Regulation of the acute myeloid leukemia cell line OCI/AML-2 by endothelial nitric oxide synthase under the control of a vascular endothelial growth factor signaling system

Review: The PI3K-AKT-mTOR signal transduction pathway in canine cancer

Tumors in dogs and humans share many similar molecular and genetic features, incentivizing a better understanding of canine neoplasms not only for the purpose of treating companion animals, but also to facilitate research of spontaneously developing tumors with similar biologic behavior and treatment approaches in an immunologically competent animal model. Multiple tumor types of both species have similar dysregulation of signal transduction through phosphatidylinositol 3-kinase (PI3K), protein kinase B (PKB; AKT), and mechanistic target of rapamycin (mTOR), collectively known as the PI3K-AKT-mTOR pathway. This review aims to delineate the pertinent aspects of the PI3K-AKT-mTOR signaling pathway in health and in tumor development. It will then present a synopsis of current understanding of PI3K-AKT-mTOR signaling in important canine cancers and advancements in targeted inhibitors of this pathway.

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.

Control of Tumor Progression by Angiocrine Factors

Tumor progression, therapy resistance and metastasis are profoundly controlled by the tumor microenvironment. The contribution of endothelial cells to tumor progression was initially only attributed to the formation of new blood vessels (angiogenesis). Research in the last decade has revealed however that endothelial cells control their microenvironment through the expression of membrane-bound and secreted factors. Such angiocrine functions are frequently hijacked by cancer cells, which deregulate the signaling pathways controlling the expression of angiocrine factors. Here, we review the crosstalk between cancer cells and endothelial cells and how this contributes to the cancer stem cell phenotype, epithelial to mesenchymal transition, immunosuppression, remodeling of the extracellular matrix and intravasation of cancer cells into the bloodstream. We also address the long-distance crosstalk of a primary tumor with endothelial cells at the pre-metastatic niche and how this contributes to metastasis.

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.

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.

Tissue-specific endothelial cells: a promising approach for augmentation of soft tissue repair in orthopedics

Biologics are playing an increasingly significant role in the practice of modern medicine and surgery in general and orthopedics in particular. Cell-based approaches are among the most important and widely used modalities in orthopedic biologics, with mesenchymal stem cells and other multi/pluripotent cells undergoing evaluation in numerous preclinical and clinical studies. On the other hand, fully differentiated endothelial cells (ECs) have been found to perform critical roles in homeostasis of visceral tissues through production of an adaptive panel of so-called "angiocrine factors." This newly discovered function of ECs renders them excellent candidates for novel approaches in cell-based biologics. Here, we present a review of the role of ECs and angiocrine factors in some visceral tissues, followed by an overview of current cell-based approaches and a discussion of the potential applications of ECs in soft tissue repair.

Cellular and plasma nitrite levels in myeloid leukemia: a pathogenetic decrease

Nitric oxide (NO) has a contributory role in hemopoietic cell growth and differentiation. The effects of NO on leukemic cell growth have been predominantly studied inin vitrosettings. This study was done to assess the alterations in nitrite level in myeloid leukemias. Thirty-six newly diagnosed cases of myeloid leukemia (16 AML and 20 CML) were enrolled in the study. Neutrophil precursors from the marrow aspirate and peripheral blood were separated into cell bands using the Percoll density gradient method of Borregard and Cowland. The blood plasma and marrow fluid was also collected. Nitrite (stable non-volatile end product of NO) was estimated in the cell bands, blood plasma and marrow fluid using Griess reagent. The mean nitrite level in all cell bands from peripheral blood, bone marrow, blood plasma, and marrow fluid of cases was significantly lower as compared to corresponding value in the controls. No significant difference between AML and CML was seen. On follow-up, analysis of 13 CML patients higher nitrite levels were seen (p>0.05). The significant decrease in nitrite levels in myeloid leukemia suggests a decrease in nitric oxide synthase (NOS) activity. Further work may unfold molecular targets for therapeutic role of NO modulators.

Fine-Tuning Tumor Endothelial Cells to Selectively Kill Cancer

Tumor endothelial cells regulate several aspects of tumor biology, from delivering oxygen and nutrients to shaping the immune response against a tumor and providing a barrier against tumor cell dissemination. Accordingly, targeting tumor endothelial cells represents an important modality in cancer therapy. Whereas initial anti-angiogenic treatments focused mainly on blocking the formation of new blood vessels in cancer, emerging strategies are specifically influencing certain aspects of tumor endothelial cells. For instance, efforts are generated to normalize tumor blood vessels in order to improve tumor perfusion and ameliorate the outcome of chemo-, radio-, and immunotherapy. In addition, treatment options that enhance the properties of tumor blood vessels that support a host’s anti-tumor immune response are being explored. Hence, upcoming anti-angiogenic strategies will shape some specific aspects of the tumor blood vessels that are no longer limited to abrogating angiogenesis. In this review, we enumerate approaches that target tumor endothelial cells to provide anti-cancer benefits and discuss their therapeutic potential.

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.

Signaling and molecular basis of bone marrow niche angiogenesis in leukemia

Angiogenesis, the process of blood vessel formation, is necessary for tissue survival in normal and pathologic conditions. Increased angiogenesis in BM niche is correlated with leukemia progression and resistance to treatment. Angiogenesis can interfere with disease progression and several angiogenic (such as vascular growth factors) as well as anti-angiogenic factors (i.e. angiostatin) can affect angiogenesis. Furthermore, miRs can affect the angiogenic process by inhibiting angiogenesis or increasing the expression of growth factors. Given the importance of angiogenesis in BM for maintenance of leukemic clones, recognition of angiogenic and anti-angiogenic factors and miRs as well as drug resistance mechanisms of leukemic blasts can improve the therapeutic strategies. We highlight the changes in angiogenic balance within the BM niche in different leukemia types. Moreover, we explored the pathways leading to drug resistance in relation to angiogenesis and attempted to assign interesting candidates for future research.

NSK-01105, a novel sorafenib derivative, inhibits human prostate tumor growth via suppression of VEGFR2/EGFR-mediated angiogenesis

The purpose of this study is to investigate the anti-angiogenic activities of NSK-01105, a novel sorafenib derivative, in in vitro, ex vivo and in vivo models, and explore the potential mechanisms. NSK-01105 significantly inhibited vascular endothelial growth factor (VEGF)-induced migration and tube formation of human umbilical vein endothelial cells at non-cytotoxic concentrations as shown by wound-healing, transwell migration and endothelial cell tube formation assays, respectively. Cell viability and invasion of LNCaP and PC-3 cells were significantly inhibited by cytotoxicity assay and matrigel invasion assay. Furthermore, NSK-01105 also inhibited ex vivo angiogenesis in matrigel plug assay. Western blot analysis showed that NSK-01105 down-regulated VEGF-induced phosphorylation of VEGF receptor 2 (VEGFR2) and the activation of epidermal growth factor receptor (EGFR). Tumor volumes were significantly reduced by NSK-01105 at 60 mg/kg/day in both xenograft models. Immunohistochemical staining demonstrated a close association between inhibition of tumor growth and neovascularization. Collectively, our results suggest a role of NSK-01105 in treatment for human prostate tumors, and one of the potential mechanisms may be attributed to anti-angiogenic activities.

Postnatal hyperoxia exposure differentially affects hepatocytes and liver haemopoietic cells in newborn rats

Premature newborns are frequently exposed to hyperoxic conditions and experimental data indicate modulation of liver metabolism by hyperoxia in the first postnatal period. Conversely, nothing is known about possible modulation of growth factors and signaling molecules involved in other hyperoxic responses and no data are available about the effects of hyperoxia in postnatal liver haematopoiesis. The aim of the study was to analyse the effects of hyperoxia in the liver tissue (hepatocytes and haemopoietic cells) and to investigate possible changes in the expression of Vascular Endothelial Growth Factor (VEGF), Matrix Metalloproteinase 9 (MMP-9), Hypoxia-Inducible Factor-1α (HIF-1α), endothelial Nitric Oxide Synthase (eNOS), and Nuclear Factor-kB (NF-kB). Experimental design of the study involved exposure of newborn rats to room air (controls), 60% O₂ (moderate hyperoxia), or 95% O₂ (severe hyperoxia) for the first two postnatal weeks. Immunohistochemical and Western blot analyses were performed. Severe hyperoxia increased hepatocyte apoptosis and MMP-9 expression and decreased VEGF expression. Reduced content in reticular fibers was found in moderate and severe hyperoxia. Some other changes were specifically produced in hepatocytes by moderate hyperoxia, i.e., upregulation of HIF-1α and downregulation of eNOS and NF-kB. Postnatal severe hyperoxia exposure increased liver haemopoiesis and upregulated the expression of VEGF (both moderate and severe hyperoxia) and eNOS (severe hyperoxia) in haemopoietic cells. In conclusion, our study showed different effects of hyperoxia on hepatocytes and haemopoietic cells and differential involvement of the above factors. The involvement of VEGF and eNOS in the liver haemopoietic response to hyperoxia may be hypothesized.

Molecular pathways: not a simple tube--the many functions of blood vessels

Although the ability of blood vessels to carry fluid and cells through neoplastic tissue is clearly important, other functions of vascular elements that drive tumor growth and progression are increasingly being recognized. Vessels can provide physical support and help regulate the stromal microenvironment within tumors, form niches for tumor-associated stem cells, serve as avenues for local tumor spread, and promote relative immune privilege. Understanding the molecular drivers of these phenotypes will be critical if we are to therapeutically target their protumorigenic effects. The potential for neoplastic cells to transdifferentiate into vascular and perivascular elements also needs to be better understood, as it has the potential to complicate such therapies. In this review, we provide a brief overview of these less conventional vascular functions in tumors.

KDR and Sema3 genes expression in bone marrow stromal cells and hematopoietic cells from leukemia patients and normal individuals

Kinase domain receptor (KDR) and Semaphorin3 (Sema3) have a functional relationship and are expressed in human bone marrow (BM). We cultured in vitro bone marrow stromal cells (BMSCs) and collected nonadherent cells from patients with acute myeloid leukemia (AML), chronic myelogenous leukemia (CML), acute lymphoblastic leukemia (ALL) and normal individuals. Reverse transcriptase polymerase chain reaction enzyme-linked immunosorbent assay (RT-PCR-ELISA) was performed to examine KDR and Sema3 genes expression, using beta2 microglobulin as an internal reference. KDR expression ratio in normal control BMSCs (97.0%, 32/33) was higher than in its corresponding nonadherent cells (70.8%, 17/24). KDR expression levels in ALL BMSCs and AML nonadherent cells were significantly higher than in normal controls. Sema3 expression ratios in nonadherent cells from AML (78.6%, 11/14) and CML (71.4%, 10/14) were both significantly lower than in normal control (100%, 27/27), its expression levels were also significantly lower than in normal control. Sema3 expression level in normal BMSCs was significantly lower than in nonadherent cells. Sema3 and KDR genes expression levels displayed a significantly positive correlation in normal control and ALL nonadherent cells (r=0.703, P=0.002; r=0.999, P=0.001). These results suggests that KDR may play a critical role in sustaining the hematopoietic microenvironment due to its high expression, and that KDR may be involved in pathogenesis of AML and ALL. Sema3 could also sustain the survival of hematopoietic cells with its high expression, while Sema3 gene expression may be inhibited in AML and CML.

Role of VEGF/VEGFR in the pathogenesis of leukemias and as treatment targets (Review)

Angiogenesis plays an important role in solid tumor growth, progression and metastasis. Evidence suggests that the progression of hematolymphoid malignancies also depends on the induction of new blood vessel formation under the influence of acute leukemia, myelodysplastic syndromes, myeloproliferative neoplasms, multiple myeloma and lymphomas. The vascular endothelial growth factor (VEGF) is the most important proangiogenic agent that activates receptors on vascular endothelial cells and promotes blood vessel regeneration. It has been demonstrated that VEGF/VEGF receptor (VEGFR) expression is upregulated in several types of hematolymphoid tumor cells accompanied with angiogenesis. The levels of VEGF/VEGFR are correlated with the treatment, relapse and prognosis of hematolymphoid tumors. In order for VEGF family and their receptors as antiangiogenic targets to treat solid tumors, several antiangiogenic agents targeting VEGF-related pathways have been used for the treatment of hematolymphoid malignancies in clinical trials. The results demonstrate a promising therapeutic intervention in multiple types of hematolymphoid tumors. This review aims to summarize recent advances in understanding the role of VEGF and angiogenesis in leukemias, mainly focusing on their upstream transcriptors, downstream targets and the correlation of VEGF/VEGFR with the treatment, relapse or prognosis of leukemia. The progress of VEGF and its receptors as attractive targets for therapies are also discussed in clinical application.

Quantification of the specific membrane capacitance of single cells using a microfluidic device and impedance spectroscopy measurement

The specific membrane capacitance (SMC) is an electrical parameter that correlates with both the electrical activity and morphology of the plasma membrane, which are physiological markers for cellular phenotype and health. We have developed a microfluidic device that enables impedance spectroscopy measurements of the SMC of single biological cells. Impedance spectra induced by single cells aspirated into the device are captured over a moderate frequency range (5 kHz-1 MHz). Maximum impedance sensitivity is achieved using a tapered microfluidic channel, which effectively routes electric fields across the cell membranes. The SMC is extracted by curve-fitting impedance spectra to an equivalent circuit model. From our measurement, acute myeloid leukemia (AML) cells are found to exhibit larger SMC values in hypertonic solutions as compared with those in isotonic solutions. In addition, AML cell phenotypes (AML2 and NB4) exhibiting varying metastatic potential yield distinct SMC values (AML2: 16.9 ± 1.9 mF/m(2) (n = 23); NB4: 22.5 ± 4.7 mF/m(2) (n = 23)). Three-dimensional finite element simulations of the microfluidic device confirm the feasibility of this approach.

Osteoblastic and vascular endothelial niches, their control on normal hematopoietic stem cells, and their consequences on the development of leukemia

Stem cell self-renewal is regulated by intrinsic mechanisms and extrinsic signals mediated via specialized microenvironments called “niches.” The best-characterized stem cell is the hematopoietic stem cell (HSC). Self-renewal and differentiation ability of HSC are regulated by two major elements: endosteal and vascular regulatory elements. The osteoblastic niche localized at the inner surface of the bone cavity might serve as a reservoir for long-term HSC storage in a quiescent state. Whereas the vascular niche, which consists of sinusoidal endothelial cell lining blood vessel, provides an environment for short-term HSC proliferation and differentiation. Both niches act together to maintain hematopoietic homeostasis. In this paper, we provide some principles applying to the hematopoietic niches, which will be useful in the study and understanding of other stem cell niches. We will discuss altered microenvironment signaling leading to myeloid lineage disease. And finally, we will review some data on the development of acute myeloid leukemia from a subpopulation called leukemia-initiating cells (LIC), and we will discuss on the emerging evidences supporting the influence of the microenvironment on chemotherapy resistance.

Activation of MDL-1 (CLEC5A) on immature myeloid cells triggers lethal shock in mice

Systemic inflammatory response syndrome (SIRS) is a potentially lethal condition, as it can progress to shock, multi-organ failure, and death. It can be triggered by infection, tissue damage, or hemorrhage. The role of tissue injury in the progression from SIRS to shock is incompletely understood. Here, we show that treatment of mice with concanavalin A (ConA) to induce liver injury triggered a G-CSF-dependent hepatic infiltration of CD11b+Gr-1+Ly6G+Ly6C+ immature myeloid cells that expressed the orphan receptor myeloid DAP12-associated lectin-1 (MDL-1; also known as CLEC5A). Activation of MDL-1 using dengue virus or an agonist MDL-1-specific antibody in the ConA-treated mice resulted in shock. The MDL-1+ cells were pathogenic, and in vivo depletion of MDL-1+ cells provided protection. Triggering MDL-1 on these cells induced production of NO and TNF-α, which were found to be elevated in the serum of treated mice and required for MDL-1-induced shock. Surprisingly, MDL-1-induced NO and TNF-α production required eNOS but not iNOS. Activation of DAP12, DAP10, Syk, PI3K, and Akt was critical for MDL-1-induced shock. In addition, Akt physically interacted with and activated eNOS. Therefore, triggering of MDL-1 on immature myeloid cells and production of NO and TNF-α may play a critical role in the pathogenesis of shock. Targeting the MDL-1/Syk/PI3K/Akt/eNOS pathway represents a potential new therapeutic strategy to prevent the progression of SIRS to shock.

The Role of PTEN in Tumor Angiogenesis

During the past 20 years, the phosphatase and tensin homolog PTEN has been shown to be involved in major physiological processes, and its mutation or loss is often associated with tumor formation. In addition PTEN regulates angiogenesis not only through its antagonizing effect on the PI3 kinase pathway mainly, but also through some phosphatase-independent functions. In this paper we delineate the role of this powerful tumor suppressor in tumor angiogenesis and dissect the underlying molecular mechanisms. Furthermore, it appears that, in a number of cancers, the PTEN status determines the response to chemotherapy, highlighting the need to monitor PTEN expression and to develop PTEN-targeted therapies.

Instructive role of the vascular niche in promoting tumour growth and tissue repair by angiocrine factors

The precise mechanisms whereby anti-angiogenesis therapy blocks tumour growth or causes vascular toxicity are unknown. We propose that endothelial cells establish a vascular niche that promotes tumour growth and tissue repair not only by delivering nutrients and O2 but also through an 'angiocrine' mechanism by producing stem and progenitor cell-active trophogens. Identification of endothelial-derived instructive angiocrine factors will allow direct tumour targeting, while diminishing the unwanted side effects associated with the use of anti-angiogenic agents.

Variations of brain endothelial nitric oxide synthase concentration in rat and mouse cortex

No information exists on the differences of eNOS concentration in brain tissue, [eNOS](br), between animals during normal and hypotensive blood pressure and both between and within animals during moderate hypotension. To address these questions, we modified a commercially available enzyme-linked immunosorbent assay (ELISA) kit for determining murine [eNOS](br) since no method exists to measure [eNOS](br). Optimization of the kit ELISA procedure using brain cortex homogenates from 3 normotensive rats and 1 wild-type and 1 eNOS(-/-) (ko) mouse included recovery evaluation for each sample and the use of an "eNOS-free" homogenate calibrator diluent obtained from a mutant eNOS-ko mouse. Initial spike-and-recovery values of 12.5-27% suggesting a substantial sample matrix effect were improved with lipid removal treatment to 37.3% and to 70% with 1:20 dilution of the sample. Calibration standards prepared using eNOS-free buffer increased recovery values to 78% in micro-punch samples. The optimized ELISA was used in micro-punch (<1mg) brain cortex samples from 6 hypotensive rats. Whole brain [eNOS](br) varied considerably from 5-11fmol/mg wet weight and was different between normo- and hypotensive animals (p=0.023). The variability of [eNOS](br) due to moderate hypotension in micro-punch rat brain cortex samples was composed of both between (24%) and within (76%) animal components. The differences and variability of [eNOS](br) between normo- and hypotensive animals, and between and within hypotensive animals suggests the potential utility of its measurement for investigations of cerebrovascular physiology and that [eNOS](br) itself could be an important factor in cerebrovascular regulation.

Expression of endothelial nitric oxide synthase and vascular endothelial growth factor in association with neovascularization in human primary astrocytoma

OBJECTIVE

To investigate the relationship between the expression of endothelial nitric oxide synthase (eNOS), vascular endothelial growth factor (VEGF) and angiogenesis in primary astrocytoma.

METHODS

Thirty-seven primary astrocytomas and 4 astrocytic hyperplasia samples were collected and divided into three groups according to histological grade. The expression of eNOS, VEGF and factor VIII related antigen (FVIIIRAg) were assayed by immunohistochemistry. Microvascular density was assessed by FVIIIRAg immunoreactivity. The intensity of immunoreactivity was graded according to the percentage of positive tumor cells.

RESULTS

No eNOS and VEGF were expressed in the astrocytes and vascular endothelium in astrocytic hyperplasia. The expression of eNOS or VEGF was light in low-grade astrocytoma and strong in glioblastoma. eNOS expression in astrocytoma was very positively correlated with VEGF. eNOS and VEGF expression in anaplastic astrocytoma was median in contrast to the low grade astrocytoma and glioblastoma. Lower microvascular density was found in low grade astrocytoma than that in higher grade malignant ones. The expressions of eNOS and VEGF were correlated with microvascular density and tumor malignancy.

CONCLUSION

This finding suggests that eNOS and VEGF may have cooperative effect in tumor angiogenesis and play an important role in the pathogenesis of primary astrocytoma.

Vascular endothelial growth factor receptor-1 and receptor-2 initiate a phosphatidylinositide 3-kinase–dependent clonogenic response in acute myeloid leukemia cells

OBJECTIVE

Vascular endothelial growth factor (VEGF) interacts with two high-affinity receptor tyrosine kinases (RTK) on vascular endothelium to initiate complementary but disparate biologic responses. We previously reported that acute myeloid leukemia (AML) cells express VEGF and one or both VEGF-A receptors, Flt-1 (VEGFR-1) and KDR (VEGFR-2). To evaluate receptor-selective trophic response to VEGF-A in AML cells, we investigated receptor-specific ligand activation responsible for VEGF-initiated clonogenic response.

MATERIALS AND METHODS

Using KG1 (VEGFR-1+/VEGFR-2+) and HL60 (VEGFR-1+) cells with differential VEGF receptor display, we investigated ligand-induced clonogenic response and receptor-initiated signaling after stimulation with VEGF-A, the VEGFR-1 selective ligand placental growth factor (PlGF), or receptor-specific antibody agonists.

RESULTS

Recombinant human (rhu)-VEGF increased S-phase fraction and stimulated colony formation in both KG1 and HL60 cells. Ligation of VEGFR-1 or VEGFR-2 with receptor-specific antibody agonists triggered equivalent and concentration-dependent stimulation of colony recovery in KG1 cells, whereas clonogenic response in HL60 cells was restricted to VEGFR-1 activation by antibody or PlGF. In serum-deprived KG1 and HL60 cells, rhu-VEGF stimulated rapid and sustained phosphorylation of Akt/PKB that was inhibited by the phosphatidyl inositol 3-kinase (PI3-K) kinase inhibitor wortmannin. Preincubation with wortmannin inhibited VEGF-induced colony formation in a concentration-dependent fashion. rhu-VEGF-induced clonogenic response and Akt phosphorylation was abolished by the VEGF-RTK inhibitor SU-5416 at concentrations greater than 10 microM, whereas MEK inhibition by PD98059 (1 and 10 microM) was ineffective. In vivo suppression of Akt phosphorylation was confirmed in myeloblast lysates from three patients with advanced myeloid malignancies treated with SU5416.

CONCLUSION

These data indicate that VEGF interaction with either VEGFR-1 or VEGFR-2 initiates a clonogenic response in AML cells that is PI3-kinase dependent. RTK inhibitors with broad specificity for angiogenic receptors represent novel therapeutics that merit further clinical investigation in AML.

Generation of a syngeneic mouse model to study the effects of vascular endothelial growth factor in ovarian carcinoma

Vascular endothelial growth factor (VEGF) performs multifaceted functions in the tumor microenvironment promoting angiogenesis, suppressing anti-tumor immune response, and possibly exerting autocrine functions on tumor cells. However, appropriate syngeneic animal models for in vivo studies are lacking. Using retroviral transfection and fluorescence-activated cell sorting, we generated a C57BL6 murine ovarian carcinoma cell line that stably overexpresses the murine VEGF164 isoform and the enhanced green fluorescent protein. VEGF164 overexpression dramatically accelerated tumor growth and ascites formation, significantly enhanced tumor angiogenesis, and substantially promoted the survival of tumor cells in vivo. In vitro, VEGF164 overexpression significantly enhanced cell survival after growth factor withdrawal and conferred resistance to apoptosis induced by cis-platin through an autocrine mechanism. VEGF/green fluorescent protein-expressing tumors were not recognized by the adaptive immune system. After vaccination, a specific anti-tumor T-cell response was detected, but tumor growth was not inhibited. This engineered murine carcinoma model should prove useful in the investigation of the role of VEGF in modulating the tumor microenvironment and affecting the complex interactions among angiogenesis mechanisms, anti-tumor immune mechanisms, and tumor cell behavior at the natural state or during therapy in ovarian carcinoma.

Soluble hepatocyte growth factor (sHGF) and vascular endothelial growth factor (sVEGF) in adult acute myeloid leukemia: relationship to disease characteristics

There is little understanding of the factors controlling the mobilization of blast cells from bone marrow to peripheral blood and tissues. The aim of this study was to evaluate the soluble hepatocyte growth factor (sHGF) and vascular endothelial growth factor (sVEGF) levels in newly diagnosed patients with acute myeloid leukemia (AML) and to correlate these levels with the clinico-pathological features. Sixty-three patients with AML and 15 normal controls were included in this study. The levels of sHGF and sVEGF were determined by enzyme linked immunosorbent assay at diagnosis and after remission induction chemotherapy. Our results revealed significantly increased plasma levels of sHGF and sVEGF at diagnosis when compared to both control and remission levels (P=0.000 for both). The sHGF and sVEGF levels differed between AML FAB subtypes (P=0.000). The highest concentrations were found in M5 followed by M4. SHGF and sVEGF were directly correlated with peripheral white cell counts (WBC) (r=0.836, P=0.000, r=0.718; P=0.000, respectively), but inversely correlated with blast cell distribution ratio (BCDR) (r=-0.785, P=0.000, r=-0.664, P=0.000, respectively). Moreover, both sHGF and sVEGF levels were significantly elevated in AML patients with extra-medullary infiltration as compared to those without (P=0.000, 0.006, respectively). The sHGF but not sVEGF levels were significantly elevated in patients who died compared to those who relapsed and to patients in complete remission (P=0.02, 0.08, respectively). Logistic regression analysis revealed that the sHGF level at diagnoses is a powerful predictor of the patient outcome, compared to sVEGF.

IN CONCLUSION

our data support the hypothesis that angiogenic factors play a functional role in blast cell movement from the bone marrow to peripheral tissues. Assessment of sHGF at AML diagnosis is likely to be helpful in predicting patient outcome and selecting optimal therapeutic regimen.