Effects of intravitreal injection of KH902, a vascular endothelial growth factor receptor decoy, on the retinas of streptozotocin-induced diabetic rats

Aims: KH902 is a fusion protein that can bind vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) through its binding ligand taken from the domains of VEGF receptor 1 and VEGF receptor 2 (VEGFR2). This study was to investigate the effects of intravitreal injection of KH902 on the retinas of streptozotocin‐induced diabetic rats. Methods: Two weeks after induction of diabetes, the left eyes of diabetic rats in each group received an intravitreal injection of phosphate‐buffered saline (PBS), Avastin or KH902 solution, respectively. Four weeks after intravitreal injection, retinal electrophysiological function and the integrity of inner blood retinal barrier (iBRB) were measured by electroretinogram and Evans blue perfusion. The protein levels of VEGF signal pathway were assayed by western blot. The expression and distribution of claudin‐5 and occludin were analysed by double immunofluorescent staining under confocal microscope. The expression of VEGFR2 and PlGF was measured by immunohistochemistry. Results: Four weeks after intravitreal injection, KH902‐treated rats had better retinal electrophysiological function, less retinal vessel leakage and lower levels of VEGFR2, PI3K, AKT, p‐AKT, p‐ERK and p‐SRC than PBS or Avastin‐treated rats. The distribution of claudin‐5 and occludin in the retinal vessels of diabetic rats treated by KH902 was smoother and more uniform than those of diabetic rats treated by PBS or Avastin. The expression of PlGF and VEGFR2 in KH902‐treated rats was decreased compared with those in PBS or Avastin‐treated rats. Conclusions: KH902 could improve retinal electrophysiological function and inhibit the breakdown of iBRB by inhibiting the expression of VEGFR2, PlGF and PI3K, and the activation of SRC, AKT and ERK.     

Role of vascular endothelial growth factor (VEGF) and placenta-derived growth factor (PlGF) in regulating human haemopoietic cell growth

Vascular endothelial growth factor (VEGF) and placental derived growth factor (PlGF) stimulate cell proliferation and differentiation by binding to their specific receptors, Flk-1/KDR and Flt-1 respectively. Flk-1/KDR-deficient murine embryos manifest failure of blood-island formation and vasculogenesis. The aim of this study was to directly evaluate the importance of VEGF, PlGF/Flt-1 and Flk-1/KDR receptor ligand interactions in regulating normal and malignant human haemopoiesis. Addition of VEGF and PlGF failed to enhance survival or cloning efficiency of human haemopoietic progenitors isolated from adult bone marrows, fetal livers or cord blood samples. This finding may be explained by the apparent absence of mRNA encoding Flt-1 and Flk-1/KDR receptors on stem cell rich CD34⁺ c-kit-R⁺ Rh123^low cells. Further studies revealed that Flt-1 R mRNA, but not Flk-1/KDR mRNA was first detectable in the more mature cells isolated from haemopoietic colonies. Accordingly, VEGF receptors are either absent, or expressed at very low level, on human haemopoietic stem/progenitor cells. Of interest, normal and malignant human haemopoietic cells appeared to secrete VEGF protein. However, in contrast to normal haemopoietic progenitors, VEGF co-stimulated HEL cell proliferation as well as CFU-GM colony formation from ∼15% of the chronic myeloid leukaemia (CML) and acute myeloid leukaemia (AML) patients studied. Therefore, although VEGF appeared to have minimal effects on normal haemopoietic cell growth it would appear to drive malignant haemopoietic cell proliferation to some degree. Of more importance, however, we speculate that VEGF may play an very important role in leukaemogenesis by stimulating growth of vascular endothelium, thereby providing a sufficient blood supply to feed the growing haematological tumour.     

t(8;21) acute myeloid leukaemia cells are dependent on vascular endothelial growth factor (VEGF)/VEGF receptor type2 pathway and phosphorylation of Akt

Several anti-angiogenic drugs have recently been clinically tested for haematological malignancies. To improve the efficacy of molecular target therapy against angiogenic molecules in acute myeloid leukaemia (AML), we examined the dependency of AML cells on the vascular endothelial growth factor (VEGF)/VEGF receptor type2 (VEGFR2) system by using VEGFR2 kinase inhibitor. Nineteen patient AML samples were cultured with or without VEGFR2 kinase inhibitor. All four t(8;21) viable AML cells showed significant reductions when treated with VEGFR2 kinase inhibitor, although VEGFR2 kinase inhibitor did not affect the cell proliferation of five t(15;17) AML samples. Other AML cases showed variable responses. VEGFR2 kinase inhibitor greatly suppressed the growth of Kasumi-1, a t(8;21) cell line in a dose-dependent manner through induction of apoptosis, but did not show any significant influence on NB4, a t(15;17) cell line. In addition, VEGFR2 kinase inhibitor potentiated the growth inhibitory effect of cytarabine in Kasumi-1. Finally, it was shown that the Akt phosphorylation was augmented by VEGF(165) in Kasumi-1, which was abrogated by VEGFR2 kinase inhibitor. NB4 showed undetectable Akt phosphorylation even with VEGF(165). These data demonstrated that t(8;21) AML cells are dependent on VEGF through VEGFR2, resulting in the phosphorylation of Akt.     

VEGFR1–mediated pericyte ablation links VEGF and PlGF to cancer-associated retinopathy

VEGF coordinates complex regulation of cellular regeneration and interactions between endothelial and perivascular cells; dysfunction of the VEGF signaling system leads to retinopathy. Here, we show that systemic delivery of VEGF and placental growth factor (PlGF) by protein implantation, tumors, and adenoviral vectors ablates pericytes from the mature retinal vasculature through the VEGF receptor 1 (VEGFR1)-mediated signaling pathway, leading to increased vascular leakage. In contrast, we demonstrate VEGF receptor 2 (VEGFR2) is primarily expressed in nonvascular photoreceptors and ganglion cells. Moreover, blockade of VEGFR1 but not VEGFR2 significantly restores pericyte saturation in mature retinal vessels. Our findings link VEGF and PlGF to cancer-associated retinopathy, reveal the molecular mechanisms of VEGFR1 ligand-mediated retinopathy, and define VEGFR1 as an important target of antiangiogenic therapy for treatment of retinopathy.     

膀胱移行细胞癌VEGF和VEGFR的表达及相关性的探讨

目的　探讨膀胱移行细胞癌 (BTCC)中血管内皮生长因子 (VEGF)及其受体 (VEGFR)的表达及与两者之间的关系。方法　采用免疫组织化学链霉菌抗生物素 过氧化物酶连接法 (S P法 )对 30例BTCC及 1 0例正常膀胱黏膜组织中VEGF及VEGFR的表达进行检测。结果　VEGF和VEGFR在绝大多数BTCC中呈阳性表达 ,平均表达率分别为 87%和 73 %。随肿瘤分期和分级的升高其表达水平升高 ,但在正常膀胱组织中未见表达。结论　BTCC中VEGF和VEGFR表达阳性 ,提示其在BTCC的血管生成和侵袭进展过程中起着重要作用 ,并将有可能为BTCC抗血管形成治疗及预防提供新的思路     

Inhibitory effect of interleukin-4 on the in vitro growth of Ph1-positive acute lymphoblastic leukemia cells

We investigated the effect of recombinant human interleukin-4 (rhIL-4) on the in vitro growth of human leukemia cells in liquid culture and 3H-thymidine incorporation and found inhibitory effects on the growth of leukemic cells from patients with Ph1-positive acute lymphoblastic leukemia (Ph1 ALL) and three Ph1 ALL cell lines. However, no inhibitory effects were seen in Ph1-positive leukemic cell lines derived from patients with chronic myelogenous leukemia in blast crisis and various types of Ph1-negative leukemia cells, including B-lineage leukemia cells. In a flow cytometry assay of IL-4 receptor (IL-4R), all three Ph1-positive ALL cell lines showed the presence of IL-4R on their cell surfaces, and the IL-4-dependent inhibition on the growth of Ph1-positive ALL cells was abrogated by the addition of either monoclonal or polyclonal antibodies against rhIL-4. Other cytokines, including IL-2, IL-3, granulocyte-macrophage colony-stimulating factor (CSF), granulocyte-CSF, and IL-6, showed no inhibitory effects on the growth of Ph1-ALL cells, but tumor necrosis factor-alpha (TNF-alpha) and interferon (IFN)-alpha, -beta, and -gamma displayed slight inhibitory effects in a high concentration. The growth inhibition induced by rhIL-4 in the Ph1-positive ALL cells was not abrogated by the addition of antibodies against either IFN-gamma or TNF-alpha. Furthermore, these cells showed no significant production of IFN-alpha, -beta, or -gamma or TNF-alpha after exposure to rhIL-4, thus indicating that the growth inhibition of Ph1-positive ALL cells by rhIL-4 is not associated with IL-4-stimulating production of these factors. rhIL-4 caused significant inhibition of the tyrosine kinase activity in these Ph1-positive ALL cells, similar to Herbimycin A, an inhibitor of tyrosine kinase that inhibited the tyrosine kinase activity in these cells. Our finding suggests that the clinical evaluation of rhIL-4 may offer promising therapeutic possibilities for patients with Ph1-positive ALL.     

A novel maxizyme vector targeting a bcr-abl fusion gene induced specific cell death in Philadelphia chromosome-positive acute lymphoblastic leukemia

Patients with Philadelphia chromosome-positive (Ph(+)) acute lymphoblastic leukemia (ALL) generally have a poor prognosis and would benefit from the development of new therapeutic approaches. We previously demonstrated that an allosterically controllable ribozyme, maxizyme (Mz), can induce apoptosis in chronic myelogenous leukemia (CML) cells. Ph(+) ALL cells harbor a bcrabl fusion gene (e1a2) encoding a 190-kDa fusion protein (p190) involved in disease pathogenesis. In this study, we have designed a Mz that specifically cleaves e1a2 mRNA and transduced this e1a2Mz into Ph(+) ALL cells using a third-generation lentiviral vector system. In 3 of 5 Ph(+) ALL cell lines, e1a2Mz transduction resulted in a significant decrease in viability and increased cell apoptosis. We observed a decrease in e1a2 mRNA in all Ph(+) ALL cells transduced with e1a2Mz, and the e1a2 mRNA level was higher in e1a2Mz-resistant cells than in e1a2Mz-sensitive cells. All samples of primary Ph(+) ALL cells tested showed e1a2Mz-induced growth inhibition and apoptosis. Importantly, e1a2Mz did not influence the colony formation of normal CD34(+) cord blood cells. These results indicate that e1a2Mz kills Ph(+) ALL cells specifically, suggesting that it may be used as a novel gene therapy strategy for Ph(+) ALL.     

Vascular endothelial growth factor promotes proliferation and function of hepatocyte-like cells in embryoid bodies formed from mouse embryonic stem cells

BACKGROUND/AIMS: Embryoid bodies (EBs) formed from embryonic stem cells (ESCs) differentiate into hepatocyte-like cells (HLCs), and are thus thought to be a useful cell source for drug testing and bioartificial liver. The aim of this study was to induce proliferation and function of ESC-derived HLCs in EBs using HLC-endothelial cell interaction. METHODS: EBs were cultured in the presence of vascular endothelial growth factor (VEGF) and/or VEGF receptor (VEGFR) inhibitors. To reproduce HLC-endothelial cell interaction, we overexpressed VEGF in ESC-derived HLCs under the control of Cyp7a1 gene in EBs. RESULTS: VEGF added to the cultured EBs increased the proliferation of ESC-derived endothelial cells, resulting in the promotion of proliferation and function of ESC-derived HLCs. In EBs, the VEGFR2 inhibitor suppressed expression of albumin and endothelial cell marker genes, whereas the inhibitor for both VEGFR1 and VEGFR2 suppressed expression of Cyp7a1 and hepatocyte growth factor (Hgf) genes. Upon exposure to VEGF, the endothelial cells in EBs increased Hgf mRNA expression. Forced VEGF expression in ESC-derived HLCs in EBs induced angiogenesis around the HLCs and resulted in an increase in the amount of HLCs. CONCLUSIONS: VEGF indirectly induces the proliferation and function of ESC-derived HLCs through VEGFR1 and VEGFR2 signaling in endothelial cells.     

The discovery of the placental growth factor and its role in angiogenesis: a historical review

The placental growth factor (PlGF) is an angiogenic protein belonging to the vascular endothelial growth factor (VEGF) family, which was discovered in 1991 by an Italian scientist, Maria Graziella Persico. Dr Persico cloned and purified PlGF and determined its structure by crystallography resolution. Furthermore, she identified VEGF receptor-1 (VEGFR-1) as the receptor for PlGF, and in collaboration with Dr Peter Carmeliet in Leuven, she generated evidence that loss of PlGF does not affect development, reproduction, or postnatal life. PlGF is expressed primarily in the placenta and is up-regulated in several pathological conditions, although its role is still controversial. Some data in literature reported that PlGF enhances pathological angiogenesis by initiating a cross-talk between VEGFR-1 and VEGFR-2, whereas other studies did not confirm these findings. Regarding the potential therapeutic employment of PlGF, recent evidence has shown that an anti-PlGF antibody may act as a potent antiangiogenic agent, and that it has the advantage of minor toxicity when combined with anti-VEGF strategies.     

Endothelin inhibits cholangiocarcinoma growth by a decrease in the vascular endothelial growth factor expression

Background: Endothelins (ET‐1, ET‐2, ET‐3) are peptides with vasoactive properties interacting with ET_A and ET_B receptors. ET‐1 inhibits secretin‐stimulated ductal secretion (hallmark of cholangiocyte growth) of cholestatic rats by interaction with ET receptors. Aim: The aims of the studies were to evaluate (i) the effect of ET‐1 on cholangiocarcinoma growth in Mz‐ChA‐1 cells and nude mice and (ii) whether ET‐1 regulation of cholangiocarcinoma growth is associated with changes in the expression of vascular endothelial growth factor‐A (VEGF‐A), VEGF‐C, VEGF receptor‐2 (VEGFR‐2) and VEGFR‐3. Methods: We determined the expression of ET_A and ET_B receptors on normal and malignant (Mz‐ChA‐1) cholangiocytes and human cholangiocarcinoma tissue and the effect of ET‐1 on the proliferation and expression of VEGF‐A, VEGF‐C (regulators of tumour angiogenesis) and its receptors, VEGFR‐2 and VEGFR‐3, in Mz‐ChA‐1 cells. In vivo, Mz‐ChA‐1 cells were injected into the flanks of athymic mice and injections of ET‐1 or saline into the tumours were performed daily. The effect of ET‐1 on tumour size, cell proliferation, apoptosis, collagen quantity and the expression of VEGF‐A and VEGF‐C and VEGFR‐2 and VEGFR‐3 were measured after 73 days. Results: Higher expression of ET_A and ET_B was observed in malignant compared with normal cholangiocytes. ET‐1 inhibited proliferation and VEGF‐A, VEGF‐C, VEGFR‐2 and VEGFR‐3 expression of Mz‐ChA‐1 cells. Chronic ET‐1 treatment decreased tumour volume, tumour cell proliferation and VEGF‐A and VEGF‐C expression but increased apoptosis and collagen tissue deposition compared with controls. Conclusions: Modulation of VEGF‐A and VEGF‐C (by ET‐1) may be important for managing cholangiocarcinoma growth.     

CD19-targeting liposomes containing imatinib efficiently kill Philadelphia chromosome-positive acute lymphoblastic leukemia cells

Patients with Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph(+) ALL) have poor prognosis despite intensive therapeutic intervention. Recently, imatinib, a BCR-ABL tyrosine kinase inhibitor, has been proven to be an effective treatment for Ph(+) ALL, but nearly all patients rapidly acquire resistance. High-dose imatinib administration might overcome this resistance; however, systemic toxicities would likely limit this approach. Therefore, a new delivery system allowing for the specific targeting of imatinib is urgently needed. Because almost all Ph(+) ALL cells express CD19 on their surface, we have developed an immunoliposome carrying anti-CD19 antibody (CD19-liposomes). The internalization efficiency of the CD19-liposomes approached 100% in all Ph(+) ALL cells but was very low in CD19(-) cells. The cytocidal effect of imatinib-encapsulated CD19-liposomes (imatinib-CD19-liposomes) on Ph(+) ALL cell lines and primary leukemia cells from patients with Ph(+) ALL was much greater than that of imatinib with or without control liposomes. Importantly, the imatinib-CD19-liposomes did not affect the colony formation of CD34(+) hematopoietic cells, even at inhibitory concentration of free imatinib. Taken together, these data clearly demonstrate that the imatinib-CD19-liposomes induced specific and efficient death of Ph(+) ALL cells. This new therapeutic approach might be a useful treatment for Ph(+) ALL with fewer side effects than free imatinib.     

Vascular endothelial growth factor-C and its receptor type-3 expressed in acute lymphocytic leukemia cases with t(1;19)

The vascular endothelial growth factor (VEGF)-C system was analyzed in two cases of acute lymphocytic leukemia (ALL) with TCF3/PBX1 fusion to determine whether the VEGF-C system influences the growth of these ALL blasts. Bone marrow non-adherent mononuclear cells were prepared from the patients, and expressions of VEGFs and VEGF receptors (VEGFRs) were analyzed based on RNA and protein levels. Cell proliferation was also assayed with or without neutralizing antibodies to VEGFs. The patients’ leukemic blasts expressed a significant amount of VEGF-C and VEGFR type-3. When anti-VEGF-C antibody was added to the blast cell cultures, cell proliferation was suppressed. These observations indicate that, in our ALL cases with TCF3/PBX1 fusion, VEGF-C autocrine stimulation plays an important role in the proliferation of ALL.     

Kinetics of placenta growth factor/vascular endothelial growth factor synergy in endothelial hydraulic conductivity and proliferation

Vascular endothelial growth factor (VEGF) was originally discovered as vascular permeability factor because of its ability to increase microvascular permeability to plasma proteins. Since then, it has been shown to induce proliferation and migration in endothelial cells. Placenta growth factor (PlGF) is a member of the VEGF family of growth factors, but has little or undetectable mitogenic activity on endothelial cells. Intriguingly, however, PlGF was able to potentiate the action of low concentrations of VEGF on endothelial cell growth and macromolecule permeability in vitro. Here we show that PlGF can potentiate the effects of VEGF on the hydraulic conductivity of certain endothelial cells and that the duration of pretreatment with PlGF determines the resulting response. Hydraulic conductivity (Lp) was calculated from the water flux across the monolayer of human umbilical vein endothelial cells (HUVECs) or bovine aortic endothelial cells (BAECs). After 2 h of exposure to VEGF(165), the Lp of BAEC monolayers increased threefold, but the Lp of HUVEC monolayers did not increase. PlGF alone induced a small (63%) increase in Lp in BAECs, but not in HUVECs. BAEC, but not HUVEC, monolayers exposed first to PlGF and then to VEGF exhibited a seven- to eightfold increase in Lp. This enhancement in BAEC Lp could be observed for 4 h after the administration of PlGF. PlGF also potentiated the effect of VEGF on BAEC proliferation. Thus, augmentation of VEGF action by PlGF depends on the duration of PlGF exposure and on the origin of endothelial cells.     

Regulation of multiple angiogenic pathways by Dll4 and Notch in human umbilical vein endothelial cells

The Notch ligand, Dll4, is essential for angiogenesis during embryonic vascular development and is involved in tumour angiogenesis. Several recent publications demonstrated that blockade of Dll4 signalling inhibits tumour growth, suggesting that it may constitute a good candidate for anti-cancer therapy. In order to understand the role of Dll4 at the cellular level, we performed an analysis of Dll4-regulated genes in HUVECs. The genes identified included several angiogenic signalling pathways, such as VEGF, FGF and HGF. In particular we identified downregulation (VEGFR2, placenta growth factor PlGF) of VEGF pathway components resulting in the overall effect of limiting the response of HUVEC to VEGF. However extensive upregulation of VEGFR1 was observed allowing continued response to its ligand PlGF but the soluble form of the VEGFR1, sVEGFR1 was also upregulated. PlGF enhanced tubulogenesis of HUVEC suggesting that downregulation of PlGF and upregulation of VEGFR1 including sVEGFR1 are important mechanisms by which Dll4 attenuates PlGF and VEGF signalling. Dll4-stimulated HUVECs had impaired ERK activation in response to VEGF and HGF indicating that Dll4 signalling negatively regulates these pathways. Dll4 expression reduced vessel sprout length in a 3D tubulogenesis assay confirming that Dll4 signalling inhibits angiogenesis. Altogether, our data suggest that Dll4 expression acts as a switch from the proliferative phase of angiogenesis to the maturation and stabilisation phase by blocking endothelial cell proliferation and allowing induction of a more mature, differentiated phenotype. The regulation of sVEGFR1 provides a novel mechanism for Dll4 signalling to regulate cells at distance, not just in adjacent cells.     

Overexpression of the soluble vascular endothelial growth factor receptor in preeclamptic patients: pathophysiological consequences

Several growth factors such as vascular endothelial growth factor (VEGF)-A and placental growth factor (PlGF) are involved in the placental vascular development. We investigated whether dysregulation in the VEGF family may explain the defective uteroplacental vascularization characterizing preeclampsia. We compared pregnancies complicated by early onset severe preeclampsia or intrauterine growth retardation to normal pregnancies. Maternal plasma, placentas, and placental bed biopsies were collected. The mRNA levels of VEGF-A, PlGF, and their receptors were quantified in placentas and placental beds. Levels of VEGF-A, PlGF, and soluble VEGF receptor (VEGFR) were assessed in maternal plasma. In compromised pregnancies, elevated levels of VEGF-A and VEGFR-1 mRNAs may reflect the hypoxic status of the placenta. On contrast, the membrane-bound VEGFR-1 was decreased in the placental bed of preeclamptic patients. Preeclampsia was associated with low levels of circulating PlGF and increased levels of total VEGF-A and soluble VEGFR-1. Free VEGF-A was undetectable in maternal blood. Immunohistochemical studies revealed that VEGF-A and PlGF were localized in trophoblastic cells. Altogether, our results suggest two different pathophysiological mechanisms associated with preeclampsia. The first one is related to an overproduction of competitive soluble VEGFR-1 that may lead to suppression of VEGF-A and PlGF effects. The second one is the down-regulation of its membrane bound form (VEGFR-1) in the placental bed, which may result in the defective uteroplacental development.     

Vascular Endothelial Growth Factor Levels in Childhood Acute Lymphoblastic and Myeloblastic Leukemia

Angiogenesis has been associated with the growth, dissemination and metastasis and has been shown to be a prognostic. Although there are some data suggesting that angiogenesis may have a role in the pathophysiology of leukemia, its role in patient prognosis is yet to be defined. We analyzed the expression level of vascular endothelial growth factor (VEGF), an angiogenesis promoter and its possible- prognostic value in bone marrow samples at the time of diagnosis and remission of acute childhood leukemia patients. Besides 46 patients diagnosed as ALL or AML, 16 children were also included as a control group in the study. Our data have demonstrated that VEGF levels of AML patients were found higher than the control group statistically (P = 0.022). However we could not find any significant difference between VEGF levels of diagnosis and remission in both AML and ALL groups by blastic VEGF expression (P > 0.05). In this study the higher levels of VEGF in AML patients is one of the main findings although we were not able to assess any role of VEGF in predicting prognosis in pediatric leukemia patients by evaluating blastic cell VEGF expression. These results have demonstrated that the relationship between angiogenesis or angiogenesis promoters and hematological malignancies is not clear and simple as different methods or different cells beside different angiogenesis promotors are involved to these studies. So that not only tumor cells and their cytokines but also surrounding cells and their cytokines must be taken into consideration with the standardized study methods in the further studies to obtain a promising treatment approach.     

A chemically defined culture of VEGFR2+ cells derived from embryonic stem cells reveals the role of VEGFR1 in tuning the threshold for VEGF in developing endothelial cells

Vascular endothelial growth factor (VEGF) is a major growth factor for developing endothelial cells (ECs). Embryonic lethality due to haploinsufficiency of VEGF in the mouse highlighted the strict dose dependency of VEGF on embryonic vascular development. Here we investigated the dose-dependent effects of VEGF on the differentiation of ES cell-derived fetal liver kinase 1 (Flk-1)/VEGF receptor 2(+) (VEGFR2(+)) mesodermal cells into ECs on type IV collagen under a chemically defined serum-free condition. These cells could grow even in the absence of VEGF, but differentiated mostly into mural cells positive for alpha-smooth muscle actin. VEGF supported in a dose-dependent manner the differentiation into ECs defined by the expression of VE-cadherin, platelet-endothelial cell adhesion molecule 1 (PECAM-1)/ CD31, CD34, and TIE2/TEK. VEGF requirement was greater at late than at early phase of culture during EC development, whereas response of VEGFR2(+) cells to VEGF-E, which is a virus-derived ligand for VEGFR2 but not for Flt-1/VEGFR1, was not dose sensitive even at late phase of culture. Delayed expression of VEGFR1 correlated with increased dose dependency of VEGF. These results suggested that greater requirement of VEGF in the maintenance than induction of ECs was due to the activity of VEGFR1 sequestering VEGF from VEGFR2 signal. The chemically defined serum-free culture system described here provides a new tool for assessing different factors for the proliferation and differentiation of VEGFR2(+) mesodermal cells.     

Binding and neutralization of vascular endothelial growth factor (VEGF) and related ligands by VEGF Trap, ranibizumab and bevacizumab

Pharmacological inhibition of VEGF-A has proven to be effective in inhibiting angiogenesis and vascular leak associated with cancers and various eye diseases. However, little information is currently available on the binding kinetics and relative biological activity of various VEGF inhibitors. Therefore, we have evaluated the binding kinetics of two anti-VEGF antibodies, ranibizumab and bevacizumab, and VEGF Trap (also known as aflibercept), a novel type of soluble decoy receptor, with substantially higher affinity than conventional soluble VEGF receptors. VEGF Trap bound to all isoforms of human VEGF-A tested with subpicomolar affinity. Ranibizumab and bevacizumab also bound human VEGF-A, but with markedly lower affinity. The association rate for VEGF Trap binding to VEGF-A was orders of magnitude faster than that measured for bevacizumab and ranibizumab. Similarly, in cell-based bioassays, VEGF Trap inhibited the activation of VEGFR1 and VEGFR2, as well as VEGF-A induced calcium mobilization and migration in human endothelial cells more potently than ranibizumab or bevacizumab. Only VEGF Trap bound human PlGF and VEGF-B, and inhibited VEGFR1 activation and HUVEC migration induced by PlGF. These data differentiate VEGF Trap from ranibizumab and bevacizumab in terms of its markedly higher affinity for VEGF-A, as well as its ability to bind VEGF-B and PlGF.     

急性白血病患者血管内皮生长因子及其受体表达的动态观察

目的探讨急性白血病(AL)患者治疗前后骨髓中血管内皮生长因子(VEGF)及其受体的表达差异以及这种表达与血管生成的相关性.方法应用EnVision免疫组织化学二步法,检测122例次成人AL患者骨髓中造血细胞VEGF及其两种特异性受体fms-样酪氨酸激酶受体(Flt-1)、激酶插入嵌合受体(KDR)蛋白的表达情况.结果化疗后获得完全缓解(CR)的患者,其VEGF、KDR蛋白的表达在治疗前为6.0(3.3～12.0)和5.3(3.3～8.0),获CR后为5.3(3.3～9.0)和2.0(1.0～4.0)差异有显著性(P<0.05;P<0.01),而在化疗后未获得CR患者中的表达差异无显著性.在缓解后复发患者中的表达又升高到初发时的水平.各组初发患者Flt-1的表达水平与对照组之间差异无显著性,但CR期Flt-1的表达水平在CR组为3.3(1.7～5.3),复发组为3.3(2.0～5.3)与初发及对照组差异有显著性(P<0.01).微血管数处于高水平组的VEGF及KDR表达显著高于微血管处于低水平组者(P<0.01).骨髓原始细胞与急性髓系白血病(AML)初发患者VEGF和KDR的表达之间成正相关(r=0.429,0.359;P=0.005,0.02);与急性淋巴细胞白血病(ALL)初发患者VEGF的表达之间成正相关(r=0.522,P=0.03).结论 VEGF及其两种特异性细胞受体Flt-1, KDR在造血细胞及血管内皮细胞中表达.提示VEGF可能是白血病细胞的一种自分泌因子,同时作为一种旁分泌因子调控患者骨髓中的血管新生反应.VEGF及其细胞受体KDR可能构成抗血管新生和抗白血病治疗的新靶点.