Targeting angiogenesis: progress with anti-VEGF treatment with large molecules

Computational modelling of anti-angiogenic therapies based on multiparametric molecular imaging data

Computational tumour models have emerged as powerful tools for the optimization of cancer therapies; ideally, these models should incorporate patient-specific imaging data indicative of therapeutic response. The purpose of this study was to develop a tumour modelling framework in order to simulate the therapeutic effects of anti-angiogenic agents based upon clinical molecular imaging data. The model was applied to positron emission tomography (PET) data of cellular proliferation and hypoxia from a phase I clinical trial of bevacizumab, an antibody that neutralizes the vascular endothelial growth factor (VEGF). When using pre-therapy PET data in combination with literature-based dose response parameters, simulated follow-up hypoxia data yielded good qualitative agreement with imaged hypoxia levels. Improving the quantitative agreement with follow-up hypoxia and proliferation PET data required tuning of the maximum vascular growth fraction (VGF(max)) and the tumour cell cycle time to patient-specific values. VGF(max) was found to be the most sensitive model parameter (CV = 22%). Assuming availability of patient-specific, intratumoural VEGF levels, we show how bevacizumab dose levels can potentially be 'tailored' to improve levels of tumour hypoxia while maintaining proliferative response, both of which are critically important in the context of combination therapy. Our results suggest that, upon further validation, the application of image-driven computational models may afford opportunities to optimize dosing regimens and combination therapies in a patient-specific manner.

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

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

Safety profiles of current antiangiogenic therapies for metastatic colorectal cancer

The biological agents approved for the treatment of patients with metastatic colorectal cancer - bevacizumab, a monoclonal antibody that targets vascular endothelial growth factor A, along with cetuximab and panitumumab, two monoclonal antibodies that target the epidermal growth factor receptor - are associated with a number of adverse events that range in severity from relatively mild to potentially life threatening. Hypertension, thromboembolic events, proteinuria, bleeding, and gastrointestinal perforation have all been associated with bevacizumab, while dermatologic toxicities are common with cetuximab and panitumumab. Hypersensitivity reactions and hypomagnesemia are also a concern with cetuximab and panitumumab. The frequency of these adverse events in randomized clinical trials is reviewed, and recommendations for managing these events in patients undergoing treatment for metastatic colorectal cancer are provided.

Overcoming resistance to antiangiogenic therapies

The concept of targeting new blood vessel formation, or angiogenesis, in tumors is an important advancement in cancer therapy, resulting, in part, from the development of such biologic agents as bevacizumab, a monoclonal antibody directed against vascular endothelial growth factor (VEGF)-A. The rationale for antiangiogenic therapy is based on the hypothesis that if tumors are limited in their capacity to obtain a new blood supply, so too is their capacity for growth and metastasis. Additional evidence suggests that pruning and/or "normalization" of irregular tumor vasculature and reduction of hypoxia may facilitate greater access of cytotoxic chemotherapy (CT) to the tumor. Indeed, for metastatic colorectal cancer, bevacizumab in combination with established CT regimens has efficacy superior to that of CT alone. Despite ~2-month longer progression-free and overall survival times than with CT alone, patients still progress, possibly because of alternative angiogenic "escape" pathways that emerge independent of VEGF-A, or are driven by hypoxic stress on the tumor. Other VEGF family members may contribute to resistance, and many factors that contribute to the regulation of tumor angiogenesis function as part of a complex network, existing in different concentrations and spatiotemporal gradients and producing a wide range of biologic responses. Integrating these concepts into the design and evaluation of new antiangiogenic therapies may help overcome resistance mechanisms and allow for greater efficacy over longer treatment periods.

Expression and purification of recombinant human serum albumin fusion protein with VEGF165b in Pichia pastoris

VEGF165b is an endogenous transcriptional splice variant of VEGF and has been shown to have a therapeutic potency as an anti-cancer agent. In this report, a fusion gene consisting of a human VEGF165b and a human albumin (HSA) gene was constructed and then inserted into a pPIC9k vector. The recombinant fusion protein, rhHSA-VEGF165b, was over expressed in the methylotrophic yeast Pichia pastoris under the control of AOX1 promoter. After induction with methanol, the expression level of rhHSA-VEGF165b was 275 mg/L in broth. The fusion protein rhHSA-VEGF165b was purified to more than 95% purity by using Blue Sepharose Fast Flow and SP Sepharose Fast Flow. Biological activity of the prepared rhHSA-VEGF165b was characterized by transwell migration assay, retaining about 9% of that of unmodified rhVEGF165b on a molar basis. Data from mice show that the serum half-life time of rhHSA-VEGF165b was nearly 20 times longer than that of rhVEGF165b.

In vivo tumor targeting and imaging with anti-vascular endothelial growth factor antibody-conjugated dextran-coated iron oxide nanoparticles

Background

Active targeting by specific antibodies combined with nanoparticles is a promising technology for cancer imaging and detection by magnetic resonance imaging (MRI). The aim of the present study is to investigate whether the systemic delivery of antivascular endothelial growth factor antibodies conjugating to the surface of functionalized supermagnetic iron oxide nanoparticles (anti-VEGF-NPs) led to target-specific accumulation in the tumor.

Methods

The VEGF expression in human colon cancer and in Balb/c mice bearing colon cancers was examined by immunohistochemistry. The distribution of these anti-VEGF-NPs particles or NPs particles were evaluated by MRI at days 1, 2, or 9 after the injection into the jugular vein of Balb/c mice bearing colon cancers. Tumor and normal tissues (liver, spleen, lung, and kidney) were collected and were examined by Prussian blue staining to determine the presence and distribution of NPs in the tissue sections.

Results

VEGF is highly expressed in human and mouse colon cancer tissues. MRI showed significant changes in the T*₂ signal and T₂ relaxation in the anti-VEGF-NP- injected-mice, but not in mice injected with NP alone. Examination of paraffin sections of tumor tissues stained for the iron constituent of the NPs with Prussian blue revealed a strong blue reaction in the tumors of anti-VEGF-NP-treated mice, but only a weak reaction in mice injected with NPs. In both groups, at all time points, Prussian blue-stained liver and spleen sections showed only light staining, while stained cells were rarely detected in kidney and lung sections. Transmission electron microscopy showed that many more electron-dense particles were present in endothelial cells, tumor cells, and extracellular matrix in tumor tissues in mice injected with anti-VEGF-NPs than in NP-injected mice.

Conclusion

These results demonstrated in vivo tumor targeting and efficient accumulation of anti-VEGF-NPs in tumor tissues after systemic delivery in a colon cancer model, showing that anti-VEGF-NPs have potential for use as a molecular-targeted tumor imaging agent in vivo.

MiR-145 inhibits tumor angiogenesis and growth by N-RAS and VEGF

MiR-145 is known as a tumor suppressor in numerous human cancers. However, its role in tumor angiogenesis remains poorly defined. In this study, we found that miR-145 was significantly downregulated in breast cancer tissues by using 106 cases of normal and cancer tissues as well as in breast cancer cells. MiR-145 exhibited inhibitory role in tumor angiogenesis, cell growth and invasion and tumor growth through the post-transcriptional regulation of the novel targets N-RAS and VEGF-A. In addition, we provide evidence that the expression levels of miR-145 correlate inversely with malignancy stages of breast tumors, although there is no association between miR-145 levels and hormone receptor levels in breast cancer. Taken together, these results demonstrate that miR-145 plays important inhibitory role in breast cancer malignancy by targeting N-RAS and VEGF-A, which may be potential therapeutic and diagnostic targets.

The isoflavone metabolite 6-methoxyequol inhibits angiogenesis and suppresses tumor growth

BACKGROUND

Increased consumption of plant-based diets has been linked to the presence of certain phytochemicals, including polyphenols such as flavonoids. Several of these compounds exert their protective effect via inhibition of tumor angiogenesis. Identification of additional phytochemicals with potential antiangiogenic activity is important not only for understanding the mechanism of the preventive effect, but also for developing novel therapeutic interventions.

RESULTS

In an attempt to identify phytochemicals contributing to the well-documented preventive effect of plant-based diets on cancer incidence and mortality, we have screened a set of hitherto untested phytoestrogen metabolites concerning their anti-angiogenic effect, using endothelial cell proliferation as an end point. Here, we show that a novel phytoestrogen, 6-methoxyequol (6-ME), inhibited VEGF-induced proliferation of human umbilical vein endothelial cells (HUVE) cells, whereas VEGF-induced migration and survival of HUVE cells remained unaffected. In addition, 6-ME inhibited FGF-2-induced proliferation of bovine brain capillary endothelial (BBCE) cells. In line with its role in cell proliferation, 6-ME inhibited VEGF-induced phosphorylation of ERK1/2 MAPK, the key cascade responsible for VEGF-induced proliferation of endothelial cells. In this context, 6-ME inhibited in a dose dependent manner the phosphorylation of MEK1/2, the only known upstream activator of ERK1/2. 6-ME did not alter VEGF-induced phosphorylation of p38 MAPK or AKT, compatible with the lack of effect on VEGF-induced migration and survival of endothelial cells. Peri-tumor injection of 6-ME in A-431 xenograft tumors resulted in reduced tumor growth with suppressed neovasularization compared to vehicle controls (P < 0.01).

CONCLUSIONS

6-ME inhibits VEGF- and FGF2-induced proliferation of ECs by targeting the phosphorylation of MEK1/2 and it downstream substrate ERK1/2, both key components of the mitogenic MAPK pathway. Injection of 6-ME in mouse A-431 xenograft tumors results to tumors with decreased neovascularization and reduced tumor volume suggesting that 6-ME may be developed to a novel anti-angiogenic agent in cancer treatment.

Ginsenoside Rg3 attenuates tumor angiogenesis via inhibiting bioactivities of endothelial progenitor cells

Accumulating evidence suggests that Ginsenoside Rg3 appears to inhibit tumor growth including Lewis lung carcinoma, intestinal adenocarcinomas or B16 melanoma by inhibiting cell proliferation, tumor cell invasion and metastasis. Endothelial progenitor cells (EPCs) appear to play a key role in the growth of early tumors by intervening with the angiogenic switch promoting tumor neovessel formation by producing angiogenic cytokines during tumor progression. This paper reports a novel mechanism of Ginsenoside Rg3, a candidate anticancer bio-molecule, on tumor angiogenesis by inhibiting the multiple bioactivities of EPCs. When Ginsenoside Rg3 was applied to the ex vivo cultured outgrowth ECs, a type of EPCs, it inhibited the cell proliferation, cell migration and tubular formation of EPCs. Importantly, Ginsenoside Rg3 attenuated the phosphorylation cascade of the VEGF dependent p38/ERK signaling in vitro. The xenograft tumor model clearly showed that Ginsenoside Rg3 suppresses tumor growth and tumor angiogenesis by inhibiting the mobilization of EPCs from the bone marrow microenvironment to the peripheral circulation and modulates VEGF-dependent tumor angiogenesis. In conclusion, this study provides a potential therapeutic molecule, Ginsenoside Rg3, as an anticancer drug by inhibiting the EPC bioactivities.

Blocking αvβ3 integrin by a recombinant RGD disintegrin impairs VEGF signaling in endothelial cells

Vascular endothelial growth factor (VEGF) and αvβ3 integrin are key molecules that actively participate in tumor angiogenesis and metastasis. Some integrin-blocking molecules are currently under clinical trials for cancer and metastasis treatment. However, the mechanism of action of such inhibitors is not completely understood. We have previously demonstrated the anti-angiogenic and anti-metastatic properties of DisBa-01, a recombinant His-tag RGD-disintegrin from Bothrops alternatus snake venom in some experimental models. DisBa-01 blocks αvβ3 integrin binding to vitronectin and inhibits integrin-mediated downstream signaling cascades and cell migration. Here we add some new information on the mechanism of action of DisBa-01 in the tumor microenvironment. DisBa-01 supports the adhesion of fibroblasts and MDA-MB-231 breast cancer cells but it inhibits the adhesion of these cells to type I collagen under flow in high shear conditions, as a simulation of the blood stream. DisBa-01 does not affect the release of VEGF by fibroblasts or breast cancer cells but it strongly decreases the expression of VEGF mRNA and of its receptors, vascular endothelial growth factor receptors 1 and 2 (VEGFR1 and VEGFR2) in endothelial cells. DisBa-01 at nanomolar concentrations also modulates metalloprotease 2 (MMP-2) and 9 (MMP-9) activity, the latter being decreased in fibroblasts and increased in MDA-MB-231 cells. In conclusion, these results demonstrate that αvβ3 integrin inhibitors may induce distinct effects in the cells of the tumor microenvironment, resulting in blockade of angiogenesis by impairing of VEGF signaling and in inhibition of tumor cell motility.

Targeting the proangiogenic VEGF-VEGFR protein-protein interface with drug-like compounds by in silico and in vitro screening

Protein-protein interactions play a central role in medicine, and their modulation with small organic compounds remains an enormous challenge. Because it has been noted that the macromolecular complexes modulated to date have a relatively pronounced binding cavity at the interface, we decided to perform screening experiments over the vascular endothelial growth factor receptor (VEGFR), a validated target for antiangiogenic treatments with a very flat interface. We focused the study on the VEGFR-1 D2 domain, and 20 active compounds were identified. These small compounds contained a (3-carboxy-2-ureido)thiophen unit and had IC(50) values in the low micromolar range. The most potent compound inhibited the VEGF-induced VEGFR-1 transduction pathways. Our findings suggest that our best hit may be a promising scaffold to probe this macromolecular complex and for the development of treatments of VEGFR-1-dependent diseases.

Functional and pharmacological characterization of a VEGF mimetic peptide on reparative angiogenesis

Vascular endothelial growth factor (VEGF) is the main regulator of physiological and pathological angiogenesis. Low molecular weight molecules able to stimulate angiogenesis have interesting medical application for example in regenerative medicine, but at present none has reached the clinic. We reported that a VEGF mimetic helical peptide, QK, designed on the VEGF helix sequence 17-25, is able to bind and activate the VEGF receptors, producing angiogenesis. In this study we evaluate the pharmacological properties of peptide QK with the aim to propose it as a VEGF-mimetic drug to be employed in reparative angiogenesis. We show that the peptide QK is able to recapitulate all the biological activities of VEGF in vivo and on endothelial cells. In experiments evaluating sprouting from aortic ring and vessel formation in an in vivo angiogenesis model, the peptide QK showed biological effects comparable with VEGF. At endothelial level, the peptide up-regulates VEGF receptor expression, activates intracellular pathways depending on VEGFR2, and consistently it induces endothelial cell proliferation, survival and migration. When added to angiogenic factors (VEGF and/or FGF-2), QK produces an improved biological action, which resulted in reduced apoptosis and accelerated in vitro wound healing. The VEGF-like activity of the short peptide QK, characterized by lower cost of production and easier handling compared to the native glycoprotein, suggests that it is an attractive candidate to be further developed for application in therapeutic angiogenesis.

Vascular endothelial growth factor (VEGF), VEGF receptors and their inhibitors for antiangiogenic tumor therapy

Vascular endothelial growth factor (VEGF) and its receptors (VEGFRs) have crucial roles in both physiological and pathological angiogenesis. The VEGF family consists of VEGF-A (generally called VEGF), VEGF-B, VEGF-C, VEGF-D, and placental growth factor (PlGF). These peptides show different affinities for VEGFR subtypes. VEGFR exists as three subtypes, VEGFR-1, VEGFR-2, and VEGFR-3, and is structurally related to platelet-derived growth factor receptors. All subtypes possess seven immunoglobulin-like domains in the extracellular region and a tyrosine kinase domain in the intracellular region. VEGF-A activates VEGFR-1 and VEGFR-2, whereas VEGF-B and PlGF bind to only VEFGR-1. VEGF-C and VEGF-D only bind to VEGFR-3. VEGFR-1 (fms-like tyrosine kinase-1, Flt-1) negatively regulates embryonic vasculogenesis and is involved in tumor angiogenesis via activation of monocytes and macrophages. VEGFR-2 (KDR in humans or Flk-1 in mice) is predominantly responsible for both embryonic vasculogenesis and tumor angiogenesis. In contrast, VEGFR-3 (Flt-4) regulates lymphangiogenesis. Consequently, VEGF-A and VEGFR-2 are currently the main targets for antiangiogenic therapy. Bevacizumab is a humanized monoclonal antibody against VEGF-A, and aflibercept (VEGF-Trap) is a soluble fusion protein of the extracelluar domain of VEGFR-1 and VEGFR-2 and the Fc region of immunoglobulin G (IgG). They neutralize VEGF-A, resulting in prevention of tumor angiogenesis. VEGFR tyrosine kinase inhibitors such as sunitinib and sorafenib are also effective in antiangiogenic tumor therapy by inhibiting VEGFR signaling. Anti-VEGF drugs are a promising therapy for cancer patients.

Vascular endothelial growth factor-C promotes alloimmunity by amplifying antigen-presenting cell maturation and lymphangiogenesis

PURPOSE

To investigate the role of anti-vascular endothelial growth factor (VEGF)-C therapy in corneal graft survival and concomitant suppression of hem- and lymph-angiogenesis.

METHODS

Corneal suture model in BALB/c mice was placed and immunohistochemical staining was performed with CD31/PECAM-1 and LYVE-1 to quantify the level of blood and lymphatic vessels. Corneal transplants were done in BALB/c mice from C57BL/6 mice donors; grafts were subsequently scored for opacity. VEGF-C was blocked in the angiogenesis and transplant model using neutralizing monoclonal anti-VEGF-C (VGX-100) by intraperitoneal injection. To determine the function of VEGF-C in maturation of antigen-presenting cells (APCs), bone marrow-derived dendritic cells were generated and matured in the presence or absence of VEGF-C.

RESULTS

VEGF-C expression was demonstrated to be markedly upregulated in corneal graft rejection. VEGF-C blockade, through administration of a VEGF-C blocking monoclonal antibody, suppresses corneal angiogenic responses, inhibits trafficking and maturation of APCs, and significantly improves allotransplant survival.

CONCLUSIONS

These data suggest VEGF-C as a potentially important target in corneal transplant pharmacotherapy and immunobiology.

Disruption of vascular homeostasis in patients with Kawasaki disease: involvement of vascular endothelial growth factor and angiopoietins

OBJECTIVE

In Kawasaki disease (KD), a pediatric vasculitis of medium-sized arteries, the coronary arteries are most commonly affected. Angiopoietins and vascular endothelial growth factor (VEGF) play an important role in maintaining vascular homeostasis. Recently, we identified ANGPT1 and VEGFA as susceptibility loci for KD. This study was undertaken to fine-map these associations and to gain further insight into their role in this vasculitis of unknown etiology to further the search for improved diagnostic and therapeutic options.

METHODS

A total of 292 single-nucleotide polymorphisms (SNPs) located in VEGF and ANGPT and their receptors were genotyped in 574 families, including 462 trios. For replication, 123 cases and 171 controls were genotyped.

RESULTS

A significant association with KD susceptibility was observed with 5 SNPs in the ANGPT1 gene (most significantly associated SNP +265037 C>T; Pcombined=2.3×10(-7) ) and 2 SNPs in VEGFA (most significantly associated SNP rs3025039; Pcombined=2.5×10(-4) ). Both ANGPT1 +265037 C>T and VEGFA rs3025039 are located in 3' regulatory regions at putative transcription factor binding sites. We observed significantly down-regulated transcript levels of angiopoietin 1 (Ang-1) in patients with acute KD compared to patients with convalescent KD. In patients with acute KD, high serum protein levels of VEGF and Ang-2 were observed compared to patients with convalescent KD and to both controls with and controls without fever. Immunohistochemistry demonstrated VEGF and angiopoietin expression in the coronary artery wall in autopsy tissue.

CONCLUSION

Our data support the hypothesis that dysregulation of VEGF and angiopoietins contributes to the disruption of vascular homeostasis in KD.

Integrins and their extracellular matrix ligands in lymphangiogenesis and lymph node metastasis

In the 1970s, the late Judah Folkman postulated that tumors grow proportionately to their blood supply and that tumor angiogenesis removed this limitation promoting growth and metastasis. Work over the past 40 years, varying from molecular examination to clinical trials, verified this hypothesis and identified a host of therapeutic targets to limit tumor angiogenesis, including the integrin family of extracellular matrix receptors. However, the propensity for some tumors to spread through lymphatics suggests that lymphangiogenesis plays a similarly important role. Lymphangiogenesis inhibitors reduce lymph node metastasis, the leading indicator of poor prognosis, whereas inducing lymphangiogenesis promotes lymph node metastasis even in cancers not prone to lymphatic dissemination. Recent works highlight a role for integrins in lymphangiogenesis and suggest that integrin inhibitors may serve as therapeutic targets to limit lymphangiogenesis and lymph node metastasis. This review discusses the current literature on integrin-matrix interactions in lymphatic vessel development and lymphangiogenesis and highlights our current knowledge on how specific integrins regulate tumor lymphangiogenesis.

Effect of Sanguisorba officinalis L on breast cancer growth and angiogenesis

OBJECTIVE

Sanguisorba officinalis L. (SA) has shown anti-inflammation, hematopoiesis and immunity enhancing properties. No detailed studies have been reported on its anti-cancer effects. This study therefore was undertaken to analyze its effects on human breast cancer utilizing in vitro and in vivo methodologies.

METHODS

Human breast cancer cell lines MCF-7 and MDA-MB-231 were utilized for evaluating SA influences on tumor progression and angiogenesis processes like proliferation, the cell cycle, apoptosis, tube formation and migration abilities. Both cancer xenografts were also used to determine the herb efficacy in vivo. Bioactivity-guided fractionation was carried out to determine the bioactive compounds in SA.

RESULTS

SA inhibited proliferation, induced S phase arrest and triggered mitochondrial pathway apoptosis in both cancer cells. Angiogenesis experiments revealed that SA inhibited VEGF expression in both cancer cell lines. Meanwhile, the proliferation, tube formation and migration abilities of endothelial cells were also inhibited. In vivo experiments demonstrated that SA reduced tumor size and neoangiogenesis in both cancer xenografts. Gallic acid and ellagic acid were finally identified as bioactive compounds in SA.

CONCLUSIONS

SA might be of value as a breast cancer preventive and therapeutic agent by inducing apoptosis and inhibiting angiogenesis. Further research is needed to evaluate its metabolism and synergistic effects with chemotherapeutic drugs.

Phase II trial of erlotinib and bevacizumab in patients with advanced upper gastrointestinal cancers

BACKGROUND

Patients with upper gastrointestinal cancers have a poor prognosis and only few treatment options. The epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGF) are valid targets in many solid tumours, and they have synergistic effects in preclinical studies.

METHODS

In this multi-center phase II trial patients with chemoresistant, metastatic upper gastrointestinal cancer were treated with erlotinib (150 mg daily) and bevacizumab (10 mg/kg every two weeks). Primary endpoint was overall response rate (ORR). Secondary endpoints were progression free survival (PFS), overall survival (OS), toxicity and biomarker correlates. Plasma samples were analysed for EGFR and angiogenesis related markers using quantitative immunoassays.

RESULTS

One hundred and two patients were enrolled in the trial between June 2006 and October 2007. The most common toxicities were skin reaction, diarrhoea, and fatigue. ORR was 6%, median PFS was 2.2 months, and OS 4.3 months. Low concentration of urokinase plasminogen activator receptor (uPAR) domain I was correlated to longer PFS and OS.

DISCUSSION

The combination of erlotinib and bevacizumab is well tolerated, however, with low clinical activity in patients with chemoresistant UGI cancer. Some patients do benefit from the therapy, and uPAR forms are potential biomarkers in these patients.

Metronomic oral cyclophosphamide in patients with advanced solid tumors

BACKGROUND

Cure is rarely achieved in patients with advanced metastatic solid tumors, and quality of life including times without burdening therapies is an important endpoint. Metronomic oral cyclophosphamide (Cy) has been studied before and is a reasonable option.

PATIENTS AND METHODS

24 patients with a mean age of 64.4 years (range 36-82 years) were studied. 18 patients had breast cancer, 4 prostate cancer, 1 uterine carcinoma, and 1 carcinoma of unknown primary.

RESULTS

All patients had advanced disease with a mean of 2 metastatic sites. Cy was given at a mean dosage of 52 mg daily. Time from diagnosis to start of Cy was 108.6 ± 7.6 months, and from occurrence of metastatic disease to Cy 45.8 ± 45.6 months. Patients had received a mean of 4.2 ± 2.1 prior regimens for metastatic disease. The mean time to treatment failure was 6.4 ± 5.4 months, and mean overall survival was 12.7 ± 7.3 months. Patients received 2.1 ± 1.4 further treatments upon progression. Main toxicities were grade 1 and 2 (n = 25); 3 patients had grade 3 nausea, leucopenia, and elevated gamma glutamyl transferase, respectively.

CONCLUSION

Low-dose oral Cy is a reasonable, generally well tolerated, and inexpensive option for patients with advanced solid tumors.

Metabolic effects of anti-angiogenic therapy in tumors

Anti-angiogenic therapy has recently been added to the panel of cancer therapeutics, but predictive biomarkers of response are still not available. In animal models, anti-angiogenic therapy causes tumor starvation by increasing hypoxia and impairing nutrients supply. It is thus conceivable that angiogenesis inhibition causes remarkable metabolic perturbations in tumors, although they remain largely uncharted. We review here recent acquisitions about metabolic effects of angiogenesis blockade in tumors and discuss the possibility that some metabolic features of tumor cells - i.e. their dependency from glucose as primary energy substrate - might affect tumor responses to anti-VEGF treatment.

Aflibercept in the treatment of metastatic colorectal cancer

Colorectal cancer is the third most common cancer in the US. In recent decades, an improved understanding of the role of the angiogenesis pathway in colorectal cancer has led to advancements in treatment. Bevacizumab has been shown to improve the progression-free survival and overall survival when combined with cytotoxic chemotherapy in patients with metastatic colorectal cancer, and at present is the only antiangiogenesis agent approved for the treatment of this cancer. Aflibercept is a novel angiogenesis-targeting agent, and has demonstrated efficacy in treating metastatic colorectal cancer in a recent randomized Phase III trial. Here we review the role of angiogenesis in the tumorigenesis of colorectal cancer, strategies for targeting angiogenesis, and the clinical development of aflibercept.

Ras homolog gene family, member A promotes p53 degradation and vascular endothelial growth factor-dependent angiogenesis through an interaction with murine double minute 2 under hypoxic conditions

BACKGROUND

Tumor neovascularization (TNV) is a common pathologic basis for malignant growth and metastasis. However, the mechanism of TNV pathogenesis is not fully understood. Ras homolog gene family, member A (RhoA), a Rho guanosine triphosphatase (GTPase) family member, may be involved in a hypoxia-induced vascular endothelial growth factor (VEGF) pathway that regulates TNV angiogenesis through an unclear mechanism.

METHODS

The regulation of RhoA on p53, the p53 binding protein homolog murine double minute 2 (MDM2), and VEGF was analyzed in hypoxic MCF-7 cells using Western blot analysis, real-time polymerase chain reaction (PCR) analysis, coimmunoprecipitation, and immunofluorescence staining assays. Changes in proliferation, invasion, migration, stress fiber formation, and tube formation were detected in an MCF-7 human umbilical vein endothelial cell (HUVEC) coculture system. Correlations of RhoA expression with MDM2, wild-type p53 (wt-p53), and VEGF expression in breast cancer tissues and relations between RhoA and breast cancer clinical features were analyzed by immunohistochemistry.

RESULTS

Activated RhoA down-regulated p53 protein, which increased VEGF expression in hypoxic MCF-7 cells; whereas p53 messenger RNA levels were not altered. In addition, the ubiquitin-mediated degradation of p53 was enhanced by active RhoA. RhoA and MDM2 colocalized in the cytoplasm of hypoxic MCF-7 cells and interacted with each other physically. Furthermore, nutlin-3, a specific MDM2 inhibitor, was capable of reducing activated RhoA-induced p53 protein stability and attenuating VEGF accumulation. In an MCF-7-HUVEC coculture system, nutlin-3 effectively inhibited HUVEC proliferation, invasion, migration, stress fiber formation, and tube formation mediated by activated RhoA under hypoxic conditions. Data from 129 clinical breast cancer specimens with wt-p53 revealed that high RhoA expression was correlated with high MDM2 expression, low wt-p53 expression, and high VEGF expression.

CONCLUSIONS

The current data suggested that activated RhoA promotes VEGF expression and hypoxia-induced angiogenesis through the up-regulation of MDM2 to decrease p53 stability.

Real-time visualization and characterization of tumor angiogenesis and vascular response to anticancer therapies

In vivo angiogenesis assays provide more physiologically relevant information about tumor vascularization than in vitro studies because they take the complex interactions among cancer cells, endothelial cells, mural cells, and tumor stroma into consideration. Traditional microscopic assessment of vascular density conducted by immunostaining of tissue sections or by lectin angiogram visualization of tumor vessels is invasive and requires the sacrifice of tumor-bearing animals. Therefore, it prohibits longitudinal time-course observation in a single animal and requires a large number of animals at each time point to derive statistically-meaningful observations. Additionally, heterogenous behavior among different tumors will inevitably introduce individual biological variance that may obscure reliable interpretation of the results. While various artificial in vivo angiogenesis assays, such as the Matrigel implant assay, chick chorioallatoic membrane assay, and dorsal skin fold chamber assay have been developed and employed to more directly observe the progression of physiological angiogenesis, they can not appropriately assess tumor angiogenic progression or tumor vascular regression in response to therapeutic intervention. Here, we describe a noninvasive method and a detailed protocol that we have developed and optimized using the Olympus OV-100 in vivo imaging system for real-time high-resolution visualization and assessment of tumor angiogenesis and vascular response to anticancer therapies in live animals. We show that using this approach, tumor vessels can be monitored longitudinally through the whole vasculogenesis and angiogenesis process in the same mouse. Further, morphologic changes of the same vessel prior to and after drug treatments can be captured with microscopic high resolution. Moreover, the multichannel co-imaging capability of the OV-100 allows us to analyze and compare tumor vessel permeability before and after antiangiogenesis therapy by employing a near-infrared blood pool reagent, or by visualizing improved cytotoxic drug delivery upon tumor vessel normalization by using a fluorophore tagged drug. This noninvasive method can be readily applied to orthotopically transplanted breast cancer models as well as to subcutaneously-transplanted tumor models.

Treatment regimen with bevacizumab decreases mean platelet volume in patients with metastatic colon cancer

The risk of thromboemboli is increased in patients with cancer, and this is precipitated by the chemotherapeutic agents. Bevacizumab is an anti-vascular endothelial growth factor monoclonal antibody and has an importance in the treatment of metastatic colon cancer. The association between bevacizumab, which is demonstrated to increase the risk of thromboemboli, and mean platelet volume (MPV), which is a marker of thrombocyte function, has been investigated within study. A total of 74 patients with metastatic colon cancer were included in the study and the levels of platelets (PLTs), MPV, and platecrit (PCT) values were recorded in SPSS 16.0 program both at baseline and at the >third month. There were significant decreases in 3 parameters (PLT, MPV, and PCT) during the treatment period with bevacizumab (P = .009, P = .001, and P = .000, respectively). Unlike cases with thrombosis, there is a significant decrease in MPV in combination treatments with bevacizumab.

Signaling pathways governing tumor angiogenesis

Angiogenesis is regulated by the highly coordinated function of various proteins with pro- and antiangiogenic functions. Proangiogenic factors include vascular endothelial growth factor (VEGF), fibroblast growth factor, platelet-derived growth factor, insulin-like growth factor, transforming growth factor, angiopoietins, and several chemokines; antiangiogenic factors include thrombospondin-1, angiostatin, and endostatin. Matrix metalloproteinases display a dual role in vascular development. Notch signaling affects remodeling of the primary vascular network of uniformly sized vessels into functionally and morphologically distinct arteries, veins, and capillaries. Tumors, described as 'wounds that never heal', lose the appropriate balance among these factors. Although VEGF-targeted therapies are showing promise, new angiogenesis targets are needed to make additional gains. Here, we highlight recent advances in our understanding of the regulation of tumor angiogenesis and discuss the potential of molecular targeting as a new therapeutic approach.

Combined treatment targeting HIF-1α and Stat3 is a potent strategy for prostate cancer therapy

BACKGROUND

The Stat3 pathway and the hypoxia-sensing pathway are both up-regulated in prostate cancer. Stat3 is a specific regulator of pro-carcinogenic inflammation and represents a promising therapeutic target. Hypoxia-inducible factor-1 (HIF-1)α, which mediates the cellular response to hypoxia, has been demonstrated to be over-expressed in many human cancers and is associated with poor prognosis and treatment failure in clinic. To develop a potent strategy to increase therapeutic efficacy and reduce drug resistance in prostate cancer therapy, we combined two anti-cancer agents: T40214 (a p-Stat3 inhibitor) and JG244 (a HIF-1α inhibitor) together to treat nude mice bearing human prostate tumor (DU145) and immunocompetent mice (C57BL/6) bearing murine prostate tumor (TRAMP-C2).

METHODS

We employed in vitro and in vivo assays, including Western blots, cell cycle analysis, immunohistochemistry, TUNEL and xenograft models to determine the drug efficacy and mechanism of combination treatment of T40214 and JG244.

RESULTS

We found that compared to treatment by T40214 or JG244 alone, the combination treatment using T40214 and JG244 together significantly suppressed growth of human or murine prostate tumors. Also, compared with apoptotic cells induced by T40214 or JG244 alone, the combined treatment greatly increased apoptosis in DU145 (P < 0.006) and TRAMP-C2 tumors (P < 0.008).

CONCLUSIONS

Our results suggested that combination treatment including a HIF-1α/2α inhibitor not only has therapeutic efficacy in targeting HIF-1α/2α, but also could reduce the hypoxia-induced drug resistance to other therapies (e.g., T40214) and enhance drug efficacy. This approach could make prostate cancer treatments more effective.

Development of regional chemotherapies: feasibility, safety and efficacy in clinical use and preclinical studies

Conventional oral and intravenous chemotherapies permeate throughout the body, exposing healthy tissues to similar cytotoxic drug levels as tumors. This leads to significant dose-limiting toxicities that may prevent patients from receiving sufficient treatment to overcome cancers. Therefore, a number of locoregional drug-delivery strategies have been evaluated and implemented in preclinical studies, clinical trials and in practice, in the past decades to minimize systemic toxicities from chemotherapeutic agents and to improve treatment outcomes. Localized treatment is beneficial because many cancers, such as melanoma, peritoneal cancer and breast cancer, advance locally adjacent to the site of the primary tumors prior to their circulatory invasion. In this article, we will review the feasibility, safety and efficacy of multiple localized chemotherapies in clinical use and preclinical development.

FGF-dependent regulation of VEGF receptor 2 expression in mice

Numerous studies have suggested a link between the angiogenic FGF and VEGF signaling pathways; however, the nature of this link has not been established. To evaluate this relationship, we investigated VEGF signaling in ECs with disrupted FGF signaling in vitro and in vivo. ECs lacking FGF signaling became unresponsive to VEGF, caused by downregulation of VEGF receptor 2 (VEGFR2) expression after reduced Vegfr2 enhancer activation. FGF mediated VEGFR2 expression via activation of Erk1/2. Transcriptional analysis revealed that Ets transcription factors controlled VEGFR2 expression in an FGF- and Erk1/2-dependent manner. Mice with defective FGF signaling exhibited loss of vascular integrity and reduced vascular morphogenesis. Thus, basal FGF stimulation of the endothelium is required for maintenance of VEGFR2 expression and the ability to respond to VEGF stimulation and accounts for the hierarchic control of vascular formation by FGFs and VEGF.

The VEGF family in cancer and antibody-based strategies for their inhibition

Angiogenesis is required in normal physiological processes, but is also involved in tumor growth, progression and metastasis. Vascular endothelial growth factor (VEGF), a primary mediator of angiogenesis in normal physiology and in disease, and other VEGF family members and their receptors provide targets that have been explored extensively for cancer therapy. Small molecule inhibitors and antibody/protein-based strategies that target the VEGF pathway have been studied in multiple types of cancer. This review will focus on VEGF pathway targeting antibodies that are currently being evaluated in pre-clinical and clinical studies.

Bevacizumab enhances the therapeutic efficacy of Irinotecan against human head and neck squamous cell carcinoma xenografts

Combining antiangiogenic agents with traditional cytotoxic chemotherapy offers the potential to target both vascular and cellular components of a growing tumor mass. Here, we examined the antitumor activity of the vascular endothelial growth factor antibody, Bevacizumab (Avastin®) in combination with the topoisomerase I inhibitor, Irinotecan (CPT-11) against human head and neck squamous cell carcinoma (HNSCC) xenografts. Bevacizumab was administered daily (at 5 or 20mg/kg) to nude mice bearing FaDu HNSCC xenografts for 28days with the first dose beginning seven days prior to Irinotecan (100mg/kg, weekly × 4). Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and immunohistochemical (IHC) methods were employed to study the antiangiogenic effects of Bevacizumab in vivo. Kinetics of tumor response to treatment was studied by monitoring tumor volume over a 60-day period. DCE-MRI detected a significant reduction in vascular permeability following treatment with Bevacizumab (5mg/kg) while high dose Bevacizumab (20mg/kg) induced significant microvascular damage and tumor necrosis, confirmed by immunohistochemistry (IHC). Irinotecan alone resulted in complete tumor regression (cures) in ∼40% of animals while Bevacizumab alone did not result in any cures. Treatment with Bevacizumab (5mg/kg/day×28days) in combination with Irinotecan (100mg/kg, weekly × 4) was highly effective in inhibiting FaDu tumor growth and resulted in complete tumor regression in 80% of animals. These results demonstrate that long term administration of Bevacizumab effectively modulates chemotherapeutic efficacy against HNSCC xenografts. Further investigation into the therapeutic potential of this combination strategy against HNSCC is warranted.

Glycolytic phenotype and AMP kinase modify the pathologic response of tumor xenografts to VEGF neutralization

VEGF antagonists are now widely used cancer therapeutics, but predictive biomarkers of response or toxicity remain unavailable. In this study, we analyzed the effects of anti-VEGF therapy on tumor metabolism and therapeutic response by using an integrated set of imaging techniques, including bioluminescence metabolic imaging, 18-fluorodeoxyglucose positron emission tomography, and MRI imaging and spectroscopy. Our results revealed that anti-VEGF therapy caused a dramatic depletion of glucose and an exhaustion of ATP levels in tumors, although glucose uptake was maintained. These metabolic changes selectively accompanied the presence of large necrotic areas and partial tumor regression in highly glycolytic tumors. In addition, we found that the central metabolic protein kinase AMP-activated protein kinase (AMPK)-a cellular sensor of ATP levels that supports cell viability in response to energy stress-was activated by anti-VEGF therapy in experimental tumors. AMPK-α2 attenuation increased glucose consumption, tumor cell sensitivity to glucose starvation, and tumor necrosis following anti-VEGF therapy. Taken together, our findings reveal functional links between the Warburg effect and the AMPK pathway with therapeutic responses to VEGF neutralization in tumor xenograft models.

Tumors that acquire resistance to low-dose metronomic cyclophosphamide retain sensitivity to maximum tolerated dose cyclophosphamide

Low-dose metronomic (LDM) chemotherapy is emerging as an alternative or supplemental dosing strategy to conventional maximum tolerated dose (MTD) chemotherapy. It is characterized primarily, but not exclusively, by antiangiogenic mechanisms of action and the absence of high-grade adverse effects commonly seen with MTD chemotherapy. However, similar to other anticancer therapies, inherent resistance to LDM chemotherapy is common. Moreover, even tumors that initially respond to metronomic regimens eventually develop resistance through mechanisms that are as yet unknown. Thus, we have developed in vivo models of PC-3 human prostate cancer cells resistant to extended LDM cyclophosphamide therapy. Such PC-3 variants show stable resistance to LDM cyclophosphamide in vivo yet retain in vitro sensitivity to 4-hydroperoxy-cyclophosphamide (precursor of the active cyclophosphamide metabolite 4-hydroxy-cyclophosphamide) and other chemotherapeutic agents, namely, docetaxel and doxorubicin. Moreover, LDM cyclophosphamide-resistant PC-3 variants remain sensitive to MTD cyclophosphamide therapy in vivo. Conversely, PC-3 variants made resistant in vivo to MTD cyclophosphamide show varying levels of resistance to metronomic cyclophosphamide when grown in mice. These results and additional studies of variants of the breast cancer cell line MDA-MB-231 suggest that resistance to LDM cyclophosphamide is a distinct phenomenon from resistance to MTD cyclophosphamide and that LDM cyclophosphamide administration does not select for MTD chemotherapy resistance. As such, our findings have various implications for the clinical use of metronomic chemotherapy.

Gamma-secretase inhibitor treatment promotes VEGF-A-driven blood vessel growth and vascular leakage but disrupts neovascular perfusion

The Notch signaling pathway is essential for normal development due to its role in control of cell differentiation, proliferation and survival. It is also critically involved in tumorigenesis and cancer progression. A key enzyme in the activation of Notch signaling is the gamma-secretase protein complex and therefore, gamma-secretase inhibitors (GSIs)—originally developed for Alzheimer's disease—are now being evaluated in clinical trials for human malignancies. It is also clear that Notch plays an important role in angiogenesis driven by Vascular Endothelial Growth Factor A (VEGF-A)—a process instrumental for tumor growth and metastasis. The effect of GSIs on tumor vasculature has not been conclusively determined. Here we report that Compound X (CX), a GSI previously reported to potently inhibit Notch signaling in vitro and in vivo, promotes angiogenic sprouting in vitro and during developmental angiogenesis in mice. Furthermore, CX treatment suppresses tumor growth in a mouse model of renal carcinoma, leads to the formation of abnormal vessels and an increased tumor vascular density. Using a rabbit model of VEGF-A-driven angiogenesis in skeletal muscle, we demonstrate that CX treatment promotes abnormal blood vessel growth characterized by vessel occlusion, disrupted blood flow, and increased vascular leakage. Based on these findings, we propose a model for how GSIs and other Notch inhibitors disrupt tumor blood vessel perfusion, which might be useful for understanding this new class of anti-cancer agents.

The EPR effect: Unique features of tumor blood vessels for drug delivery, factors involved, and limitations and augmentation of the effect

The enhanced permeability and retention (EPR) effect is a unique phenomenon of solid tumors related to their anatomical and pathophysiological differences from normal tissues. For example, angiogenesis leads to high vascular density in solid tumors, large gaps exist between endothelial cells in tumor blood vessels, and tumor tissues show selective extravasation and retention of macromolecular drugs. This EPR effect served as a basis for development of macromolecular anticancer therapy. We demonstrated methods to enhance this effect artificially in clinical settings. Of great importance was increasing systolic blood pressure via slow angiotensin II infusion. Another strategy involved utilization of NO-releasing agents such as topical nitroglycerin, which releases nitrite. Nitrite is converted to NO more selectively in the tumor tissues, which leads to a significantly increased EPR effect and enhanced antitumor drug effects as well. This review discusses molecular mechanisms of factors related to the EPR effect, the unique anatomy of tumor vessels, limitations and techniques to avoid such limitations, augmenting tumor drug delivery, and experimental and clinical findings.

CXCL12 (SDF1alpha)-CXCR4/CXCR7 pathway inhibition: an emerging sensitizer for anticancer therapies?

Addition of multiple molecularly targeted agents to the existing armamentarium of chemotherapeutics and radiotherapies represents a significant advance in the management of several advanced cancers. In certain tumor types with no efficacious therapy options, these agents have become the first line of therapy, for example, sorafenib in advanced hepatocellular carcinoma or bevacizumab in recurrent glioblastoma. Unfortunately, in many cases, the survival benefits are modest, lasting only weeks to a few months. Moreover, they may not show benefit in patients with localized disease (i.e., in the adjuvant setting). Recent studies have provided increasing evidence that activation of the chemokine CXCL12 (SDF1α) pathway is a potential mechanism of tumor resistance to both conventional therapies and biological agents via multiple complementary actions: (i) by directly promoting cancer cell survival, invasion, and the cancer stem and/or tumor-initiating cell phenotype; (ii) by recruiting "distal stroma" (i.e., myeloid bone marrow-derived cells) to indirectly facilitate tumor recurrence and metastasis; and (iii) by promoting angiogenesis directly or in a paracrine manner. Here, we discuss recent preclinical and clinical data that support the potential use of anti-CXCL12 agents (e.g., AMD3100, NOX-A12, or CCX2066) as sensitizers to currently available therapies by targeting the CXCL12/CXCR4 and CXCL12/CXCR7 pathways.

Bevacizumab potentiates chemotherapeutic effect on T-leukemia/lymphoma cells by direct action on tumor endothelial cells

Vascular endothelial growth factor-A, an angiogenesis stimulator expressed on both tumor endothelial and malignant T cells, is involved in tumor progression in T-leukemia/lymphoma. Here, we assessed the impact of therapeutic vascular endothelial growth factor-A blockade on tumor-endothelial cell interaction and on tumor progression. In a murine xenograft T-leukemia/lymphoma model, combined bevacizumab (monoclonal antibody against vascular endothelial growth factor-A) with doxorubicin, compared with doxorubicin alone, significantly delayed tumor growth and induced prevalence of tumor cell apoptosis over mitosis. More importantly, the combined treatment induced endothelial cell swelling, microvessel occlusions, and tumor necrosis. In vitro, co-culture of endothelial cells with T-leukemia/lymphoma cells showed that doxorubicin induced expression of intracellular cell adhesion molecule-1, provided endothelial and malignant T cells were in direct contact. This was abrogated by bevacizumab treatment with doxorubicin. Taken together, bevacizumab enhances the chemotherapeutic effect on T-leukemia/lymphoma cells. Directly targeting tumor endothelial cells might be a promising therapeutic strategy to counteract tumor progression in T-cell malignancies.

PET imaging of tumor angiogenesis in mice with VEGF-A-targeted (86)Y-CHX-A″-DTPA-bevacizumab

Bevacizumab is a humanized monoclonal antibody that binds to tumor-secreted vascular endothelial growth factor (VEGF)-A and inhibits tumor angiogenesis. In 2004, the antibody was approved by the US Food and Drug Administration (FDA) for the treatment of metastatic colorectal carcinoma in combination with chemotherapy. This report describes the preclinical evaluation of a radioimmunoconjugate, (86)Y-CHX-A″-DTPA-bevacizumab, for potential use in Positron Emission Tomography (PET) imaging of VEGF-A tumor angiogenesis and as a surrogate marker for (90)Y-based radioimmunotherapy. Bevacizumab was conjugated to CHX-A″-DTPA and radiolabeled with (86)Y. In vivo biodistribution and PET imaging studies were performed on mice bearing VEGF-A-secreting human colorectal (LS-174T), human ovarian (SKOV-3) and VEGF-A-negative human mesothelioma (MSTO-211H) xenografts. Biodistribution and PET imaging studies demonstrated highly specific tumor uptake of the radioimmunoconjugate. In mice bearing VEGF-A-secreting LS-174T, SKOV-3 and VEGF-A-negative MSTO-211H tumors, the tumor uptake at 3 days postinjection was 13.6 ± 1.5, 17.4 ± 1.7 and 6.8 ± 0.7 % ID/g, respectively. The corresponding tumor uptake in mice coinjected with 0.05 mg cold bevacizumab were 5.8 ± 1.3, 8.9 ± 1.9 and 7.4 ± 1.0 % ID/g, respectively at the same time point, demonstrating specific blockage of the target in VEGF-A-secreting tumors. The LS-174T and SKOV3 tumors were clearly visualized by PET imaging after injecting 1.8-2.0 MBq (86)Y-CHX-A″-DTPA-bevacizumab. Organ uptake quantified by PET closely correlated (r(2) = 0.87, p = 0.64, n = 18) to values determined by biodistribution studies. This preclinical study demonstrates the potential of the radioimmunoconjugate, (86)Y-CHX-A″-DTPA-bevacizumab, for noninvasive assessment of the VEGF-A tumor angiogenesis status and as a surrogate marker for (90)Y-CHX-A″-DTPA-bevacizumab radioimmunotherapy.

Endothelial von Willebrand factor regulates angiogenesis

The regulation of blood vessel formation is of fundamental importance to many physiological processes, and angiogenesis is a major area for novel therapeutic approaches to diseases from ischemia to cancer. A poorly understood clinical manifestation of pathological angiogenesis is angiodysplasia, vascular malformations that cause severe gastrointestinal bleeding. Angiodysplasia can be associated with von Willebrand disease (VWD), the most common bleeding disorder in man. VWD is caused by a defect or deficiency in von Willebrand factor (VWF), a glycoprotein essential for normal hemostasis that is involved in inflammation. We hypothesized that VWF regulates angiogenesis. Inhibition of VWF expression by short interfering RNA (siRNA) in endothelial cells (ECs) caused increased in vitro angiogenesis and increased vascular endothelial growth factor (VEGF) receptor-2 (VEGFR-2)-dependent proliferation and migration, coupled to decreased integrin αvβ3 levels and increased angiopoietin (Ang)-2 release. ECs expanded from blood-derived endothelial progenitor cells of VWD patients confirmed these results. Finally, 2 different approaches, in situ and in vivo, showed increased vascularization in VWF-deficient mice. We therefore identify a new function of VWF in ECs, which confirms VWF as a protein with multiple vascular roles and defines a novel link between hemostasis and angiogenesis. These results may have important consequences for the management of VWD, with potential therapeutic implications for vascular diseases.

Increased efficacy of breast cancer chemotherapy in thrombocytopenic mice

Platelets contribute to homeostasis of the tumor vasculature by helping prevent hemorrhage. Thus, we hypothesized that inducing thrombocytopenia would increase tumor vascular leakiness and facilitate the effective delivery of chemotherapeutic agents to tumors. In a mammary carcinoma murine model, platelet depletion induced bleeding specifically at the tumor site, favoring the accumulation of fluorescently labeled microspheres only in the tumor. Moreover, induction of thrombocytopenia in tumor-bearing mice before injection of paclitaxel increased its intratumoral accumulation and reduced growth of both slow- and fast-growing tumors, compared with mice with normal platelet counts that were treated only with paclitaxel. Histologic analysis confirmed the expectation of an increase in tumor apoptosis and a reduction in tumor proliferation in thrombocytopenic mice receiving chemotherapy. No increased toxicity was seen in other organs or blood cells. Taken together, our results indicate that low platelet count selectively induces leakiness of tumor vessels and favors the delivery of chemotherapy to tumor sites, enhancing its tumoricidal effects.

Dietary flavonoids as cancer prevention agents

Dietary agents identified from fruits and vegetables contribute to keeping balanced cell proliferation and preventing cell carcinogenesis. Dietary flavonoids, combined with other components such as various vitamins, play an important role in cancer prevention. Flavonoids act on reactive oxygen species, cell signal transduction pathways related to cellular proliferation, apoptosis, and angiogenesis. Many studies demonstrate that flavonoids are responsible for chemoprevention, although mechanisms of action remain to be investigated. Overall, exciting data show that dietary flavonoids could be considered as a useful cancer preventive approach. This review summarizes recent advancements on potential cancer preventive effects and mechanic insight of dietary flavonoids.

Zinc downregulates HIF-1α and inhibits its activity in tumor cells in vitro and in vivo

Background

Hypoxia inducible factor-1α (HIF-1α) is responsible for the majority of HIF-1-induced gene expression changes under hypoxia and for the “angiogenic switch” during tumor progression. HIF-1α is often upregulated in tumors leading to more aggressive tumor growth and chemoresistance, therefore representing an important target for antitumor intervention. We previously reported that zinc downregulated HIF-1α levels. Here, we evaluated the molecular mechanisms of zinc-induced HIF-1α downregulation and whether zinc affected HIF-1α also in vivo.

Methodology/Principal Findings

Here we report that zinc downregulated HIF-1α protein levels in human prostate cancer and glioblastoma cells under hypoxia, whether induced or constitutive. Investigations into the molecular mechanisms showed that zinc induced HIF-1α proteasomal degradation that was prevented by treatment with proteasomal inhibitor MG132. HIF-1α downregulation induced by zinc was ineffective in human RCC4 VHL-null renal carcinoma cell line; likewise, the HIF-1αP402/P564A mutant was resistant to zinc treatment. Similarly to HIF-1α, zinc downregulated also hypoxia-induced HIF-2α whereas the HIF-1β subunit remained unchanged. Zinc inhibited HIF-1α recruitment onto VEGF promoter and the zinc-induced suppression of HIF-1-dependent activation of VEGF correlated with reduction of glioblastoma and prostate cancer cell invasiveness in vitro. Finally, zinc administration downregulated HIF-1α levels in vivo, by bioluminescence imaging, and suppressed intratumoral VEGF expression.

Conclusions/Significance

These findings, by demonstrating that zinc induces HIF-1α proteasomal degradation, indicate that zinc could be useful as an inhibitor of HIF-1α in human tumors to repress important pathways involved in tumor progression, such as those induced by VEGF, MDR1, and Bcl2 target genes, and hopefully potentiate the anticancer therapies.