Vascular endothelial growth factor signaling in acute myeloid leukemia

Transforming the Niche: The Emerging Role of Extracellular Vesicles in Acute Myeloid Leukaemia Progression

Acute myeloid leukaemia (AML) management remains a significant challenge in oncology due to its low survival rates and high post-treatment relapse rates, mainly attributed to treatment-resistant leukaemic stem cells (LSCs) residing in bone marrow (BM) niches. This review offers an in-depth analysis of AML progression, highlighting the pivotal role of extracellular vesicles (EVs) in the dynamic remodelling of BM niche intercellular communication. We explore recent advancements elucidating the mechanisms through which EVs facilitate complex crosstalk, effectively promoting AML hallmarks and drug resistance. Adopting a temporal view, we chart the evolving landscape of EV-mediated interactions within the AML niche, underscoring the transformative potential of these insights for therapeutic intervention. Furthermore, the review discusses the emerging understanding of endothelial cell subsets' impact across BM niches in shaping AML disease progression, adding another layer of complexity to the disease progression and treatment resistance. We highlight the potential of cutting-edge methodologies, such as organ-on-chip (OoC) and single-EV analysis technologies, to provide unprecedented insights into AML-niche interactions in a human setting. Leveraging accumulated insights into AML EV signalling to reconfigure BM niches and pioneer novel approaches to decipher the EV signalling networks that fuel AML within the human context could revolutionise the development of niche-targeted therapy for leukaemia eradication.

Pharmacological Inhibition of PIP4K2 Potentiates Venetoclax-Induced Apoptosis in Acute Myeloid Leukemia

Phosphatidylinositol-5-phosphate 4-kinase type 2 (PIP4K2) protein family members (PIP4K2A, PIP4K2B, and PIP4K2C) participate in the generation of PIP4,5P2, which acts as a secondary messenger in signal transduction, a substrate for metabolic processes, and has structural functions. In patients with acute myeloid leukemia (AML), high PIP4K2A and PIP4K2C levels are independent markers of a worse prognosis. Recently, our research group reported that THZ-P1-2 (PIP4K2 pan-inhibitor) exhibits anti-leukemic activity by disrupting mitochondrial homeostasis and autophagy in AML models. In the present study, we characterized the expression of PIP4K2 in the myeloid compartment of hematopoietic cells, as well as in AML cell lines and clinical samples with different genetic abnormalities. In ex vivo assays, PIP4K2 expression levels were related to sensitivity and resistance to several antileukemia drugs and highlighted the association between high PIP4K2A levels and resistance to venetoclax. The combination of THZ-P1-2 and venetoclax showed potentiating effects in reducing viability and inducing apoptosis in AML cells. A combined treatment differentially modulated multiple genes, including TAp73, BCL2, MCL1, and BCL2A1. In summary, our study identified the correlation between the expression of PIP4K2 and the response to antineoplastic agents in ex vivo assays in AML and exposed vulnerabilities that may be exploited in combined therapies, which could result in better therapeutic responses.

The role of bone marrow microenvironment (BMM) cells in acute myeloid leukemia (AML) progression: immune checkpoints, metabolic checkpoints, and signaling pathways

Acute myeloid leukemia (AML) comprises a multifarious and heterogeneous array of illnesses characterized by the anomalous proliferation of myeloid cells in the bone marrow microenvironment (BMM). The BMM plays a pivotal role in promoting AML progression, angiogenesis, and metastasis. The immune checkpoints (ICs) and metabolic processes are the key players in this process. In this review, we delineate the metabolic and immune checkpoint characteristics of the AML BMM, with a focus on the roles of BMM cells e.g. tumor-associated macrophages, natural killer cells, dendritic cells, metabolic profiles and related signaling pathways. We also discuss the signaling pathways stimulated in AML cells by BMM factors that lead to AML progression. We then delve into the roles of immune checkpoints in AML angiogenesis, metastasis, and cell proliferation, including co-stimulatory and inhibitory ICs. Lastly, we discuss the potential therapeutic approaches and future directions for AML treatment, emphasizing the potential of targeting metabolic and immune checkpoints in AML BMM as prognostic and therapeutic targets. In conclusion, the modulation of these processes through the use of directed drugs opens up new promising avenues in combating AML. Thereby, a comprehensive elucidation of the significance of these AML BMM cells' metabolic and immune checkpoints and signaling pathways on leukemic cells can be undertaken in the future investigations. Additionally, these checkpoints and cells should be considered plausible multi-targeted therapies for AML in combination with other conventional treatments in AML. Video Abstract.

An optimized herbal combination for the treatment of liver fibrosis: Hub genes, bioactive ingredients, and molecular mechanisms

ETHNOPHARMACOLOGICAL RELEVANCE

Liver fibrosis is a chronic liver disease that can lead to cirrhosis, liver failure, and hepatocellular carcinoma, and it is associated with long-term adverse outcomes and mortality. As a primary resource for complementary and alternative medicine, traditional Chinese medicine (TCM) has accumulated a large number of effective formulas for the treatment of liver fibrosis in clinical practice. However, studies on how to systematically optimize TCM formulas are still lacking.

AIM OF THE REVIEW

To provide a methodological reference for the systematic optimization of TCM formulae against liver fibrosis and explored the underlying molecular mechanisms; To provide an efficient method for searching for lead compounds from natural sources and developing from herbal medicines; To enable clinicians and patients to make more reasonable choices and promote the effective treatment toward those patients with liver fibrosis.

MATERIALS AND METHODS

TCM formulas related to treating liver fibrosis were collected from the Web of Science, PubMed, the China National Knowledge Infrastructure (CNKI), Wan Fang, and the Chinese Scientific Journals Database (VIP). Furthermore, the TCM compatibility patterns were mined using association analysis. The core TCM combinations were found by designing an optimized formulas algorithm. Finally, the hub target proteins, potential molecular mechanisms, and active compounds were explored through integrative pharmacology and docking-based inverse virtual screening (IVS) approaches.

RESULTS

We found that the herbs for reinforcing deficiency, activating blood, removing blood stasis, and clearing heat were the basis of TCM formulae patterns. Furthermore, the combination of Salviae Miltiorrhizae (Salvia miltiorrhiza Bunge; Chinese salvia/Danshen), Astragali Radix (Astragalus membranaceus (Fisch.) Bunge; Astragalus/Huangqi), and Radix Bupleuri (Bupleurum chinense DC.; Bupleurum/Chaihu) was identified as core groups. A total of six targets (TNF, STAT3, EGFR, IL2, ICAM1, PTGS2) play a pivotal role in TCM-mediated liver fibrosis inhibition. (-)-Cryptotanshinone, Tanshinaldehyde, Ononin, Thymol, Daidzein, and Formononetin were identified as active compounds in TCM. And mechanistically, TCM could affect the development of liver fibrosis by regulating inflammation, immunity, angiogenesis, antioxidants, and involvement in TNF, MicroRNAs, Jak-STAT, NF-kappa B, and C-type lectin receptors (CLRs) signaling pathways. Molecular docking results showed that key components had good potential to bind to the target genes.

CONCLUSION

In summary, this study provides a methodological reference for the systematic optimization of TCM formulae and exploration of underlying molecular mechanisms.

Presentation of Chloromas in B-Mode Ultrasound and Contrast-Enhanced Ultrasound

Chloromas, also referred to as myeloid sarcomas, describe rare extramedullary tumor aggregates of malignant myeloid progenitor cells. The aim of this study was investigate the diagnostic features and characteristics of chloromas using contrast-enhanced ultrasound (CEUS). Between July 2007 and April 2021, 15 patients with 20 myeloid neoplasms and suspected chloroma manifestations were examined using B-mode US (B-US) and CEUS. Clinical data and B-US (echogenicity, border, size) and CEUS (hyper-, iso-, hypo- or complex enhancement) characteristics were retrospectively analyzed. Absolute and relative frequencies were determined. In B-US, the chloromas were most frequently hypo-echoic (n = 15, 75%). In addition, a hyperechoic (n = 2, 10%) or echocomplex (n = 3, 15%) presentation was observed. On CEUS, 7 chloromas (35%) had an arterial hyperenhancement, 8 (40%) an iso-enhancement and 3 (15%) a complex enhancement. Two chloromas (10%) did not exhibit any enhancement. We describe for the first time CEUS and B-US patterns of chloromas. They are typically hypo-echoic on B-US and have a strong iso- or hyperenhancement on CEUS, which may help in the differential diagnosis of some unclear masses (e.g., hematoma, abscess) in patients with myeloid neoplasias. Nevertheless, histology is necessary for a reliable diagnosis.

Synergistic Lethality Effects of Apatinib and Homoharringtonine in Acute Myeloid Leukemia

Purpose

The significance of vascular endothelial growth factor receptor (VEGFR)-2 in numerous solid tumors and acute myeloid leukemia (AML) has been demonstrated, but Apatinib remains largely unexplored. In this study, whether Apatinib combined with homoharringtonine (HHT) kills AML cell lines and its possible mechanisms have been explored.

Methods

AML cell lines were treated with Apatinib and HHT in different concentrations with control, Apatinib alone, HHT alone, and Apatinib combined with HHT. The changes of IC₅₀ were measured by CCK8 assay, and apoptosis rate, cell cycle, and the mitochondrial membrane potential in each group were measured by flow cytometry. Finally, the possible cytotoxicity mechanism was analyzed by Western blotting.

Results

Our results noted that Apatinib combined with HHT remarkably inhibited cell proliferation, reduced the capacity of colony-forming, and induced apoptosis and cell cycle arrest in AML cells. Mechanistically, Apatinib and HHT play a role as a suppressor in the expression of VEGFR-2 and the downstream signaling cascades, such as the PI3K, MAPK, and STAT3 pathways.

Conclusion

Our preclinical data demonstrate that Apatinib combined with HHT exerts a better antileukemia effect than Apatinib alone by inhibiting the VEGFR-2 signaling pathway, suggesting the potential role of Apatinib and HHT in the treatment of AML. This study provides clinicians with innovative combination therapies and new therapeutic targets for the treatment of AML.

Studying the potential of upregulated PTGS2 and VEGF-C besides hyper-methylation of PTGS2 promoter as biomarkers of Acute myeloid leukemia

Hereby, we aimed to investigate the expression of prostaglandin-endoperoxide synthase 2 (PTGS2) and Vascular Endothelial Factor-C (VEGF-C) besides the methylation of PTGS2 in AML patients. VEGF-C and PTGS2 expression analysis were evaluated in newly diagnosed AML patients and healthy controls by quantitative Reverse Transcriptase PCR method. Also, PTGS2 methylation status was evaluated by Methylation-Sensitive High-Resolution Melting Curve Analysis (MS-HRM). While 34% of patients were female, the mean age of the patients was 43.41 ± 17.60 years suffering mostly from M4 (48.21%) type of AML. Although methylation level between patients and controls was not significantly different, none of the normal controls showed methylation in the PTGS2 promoter. PTGS2 and VEGF-C levels were elevated in AML cases and correlated with WBC, Platelet, and Hemoglobin levels. The survival of patients with overexpressed VEGF-C and PTGS2 was poorer than others. It can be concluded that PTGS2 and especially VEGF-C expression but not PTGS2 methylation can be considered as diagnostic biomarkers for AML.

The effect of novel synthetic semicarbazone- and thiosemicarbazone-linked 1,2,3-triazoles on the apoptotic markers, VEGFR-2, and cell cycle of myeloid leukemia

Vascular Endothelial Growth Factor II (VEGFR-2) has been proved as a rational target in cancer therapy. Although currently prescribed VEGFR-2 inhibitors are showing potent antitumor activity, they are often causing serious unwanted effects, restricting their extensive use as chemotherapeutics. Herein, after analyzing the structures of the effective VEGFR-2 inhibitor molecules, we report the synthesis of a new set of semicarbazone- and thiosemicarbazone-linked 1,2,3-triazoles with expected potency of inhibiting the VEGFR-2 signaling. The design of new compounds considered maintaining the essential pharmacophoric features of sorafenib for effective binding with the receptor target. All compounds have been evaluated for their growth inhibition effect against a panel of sixty cancer cells at the National Cancer Institute. Leukemia cancer cells, especially HL-60 and SR, were shown to be the most sensitive to the cytotoxic effect of new compounds. Thiosemicarbazones 21, 26, and 30 exhibited the best activity against almost all tested cancer cells. Therefore, a set of subsequent in vitro biological evaluations has been performed to understand the mechanistic effect of these compounds further. They inhibited the VEGFR-2 with IC₅₀ values of 0.128, 0.413, and 0.067 µM respectively compared with 0.048 µM of Sorafenib. The probable mechanistic effect of 30 has been further evaluated on a number of apoptotic and antiapoptotic markers including BAX, BCL2, caspase-3, and caspase-9. Results revealed the potential of the thiosemicarbazone-linked triazole 30 to induce both the early and the late apoptosis, elevate BAX/BCL2 ratio, induce caspase-3 & caspase-9, and arrest the HL-60 cell cycle at the G2/M and G0-G1 phases. Molecular docking of new semicarbazones and thiosemicarbazones into the proposed biological target receptor has also been performed. Results of docking studies proved the potential of new semicarbazone- and thiosemicarbazone-linked 1,2,3-triazoles to effectively bind with crucial residues of the VEGFR-2 binding pocket.

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

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

Leukemic Stem Cells: From Leukemic Niche Biology to Treatment Opportunities

Acute myeloid leukemia (AML) is one of the most common types of leukemia in adults. While complete remission can be obtained with intensive chemotherapy in young and fit patients, relapse is frequent and prognosis remains poor. Leukemic cells are thought to arise from a pool of leukemic stem cells (LSCs) which sit at the top of the hierarchy. Since their discovery, more than 30 years ago, LSCs have been a topic of intense research and their identification paved the way for cancer stem cell research. LSCs are defined by their ability to self-renew, to engraft into recipient mice and to give rise to leukemia. Compared to healthy hematopoietic stem cells (HSCs), LSCs display specific mutations, epigenetic modifications, and a specific metabolic profile. LSCs are usually considered resistant to chemotherapy and are therefore the drivers of relapse. Similar to their HSC counterpart, LSCs reside in a highly specialized microenvironment referred to as the “niche”. Bidirectional interactions between leukemic cells and the microenvironment favor leukemic progression at the expense of healthy hematopoiesis. Within the niche, LSCs are thought to be protected from genotoxic insults. Improvement in our understanding of LSC gene expression profile and phenotype has led to the development of prognosis signatures and the identification of potential therapeutic targets. In this review, we will discuss LSC biology in the context of their specific microenvironment and how a better understanding of LSC niche biology could pave the way for new therapies that target AML.

A Role for the Bone Marrow Microenvironment in Drug Resistance of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease with a poor prognosis and remarkable resistance to chemotherapeutic agents. Understanding resistance mechanisms against currently available drugs helps to recognize the therapeutic obstacles. Various mechanisms of resistance to chemotherapy or targeted inhibitors have been described for AML cells, including a role for the bone marrow niche in both the initiation and persistence of the disease, and in drug resistance of the leukemic stem cell (LSC) population. The BM niche supports LSC survival through direct and indirect interactions among the stromal cells, hematopoietic stem/progenitor cells, and leukemic cells. Additionally, the BM niche mediates changes in metabolic and signal pathway activation due to the acquisition of new mutations or selection and expansion of a minor clone. This review briefly discusses the role of the BM microenvironment and metabolic pathways in resistance to therapy, as discovered through AML clinical studies or cell line and animal models.

Fetal hematopoietic stem cell homing is controlled by VEGF regulating the integrity and oxidative status of the stromal-vascular bone marrow niches

Hematopoietic stem and progenitor cell (HSPC) engraftment after transplantation during anticancer treatment depends on support from the recipient bone marrow (BM) microenvironment. Here, by studying physiological homing of fetal HSPCs, we show the critical requirement of balanced local crosstalk within the skeletal niche for successful HSPC settlement in BM. Transgene-induced overproduction of vascular endothelial growth factor (VEGF) by osteoprogenitor cells elicits stromal and endothelial hyperactivation, profoundly impacting the stromal-vessel interface and vascular architecture. Concomitantly, HSPC homing and survival are drastically impaired. Transcriptome profiling, flow cytometry, and high-resolution imaging indicate alterations in perivascular and endothelial cell characteristics, vascular function and cellular metabolism, associated with increased oxidative stress within the VEGF-enriched BM environment. Thus, developmental HSPC homing to bone is controlled by local stromal-vascular integrity and the oxidative-metabolic status of the recipient milieu. Interestingly, irradiation of adult mice also induces stromal VEGF expression and similar osteo-angiogenic niche changes, underscoring that our findings may contribute targets for improving stem cell therapies.

•

Establishment of BM hematopoiesis is coupled to development of the skeletal niches

•

Primary HSPC seeding of bone depends on balanced molecular crosstalk in the niche

•

Stromal VEGF triggers EC activation and controls stromal-vascular niche integrity

•

Excessive skeletal VEGF deranges cell metabolism and induces oxidative stress in BM

Niche-directed therapy in acute myeloid leukemia: optimization of stem cell competition for niche occupancy

Acute myeloid leukemia (AML) is an aggressive malignancy of stem cell origin that contributes to significant morbidity and mortality. The long-term prognosis remains dismal given the high likelihood for primary refractory or relapsed disease. An essential component of relapse is resurgence from the bone marrow. To date, the murine hematopoietic stem cell (HSC) niche has been clearly defined, but the human HSC niche is less well understood. The design of niche-based targeted therapies for AML must account for which cellular subsets compete for stem cell occupancy within respective bone marrow microenvironments. In this review, we highlight the principles of stem cell niche biology and discuss translational insights into the AML microenvironment as of 2021. Optimization of competition for niche occupancy is important for the elimination of measurable residual disease (MRD). Some of these novel therapeutics are in the pharmacologic pipeline for AML and may be especially useful in the setting of MRD.

Therapeutic Targeting of the Leukaemia Microenvironment

In recent decades, the conduct of uniform prospective clinical trials has led to improved remission rates and survival for patients with acute myeloid leukaemia and acute lymphoblastic leukaemia. However, high-risk patients continue to have inferior outcomes, where chemoresistance and relapse are common due to the survival mechanisms utilised by leukaemic cells. One such mechanism is through hijacking of the bone marrow microenvironment, where healthy haematopoietic machinery is transformed or remodelled into a hiding ground or "sanctuary" where leukaemic cells can escape chemotherapy-induced cytotoxicity. The bone marrow microenvironment, which consists of endosteal and vascular niches, can support leukaemogenesis through intercellular "crosstalk" with niche cells, including mesenchymal stem cells, endothelial cells, osteoblasts, and osteoclasts. Here, we summarise the regulatory mechanisms associated with leukaemia-bone marrow niche interaction and provide a comprehensive review of the key therapeutics that target CXCL12/CXCR4, Notch, Wnt/b-catenin, and hypoxia-related signalling pathways within the leukaemic niches and agents involved in remodelling of niche bone and vasculature. From a therapeutic perspective, targeting these cellular interactions is an exciting novel strategy for enhancing treatment efficacy, and further clinical application has significant potential to improve the outcome of patients with leukaemia.

Extinguishing the Embers: Targeting AML Metabolism

Acute myeloid leukemia (AML) is a cancer derived from the myeloid lineage of blood cells, characterized by overproduction of leukemic blasts. Although therapeutic improvements have made a significant impact on the outcomes of patients with AML, survival rates remain low due to a high incidence of relapse. Similar to how wildfires can reignite from hidden embers not extinguished from an initial round of firefighting, leukemic stem cells (LSCs) are the embers remaining after completion of traditional chemotherapeutic treatments. LSCs exhibit a unique metabolic profile and contain metabolically distinct subpopulations. In this review, we detail the metabolic features of LSCs and how thetse characteristics promote resistance to traditional chemotherapy. We also discuss new therapeutic approaches that target metabolic vulnerabilities of LSC to selectively eradicate them.

The Dynamic Interface Between the Bone Marrow Vascular Niche and Hematopoietic Stem Cells in Myeloid Malignancy

Hematopoietic stem cells interact with bone marrow niches, including highly specialized blood vessels. Recent studies have revealed the phenotypic and functional heterogeneity of bone marrow endothelial cells. This has facilitated the analysis of the vascular microenvironment in steady state and malignant hematopoiesis. In this review, we provide an overview of the bone marrow microenvironment, focusing on refined analyses of the marrow vascular compartment performed in mouse studies. We also discuss the emerging role of the vascular niche in “inflamm-aging” and clonal hematopoiesis, and how the endothelial microenvironment influences, supports and interacts with hematopoietic cells in acute myeloid leukemia and myelodysplastic syndromes, as exemplar states of malignant myelopoiesis. Finally, we provide an overview of strategies for modulating these bidirectional interactions to therapeutic effect in myeloid malignancies.

Quercetin Induces Apoptosis via Downregulation of Vascular Endothelial Growth Factor/Akt Signaling Pathway in Acute Myeloid Leukemia Cells

Acute myeloid leukemia (AML) is an aggressive haematological malignancy characterized by highly proliferative accumulation of immature and dysfunctional myeloid cells. Quercetin (Qu), one kind of flavonoid, exhibits anti-cancer property in multiple types of solid tumor, but its effect on acute myeloid leukemia is less studied, and the underlying mechanisms still largely unknown. This study aimed to explore the specific target and potential mechanism of quercetin-induced cell death in AML. First, we found that quercetin induces cell death in the form of apoptosis, which was caspase dependent. Second, we found that quercetin-induced apoptosis depends on the decrease of mitochondria membrane potential (MMP) and Bcl-2 proteins. With quantitative chemical proteomics, we observed the downregulation of VEGFR2 and PI3K/Akt signaling in quercetin-treated cells. Consistently, cell studies also identified that VEGFR2 and PI3K/Akt signaling pathways are involved in the action of quercetin on mitochondria and Bcl-2 proteins. The decrease of MMP and cell death could be rescued when PI3K/Akt signaling is activated, suggesting that VEGFR2 and PI3K/Akt exert as upstream regulators for quercetin effect on apoptosis induction in AML cells. In conclusion, our findings from this study provide convincing evidence that quercetin induces cell death via downregulation of VEGF/Akt signaling pathways and mitochondria-mediated apoptosis in AML cells.

LINC00649 underexpression is an adverse prognostic marker in acute myeloid leukemia

BACKGROUND

Long noncoding RNAs (lncRNA) play a role in leukemogenesis, maintenance, development, and therapeutic resistance of AML. While few studies have focused on the prognostic significance of LINC00649 in AML, which we aim to investigate in this present study.

METHODS

We compared the expression level of LINC00649 between AML patients and healthy controls. The Kaplan-Meier curves of AML patients expressing high versus low level of LINC00649 was performed. The LINC00649 correlated genes/miRNAs/lncRNAs and methylation CpG sites were screened by Pearson correlation analysis with R (version 3.6.0), using TCGA-LAML database. The LINC00649 associated ceRNA network was established using lncBase 2.0 and miRWalk 2.0 online tools, combining results from correlation analysis. Finally, a prediction model was constructed using LASSO-Cox regression.

RESULTS

LINC00649 was underexpressed in bone marrow of AML group than that in healthy control group. The patients of LINC00649-low group have significantly inferior PFS and OS. A total of 154 mRNAs, 31 miRNAs, 28 lncRNAs and 1590 methylated CpG sites were identified to be significantly correlated with LINC00649. Furthermore, the network of ceRNA was established with 6 miRNAs and 122 mRNAs. The Lasso-Cox model fitted OS/PFS to novel prediction models, which integrated clinical factors, ELN risk stratification, mRNA/miRNA expression and methylation profiles. The analysis of time-dependent ROC for our model showed a superior AUC (AUC = 0.916 at 1 year, AUC = 0.916 at 3 years, and AUC = 0.891 at 5 years).

CONCLUSIONS

Low expression of LINC00649 is a potential unfavorable prognostic marker for AML patients, which requires the further validation. The analysis by LASSO-COX regression identified a novel comprehensive model with a superior diagnostic utility, which integrated clinical and genetic variables.

Osteocytes control myeloid cell proliferation and differentiation through Gsα-dependent and -independent mechanisms

Osteocytes, the bone cells embedded in the mineralized matrix, control bone modeling, and remodeling through direct contact with adjacent cells and via paracrine and endocrine factors that affect cells in the bone marrow microenvironment or distant organs. Osteocytes express numerous G protein-coupled receptors (GPCRs) and thus mice lacking the stimulatory subunit of G-protein (Gsα) in osteocytes (Dmp1-Gsα^KO mice) have abnormal myelopoiesis, osteopenia, and reduced adipose tissue. We previously reported that the severe osteopenia and the changes in adipose tissue present in these mice were mediated by increased sclerostin, which suppress osteoblast functions and promote browning of white adipocytes. Inversely, the myeloproliferation was driven by granulocyte colony-stimulating factor (G-CSF) and administration of neutralizing antibodies against G-CSF only partially restored the myeloproliferation, suggesting that additional osteocyte-derived factors might be involved. We hypothesized that osteocytes secrete Gsα-dependent factor(s) which regulate the myeloid cells proliferation. To identify osteocyte-secreted proteins, we used the osteocytic cell line Ocy454 expressing or lacking Gsα expression (Ocy454-Gsα^cont and Ocy454-Gsα^KO ) to delineate the osteocyte "secretome" and its regulation by Gsα. Here we reported that factors secreted by osteocytes increased the number of myeloid colonies and promoted macrophage proliferation. The proliferation of myeloid cells was further promoted by osteocytes lacking Gsα expression. Myeloid cells can differentiate into bone-resorbing osteoclasts, therefore, we hypothesized that osteocyte-secreted factors might also regulate osteoclastogenesis in a Gsα-dependent manner. Conditioned medium (CM) from Ocy454 (both Gsα^cont and Gsα^KO ) significanlty increased the proliferation of bone marrow mononuclear cells (BMNC) and, at the same time, inhibited their differentiation into mature osteoclasts via a Gsα-dependent mechanism. Proteomics analysis of CM from Ocy454 Gsα^cont and Gsα^KO cells identified neuropilin-1 (Nrp-1) and granulin (Grn) as osteocytic-secreted proteins upregulated in Ocy454-Gsα^KO cells compared to Ocy454-Gsα^cont , whereas semaphorin3A was significantly suppressed. Treatment of Ocy454-Gsα^cont cells with recombinant proteins or knockdown of Nrp-1 and Grn in Ocy454-Gsα^KO cells partially rescued the inhibition of osteoclasts, demonstrating that osteocytes control osteoclasts differentiation through Nrp-1 and Grn which are regulated by Gsα signaling.

RNA-Binding Proteins in Acute Leukemias

Acute leukemias are genetic diseases caused by translocations or mutations, which dysregulate hematopoiesis towards malignant transformation. However, the molecular mode of action is highly versatile and ranges from direct transcriptional to post-transcriptional control, which includes RNA-binding proteins (RBPs) as crucial regulators of cell fate. RBPs coordinate RNA dynamics, including subcellular localization, translational efficiency and metabolism, by binding to their target messenger RNAs (mRNAs), thereby controlling the expression of the encoded proteins. In view of the growing interest in these regulators, this review summarizes recent research regarding the most influential RBPs relevant in acute leukemias in particular. The reported RBPs, either dysregulated or as components of fusion proteins, are described with respect to their functional domains, the pathways they affect, and clinical aspects associated with their dysregulation or altered functions.

Increased circulating vascular endothelial growth factor in acute myeloid leukemia patients: a systematic review and meta-analysis

BACKGROUND

Vascular endothelial growth factor (VEGF) is one of the angiogenesis regulators, which plays an important role in tumor angiogenesis and tumor progression. Current studies have found that VEGF plays an important role in hematologic diseases including acute myeloid leukemia (AML). However, the circulating levels of VEGF in AML were still controversial among published studies.

METHODS

Three databases including PubMed, EMBASE, and Cochrane Library databases were searched up to February 2020. All articles included in the meta-analysis met our inclusion and exclusion criteria. Studies will be screened and data extracted by two independent investigators. The Newcastle-Ottawa Scale (NOS) and the Risk of Bias In Non-randomized Studies of Interventions (ROBINS-I) tool were applied to evaluate the quality of the included studies. A random-effects model was applied to pool the standardized mean difference (SMD). Heterogeneity test was performed by the Q statistic and quantified using I². All statistical analysis was conducted in Stata 12.0 software.

RESULTS

Fourteen case-control studies were finally included in this systematic review and meta-analysis. Heterogeneity was high in our included studies (I² = 91.1%, P < 0.001). Sensitivity analysis showed no significant change when any one study was excluded using random-effect methods (P > 0.05). Egger's linear regression test showed that no publication bias existed (P > 0.05). Patients with AML, mainly those newly diagnosed and untreated, have higher VEGF levels (SMD = 0.85, 95% CI 0.28-1.42). Moreover, AML patients in n ≥ 40 group, plasma group, Asia and Africa group, and age ≥ 45 group had higher circulating VEGF levels (all P < 0.05).

CONCLUSIONS

Compared to healthy controls, our meta-analysis shows a significantly higher level of circulating VEGF in AML patients, and it is associated with sample size, sample type, region, and age.

Design and Synthesis of New Sulfonamides-Based Flt3 Inhibitors

Background:

Flt3 is an oncogenic kinase involved in different leukemias. It is most prominently associated with acute myeloid leukemia (AML). Flt3-specific inhibitors have shown promising results in interfering with AML.

Methods:

The crystallographic structures of two inhibitors complexed within Flt3, namely, quizartinib and F6M, were used to guide the synthesis of new sulfonamide-based Flt3 inhibitors.

Results:

One of the prepared compounds showed low micromolar anti-Flt3 bioactivity, and interestingly, low micromolar bioactivity against the related oncogenic kinase VEGFR2.

Conclusion:

Sulfonamides were successfully used as privileged scaffolds for the synthesis of novel Flt3 inhibitors of micromolar potencies.

7‑Difluoromethyl‑5,4'‑dimethoxygenistein exerts anti‑angiogenic effects on acute promyelocytic leukemia HL‑60 cells by inhibiting the TLR4/NF‑κB signaling pathway

Angiogenesis plays an important role in the development and metastasis of tumors, and anti-angiogenesis agents are used to treat tumors. For example, the acute promyelocytic leukemia (APL) may be treated with arsenic trioxide. Angiogenesis in APL is a multi-step dynamic equilibrium process coordinated by various angiogenic stimulators and inhibitors, which play key roles in the occurrence, progression and chemosensitivity of this disease. Our research group previously synthesized 7-difluoromethyl-5,4′-dimethoxygenistein (DFMG), and found that it inhibits angiogenesis during atherosclerotic plaque formation. In the present study, the effect and mechanism of DFMG in angiogenesis induced by APL HL-60 cells was investigated using a chick embryo chorioallantoic membrane model and Matrigel tubule formation assays. The results obtained revealed an anti-angiogenesis effect of DFMG towards HL-60 cells. When the Toll-like receptor 4/nuclear factor-κB (TLR4/NF-κB) signaling pathway was inhibited, the anti-angiogenic effect of DFMG was further enhanced. However, when the TLR4/NF-κB signaling pathway was activated, the anti-angiogenic effect of DFMG was attenuated. These results demonstrated that DFMG inhibits angiogenesis induced by APL HL-60 cells, and provides insights into the mechanism by which DFMG inhibits the TLR4/NF-κB signaling pathway. In conclusion, in the present study, the anti-angiogenesis effect of DFMG on APL has been reported, and the mechanism by which DFMG induced the anti-angiogenesis effect was explored. These findings have provided a potential new drug candidate for the treatment of patients with APL.

Dynamic responses of the haematopoietic stem cell niche to diverse stresses

Adult haematopoietic stem cells (HSCs) mainly reside in the bone marrow, where stromal and haematopoietic cells regulate their function. The steady state HSC niche has been extensively studied. In this Review, we focus on how bone marrow microenvironment components respond to different insults including inflammation, malignant haematopoiesis and chemotherapy. We highlight common and unique patterns among multiple cell types and their environment and discuss current limitations in our understanding of this complex and dynamic tissue.

The Yin and Yang of the Bone Marrow Microenvironment: Pros and Cons of Mesenchymal Stromal Cells in Acute Myeloid Leukemia

Mesenchymal stromal cells (MSCs) have, for a long time, been recognized as pivotal contributors in the set up and maintenance of the hematopoietic stem cell (HSC) niche, as well as in the development and differentiation of the lympho-hematopoietic system. MSCs also have a unique immunomodulatory capacity, which makes them able to affect, both in vitro and in vivo, the function of immune cells. These features, namely the facilitation of stem cell engraftment and the inhibition of lymphocyte responses, have both proven essential for successful allogeneic stem cell transplantation (allo-SCT), which remains the only curative option for several hematologic malignancies. For example, in steroid-refractory acute graft-vs. host disease developing after allo-SCT, MSCs have produced significant results and are now considered a treatment option. However, more recently, the other side of the MSC coin has been unveiled, because of their emerging role in creating a protective and immune-tolerant microenvironment able to support the survival of leukemic cells and affect the response to therapies. In this light, it has been proposed that the failure of current treatments to efficiently override the stroma-mediated protection of leukemic cells accounts for the high rate of relapse in acute myeloid leukemia, at least in part. In this review, we will focus on emerging microenvironment-driven mechanisms conferring a survival advantage to leukemic cells overt physiological HSCs. This body of evidence increasingly highlights the opportunity to consider tumor-microenvironment interactions when designing new therapeutic strategies.

CS2164 suppresses acute myeloid leukemia cell growth via inhibiting VEGFR2 signaling in preclinical models

Acute myeloid leukemia (AML) arises from neoplastic transformation of hematopoietic stem and progenitor cells, and resistance to conventional chemotherapy remains one of the greatest challenges in treating the disease. Extensive data have demonstrated that angiogenesis is associated with AML progression and chemotherapy resistance. Thus, targeting angiogenesis may be a promising approach for AML treatment. In this study, we investigated the effectiveness of CS2164 (named as Chiauranib), a novel receptor tyrosine kinase inhibitor, in AML cells. Our results illustrated that CS2164 significantly suppressed cell proliferation and abolished clonogenicity in AML cells in a dose- and time-dependent manner. Meanwhile, CS2164 markedly induced apoptosis of AML cell lines and primary AML cells from 42 adult patients. Furthermore, we found that CS2164 has a comprehensive activity against AML irrespective of disease status and genetic mutations. Also, CS2164 suppressed AML growth in xenograft models in vivo. Mechanistically, CS2164-induced cytotoxicity was closely associated with inhibition of VEGFR2 and its downstream signaling cascades, including Src/Fyn/p38 and Erk/MEK. In conclusion, our study indicates that CS2164 exerts anti-leukemia effect by inducing apoptosis through suppressing the VEGFR2 pathway, supporting a potential role for CS2164 in the treatment of AML.

Alterations in multipotent mesenchymal stromal cells from the bone marrow of acute myeloid leukemia patients at diagnosis and during treatment

We analyzed multipotent mesenchymal stromal cells (MMSCs) from the bone marrow (BM) of 33 acute myeloid leukemia (AML) patients at diagnosis, after the first course of chemotherapy (day 37), and at days 100 and 180 after diagnosis. All patients were treated according to the AML 01.10 protocol. Cumulative production of MMSCs from AML patients at diagnosis was normal but increased during treatment. Most of the studied genes were upregulated at AML diagnosis, some (IL6, IL1B, LIF) remained upregulated during treatment, and others were downregulated (FGFR1, ICAM1) or normalized. A few genes were normal at diagnosis but decreased during treatment (FGF2, FGFR2, VEGF, SDF1, SOX9, TGFB1). The upregulation of proinflammatory genes both at diagnosis and during remission reflects ongoing inflammation. PDGFRB expression was upregulated in MMSCs from patients in relapse versus those in remission. The AML 01.10 protocol downregulates the expression of genes related to proliferation, differentiation and niche formation.

Contribution and prognostic value of TSGA10 gene expression in patients with acute myeloid leukemia (AML)

BACKGROUND

Different studies have investigated TSGA10 expression in various cancerous tissues but, so far no study has been conducted on newly diagnosed (ND) AML patients. The association of TSGA10 gene expression with hypoxia inducible factor (HIF) and angiogenic factors has remained to be fully elucidated and is still a controversial issue. The present study was designed to investigate this association in patients newly diagnosed with AML.

METHODS

We evaluated TSGA10, HIF-1α and VEGF mRNA levels in ND AML patients and healthy subjects using real-time PCR technique. Data were analyzed via comparative Livak method.

RESULTS

Based on the results of this study, TSGA10 gene expression was decreased in 28 out of 30 (93.3%) samples while VEGF and HIF-1α expression levels were increased in all ND AML patients compared to healthy controls. Diagnostic evaluation was performed by receiver operating characteristic (ROC) curve and area under the curve (AUC) calculation. Respectively, using cut-off relative quantification of 1.604, 0.0329, and 0.0042, the sensitivity values of TSGA10, VEGF, and HIF-1α gene expression were 86.7%, 90%, and 100%. Also, specificity values were 100%, 100% and 100%, respectively. TSGA10 expression was shown to be reduced in ND AML patients compared with healthy subjects and we found a negative correlation between TSGA10 and VEGF expression.

CONCLUSIONS

Since TSGA10 interacts with HIF-1 and affects its transcriptional activity, in ND AML patients with decreased TSGA10 expression, VEGF expression was high suggesting a TSGA10 mediated regulation of HIF-1 target genes. Altogether, the current study showed that TSGA10 could be considered as a tumor suppressor in AML patients.

Exosomes derived from acute myeloid leukemia cells promote chemoresistance by enhancing glycolysis-mediated vascular remodeling

Acute myeloid leukemia (AML) is the most common type of leukemia in adults. AML cells secrete angiogenic factors to remodel vasculature and acquire chemoresistance; however, antiangiogenic drugs are often ineffective in AML treatment. Cancer cell-derived exosomes can induce angiogenesis, but their role in vascular remodeling during AML is unclear. Here, we found that exosomes secreted by AML cells promoted proliferation and migration and tube-forming activity of human umbilical vein endothelial cells (HUVECs), whereas HUVECs conferred chemoresistance to AML cells. AML cell-derived exosomes contained vascular endothelial growth factor (VEGF) and VEGF receptor (VEGFR) messenger RNA and induced VEGFR expression in HUVECs. Furthermore, they enhanced glycolysis, which correlated with HUVEC proliferation, tube formation, and resistance to apoptosis. Thus, AML cells secrete VEGF/VEGFR-containing exosomes that induce glycolysis in HUVECs leading to vascular remodeling and acquisition of chemoresistance. These findings may contribute to the development of novel therapeutic strategies targeting exosomes in AML.

Highly selective anthraquinone-chalcone hybrids as potential antileukemia agents

A series of 23 novel anthraquinone-chalcone hybrids containing amide function was synthesized and structurally characterized. Sixteen compounds exerted strong cytotoxic activities against K562, Jurkat and HL-60 leukemia cell lines and significantly lower cytotoxic effects against normal MRC-5 cells, indicating very high selectivity in their anticancer action. The compounds 6g, 6u and 6v activate apoptosis in K562 cells through the extrinsic and intrinsic apoptotic pathway. The compound 6e triggered apoptosis in K562 cells only through the extrinsic apoptotic pathway. Treatment of K562 cells with each of these four compounds caused decrease in the expression levels of MMP2, MMP9, and VEGF, suggesting their anti-invasive, antimetastatic and antiangiogenic properties. The compounds 6g and 6v downregulated expression levels of miR-155 in K562 cells, while compounds 6e and 6u upregulated miR-155 levels in treated cells, in comparison with control cells. The structure-based 3-D QSAR models for 6f, 6e, 6i and 6l describe pro-apoptotic activity against caspase-3.

Inhibitory Effects of Arsenic Trioxide and Thalidomide on Angiogenesis and Vascular Endothelial Growth Factor Expression in Leukemia Cells

Acute myeloid leukemia (AML) is a blood disorder characterized by uncontrolled proliferation of myeloid progenitors and decrease in the apoptosis rate. The vascular endothelial growth factor (VEGF) promotes blood vessel regeneration which might play important roles in development and progression of neoplasia. Our previous studies focused on cytotoxicity and anticancer effects of arsenic trioxide (ATO) and thalidomide (THAL) as an anti-VEGF compound in the AML cell model. ATO also affects regulatory genes involved in cell proliferation and apoptosis. The aim of present study was to examine the effects of ATO and THAL alone and in combination on U937 and KG-1 cells, with attention to mRNA expression for VEGF isoforms. Growth inhibitory effects was assessed by MTT assay and apoptosis induction was determined by Annexin/PI staining. mRNA expression levels were evaluated by real-time PCR. Our data indicated that ATO (1.618μM and 1μM in KG-1 and U937 cell lines respectively), THAL (80μM and 60μM) and their combination inhibited proliferation and induced apoptosis in our cell lines. mRNA expression of VEGF (A, B) decreased while C and D isoforms did not show any significant changes. Taken together, according to the obtained results, the VEGF autocrine loop could be a target as a therapeutic strategy for cases of AML.

Apatinib exhibits anti-leukemia activity in preclinical models of acute lymphoblastic leukemia

Background

Acute lymphoblastic leukemia (ALL) is a clonal malignant disorder characterized by an uncontrolled proliferation of immature B or T lymphocytes. Extensive studies have suggested an involvement of angiogenesis signaling in ALL progression and resistance to treatment. Thus, targeting angiogenesis with anti-angiogenic drugs may be a promising approach for ALL treatment. In this study, we investigated the effectiveness of Apatinib, a novel receptor tyrosine kinase inhibitor selectively targeting VEGFR-2 in ALL cells.

Method

ALL cell lines were treated with different concentration of Apatinib and then CCK8 assay, flow cytometry were used to determine the IC₅₀ value and cell apoptosis, respectively. The effect of Apatinib against primary ALL cells from 11 adult patients and normal counterparts were also analyzed by apoptosis with flow cytometry. Next, we used western bolting and mass cytometry (CyTOF) assay to explore the underlying mechanism of the cytotoxicity of Apatinib. Finally, the anti-leukemia activity was further evaluated in an in vivo xenograft model of ALL.

Results

Our results showed that Apatinib significantly inhibited cell growth and promoted apoptosis in both B and T lineage ALL cell lines in a dose- and time-dependent manner. The IC₅₀ values of Apatinib against Nalm6, Reh, Jurkat and Molt4 for 48 h were 55.76 ± 13.19, 51.53 ± 10.74, 32.43 ± 5.58, 39.91 ± 9.88 μmol/L, and for 72 h were 30.34 ± 2.65, 31.96 ± 3.92, 17.62 ± 5.90, and 17.65 ± 2.17 μmol/L respectively. Similarly, Apatinib shows cytotoxic activity against primary adult ALL cells while sparing their normal counterparts in vitro. Moreover, Apatinib suppressed ALL growth and progression in an in vivo xenograft model. Mechanistically, Apatinib-induced cytotoxicity was closely associated with inhibition of VEGFR2 and its downstream signaling cascades, including the PI3 K, MAPK and STAT3 pathways.

Conclusion

Our study indicates that Apatinib exerts its anti-leukemia effect by inducing apoptosis through suppressing the VEGFR2 signaling pathway, supporting a potential role for Apatinib in the treatment of ALL.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1421-y) contains supplementary material, which is available to authorized users.

Glioblastoma and acute myeloid leukemia: malignancies with striking similarities

Acute myeloid leukemia (AML) and glioblastoma (GB) are two malignancies associated with high incidence of treatment refractoriness and generally, uniformly poor survival outcomes. While the former is a hematologic (i.e. a "liquid") malignancy and the latter a solid tumor, the two diseases share both clinical and biochemical characteristics. Both diseases exist predominantly in primary (de novo) forms, with only a small subset of each progressing from precursor disease states like the myelodysplastic syndromes or diffuse glioma. More importantly, the primary and secondary forms of each disease are characterized by common sets of mutations and gene expression abnormalities. The primary versions of AML and GB are characterized by aberrant RAS pathway, matrix metalloproteinase 9, and Bcl-2 expression, and their secondary counterparts share abnormalities in TP53, isocitrate dehydrogenase, ATRX, inhibitor of apoptosis proteins, and survivin that both influence the course of the diseases themselves and their progression from precursor disease. An understanding of these shared features is important, as it can be used to guide both the research about and treatment of each.

Increased Vascular Permeability in the Bone Marrow Microenvironment Contributes to Disease Progression and Drug Response in Acute Myeloid Leukemia

The biological and clinical behaviors of hematological malignancies can be influenced by the active crosstalk with an altered bone marrow (BM) microenvironment. In the present study, we provide a detailed picture of the BM vasculature in acute myeloid leukemia using intravital two-photon microscopy. We found several abnormalities in the vascular architecture and function in patient-derived xenografts (PDX), such as vascular leakiness and increased hypoxia. Transcriptomic analysis in endothelial cells identified nitric oxide (NO) as major mediator of this phenotype in PDX and in patient-derived biopsies. Moreover, induction chemotherapy failing to restore normal vasculature was associated with a poor prognosis. Inhibition of NO production reduced vascular permeability, preserved normal hematopoietic stem cell function, and improved treatment response in PDX.

Monocarboxylate transporter 1 (MCT1), a tool to stratify acute myeloid leukemia (AML) patients and a vehicle to kill cancer cells

Dysregulation of glucose/lactate dynamics plays a role in cancer progression, and MCTs are key elements in metabolic remodeling. VEGF is a relevant growth factor in the maintenance of bone marrow microenvironment and it is also important in hematological diseases.

Our aim was to investigate the role of VEGF in the metabolic adaptation of Acute myeloid leukemia (AML) cells by evaluating the metabolic profiles and cell features according to the AML lineage and testing lactate as a metabolic coin.

Our in vitro results showed that AML promyelocytic (HL60) and monocytic (THP1) (but not erythroid- HEL) lineages are well adapted to VEGF and lactate rich environment. Their metabolic adaptation relies on high rates of glycolysis to generate intermediates for PPP to support cell proliferation, and on the consumption of glycolysis-generated lactate to supply biomass and energy production. VEGF orchestrates this metabolic network by regulating MCT1 expression. Bromopyruvic acid (BPA) was proven to be an effective cytotoxic in AML, possibly transported by MCT1.

Our study reinforces that targeting metabolism can be a good strategy to fight cancer. MCT1 expression at the time of diagnosis can assist on the identification of AML patients that will benefit from BPA therapy. Additionally, MCT1 can be used in targeted delivery of conventional cytotoxic drugs.

Peptide microarray profiling identifies phospholipase C gamma 1 (PLC-γ1) as a potential target for t(8;21) AML

The t(8;21) (q22;q22) chromosomal translocation is one of the most frequent genetic alterations in acute myeloid leukemia (AML) which has a need for improved therapeutic strategies. We found PLC-γ1 as one of the highest phosphorylated peptides in t(8;21) AML samples compared to NBM or CN-AML in our previous peptide microarray. PLC-γ1 is known to play a role in cancer progression, however, the impact of PLC-γ1 in AML is currently unknown. Therefore, we aimed to study the functional role of PLC-γ1 by investigating the cellular growth, survival and its underlying mechanism in t(8;21) AML.

In this study, PLC-γ1 expression was significantly higher in t(8;21) AML compared to other karyotypes. The PLC-γ1 protein expression was suppressed in AML1-ETO knock down cells indicating that it might induce kasumi-1 cell death. ShRNA-mediated PLC-γ1 knockdown in kasumi-1 cells significantly blocked cell growth, induced apoptosis and cell cycle arrest which was explained by the increased activation of apoptotic related and cell cycle regulatory protein expressions. Gene expression array analysis showed the up-regulation of apoptotic and DNA damage response genes together with the downregulation of cell growth, proliferation and differentiation genes in the PLC-γ1 suppressed kasumi-1 cells, consistent with the observed phenotypic effects. Importantly, PLC-γ1 suppressed kasumi-1 cells showed higher chemosensitivity to the chemotherapeutic drug treatments and lower cell proliferation upon hypoxic stress.

Taken together, these in vitro finding strongly support an important role for PLC-γ1 in the survival of t(8;21) AML mimicking kasumi-1 cells and identify PLC-γ1 as a potential therapeutic target for t(8;21) AML treatment.

SEMA3A partially reverses VEGF effects through binding to neuropilin-1

Cross-talk between hematopoietic stem cells (HSCs) and bone marrow stromal cells (BMSCs) is essential for HSCs regulation and leukemogenesis. Studying bone marrow of myelodysplasia patients, a pre-leukemic condition, we found mRNA overexpression of vascular endothelial growth factor A (VEGFA) in CD34⁺ HSCs and semaphorin 3A (SEMA3A) in BMSCs. To better understand the role of VEGFA and SEMA3A in leukemogenesis, we recruited 30 myelodysplastic syndrome (MDS) patients, 29 acute myeloid leukemia (6 secondary to MDS) patients and 12 controls. We found higher VEGFA expression in de novo AML patients (without prior MDS) group (p=0.0073) and higher SEMA3A expression in all BMSCs patient's samples compared to control group. We then overexpressed VEGFA in an acute myelogenous leukemia cell line, KG1 cells, and in normal CD34⁺ cells. This overexpression increased KG1 (p=0.045) and CD34⁺ cell (p=0.042) viability and KG1 (p=0.042) and CD34⁺ cell (p=0.047) proliferation. Moreover, KG1 and CD34⁺ cells overexpressing VEGFA also had increased proliferation when co-cultured with human marrow stromal HS5 cells (p=0.045 and p=0.02, respectively). However, co-culture of these transformed cells with HS5 cells overexpressing SEMA3A reduced KG1 (p=0.004) and CD34⁺ (p=0.009) proliferation. Co-culture of KG1 transformed cells with HS27 cells overexpressing SEMA3A reduced KG1 proliferation as well (p=0.01). To investigate whether the dominant SEMA3A effect over VEGFA could be due to competition for neuropilin1 receptor (NRP1), we performed immunoprecipitation with anti-NRP1 antibody of cell extracts of co-cultured KG1 and HS5 cells, induced or not by VEGFA and SEMA3A recombinant proteins. Results showed a preferential association of NRP1 with SEMA3A, suggesting that SEMA3A can partially reverse the effects caused by the VEGFA preventing its binding with the NRP1 receptor. Since both hematopoietic cells, leukemic and normal, showed similar behavior, we suppose that the attempt to reversion of VEGF effects by SEMA3A is a homeostatic phenomenon in the hematopoietic niche. Finally, we conclude that VEGFA overexpression confers AML cell advantages and SEMA3A may partially reverse this effect; thus, SEMA3A protein combined with VEGFA inhibitors could be beneficial for AML treatment.

Mesenchymal Stem Cells Support Survival and Proliferation of Primary Human Acute Myeloid Leukemia Cells through Heterogeneous Molecular Mechanisms

Acute myeloid leukemia (AML) is a bone marrow malignancy, and various bone marrow stromal cells seem to support leukemogenesis, including osteoblasts and endothelial cells. We have investigated how normal bone marrow mesenchymal stem cells (MSCs) support the in vitro proliferation of primary human AML cells. Both MSCs and primary AML cells show constitutive release of several soluble mediators, and the mediator repertoires of the two cell types are partly overlapping. The two cell populations were cocultured on transwell plates, and MSC effects on AML cells mediated through the local cytokine/soluble mediator network could thus be evaluated. The presence of normal MSCs had an antiapoptotic and growth-enhancing effect on primary human AML cells when investigating a group of 51 unselected AML patients; this was associated with increased phosphorylation of mTOR and its downstream targets, and the effect was independent of cytogenetic or molecular-genetic abnormalities. The MSCs also supported the long-term proliferation of the AML cells. A subset of the patients also showed an altered cytokine network with supra-additive levels for several cytokines. The presence of cytokine-neutralizing antibodies or receptor inhibitors demonstrated that AML cells derived from different patients were heterogeneous with regard to effects of various cytokines on AML cell proliferation or regulation of apoptosis. We conclude that even though the effects of single cytokines derived from bone marrow MSCs on human AML cells differ among patients, the final cytokine-mediated effects of the MSCs during coculture is growth enhancement and inhibition of apoptosis.

De novo AML exhibits greater microenvironment dysregulation compared to AML with myelodysplasia-related changes

The interaction between the bone marrow microenvironment and malignant hematopoietic cells can result in the protection of leukemia cells from chemotherapy in both myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). We, herein, characterized the changes in cytokine expression and the function of mesenchymal stromal cells (MSC) in patients with MDS, AML with myelodysplasia-related changes (MRC), a well-recognized clinical subtype of secondary AML, and de novo AML. We observed a significant inhibitory effect of MDS-MSC on T lymphocyte proliferation and no significant differences in any of the cytokines tested. AML-MSC inhibited T-cell proliferation only at a very low MSC/T cell ratio. When compared to the control, AML-MRCderived MSC presented a significant increase in IL6 expression, whereas de novo AML MSC presented a significant increase in the expression levels of VEGFA, CXCL12, RPGE2, IDO, IL1β, IL6 and IL32, followed by a decrease in IL10 expression. Furthermore, data indicate that IL-32 regulates stromal cell proliferation, has a chemotactic potential and participates in stromal cell crosstalk with leukemia cells, which could result in chemoresistance. Our results suggest that the differences between AML-MRC and de novo AML also extend into the leukemic stem cell niche and that IL-32 can participate in the regulation of the bone marrow cytokine milieu.

miR-125b promotes MLL-AF9-driven murine acute myeloid leukemia involving a VEGFA-mediated non-cell-intrinsic mechanism

The hematopoietic stem cell-enriched miR-125 family microRNAs (miRNAs) are critical regulators of hematopoiesis. Overexpression of miR-125a or miR-125b is frequent in human acute myeloid leukemia (AML), and the overexpression of these miRNAs in mice leads to expansion of hematopoietic stem cells accompanied by perturbed hematopoiesis with mostly myeloproliferative phenotypes. However, whether and how miR-125 family miRNAs cooperate with known AML oncogenes in vivo, and how the resultant leukemia is dependent on miR-125 overexpression, are not well understood. We modeled the frequent co-occurrence of miR-125b overexpression and MLL translocations by examining functional cooperation between miR-125b and MLL-AF9 By generating a knock-in mouse model in which miR-125b overexpression is controlled by doxycycline induction, we demonstrated that miR-125b significantly enhances MLL-AF9-driven AML in vivo, and the resultant leukemia is partially dependent on continued overexpression of miR-125b Surprisingly, miR-125b promotes AML cell expansion and suppresses apoptosis involving a non-cell-intrinsic mechanism. MiR-125b expression enhances VEGFA expression and production from leukemia cells, in part by suppressing TET2 Recombinant VEGFA recapitulates the leukemia-promoting effects of miR-125b, whereas knockdown of VEGFA or inhibition of VEGF receptor 2 abolishes the effects of miR-125b In addition, significant correlation between miR-125b and VEGFA expression is observed in human AMLs. Our data reveal cooperative and dependent relationships between miR-125b and the MLL oncogene in AML leukemogenesis, and demonstrate a miR-125b-TET2-VEGFA pathway in mediating non-cell-intrinsic leukemia-promoting effects by an oncogenic miRNA.

Antileukemic effects of midostaurin in acute myeloid leukemia - the possible importance of multikinase inhibition in leukemic as well as nonleukemic stromal cells

INTRODUCTION

Midostaurin is a multikinase inhibitor that inhibits receptor tyrosine kinases (Flt3, CD117/c-kit, platelet-derived growth factor receptor, vascular endothelial growth factor receptor 2) as well as non-receptor tyrosine kinases (Frg, Src, Syk, Protein kinase C). Combination of midostaurin with conventional intensive chemotherapy followed by one year maintenance monotherapy was recently reported to improve the survival of acute myeloid leukemia (AML) patients with Flt3 mutations. Areas covered: Relevant publications were identified through literature searches in the PubMed database. We searched for (i) original articles describing the results from clinical studies; (ii) published articles describing the importance of midostaurin-inhibited kinases for leukemogenesis and chemosensitivity. Expert opinion: Midostaurin monotherapy is well tolerated, combined with conventional chemotherapy gastrointestinal toxicity increases significantly. Midostaurin alters anthracycline pharmacokinetics. Furthermore, its antileukemic effects may not only be mediated through Flt3 inhibition alone; the inhibition of other kinases may also be important for the overall antileukemic effect. Midostaurin may then have direct effects on the leukemic cells but also indirect antileukemic effects through inhibition of the AML-supporting effects of neighboring stromal cells in the bone marrow microenvironment. Midostaurin may thus be used in combination with intensive chemotherapy, as maintenance treatment or as disease-stabilizing treatment for elderly unfit patients.

Profiling of microRNAs in AML cells following overexpression or silencing of the VEGF gene

Acute myeloid leukemia (AML) is a disease of the hematopoietic progenitor cells associated with heterogeneous clonal proliferation. Vascular endothelial growth factor (VEGF) and its receptors play important roles in the regulation of angiogenesis during physiological and pathological processes. It is thought that AML cells have an autocrine VEGF pathway that contributes to the development and progression of AML. In addition, growing evidence has suggested that numerous microRNAs are involved in AML. The present study aimed to investigate the relationship between VEGF dysregulation and microRNA profiles in AML cells and patients. VEGF-overexpressing and VEGF-knockdown leukemia cells were constructed and changes in the patterns of microRNA expression were analyzed using a microRNA array. Subsequently, mononuclear cells from the blood of patients with AML showing high or low expression levels of VEGF were obtained and were used to assess the patterns of microRNA expression by reverse transcription-quantitative polymerase chain reaction. The results of the present study suggested that downregulation of VEGF markedly altered the profile of microRNAs in AML cells, while upregulation of VEGF did not. Examination of clinical samples from patients with AML showed that several microRNAs were closely associated with the expression level of VEGF, including miR-20a, miR-93, miR-16-5p, miR-17-5p, miR-124-5p and miR-17-3p. These results suggested that VEGF may be a pivotal protein that can both receive and initiate signals in leukemia cells.

Myeloid malignancies and the microenvironment

Research in the last few years has revealed a sophisticated interaction network between multiple bone marrow cells that regulate different hematopoietic stem cell (HSC) properties such as proliferation, differentiation, localization, and self-renewal during homeostasis. These mechanisms are essential to keep the physiological HSC numbers in check and interfere with malignant progression. In addition to the identification of multiple mutations and chromosomal aberrations driving the progression of myeloid malignancies, alterations in the niche compartment recently gained attention for contributing to disease progression. Leukemic cells can remodel the niche into a permissive environment favoring leukemic stem cell expansion over normal HSC maintenance, and evidence is accumulating that certain niche alterations can even induce leukemic transformation. Relapse after chemotherapy is still a major challenge during treatment of myeloid malignancies, and cure is only rarely achieved. Recent progress in understanding the niche-imposed chemoresistance mechanisms will likely contribute to the improvement of current therapeutic strategies. This article discusses the role of different niche cells and their stage- and disease-specific roles during progression of myeloid malignancies and in response to chemotherapy.

Endothelial progenitor cells in hematologic malignancies

Studies carried out in the last years have improved the understanding of the cellular and molecular mechanisms controlling angiogenesis during adult life in normal and pathological conditions. Some of these studies have led to the identification of some progenitor cells that sustain angiogenesis through indirect, paracrine mechanisms (hematopoietic angiogenic cells) and through direct mechanisms, i.e., through their capacity to generate a progeny of phenotypically and functionally competent endothelial cells [endothelial colony forming cells (ECFCs)]. The contribution of these progenitors to angiogenetic processes under physiological and pathological conditions is intensively investigated. Angiogenetic mechanisms are stimulated in various hematological malignancies, including chronic myeloid leukemia (CML), acute myeloid leukemia (AML), myelodysplastic syndromes and multiple myeloma, resulting in an increased angiogenesis that contributes to disease progression. In some of these conditions there is preliminary evidence that some endothelial cells could derive from the malignant clone, thus leading to the speculation that the leukemic cell derives from the malignant transformation of a hemangioblastic progenitor, i.e., of a cell capable of differentiation to the hematopoietic and to the endothelial cell lineages. Our understanding of the mechanisms underlying increased angiogenesis in these malignancies not only contributed to a better knowledge of the mechanisms responsible for tumor progression, but also offered the way for the discovery of new therapeutic targets.

SIRT2 is an unfavorable prognostic biomarker in patients with acute myeloid leukemia

SIRT2 is a member of the NAD+ dependent deacetylases. In this study, the associations between SIRT2 expression and molecular and clinical characteristics of patients with acute myeloid leukemia (AML) were evaluated by data from The Cancer Genome Atlas. SIRT2 was overexpressed in the intermediate- and poor-risk groups of patients, compared to the favorable-risk group of patients (P = 0.002 and 0.004, respectively). High SIRT2 expression was associated with significantly shorter overall survival (OS; P = 0.0005) and event-free survival (EFS; P = 0.0002) than low SIRT2 expressio in a cohort of 167 patients with AML. Multivariate analyses revealed that high SIRT2 expression was associated with shorter OS (P = 0.031) and EFS (P = 0.020). Gene-expression profiling showed 259 differential expressed genes including CD4, CD14 and IL10. Gene sets like MAPK signaling pathway, VEGF signaling pathway and acute myeloid leukemia were upregulated in SIRT2^high patients. We also found different methylation patterns in these two groups. OS and EFS of SIRT2^high patients who did not undergo transplantation were significantly shorter than those of SIRT2^low patients (P = 0.0120 and P = 0.0107, respectively). Taken together, these findings suggest that high SIRT2 expression is a novel and unfavorable prognostic biomarker for AML risk-stratification.