targeted benefit in EVI1-overexpressing malignancies.

CARM1 Is Essential for Myeloid Leukemogenesis but Dispensable for Normal Hematopoiesis

Chromatin-modifying enzymes, and specifically the protein arginine methyltransferases (PRMTs), have emerged as important targets in cancer. Here, we investigated the role of CARM1 in normal and malignant hematopoiesis. Using conditional knockout mice, we show that loss of CARM1 has little effect on normal hematopoiesis. Strikingly, knockout of Carm1 abrogates both the initiation and maintenance of acute myeloid leukemia (AML) driven by oncogenic transcription factors. We show that CARM1 knockdown impairs cell-cycle progression, promotes myeloid differentiation, and ultimately induces apoptosis. Finally, we utilize a selective, small-molecule inhibitor of CARM1 to validate the efficacy of CARM1 inhibition in leukemia cells in vitro and in vivo. Collectively, this work suggests that targeting CARM1 may be an effective therapeutic strategy for AML.

Reversal of Methotrexate-Induced Folate Pool Depletion by Thymidine in a Human Leukemia Cell Line in Vitro

In an In vitro study using a human monocytic leukemia cell line, U-937, the effects of interferon-γ (IFN-γ) in combination with the antifolate methotrexate and the role of thymidine introduced as a biochemical modulator were investigated. Methotrexate alone or in combination with INF-γ was found to enhance the induction of morphologic and functional monocytic differentiation in the U-937 cell line. Various cellular effects with the addition of thymidine to the medium with methotrexate and IFN-γ were studied. Enhanced inhibition of cell growth and perturbation of the cell cycle were noted when methotrexate and IFN-γ were used in combination, but not when methotrexate was used alone. The reduction of cellular folate by methotrexate was also enhanced in combination with IFN-γ. Cell cycle delay, resulting in cell growth inhibition of folate depletion, caused the induction of differentiation in U-937 cells, which was found to be greater with methotrexate + IFN-γ than with methotrexate alone. Cellular differentiation, as assessed by nitroblue tetrazolium reduction assay, indirect immunofluorescence and morphology, showed better effects towards the differentiation of U-937 cells when the agents were used in combination. However, addition of thymidine to the medium was found to cancel all the aforementioned effects. The addition of thymidine to the medium also caused reversal of the inhibitory effect of methotrexate and IFN-γ on cell growth and repletion of the endogenous folate level. Repletion of the folate level by exogenous thymidine is a new possibility for the role of the thymidine in cellular growth.

Capsicodendrin from Cinnamosma fragrans Exhibits Antiproliferative and Cytotoxic Activity in Human Leukemia Cells: Modulation by Glutathione

Capsicodendrin (CPCD, 1), an epimeric mixture of a dimeric drimane-type sesquiterpene, is one of the major compounds present in the three endemic species of Madagascan traditional chemopreventive plants: Cinnamosma species ( C. fragrans, C. macrocarpa, and C. madagascariensis). Despite the popular use of Cinnamosma in Madagascan traditional medicine and the reported antiproliferative properties of CPCD, elucidation of its mechanism(s) of action is still to be accomplished. In the present study, CPCD at low micromolar concentrations was cytotoxic and induced apoptosis in human myeloid leukemia cells in a time- and concentration-dependent manner. The activity of CPCD in HL-60 and K562 cells was modulated by glutathione (GSH), since depletion of this intracellular thiol-based antioxidant with buthionine sulfoximine resulted in significantly ( p < 0.05) greater potency in antiproliferation assays. GSH depletion also significantly potentiated the cytotoxic activity in CPCD-treated human HL-60 cells. Single-cell gel electrophoresis (Comet) assays revealed that GSH depletion in HL-60 cells enhanced the formation of DNA strand breaks in the presence of CPCD. Although CPCD does not contain an obvious Michael acceptor in its structure, ¹H NMR analyses indicated that cinnamodial (2), a monomer of CPCD, was formed within a few hours when dissolved in DMSO- d₆ and interacts with GSH to form a covalent bond via Michael addition at the C-7 carbon. Together the results strongly suggest that 2 is responsible for the DNA-damaging, pro-apoptotic, and cytotoxic effects of CPCD and that depletion of GSH enhances overall activity by diminishing covalent interaction between GSH and this 2-alkenal decomposition product of CPCD.

A novel miR-375-HOXB3-CDCA3/DNMT3B regulatory circuitry contributes to leukemogenesis in acute myeloid leukemia

BACKGROUND

Acute myeloid leukemia (AML) is a heterogeneous group of hematopoietic malignancies due to sophisticated genetic mutations and epigenetic dysregulation. MicroRNAs (miRNAs), a class of small non-coding RNAs, are important regulators of gene expression in all biological processes, including leukemogenesis. Recently, miR-375 has been reported to be a suppressive miRNA in multiple types of cancers, but its underlying anti-leukemia activity in AML is largely unknown.

METHODS

Quantitative reverse transcriptase PCR (qRT-PCR) was used to measure the expression of miR-375 and HOXB3 in leukemic cells and normal controls. Targets of miR-375 were confirmed by western blot and luciferase assay. Phenotypic effects of miR-375 overexpression and HOXB3 knockdown were assessed using viability (trypan blue exclusion assay), colony formation/replating, as well as tumor xenograft assays in vivo.

RESULTS

The expression of miR-375 was substantially decreased in leukemic cell lines and primary AML blasts compared with normal controls, because DNA hypermethylation of precursor-miR-375 (pre-miR-375) promoter was discovered in leukemic cells but not in normal controls. Lower expression of miR-375 predicted poor outcome in AML patients. Furthermore, forced expression of miR-375 not only decreased proliferation and colony formation in leukemic cells but also reduced xenograft tumor size and prolonged the survival time in a leukemia xenograft mouse model. Mechanistically, overexpression of miR-375 reduced HOXB3 expression and repressed the activity of a luciferase reporter through binding 3'-untranslated regions (3'-UTR) of HOXB3 mRNA. Overexpression of HOXB3 partially blocked miR-375-induced arrest of proliferation and reduction of colony number, suggesting that HOXB3 plays an important role in miR-375-induced anti-leukemia activity. Knockdown of HOXB3 by short hairpin RNAs reduced the expression of cell division cycle associated 3 (CDCA3), which decreased cell proliferation. Furthermore, HOXB3 induced DNA methyltransferase 3B (DNMT3B) expression to bind in the pre-miR-375 promoter and enhanced DNA hypermethylation of pre-miR-375, leading to the lower expression of miR-375.

CONCLUSIONS

Collectively, we have identified a miR-375-HOXB3-CDCA3/DNMT3B regulatory circuitry which contributes to leukemogenesis and suggests a therapeutic strategy of restoring miR-375 expression in AML.

A non-cell-autonomous role for Pml in the maintenance of leukemia from the niche

Disease recurrence after therapy, due to the persistence of resistant leukemic cells, represents a fundamental problem in the treatment of leukemia. Elucidating the mechanisms responsible for the maintenance of leukemic cells, before and after treatment, is therefore critical to identify curative modalities. It has become increasingly clear that cell-autonomous mechanisms are not solely responsible for leukemia maintenance. Here, we report a role for Pml in mesenchymal stem cells (MSCs) in supporting leukemic cells of both CML and AML. Mechanistically, we show that Pml regulates pro-inflammatory cytokines within MSCs, and that this function is critical in sustaining CML-KLS and AML ckit+ leukemic cells non-cell autonomously.