Mechanistic insights on the inhibition of tumor angiogenesis

Scandium-44: Diagnostic Feasibility in Tumor-Related Angiogenesis

Angiogenesis-related cell-surface molecules, including integrins, aminopeptidase N, vascular endothelial growth factor, and gastrin-releasing peptide receptor (GRPR), play a crucial role in tumour formation. Radiolabelled imaging probes targeting angiogenic biomarkers serve as valuable vectors in tumour identification. Nowadays, there is a growing interest in novel radionuclides other than gallium-68 (⁶⁸Ga) or copper-64 (⁶⁴Cu) to establish selective radiotracers for the imaging of tumour-associated neo-angiogenesis. Given its ideal decay characteristics (E_β⁺_average: 632 KeV) and a half-life (T_1/2 = 3.97 h) that is well matched to the pharmacokinetic profile of small molecules targeting angiogenesis, scandium-44 (⁴⁴Sc) has gained meaningful attention as a promising radiometal for positron emission tomography (PET) imaging. More recently, intensive research has been centered around the investigation of ⁴⁴Sc-labelled angiogenesis-directed radiopharmaceuticals. Previous studies dealt with the evaluation of ⁴⁴Sc-appended a_vb₃ integrin-affine Arg-Gly-Asp (RGD) tripeptides, GRPR-selective aminobenzoyl-bombesin analogue (AMBA), and hypoxia-associated nitroimidazole derivatives in the identification of various cancers using experimental tumour models. Given the tumour-related hypoxia- and angiogenesis-targeting capability of these PET probes, ⁴⁴Sc seems to be a strong competitor of the currently used positron emitters in radiotracer development. In this review, we summarize the preliminary preclinical achievements with ⁴⁴Sc-labelled angiogenesis-specific molecular probes.

Semaphorin 7a participants in pterygium by regulating vascular endothelial growth factor

AIM

To investigate the relationship between semaphorin 7a expression and cell proliferation and migration in pterygium fibroblasts.

METHODS

Twenty-six patients with surgically diagnosed pterygium were enrolled, including 15 cases of primary pterygium and 11 cases of recurrent pterygium. In addition, 12 cases of normal conjunctival tissue were collected. The expression of semaphorin 7a in normal conjunctival tissue, primary pterygium and recurrent pterygium was detected by real-time polymerase chain reaction. Recurrent pterygium fibroblasts were isolated and cultured, and the expression of semaphorin 7a was silenced by small interfering RNA (siRNA) interference technique. Furthermore, the effects of si-semaphorin 7a interference on the mRNA and protein levels of β1-integrin, vascular endothelial growth factor A (VEGFA) and vascular endothelial growth factor receptor (VEGFR), and on fibroblast proliferation were analyzed. Transwell assay was used to detect the effect of semaphorin 7a interference on fibroblast migration.

RESULTS

Semaphorin 7a was highly expressed in the primary pterygium and recurrent pterygium samples than that of the normal conjunctival tissue. Compared with the primary pterygium, the expression of semaphoring 7a in the recurrent pterygium samples was significantly increased (P<0.05). The mRNA and protein expression levels of β1-integrin, VEGFA and VEGFR were decreased after si-semaphorin 7a transfection, and as well as the cell proliferation and migration.

CONCLUSION

Semaphorin 7a might play important roles in the pathogenesis of pterygium by affecting the expression of β1-integrin, VEGFA and VEGFR.

Multimodality Imaging in Tumor Angiogenesis: Present Status and Perspectives

Angiogenesis is a complex biological process that plays a central role in progression of tumor growth and metastasis. It led to a search for antiangiogenic molecules, and to design antiangiogenic strategies for cancer treatment. Noninvasive molecular imaging, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), could be useful for lesion detection, to select patients likely to respond to antiangiogenic therapies, to confirm successful targeting, and dose optimization. Additionally, nuclear imaging techniques could also aid in the development of new angiogenesis-targeted drugs and their validation. Angiogenesis imaging can be categorized as targeted at three major cell types: (I) non-endothelial cell targets, (II) endothelial cell targets, and (III) extracellular matrix proteins and matrix proteases. Even if radiopharmaceuticals studying the metabolism and hypoxia can be also used for the study of angiogenesis, many of the agents used in nuclear imaging for this purpose are yet to be investigated. The purpose of this review is to describe the role of molecular imaging in tumor angiogenesis, highlighting the advances in this field.

Biodistribution of the ¹⁸F-FPPRGD₂ PET radiopharmaceutical in cancer patients: an atlas of SUV measurements

PURPOSE

The aim of this study was to investigate the biodistribution of 2-fluoropropionyl-labeled PEGylated dimeric arginine-glycine-aspartic acid (RGD) peptide (PEG3-E[c{RGDyk}]2) ((18)F-FPPRGD2) in cancer patients and to compare its uptake in malignant lesions with (18)F-FDG uptake.

METHODS

A total of 35 patients (11 men, 24 women, mean age 52.1 ± 10.8 years) were enrolled prospectively and had (18)F-FPPRGD2 PET/CT prior to treatment. Maximum standardized uptake values (SUVmax) and mean SUV (SUVmean) were measured in 23 normal tissues in each patient, as well as in known or suspected cancer lesions. Differences between (18)F-FPPRGD2 uptake and (18)F-FDG uptake were also evaluated in 28 of the 35 patients.

RESULTS

Areas of high (18)F-FPPRGD2 accumulation (SUVmax range 8.9 - 94.4, SUVmean range 7.1 - 64.4) included the bladder and kidneys. Moderate uptake (SUVmax range 2.1 - 6.3, SUVmean range 1.1 - 4.5) was found in the choroid plexus, salivary glands, thyroid, liver, spleen, pancreas, small bowel and skeleton. Compared with (18)F-FDG, (18)F-FPPRGD2 showed higher tumor-to-background ratio in brain lesions (13.4 ± 8.5 vs. 1.1 ± 0.5, P < 0.001), but no significant difference in body lesions (3.2 ± 1.9 vs. 4.4 ± 4.2, P = 0.10). There was no significant correlation between the uptake values (SUVmax and SUVmean) for (18)F FPPRGD2 and those for (18)F-FDG.

CONCLUSION

The biodistribution of (18)F-FPPRGD2 in cancer patients is similar to that of other RGD dimer peptides and it is suitable for clinical use. The lack of significant correlation between (18)F-FPPRGD2 and (18)F-FDG uptake confirms that the information provided by each PET tracer is different.

Sunitinib impedes brain tumor progression and reduces tumor-induced neurodegeneration in the microenvironment

Malignant gliomas can be counted to the most devastating tumors in humans. Novel therapies do not achieve significant prolonged survival rates. The cancer cells have an impact on the surrounding vital tissue and form tumor zones, which make up the tumor microenvironment. We investigated the effects of sunitinib, a small molecule multitargeted receptor tyrosine kinase inhibitor, on constituents of the tumor microenvironment such as gliomas, astrocytes, endothelial cells, and neurons. Sunitinib has a known anti-angiogenic effect. We found that sunitinib normalizes the aberrant tumor-derived vasculature and reduces tumor vessel pathologies (i.e. auto-loops). Sunitinib has only minor effects on the normal, physiological, non-proliferating vasculature. We found that neurons and astrocytes are protected by sunitinib against glutamate-induced cell death, whereas sunitinib acts as a toxin towards proliferating endothelial cells and tumor vessels. Moreover, sunitinib is effective in inducing glioma cell death. We determined the underlying pathways by which sunitinib operates as a toxin on gliomas and found vascular endothelial growth factor receptor 2 (VEGFR2, KDR/Flk1) as the main target to execute gliomatoxicity. The apoptosis-inducing effect of sunitinib can be mimicked by inhibition of VEGFR2. Knockdown of VEGFR2 can, in part, foster the resistance of glioma cells to receptor tyrosine kinase inhibitors. Furthermore, sunitinib alleviates tumor-induced neurodegeneration. Hence, we tested whether temozolomide treatment could be potentiated by sunitinib application. Here we show that sunitinib can amplify the effects of temozolomide in glioma cells. Thus, our data indicate that combined treatment with temozolomide does not abrogate the effects of sunitinib. In conclusion, we found that sunitinib acts as a gliomatoxic agent and at the same time carries out neuroprotective effects, reducing tumor-induced neurodegeneration. Thus, this report uncovered sunitinib's actions on the brain tumor microenvironment, revealing novel aspects for adjuvant approaches and new clinical assessment criteria when applied to brain tumor patients.

The association between expressions of Ras and CD68 in the angiogenesis of breast cancers

Objective

Angiogenesis is a critical step of breast cancer metastasis. Oncogenic Ras promotes the remodeling of cancer microenviroment. Tumor-associated macrophages (TAMs) are a prominent inflammatory cell population emerging in the microenviroment and facilitating the angiogenesis and metastasis. In the present study, we tried to investigate the relationship between the expression of Ras and infiltration of TAM, both of which could further promote angiogenesis.

Methods

Expressions of Ras, CD68 and CD34 were assessed by immunohistochemistry. The infiltration of macrophages was evaluated by counting the number of CD68⁺ cells. Vessel endothelial cells were defined as CD34⁺ cells. Angiogenesis vascularity was defined by microvessel density (MVD) assay through counting the number of vessels per field counted in the area of highest vascular density. The Kaplan–Meier survival analysis was used to estimate the overall survival (OS). Macrophages were derived from monocytes in the presence of macrophage colony-stimulating-factor (MCSF). Breast cancer cells were treated with macrophage-conditioned medium (MCM) and tested the expressions of K-, H- and N-Ras by using realtime-PCR.

Results

Ras positive status was correlated with ER, PR and Her-2 positivity, larger tumour size and lymph node metastasis, as well as higher TNM stages. A higher number of CD68⁺ cells was correlated with larger tumour size, higher TNM stages and Her-2 positivity. Both Ras positivity and infiltration of CD68⁺ macrophages correlated with poor OS. The number of CD68⁺ cells was positively correlated with the expression of Ras. Treatment with MCM did not up-regulate but repressed the expression of Ras. Both up-regulation of Ras and infiltration of TAMs correlated with increased MVD.

Conclusion

Expression of Ras and infiltration of TAM were positively correlated, and both participated in angiogenesis. Elevated Ras could be responsible for the infiltration of TAM.

Over-expression of beclin-1 in gallbladder carcinoma and its relationship with prognosis

AIM OF THE STUDY

We determined the expression of beclin-1 in gallbladder carcinoma, analyzed the association of beclin-1 expression with clinicopathologic parameters and prognosis, and investigated the relationship between microvessel density and beclin-1 expression.

MATERIAL AND METHODS

Tissue microarray blocks containing 118 primary gallbladder tumor sites were used. Clinical parameters and prognostic data were collected. Expression of beclin-1 in these specimens was analyzed by immunohistochemical studies and confirmed by Western blotting. Microvessel density was counted using immunohistochemical staining.

RESULTS

The overall rate of over-expression of beclin-1 was 68.1% (80 of 118). Over-expression of beclin-1 was significantly associated with TNM stage and liver metastasis. Over-expression of beclin-1 has no significant relationship with age, sex, lymphatic metastasis, or tumor differentiation. Based on the Kaplan-Meier method, over-expression of beclin-1 showed no significant difference for the overall survival rate in patients with gallbladder cancer. The multivariate Cox regression analysis demonstrated that beclin-1 was not an independent prognostic factor for gallbladder cancer.

CONCLUSIONS

Beclin-1 might play roles in the development of gallbladder cancer. However, beclin-1 may not be an effective prognostic factor for gallbladder cancer.

Imaging tumor angiogenesis: the road to clinical utility

OBJECTIVE

Tumor growth and progression require the formation of new blood vessels from preexisting vasculature, a process called angiogenesis. The ability to noninvasively visualize angiogenesis may provide new opportunities to more appropriately select patients for antiangiogenesis treatment and to monitor treatment efficacy.

CONCLUSION

The superior molecular sensitivity of PET and the lack of radiation from MRI and contrast-enhanced ultrasound put these techniques at the forefront of clinical translation.

Prospective study of thrombospondin-1 mimetic peptides, ABT-510 and ABT-898, in dogs with soft tissue sarcoma

BACKGROUND

Exposure to anti-angiogenic thrombospondin-1 (TSP-1) mimetic peptides (MPs) has resulted in sporadic anti-tumor activity in humans and dogs.

HYPOTHESIS

Novel TSP-1 MPs formulations will be safe, tolerated, and clinically active in soft tissue sarcoma (STS) in dogs.

ANIMALS

Sixty-two client-owned dogs with measurable STS were enrolled, excluding hemangiosarcoma.

METHODS

A prospective, single agent, multicenter, open-label study assessing ABT-510 bolus, ABT-898 bolus, or ABT-898 depot formulations of TSP-1 in dogs. Endpoints included tolerability, antitumor activity, and the assessment of ability of clinical covariates and circulating endothelial cells (CEC) concentration to predict tumor response.

RESULTS

Two non-dose-limiting toxicoses possibly attributed to treatment were observed (keratitis and osteoarthritis). Antitumor activity (10/44 = 23% responses) was observed in study subjects who received treatment for >28 days (n = 44) including both partial (7) and minimal responses (3). Responses were disproportionately seen in dogs receiving ABT-898 formulations (9/28 = 32%) versus those receiving ABT-510 (1/16 = 6%; P < .045). Disease stabilization for >84 days was also documented (8/44 = 18%). Slow rates of tumor progression before study entry correlated with anti-tumor activity in treated dogs, whereas no significant association was found between changes in total CEC concentration and tumor response (P = .28) or time to progression (P = .42).

CONCLUSIONS AND CLINICAL IMPORTANCE

Safely achieved antitumor activity was documented with TSP-1 MPs in dogs with STS. The most notable activity was achieved with the ABT-898 formulations.

The expression of pigment epithelium-derived factor in bladder transitional cell carcinoma

Background

Pigment epithelium-derived factor (PEDF) is an anti-angiogenic factor. The purpose of this study is to examine the involvement of PEDF in the angiogenesis and biological behavior of bladder transitional cell carcinoma (TCC).

Methods

We examined the expression of PEDF in 99 bladder TCCs and ten non-neoplastic tissues, and evaluated microvessel density (MVD).

Results

The positive immunoreactivity for PEDF was seen in normal urothelium in 60% (6/10) and TCC in 13% (13/99). The PEDF expression had a significant correlation with MVD, i.e., a low MVD in 42% (5/12), a middle MVD in 11% (8/76) and a high MVD 0% (0/11) of tumors. The PEDF expression was not significantly correlated with the differentiation and invasion of TCC, but the degree of MVD was significantly higher in both high grade TCC and the pT2 tumors.

Conclusions

The degree of PEDF expression is significantly higher in normal bladder urothelium than bladder TCC; it is inversely correlated with the angiogenesis; and it is not related to the differentiation and progression of TCC. It can therefore be concluded that bladder TCC would initially occur if there is a lack of the PEDF expression.

Changes in the gene expression profile of A375 human melanoma cells induced by overexpression of multifunctional pigment epithelium-derived factor

Pigment epithelium-derived factor (PEDF) is a broad-spectrum angiogenesis inhibitor that displays potent antimetastatic activity in multiple tumor types. We have previously shown that PEDF prevents primary tumor growth and metastatic spread of human melanoma in mouse experimental models. Consistent with these observations, PEDF expression is lost at the late stages of melanoma progression, allowing melanoma cells to become angiogenic, migratory, and invasive. PEDF's ability to modify the interplay between the host and tumor tissues strongly supports its use as a therapeutic agent for the treatment of metastatic melanoma. However, transition to the clinic requires a more detailed knowledge of the molecular mechanisms underpinning PEDF's activity. In this study, we describe changes in the gene expression profile of A375 human melanoma cells induced by PEDF overexpression. PEDF modulated diverse categories of genes known to be involved in angiogenesis and migration. It downregulated cytokines such as interleukin-8 and extracellular matrix proteins such as collagen IV, while it upregulated fibronectin. Multiple transcripts previously described as contributing to the acquisition of malignant phenotype by melanoma were also diminished by PEDF overexpression, among which we validated galectin 3 and jagged 1. In addition, PEDF downregulated S100β and melanoma inhibitory activity, which are widely used in the pathological diagnosis of melanoma. Interestingly, PEDF increased the expression of melanophilin and decreased rab27A, which are relevant targets for melanosome transport; suggesting that PEDF could directly impinge on melanocytic lineage-specific processes. Our study identifies new molecular targets and signaling pathways that may potentially contribute to determine PEDF's ability to restrict the aggressiveness of A375 human melanoma cells.

Inhibition of chemical cautery-induced corneal neovascularization by topical pigment epithelium-derived factor eyedrops

PURPOSE

To evaluate the effect of topically administered pigment epithelium-derived factor (PEDF) on experimentally induced corneal neovascularization (NV) in a rat model.

METHODS

Corneal chemical cauterization was induced in the left eye by using silver nitrate sticks in 160 anesthetized male Sprague-Dawley rats. The rats were randomly assigned to 4 groups with 40 rats each for topical administration of recombinant PEDF, chloramphenicol, chondroitin sulfate, and normal saline (as control). At different intervals (3, 10, 15, and 30 days) of the treatment, rats were euthanized and the corneas removed for immunohistochemistry and Western blot analyses to measure expression levels of PEDF, vascular endothelial growth factor (VEGF), and CD34, an endothelial maker. The right eyes were used as normal control.

RESULTS

There were high levels of PEDF expression and low levels of VEGF and CD34 in the normal cornea. VEGF and CD34 levels were significantly induced by chemical cauterization in the groups treated with chloramphenicol, chondroitin sulfate, and normal saline, demonstrating corneal NV. The VEGF and CD34 levels reached a plateau in the cornea on the 10th day after cauterization and remained at high levels thereafter. In contrast, the PEDF treatment prevented the overexpression of VEGF and CD34 induced by the cauterization.

CONCLUSIONS

PEDF downregulates VEGF expression and inhibits corneal NV induced by chemical cauterization. The results suggested that PEDF has therapeutic potential for corneal neovascular diseases.

Evaluation of protein pigment epithelium-derived factor (PEDF) and microvessel density (MVD) as prognostic indicators in breast cancer

PURPOSE

Angiogenesis, which plays an important role in tumor growth and metastasis, is regulated by a balance between angiogenic stimulators and inhibitors. Pigment epithelium-derived factor (PEDF), a secreted glycoprotein is an important inhibitor of angiogenesis. Although the precise mechanisms by which PEDF exerts its actions remain poorly understood, there is growing evidence supporting the role of PEDF as a candidate antitumor agent. In this study, we investigated the role of PEDF in breast cancer.

METHODS

We investigated the correlation of PEDF protein levels with cancer progression and prognosis in patients with invasive ductal breast cancer (IDC). We used immunohistochemistry in a cohort of 119 breast cancer patients to examine the expression of PEDF protein with an anti-PEDF antibody and to measure the microvessel density (MVD) with an anti-CD34 antibody.

RESULTS

PEDF was an endogenous inhibitor of angiogenesis in endothelial cells. Decreased intratumoral expression of PEDF was associated with a higher microvessel density (MVD), a more metastatic phenotype, and poorer clinical outcome. PEDF was positive in 43.7% patients. Patients with low PEDF expression had a significantly higher MVD count when compared with patients with high PEDF expression. In univariate and multivariate analysis, PEDF was an independent prognostic factor.

CONCLUSION

The inverse correlation between PEDF expression and MVD in human breast cancer suggests that low PEDF expression is associated with angiogenesis in breast cancer. PEDF expression is therefore a potentially useful prognostic marker for breast cancer.

Pigment epithelium-derived factor inhibits lysosomal degradation of Bcl-xL and apoptosis in HepG2 cells

Pigment epithelium-derived factor (PEDF) has several biological actions on tumor cells, but its effects are cell-type dependent. The aim of this study was to examine the pathophysiological role of PEDF in hepatocellular carcinoma (HCC). PEDF expression was examined in various hepatoma cell lines and human HCC tissues, and was seen in various hepatoma cell lines including HepG2 cells. In human HCC tissues, PEDF expression was higher than in adjacent non-HCC tissues. In addition, serum PEDF levels were higher in HCC patients than in non-HCC patients, and curative treatment of HCC caused significant reductions in serum PEDF levels compared with pretreatment levels. In vitro experiments, camptothecin (CPT) was used to induce apoptosis and the effect of PEDF was investigated by knockdown of the PEDF gene in CPT-treated HepG2 cells. Knockdown of the PEDF gene enhanced CPT-induced apoptosis, simultaneously down-regulating Bcl-xL expression in HepG2 cells. Expression of apoptosis-related molecules and effects of bafilomycin A1 on CPT-induced apoptosis were also examined in PEDF gene knockdown HepG2 cells. Treatment with bafilomycin A1 suppressed CPT-induced decreases in Bcl-xL expression and increases in apoptosis in PEDF gene knockdown HepG2 cells. PEDF may, therefore, exert anti-apoptotic effects through inhibition of lysosomal degradation of Bcl-xL in CPT-treated HepG2 cells.

The HMG-CoA Reductase Pathway, Statins and Angioprevention

Angiogenesis is one of the earliest and essential phenotypes acquired by tumors during carcinogenesis and thus might be a potential target for chemoprevention. Key to developing antiangiogenic chemoprevention is to identify new molecular targets and effective angiogenesis inhibitors. HMG-CoA reductase inhibitors, or statins, were originally designed to reduce cholesterol biosynthesis and have been extensively used as prevention drugs against hyperlipidemia and cardiovascular conditions. Recent research has found that statins promote endothelial death and inhibit experimental angiogenesis induced by growth factors or tumor, laying a foundation for developing statin-based angiopreventive strategies. This article reviews the biological effects of statins on endothelial cells and angiogenesis, possible underlying mechanisms and perspectives on future application of statins in preventing pathological angiogenesis.

Following up tumour angiogenesis: from the basic laboratory to the clinic

Preceded by three decades of intense basic research on tumour angiogenesis, we are assisting to the translation of anti-antiangiogenic therapies as medical oncologists are increasingly using pioneering anti-angiogenic drugs in combination with standard treatments. While basic knowledge in the field of angiogenesis is reaching maturity and our level of understanding of the complex process of vessel development and growth in health and disease has been enriched at the molecular and cellular levels, the translation of this knowledge to the clinic is still in its infancy. Identifying the most suitable drugs, and the optimal dosage and schedule, as well as monitoring patients' responses to anti-angiogenic therapy, remain challenging issues that currently limit the benefit of this new therapeutic approach in cancer. This review will focus on a comprehensive description of the experimental assays in which angiogenesis research has been founded and how the different assays complement and provide relevant information for the task of characterising the angiogenic properties of diverse tumours, giving us a variety of tools to follow up tumour angiogenesis in research models. Following up tumour angiogenesis in patients and their response to antiangiogenic therapy is a more challenging task that will benefit in the near future from the use of non-invasive imaging methods as well as molecular and cellular biomarkers of angiogenesis suitable for clinical oncology. As both the design of the anti-angiogenic therapies and monitoring of the response are improved in the coming years to properly tailor them to the angiogenic profile of every patient, we hope to achieve increasing response and benefit of including antiangiogenic drugs as standard in cancer therapy.

Subconjunctival bevacizumab injection for corneal neovascularization in recurrent pterygium

PURPOSE

We report on the use of subconjunctival bevacizumab on corneal vessel density in recurrent pterygia.

METHODS

The charts of 5 patients with recurrent pterygium, who received subconjunctival injections of bevacizumab (2.5 mg/0.1 ml) were retrospectively reviewed. Ophthalmic evaluation included Snellen visual acuity (VA), tonometry and complete examination before the injection and at 1 week and 1 and 3 months thereafter. Digital photographs of the eyes were analyzed by image analysis software to determine the area of cornea covered by new vessels as a percentage of the total corneal area.

RESULTS

No ocular or systemic adverse events were observed. No change in visual acuity was noted in any patient following the injection. The mean change in corneal vascularization after one bevacizumab injection was 0.03%+/-0.45, while after two injections the change was 0.025%+/-0.19 (both not statistically different than zero, t-test).

CONCLUSIONS

Short-term results suggest that subconjunctival bevacizumab is well tolerated but does not cause regression of corneal vessels in recurrent pterygium.

Kallikrein-binding protein suppresses growth of hepatocellular carcinoma by anti-angiogenic activity

Effect of kallikrein-binding protein (KBP), an endogenous angiogenic inhibitor, on the growth of hepatocellular carcinoma and the possible mechanism were investigated. KBP inhibited proliferation and induced apoptosis of endothelial cells, but had no effect on the proliferation and apoptosis of hepatocarcinoma cell line HepG2. Intraperitoneal injection of KBP significantly suppressed the tumor growth and inhibited intratumoral neovascularization both in grafted hepatocarcinoma mice and xenografted hepatocarcinoma athymic mice. Moreover, KBP reduced expression of VEGF and HIF-1alpha nuclear translocation in HepG2 cells and xenografts. Down-regulation of VEGF in tumor cells through inhibiting HIF-1alpha may represent a novel mechanism for the anti-angiogenic and anti-tumor activity of KBP.

Targeting matrix metalloproteinases and endothelial cells with a fusion peptide against tumor

Development of novel therapy for patients with tumor is still a challenge at the present time. We designed a fusion peptide (RK5) with two targets as a novel agent against tumor. The fusion peptide RK5 containing the kringle 5 fragment of human plasminogen and a decapeptide (CTTHWGFTLC) was constructed and expressed in yeast. Matrix metalloproteinase (MMP) activity, proliferation, and migration of endothelial cells were examined in vitro, respectively. Angiogenesis, tumor growth, metastasis, and survival time were evaluated in in vivo models. Administration of RK5 was delivered by both protein and gene approach. The results showed that RK5 inhibited the activity of MMP-9 and exhibited more inhibitory effects on proliferation and migration of endothelial cells than that of kringle 5 fragment and decapeptide individually. RK5 also inhibited angiogenesis, tumor growth, and metastasis and increased survival time of mice bearing tumor. In addition, the effectiveness of RK5 could be achieved by both protein and gene delivery. In conclusion, RK5 has potential to inhibit tumor growth and metastasis and to prolong survival time of animals bearing tumor. Therefore, fusion peptide RK5 with two targets provides a new design for the development of antitumor drugs and has potential for clinical application.

An expression signature of syndecan-1 (CD138), E-cadherin and c-met is associated with factors of angiogenesis and lymphangiogenesis in ductal breast carcinoma in situ

INTRODUCTION

Heparan sulphate proteoglycan syndecan-1 modulates cell proliferation, adhesion, migration and angiogenesis. It is a coreceptor for the hepatocyte growth factor receptor c-met, and its coexpression with E-cadherin is synchronously regulated during epithelial-mesenchymal transition. In breast cancer, changes in the expression of syndecan-1, E-cadherin and c-met correlate with poor prognosis. In this study we evaluated whether coexpression of these functionally linked prognostic markers constitutes an expression signature in ductal carcinoma in situ (DCIS) of the breast that may promote cell proliferation and (lymph)angiogenesis.

METHODS

Expression of syndecan-1, E-cadherin and c-met was detected immunohistochemically using a tissue microarray in tumour specimens from 200 DCIS patients. Results were correlated with the expression patterns of angiogenic and lymphangiogenic markers. Coexpression of the three prognostic markers was evaluated in human breast cancer cells by confocal immunofluorescence microscopy and RT-PCR.

RESULTS

Coexpression and membrane colocalization of the three markers was confirmed in MCF-7 cells. E-cadherin expression decreased, and c-met expression increased progressively in more aggressive cell lines. Tissue microarray analysis revealed strong positive staining of tumour cells for syndecan-1 in 72%, E-cadherin in 67.8% and c-met in 48.6% of DCIS. E-cadherin expression was significantly associated with c-met and syndecan-1. Expression of c-met and syndecan-1 was significantly more frequent in the subgroup of patients with pure DCIS than in those with DCIS and a coexisting invasive carcinoma. Levels of c-met and syndecan-1 expression were associated with HER2 expression. Expression of c-met significantly correlated with expression of endothelin A and B receptors, vascular endothelial growth factor (VEGF)-A and fibroblast growth factor receptor-1, whereas E-cadherin expression correlated significantly with endothelin A receptor, VEGF-A and VEGF-C staining.

CONCLUSION

Syndecan-1, E-cadherin and c-met constitute a marker signature associated with angiogenic and lymphangiogenic factors in DCIS. This coexpression may reflect a state of parallel activation of different signal transduction pathways, promoting tumour cell proliferation and angiogenesis. Our findings have implications for future therapeutic approaches in terms of a multiple target approach, which may be useful early in breast cancer progression.

Preclinical Evaluation of Antiangiogenic Thrombospondin-1 Peptide Mimetics, ABT-526 and ABT-510, in Companion Dogs with Naturally Occurring Cancers

PURPOSE

The angiogenic phenotype of malignant cancers has been established as a target for cancer therapy. ABT-526 and ABT-510, two peptide mimetics of thrombospondin-1 (TSP-1), block angiogenesis in vitro and in vivo and slow tumor growth in mice. To guide the clinical development of these drugs, translational studies in dogs with naturally occurring cancers were initiated.

EXPERIMENTAL DESIGN

A prospective open-label trial using ABT-510 or ABT-526 in pet dogs with measurable malignant spontaneously arising tumors. Endpoints included safety, pharmacokinetics, antitumor activity, and preliminary assessment of changes in circulating endothelial cell populations.

RESULTS

Two-hundred and forty-two dogs were sequentially entered to this open-label trial. The elimination half-life for ABT-510 and ABT-526 was 0.7 and 0.8 h, respectively (range, 0.5-1 h). No dose-limiting toxicities were seen in any dogs (N = 242). Forty-two dogs receiving peptide had objective responses (>50% reduction in tumor size; n = 6) or significant disease stabilization. Most objective responses were seen after 60 days of exposure to the TSP-1 peptide. Antitumor activity was similar for both peptides and was seen in several histologies, including mammary carcinoma, head and neck carcinoma, soft tissue sarcoma, cutaneous T-cell lymphoma, and non-Hodgkin's lymphoma. Assessment of circulating endothelial cell populations in a small subset of dogs suggested that effective exposure to TSP-1 peptides may be associated with reductions in circulating endothelial cells.

CONCLUSIONS

These results support the safety and activity of ABT-526 and ABT-510 in dogs with naturally occurring malignant cancers. Data from this preclinical trial support the development of TSP-1 mimetic peptides as anticancer agents.

Angiotensinogen impairs angiogenesis in the chick chorioallantoic membrane

Angiotensinogen shares with other members of the serine protease inhibitor (serpin) family antiangiogenic properties. Angiotensinogen inhibits in vitro endothelial cell proliferation, and is antiangiogenic in ovo in the chick chorioallantoic membrane assay. The cellular mode of action of angiotensinogen has been studied by applying purified human angiotensinogen or Chinese hamster ovary cells producing recombinant angiotensinogen onto the developing chorioallantoic membrane. Vessel density of the control and angiotensinogen-treated areas was quantitated by using Sambucus nigra lectin, a specific endothelial cell marker. After 48 h of angiotensinogen treatment by either applying purified angiotensinogen or angiotensinogen-producing Chinese hamster ovary cells, there was a 70% decrease in mesodermic vessel density in comparison to the control sections. Angiotensinogen treatment induced a strong decrease in endothelial cell proliferation of the chorioallantoic membrane vasculature, as shown by incorporation of bromo-deoxyuridine. Two days after local angiotensinogen treatment, increased apoptosis of endothelial cells of mesodermal blood vessels was detected by transferase-mediated deoxyuridine triphosphate nick end labeling assay. As assessed by in situ hybridization, the gene expression pattern of the main vascular growth factors and their receptors was not altered by angiotensinogen. Angiotensinogen, therefore, impairs angiogenesis without altering the expression level of vascular growth factors through the induction of apoptosis and decreased endothelial cell proliferation.

Pigment epithelium-derived factor as a multifunctional antitumor factor

The design of new therapeutic strategies for cancer treatment is based on the combination of drugs directed against different tumor compartments, including the tumor cells themselves and components of the stroma, such as the tumor vasculature. Indeed, several antiangiogenic compounds have entered clinical trials for use alone or in combination with conventional cytotoxic drugs. Pigment epithelium-derived factor (PEDF) is a multifunctional natural peptide with complex neurotrophic, neuroprotective, antiangiogenic, and proapoptotic biological activities, any of which could potentially be exploited for therapeutic purposes. This review summarizes recent studies that reveal the antitumor potential of PEDF based on its antiangiogenic properties and its newly discovered direct antitumor effects, which involve the induction of differentiation or apoptosis in tumor cells. We also discuss possible therapeutic applications of PEDF, based on these mechanistic insights and on the identification of functional domains that retain specific biological activities.

Structural basis for the functions of endogenous angiogenesis inhibitors

Tipping the angiogenic balance between pro- and antiangiogenic stimuli to favor vasculature induction and enhanced angiogenesis is a key event in the growth and progression of tumors. Recently, we demonstrated that the genetic loss of normal physiological levels of individual endogenous inhibitors of angiogenesis leads to a change in the balance between proangiogenic stimulators and their inhibitors, thus favoring enhanced angiogensis and increased tumor growth. Therefore, these endogenous angiogenesis inhibitors provide a physiological threshold against the induction of angiogenesis. The antiangiogenic activities of endostatin, tumstatin, and thrombospondin-1 are evaluated and correlated with their three-dimensional structure and active sites, deriving a structural basis for their activities. Collectively, structural analysis of all three inhibitors demonstrates that the active antiangiogenic sites on these molecules are exposed on the surface and available to bind their putative integrin receptors on proliferating endothelial cells.

MCT-1 oncogene contributes to increased in vivo tumorigenicity of MCF7 cells by promotion of angiogenesis and inhibition of apoptosis

Overexpression of a novel oncogene MCT-1 (multiple copies in a T cell malignancy) causes malignant transformation of murine fibroblasts. To establish its role in the pathogenesis of breast cancer in humans, we generated stable transfectants of MCF7 breast cancer cells negative for endogenous MCT-1 (MCF7-MCT-1). Overexpression of MCT-1 in these cells resulted in a slight elevation of estrogen receptor-alpha, and higher rates of DNA synthesis and growth in response to estradiol compared with the empty vector control (MCF7-EV). The pure antiestrogen fulvestrant inhibited the estradiol-stimulated proliferation of MCF7-MCT-1 cells. The MCF7-MCT-1 clones showed increased invasiveness in the presence of 50% serum compared with the MCF7-EV. In a tumor xenograft model, MCT-1-overexpressing cells showed higher take rates and formed significantly larger tumors than MCF7-EV controls. When we examined angiogenic phenotype and molecular mediators of angiogenesis in MCF7-MCT-1 tumors in vivo, we found greater microvascular density and lower apoptosis in the MCF7-MCT-1 tumors compared with MCF7-EV controls accompanied by a dramatic decline in the levels of angiogenesis inhibitor, thrombospondin-1 (TSP1). In vitro, blocking TSP1 in the medium conditioned by MCT-1-negative cells restored its angiogenic potential to that of the MCF7-MCT-1 cells. Conversely, despite an increase in mRNA encoding vascular endothelial growth factor upon MCT-1 overexpression, vascular endothelial growth factor protein levels have not been notably altered. Taken together, our results suggest that MCT-1 may contribute to the pathogenesis and progression of human breast cancer via at least two routes: promotion of angiogenesis through the decline of TSP1 and inhibition of apoptosis.

ACTIBIND, an actin-binding fungal T2-RNase with antiangiogenic and anticarcinogenic characteristics

BACKGROUND

ACTIBIND is an Aspergillus niger extracellular ribonuclease (T2-ribonuclease [RNase]) that possesses actin-binding activity. In plants, ACTIBIND inhibits the elongation and alters the orientation of pollen tubes by interfering with the intracellular actin network. The question rose whether ACTIBIND can also affect mammalian cancer development.

METHODS

Cell colony formation was performed in human colon (HT-29, Caco-2, RSB), breast (ZR-75-1), and ovarian (2780) cancer cells in the presence or absence of 1 muM ACTIBIND. In HT-29 and ZR-75-1 cells, the effect of ACTIBIND on cell migration was studied by microscopic observations and by invasion assay through Matrigel. Tube formation was assessed in human umbilical vein endothelial cells (HUVEC) in the presence of angiogenin or basic fibroblast growth factor (bFGF) (1 microg/mL each) following overnight incubation with 1 or 10 microM ACTIBIND. In an athymic mouse xenograft model, HT-29 cells were injected subcutaneously, followed by subcutaneous (0.4-8 mg/mouse/injection) or intraperitoneal (0.001-1 mg/mouse/injection) injections of ACTIBIND. In a rat dimethylhydrazine (DMH)-colorectal carcinogenesis model, ACTIBIND was released directly into the colon via osmotic micropumps (250 microg/rat/day) or given orally via microcapsules (1.6 mg/rat/day). Aberrant crypt foci, tumors in the distal colon, and tumor blood vessels were examined.

RESULTS

ACTIBIND had an anticlonogenic effect unrelated to its ribonuclease activity. It also inhibited angiogenin-induced HUVEC tube formation in a dose-responsive manner. ACTIBIND was found to bind actin in vitro. It also bound to cancer cell surfaces, leading to disruption of the internal actin network and inhibiting cell motility and invasiveness through Matrigel-coated filters. In mice, ACTIBIND inhibited HT-29 xenograft tumor development, given either as a subcutaneous or intraperitoneal treatment. In rats, ACTIBIND exerted preventive and therapeutic effects on developing colonic tumors induced by DMH. It also reduced the degree of tumor observation.

CONCLUSIONS

This study indicated that ACTIBIND is an effective antiangiogenic and anticarcinogenic factor.

Enhanced anti-angiogenic effect of a deletion mutant of plasminogen kringle 5 on neovascularization

Kringle 5 (K5), a proteolytic fragment of plasminogen, has been proved to be an angiogenic inhibitor. Previously, we have evaluated the effect of K5 on the vascular leakage and neovascularization in a rat model of oxygen-induced retinopathy. In this study, we expressed K5 and a deletion mutant of K5 (K5 mutant) in a prokaryocyte expression system and purified them by affinity chromatography. K5 mutant was generated by deleting 11 amino acids from K5 while retaining the three disulfide bonds. The anti-angiogenic activity of intact K5 and K5 mutant were compared in endothelial cells and retinal neovascularization rat model. K5 mutant inhibited the proliferation of primary human retinal capillary endothelial cells (HRCEC) in a concentration-dependent manner, with an apparent EC50 of approximate 35 nmol/L, which is twofold more potent than intact K5. In the even higher concentration range, K5 mutant did not inhibit pericytes from the same origin of HRCEC, which suggested an endothelial cell-specific inhibition. K5 mutant had no effect on normal liver cells and Bel7402 hepatoma cells even at high concentration range either. Intravitreal injection of the K5 and mutant in the oxygen-induced retinopathy rat model both resulted in significantly fewer neovascular tufts and nonperfusion area than controls with PBS injection, as shown by fluorescein angiography. Furthermore, K5 mutant exhibited more strong inhibition effect on neovascularization than intact K5 by quantification of vascular cells. These results suggest that this K5 deletion mutant is a more potent angiogenic inhibitor than intact K5 and may have therapeutic potential in the treatment of those disorders with neovascularization, such as solid tumor, diabetic retinopathy, age-related macular degeneration, rheumatoid arthritis, and hyperplasia of prostate.

In vivo upregulation of CD95 and CD95L causes synergistic inhibition of angiogenesis by TSP1 peptide and metronomic doxorubicin treatment

Antiangiogenic thrombospondin-1 (TSP1) induces endothelial cell death via a CD95-mediated cascade. We used this signaling pathway, where CD95/Fas is a rate-limiting intermediate, as a target to optimize the efficacy of TSP1 active peptide, DI-TSP. Like TSP1, DI-TSP upregulated endothelial CD95L in vivo. To modulate CD95 levels, we chose chemotherapy agent doxorubicin (DXR). DXR caused sustained upregulation of CD95 in the activated endothelium at 1/100 of the maximal tolerated dose. DI-TSP and DXR synergistically induced endothelial apoptosis in vitro, and in vivo, in developing murine vessels. Fas decoy, TSP1 receptor antibody and Pifithrin, a p53 inhibitor, severely decreased apoptosis and restored angiogenesis by DXR-DI-TSP combination, evidencing critical roles of CD95 and TSP1. Combined therapy synergistically blocked neovascularization and progression of the bladder and prostate carcinoma. Such informed design of a complex antiangiogenic therapy based on the rate-limiting molecular targets is a novel concept, which may yield new approaches to cancer treatment.

Kringle 5 of human plasminogen induces apoptosis of endothelial and tumor cells through surface-expressed glucose-regulated protein 78

Kringle 5 (K5) of human plasminogen has been shown to inhibit angiogenesis by inducing the apoptosis of proliferating endothelial cells. Peptide regions around the lysine-binding pocket of K5 largely mediate these effects, particularly the peptide PRKLYDY, which we show to compete with K5 for the binding to endothelial cells. The cell surface binding site for K5 that mediates these effects has not been defined previously. Here, we report that glucose-regulated protein 78, exposed on cell surfaces of proliferating endothelial cells as well as on stressed tumor cells, plays a key role in the antiangiogenic and antitumor activity of K5. We also report that recombinant K5-induced apoptosis of stressed HT1080 fibrosarcoma cells involves enhanced activity of caspase-7, consistent with the disruption of glucose-regulated protein 78-procaspase-7 complexes. These results establish recombinant K5 as an inhibitor of a stress response pathway, which leads to both endothelial and tumor cell apoptosis.

Two Functional Epitopes of Pigment Epithelial–Derived Factor Block Angiogenesis and Induce Differentiation in Prostate Cancer

Pigment epithelial-derived factor (PEDF), an angiogenesis inhibitor with neurotrophic properties, balances angiogenesis in the eye and blocks tumor progression. Its neurotrophic function and the ability to block vascular leakage is replicated by the PEDF 44-mer peptide (residues 58-101). We analyzed PEDFs' three-dimensional structure and identified a potential receptor-binding surface. Seeking PEDF-based antiangiogenic agents we generated and tested peptides representing the middle and lower regions of this surface. We identified previously unknown antiangiogenic epitopes consisting of the 34-mer (residues 24-57) and a shorter proximal peptide (TGA, residues 16-26) with the critical stretch L19VEEED24 and a fragment within the 44-mer (ERT, residues 78-94), which retained neurotrophic activity. The 34-mer and TGA, but not the 44-mer reproduced PEDF angioinhibitory signals hinged on c-jun-NH2-kinase-dependent nuclear factor of activated T cell deactivation and caused apoptosis. Conversely, the ERT, but not the 34-mer/TGA induced neuronal differentiation. For the 44-mer/ERT, we showed a novel ability to cause neuroendocrine differentiation in prostate cancer cells. PEDF and the peptides bound endothelial and PC-3 prostate cancer cells. Bound peptides were displaced by PEDF, but not by each other, suggesting multiple receptors. PEDF and its active fragments blocked tumor formation when conditionally expressed by PC-3 cells. The 34- and 44-mer used distinct mechanisms: the 34-mer acted on endothelial cells, blocked angiogenesis, and induced apoptosis whereas 44-mer prompted neuroendocrine differentiation in cancer cells. Our results map active regions for the two PEDF functions, signaling via distinct receptors, identify candidate peptides, and provide their mechanism of action for future development of PEDF-based tumor therapies.

High level expression of kringle 5 fragment of plasminogen in Pichia pastoris

Angiogensis can be blocked by inhibitors such as endostatin and angiostatin. The kringle 5 fragment of plasminogen also has a potent inhibitory effect on endothelial cell proliferation and leads to the inhibition of angiogenesis. It has promise in anti-angiogenic therapy due to its small size and potent inhibitory effect. Preparation of kringle 5 has been achieved through the proteolysis of native plasminogen and recombinant DNA technology. Bacterially expressed recombinant kringle 5 is mainly insoluble and expressed at low level. The refolding yield is also low. To produce recombinant human kringle 5 in a large quantity, we have genetically modified a strain of Pichia pastoris. On methanol induction, this strain expressed and secreted biologically active, recombinant kringle 5. The expression level of the engineered strain in culture reached more than 300 mgl(-1). Purification was easily achieved by precipitation, hydrophobic and DEAE ion exchange chromatography. The recovery of recombinant kringle 5 was about 50% after purification. Yeast-expressed kringle 5 has a higher activity in anti-endothelial proliferation than bacterially expressed kringle 5.

Peroxisome Proliferator-Activated Receptor γ Ligands Improve the Antitumor Efficacy of Thrombospondin Peptide ABT510

An expanding capillary network is critical for several pathologic conditions. In cancer, the decrease of antiangiogenic thrombospondin-1 (TSP1) often enables an angiogenic switch, which can be reversed with exogenous TSP1 or its peptide derivative ABT510. TSP1 acts by inducing endothelial cell apoptosis via signaling cascade initiated at CD36, a TSP1 antiangiogenic receptor. Here, we show that the ligands of nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ), 15-deoxy-Δ12,14-prostaglandin J2, troglitazone, and rosiglitazone increased PPARγ and CD36 expression in endothelial cells and improved the efficacy of TSP1 and ABT510 in a CD36-dependent manner. The ABT510 and PPARγ ligands cooperatively blocked angiogenic endothelial functions in vitro and neovascularization in vivo. In tumor xenografts, 15-deoxy-Δ12,14-prostaglandin J2 and troglitazone synergistically improved antiangiogenic and antitumor effects of ABT510. Our data provide one mechanism for the in vivo angioinhibitory effect of PPARγ ligands and show fine-tuning of the antiangiogenic efficacy via targeted up-regulation of the endothelial receptor.

β4 integrin is involved in statin-induced endothelial cell death

HMG-CoA reductase inhibitors (statins) have been shown to inhibit angiogenesis. The molecular mechanism mediating the anti-endothelial activities of statins remains unclear. The present study demonstrated that the antiangiogenic effect of atorvastatin (ATV) was associated with endothelial death. Molecular profiling data identified a 29-fold upregulation of beta4 integrin mRNA. Western blot and flow cytometry confirmed robust increases of total and cell-surface beta4 integrin. Blockage of beta4 integrin activity by antagonizing antibody abrogated ATV-induced endothelial death. The endothelial death and beta4 integrin upregulation by ATV could be reversed by intermediate metabilites of the HMG-CoA reductase pathway mevalonate or GGPP, but not by FPP, suggesting that these effects were results of specific inhibition of the pathway. These data indicate that the HMG-CoA reductase might represent an important survival pathway in angiogenic endothelial cells and thus, a potential target for antiangiogenic therapy.

Nuclear factor of activated T cells balances angiogenesis activation and inhibition

It has been demonstrated that vascular endothelial cell growth factor (VEGF) induction of angiogenesis requires activation of the nuclear factor of activated T cells (NFAT). We show that NFATc2 is also activated by basic fibroblast growth factor and blocked by the inhibitor of angiogenesis pigment epithelial–derived factor (PEDF). This suggests a pivotal role for this transcription factor as a convergence point between stimulatory and inhibitory signals in the regulation of angiogenesis.

We identified c-Jun NH₂-terminal kinases (JNKs) as essential upstream regulators of NFAT activity in angiogenesis. We distinguished JNK-2 as responsible for NFATc2 cytoplasmic retention by PEDF and JNK-1 and JNK-2 as mediators of PEDF-driven NFAT nuclear export.

We identified a novel NFAT target, caspase-8 inhibitor cellular Fas-associated death domain–like interleukin 1β–converting enzyme inhibitory protein (c-FLIP), whose expression was coregulated by VEGF and PEDF. Chromatin immunoprecipitation showed VEGF-dependent increase of NFATc2 binding to the c-FLIP promoter in vivo, which was attenuated by PEDF. We propose that one possible mechanism of concerted angiogenesis regulation by activators and inhibitors may be modulation of the endothelial cell apoptosis via c-FLIP controlled by NFAT and its upstream regulator JNK.

Decreased pigment epithelium-derived factor and increased vascular endothelial growth factor levels in pterygia

PURPOSE

Pterygia are histologically composed of proliferating fibrovascular tissue. This study compared expression levels of an angiogenic inhibitor, pigment epithelium-derived factor (PEDF), in pterygia with those in normal corneal and conjunctival tissues.

METHODS

The normal human conjunctival and corneal tissues were obtained from surgery or from donor eyes without ocular diseases. Pterygia were excised by therapeutic surgery under a microscope. Pigment epithelium-derived factor and vascular endothelial growth factor (VEGF) were measured by Western blot analysis. Their cellular localizations were determined by immunohistochemistry.

RESULTS

Intensive PEDF immunostaining was detected in all the normal corneal and conjunctival samples analyzed, predominantly in the epithelium and endothelium of the cornea and in the epithelium of the limbus and conjunctiva. Under the same immunostaining conditions, pterygial samples showed negative or faint PEDF staining. In contrast, the same pterygial samples all showed intensive VEGF staining, predominantly in the epithelium and in blood vessels. Western blot analysis confirmed that the average PEDF level in pterygia was drastically lower than those in normal corneal and conjunctival tissues, respectively. In contrast, the VEGF level in pterygia was significantly higher than in the normal tissues.

CONCLUSION

Pterygia exhibit significantly lower PEDF but higher VEGF levels than those in normal corneas and conjunctivae. The decreased PEDF level in pterygia may play a role in the formation and progression of pterygia.

Regulation of the expression of pigment epithelium-derived factor, an anti-angiogenic factor in human oral squamous cell carcinoma cell lines

Angiogenesis plays an important role in tumor growth and metastasis and is regulated by a balance between angiogenic stimulators and inhibitors. We investigated the gene expression profile of vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF), a potent endogenous anti-angiogenic factor, in human oral squamous cell carcinoma (SCC) cell lines. The treatment of SCC cells with hypoxia increased the expression of PEDF as well as VEGF. Moreover, the treatment of SCC cells with VEGF enhanced the expression of PEDF mRNA and secretion of PEDF. In LMF-4, a SCC clone producing abundant VEGF and PEDF, the addition of neutralizing VEGF antibody substantially blocked PEDF expression. These data suggest that human oral squamous cell carcinoma cells produce VEGF, which in turn regulates PEDF production, and this balance may be contributing to neovascularization in tumors.

Influence of inflammatory cytokines on arteriogenesis

Blood vessel growth after birth is limited to two major processes. Angiogenesis is the growth of new capillaries by sprouting or intussusception. The major stimulus for angiogenesis is ischemia. In contrast, arteriogenesis describes the remodeling and growth of collateral arteries from a preexisting arteriolar network. Arteriogenesis is induced after the occlusion of a major artery which induces hemodynamic and mechanical effects on the collateral vessel wall which occur with increasing blood flow velocity due to the low pressure at the reentrant site of the collateral vessel. A variety of different cytokines that act by stimulating endothelial and smooth muscle cell proliferation and migration or recruitment and activation of monocytes have been identified to stimulate angiogenesis and/or arteriogenesis (i.e., MCP-1, FGF-2, TGF-beta, VEGF, and GM-CSF). Several clinical trials have been published in that field to suggest the feasibility and safety of treatment with such cytokines or their genes. However, the results indicate that further studies are needed before proangiogenic and proarteriogenic therapies are ready for clinical application.

Kallikrein-binding protein inhibits retinal neovascularization and decreases vascular leakage

AIMS/HYPOTHESIS

Kallikrein-binding protein (KBP) is a serine proteinase inhibitor (serpin). It specifically binds to tissue kallikrein and inhibits kallikrein activity. Our study was designed to test its effects on retinal neovascularization and vascular permeability.

METHODS

Endothelial cell proliferation was determined by [(3)H] thymidine incorporation assay and apoptosis quantified by Annexin V staining and flow cytometry. Effect on retinal neovascularization was determined by fluorescein angiography and count of pre-retinal vascular cells in an oxygen-induced retinopathy (OIR) model. Vascular permeability was assayed by the Evans blue method. Vascular endothelial growth factor (VEGF) was measured by Western blot analysis and ELISA.

RESULTS

Kallikrein-binding protein specifically inhibited proliferation and induced apoptosis in retinal capillary endothelial cells. Intravitreal injection of KBP inhibited retinal neovascularization in an OIR model. Moreover, KBP decreased vascular leakage in the retina, iris and choroid in rats with OIR. Blockade of kinin receptors by specific antagonists showed significantly weaker inhibition of endothelial cells, when compared to that of KBP, suggesting that the anti-angiogenic activity of KBP is not through inhibiting kallikrein activity or kinin production. KBP competed with (125)I-VEGF for binding to endothelial cells and down-regulated VEGF production in endothelial cells and in the retina of the OIR rat model.

CONCLUSION/INTERPRETATION

Kallikrein-binding protein is a multi-functional serpin, and its vascular activities are independent of its interactions with the kallikrein-kinin system. Inhibition of VEGF binding to its receptors and down-regulation of VEGF expression could represent a mechanism for the vascular activities of KBP.

Down-regulation of vascular endothelial growth factor and up-regulation of pigment epithelium-derived factor: a possible mechanism for the anti-angiogenic activity of plasminogen kringle 5

We have previously shown that intravitreal injection of plasminogen kringle 5 (K5), a potent angiogenic inhibitor, inhibits ischemia-induced retinal neovascularization in a rat model. Here we report that K5 down-regulates an endogenous angiogenic stimulator, vascular endothelial growth factor (VEGF) and up-regulates an angiogenic inhibitor, pigment epithelium-derived factor (PEDF) in a dose-dependent manner in vascular cells and in the retina. The regulation of VEGF and PEDF by K5 in the retina correlates with its anti-angiogenic effect in a rat model of ischemia-induced retinopathy. Retinal RNA levels of VEGF and PEDF are also changed by K5. K5 inhibits the p42/p44 MAP kinase activation and nuclear translocation of hypoxia-inducible factor-1alpha, which may be responsible for the down-regulation of VEGF. Down-regulation of endogenous angiogenic stimulators and up-regulation of endogenous angiogenic inhibitors, thus leading toward restoration of the balance in angiogenic control, may represent a mechanism for the anti-angiogenic activity of K5.

Brain metastases: biology and the role of the brain microenvironment

Metastatic lesions constitute the most frequently occurring malignancy in the brain, and their detection portends a grim prognosis. Efforts to treat these lesions have failed partly because the biologic processes that govern their development are poorly understood. In recent years, it has become evident that metastases occur as a result of a multistep process involving a rigorous natural selection of cells in the primary tumor that bear molecular and biologic characteristics permitting brain metastasis. In addition, recent studies have uncovered the importance of the brain microenvironment and its contribution to the metastatic process. The development of targeted therapies against brain metastases demands a better understanding of these molecular processes and the factors that influence them. This review examines the interplay between tumor cells and host brain tissue in the context of our current understanding of the role of various molecules involved in the metastatic process.