Coexpression of hepatocyte growth factor/scatter factor (HGF/SF) and its receptor cMET predict recurrence of meningiomas

Receptor Tyrosine Kinases as Candidate Prognostic Biomarkers and Therapeutic Targets in Meningioma

Meningioma (MGM) is the most common type of intracranial tumor in adults. The validation of novel prognostic biomarkers to better inform tumor stratification and clinical prognosis is urgently needed. Many molecular and cellular alterations have been described in MGM tumors over the past few years, providing a rational basis for the identification of biomarkers and therapeutic targets. The role of receptor tyrosine kinases (RTKs) as oncogenes, including those of the ErbB family of receptors, has been well established in several cancer types. Here, we review histological, molecular, and clinical evidence suggesting that RTKs, including the epidermal growth factor receptor (EGFR, ErbB1), as well as other members of the ErbB family, may be useful as biomarkers and therapeutic targets in MGM.

Overexpression of Hepatocyte growth factor and its soluble receptor (s-cMet) in the serum of patients with different grades of meningioma

OBJECTIVES

Meningiomas are the most common primary intracranial tumor. Hepatocyte growth factor (HGF) and its receptor, cMet, were shown to be involved in meningioma. This study was aimed to determine the concentration of HGF and soluble cMet (s-cMet) in the serum of patients with different grades of meningioma.

METHODS

Ninety serum samples from different grades of meningioma patients (42 cases of grade I, 28 grade II, 20 grade III) and 51 controls were included in this study. The serum total protein concentration (TPC) was measured by a Bio-Rad protein assay and serum concentration of HGF and s-cMet by enzyme linked immunosorbent assay (ELISA).

RESULTS

No significant change in the serum TPC of patients was seen as compared to controls. We also showed that serum HGF and s-cMet concentration in meningioma patients was higher than in controls. The results showed that starting from grades I to III meningioma, a significant increase in HGF and s-cMet serum concentration was observed (HGF; 380 ± 57.69, 430.27 ± 48.72, 596.36 ± 104.49 pg/ml, respectively, as compared to controls which was 327.72 ± 49.68 pg/ml and for s-cMet was 274.45 ± 45.05, 314.81 ± 38.71, 433.54 ± 51.81 ng/ml, respectively, as compared to controls which was 213.72 ± 29.13 ng/ml). The results showed that a high concentration of HGF and s-cMet is associated with advanced grades of meningioma.

CONCLUSION

It is concluded that HGF and s-cMet serum levels increased in meningioma patients and their concentration was significantly higher in more advanced grades of the disease. It is also suggested that HGF/s-cMet might be involved in the progression of meningioma.

Meningioma-Brain Crosstalk: A Scoping Review

Background: In recent years, it has become evident that the tumoral microenvironment (TME) plays a key role in the pathogenesis of various cancers. In meningiomas, however, the TME is poorly understood, and it is unknown if glia cells contribute to meningioma growth and behaviour. Objective: This scoping review investigates if the literature describes and substantiates tumour-brain crosstalk in meningiomas and summarises the current evidence regarding the role of the brain parenchyma in the pathogenesis of meningiomas. Methods: We identified studies through the electronic database PubMed. Articles describing glia cells and cytokines/chemokines in meningiomas were selected and reviewed. Results: Monocytes were detected as the most abundant infiltrating immune cells in meningiomas. Only brain-invasive meningiomas elicited a monocytic response at the tumour-brain interface. The expression of cytokines/chemokines in meningiomas has been studied to some extent, and some of them form autocrine loops in the tumour cells. Paracrine interactions between tumour cells and glia cells have not been explored. Conclusion: It is unknown to what extent meningiomas elicit an immune response in the brain parenchyma. We speculate that tumour-brain crosstalk might only be relevant in cases of invasive meningiomas that disrupt the pial-glial basement membrane.

Reduction in Hepatocyte Growth Factor Serum Levels is Associated with Improved Prognosis in Advanced Lung Adenocarcinoma Patients Treated with Afatinib: a Phase II Trial

BACKGROUND

C-met and its ligand, hepatocyte growth factor (HGF) have been associated with the resistance mechanism of EGFR-TKIs. HGF was evaluated as a clinical-marker of response in NSCLC patients treated with afatinib.

METHODS

Sixty-six patients with stage IIIB/IV lung adenocarcinoma and progression to any-line chemotherapy received afatinib 40 mg/day. Mutational EGFR and HER2 status were assessed by RT-PCR. HER2 amplification was evaluated by FISH. Serum HGF content was measured by ELISA before and 2 months after the start of treatment. HGF levels were assessed with the objective response rate (ORR), progression-free-survival (PFS), and overall survival (OS). This trial was registered on ClinicalTrials.gov: NCT01542437.

RESULTS

Fifty patients (75 %) were EGFR mutation positive. Response was achieved in 59 % of all patients and 78 % of EGFR mutated patients. Median PFS was 10 [95 % CI 6.8-13.1] and 14.5 months [10.9-18.9] for all and EGFR mutated patients, respectively. Median OS was 22.8 [17.5-28.1] and 32.4 months [18.3-46.6] for all and EGFR mutated patients, respectively. Patients with reduced serum HGF levels had improved ORR (75 % vs 44 %; p = 0.011), PFS (15.1 [2.9-27.3] vs 6.5 months [3.9-9.1]; p = 0.005) and OS (NR vs 14.5 months [7.8 - 21.3] p = 0.007). A reduction in serum HGF levels was an independent factor associated with longer PFS (HR 0.40; p = 0.021) and OS (HR 0.31; p = 0.006) in all and EGFR mutated patients.

CONCLUSIONS

A reduction in serum HGF levels was associated with improved outcomes in patients treated with afatinib. These results suggest HGF might have a role as a mechanism of resistance to EGFR-TKIs. HGF could represent a potential therapeutic target to prevent or reverse resistance particularly in EGFR mutated patients.

Targeting MET for glioma therapy

Glioblastoma multiforme is the most common and most lethal of all primary brain tumors. Even with the standard therapy, life expectancy is still poor, with an average survival of approximately 14 months following initial diagnosis. Hence, there is an urgent need for novel treatment strategies that inhibit proliferation and angiogenesis in high-grade gliomas. One such strategy consists of inhibiting receptor tyrosine kinases, including MET and/or its ligand hepatocyte growth factor (HGF). Because of their widespread involvement in human cancer, HGF and MET have emerged as promising therapeutic targets, and some inhibitory agents that target them have already entered clinical trials. In this paper, the authors highlight recent evidence implicating HGF/MET pathway deregulation in glioblastoma multiforme, discuss therapeutic approaches to inhibit HGF/MET signaling, and summarize ongoing clinical trials targeting this pathway.

Expression of c-MET in Invasive Meningioma

Background:

Meningiomas show high recurrence rates even after curative tumor removal. The invasiveness of meningiomas may contribute to their high recurrence rates. Recently, c-MET and hepatocyte growth factor (HGF) have been reported to be involved in cancer invasion.

Methods:

We examined the immunohistochemical expression of c-MET and HGF in 100 cases of patients with meningiomas who have undergone complete tumor removal.

Results:

c-MET^-High and HGFHigh were found in 17% and 13% of meningiomas, respectively. Brain invasion was observed in 17.6% of c-MET^-High meningiomas, but in only 2.4% of c-MET^-Low meningiomas (p=.033). Bone/soft tissue invasion was observed in 23.5% of c-MET^-High meningiomas and in 9.6% of c-MET^-Low meningiomas (p=.119). HGF^-High did not show statistical association with brain invasion or bone/soft tissue invasion. c-MET^-High demonstrated shorter recurrence-free survival (RFS, 93.5±8.2 months vs 96.1±1.9 months); however, this difference was not statistically significant (p=.139). There was no association of HGF^-High with RFS.

Conclusions:

This study demonstrates that c- MET^-High is associated with brain invasion of meningiomas, and that c-MET expression may be a useful predictive marker for meningioma recurrence. Patients with invasive meningiomas with high expressions of c-MET may be good candidates for targeted therapy using c-MET inhibitors.

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.

Interrogating tumor metabolism and tumor microenvironments using molecular positron emission tomography imaging. Theranostic approaches to improve therapeutics

Positron emission tomography (PET) is a noninvasive molecular imaging technology that is becoming increasingly important for the measurement of physiologic, biochemical, and pharmacological functions at cellular and molecular levels in patients with cancer. Formation, development, and aggressiveness of tumor involve a number of molecular pathways, including intrinsic tumor cell mutations and extrinsic interaction between tumor cells and the microenvironment. Currently, evaluation of these processes is mainly through biopsy, which is invasive and limited to the site of biopsy. Ongoing research on specific target molecules of the tumor and its microenvironment for PET imaging is showing great potential. To date, the use of PET for diagnosing local recurrence and metastatic sites of various cancers and evaluation of treatment response is mainly based on [(18)F]fluorodeoxyglucose ([(18)F]FDG), which measures glucose metabolism. However, [(18)F]FDG is not a target-specific PET tracer and does not give enough insight into tumor biology and/or its vulnerability to potential treatments. Hence, there is an increasing need for the development of selective biologic radiotracers that will yield specific biochemical information and allow for noninvasive molecular imaging. The possibility of cancer-associated targets for imaging will provide the opportunity to use PET for diagnosis and therapy response monitoring (theranostics) and thus personalized medicine. This article will focus on the review of non-[(18)F]FDG PET tracers for specific tumor biology processes and their preclinical and clinical applications.

Hepatocyte growth factor sensitizes brain tumors to c-MET kinase inhibition

PURPOSE

The receptor tyrosine kinase (RTK) c-MET and its ligand hepatocyte growth factor (HGF) are deregulated and promote malignancy in cancer and brain tumors. Consequently, clinically applicable c-MET inhibitors have been developed. The purpose of this study was to investigate the not-well-known molecular determinants that predict responsiveness to c-MET inhibitors and to explore new strategies for improving inhibitor efficacy in brain tumors.

EXPERIMENTAL DESIGN

We investigated the molecular factors and pathway activation signatures that determine sensitivity to c-MET inhibitors in a panel of glioblastoma and medulloblastoma cells, glioblastoma stem cells, and established cell line-derived xenografts using functional assays, reverse protein microarrays, and in vivo tumor volume measurements, but validation with animal survival analyses remains to be done. We also explored new approaches for improving the efficacy of the inhibitors in vitro and in vivo.

RESULTS

We found that HGF coexpression is a key predictor of response to c-MET inhibition among the examined factors and identified an ERK/JAK/p53 pathway activation signature that differentiates c-MET inhibition in responsive and nonresponsive cells. Surprisingly, we also found that short pretreatment of cells and tumors with exogenous HGF moderately but statistically significantly enhanced the antitumor effects of c-MET inhibition. We observed a similar ligand-induced sensitization effect to an EGF receptor small-molecule kinase inhibitor.

CONCLUSIONS

These findings allow the identification of a subset of patients that will be responsive to c-MET inhibition and propose ligand pretreatment as a potential new strategy for improving the anticancer efficacy of RTK inhibitors.

Angiogenesis in meningiomas

Neoangiogenesis has been correlated to biological aggressiveness and an adverse clinical course of several neoplasias. Its prognostic role in meningiomas appears to be controversial. Nonetheless, if adequately quantified with specific markers and appropriate scoring methods, angiogenesis seems to be significantly associated with a high growth fraction, development of recurrences and shorter overall survival of meningiomas. As a consequence, neoangiogenesis may represent a target for therapies aimed at reducing the growth of inoperable meningiomas or recurrence risk of totally resected tumors. Even more significantly, the identification of the factors that mediate angiogenesis in meningiomas could help us to determine appropriate novel anti-angiogenic therapies for these tumors. Herein the methods for quantification of angiogenesis as well as its regulating factors in meningiomas are reviewed.

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.

Loss of heterozygosity at 1p, 7q, 17p, and 22q in meningiomas

OBJECTIVE

Allelic losses or loss of heterozygosity (LOH) at many chromosomal loci have been found in the cells of meningiomas. The objective of this study was to evaluate LOH at several loci of different chromosomes (1p32, 17p13, 7q21, 7q31, and 22q13) in different grades of meningiomas.

METHODS

Forty surgical specimens were obtained and classified as benign, atypical, and anaplastic meningiomas. After DNA extraction, ten polymorphic microsatellite markers were used to detect LOH. Medical and surgical records, as well as pathologic findings, were reviewed retrospectively.

RESULTS

LOH at 1p32 was detected in 24%, 60%, and 60% in benign, atypical, and anaplastic meningiomas, respectively. Whereas LOH at 7q21 was found in only one atypical meningioma. LOH at 7q31 was found in one benign meningioma and one atypical meningioma. LOH at 17p13 was detected in 4%, 40%, and 80% in benign, atypical, and anaplastic meningiomas, respectively. LOH at 22q13 was seen in 48%, 60%, and 60% in benign, atypical, and anaplastic meningiomas, respectively. LOH results at 1p32 and 17p13 showed statistically significant differences between benign and non-benign meningiomas.

CONCLUSION

LOH at 1p32 and 17p13 showed a strong correlation with tumor progression. On the other hand, LOH at 7q21 and 7q31 may not contribute to the development of the meningiomas.

Does protein expression predict recurrence of benign World Health Organization grade I meningioma?

The aim of this study was to assess the predictive value of recurrence of protein expression in surgical samples of meningiomas. Thus, the expression of proteins that have been reported to be associated with prognosis of meningiomas was assessed in a sample of 59 World Health Organization grade I tumors obtained after Simpson grade I to III surgical resection (complete excision) and that were followed for 6 to 16 years. The expression was investigated applying immunohistochemical and tissue microarray techniques. One protein, the hepatocytic growth factor receptor, of 22 investigated proteins, showed significantly differing expression when comparing the 38 nonrecurrent with the 21 recurrent World Health Organization grade I meningiomas. It is noteworthy however that by means of logistic regression analyses, the independent predictive value of this protein expression was not significantly associated with the recurrence. Furthermore, it is noteworthy that the proliferation rate estimated by means of Ki67 expression did not show a significant difference, being 3.3 +/- 0.4 for the nonrecurrent meningioma and 3.9 +/- 0.5 for the recurrent and ranging from 0% to 10%. A significant and differing Spearman rank order of correlation was noted between 19 pairs of the investigated proteins when comparing nonrecurrent with recurrent World Health Organization grade I meningiomas. None of these correlations, however, showed a significant association by means of logistic regression analyses. Our results indicate that the Simpson grade significantly alters the outcome of a World Health Organization I grade meningioma and a longer follow-up period significantly increases the risk of recurrence. The expression of none of the proteins or correlation between protein expressions previously reported to be of significance regarding recurrence can be recommended as a diagnostic tool while assessing the risk of recurrence of World Health Organization grade I meningiomas.

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.

Hypoxia-driven selection of the metastatic phenotype

Intratumoral hypoxia is an independent indicator of poor patient outcome and increasing evidence supports a role for hypoxia in the development of metastatic disease. Studies suggest that the acquisition of the metastatic phenotype is not simply the result of dysregulated signal transduction pathways, but instead is achieved through a stepwise selection process driven by hypoxia. Hypoxia facilitates disruption of tissue integrity through repression of E-cadherin expression, with concomitant gain of N-cadherin expression which allows cells to escape anoikis. Through upregulation of urokinase-type plasminogen activator receptor (uPAR) expression, hypoxia enhances proteolytic activity at the invasive front and alters the interactions between integrins and components of the extracellular matrix, thereby enabling cellular invasion through the basement membrane and the underlying stroma. Cell motility is increased through hypoxia-induced hepatocyte growth factor (HGF)-MET receptor signaling, resulting in cell migration towards the blood or lymphatic microcirculation. Hypoxia-induced vascular endothelial growth factor (VEGF) activity also plays a critical role in the dynamic tumor-stromal interactions required for the subsequent stages of metastasis. VEGF promotes angiogenesis and lymphangiogenesis in the primary tumor, providing the necessary routes for dissemination. VEGF-induced changes in vascular integrity and permeability promote both intravasation and extravasation, while VEGF-induced angiogenesis in the secondary tissue is essential for cell proliferation and establishment of metastatic lesions. Through regulation of these critical molecular targets, hypoxia promotes each step of the metastatic cascade and selects tumor cell populations that are able to escape the unfavorable microenvironment of the primary tumor.

Tumor-stromal cell interaction under hypoxia increases the invasiveness of pancreatic cancer cells through the hepatocyte growth factor/c-Met pathway

The hypoxic environment in tumor is reported to play an important role in pancreatic cancer progression. The interaction between stromal and cancer cells also contributes to the malignant behavior of pancreatic cancer. In the present study, we investigated whether hypoxic stimulation affects stromal as well as pancreatic cancer cells. Our findings demonstrated that hypoxia remarkably elevated the HIF-1alpha expression in both pancreatic cancer (PK8) and fibroblast cells (MRC5). Hypoxic stimulation accelerated the invasive activity of PK8 cells, and invasiveness was thus further accelerated when the hypoxic PK8 cells were cultured with conditioned medium prepared from hypoxic MRC5 cells (hypoxic conditioned medium). MMP-2, MMP-7, MT1-MMP and c-Met expressions were increased in PK8 cells under hypoxia. Hypoxic stimulation also increased the hepatocyte growth factor (HGF) secretion from MRC5 cells, which led to an elevation of c-Met phosphorylation in PK8 cells. Conversely, the elevated cancer invasion, MMP activity and c-Met phosphorylation of PK8 cells were reduced by the removal of HGF from hypoxic conditioned medium. In immunohistochemical study, the HIF-1alpha expression was observed in surrounding stromal as well as pancreatic cancer cells, thus indicating hypoxia exists in both of cancer and stromal cells. Moreover, the stromal HGF expression was found to significantly correlate with not only the stromal HIF-1alpha expression but also the c-Met expression in cancer cells. These results indicate that the hypoxic environment within stromal as well as cancer cells activates the HGF/c-Met system, thereby contributing to the aggressive invasive features of pancreatic cancer.

Increased expression of avian erythroblastosis virus E26 oncogene homolog 1 in World Health Organization grade 1 meningiomas is associated with an elevated risk of recurrence and is correlated with the expression of its target genes matrix metalloproteinase-2 and MMP-9

BACKGROUND

The transcription factor avian erythroblastosis virus E26 (V-Ets) oncogene homolog 1 (Ets-1) is involved in tumor development and progression through the transcriptional regulation of several matrix-degrading enzyme systems, including matrix metalloproteinases (MMPs). It has been demonstrated that the MMPs are expressed strongly in high-grade meningiomas. To determine the biologic significance of Ets-1 in the progression of benign meningiomas, the authors investigated the expressions of Ets-1 and its target genes MMP-2 and MMP-9 in primary and recurrent, Grade 1 meningiomas.

METHODS

The expression levels of Ets-1, MMP-2, and MMP-9 were examined by immunohistochemistry in 70 Grade 1 meningiomas, including 36 primary tumors without recurrence after 5 years of follow-up and 17 pairs of primary tumors and subsequent recurrences.

RESULTS

The results demonstrated higher expression of Ets-1, MMP-2, and MMP-9 proteins in meningiomas with subsequent recurrences compared with meningiomas from patients who had no recurrences (P < .001). In addition, Ets-1 expression was correlated with the expression of both MMP-2 and MMP-9.

CONCLUSIONS

Ets-1 may be involved in meningioma recurrence by up-regulating MMP-2 and MMP-9. Increased expression of these genes in World Health Organization grade 1 meningiomas may serve as an indicator for a high risk of recurrence.

Clinico-pathological and immunohistochemical characteristics associated to recurrence/regrowth of craniopharyngiomas

BACKGROUND

Craniopharyngioma is a rare, benign epithelial brain tumor of the suprasellar region with a high rate of recurrence. Clinical and histopathological features that might be predictors of recurrence/regrowth have not been clearly delineated.

METHODS

We compared recurrence/regrowth of the tumors with the clinico-pathological characteristics, vascular density, cell proliferation index, and immunohistochemical profile (cytokeratins, epithelial membrane antigen [EMA], carcinoembrionary antigen [CEA], and laminin) of 47 patients with craniopharyngioma followed for more than 5 years.

RESULTS

Tumors were adamantinomatous in 42 cases (89%) and papillary squamous in 5 cases (11%). Immunoreactivity for cytokeratin 8/18/19 was positive in 64%; cytokeratin 5 in 42%; laminin 8 in 62%; and CEA in 21%. The cell proliferation index and vascular density were greater in adamantinomatous than in papillary tumors (22+/-6 versus 17+/-3, p=0.05; and 21+/-3 versus 17+/-3, p=0.037, respectively); they were neither related to recurrence nor to regrowth. No significant differences were found between adamantinomatous and papillary tumors regarding the presence of cytokeratin, laminin, CEA or glial fibrillary acidic protein (GFAP). Recurrence rate at 5 years was 59%. No relation was found between recurrence and adjuvant radiotherapy (AR). Residual tumor after surgery, whorl-like arrays (p=0.04) and immunoreactivity for p53 (p=0.022) were significantly related to recurrence/regrowth.

CONCLUSIONS

Residual tumor after surgery, immunoreactivity to p53 and presence of whorl-like arrays are associated to recurrence/regrowth of craniopharyngioma.

Holistic and network analysis of meningioma pathogenesis and malignancy

Meningiomas, which originate from arachnoid cells and constitute the largest subgroup of all intracranial tumors, are generally benign, yet have the capacity to progress into a higher histological grade of malignancy associated with an increase in biological aggressivity and/or capacity to recur. To elucidate meningioma pathogenesis and malignancy, we applied a holistic and network approach analyzing cDNA and tissue microarray results. A potential pathway leading to meningioma angiogenesis, apoptosis and proliferation was evidenced as well as a regulatory network of the biomarkers including Ki-67, AR, CD34, P53, c-MYC, etc. which might support clinical research. In this potential pathway, ITGB1 could be the most important "superoncogene" playing a vital role in apoptosis and proliferation, while FOXO3A, MDM4 and MT3 are important to the malignancy process. Some genes are first reported that could explain why radiation induces meningioma and why more female than male patients are affected. Further, we present the hypothesis that HIV-Tat protein might have a close relationship with meningioma pathogenesis and malignancy.

Scatter factor/hepatocyte growth factor in brain tumor growth and angiogenesis

The multifunctional growth factor scatter factor/hepatocyte growth factor (SF/HGF) and its receptor tyrosine kinase c-Met have emerged as key determinants of brain tumor growth and angiogenesis. SF/HGF and c-Met are expressed in brain tumors, the expression levels frequently correlating with tumor grade, tumor blood vessel density, and poor prognosis. Overexpression of SF/HGF and/or c-Met in brain tumor cells enhances their tumorigenicity, tumor growth, and tumor-associated angiogenesis. Conversely, inhibition of SF/HGF and c-Met in experimental tumor xenografts leads to inhibition of tumor growth and tumor angiogenesis. SF/HGF is expressed and secreted mainly by tumor cells and acts on c-Met receptors that are expressed in tumor cells and vascular endothelial cells. Activation of c-Met leads to induction of proliferation, migration, and invasion and to inhibition of apoptosis in tumor cells as well as in tumor vascular endothelial cells. Activation of tumor endothelial c-Met also induces extracellular matrix degradation, tubule formation, and angiogenesis in vivo. SF/HGF induces brain tumor angiogenesis directly through only partly known mechanisms and indirectly by regulating other angiogenic pathways such as VEGF. Different approaches to inhibiting SF/HGF and c-Met have been recently developed. These include receptor antagonism with SF/HGF fragments such as NK4, SF/HGF, and c-Met expression inhibition with U1snRNA/ribozymes; competitive ligand binding with soluble Met receptors; neutralizing antibodies to SF/HGF; and small molecular tyrosine kinase inhibitors. Use of these inhibitors in experimental tumor models leads to inhibition of tumor growth and angiogenesis. In this review, we summarize current knowledge of how the SF/HGF:c-Met pathway contributes to brain tumor malignancy with a focus on glioma angiogenesis.