Expression and localization of placenta growth factor and PlGF receptors in human meningiomas

Angiogenic signaling pathways and anti-angiogenic therapy for cancer

Angiogenesis, the formation of new blood vessels, is a complex and dynamic process regulated by various pro- and anti-angiogenic molecules, which plays a crucial role in tumor growth, invasion, and metastasis. With the advances in molecular and cellular biology, various biomolecules such as growth factors, chemokines, and adhesion factors involved in tumor angiogenesis has gradually been elucidated. Targeted therapeutic research based on these molecules has driven anti-angiogenic treatment to become a promising strategy in anti-tumor therapy. The most widely used anti-angiogenic agents include monoclonal antibodies and tyrosine kinase inhibitors (TKIs) targeting vascular endothelial growth factor (VEGF) pathway. However, the clinical benefit of this modality has still been limited due to several defects such as adverse events, acquired drug resistance, tumor recurrence, and lack of validated biomarkers, which impel further research on mechanisms of tumor angiogenesis, the development of multiple drugs and the combination therapy to figure out how to improve the therapeutic efficacy. Here, we broadly summarize various signaling pathways in tumor angiogenesis and discuss the development and current challenges of anti-angiogenic therapy. We also propose several new promising approaches to improve anti-angiogenic efficacy and provide a perspective for the development and research of anti-angiogenic therapy.

Chimeric Antigen Receptor (CAR) T Cell Therapy for Metastatic Melanoma: Challenges and Road Ahead

Metastatic melanoma is the most aggressive and difficult to treat type of skin cancer, with a survival rate of less than 10%. Metastatic melanoma has conventionally been considered very difficult to treat; however, recent progress in understanding the cellular and molecular mechanisms involved in the tumorigenesis, metastasis and immune escape have led to the introduction of new therapies. These include targeted molecular therapy and novel immune-based approaches such as immune checkpoint blockade (ICB), tumor-infiltrating lymphocytes (TILs), and genetically engineered T-lymphocytes such as chimeric antigen receptor (CAR) T cells. Among these, CAR T cell therapy has recently made promising strides towards the treatment of advanced hematological and solid cancers. Although CAR T cell therapy might offer new hope for melanoma patients, it is not without its shortcomings, which include off-target toxicity, and the emergence of resistance to therapy (e.g., due to antigen loss), leading to eventual relapse. The present review will not only describe the basic steps of melanoma metastasis, but also discuss how CAR T cells could treat metastatic melanoma. We will outline specific strategies including combination approaches that could be used to overcome some limitations of CAR T cell therapy for metastatic melanoma.

Occurrence of Fibrotic Tumor Vessels in Grade I Meningiomas Is Strongly Associated with Vessel Density, Expression of VEGF, PlGF, IGFBP-3 and Tumor Recurrence

Angiogenesis is a key feature during oncogenesis and remains a potential target of antiangiogenic therapy. While commonly described in high-grade lesions, vascularization and its correlation with prognosis in grade I meningiomas is largely unexplored. In the histological classification, not only the number but also the composition of blood vessels seems to be important. Therefore, tumor vessel density and fibrosis were correlated with clinical and imaging variables and prognosis in 295 patients with intracranial grade I meningioma. Expression of pro-angiogenic proteins within the meningiomas was investigated by proteome analyses and further validated by immunohistochemical staining. Fibrotic tumor vessels (FTV) were detected in 48% of all tumors and strongly correlated with vessel density, but not with the histopathological tumor subtype. Occurrence of FTV was correlated with a 2-fold increased risk of recurrence in both univariate and multivariate analyses. Explorative proteome analyses revealed upregulation of VEGF (vascular endothelial growth factor), PlGF (placental growth factor), and IGFBP-3 (insulin-like growth factor-binding protein-3) in tumors displaying FTV. Immunohistochemical analyses confirmed strong correlations between tumor vessel fibrosis and expression of VEGF, PlGF, and IGFBP-3. Presence of FTV was strongly associated with disruption of the arachnoid layer on preoperative MRI in univariate and multivariate analyses. In summary, the occurrence of fibrotic tumor vessels in grade I meningiomas is strongly associated with vessel density, disruption of the arachnoid layer, expression of VEGF, PlGF, IGFBP-3 and tumor recurrence.

A Novel 4-Gene Score to Predict Survival, Distant Metastasis and Response to Neoadjuvant Therapy in Breast Cancer

We generated a 4-gene score with genes upregulated in LM2-4, a metastatic variant of MDA-MB-231 (DOK 4, HCCS, PGF, and SHCBP1) that was strongly associated with disease-free survival (DFS) in TCGA cohort (hazard ratio [HR]>1.2, p < 0.02). The 4-gene score correlated with overall survival of TCGA (HR = 1.44, p < 0.001), which was validated with DFS and disease-specific survival of METABRIC cohort. The 4-gene score was able to predict worse survival or clinically aggressive tumors, such as high Nottingham pathological grade and advanced cancer staging. High score was associated with worse survival in the hormonal receptor (HR)-positive/Her2-negative subtype. High score enriched cell proliferation-related gene sets in GSEA. The score was high in primary tumors that originated, in and metastasized to, brain and lung, and it predicted worse progression-free survival for metastatic tumors. Good tumor response to neoadjuvant chemotherapy or hormonal therapy was accompanied by score reduction. High scores were also predictive of response to neoadjuvant chemotherapy for HR-positive/Her2-negative subtype. High score tumors had increased expression of T cell exhaustion marker genes, suggesting that the score may also be a biomarker for immunotherapy response. Our novel 4-gene score with both prognostic and predictive values may, therefore, be clinically useful particularly in HR-positive breast cancer.

Vascular endothelial growth factors and placenta growth factor in retinal vasculopathies: Current research and future perspectives

Vision loss due to disease or degeneration of the eye (retina, choroid, retinal veins, or macula) is a leading cause of blindness worldwide. In most cases, vision-threatening ocular diseases are accompanied by abnormal changes in the vasculature of the eye, especially the retina, and these conditions are collectively referred to as retinal vasculopathies. Impaired blood supply or hypoxia stimulates angiogenesis in the vascular and non-vascular sections of the eye, which results in neovascularization, leading to conditions such as diabetic retinopathy or age-related macular degeneration. Studies show that vascular endothelial growth factors: VEGF-A, VEGF-B, and placental growth factor (PlGF) are elevated in these diseases, and hence, these factors could be used as markers for disease prognosis and therapy. In this review, we discuss the function of these growth factors in normal development and disease, with focus on ocular disorders and emphasize the importance of accurately determining their levels in the vitreous and serum of patients for correct diagnosis and therapy.

Placental growth factor deficiency is associated with impaired cerebral vascular development in mice

STUDY HYPOTHESIS

Placental growth factor (PGF) is expressed in the developing mouse brain and contributes to vascularization and vessel patterning.

STUDY FINDING

PGF is dynamically expressed in fetal mouse brain, particularly forebrain, and is essential for normal cerebrovascular development.

WHAT IS KNOWN ALREADY

PGF rises in maternal plasma over normal human and mouse pregnancy but is low in many women with the acute onset hypertensive syndrome, pre-eclampsia (PE). Little is known about the expression of PGF in the fetus during PE. Pgf  (-/-) mice appear normal but recently cerebral vascular defects were documented in adult Pgf  (-/-) mice.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Here, temporal-spatial expression of PGF is mapped in normal fetal mouse brains and cerebral vasculature development is compared between normal and congenic Pgf  (-/-) fetuses to assess the actions of PGF during cerebrovascular development. Pgf/PGF, Vegfa/VEGF, Vegf receptor (Vegfr)1 and Vegfr2 expression were examined in the brains of embryonic day (E)12.5, 14.5, 16.5 and 18.5 C57BL/6 (B6) mice using quantitative PCR and immunohistochemistry. The cerebral vasculature was compared between Pgf  (-/-) and B6 embryonic and adult brains using whole mount techniques. Vulnerability to cerebral ischemia was investigated using a left common carotid ligation assay.

MAIN RESULTS AND THE ROLE OF CHANCE

Pgf/PGF and Vegfr1 are highly expressed in E12.5-14.5 forebrain relative to VEGF and Vegfr2. Vegfa/VEGF is relatively more abundant in hindbrain (HB). PGF and VEGF expression were similar in midbrain. Delayed HB vascularization was seen at E10.5 and 11.5 in Pgf  (-/-) brains. At E14.5, Pgf  (-/-) circle of Willis showed unilateral hypoplasia and fewer collateral vessels, defects that persisted post-natally. Functionally, adult Pgf  (-/-) mice experienced cerebral ischemia after left common carotid arterial occlusion while B6 mice did not.

LIMITATIONS, REASONS FOR CAUTION

Since Pgf  (-/-) mice were used, consequences of complete absence of maternal and fetal PGF were defined. Therefore, the effects of maternal versus fetal PGF deficiency on cerebrovascular development cannot be separated. However, as PGF was strongly expressed in the developing brain at all timepoints, we suggest that local PGF has a more important role than distant maternal or placental sources. Full PGF loss is not expected in PE pregnancies, predicting that the effects of PGF deficiency identified in this model will be more severe than any effects in PE-offspring.

WIDER IMPLICATIONS OF THE FINDINGS

These studies provoke the question of whether PGF expression is decreased and cerebral vascular maldevelopment occurs in fetuses who experience a preeclamptic gestation. These individuals have already been reported to have elevated risk for stroke and cognitive impairments.

LARGE SCALE DATA

N/A.

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by awards from the Natural Sciences and Engineering Research Council, the Canada Research Chairs Program and the Canadian Foundation for Innovation to B.A.C. and by training awards from the Universidade Federal de Pernambuco and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Brazil to R.L.L.; Queen's University to V.R.K. and the Canadian Institutes of Health Research to M.T.R. The work of P.C. is supported by the Belgian Science Policy BELSPO-IUAP7/03, Structural funding by the Flemish Government-Methusalem funding, and the Flemish Science Fund-FWO grants. There were no competing interests.

Hormone-dependent shrinkage of a sphenoid wing meningioma after pregnancy: case report

Meningiomas are known to be associated with female sex hormones. Worsening neurological symptoms or newly diagnosed meningiomas have been described in the context of elevated levels of sex hormones, for example, in pregnancy. To the authors’ knowledge, tumor shrinkage after the normalization of hormones has not been described, even if it is known that neurological deficits due to meningioma compression may improve after giving birth.

A 32-year-old female patient presented with severe headache and vision disturbances at the end of her second pregnancy. Magnetic resonance imaging revealed an extended mass at the lateral left-sided sphenoid wing that was suspected to be a meningioma. After delivery, the patient’s symptoms improved, and MRI obtained 2 months postpartum showed significant shrinkage of the lesion.

Significant tumor shrinkage can occur after pregnancy. Thus, repeat imaging is indicated in these patients.

ERK1/2 and AKT are vital factors in regulation of the migration of rat Schwann cells

After peripheral nerve injury, Wallerian degeneration (WD) occurs in the distal nerve segment. During the process of degeneration, Schwann cells (SCs) dedifferentiate, proliferate and migrate to align in “bands of Büngner”, providing structural guidance and growth-promoting substrates to regenerating axons. The molecular signals that trigger SCs migration remain unclear. Here, we explored the molecular characteristics of the migration of cultured SCs prepared from rat sciatic nerves that had degenerated. The results revealed that elevated p-ERK1/2 was coupled with the migration of SCs, activated either by nerve degeneration or the addition of placenta growth factor. However, the inhibition of ERK1/2 activity, which activated the PI3K pathway, did not show a significant negative effect on SC migratory potential. Combined inhibition of ERK1/2 and AKT activity resulted in a significant decrease in SCs motility. These molecular characteristics suggest that both the ERK1/2 and AKT signals are involved in the migratory potential of SCs. It may be helpful to understand the process of nerve regeneration and perspective on promoting peripheral nerve regeneration.

Novel therapies for meningiomas

Although advances in surgery, radiation therapy and stereotactic radiosurgery have significantly improved the treatment of meningiomas, there remains an important subset of patients who remain refractory to conventional therapy. Treatment with chemotherapeutic agents such as hydroxyurea and alpha-interferon has provided minimal benefit. In this review, the role of newly emerging novel therapies for meningiomas, with a focus on targeted molecular agents, will be discussed.

Combined blockade of HER2 and VEGF exerts greater growth inhibition of HER2-overexpressing gastric cancer xenografts than individual blockade

Gastric cancer overexpressing the human epidermal growth factor 2 (HER2) protein has a poor outcome, although a combination of chemotherapy and the anti-HER2 antibody trastuzumab has been approved for the treatment of advanced gastric cancer. Vascular endothelial growth factor (VEGF) expression in gastric cancer is correlated with recurrence and poor prognosis; however, the anti-VEGF antibody bevacizumab has shown limited efficacy against gastric cancer in clinical trials. In this study, we evaluated the antitumor effects of trastuzumab; VEGF-Trap binding to VEGF-A, VEGF-B and placental growth factor (PlGF); and a combination of trastuzumab and VEGF-Trap in a gastric cancer xenograft model. Although trastuzumab and VEGF-Trap each moderately inhibited tumor growth, the combination of these agents exerted greater inhibition compared with either agent alone. Immunohistochemical analyses indicated that the reduction in tumor growth was associated with decreased proliferation and increased apoptosis of tumor cells and decreased tumor vascular density. The combined treatment resulted in fewer proliferating tumor cells, more apoptotic cells and reduced tumor vascular density compared with treatment with trastuzumab or VEGF-Trap alone, indicating that trastuzumab and VEGF-Trap had additive inhibitory effects on the tumor growth and angiogenesis of the gastric cancer xenografts. These data suggest that trastuzumab in combination with VEGF-Trap may represent an effective approach to treating HER2-overexpressing gastric cancer.

Flt-1 in colorectal cancer cells is required for the tumor invasive effect of placental growth factor through a p38-MMP9 pathway

Background

Placenta growth factor (PlGF), a dimeric glycoprotein with 53% homology to VEGF, binds to VEGF receptor-1 (Flt-1), but not to VEGF receptor-2 (Flk-1), and may function by modulating VEGF activity. We previously have showed that PlGF displays prognostic value in colorectal cancer (CRC) but the mechanism remains elucidated.

Results

Overexpression of PlGF increased the invasive/migration ability and decreased apoptosis in CRC cells showing Flt-1 expression. Increased migration was associated with increasing MMP9 via p38 MAPK activation. Tumors grew faster, larger; with higher vascularity from PlGF over-expression cells in xenograft assay. In two independent human CRC tissue cohorts, PlGF, MMP9, and Flt-1 expressions were higher in the advanced than the localized disease group. PlGF expression correlated with MMP9, and Flt-1 expression. CRC patients with high PlGF and high Flt-1 expression in tissue had poor prognosis.

Conclusion

PlGF/Flt-1 signaling plays an important role in CRC progression, blocking PlGF/Flt-1 signaling maybe an alternative therapy for CRC.

Genetic and environmental factors influencing the Placental Growth Factor (PGF) variation in two populations

Placental Growth Factor (PGF) is a key molecule in angiogenesis. Several studies have revealed an important role of PGF primarily in pathological conditions (e.g.: ischaemia, tumour formation, cardiovascular diseases and inflammatory processes) suggesting its use as a potential therapeutic agent. However, to date, no information is available regarding the genetics of PGF variability. Furthermore, even though the effect of environmental factors (e.g.: cigarette smoking) on angiogenesis has been explored, no data on the influence of these factors on PGF levels have been reported so far. Here we have first investigated PGF variability in two cohorts focusing on non-genetic risk factors: a study sample from two isolated villages in the Cilento region, South Italy (N=871) and a replication sample from the general Danish population (N=1,812). A significant difference in PGF mean levels was found between the two cohorts. However, in both samples, we observed a strong correlation of PGF levels with ageing and sex, men displaying PGF levels significantly higher than women. Interestingly, smoking was also found to influence the trait in the two populations, although differently. We have then focused on genetic risk factors. The association between five single nucleotide polymorphisms (SNPs) located in the PGF gene and the plasma levels of the protein was investigated. Two polymorphisms (rs11850328 and rs2268614) were associated with the PGF plasma levels in the Cilento sample and these associations were strongly replicated in the Danish sample. These results, for the first time, support the hypothesis of the presence of genetic and environmental factors influencing PGF plasma variability.

Protein expression changes during human triple negative breast cancer cell line progression to lymph node metastasis in a xenografted model in nude mice

Triple negative breast cancers (TNBC) lacking hormone receptors and HER-2 amplification are very aggressive tumors. Since relevant differences between primary tumors and metastases could arise during tumor progression as evidenced by phenotypic discordances reported for hormonal receptors or HER-2 expression, in this analysis we studied changes that occurred in our TNBC model IIB-BR-G throughout the development of IIB-BR-G-_MTS6 metastasis to the lymph nodes (LN) in nude mice, using an antibody-based protein array to characterize their expression profile. We also analyzed their growth kinetics, migration, invasiveness and cytoskeleton structure in vitro and in vivo.

In vitro IIB-BR-G-_MTS6 cells grew slower but showed higher anchorage independent growth. In vivo IIB-BR-G-_MTS6 tumors grew significantly faster and showed a 100% incidence of LN metastasis after s.c. inoculation, although no metastasis was observed for IIB-BR-G. CCL3, IL1β, CXCL1, CSF2, CSF3, IGFBP1, IL1α, IL6, IL8, CCL20, PLAUR, PlGF and VEGF were strongly upregulated in IIB-BR-G-_MTS6 while CCL4, ICAM3, CXCL12, TNFRSF18, FIGF were the most downregulated proteins in the metastatic cell line. IIB-BR-G-_MTS6 protein expression profile could reflect a higher NFκB activation in these cells. In vitro, IIB-BR-G displayed higher migration but IIB-BR-G-_MTS6 had more elevated matrigel invasion ability. In agreement with that observation, IIB-BR-G-_MTS6 had an upregulated expression of MMP1, MMP9, MMP13, PLAUR and HGF. IIB-BR-G-_MTS6 tumors presented also higher local lymphatic invasion than IIB-BR-G but similar lymphatic vessel densities. VEGFC and VEGFA/B expression were higher both in vitro and in vivo for IIB-BR-G-_MTS6. IIB-BR-G-_MTS6 expressed more vimentin than IB-BR-G cells, which was mainly localized in the cellular extremities and both cell lines are E-cadherin negative.

Our results suggest that IIB-BR-G-_MTS6 cells have acquired a pronounced epithelial-to-mesenchymal transition phenotype. Protein expression changes observed between primary tumor-derived IIB-BR-G and metastatic IIB-BR-G-_MTS6 TNBC cells suggest potential targets involved in the control of metastasis.

The Roles of Angiogenesis in Malignant Melanoma: Trends in Basic Science Research over the Last 100 Years

Blood vessels arose during evolution carrying oxygen and nutrients to distant organs via complex networks of blood vessels penetrating organs and tissues. Mammalian cells require oxygen and nutrients for survival, of which oxygen has a diffusion limit of 100 to 200 μm between cell and blood vessel. For growth beyond this margin, cells must recruit new blood vessels, first by vasculogenesis, where embryonic vessels form from endothelial precursors, then angiogenesis which is the sprouting of interstitial tissue columns into the lumen of preexisting blood vessels. Angiogenesis occurs in many inflammatory diseases and in many malignant disease states, including over 90% of solid tumours. Malignant melanoma (MM) is the most lethal skin cancer, highly angiogenic, highly metastatic, and refractory to all treatments. Raised serum levels of vascular endothelial growth factor (VEGF) strongly correlate MM disease progression and poor prognosis. Melanoma cells secrete several proangiogenic cytokines including VEGF-A, fibroblast growth factor (FGF-2), platelet growth factor (PGF-1), interleukin-8 (IL-8), and transforming growth factor (TGF-1) that modulate the angiogenic switch, changing expression levels during tumour transition from radial to invasive vertical and then metastatic growth. We highlight modern and historical lines of research and development that are driving this exciting area of research currently.

Blood vessel maturation, vascular phenotype and angiogenic potential in malignant melanoma: one step forward for overcoming anti-angiogenic drug resistance?

Angiogenesis is a pivotal process for growth, invasion and spread of the majority of solid tumors including melanoma. Anti-angiogenic agents have not been systematically tested in patients with advanced melanoma. Clinical efficacy of angiogenesis inhibitors targeting endothelial cells has not been as affirmative as initially hoped and improved clinical outcomes have been observed in combination with chemotherapy or additional drugs for many types of human cancer. However, angiogenesis is not only dependent on endothelial cell invasion and proliferation, it also requires pericyte coverage of vascular sprouts for stabilization and maturation of vascular walls. Recent data suggest that pericytes might be able to confer resistance to anti-vascular endothelial growth factor (VEGF) therapy. This review will focus on the significance of the vascular phenotype but also on the impact of pericyte-mediated vessel maturation for the susceptibility to anti-angiogenic therapy, including malignant melanoma, which we identified as crucial factor regarding therapeutic efficacy.

A pregnant female with a large intracranial mass: Reviewing the evidence to obtain management guidelines for intracranial meningiomas during pregnancy

INTRODUCTION

Non-obstetric surgery for intracranial meningioma is uncommon during pregnancy and poses significant risks to both the mother and the fetus. We present a case of a parturient that presented with acute mental status changes and we illustrate the decision making process that resulted in a best-possible outcome.

CASE DESCRIPTION

A woman at 29-week gestation presented with acute language and speech deficits and deteriorating mental status after 2 weeks of headache. Imaging demonstrated a large intracranial mass. A multidisciplinary meeting was held to determine the best treatment plan. The decision was to proceed with caesarean delivery under epidural anesthesia to allow intraoperative monitoring of neurological function. Six hours after successful delivery, the patient had acute mental status changes and she was taken to the operating room immediately for resection of her tumor, which turned out to be a clear cell meningioma.

DISCUSSION

Cerebral meningioma is usually a slow-growing tumor; however, during pregnancy, the mass may expand rapidly due to hormonal receptor expression. The presentation of this patient would have normally led to urgent resection of the mass. But the complicating factor was her 29-week pregnancy as standard intraoperative treatment during neurosurgery is known to adversely affect the fetus. A multidisciplinary meeting was critical for this patient's care, and is recommended by us when treating such patients.

Medical therapies for meningiomas

Meningiomas are the most common primary brain tumor in adults. Although the majority of these tumors can be effectively treated with surgery and radiation therapy, an important subset of patients have inoperable tumors, or develop recurrent disease after surgery and radiotherapy, and require some form of medical therapy. There are increasing numbers of studies evaluating various medical therapies but the results remain disappointing. Chemotherapies and hormonal therapies have been generally ineffective, although somatostatin analogues may have therapeutic potential. There is also increasing interest in targeted molecular therapies. Agents inhibiting platelet derived growth factor receptors and epidermal growth factor receptors have shown little efficacy, but molecular agents inhibiting vascular endothelial growth factor receptors appear to have some promise. As with other tumors, advances in the medical therapies for meningiomas will require improved understanding of the molecular pathogenesis of these tumors, more predictive preclinical models, and efficient mechanisms for conducting clinical trials, given the small population of eligible patients.

Kinetics of angiogenic changes in a new mouse model for hepatocellular carcinoma

BACKGROUND

The increasing incidence of hepatocellular carcinoma in Western countries has led to an expanding interest of scientific research in this field. Therefore, a vast need of experimental models that mimic the natural pathogenesis of hepatocellular carcinoma (HCC) in a short time period is present. The goal of our study was (1) to develop an efficient mouse model for HCC research, in which tumours develop in a natural background of fibrosis and (2) to assess the time-dependent angiogenic changes in the pathogenesis of HCC.

METHODS

Weekly intraperitoneal injections with the hepatocarcinogenic compound N-nitrosodiethylamine was applied as induction method and samples were taken at several time points to assess the angiogenic changes during the progression of HCC.

RESULTS

The N-nitrosodiethylamine-induced mouse model provides well vascularised orthotopic tumours after 25 weeks. It is a representative model for human HCC and can serve as an excellent platform for the development of new therapeutic targets.

Angiogenesis and progression in human melanoma

In tumor growth, angiogenesis, the process of new-formation of blood vessels from pre-existing ones, is uncontrolled and unlimited in time. The vascular phase is characterized by the new-formation of vascular channels that enhances tumor cell proliferation, local invasion and hematogenous metastasis. Human malignant melanoma is a highly metastatic tumor with poor prognosis, and high resistance to treatment. Parallel with progression, melanoma acquires a rich vascular network, whereas an increasing number of tumor cells express the laminin receptor, which enables their adhesion to the vascular wall, favouring tumor cell extravasation and metastases. Melanoma neovascularization has been correlated with poor prognosis, overall survival, ulceration and increased rate of relapse. Secretion of various angiogenic cytokines, i.e. VEGF-A, FGF-2, PGF-1 and -2, IL-8, and TGF-1 by melanoma cells promote the angiogenic switch and has been correlated to transition from the radial to the vertical growth phase, and to the metastatic phase. Moreover, melanoma cells overexpress alphavbeta3, alphavbeta5, alpha2beta1 and alpha5beta1 integrins and release, together with stromal cells, higher amount of metalloproteases that increasing their invasive potential and angiogenesis. Basing on these observations, different molecular targets of antiangiogenic molecules has be recognized and various antiangiogenic agents are currently in preclinical and clinical trials for melanoma.

Metal transcription factor-1 is involved in hypoxia-dependent regulation of placenta growth factor in trophoblast-derived cells

Placenta growth factor (PlGF) is a placental angiogenic factor. Metal-responsive transcription factor (MTF)-1 was reported to take part in the hypoxic induction of PlGF in RAS-transformed mouse fibroblasts. We contrarily showed that PlGF mRNA and protein levels decreased under hypoxia in a choriocarcinoma BeWo cell line derived from trophoblast. In this report, we examined whether hypoxia-dependent regulation of the PlGF gene in these cells also depends on MTF-1. We analyzed the effect of hypoxia on MTF-1 expression, and it was revealed to be decreased. Moreover, MTF-1 small interfering RNA treatment decreased PlGF mRNA level. To investigate the transcription of PlGF under hypoxia, we cloned promoter region of the human PlGF. Promoter deletion analysis suggested that triple repeats of metal-responsive element located between -511 and -468 bp in the promoter are important for the hypoxic regulation of PlGF. Treatment with MTF-1 small interfering RNA resulted in the significant decreased luciferase activity in PlGF reporter constructs. Chromatin immunoprecipitation showed the binding of the MTF-1 protein to the promoter region. We examined MTF-1 immunoreactivity in trophoblasts of term placental tissue from patients with normal pregnancies and preeclampsia, which represents a condition of placental hypoxia. Immunoreactivity of the MTF-1 protein was decreased in placentas from pregnant women with preeclampsia when compared with those from normal pregnant women. Taken together, these findings suggest that MTF-1 is involved in hypoxia-dependent regulation of PlGF in trophoblast-derived cells.

FLT1 and its ligands VEGFB and PlGF: drug targets for anti-angiogenic therapy?

Less than 5 years ago, it was still not clear whether anti-angiogenic drugs would prove successful in the clinic. After numerous patients with cancer or age-related macular degeneration have been treated with these drugs, they have now become part of the standard range of therapeutic tools. Despite this milestone, anti-angiogenic therapy still faces a number of clinical hurdles, such as improving efficacy, avoiding escape and resistance, and minimizing toxicity. Hopefully, other agents with complementary mechanisms, such as those that target placental growth factor, will offer novel opportunities for improved treatment.

Expression of vascular endothelial growth factor-A and mRNA stability factor HuR in human meningiomas

We studied the expression of vascular endothelial growth factor-A (VEGF-A) and mRNA stability factor HuR in 40 supratentorial meningiomas using RT-PCR, ELISA and immunohistochemistry, and analyzed their associations with the clinicopathological characteristics, including microvascular density (MVD), peritumoral brain edema (PTBE), histological subtypes and grades, and the performance of preoperative arterial embolization. Furthermore, we investigated the involvement of HuR in the upregulation of VEGF-A expression using primary meningioma cell cultures. The level of VEGF-A is elevated in meningiomas with PTBE and in higher grade meningiomas. Preoperative arterial embolization did not significantly increase the level of VEGF-A, but it did increase the expression of HuR in tumor tissues. HuR expression was correlated positively with VEGF-A expression in meningioma tissues. In in vitro experiments, hypoxia induced the upregulation of VEGF-A expression and the cytoplasmic translocation of HuR protein in meningioma cells, and inhibition of the cytoplasmic translocation of HuR reduced the upregulation of VEGF-A expression in meningioma cells. These findings suggest that the expression of VEGF-A relates to the development of PTBE with meningiomas and the histological grade, and that HuR is involved in the upregulation of VEGF-A expression in human meningiomas.

Angiogenesis in melanoma

The process of angiogenesis is crucial for progression and metastasis of the majority of solid tumors including melanomas. The current review summarizes existing knowledge of the mechanisms of angiogenesis in melanoma, as well as current anti-angiogenic therapeutic strategies and their targets. We focus primarily on the role of key growth factors that are secreted by melanoma cells and known to trigger angiogenic responses, and their receptors as expressed on both endothelial and melanoma cells. Many of these growth factors function in synergy with receptors for extracellular matrix, integrins, and matrix metalloproteinases (MMPs). All of these systems of molecules are activated during major stages of angiogenesis such as endothelial migration, proliferation, and reorganization of surrounding extracellular matrix. The blockade of these molecules and their downstream pathways leads to inhibition of melanoma vascularization. Thus, these classes of molecules are essential for melanoma angiogenesis and, therefore, might serve as promising targets for therapeutic intervention. Many recently developed compounds targeting key pathways in angiogenesis are in their final stages of clinical trials.

Targeted drug therapy for meningiomas

✓ Although advances in surgery, radiation therapy, and stereotactic radiosurgery have significantly improved the treatment of meningiomas, there remains an important subset of patients whose tumors are refractory to conventional therapy. Treatment with traditional chemotherapeutic agents has provided minimal benefit. In this review, the role of targeted molecular therapies for recurrent or progressive meningiomas is discussed.

Role of placenta growth factor in malignancy and evidence that an antagonistic PlGF/Flt-1 peptide inhibits the growth and metastasis of human breast cancer xenografts

The angiogenic growth factor placenta growth factor (PlGF) is implicated in several pathologic processes, including the growth and spread of cancer. We found by immunohistochemistry that 36% to 60% and 65% of primary breast cancers express PlGF and its receptor Flt-1, respectively. These findings suggest that PlGF may be active in tumor growth and metastasis beyond its role in angiogenesis. It was found that exogenously added PlGF (2 nmol/L), in contrast to vascular endothelial growth factor (2 nmol/L), significantly stimulated in vitro motility and invasion of the human breast tumor lines MCF-7 and MDA-MB-231. A PlGF-2/Flt-1-inhibiting peptide, binding peptide 1 (BP1), that binds Flt-1 at or near the heparin-binding site was identified and synthesized. Both PlGF-stimulated motility and invasion were prevented by treatment with BP1 (P < 0.05), as well as by anti-PlGF antibody. Treatment of mice bearing s.c. MDA-MB-231 with BP1 (200 mug i.p., twice per week) decreased the number of spontaneous metastatic lung nodules by 94% (P < 0.02), whereas therapy of animals with orthotopic mammary fat pad tumors decreased pulmonary metastases by 82% (P < 0.02). These results indicate, for the first time, that PlGF stimulates the metastatic phenotype in these breast cancer cells, whereas therapy with a PlGF-2/Flt-1 heparin-blocking peptide reduces the growth and metastasis of human breast cancer xenografts.

Placenta growth factor expression in human atherosclerotic carotid plaques is related to plaque destabilization

BACKGROUND AND PURPOSE

Placenta growth factor (PlGF) mediates angiogenesis and inflammation, but its role in human atherosclerosis is unknown. This study was designed to test the hypothesis that PlGF-expression in human atherosclerotic carotid plaques is related to inflammation, vascularization and clinical plaque instability.

METHODS

The expression of PlGF, C-reactive protein (CRP) and CD40L was analyzed with Western blots in carotid plaques of 60 patients. Cellular infiltration (CD68, CD3) and vascularization (von-Willebrand-factor) was assessed by immunohistochemistry.

RESULTS

Symptomatic patients showed higher levels of PlGF than asymptomatic patients (115.4+/-8.2 versus 83.6+/-10.5 densitometric units (DU), p<0.05) and higher grading for inflammatory cells and microvessels (CD3: 2.3+/-0.1 versus 0.6+/-0.1, p<0.001, CD68: 2.4+/-0.1 versus 0.8+/-0.1, p<0.001, microvessels: 2.3+/-0.1 versus 1.5+/-0.1, p<0.01). PlGF-expression showed a positive correlation to the expression of CRP (r=0.5, p<0.001) and CD40L (r=0.4, p<0.01).

CONCLUSIONS

PlGF-expression within human atherosclerotic lesions is associated with plaque inflammation and microvascular density, suggesting a role for PlGF in plaque destabilization and, thus, in clinical manifestation of the disease.

KRN951, a highly potent inhibitor of vascular endothelial growth factor receptor tyrosine kinases, has antitumor activities and affects functional vascular properties

Vascular endothelial growth factor (VEGF) plays a key role in tumor angiogenesis by stimulating the proangiogenic signaling of endothelial cells via activation of VEGF receptor (VEGFR) tyrosine kinases. Therefore, VEGFRs are an attractive therapeutic target for cancer treatment. In the present study, we show that a quinoline-urea derivative, KRN951, is a novel tyrosine kinase inhibitor for VEGFRs with antitumor angiogenesis and antigrowth activities. KRN951 potently inhibited VEGF-induced VEGFR-2 phosphorylation in endothelial cells at in vitro subnanomolar IC50 values (IC50 = 0.16 nmol/L). It also inhibited ligand-induced phosphorylation of platelet-derived growth factor receptor-beta (PDGFR-beta) and c-Kit (IC50 = 1.72 and 1.63 nmol/L, respectively). KRN951 blocked VEGF-dependent, but not VEGF-independent, activation of mitogen-activated protein kinases and proliferation of endothelial cells. In addition, it inhibited VEGF-mediated migration of human umbilical vein endothelial cells. Following p.o. administration to athymic rats, KRN951 decreased the microvessel density within tumor xenografts and attenuated VEGFR-2 phosphorylation levels in tumor endothelium. It also displayed antitumor activity against a wide variety of human tumor xenografts, including lung, breast, colon, ovarian, pancreas, and prostate cancer. Furthermore, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) analysis revealed that a significant reduction in tumor vascular hyperpermeability was closely associated with the antitumor activity of KRN951. These findings suggest that KRN951 is a highly potent, p.o. active antiangiogenesis and antitumor agent and that DCE-MRI would be useful in detecting early responses to KRN951 in a clinical setting. KRN951 is currently in phase I clinical development for the treatment of patients with advanced cancer.

Human blood late outgrowth endothelial cells for gene therapy of cancer: determinants of efficacy

Human adult blood late outgrowth endothelial cells (BOECs) are potential yet untested cellular vehicles to target tumor-cytotoxic effectors to tumors. We show that, following intravenous injection into irradiated mice, BOECs home to Lewis lung carcinoma (LLC) lung metastases, but less so to liver or kidney metastases. BOECs targeted most but not all of the lung metastases, to a different degree. While most of the homed BOECs took up an extravascular position, some integrated into tumor vessels. Sequestration into normal tissue was low. Placental growth factor mediated both migration and invasion of BOECs into LLC spheroid masses in vitro, as did VEGF. When armed with a suicide gene, BOECs exerted a bystander effect on LLC cells in vitro and in vivo. Surprisingly, i.v. administration of armed BOECs into mice bearing multi-organ LLC metastases did not prolong survival. In addition to homing efficacy other parameters impacted upon the efficacy of BOECs. These include the ultimate susceptibility of BOECs to suicide gene-induced cell death, their paracrine proliferative effect on LLC cells and their low proliferation rate compared to LLC cells. Addressing these determinants may make BOECs a useful addition to the arsenal of tumor-targeting moieties.

Increased melanoma growth and metastasis spreading in mice overexpressing placenta growth factor

Placenta growth factor (PlGF), a member of the vascular endothelial growth factor family, plays an important role in adult pathological angiogenesis. To further investigate PlGF functions in tumor growth and metastasis formation, we used transgenic mice overexpressing PlGF in the skin under the control of the keratin 14 promoter. These animals showed a hypervascularized phenotype of the skin and increased levels of circulating PlGF with respect to their wild-type littermates. Transgenic mice and controls were inoculated intradermally with B16-BL6 melanoma cells. The tumor growth rate was fivefold increased in transgenic animals compared to wild-type mice, in the presence of a similar percentage of tumor necrotic tissue. Tumor vessel area was increased in transgenic mice as compared to controls. Augmented mobilization of endothelial and hematopoietic stem cells from the bone marrow was observed in transgenic animals, possibly contributing to tumor vascularization. The number and size of pulmonary metastases were significantly higher in transgenic mice compared to wild-type littermates. Finally, PlGF promoted tumor cell invasion of the extracellular matrix and increased the activity of selected matrix metalloproteinases. These findings indicate that PlGF, in addition to enhancing tumor angiogenesis and favoring tumor growth, may directly influence melanoma dissemination.

Delineation, functional validation, and bioinformatic evaluation of gene expression in thyroid follicular carcinomas with the PAX8-PPARG translocation

A subset of follicular thyroid carcinomas contains a balanced translocation, t(2;3)(q13;p25), that results in fusion of the paired box gene 8 (PAX8) and peroxisome proliferator-activated receptor gamma (PPARG) genes with concomitant expression of a PAX8-PPARgamma fusion protein, PPFP. PPFP is thought to contribute to neoplasia through a mechanism in which it acts as a dominant-negative inhibitor of wild-type PPARgamma. To better understand this type of follicular carcinoma, we generated global gene expression profiles using DNA microarrays of a cohort of follicular carcinomas along with other common thyroid tumors and used the data to derive a gene expression profile characteristic of PPFP-positive tumors. Transient transfection assays using promoters of four genes whose expression was highly associated with the translocation showed that each can be activated by PPFP. PPFP had unique transcriptional activities when compared with PAX8 or PPARgamma, although it had the potential to function in ways qualitatively similar to PAX8 or PPARgamma depending on the promoter and cellular environment. Bioinformatics analyses revealed that genes with increased expression in PPFP-positive follicular carcinomas include known PPAR target genes; genes involved in fatty acid, amino acid, and carbohydrate metabolism; micro-RNA target genes; and genes on chromosome 3p. These results have implications for the neoplastic mechanism of these follicular carcinomas.

Effect of sinomenine on gene expression of the IL-1β-activated human synovial sarcoma

Sinomenine is an alkaloid with pharmacological effects of anti-inflammation, anti-angiogenesis, anti-arthritis and immunosuppression. This study aimed to investigate the effect of sinomenine on gene expression of human synovial sarcoma cells (Hs701.T) activated by IL-1 beta. The proliferative effect of sinomenine was examined in the presence or absence of IL-1 beta by the [3H]-thymidine incorporation and MTT assay, respectively. Using DNA microarray technology and RT-PCR, the activating action of IL-1 beta and modulatory effect of sinomenine on Hs701.T were simultaneously determined. Results showed that IL-1 beta could stimulate the proliferation and gene expression of Hs701.T cells. Sinomenine could significantly inhibit proliferation of IL-1 beta-activated Hs701.T cells and suppress expression of 17 genes including IL-6, PlGF, Daxx, and HSP27. These genes were found to be important in tumor progression through the mediation of inflammation, cell adhesion, proliferation, apoptosis and angiogenesis. In conclusion, our study provides supplementary information for the further studies on the pharmacological effects of sinomenine acting on synovial sarcoma.

Expression and localization of VEGF-C and VEGFR-3 in glioblastomas and haemangioblastomas

Primary human brain tumours account for approximately 2% of all cancers. High levels of expression of vascular endothelial growth factor-A (VEGF-A), a potent angiogenic factor, are linked to poor prognosis. In contrast, the potential role in human brain tumour biology of newer VEGF family members, VEGF-C and VEGF-D, both of which are lymphangiogenic factors, is poorly understood. In the present study, the expression of all VEGFs (VEGF-A, -B, -C, and -D) and their receptors (VEGFR-1, -2, and -3) has been assessed in 39 primary human brain tumours. The well-established findings were confirmed with VEGF-A. Surprisingly, however, VEGF-C and VEGF-D, as well as VEGFR-3, were expressed in some tumour types such as haemangioblastomas and glioblastomas, despite their lack of lymphatic vessels. VEGF-C and VEGFR-3 transcripts were localized to the tumour palisade around necrotic areas in glioblastomas and were evenly distributed throughout haemangioblastomas. VEGF-C protein was localized by immunohistochemistry to the palisade layer in glioblastomas. More than 50% of VEGF-C-positive cells also expressed the intermediate-stage inflammatory macrophage marker CD163; however, a significant proportion of VEGF-C-positive cells were CD163-negative. These data demonstrate the presence of molecules, primarily described as regulators of lymphangiogenesis, in normal human brain and brain tumours that are devoid of lymphatics. Their localization in macrophages points to a role in tumour-associated inflammation.

The biology of vascular endothelial growth factor-B (VEGF-B)

The formation of new blood vessels (angiogenesis) is critical for both embryonic development and a variety of normal postnatal physiological processes. Various pathological processes, most notably tumour growth and chronic inflammation, are also known to be dependent on the new vessel formation. Amongst the variety of factors that contribute to the regulation of this complex process, vascular endothelial growth factor (VEGF or VEGF-A) is arguably the most well characterised. The VEGF family of growth factors is now known to comprise of VEGF-A plus four additional members, including VEGF-B. In contrast to VEGF-A, surprisingly little is known about the precise biological role of VEGF-B. Unlike VEGF-A, which binds to the two receptor tyrosine kinases VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1/KDR), VEGF-B binds only to VEGFR-1 and the functional significance of VEGFR-1 signalling has remained problematic. More recently, however, evidence has emerged suggesting a key role for VEGFR-1 signalling in pathological angiogenesis and this has raised the possibility that, like VEGF-A, VEGFR-1 specific ligands such as VEGF-B may provide for novel therapeutic strategies and/or represent new therapeutic targets. Here we review current knowledge of the biology of VEGF-B. We note that although analysis to date, including expression profiling and the generation of gene targetted mice, has provided only limited insights, future studies using recently generated recombinant proteins and antagonist monoclonal antibodies should provide for a more comprehensive understanding.

Placenta growth factor is over-expressed and has prognostic value in human breast cancer

Placenta growth factor (PlGF) belongs to the vascular endothelial growth factor (VEGF) family, a group of angiogenic factors that are crucial for tumour angiogenesis. Very little is known about the significance of PlGF in human cancer. We hypothesise that PlGF may have a potent influence in breast cancer. This study examined PlGF levels in human breast cancer in relation to patient's clinical parameters. PlGF expression and distribution was examined quantitatively using real-time quantitative polymerase chain reaction (Q-PCR) on a cohort of human breast cancer tissue (n = 119) and background breast tissue (n = 33), qualitatively using reverse transcriptase polymerase chain reaction (RT-PCR) on a range of cell lines, and immunohistochemically on patient samples. All these techniques revealed that PlGF expression was dramatically increased (P = 0.028) in breast cancer tissues compared with normal breast tissue. We demonstrate that PlGF displays prognostic value through analysis of patient survival status (6-year follow-up), as elevated levels of PlGF were significantly associated (P = 0.017) with recurrence, metastasis and patient mortality. Our study has shown that PlGF is over-expressed in breast cancer tissues and correlates with patient prognosis, and is likely to play a major role in the pathogenesis of tumours.

Expression of VEGF and its receptors in different brain tumors

INTRODUCTION

Vascular endothelial growth factor (VEGF) and its receptors VEGFR-1 and -2 are considered to play a major in tumor angiogenesis, which is a prerequisite for growth of solid tumors. Glioblastoma multiforme is a prominent example of VEGF-induced tumor vascularization; however, little is known about VEGF and in particular VEGFR expression in other types of brain tumors.

METHODS

VEGFR mRNA was quantified by real time RT-PCR in 12 different types of brain tumors and compared to VEGF protein content measured by ELISA. VEGF splice variants were determined by an RT-PCR method.

RESULTS

VEGF protein was highest in glioblastoma and metastatic kidney tumors. In all types of tumors the diffusible splice forms VEGF(121) and VEGF(165) were expressed; VEGF(189) was minor in a few tumors. Expression of VEGF receptors did not necessarily correlate with VEGF content. Both were highly expressed in glioblastomas, but in meningiomas VEGF was low and VEGFR high, and in metastatic tumors the reverse. With few exceptions, in particular oligodendrogliomas, VEGFR-1 expression was parallel to VEGFR-2 expression. Interestingly, for the astrocytic gliomas, the expression of VEGFR correlated well to the tumor malignancy, even better than VEGF content.

CONCLUSIONS

These results show that VEGF and VEGFR expression in various types of brain tumors differ and are not necessarily parallel.

KRN633: A selective inhibitor of vascular endothelial growth factor receptor-2 tyrosine kinase that suppresses tumor angiogenesis and growth

Vascular endothelial growth factor (VEGF) and its receptor VEGFR-2 play a central role in angiogenesis, which is necessary for solid tumors to expand and metastasize. Specific inhibitors of VEGFR-2 tyrosine kinase are therefore thought to be useful for treating cancer. We showed that the quinazoline urea derivative KRN633 inhibited tyrosine phosphorylation of VEGFR-2 (IC50 = 1.16 nmol/L) in human umbilical vein endothelial cells. Selectivity profiling with recombinant tyrosine kinases showed that KRN633 was highly selective for VEGFR-1, -2, and -3. KRN633 also blocked the activation of mitogen-activated protein kinases by VEGF, along with human umbilical vein endothelial cell proliferation and tube formation. The propagation of various cancer cell lines in vitro was not inhibited by KRN633. However, p.o. administration of KRN633 inhibited tumor growth in several in vivo tumor xenograft models with diverse tissue origins, including lung, colon, and prostate, in athymic mice and rats. KRN633 also caused the regression of some well-established tumors and those that had regrown after the cessation of treatment. In these models, the trough serum concentration of KRN633 had a more significant effect than the maximum serum concentration on antitumor activity. KRN633 was well tolerated and had no significant effects on body weight or the general health of the animals. Histologic analysis of tumor xenografts treated with KRN633 revealed a reduction in the number of endothelial cells in non-necrotic areas and a decrease in vascular permeability. These data suggest that KRN633 might be useful in the treatment of solid tumors and other diseases that depend on pathologic angiogenesis.

Regulation of malignant progression by the hypoxia-sensitive transcription factors HIF-1alpha and MTF-1

Solid tumors are known to develop microenvironmental hypoxia or anoxia due to malfunction and malformation of blood vessels and the energy demands of the highly proliferative tumor cells. Oxygen deprivation can cause aberrant modifications of signaling pathways and their downstream transcription factors that are believed to contribute to malignancy. Here, we review the latest studies related to the involvement of hypoxia-inducible transcription factor-1alpha (HIF-1alpha), the first known mammalian intracellular hypoxia sensor, in tumor development. We propose that a second far less studied protein, metal transcription factor-1 (MTF-1), acts as a more general oxygen sensor, responding to both hypoxia and oxidative stress, and is also intimately involved in malignant progression. Existing evidence suggests that activation of these two ubiquitous proteins, by hypoxia and genetic modifications, modulate the expression patterns of a number of important proteins involved in tumorigenesis.

The significance of placenta growth factor in angiogenesis and clinical outcome of human gastric cancer

Placenta growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family of proangiogenic factors and its overexpression has been linked to pathological angiogenesis. We studied the relationship between the expression of PlGF and VEGF in human gastric cancer tissues and microvessel density (MVD), as well as clinical outcome in 79 patients with gastric cancer by using an enzyme immunoassay for PlGF and VEGF expression levels in gastric cancers and surrounding non-cancerous mucosa. PlGF protein levels were significantly higher in tumor than in the corresponding non-tumorous mucosa (median value 48.5 vs 9.8 pg/mg, P < 0.001). In contrast, VEGF protein levels were not (66.7 vs 80.7 pg/mg, P = 0.522). VEGF expression level was not significantly correlated with MVD, patient survival, and clinicopathological factors except Lauren classification in this study. PlGF may be an important angiogenic factor in human gastric cancer, and PlGF expression level was significantly correlated with serosal invasion, positive lymph node metastases, tumor stages, and patient survival.

Loss of metal transcription factor-1 suppresses tumor growth through enhanced matrix deposition

Metal transcription factor-1 (MTF-1) is a ubiquitous transcriptional regulator and chromatin insulator with roles in cellular stress responses and embryonic development. The studies described herein establish for the first time the involvement of MTF-1 in tumor development. Genetically manipulated ras-transformed mouse embryonic fibroblasts (MEFs), wild-type (MTF-1+/+), or nullizygous for MTF-1 (MTF-1-/-) were used to develop fibrosarcoma tumors. Loss of MTF-1 resulted in delayed tumor growth associated with increased matrix collagen deposition and reductions in vasculature density. Molecular consequences of MTF-1 loss include increased expression and activation of the transforming growth factor-beta1 (TGF-beta1) and tissue transglutaminase (tTG), two proteins with documented roles in the production and stabilization of extracellular matrix (ECM). Our findings support the hypothesis that MTF-1 enhances the ability of the developing tumor mass to evade fibrosis and scarring of the tumor, a critical step in tumor cell proliferation.

Genetic dissection of tumor angiogenesis: are PlGF and VEGFR-1 novel anti-cancer targets?

Many proliferative diseases, most typically cancer, are driven by uncontrolled blood vessel growth. Genetic studies have been very helpful in unraveling the cellular and molecular players in pathological blood vessel formation and have provided opportunities to reduce tumor growth and metastasis. The fact that tumor vessels and normal blood vessels have distinct properties may help in designing more specific--and therefore safer--anti-angiogenic strategies. Such strategies may interfere with angiogenesis at the cellular or molecular level. Possible molecular targets include angiogenic growth factors and their receptors, proteinases, coagulation factors, junctional/adhesion molecules and extracellular matrix (ECM) components. Some anti-angiogenic drugs, i.e., vascular endothelial growth factor (VEGF) antibodies and VEGF receptor-2 (VEGFR-2) inhibitors, have progressed into clinical cancer trials. While the results of these trials support the potential of anti-angiogenic therapy to treat cancer, they also demonstrate the need for more effective and safer alternatives. Targeting placental growth factor (PlGF) or VEGFR-1 may constitute such an alternative since animal studies have proven their pleiotropic working mechanism and attractive safety profile. Together, these insights may bring anti-angiogenic drugs closer from bench to bedside.

Angiogenesis in intracranial meningiomas: immunohistochemical and molecular study

Much of the morbidity of intracranial meningiomas is related to the degree of tumour vascularity and the extent of peritumoural vasogenic oedema. Several studies have shown that vascular endothelial growth factor (VEGF) is up-regulated in meningiomas, although its relationship with tumour vasculature is still unclear. In order to better understand the angiogenic assessment of intracranial meningiomas, we analysed its vascular pattern, both as number and as morphologic configuration of microvessels. Moreover, we investigated the mRNA-VEGF expression, relating this expression to vascular pattern. A total of 40 intracranial meningiomas, classified as benign (31 cases), atypical (7 cases), and anaplastic (2 cases) were analysed. RT-PCR analyses of mRNA-VEGF and competitive-PCR were performed. VEGF expression and microvessel density (MVD) were also immunohistochemically investigated. Grade II-III meningiomas showed numerous small microvessels (mean: 34), while the majority of Grade I showed few larger vessels (mean: 13.09) (P = 0.000003). A microvessel pattern overlapping into atypical subtype was found in eignt of the 31 (25.8%) Grade I meningiomas. A significant association was found between grading and vascular pattern (P = 0.0002), as well as between the MVD and the immunohistochemical expression of VEGF (P = 0.0005). The expression of mRNA agreed with the immunohistochemical expression of the protein (P < 0.0001). A total of 39 cases expressed the 121 VEGF isoform and, among these, 28 cases also expressed the 165 isoform. Only 9 cases expressed both isoforms 165 and 189. Grade II and III meningiomas showed a preponderant expression of soluble isoforms (121 and 165). These results prompt us to speculate that the microvessel pattern could underlie a higher metabolic demand, probably due to a rapid growth with a consequent worse clinical behaviour of the tumour. In this sense, the vascular pattern may be used as a prognostic factor, in order to mostly focus attention on those Grade I meningiomas which have a higher likelihood of either recurrence or development of perilesional oedema. The pattern of vasculature itself seems to be dependent on the types of VEGF isoforms: the Grade II-III meningiomas (that presented numerous microvessels) expressed the soluble isoforms 121 and 165, while the isoform 189 was more frequently detected in Grade I meningiomas.

Angiogenic factors in the central nervous system

The past decade has seen considerable advances in the understanding of angiogenesis. Blood vessel development and growth in the central nervous system are tightly controlled processes that are regulated by angiogenic factors. Angiogenic factors have been implicated in the pathogenesis of a wide variety of disorders, including primary and metastatic brain tumors, aneurysms, arteriovenous malformations, and cavernous malformations. The potential clinical applications of angiogenesis research include inhibition of angiogenesis to control brain tumors and therapeutic angiogenesis to promote collateral blood vessel formation among patients at risk of ischemia. This article summarizes the processes of blood vessel formation in the brain, examines the angiogenic factors that are prominent in the central nervous system, reviews the clinical use of angiogenesis inhibitors, and identifies areas for future investigation.

Altered tumor vessel maturation and proliferation in placenta growth factor-producing tumors: potential relationship to post-therapy tumor angiogenesis and recurrence

Cells in human tumor xenografts express similar levels of angiogenic growth factors before treatment. After radioimmunotherapy (RAIT) surviving tumor cells upregulate angiogenic growth factors, including placenta growth factor (PlGF), in a tumor-specific pattern. To determine the role of post-treatment PlGF expression on blood vessel recovery, tumor xenografts were assayed for post-RAIT vessel density (CD34+), proliferation (PCNA+) and maturity (SMA+ pericytes/mural cells). To further analyze the role of PlGF in blood vessel formation, PlGF-containing Matrigel implants were also assessed in a similar manner. The xenografts producing post-treatment PlGF increased CD34+ microvessel density 2- to 4-fold over untreated controls (p < 0.05) within 3 weeks of RAIT treatment. The proportion of mature microvessels (SMA+) decreased. Pericyte coverage and density of microvessels remained stable in the tumor that expressed neither PlGF nor VEGF after treatment. Hemoglobin content of PlGF-containing Matrigel implants was 5.7-fold that of anti-PlGF/anti-VEGF treated controls (Day 6, p < 0.03). The vessel density in PlGF-implants averaged 36.8 +/- 10.6/mm compared to 4.9 +/- 6.5/mm(2) in controls (p < 0.001). Vessels of PlGF-implants were lined by vWF+ cells, which were mostly flt-1+. These findings point to a role for PlGF in rapid restoration of tumor blood supply after treatment and thus, to enhanced likelihood of tumor regrowth. Likewise, the cells of primary human tumors that upregulate PlGF after treatment may be more likely to survive and form recurring tumors. Prevention of this angiogenic response to treatment may require administration of anti-angiogenic therapy during, rather than after, treatment.

Angiogenesis in brain tumors

Angiogenesis is a complex process regulated by multiple stimulatory and inhibitory factors that are able to modulate the migration and/or proliferation of microvascular cells with the objective of formation of neovasculature from preexisting vessels. It involves well-coordinated steps including production and release of angiogenic factors, proteolytic degradation of extracellular matrix components to allow formation of capillary sprout, proliferation and directional migration of microvascular cells, and the final composition of new vessels [Senger (1996) Am. J. Pathol. 149:1-7]. Angiogenesis is present in a number of hypoxic and/or ischemic conditions in the central nervous system, in particular in infarctions and infectious processes. Angiogenesis also plays an important role in malignant primary tumors. Glioblastomas, the most malignant gliomas in adults, are among the most angiogenic of all human tumors. This review will examine recent data of the role of angiogenic growth factors in the neoplastic and reactive conditions in the brain.