Autocrine stimulation of VEGFR-2 activates human leukemic cell growth and migration

Effects of Angiogenic Factors on the Epithelial-to-Mesenchymal Transition and Their Impact on the Onset and Progression of Oral Squamous Cell Carcinoma: An Overview

High levels of vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF)-2 and angiopoietin (ANG)-2 are found in tissues from oral squamous cell carcinoma (OSCC) and oral potentially malignant disorders (OPMDs). As might be expected, VEGF, FGF-2, and ANG-2 overexpression parallels the development of new blood and lymphatic vessels that nourish the growing OPMDs or OSCCs and provide the latter with metastatic routes. Notably, VEGF, FGF-2, and ANG-2 are also linked to the epithelial-to-mesenchymal transition (EMT), a trans-differentiation process that respectively promotes or exasperates the invasiveness of normal and neoplastic oral epithelial cells. Here, we have summarized published work regarding the impact that the interplay among VEGF, FGF-2, ANG-2, vessel generation, and EMT has on oral carcinogenesis. Results from the reviewed studies indicate that VEGF, FGF-2, and ANG-2 spark either protein kinase B (AKT) or mitogen-activated protein kinases (MAPK), two signaling pathways that can promote both EMT and new vessels' formation in OPMDs and OSCCs. Since EMT and vessel generation are key to the onset and progression of OSCC, as well as to its radio- and chemo-resistance, these data encourage including AKT or MAPK inhibitors and/or antiangiogenic drugs in the treatment of this malignancy.

Mesenchymal Stromal Cell Senescence Induced by Dnmt3a -Mutant Hematopoietic Cells is a Targetable Mechanism Driving Clonal Hematopoiesis and Initiation of Hematologic Malignancy

Clonal hematopoiesis (CH) can predispose to blood cancers due to enhanced fitness of mutant hematopoietic stem and progenitor cells (HSPCs), but the mechanisms driving this progression are not understood. We hypothesized that malignant progression is related to microenvironment-remodelling properties of CH-mutant HSPCs. Single-cell transcriptomic profiling of the bone marrow microenvironment in Dnmt3a R878H/+ mice revealed signatures of cellular senescence in mesenchymal stromal cells (MSCs). Dnmt3a R878H/+ HSPCs caused MSCs to upregulate the senescence markers SA-β-gal, BCL-2, BCL-xL, Cdkn1a (p21) and Cdkn2a (p16), ex vivo and in vivo . This effect was cell contact-independent and can be replicated by IL-6 or TNFα, which are produced by Dnmt3a R878H/+ HSPCs. Depletion of senescent MSCs in vivo reduced the fitness of Dnmt3a R878H/+ hematopoietic cells and the progression of CH to myeloid neoplasms using a sequentially inducible Dnmt3a ; Npm1 -mutant model. Thus, Dnmt3a -mutant HSPCs reprogram their microenvironment via senescence induction, creating a self-reinforcing niche favoring fitness and malignant progression.

Statement of Significance

Mesenchymal stromal cell senescence induced by Dnmt3a -mutant hematopoietic stem and progenitor cells drives clonal hematopoiesis and initiation of hematologic malignancy.

FLT4 as a marker for predicting prognostic risk of refractory acute myeloid leukemia

Treating patients with refractory acute myeloid leukemia (AML) remains challenging. Currently there is no effective treatment for refractory AML. Increasing evidence has demonstrated that refractory/relapsed AML is associated with leukemic blasts which can confer resistance to anticancer drugs. We have previously reported that high expression of Fms-related tyrosine kinase 4 (FLT4) is associated with increased cancer activity in AML. However, the functional role of FLT4 in leukemic blasts remains unknown. Here, we explored the significance of FLT4 expression in leukemic blasts of refractory patients and mechanisms involved in the survival of AML blasts. Inhibition or absence of FLT4 in AML blasts suppressed homing to bone marrow of immunocompromised mice and blocked engraftment of AML blasts. Moreover, FLT4 inhibition by MAZ51, an antagonist, effectively reduced the number of leukemic cell-derived colony-forming units and increased apoptosis of blasts derived from refractory patients when it was co-treated with cytosine arabinoside under vascular endothelial growth factor C, its ligand. AML patients who expressed high cytosolic FLT4 were linked to an AML-refractory status by internalization mechanism. In conclusion, FLT4 has a biological function in leukemogenesis and refractoriness. This novel insight will be useful for targeted therapy and prognostic stratification of AML.

A randomized phase 2 trial of nintedanib and low-dose cytarabine in elderly patients with acute myeloid leukemia ineligible for intensive chemotherapy

We investigated the safety and efficacy of nintedanib added to low-dose cytarabine (LDAC) in a phase 1/2 study in patients 60 years or older with newly diagnosed or relapsed/refractory (r/r) AML ineligible for intensive chemotherapy. The results of the dose-finding phase 1 part have been previously published. Patients were randomized 1:1 to LDAC plus nintedanib or LDAC plus placebo stratified by AML status (newly diagnosed vs r/r). LDAC was applied subcutaneously at 20 mg twice daily on days 1 to 10. Nintedanib/placebo was orally administered twice daily on days 1 to 28 in 28-day cycles. The primary endpoint was overall survival (OS). Between 05/2017 and 09/2019, 31 patients were randomized and 30 were treated, before the study was terminated prematurely due to slow recruitment. Median (range) age of patients was 76 (60-84) years. Twenty-two patients (73%) had r/r AML. Median OS in patients treated with LDAC and nintedanib was 3.4 months, compared with 3.6 months in those treated in the placebo arm, with a HR adjusted for AML status of 1.19 (corresponding confirmatory adjusted 95% CI, 0.55-2.56; univariate log-rank P = 0.96). In the 22 patients with r/r AML, median OS was 3.0 months in the nintedanib and 3.6 months in the placebo arm (P = 0.36). One patient in the nintedanib and two patients in the placebo arm achieved a CR and entered maintenance treatment. Nintedanib showed no superior therapeutic activity over placebo when added to LDAC in elderly AML patients considered unfit for intensive chemotherapy. The trial was registered at clinicaltrials.gov NCT01488344.

Prognostic importance of thrombospondin-1, VEGF, PDGFR- β in diffuse large B-cell lymphoma

Aim: In this study, we aimed to investigate the relationship between the staining rates of thrombospondin-1, VEGF, and PDGFR-in tissue preparations in patients diagnosed with DLBCL and their clinical features at the time of diagnosis, and response to treatment and prognosis. Material and Method: A total of 44 patients with a diagnosis of DLBCL and 13 patients diagnosed with control reactive lymphadenopathy were included in this study. After immunohistochemical staining of the pathology preparations of the patient and control groups with VEGF, PDGFR-β and thrombospondin-1 stains, the clinical characteristics of the patients and the relationship between survival analysis and staining rates were statistically analyzed. Results: When the patients were compared with the control group in terms of VEGF, PDGFR-β, and thrombospondin-1 staining rates, we found that staining with PDGFR-β was lower in patients (p=0.009). Although it was not statistically significant for PDGFR-β, it was observed that 5-year OS and PFS values were low in patients with high levels of expression, on the contrary, 5-year OS was low in patients with high thrombospondin staining rate. A negative correlation was observed between thrombospondin-1 and PDGFR-β (p=0.003, r=-0.440). Conclusion: As a result, although no relationship was found between VEGF and survival in our study, it was observed that PDGFR-β and thrombospondin-1 were effective in prognosis. A negative correlation was observed between thrombospondin-1 and PDGFR-β.

Targeting metabolism: A potential strategy for hematological cancer therapy

Most hematological cancer-related relapses and deaths are caused by metastasis; thus, the importance of this process as a target of therapy should be considered. Hematological cancer is a type of cancer in which metabolism plays an essential role in progression. Therefore, we are required to block fundamental metastatic processes and develop specific preclinical and clinical strategies against those biomarkers involved in the metabolic regulation of hematological cancer cells, which do not rely on primary tumor responses. To understand progress in this field, we provide a summary of recent developments in the understanding of metabolism in hematological cancer and a general understanding of biomarkers currently used and under investigation for clinical and preclinical applications involving drug development. The signaling pathways involved in cancer cell metabolism are highlighted and shed light on how we could identify novel biomarkers involved in cancer development and treatment. This review provides new insights into biomolecular carriers that could be targeted as anticancer biomarkers.

Vascular Endothelial Growth Factor Receptors [VEGFR] as Target in Breast Cancer Treatment: Current Status in Preclinical and Clinical Studies and Future Directions

Breast cancer [BC] is one of the most common cancers among women, one of the leading causes of a considerable number of cancer-related death globally. Among all procedures leading to the formation of breast tumors, angiogenesis has an important role in cancer progression and outcomes. Therefore, various anti-angiogenic strategies have developed so far to enhance treatment's efficacy in different types of BC. Vascular endothelial growth factors [VEGFs] and their receptors are regarded as the most well-known regulators of neovascularization. VEGF binding to vascular endothelial growth factor receptors [VEGFRs] provides cell proliferation and vascular tissue formation by the subsequent tyrosine kinase pathway. VEGF/VEGFR axis displays an attractive target for anti-angiogenesis and anti-cancer drug design. This review aims to describe the existing literature regarding VEGFR inhibitors, focusing on BC treatment reported in the last two decades.

Coculture in vitro with endothelial cells induces cytarabine resistance of acute myeloid leukemia cells in a VEGF-A/VEGFR-2 signaling-independent manner

An interaction between acute myeloid leukemia (AML) cells and endothelial cells in the bone marrow seems to play a critical role in chemosensitivity on leukemia treatment. The endothelial niche reportedly enhances the paracrine action of the soluble secretory proteins responsible for chemoresistance in a vascular endothelial growth factor A (VEGF-A)/VEGF receptor 2 (VEGFR-2) signaling pathway-dependent manner. To further investigate the contribution of VEGF-A/VEGFR-2 signaling to the chemoresistance of AML cells, a biochemical assay system in which the AML cells were cocultured with human endothelial EA.hy926 cells in a monolayer was developed. By coculture with EA.hy926 cells, this study revealed that the AML cells resisted apoptosis induced by the anticancer drug cytarabine. SU4312, a VEGFR-2 inhibitor, attenuated VEGFR-2 phosphorylation and VEGF-A/VEGFR-2 signaling-dependent endothelial cell migration; thus, this inhibitor was observed to block VEGF-A/VEGFR-2 signaling. Interestingly, this inhibitor did not reverse the chemoresistance. When VEGFR-2 was knocked out in EA.hy926 cells using the CRISPR-Cas9 system, the cytarabine-induced apoptosis of AML cells did not significantly change compared with that of wild-type cells. Thus, coculture-induced chemoresistance appears to be independent of VEGF-A/VEGFR-2 signaling. When the transwell, a coculturing device, separated the AML cells from the EA.hy926 cells in a monolayer, the coculture-induced chemoresistance was inhibited. Given that the migration of VEGF-A/VEGFR-2 signaling-dependent endothelial cells is necessary for the endothelial niche formation in the bone marrow, VEGF-A/VEGFR-2 signaling contributes to chemoresistance by mediating the niche formation process, but not to the chemoresistance of AML cells in the niche.

Leukaemia: a model metastatic disease

In contrast to solid cancers, which often require genetic modifications and complex cellular reprogramming for effective metastatic dissemination, leukaemic cells uniquely possess the innate ability for migration and invasion. Dedifferentiated, malignant leukocytes retain the benign leukocytes' capacity for cell motility and survival in the circulation, while acquiring the potential for rapid and uncontrolled cell division. For these reasons, leukaemias, although not traditionally considered as metastatic diseases, are in fact models of highly efficient metastatic spread. Accordingly, they are often aggressive and challenging diseases to treat. In this Perspective, we discuss the key molecular processes that facilitate metastasis in a variety of leukaemic subtypes, the clinical significance of leukaemic invasion into specific tissues and the current pipeline of treatments targeting leukaemia metastasis.

The Role of Hypoxic Bone Marrow Microenvironment in Acute Myeloid Leukemia and Future Therapeutic Opportunities

Acute myeloid leukemia (AML) is a hematologic malignancy caused by a wide range of alterations responsible for a high grade of heterogeneity among patients. Several studies have demonstrated that the hypoxic bone marrow microenvironment (BMM) plays a crucial role in AML pathogenesis and therapy response. This review article summarizes the current literature regarding the effects of the dynamic crosstalk between leukemic stem cells (LSCs) and hypoxic BMM. The interaction between LSCs and hypoxic BMM regulates fundamental cell fate decisions, including survival, self-renewal, and proliferation capacity as a consequence of genetic, transcriptional, and metabolic adaptation of LSCs mediated by hypoxia-inducible factors (HIFs). HIF-1α and some of their targets have been associated with poor prognosis in AML. It has been demonstrated that the hypoxic BMM creates a protective niche that mediates resistance to therapy. Therefore, we also highlight how hypoxia hallmarks might be targeted in the future to hit the leukemic population to improve AML patient outcomes.

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.

Quantitative proteome profiling stratifies fibroepithelial lesions of the breast

Breast fibroepithelial lesions (FELs) include heterogeneous pathological tumors, involving indolent fibroadenoma (FAD) to potentially aggressive phyllodes tumors (PTs). The current grading system remains unreliable in differentiating these tumors due to histological heterogeneity and lack of appropriate markers to monitor the sudden and unpredictable malignant transformation of PTs. Thus, there exists an imminent need for a marker-based diagnostic approach to augment the conventional histological platform that could lead to accurate diagnosis and distinction of FELs. The high- throughput quantitative proteomic analysis suggested that FAD and PTs form distinct clusters away from borderline and malignant though there exist marked differences between them. Interestingly, over-expression of extracellular matrices (ECM) related proteins and epithelial-mesenchymal transition (EMT) markers in borderline PTs led us to hypothesize a model of deposition and degradation leading to ECM remodeling and EMT acquisition triggering its malignant transformation. We also identified three candidate biomarkers such as MUCL1, HTRA1, and VEGDF uniquely expressed in FAD, borderline, and malignant PTs, respectively, which were further validated using immunohistochemistry. The present work shed light on a brief mechanistic framework of PTs aggressive nature and present potential biomarkers to differentiate overlapping FELs that would be of practical utility in augmenting existing diagnosis and disease management for this rare tumor.

A narrative review of central nervous system involvement in acute leukemias

Acute leukemias (both myeloid and lymphoblastic) are a group of diseases for which each year more successful therapies are implemented. However, in a subset of cases the overall survival (OS) is still exceptionally low due to the infiltration of leukemic cells in the central nervous system (CNS) and the subsequent formation of brain tumors. The CNS involvement is more common in acute lymphocytic leukemia (ALL), than in adult acute myeloid leukemia (AML), although the rates for the second case might be underestimated. The main reasons for CNS invasion are related to the expression of specific adhesion molecules (VLA-4, ICAM-1, VCAM, L-selectin, PECAM-1, CD18, LFA-1, CD58, CD44, CXCL12) by a subpopulation of leukemic cells, called “sticky cells” which have the ability to interact and adhere to endothelial cells. Moreover, the microenvironment becomes hypoxic and together with secretion of VEGF-A by ALL or AML cells the permeability of vasculature in the bone marrow increases, coupled with the disruption of blood brain barrier. There is a single subpopulation of leukemia cells, called leukemia stem cells (LSCs) that is able to resist in the new microenvironment due to its high adaptability. The LCSs enter into the arachnoid, migrate, and intensively proliferate in cerebrospinal fluid (CSF) and consequently infiltrate perivascular spaces and brain parenchyma. Moreover, the CNS is an immune privileged site that also protects leukemic cells from chemotherapy. CD56/NCAM is the most important surface molecule often overexpressed by leukemic stem cells that offers them the ability to infiltrate in the CNS. Although asymptomatic or with unspecific symptoms, CNS leukemia should be assessed in both AML/ALL patients, through a combination of flow cytometry and cytological analysis of CSF. Intrathecal therapy (ITT) is a preventive measure for CNS involvement in AML and ALL, still much research is needed in finding the appropriate target that would dramatically lower CNS involvement in acute leukemia.

Dormancy in the Tumor Microenvironment

Tumor cells frequently disseminate to distant organ sites, where they encounter permissive or restrictive environments that enable them to grow and colonize or enter a dormant state. Tumor dormancy is not strictly defined, but generally describes a tumor cell that is non-proliferative or in a state of balanced equilibrium, in which the proliferation rate of the tumor cell or cells is equal to its rate of cell death. The mechanisms that regulate tumor cell entry into and exit from dormancy are poorly understood, but microenvironmental features as well as tumor cell intrinsic factors play an important role in mediating this transition. Upon homing to distant metastatic sites, tumor cells may disseminate into various niches, most frequently the perivascular, hematopoietic stem cell, or endosteal/osteogenic niche. Tumor cells sense the cytokines, growth factors, and chemo-attractants from each of these niches, and tumor cell expression of cognate ligands and receptors can determine whether a tumor cell enters or exits dormancy. In addition to the secreted factors and cell-cell interactions that regulate dormancy, the cellular milieu also impacts upon disseminated tumor cells to promote or restrain their growth in distant metastatic sites. In this chapter we will discuss the role of the osteogenic and perivascular niche on dormant tumor cells, as well as the impact of hypoxia (low oxygen tensions) and the immune system on the restriction and outgrowth of dormant, disseminated tumor cells.

Antiproliferative Effects of St. John's Wort, Its Derivatives, and Other Hypericum Species in Hematologic Malignancies

Hypericum is a widely present plant, and extracts of its leaves, flowers, and aerial elements have been employed for many years as therapeutic cures for depression, skin wounds, and respiratory and inflammatory disorders. Hypericum also displays an ample variety of other biological actions, such as hypotensive, analgesic, anti-infective, anti-oxidant, and spasmolytic abilities. However, recent investigations highlighted that this species could be advantageous for the cure of other pathological situations, such as trigeminal neuralgia, as well as in the treatment of cancer. This review focuses on the in vitro and in vivo antitumor effects of St. John’s Wort (Hypericum perforatum), its derivatives, and other Hypericum species in hematologic malignancies. Hypericum induces apoptosis in both myeloid and lymphoid cells. Other Hypericum targets include matrix metalloproteinase-2, vascular endothelial growth factor, and matrix metalloproteinase-9, which are mediators of cell migration and angiogenesis. Hypericum also downregulates the expression of proteins that are involved in the resistance of leukemia cells to chemotherapeutic agents. Finally, Hypericum and its derivatives appear to have photodynamic effects and are candidates for applications in tumor photodynamic therapy. Although the in vitro studies appear promising, controlled in vivo studies are necessary before we can hypothesize the introduction of Hypericum and its derivatives into clinical practice for the treatment of hematologic malignancies.

Current and emerging molecular and epigenetic disease entities in acute myeloid leukemia and a critical assessment of their therapeutic modalities

Acute myeloid leukemia (AML) is the most frequently diagnosed acute leukemia, and its incidence increases with age. Although the etiology of AML remains unknown, exposure to genotoxic agents or some prior hematologic disorders could lead to the development of this condition. The pathogenesis of AML involves the development of malignant transformation of hematopoietic stem cells that undergo successive genomic alterations, ultimately giving rise to a full-blown disease. From the disease biology perspective, AML is considered to be extremely complex with significant genetic, epigenetic, and phenotypic variations. Molecular and cytogenetic alterations in AML include mutations in those subsets of genes that are involved in normal cell proliferation, maturation and survival, thus posing significant challenge to targeting these pathways without attendant toxicity. In addition, multiple malignant cells co-exist in the majority of AML patients. Individual subclones are characterized by unique genetic and epigenetic abnormalities, which contribute to the differences in their response to treatment. As a result, despite a dramatic progress in our understanding of the pathobiology of AML, not much has changed in therapeutic approaches to treat AML in the past four decades. Dose and regimen modifications with improved supportive care have contributed to improved outcomes by reducing toxicity-related side effects. Several drug candidates are currently being developed, including targeted small-molecule inhibitors, cytotoxic chemotherapies, monoclonal antibodies and epigenetic drugs. This review summarizes the current state of affairs in the pathobiological and therapeutic aspects of AML.

Molecular Bases of VEGFR-2-Mediated Physiological Function and Pathological Role

The vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) play crucial roles in vasculogenesis and angiogenesis. Angiogenesis is an important mechanism in many physiological and pathological processes, and is involved in endothelial cell proliferation, migration, and survival, then leads to further tubulogenesis, and finally promotes formation of vessels. This series of signaling cascade pathways are precisely mediated by VEGF/VEGFR-2 system. The VEGF binding to the IgD2 and IgD3 of VEGFR-2 induces the dimerization of the receptor, subsequently the activation and trans-autophosphorylation of the tyrosine kinase, and then the initiation of the intracellular signaling cascades. Finally the VEGF-activated VEGFR-2 stimulates and mediates variety of signaling transduction, biological responses, and pathological processes in angiogenesis. Several crucial phosphorylated sites Tyr801, Try951, Try1175, and Try1214 in the VEGFR-2 intracellular domains mediate several key signaling processes including PLCγ-PKC, TSAd-Src-PI3K-Akt, SHB-FAK-paxillin, SHB-PI3K-Akt, and NCK-p38-MAPKAPK2/3 pathways. Based on the molecular structure and signaling pathways of VEGFR-2, the strategy of the VEGFR-2-targeted therapy should be considered to employ in the treatment of the VEGF/VEGFR-2-associated diseases by blocking the VEGF/VEGFR-2 signaling pathway, inhibiting VEGF and VEGFR-2 gene expression, blocking the binding of VEGF and VEGFR-2, and preventing the proliferation, migration, and survival of vascular endothelial cells expressing VEGFR-2.

Old Player-New Tricks: Non Angiogenic Effects of the VEGF/VEGFR Pathway in Cancer

Angiogenesis has long been considered to facilitate and sustain cancer growth, making the introduction of anti-angiogenic agents that disrupt the vascular endothelial growth factor/receptor (VEGF/VEGFR) pathway an important milestone at the beginning of the 21st century. Originally research on VEGF signaling focused on its survival and mitogenic effects towards endothelial cells, with moderate so far success of anti-angiogenic therapy. However, VEGF can have multiple effects on additional cell types including immune and tumor cells, by directly influencing and promoting tumor cell survival, proliferation and invasion and contributing to an immunosuppressive microenvironment. In this review, we summarize the effects of the VEGF/VEGFR pathway on non-endothelial cells and the resulting implications of anti-angiogenic agents that include direct inhibition of tumor cell growth and immunostimulatory functions. Finally, we present how previously unappreciated studies on VEGF biology, that have demonstrated immunomodulatory properties and tumor regression by disrupting the VEGF/VEGFR pathway, now provide the scientific basis for new combinational treatments of immunotherapy with anti-angiogenic agents.

In Vitro Modeling of Non-Solid Tumors: How Far Can Tissue Engineering Go?

In hematological malignancies, leukemias or myelomas, malignant cells present bone marrow (BM) homing, in which the niche contributes to tumor development and drug resistance. BM architecture, cellular and molecular composition and interactions define differential microenvironments that govern cell fate under physiological and pathological conditions and serve as a reference for the native biological landscape to be replicated in engineered platforms attempting to reproduce blood cancer behavior. This review summarizes the different models used to efficiently reproduce certain aspects of BM in vitro; however, they still lack the complexity of this tissue, which is relevant for fundamental aspects such as drug resistance development in multiple myeloma. Extracellular matrix composition, material topography, vascularization, cellular composition or stemness vs. differentiation balance are discussed as variables that could be rationally defined in tissue engineering approaches for achieving more relevant in vitro models. Fully humanized platforms closely resembling natural interactions still remain challenging and the question of to what extent accurate tissue complexity reproduction is essential to reliably predict drug responses is controversial. However, the contributions of these approaches to the fundamental knowledge of non-solid tumor biology, its regulation by niches, and the advance of personalized medicine are unquestionable.

α4β1 integrin associates with VEGFR2 in CLL cells and contributes to VEGF binding and intracellular signaling

α4β1 integrin and VEGFR2 function as a receptor complex for VEGF in CLL cells. Contribution to VEGF functions in CLL is a novel pathological role for α4β1 integrin in this malignancy.

Location First: Targeting Acute Myeloid Leukemia Within Its Niche

Despite extensive research and development of new treatments, acute myeloid leukemia (AML)-backbone therapy has remained essentially unchanged over the last decades and is frequently associated with poor outcomes. Eradicating the leukemic stem cells (LSCs) is the ultimate challenge in the treatment of AML. Emerging evidence suggests that AML remodels the bone marrow (BM) niche into a leukemia-permissive microenvironment while suppressing normal hematopoiesis. The mechanism of stromal-mediated protection of leukemic cells in the BM is complex and involves many adhesion molecules, chemokines, and cytokines. Targeting these factors may represent a valuable approach to complement existing therapies and overcome microenvironment-mediated drug resistance. Some strategies for dislodging LSCs and leukemic blasts from their protective niche have already been tested in patients and are in different phases of the process of clinical development. Other strategies, such as targeting the stromal cells remodeling processes, remain at pre-clinical stages. Development of humanized xenograft mouse models, which overcome the mismatch between human leukemia cells and the mouse BM niche, is required to generate physiologically relevant, patient-specific human niches in mice that can be used to unravel the role of human AML microenvironment and to carry out preclinical studies for the development of new targeted therapies.

Bone marrow niches in haematological malignancies

Haematological malignancies were previously thought to be driven solely by genetic or epigenetic lesions within haematopoietic cells. However, the niches that maintain and regulate daily production of blood and immune cells are now increasingly being recognized as having an important role in the pathogenesis and chemoresistance of haematological malignancies. Within haematopoietic cells, the accumulation of a small number of recurrent mutations initiates malignancy. Concomitantly, specific alterations of the niches, which support haematopoietic stem cells and their progeny, can act as predisposition events, facilitating mutant haematopoietic cell survival and expansion as well as contributing to malignancy progression and providing protection of malignant cells from chemotherapy, ultimately leading to relapse. In this Perspective, we summarize our current understanding of the composition and function of the specialized haematopoietic niches of the bone marrow during health and disease. We discuss disease mechanisms (rather than malignancy subtypes) to provide a comprehensive description of key niche-associated pathways that are shared across multiple haematological malignancies. These mechanisms include primary driver mutations in bone marrow niche cells, changes associated with increased hypoxia, angiogenesis and inflammation as well as metabolic reprogramming by stromal niche cells. Consequently, remodelling of bone marrow niches can facilitate immune evasion and activation of survival pathways favouring malignant haematopoietic cell maintenance, defence against excessive reactive oxygen species and protection from chemotherapy. Lastly, we suggest guidelines for the handling and biobanking of patient samples and analysis of the niche to ensure that basic research identifying therapeutic targets can be more efficiently translated to the clinic. The hope is that integrating knowledge of how bone marrow niches contribute to haematological disease predisposition, initiation, progression and response to therapy into future clinical practice will likely improve the treatment of these disorders.

Expressions of vascular endothelial growth factor receptors, Flk1 and Flt1, in rat skin mast cells during development

Vascular endothelial growth factor-A (VEGF-A) is a principal regulator of hematopoiesis as well as angiogenesis. However, the functions of VEGF-A and its receptors (VEGFRs) in the differentiation of mast cells (MCs) in the skin remain unclear. The aim of this study was to determine the expression patterns of two VEGFRs (Flk1 and Flt1) in the skin MCs during development and maturation in rats. From the 17th days of embryonic development (E17) to 1 day after birth (Day 1), most of skin MCs were immature cells containing predominant alcian blue (AB)⁺ rather than safranin O (SO)⁺ granules (AB>SO MCs). AB>SO MC proportions gradually decreased, while mature AB<SO MC proportions increased from Day 7 to 28. Flk1⁺ MC proportions increased from E20 and reached to approximately 90% from Day 1 to 21, thereafter decreased to about 10% at Day 60 and 90. Flk1⁺ MC proportions changed almost in parallel with the numbers of MCs and Ki67⁺ MC proportions from E17 to Day 90. The proportions of MCs with both nuclear and cytoplasmic Flt1-immunoreactivity were markedly increased at Day 28, when the proportions of nuclear Flk1⁺, Ki67⁺, and AB>SO MCs had significantly decreased, and AB<SO MC proportions significantly increased. Considering that the main function of Flt1 is suppression of Flk1 effects, our results indicated that cross-talk between Flk1 and Flt1 regulates the proliferation and maturation of the skin MCs during late embryonic and neonatal development in rats.

Apatinib exhibits cytotoxicity toward leukemia cells by targeting VEGFR2-mediated prosurvival signaling and angiogenesis

OBJECTIVE

Vascular permeability contributes to disease progression and drug resistance in hematological malignancies, including AML. Thus, targeting angiogenic signaling is a promising treatment strategy, especially for relapsed and resistant AML. The aim of this study was to evaluate the efficacy of apatinib, a novel receptor tyrosine kinase inhibitor that selectively targets VEGFR2.

METHODS

Several AML cell lines were exposed to various concentrations of apatinib, and then CCK8 and Annexin V/PI assays were performed to determine IC50 values and apoptosis, respectively. The effect of apatinib against primary AML cells from 57 adult patients and 11 normal controls was also analyzed utilizing an apoptosis assay. Next, we tested the underlying mechanism of apatinib in AML using western blotting and mass cytometry (CyTOF). Finally, the activity of apatinib against tumor growth and angiogenesis was further evaluated in vivo in xenograft models.

RESULTS

We found apatinib significantly inhibited growth and promoted apoptosis in AML cell lines in vitro. Similarly, apatinib showed cytotoxicity against primary AML cells but didn't affect normal BMMCs. Its effect was highly correlated with several clinical features, such as NPM1 mutation, extramedullary infiltration, relapsed/refractory disease, and M2 and M5 FAB subtypes. In addition, apatinib suppressed AML growth and attenuated angiogenesis in xenograft models. Mechanistically, apatinib-induced cytotoxicity was closely associated with inhibition of the VEGFR2-mediated Src/STAT3 and AKT/mTOR pathways and induction of mitochondria-mediated apoptosis.

CONCLUSION

Apatinib exerts antileukemia effects by targeting VEGFR2-induced prosurvival signaling and angiogenesis, thus providing a rationale for the application of apatinib in AML.

Role of VEGFs/VEGFR-1 Signaling and its Inhibition in Modulating Tumor Invasion: Experimental Evidence in Different Metastatic Cancer Models

The vascular endothelial growth factor (VEGF) family members, VEGF-A, placenta growth factor (PlGF), and to a lesser extent VEGF-B, play an essential role in tumor-associated angiogenesis, tissue infiltration, and metastasis formation. Although VEGF-A can activate both VEGFR-1 and VEGFR-2 membrane receptors, PlGF and VEGF-B exclusively interact with VEGFR-1. Differently from VEGFR-2, which is involved both in physiological and pathological angiogenesis, in the adult VEGFR-1 is required only for pathological angiogenesis. Besides this role in tumor endothelium, ligand-mediated stimulation of VEGFR-1 expressed in tumor cells may directly induce cell chemotaxis and extracellular matrix invasion. Furthermore, VEGFR-1 activation in myeloid progenitors and tumor-associated macrophages favors cancer immune escape through the release of immunosuppressive cytokines. These properties have prompted a number of preclinical and clinical studies to analyze VEGFR-1 involvement in the metastatic process. The aim of the present review is to highlight the contribution of VEGFs/VEGFR-1 signaling in the progression of different tumor types and to provide an overview of the therapeutic approaches targeting VEGFR-1 currently under investigation.

Angiocrine endothelium: from physiology to cancer

The concept of cancer as a cell-autonomous disease has been challenged by the wealth of knowledge gathered in the past decades on the importance of tumor microenvironment (TM) in cancer progression and metastasis. The significance of endothelial cells (ECs) in this scenario was initially attributed to their role in vasculogenesis and angiogenesis that is critical for tumor initiation and growth. Nevertheless, the identification of endothelial-derived angiocrine factors illustrated an alternative non-angiogenic function of ECs contributing to both physiological and pathological tissue development. Gene expression profiling studies have demonstrated distinctive expression patterns in tumor-associated endothelial cells that imply a bilateral crosstalk between tumor and its endothelium. Recently, some of the molecular determinants of this reciprocal interaction have been identified which are considered as potential targets for developing novel anti-angiocrine therapeutic strategies.

Binding and Structural Properties of DNA Aptamers with VEGF-A-Mimic Activity

Vascular endothelial growth factors (VEGFs) are hypoxia-inducible secreted proteins to promote angiogenesis, in which VEGF-A is an important molecule that binds and activates VEGF receptor-1 (VEGFR-1) and VEGFR-2. In this study, two DNA aptamers, Apt01 and Apt02, were successfully isolated by alternating consecutive systematic evolution of ligands by exponential enrichment (SELEX) against VEGFR-1 and -2 using deep sequencing analysis in an early selection round. Their binding affinities for VEGFR-2 were lower than that of VEGFR-1, which is similar to that of VEGF-A. Structural analyses with the measurements of circular dichroism spectra and ultraviolet melting curve showed that Apt01 possessed the stem-loop structure in the molecule, whereas Apt02 formed G-quadruplex structures. In addition, Apt02 accelerated a tube formation of human umbilical vein endothelial cells faster than Apt01, which was affected by difference of binding affinity and nuclease resistance due to G-quadruplex structures. These results demonstrated that Apt02 might have a potential to function as an alternative to VEGF-A.

Novel human Ab against vascular endothelial growth factor receptor 2 shows therapeutic potential for leukemia and prostate cancer

Vascular endothelial growth factor receptor 2 (VEGFR2) is highly expressed in tumor‐associated endothelial cells, where it modulates tumor‐promoting angiogenesis, and it is also found on the surface of tumor cells. Currently, there are no Ab therapeutics targeting VEGFR2 approved for the treatment of prostate cancer or leukemia. Therefore, development of novel efficacious anti‐VEGFR2 Abs will benefit cancer patients. We used the Institute of Cellular and Organismic Biology human Ab library and affinity maturation to develop a fully human Ab, anti‐VEGFR2‐AF, which shows excellent VEGFR2 binding activity. Anti‐VEGFR2‐AF bound Ig‐like domain 3 of VEGFR2 extracellular region to disrupt the interaction between VEGF‐A and VEGFR2, neutralizing downstream signaling of the receptor. Moreover, anti‐VEGFR2‐AF inhibited capillary structure formation and exerted Ab‐dependent cell‐mediated cytotoxicity and complement‐dependent cytotoxicity in vitro. We found that VEGFR2 is expressed in PC‐3 human prostate cancer cell line and associated with malignancy and metastasis of human prostate cancer. In a PC‐3 xenograft mouse model, treatment with anti‐VEGFR2‐AF repressed tumor growth and angiogenesis as effectively and safely as US FDA‐approved anti‐VEGFR2 therapeutic, ramucirumab. We also report for the first time that addition of anti‐VEGFR2 Ab can enhance the efficacy of docetaxel in the treatment of a prostate cancer mouse model. In HL‐60 human leukemia‐xenografted mice, anti‐VEGFR2‐AF showed better efficacy than ramucirumab with prolonged survival and reduced metastasis of leukemia cells to ovaries and lymph nodes. Our findings suggest that anti‐VEGFR2‐AF has strong potential as a cancer therapy that could directly target VEGFR2‐expressing tumor cells in addition to its anti‐angiogenic action.

Effects of vascular endothelial growth factor and epidermal growth factor on biological properties of gastric cancer cells

INTRODUCTION

The exfoliation of exfoliative cells from gastric serosa into the peritoneum is the main cause of peritoneal metastasis, which is the most common form of postoperative recurrence in gastric cancer. This study investigates the effects of vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF) on the biological properties of gastric cancer cells.

MATERIAL AND METHODS

mRNA expression of VEGF and EGF in gastric cancer tissues from 80 patients suffering from serosa-infiltrated gastric cancer (T₃) was examined. The differences of proliferation, movement, adhesion and invasion among 4 gastric cancer cell lines were analysed. The mRNA expression of EGF, EGFR, VEGF and VEGFR in the gastric cancer cell lines was examined before and after adding endostatin (Endostar) or cetuximab (Erbitux) to observe changes of gastric cancer cells.

RESULTS

mRNA levels of EGF and VEGF in positive exfoliative cytology cases were significantly higher than negative cases (p < 0.05). The biological properties were reduced sequentially in MGC803, HGC27, BGC823 and SGC7901 (p < 0.05). The mRNA expression of EGF, EGFR, VEGF and VEGFR was the strongest in MGC803, but was attenuated significantly after treatment (p < 0.05).

CONCLUSIONS

Lower survival was related to positive exfoliative cytology, lymphatic node metastasis, serosa-infiltrated and poorly differentiated gastric cancer. The expression of VEGF and EGF was correlated with the properties of gastric cancer cells. Specific inhibition of VEGF and EGF may impair the biological properties of gastric cancer cells in vitro.

Dynamins 2 and 3 control the migration of human megakaryocytes by regulating CXCR4 surface expression and ITGB1 activity

Megakaryocyte (MK) migration from the bone marrow periosteal niche toward the vascular niche is a prerequisite for proplatelet extension and release into the circulation. The mechanism for this highly coordinated process is poorly understood. Here we show that dynasore (DNSR), a small-molecule inhibitor of dynamins (DNMs), or short hairpin RNA knockdown of DNM2 and DNM3 impairs directional migration in a human MK cell line or MKs derived from cultured CD34⁺ cells. Because cell migration requires actin cytoskeletal rearrangements, we measured actin polymerization and the activity of cytoskeleton regulator RhoA and found them to be decreased after inhibition of DNM2 and DNM3. Because SDF-1α is important for hematopoiesis, we studied the expression of its receptor CXCR4 in DNSR-treated cells. CXCR4 expression on the cell surface was increased, at least partially because of slower endocytosis and internalization after SDF-1α treatment. Combined inhibition of DNM2 and DNM3 or forced expression of dominant-negative Dnm2-K44A or GTPase-defective DNM3 diminished β1 integrin (ITGB1) activity. DNSR-treated MKs showed an abnormally clustered staining pattern of Rab11, a marker of recycling endosomes. This suggests decreased recruitment of the recycling pathway in DNSR-treated cells. Altogether, we show that the GTPase activity of DNMs, which governs endocytosis and regulates cell receptor trafficking, exerts control on MK migration toward SDF-1α gradients, such as those originating from the vascular niche. DNMs play a critical role in MKs by triggering membrane-cytoskeleton rearrangements downstream of CXCR4 and integrins.

LINC00628 suppresses migration and invasion of hepatocellular carcinoma by its conserved region interacting with the promoter of VEGFA

Accumulated evidence revealed that numerous long noncoding RNAs (lncRNAs) have been found to be involved in the development and progression of hepatocellular carcinoma (HCC). LINC00628, a member of lncRNAs, has been reported to act as a tumor suppressor in gastric cancer and breast cancer. However, its potential role in HCC still remains unknown. Herein, we characterized the function of LINC00628 in HCC. Our investigation has revealed that LINC00628 were dramatically decreased in HCC tissues and cells, and inhibited the migration and invasion of HCC cells in vitro and in vivo. Moreover, LINC00628 exerted its tumor suppressive function by repressing the vascular endothelial growth factor A (VEGFA) promoter activity. A highly conserved region element in LINC00628 was identified by a cross-species comparative analysis, which is required for LINC00628 exerted its function. Dual-luciferase reporter assay showed that the conserved sequence mediated the interaction with a specific region of VEGFA promoter, resulting in a decrease of VEGFA expression. In conclusion, our results demonstrated that LINC00628 could function as a tumor suppressor in HCC via its conserved sequence elements interacting with a particular region of VEGFA promoter, suggesting that LINC00628 may serve as a novel promising target for diagnosis and therapy in HCC.

Targeting Leukemia Stem Cell-Niche Dynamics: A New Challenge in AML Treatment

One of the most urgent needs in AML is to improve the disease cure rate as relapse still occurs in 60–80% of patients. Recent evidence suggests that dismal clinical outcomes may be improved by a better definition of the tight interaction between the AML cell population and the bone marrow (BM) microenvironment (“the niche”); the latter has been progressively highlighted to have an active role in the disease process. It has now been well established that the leukemic population may misinterpret niche-derived signals and remodel the niche, providing a shelter to AML cells and protecting them from the cytotoxic effects of chemoradiotherapy. Novel imaging technological advances and preclinical disease models have revealed that, due to the finite number of BM niches, leukemic stem cells (LSCs) and normal hematopoietic stem cells (HSCs) compete for the same functional areas. Thus, the removal of LSCs from the BM niche and the promotion of normal HSC engraftment should be the primary goals in antileukemic research. In addition, it is now becoming increasingly clear that AML-niche dynamics are disease stage specific. In AML, the niche has been linked to disease pathogenesis in the preleukemic stage, the niche becomes permissive once leukemic cells are established, and the niche is transformed into a self-reinforcing structure at a later disease stage. These concepts have been fostered by the demonstration that, in unrelated AML types, endosteal vessel loss occurs as a primary AML-induced niche alteration, and additional AML-induced alterations of the niche and normal hematopoiesis evolve focally and in parallel. Obviously, this endosteal vessel loss plays a fundamental role in AML pathogenesis by causing excessive vascular permeability, hypoxia, altered perfusion, and reduced drug delivery. Each of these alterations may be effectively targeted by various therapeutic procedures, but preservation of endosteal vessel integrity might be the best option for any future antileukemic treatment.

Promotion of angiogenesis by M13 phage and RGD peptide in vitro and in vivo

One of the most important goals of regenerative medicines is to generate alternative tissues with a developed vascular network. Endothelial cells are the most important cell type required in angiogenesis process, contributing to the blood vessels formation. The stimulation of endothelial cells to initiate angiogenesis requires appropriate extrinsic signals. The aim of this study was to evaluate the effects of M13 phage along with RGD peptide motif on in vitro and in vivo vascularization. The obtained results demonstrated the increased cellular proliferation, HUVECs migration, cells altered morphology, and cells attachment to M13 phage-RGD coated surface. In addition, the expression of Vascular Endothelial Growth Factor A (VEGF-A), VEGF Receptors 2 and 3, Matrix Metalloproteinase 9 (MMP9), and epithelial nitric oxide synthase (eNOS) transcripts were significantly upregulated due to the HUVECs culturing on M13 phage-RGD coated surface. Furthermore, VEGF protein secretion, nitric oxide, and reactive oxygen species (ROS) production were significantly increased in cells cultured on M13 phage-RGD coated surface.

Overexpression of heme oxygenase-1 in microenvironment mediates vincristine resistance of B-cell acute lymphoblastic leukemia by promoting vascular endothelial growth factor secretion

Chemoresistance often causes treatment failure of B-cell acute lymphoblastic leukemia (B-ALL). However, the mechanism remains unclear at present. Herein, overexpression of heme oxygenase-1 (HO-1) was found in the bone marrow stromal cells (BMSCs) from B-ALL patients developing resistance to vincristine (VCR), a chemotherapeutic agent. Two B-ALL cell lines Super B15 and CCRF-SB were cocultured with BMSCs transfected with lentivirus to regulate the expression of HO-1. Silencing HO-1 expression in BMSCs increased the apoptotic rates of B-ALL cell lines induced by VCR, whereas upregulating HO-1 expression reduced the rate. Cell cycle can be arrested in the G2/M phase by VCR. In contrast, B-ALL cells were arrested in the G0/G1 phase due to HO-1 overexpression in BMSCs, which avoided damage from the G2/M phase. Vascular endothelial growth factor (VEGF) in BMSCs, as a key factor in the microenvironment-associated chemoresistance, was also positively coexpressed with HO-1. VEGF secretion was markedly increased in BMSCs with HO-1 upregulation but decreased in BMSCs with HO-1 silencing. B-ALL cell lines became resistant to VCR when cultured with VEGF recombinant protein, so VEGF secretion induced by HO-1 expression may promote the VCR resistance of B-ALL cells. As to the molecular mechanism, the PI3K/AKT pathway mediated regulation of VEGF by HO-1. In conclusion, this study clarifies a mechanism by which B-ALL is induced to resist VCR through HO-1 overexpression in BMSCs, and provides a novel strategy for overcoming VCR resistance in clinical practice.

The neuropeptide receptor calcitonin receptor-like (CALCRL) is a potential therapeutic target in acute myeloid leukemia

Calcitonin receptor-like (CALCRL) is a G-protein-coupled neuropeptide receptor involved in the regulation of blood pressure, angiogenesis, cell proliferation, and apoptosis, and is currently emerging as a novel target for the treatment of migraine. This study characterizes the role of CALCRL in acute myeloid leukemia (AML). We analyzed CALCRL expression in collectively more than 1500 well-characterized AML patients from five international cohorts (AMLCG, HOVON, TCGA, Leucegene, and UKM) and evaluated associations with survival. In the AMLCG analytic cohort, increasing transcript levels of CALCRL were associated with decreasing complete remission rates (71.5%, 53.7%, 49.6% for low, intermediate, high CALCRL expression), 5-year overall (43.1%, 26.2%, 7.1%), and event-free survival (29.9%, 15.8%, 4.7%) (all P < 0.001). CALCRL levels remained associated with all endpoints on multivariable regression analyses. The prognostic impact was confirmed in all validation sets. Genes highly expressed in CALCRL^high AML were significantly enriched in leukemic stem cell signatures and CALCRL levels were positively linked to the engraftment capacity of primary patient samples in immunocompromised mice. CRISPR-Cas9-mediated knockout of CALCRL significantly impaired colony formation in human myeloid leukemia cell lines. Overall, our study demonstrates that CALCRL predicts outcome beyond existing risk factors and is a potential therapeutic target in AML.

Stress and catecholamines modulate the bone marrow microenvironment to promote tumorigenesis

High vascularization and locally secreted factors make the bone marrow (BM) microenvironment particularly hospitable for tumor cells and bones to a preferred metastatic site for disseminated cancer cells of different origins. Cancer cell homing and proliferation in the BM are amongst other regulated by complex interactions with BM niche cells (e.g. osteoblasts, endothelial cells and mesenchymal stromal cells (MSCs)), resident hematopoietic stem and progenitor cells (HSPCs) and pro-angiogenic cytokines leading to enhanced BM microvessel densities during malignant progression. Stress and catecholamine neurotransmitters released in response to activation of the sympathetic nervous system (SNS) reportedly modulate various BM cells and may thereby influence cancer progression. Here we review the role of catecholamines during tumorigenesis with particular focus on pro-tumorigenic effects mediated by the BM niche.

Hematopoietic niche drives FLT3-ITD acute myeloid leukemia resistance to quizartinib via STAT5-and hypoxia-dependent upregulation of AXL

Internal tandem duplication in Fms-like tyrosine kinase 3 (FLT3-ITD) is the most frequent mutation observed in acute myeloid leukemia (AML) and correlates with poor prognosis. FLT3 tyrosine kinase inhibitors are promising for targeted therapy. Here, we investigated mechanisms dampening the response to the FLT3 inhibitor quizartinib, which is specific to the hematopoietic niche. Using AML primary samples and cell lines, we demonstrate that convergent signals from the hematopoietic microenvironment drive FLT3-ITD cell resistance to quizartinib through the expression and activation of the tyrosine kinase receptor AXL. Indeed, cytokines sustained phosphorylation of the transcription factor STAT5 in quizartinib-treated cells, which enhanced AXL expression by direct binding of a conserved motif in its genomic sequence. Likewise, hypoxia, another well-known hematopoietic niche hallmark, also enhanced AXL expression. Finally, in a xenograft mouse model, inhibition of AXL significantly increased the response of FLT3-ITD cells to quizartinib exclusively within a bone marrow environment. These data highlight a new bypass mechanism specific to the hematopoietic niche that hampers the response to quizartinib through combined upregulation of AXL activity. Targeting this signaling offers the prospect of a new therapy to eradicate resistant FLT3-ITD leukemic cells hidden within their specific microenvironment, thereby preventing relapses from FLT3-ITD clones.

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.

Hematopoiesis and microenvironment in hematological malignancies

Adult hematopoietic stem cells (HSCs) and progenitors (HPCs) reside in the bone marrow, a highly orchestrated architecture. In the bone marrow, the process of how HSCs exert self-renewal and differentiation is tightly regulated by the surrounding microenvironment, or niche. Recent advances in imaging technologies and numerous knockout or knockin mouse models have greatly improved our understanding of the organization of the bone marrow niche. This niche compartment includes a complex network of mesenchymal stem cells (MSC), osteolineage cells, endothelial cells (arterioles and sinusoids), sympathetic nerves, nonmyelinating Schwann cells and megakaryocytes. In addition, different types of mediators, such as cytokines/chemokines, reactive oxygen species (ROS) and exosomes play a pivotal role in regulating the function of hematopoietic cells. Therefore, the niche components and the hematopoietic system make up an ecological environment that maintains the homeostasis and responds to stress, damage or disease conditions. On the other hand, the niche compartment can become a traitor that can do harm to normal hematopoietic cells under pathological conditions. Studies on the diseased bone marrow niche have only recently begun to appear in the extant literature. In this short review, we discuss the most recent advances regarding the behaviors of normal hematopoietic cells and their niche alterations in hematological malignancies.

Effect of High VEGF-C mRNA Expression on Achievement of Complete Remission in Adult Acute Myeloid Leukemia

Although vascular endothelial growth factor-C (VEGF-C) is known to be expressed in acute myeloid leukemia (AML) blasts, the relevance of VEGF-C in the clinical setting remains to be fully explored. We examined the effect of VEGF-C on achievement of complete remission (CR) in adult de novo AML and immune cell population profiles according to VEGF-C mRNA expression. In comparison of VEGF-C expression between the no-CR and CR groups, the CR group showed a trend toward higher levels of plasma VEGF-C (P = .088), whereas mRNA expression of VEGF-C was downregulated (P = .008). Next, patients with continuous data for VEGF-C were divided into two groups (low vs. high) by a ROC curve analysis. The low- versus high-level groups for plasma VEGF-C (RR of 0.20, P = .030), mRNA expression of VEGF-C (RR of 18.75, P = .003), and the ratio of plasma level to mRNA expression (RR of 0.05, P = .007) were potential predictors of CR on univariate analysis. After adjusting for potential clinical factors including genetic group, multivariate analyses revealed that high VEGF-C mRNA expression was an independent risk factor for failure of induction chemotherapy. Furthermore, patients with high VEGF-C mRNA expression had a lower frequency of NKT and CD8+ cells and showed a trend for a lower frequency of NK cells. These results suggest that interruption of VEGF-C signaling might be a potential therapeutic target for antileukemic treatment in AML patients.

Vascular Endothelial Growth Factor-A Exerts Diverse Cellular Effects via Small G Proteins, Rho and Rap

Vascular endothelial growth factors (VEGFs) include five molecules (VEGF-A, -B, -C, -D, and placental growth factor), and have various roles that crucially regulate cellular functions in many kinds of cells and tissues. Intracellular signal transduction induced by VEGFs has been extensively studied and is usually initiated by their binding to two classes of transmembrane receptors: receptor tyrosine kinase VEGF receptors (VEGF receptor-1, -2 and -3) and neuropilins (NRP1 and NRP2). In addition to many established results reported by other research groups, we have previously identified small G proteins, especially Ras homologue gene (Rho) and Ras-related protein (Rap), as important mediators of VEGF-A-stimulated signaling in cancer cells as well as endothelial cells. This review article describes the VEGF-A-induced signaling pathways underlying diverse cellular functions, including cell proliferation, migration, and angiogenesis, and the involvement of Rho, Rap, and their related molecules in these pathways.

A vicious loop of fatty acid-binding protein 4 and DNA methyltransferase 1 promotes acute myeloid leukemia and acts as a therapeutic target

Aberrant DNA methylation mediated by deregulation of DNA methyltransferases (DNMT) is a key hallmark of acute myeloid leukemia (AML), yet efforts to target DNMT deregulation for drug development have lagged. We previously demonstrated that upregulation of fatty acid-binding protein 4 (FABP4) promotes AML aggressiveness through enhanced DNMT1-dependent DNA methylation. Here, we demonstrate that FABP4 upregulation in AML cells occurs through vascular endothelial growth factor (VEGF) signaling, thus elucidating a crucial FABP4-DNMT1 regulatory feedback loop in AML biology. We show that FABP4 dysfunction by its selective inhibitor BMS309403 leads to downregulation of DNMT1, decrease of global DNA methylation and re-expression of p15INK4B tumor suppressor gene by promoter DNA hypomethylation in vitro, ex vivo and in vivo. Functionally, BMS309403 suppresses cell colony formation, induces cell differentiation, and, importantly, impairs leukemic disease progression in mouse models of leukemia. Our findings highlight AML-promoting properties of the FABP4-DNMT1 vicious loop, and identify an attractive class of therapeutic agents with a high potential for clinical use in AML patients. The results will also assist in establishing the FABP4-DNMT1 loop as a target for therapeutic discovery to enhance the index of current epigenetic therapies.

Bone marrow VEGFC expression is associated with multilineage dysplasia and several prognostic markers in adult acute myeloid leukemia, but not with survival

Vascular endothelial growth factor C (VEGFC) stimulates leukemia cell proliferation and survival, and promotes angiogenesis. We studied VEGFC expression in bone marrow samples from 353 adult acute myeloid leukemia (AML) patients and its relationship with several clinical, cytogenetic, and molecular variables. We also studied the expression of 84 genes involved in VEGF signaling in 24 patients. We found that VEGFC expression was higher in AML patients with myelodysplasia-related changes (AML-MRC) than in patients with non-AML-MRC. We also found an association between VEGFC expression and the patient cytogenetic risk group, with those with a worse prognosis having higher VEGFC expression levels. No correlation was observed between VEGFC expression and survival or complete remission. VEGFC expression strongly correlated with expression of the VEGF receptors FLT1, KDR, and NRP1. Thus, in this series, VEGFC expression was increased in AML-MRC and in subgroups with a poorer prognosis, but has no impact on survival.

Antitumor effects of Tubeimoside-1 in NCI-H1299 cells are mediated by microRNA-126-5p-induced inactivation of VEGF-A/VEGFR-2/ERK signaling pathway

Tubeimoside-1 (TBMS1), a triterpenoid saponin isolated from the tuber of Bolbostemma paniculatum (Maxim) Franquet, serves an universal suppressive role in multiple cancer types, including lung cancer. However, the mechanism involved in non-small cell lung cancer (NSCLC) cells by which TBMS1 elicits its antitumor effects is not yet completely understood. The present study indicated that 10 µmol/l TBMS1 significantly enhanced apoptosis and notably blocked the migration and invasion of NCI-H1299 cells. These effects were reversed following transfection with miR-126-5p inhibitor into TBMS1-treated NCI-H1299 cells. Vascular endothelial growth factor-A (VEGF-A) is a target gene for miR-126-5p. Notably, results suggested that the downregulated VEGF-A and VEGFR-2 in TBMS1-treated NCI-H1299 cells were upregulated after inhibiting miR-126-5p, and overexpression of VEGF-A or VEGFR-2 could significantly reduce apoptosis and promote the migration and invasion of TBMS1-treated NCI-H1299 cells. Furthermore, TBMS1 combined with TBHQ (an ERK activator) dramatically suppressed TBMS1-induced apoptosis and stimulated TBMS1-reduced migration and invasion in NCI-H1299 cells, suggesting that TBMS1 inhibits the ERK signaling pathway and represses the growth and metastasis of NCI-H1299 cells. Further study demonstrated that either inhibiting miR-126-5p or overexpressing VEGF-A and VEGFR-2 in TBMS1-treated NCI-H1299 cells elevated the mRNA expression levels and phosphorylation levels of MEK1, as well as ERK. To conclude, TBMS1 increases miR-126-5p expression, whereas overexpressing miR-126-5p inactivates VEGF-A/VEGFR-2/ERK signaling pathway, which ultimately actuates the pro-apoptotic and anti-metastatic effects in NCI-H1299 cells. Therefore, the present findings provide a theoretical foundation for TBMS1 as a potential candidate in NSCLC treatment.

LW-215, a newly synthesized flavonoid, exhibits potent anti-angiogenic activity in vitro and in vivo

LW-215 is a newly synthesized flavonoid, which is the derivative of wogonin. Our group has previously confirmed that wogonin has an anti-angiogenic activity, while the anti-angiogenic effect of LW-215 is unclear. In this study, we explored whether LW-215 can inhibit angiogenesis and further probed the potential molecular mechanisms. We found that LW-215 inhibited migration and tube formation in human umbilical vein endothelial cells (HUVECs) and immortalized endothelial EA.hy926 cells without a significant decrease in cell viability. Microvessels sprouting from rat aortic ring and chicken chorioallantoic membrane (CAM) model also revealed that LW-215 could suppress angiogenesis in vivo. Western blot and ELISA analysis indicated that LW-215 could prevent VEGFR2 activation though reducing VEGF autocrine other than VEGFR1. Thus, its downstream kinases, such as Akt, ERK and p38 signaling, were inhibited. Taken together, these results fully showed that LW-215 might be a promising anti-angiogenesis agent.

VEGFR2-Mediated Reprogramming of Mitochondrial Metabolism Regulates the Sensitivity of Acute Myeloid Leukemia to Chemotherapy

Metabolic reprogramming is central to tumorigenesis, but whether chemotherapy induces metabolic features promoting recurrence remains unknown. We established a mouse xenograft model of human acute myeloid leukemia (AML) that enabled chemotherapy-induced regressions of established disease followed by lethal regrowth of more aggressive tumor cells. Human AML cells from terminally ill mice treated with chemotherapy (chemoAML) had higher lipid content, increased lactate production and ATP levels, reduced expression of peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), and fewer mitochondria than controls from untreated AML animals. These changes were linked to increased VEGFR2 signaling that counteracted chemotherapy-driven cell death; blocking of VEGFR2 sensitized chemoAML to chemotherapy (re-)treatment and induced a mitochondrial biogenesis program with increased mitochondrial mass and oxidative stress. Accordingly, depletion of PGC-1α in chemoAML cells abolished such induction of mitochondrial metabolism and chemosensitization in response to VEGFR2 inhibition. Collectively, this reveals a mitochondrial metabolic vulnerability with potential therapeutic applications against chemotherapy-resistant AML.Significance: These findings reveal a mitochondrial metabolic vulnerability that might be exploited to kill chemotherapy-resistant acute myeloid leukemia cells. Cancer Res; 78(3); 731-41. ©2017 AACR.

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.