Promises and pitfalls of anti-angiogenic therapy in clinical trials

Critical role of exosome, exosomal non-coding RNAs and non-coding RNAs in head and neck cancer angiogenesis

Head and neck cancer (HNC) refers to the epithelial malignancies of the upper aerodigestive tract. HNCs have a constant yet slow-growing rate with an unsatisfactory overall survival rate globally. The development of new blood vessels from existing blood conduits is regarded as angiogenesis, which is implicated in the growth, progression, and metastasis of cancer. Aberrant angiogenesis is a known contributor to human cancer progression. Representing a promising therapeutic target, the blockade of angiogenesis aids in the reduction of the tumor cells oxygen and nutrient supplies. Despite the promise, the association of existing anti-angiogenic approaches with severe side effects, elevated cancer regrowth rates, and limited survival advantages is incontrovertible. Exosomes appear to have an essential contribution to the support of vascular proliferation, the regulation of tumor growth, tumor invasion, and metastasis, as they are a key mediator of information transfer between cells. In the exocrine region, various types of noncoding RNAs (ncRNAs) identified to be enriched and stable and contribute to the occurrence and progression of cancer. Mounting evidence suggest that exosome-derived ncRNAs are implicated in tumor angiogenesis. In this review, the characteristics of angiogenesis, particularly in HNC, and the impact of ncRNAs on HNC angiogenesis will be outlined. Besides, we aim to provide an insight on the regulatory role of exosomes and exosome-derived ncRNAs in angiogenesis in different types of HNC.

A novel method of screening combinations of angiostatics identifies bevacizumab and temsirolimus as synergistic inhibitors of glioma-induced angiogenesis

Tumor angiogenesis is critical for the growth and progression of cancer. As such, angiostasis is a treatment modality for cancer with potential utility for multiple types of cancer and fewer side effects. However, clinical success of angiostatic monotherapies has been moderate, at best, causing angiostatic treatments to lose their early luster. Previous studies demonstrated compensatory mechanisms that drive tumor vascularization despite the use of angiostatic monotherapies, as well as the potential for combination angiostatic therapies to overcome these compensatory mechanisms. We screened clinically approved angiostatics to identify specific combinations that confer potent inhibition of tumor-induced angiogenesis. We used a novel modification of the ex ovo chick chorioallantoic membrane (CAM) model that combined confocal and automated analyses to quantify tumor angiogenesis induced by glioblastoma tumor onplants. This model is advantageous due to its low cost and moderate throughput capabilities, while maintaining complex in vivo cellular interactions that are difficult to replicate in vitro. After screening multiple combinations, we determined that glioblastoma-induced angiogenesis was significantly reduced using a combination of bevacizumab (Avastin®) and temsirolimus (Torisel®) at doses below those where neither monotherapy demonstrated activity. These preliminary results were verified extensively, with this combination therapy effective even at concentrations further reduced 10-fold with a CI value of 2.42E-5, demonstrating high levels of synergy. Thus, combining bevacizumab and temsirolimus has great potential to increase the efficacy of angiostatic therapy and lower required dosing for improved clinical success and reduced side effects in glioblastoma patients.

The pharmaceutical multi-activity of metallofullerenol invigorates cancer therapy

Currently, cancer continues to afflict humanity. The direct destruction and killing of tumor cells by surgery, radiation and chemotherapy gives rise to many side effects and compromised efficacy. Encouragingly, the rapid development of nanotechnology offers attractive opportunities to revolutionize the current situation of cancer therapy. Metallofullerenol Gd@C82(OH)22, in contrast to chemotherapeutics that directly kill tumor cells, demonstrates anti-tumor behavior with high efficiency and low toxicity by modulating the tumor microenvironment. Furthermore, Gd@C82(OH)22 has been recently reported to specifically target cancer stem cells. In this review, we give a concise introduction to the development of the fullerene family and then report the anti-tumor activity of Gd@C82(OH)22 based on its unique physicochemical characteristics, followed by a comprehensive summary of the anti-tumor biological mechanisms which target different components of the tumor microenvironment as well as the biodistribution and toxicity of Gd@C82(OH)22. Finally, we describe Gd@C82(OH)22 as a "particulate medicine" to highlight its distinctions from conventional "molecular medicine", with considerable emphasis on the advantages of nanomedicine. The in-depth investigation of Gd@C82(OH)22 undoubtedly provides a constructive reference for the development of other nanomedicines, especially in the fullerene family. The application of nanotechnology in the medical field definitely provides a promising and favorable future for improving the current status of cancer therapy.

Targeted Therapies in Veterinary Oncology

Advances in molecular biology have permitted a much more detailed understanding of cellular dysfunction at the molecular and genetic levels in cancer cells. This has resulted in the identification of novel targets for therapeutic intervention, including proteins that regulate signal transduction, gene expression, and protein turnover. In many instances, small molecules are used to disrupt the function of these targets, often through competitive inhibition of ATP binding or the prevention of necessary protein-protein interactions. More than 40 small molecule inhibitors are now approved to treat a variety of human cancers, substantially impacting patient outcomes.

Silencing Of Circular RNA-ZNF609 Ameliorates Vascular Endothelial Dysfunction

Vascular dysfunction is a hallmark of ischemic, cancer, and inflammatory diseases, contributing to disease progression. Circular RNAs (circRNAs) are endogenous non-coding RNAs, which have been reported to be abnormally expressed in many human diseases. In this study, we used retinal vasculature to determine the role of circular RNA in vascular dysfunction. We revealed that cZNF609 was significantly up-regulated upon high glucose and hypoxia stress in vivo and in vitro. cZNF609 silencing decreased retinal vessel loss and suppressed pathological angiogenesis in vivo. cZNF609 silencing increased endothelial cell migration and tube formation, and protected endothelial cell against oxidative stress and hypoxia stress in vitro. By contrast, transgenic overexpression of cZNF609 showed an opposite effects. cZNF609 acted as an endogenous miR-615-5p sponge to sequester and inhibit miR-615-5p activity, which led to increased MEF2A expression. MEF2A overexpression could rescue cZNF609 silencing-mediated effects on endothelial cell migration, tube formation, and apoptosis. Moreover, dysregulated cZNF609 expression was detected in the clinical samples of the patients with diabetes, hypertension, and coronary artery disease. Intervention of cZNF609 expression is promising therapy for vascular dysfunction.

Modulated cellular delivery of anti-VEGF siRNA (bevasiranib) by incorporating supramolecular assemblies of hydrophobically modified polyamidoamine dendrimer in stealth liposomes

A novel lipopolymer based system was designed and characterized for cellular delivery of anti-VEGF siRNA in SKBR-3 breast tumor cell line. Polyamidoamine (PAMAM) dendrimers of low generations (G1, G2 and G3) were incorporated into polyethylene glycol (PEG)-stabilized liposomes by following the consecutive steps: (a) synthesis of the cholesterol conjugates (40% molar ratio of cholesterol to primary amines of PAMAM), (b) incorporation of the conjugates in liposome by lipid mixing and (c) microencapsulation of the siRNA using the ethanol drop method. The cholesterol conjugates of PAMAM dendrimers (G1-Chol40%, G2-Chol40% and G3-Chol40%) formed self assembly with low CMC values (<11μg/ml). Not only did G2-Chol40% show the highest lipid mixing among the cholesterol conjugates, but also, had the lowest leakage of encapsulated carboxyfluorescein tracer. Various N(amine))/L(lipid)/P(phosphate) mole ratios were investigated for siRNA condensation by ethidium bromide dye exclusion assay. The optimum N/L/P ratio of 20:33:10 was chosen for microencapsulation of anti-VEGF siRNA by ethanol drop method, showing particle size of 130nm, zeta-potential of +4mV, siRNA loading efficiency and capacity of 96% and 13wt%, and high stability against heparin sulfate (extracellular matrix). TEM shows uniform and discrete oligo- or multi-lamellar vesicular structures. The liposome incorporating G2-Chol40% was successfully internalized into SKBR-3 cells mainly through clathrin-mediated endocytosis, which was able to escape from endosomes and showed a significantly higher sequence-specific inhibition of VEGF expression and cell growth than the respective G2-Chol40%/siRNA dendriplexes. Importantly, the cytotoxicity decreased with incorporation of G2-Chol40% in the liposomes.

Small molecule inhibitors in veterinary oncology practice

Recent advances in molecular biology have permitted the identification and characterization of specific abnormalities regarding cell signaling and function in cancer cells. Proteins that are found to be dysregulated in cancer cells can serve as relevant targets for therapeutic intervention. Although there are several approaches to block proteins that contribute to cellular dysfunction, the one most commonly used involves a class of therapeutics called small molecule inhibitors. Such inhibitors work by disrupting critical pathways/processes in cancer cells, thereby preventing their ability to grow and survive.

Investigational platelet-derived growth factor receptor kinase inhibitors in breast cancer therapy

INTRODUCTION

Aberrant regulation of platelet-derived growth factors (PDGFs) and their receptors (PDGFR) has been shown to be involved in many solid tumors, including breast cancer. PDGFR-α and PDGFR-β expressions were documented in breast cancer and are correlated with tumor aggressiveness and metastasis. Preclinical evidence further suggests tumor stimulatory roles of PDGFRs expressed by tumor stroma cells and indicates a deleterious effect of stromal PDGFRs on intratumoral drug uptake.

AREAS COVERED

This review summarizes the present understanding of PDGF signaling in breast cancer based on experimental studies and available clinical trials. It also provides a critical discussion of selected ongoing clinical trials in patients with breast cancer involving PDGFR inhibition with tyrosine kinase inhibitors, specifically in endocrine responsive breast cancer.

EXPERT OPINION

An increased molecular understanding of response and resistance mechanisms to endocrine therapy will be essential for therapeutic advances in PDGFR-directed cancer therapy. Future developments in the field will rely on clinical studies where prospective analyses of target expression in breast cancer cells and in the tumor stroma are included. More selective PDGFR inhibitors with reduced side effects will be crucial for combinatorial therapies. Development of sensitive diagnostics is of critical importance for patient selection and monitoring of therapeutic effects.

Kinase dysfunction and kinase inhibitors

With recent advances in molecular biology, abnormalities in cancer cells that contribute to dysregulation of cell survival and proliferation are being characterized with greater precision. Through this process, key abnormalities in cancer cells involving proteins that regulate signal transduction, migration, mitosis and other critical processes have been identified. Such abnormalities often involve a class of proteins called kinases that act to phosphorylate other proteins in the cell, resulting in activation of these proteins in the absence of appropriate stimulation/regulation. Given their role in tumour biology, substantial effort has been directed at blocking the function of these proteins. Several approaches have been used, including monoclonal antibodies and small molecule inhibitors. While antibodies are primarily directed at cell surface proteins, small molecule inhibitors, also known as kinase inhibitors, target proteins throughout the cell. A variety of kinase inhibitors have been approved for the treatment of human cancers. In some instances, these inhibitors have exhibited significant clinical efficacy, and it is likely that their biological activity will be further enhanced as combination regimens with standard treatment modalities are explored. The use of kinase inhibitors in dogs and cats is relatively recent, although two inhibitors, toceranib (Palladia; Pfizer Animal Health, Madison, NJ, USA) and masitinib (Kinavet; Catalent Pharma Solutions, Somerset, NJ, USA) have been approved by the Federal Drug Administration (USA) for use in dogs. This article reviews the biology of protein kinase dysfunction in human and animal cancers, and the application of specific kinase inhibitors to veterinary cancer patients.

Tyrosine kinase inhibitors (TKIs) in human and pet tumours with special reference to breast cancer: a comparative review

Tyrosine kinase receptors (TKRs) play a key role in tumour cell proliferation and survival since they are involved in endothelial cell activation leading to tumour neoangiogenesis. In particular, vascular endothelial growth factor receptors (VEGFRs), platelet-derived growth factor receptor (PDGFR), stem cell factor receptor (c-KitR), and colony-stimulating factor 1 (CSF-1) are overexpressed or constitutively activated in human and pet malignancies. A variety of small molecule inhibitors targeting specific tyrosine kinases (known as tyrosine kinase inhibitors or TKIs) have recently been approved, or are under investigation, for the treatment of human cancer. TKI application in animal cancer is however relatively recent. This review aims to illustrate the major aspects of tyrosine kinase dysfunctions, with special regard to human and animal cancer of the mammary gland, providing an update on the background of the anti-angiogenic and anti-neoplastic properties of TKIs in human and veterinary cancer.

Ocular angiogenesis: mechanisms and recent advances in therapy

Ocular angiogenesis, the formation of new blood vessels from the existing vascular tree, is an important cause for severe loss of vision. It can occur in a spectrum of ocular disorders such as age-related macular degeneration (AMD), diabetic retinopathy, retinal artery or vein occlusion, and retinopathy of prematurity (ROP). One of the underlying causes of vision loss in proliferative retinal diseases is the increased vascular permeability leading to retinal edema, vascular fragility resulting in hemorrhage, or fibrovascular proliferation with tractional and rhegmatogenous retinal detachment. Pro- and antiangiogenic factors regulate an "angiogenic switch," which when turned on, leads to the pathogenesis of the above ocular diseases. Although neovascularization tends to occur at a relatively late stage in the course of many ocular disorders, it is an attractive target for therapeutic intervention, since it represents a final common pathway in processes that are multifactorial in etiology and is the event that typically leads directly to visual loss. Identification of these angiogenesis regulators has enabled the development of novel therapeutic approaches. In this light, antibodies directed against common markers of neovasculature, expressed in different diseases, may open up a very general and widely applicable approach for diagnostic and therapeutic interventions. Local gene transfer, that is, the intraocular delivery of recombinant viruses carrying genes encoding angiostatic proteins and small interfering RNA (siRNA) against vascular endothelial growth factor (VEGF) and VEGF receptors, offers the possibility of targeted, sustained, and regulatable delivery of angiostatic proteins and other angiogenic regulators to the retina. Recent progress has enabled the planning of clinical trials of gene therapy for ocular neovascularization.

Potent angiogenesis inhibition by the particulate form of fullerene derivatives

Antiangiogenesis is an effective strategy for cancer treatment because uncontrolled tumor growth depends on tumor angiogenesis and sufficient blood supply. Great progress has been made in developing a "molecular" form of angiogenesis inhibitors; however, the narrow inhibition spectrum limits anticancer efficacy as those inhibitors that usually target a few or even a single angiogenic factor among many angiogenic factors might initially be effective but ultimately lead to the failure of the treatment due to the induction of expression of other angiogenic factors. In this work, we report that with a multiple hydroxyl groups functionalized surface, the Gd@C(82)(OH)(22) fullerenic nanoparticles (f-NPs) are capable of simultaneously downregulating more than 10 angiogenic factors in the mRNA level that is further confirmed at the protein level. After studying this antiangiogenesis activity of the f-NPs by cellular experiment, we further investigated its anticancer efficacy in vivo. A two-week treatment with the f-NPs decreased >40% tumor microvessels density and efficiently lowered the speed of blood supply to tumor tissues by approximately 40%. Efficacy of the treatment using f-NPs in nude mice was comparable to the clinic anticancer drug paclitaxel, while no pronounced side effects were found. These findings indicate that the f-NPs with multiple hydroxyl groups serve as a potent antiangiogenesis inhibitor that can simultaneously target multiple angiogenic factors. We propose that using nanoscale "particulate" itself as a new form of medicine (particulate medicine) may be superior to the traditional "molecular" form of medicine (molecular medicine) in cancer treatment.

Antiangiogenics and radiotherapy

Antiangiogenic therapies are one of the fore-runners of the new generation of anticancer drugs aimed at tumour-specific molecular targets. Up until the beginning of this century, the general opinion was that targeted agents should show antitumour activity when used as single agents. However, it has now become clear that much greater improvements in therapeutic activity may be achieved by combining the novel agents with conventional cytotoxic therapies already in use in the clinic. Radiotherapy is currently used to treat half of all cancer patients at some stage in their therapy, although the development of radioresistance is an ongoing problem. It is therefore reasonable to expect that any novel molecularly-targeted agent which reaches the clinic will be used in combination with radiotherapy. The rationale for combining antiangiogenics in particular with radiotherapy exists, as radiotherapy has been shown to kill proliferating endothelial cells, suggesting that inhibiting angiogenesis may sensitise endothelial cells to the effects of radiation. Furthermore, targeting the vasculature may paradoxically increase oxygenation within tumours, thereby enhancing radiotherapy efficacy. In this review we present an update on the use of antiangiogenic methods in combination with radiotherapy.

Tyrosine kinase inhibitors in veterinary medicine

Substantial progress in the field of molecular biology has permitted the identification of key abnormalities in cancer cells involving cell proteins that regulate signal transduction, cell survival, and cell proliferation. Such abnormalities often involve a class of proteins called tyrosine kinases that act to phosphorylate other proteins in the cell, tightly regulating a variety of cellular processes. A variety of small molecule inhibitors that target specific tyrosine kinases (known as tyrosine kinase inhibitors [TKIs]) have now been approved for the treatment of human cancer, and it is likely many more will become available in the near future. In some instances these inhibitors have exhibited significant clinical efficacy, and it is likely their biologic activity will be further enhanced as combination regimens with standard treatment modalities are explored. Although TKIs have been used extensively in humans, their application to cancers in dogs and cats is relatively recent. The TKIs Palladia (toceranib), Kinavet (masitinib), and Gleevec (imatinib) have been successfully used in dogs, and more recently Gleevec in cats. This article will review the biology of tyrosine kinase dysfunction in human and animal cancers, and the application of specific TKIs to veterinary cancer patients.

Blood vessel maturation in human uveal melanoma: spatial distribution of neovessels and mature vasculature

PURPOSE

The aims of this study are (1) to evaluate the spatial distribution of neovessels and mature vessels in human uveal melanoma tumors and (2) to determine whether vessel maturation is associated with the major indicators for poor prognosis.

METHODS

Immunohistochemical analyses were performed on human tissue specimens from enucleated eyes (n = 14) to assess total vessels, neovessels, mature vessels, and cell proliferation. Tumor morphology was analyzed by hematoxylin and eosin and modified periodic acid-Schiff (PAS) staining.The spatial distribution of neovessels and mature vessels was analyzed by immunohistochemistry, and correlated with major indicators of poor prognosis (i.e., aggressive PAS patterns, epithelioid cytology, mitotic figures, extraocular extension, anterior tumor location, ciliary body involvement, large tumor size, cell proliferation, and angiogenic activity).

RESULTS

Neovesseldensity was greater than mature vessel density in apical (p = 0.17), central (p = 0.036), and peripheral (p = 0.31) regions of the tumors, while mature vessel density was greater than neovessel density in basal areas of the tumor (p = 0.47). This pattern indicated that vessel maturation begins at the base of the tumor and later extends to the peripheral and apical regions. The difference between mature and neovessel densities for the apical (-0.8 +/- 1.9) and central areas (-0.8 +/- 1.3) of the tumor was significantly higher than the difference obtained for the basal area (0.3 +/- 1.6; p = 0.014 and p = 0.012, respectively), indicating a higher density of mature vessels compared to neovessels at the base. Statistical correlations were found between mature vessel density and tumor size (r = 0.48, p = 0.084), cell proliferation (r = 0.62, p = 0.042), and mitotic figures (r = 0.76, p = 0.001).

CONCLUSIONS

Significant differences exist in the spatial distribution of mature versus neovessels in human uveal melanoma. Vessel maturation is associated with known clinical and pathologic indicators of poor prognosis (e.g., cell proliferation). Antiangiogenic therapy should be considered for the treatment of ocular malignancies; however, the results of this study indicate that blood vessel maturation heterogeneity may limit the efficacy of vessel targeting agents.

Incorporation of endothelial progenitor cells into the neovasculature of malignant glioma xenograft

Endothelial progenitor cells (EPCs) are important initiators of vasculogenesis in the process of tumor neovascularization. However, it is unclear how circulating EPCs contribute to the formation of tumor microvessels. In this study, we isolated CD34(+)/CD133(+) cells from human umbilical cord blood (HUCB) and obtained EPCs with the capacities of forming colonies, uptaking acetylated low-density lipoprotein (ac-LDL), binding lectins and expressing vascular endothelial growth factor (VEGF) receptor 2 (VEGFR-2, KDR), CD31 and von Willebrand factor (vWF). These EPCs were actively proliferative and migratory, and could formed capillary-like tubules in response to VEGF. When injected into mice bearing subcutaneously implanted human malignant glioma, EPCs specifically accumulated at the sites of tumors and differentiated into mature endothelial cells (ECs), which accounted for 18% ECs of the tumor microvessels. The incorporation of circulating EPCs into tumor vessel walls significantly affected the morphology and structure of the vasculature. Our results suggest that circulating EPCs constitute important components of tumor microvessel network and contribute to tumor microvascular architecture phenotype heterogeneity.

Sorafenib in lung cancer: clinical developments and future directions

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related death in the United States. Angiogenesis, primarily mediated through vascular endothelial growth factor (VEGF), is one of the key steps in tumor growth and metastasis. VEGF is now a validated target for NSCLC based on the results of the Eastern Cooperative Oncology Group trial E4599 which showed that the addition of bevacizumab, a VEGF monoclonal antibody, to cytotoxic chemotherapy improves survival compared with chemotherapy alone in patients with metastatic NSCLC. As NSCLC has complex and integrated signaling pathways, a rational approach is to target more than one of these pathways concurrently. Sorafenib, which is approved for the treatment of renal cell carcinoma, is a multitargeted signal transduction inhibitor that inhibits raf-kinases, VEGF receptor-2, platelet derived growth factor receptor-B, and c-kit. In a phase II monotherapy trial in patients with previously treated NSCLC, sorafenib demonstrated activity with a disease control rate and survival rate comparable to other small molecules. Additionally, sorafenib has shown preliminary activity in combination with chemotherapy and with epidermal growth factor receptor inhibitors. Future directions will include the development of rational combinations either with cytotoxic compounds or biologically targeted compounds and the identification of subsets of patients that might benefit from the other targets of sorafenib.

Differential effects of black raspberry and strawberry extracts on BaPDE-induced activation of transcription factors and their target genes

The chemopreventive properties of edible berries have been demonstrated both in vitro and in vivo, however, the specific molecular mechanisms underlying their anti-cancer effects are largely unknown. Our previous studies have shown that a methanol extract fraction of freeze-dried black raspberries inhibits benzoapyrene (BaP)-induced transformation of Syrian hamster embryo cells. This fraction also blocks activation of activator protein-1 (AP-1) and nuclear factor kappaB (NF-kappaB) induced by benzoapyrene diol-epoxide (BaPDE) in mouse epidermal JB6 Cl 41 cells. To determine if different berry types exhibit specific mechanisms for their anti-cancer effects, we compared the effects of extract fractions from both black raspberries and strawberries on BaPDE-induced activation of various signaling pathways in Cl 41 cells. Black raspberry fractions inhibited the activation of AP-1, NF-kappaB, and nuclear factor of activated T cells (NFAT) by BaPDE as well as their upstream PI-3K/Akt-p70(S6K) and mitogen-activated protein kinase pathways. In contrast, strawberry fractions inhibited NFAT activation, but did not inhibit the activation of AP-1, NF-kappaB or the PI-3K/Akt-p70(S6K) and mitogen-activated protein kinase pathways. Consistent with the effects on NFAT activation, tumor necrosis factor-alpha (TNF-alpha) induction by BaPDE was blocked by extract fractions of both black raspberries and strawberries, whereas vascular endothelial growth factor (VEGF) expression, which depends on AP-1 activation, was suppressed by black raspberry fractions but not strawberry fractions. These results suggest that black raspberry and strawberry components may target different signaling pathways in exerting their anti-carcinogenic effects.

The role of small molecule inhibitors for veterinary patients

Advances in molecular biology over the past several years have permitted a much more detailed understanding of cellular dysfunction at the biochemical level in cancer cells. This has resulted in the identification of novel targets for therapeutic intervention, including proteins that regulate signal transduction, gene expression, and protein turnover. In many instances, small molecules are used to disrupt the function of these targets, often through competitive inhibition of ATP binding or the prevention of necessary protein-protein interactions. Future challenges lie in identifying appropriate targets for intervention and combining small molecule inhibitors with standard treatment modalities, such as radiation therapy and chemotherapy.

Alpha-v integrins as therapeutic targets in oncology

Integrins are heterodimeric cell adhesion receptors that mediate intercellular communication through cell-extracellular matrix interactions and cell-cell interactions. Integrins have been demonstrated to play a direct role in cancer progression, specifically in tumor cell survival, tumor angiogenesis, and metastasis. Therefore, agents targeted against integrin function have potential as effective anticancer therapies. Numerous anti-integrin agents, including monoclonal antibodies and small-molecule inhibitors, are in clinical development for the treatment of solid and hematologic tumors. This review focuses on the role of alpha(v) integrins in cancer progression, the current status of integrin-targeted agents in development, and strategies for the clinical development of anti-integrin therapies.

Molecular imaging of VEGF receptors in angiogenic vasculature with single-chain VEGF-based probes

We describe a new generation of protein-targeted contrast agents for multimodal imaging of the cell-surface receptors for vascular endothelial growth factor (VEGF). These receptors have a key role in angiogenesis and are important targets for drug development. Our probes are based on a single-chain recombinant VEGF expressed with a cysteine-containing tag that allows site-specific labeling with contrast agents for near-infrared fluorescence imaging, single-photon emission computed tomography or positron emission tomography. These probes retain VEGF activities in vitro and undergo selective and highly specific focal uptake into the vasculature of tumors and surrounding host tissue in vivo. The fluorescence contrast agent shows long-term persistence and co-localizes with endothelial cell markers, indicating that internalization is mediated by the receptors. We expect that multimodal imaging of VEGF receptors with these probes will be useful for clinical diagnosis and therapeutic monitoring, and will help to accelerate the development of new angiogenesis-directed drugs and treatments.

Combination angiostatic therapy completely inhibits ocular and tumor angiogenesis

Angiostatic therapies designed to inhibit neovascularization associated with multiple pathological conditions have only been partially successful; complete inhibition has not been achieved. We demonstrate synergistic effects of combining angiostatic molecules that target distinct aspects of the angiogenic process, resulting in the complete inhibition of neovascular growth associated with development, ischemic retinopathy, and tumor growth, with little or no effect on normal, mature tissue vasculature. Tumor vascular obliteration using combination angiostatic therapy was associated with reduced tumor mass and increased survival in a rat 9L gliosarcoma model, whereas individual monotherapies were ineffective. Significant compensatory up-regulation of several proangiogenic factors was observed after treatment with a single angiostatic agent. In contrast, treatment with combination angiostatic therapy significantly reduced compensatory up-regulation. Therapies that combine angiostatic molecules targeting multiple, distinct aspects of the angiogenic process may represent a previously uncharacterized paradigm for the treatment of many devastating diseases with associated pathological neovascularization.

Angiogenesis and antiangiogenic therapy in hematologic malignancies

Angiogenesis, the generation of new blood capillaries from preexisting blood vessels, is tightly regulated in the adult organism. Although many of the initial studies were performed on solid tumors, increasing evidence indicates that angiogenesis also plays an important role in hematologic malignancies. Overexpression of angiogenic factors in particular VEGF and bFGF in most hematologic malignancies may explain the increased angiogenesis found in these malignancies and correlate with poor prognosis as well as decreased overall survival. In this review, we focus on the current literature of angiogenesis and antiangiogenic therapy in hematologic malignancies, and finally describe advances and potential challenges in antiangiogenic treatment in hematologic malignancies.

Anti-angiogenic drugs: from bench to clinical trials

Angiogenesis, the generation of new capillaries through a process of pre-existing microvessel sprouting, is under stringent control and normally occurs only during embryonic and post-embryonic development, reproductive cycle, and wound repair. However, in many pathological conditions (solid tumor progression, metastasis, diabetic retinopathy, hemangioma, arthritis, psoriasis and atherosclerosis among others), the disease appears to be associated with persistent upregulated angiogenesis. The development of specific anti-angiogenic agents arises as an attractive therapeutic approach for the treatment of cancer and other angiogenesis-dependent diseases. The formation of new blood vessels is a complex multi-step process. Endothelial cells resting in the parent vessels are activated by an angiogenic signal and stimulated to synthesize and release degradative enzymes allowing endothelial cells to migrate, proliferate and finally differentiate to give rise to capillary tubules. Any of these steps may be a potential target for pharmacological intervention. In spite of the disappointing results obtained initially in clinical trials with anti-angiogenic drugs, recent reports with positive results in phases II and III trials encourage expectations in their therapeutic potential. This review discusses the current approaches for the discovery of new compounds that inhibit angiogenesis, with emphasis on the clinical developmental status of anti-angiogenic drugs.

Anti-angiogenic therapy: Prospects for treatment of ocular tumors

The growth of new blood vessels (angiogenesis) within tumors is essential for tumor growth, maintenance, and metastasis. Angiogenesis research has identified a host of pro- and anti-angiogenic factors that regulate an "angiogenic switch," which when turned on, allows tumors to assume a more aggressive form. Angiogensis inhibitors that target this switch are in clinical trials for a wide array of tumor types. Although angiogenesis inhibitors are already widely used to treat ocular disease, only limited case reports are currently available for the use of angiogenesis inhibitors to treat ocular tumors. Evidence for angiogenesis in the growth and spread of uveal melanoma, retinoblastoma, and von Hippel Lindau (VHL) disease exists. The very limited trials of angiogenesis inhibitors in the treatment of uveal melanoma and VHL are promising, although more extensive controlled trials will be needed to confirm their efficacy.

Angiogenic Profile of Soft Tissue Sarcomas Based on Analysis of Circulating Factors and Microarray Gene Expression

BACKGROUND

Broader understanding of diverse angiogenic pathways in a particular cancer can lead to better utilization of anti-angiogenic therapies. The aim of this study was to develop profiles of angiogenesis-related gene and protein expression for various histologic subtypes of soft tissue sarcomas (STS) growing in different sites.

MATERIALS AND METHODS

Plasma levels of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), angiopoietin 2 (Ang2), and leptin were determined in 108 patients with primary STS. Gene expression patterns were analyzed in 38 STS samples and 13 normal tissues using oligonucleotide microarrays.

RESULTS

VEGF and bFGF plasma levels were elevated 10-13 fold in STS patients compared to controls. VEGF levels were broadly elevated while bFGF levels were higher in patients with fibrosarcomas and leiomyosarcomas. Ang2 levels correlated with tumor size and were most elevated for tumors located in the trunk, while leptin levels were highest in patients with liposarcomas. Hierarchical clustering of microarray data based on angiogenesis-related gene expression demonstrated that histologic subtypes of STS often shared similar expression patterns, and these patterns were distinctly different from those of normal tissues. Matrix metalloproteinase 2, platelet-derived growth factor receptor, alpha and Notch 4 were among several genes that were up-regulated at least 7-fold in STS.

CONCLUSIONS

STS demonstrate significant heterogeneity in their angiogenic profiles based on size, histologic subtype, and location of tumor growth, which may have implications for anti-angiogenic strategies. Comparison of STS to normal tissues reveals a panel of upregulated genes that may be targets for future therapies.

Intra-arterial adenoviral mediated tumor transfection in a novel model of cancer gene therapy

Background

The aim of the present study was to develop and characterize a novel in vivo cancer gene therapy model in which intra-arterial adenoviral gene delivery can be characterized. In this model, the rat cremaster muscle serves as the site for tumor growth and provides convenient and isolated access to the tumor parenchyma with discrete control of arterial and venous access for delivery of agents.

Results

Utilizing adenovirus encoding the green fluorescent protein we demonstrated broad tumor transfection. We also observed a dose dependant increment in luciferase activity at the tumor site using an adenovirus encoding the luciferase reporter gene. Finally, we tested the intra-arterial adenovirus dwelling time required to achieve optimal tumor transfection and observed a minimum time of 30 minutes.

Conclusion

We conclude that adenovirus mediated tumor transfection grown in the cremaster muscle of athymic nude rats via an intra-arterial route could be achieved. This model allows definition of the variables that affect intra-arterial tumor transfection. This particular study suggests that allowing a defined intra-tumor dwelling time by controlling the blood flow of the affected organ during vector infusion can optimize intra-arterial adenoviral delivery.

Reversal of temporal and spatial heterogeneities in tumor perfusion identifies the tumor vascular tone as a tunable variable to improve drug delivery

Maturation of tumor vasculature involves the recruitment of pericytes that protect the endothelial tubes from a variety of stresses, including antiangiogenic drugs. Mural cells also provide mature tumor blood vessels with the ability to either relax or contract in response to substances present in the tumor microenvironment. The observed cyclic alterations in tumor blood flow and the associated deficit in chemotherapeutic drug delivery could in part arise from this vasomodulatory influence. To test this hypothesis, we focused on endothelin-1 (ET-1), which, besides its autocrine effects on tumor cell growth, is a powerful vasoconstrictor. We first document that an ET(A) receptor antagonist induced relaxation of microdissected tumor arterioles and selectively and quantitatively increased tumor blood flow in experimental tumor models. We then combined dye staining of functional vessels, fluorescent microsphere-based mapping, and magnetic resonance imaging to identify heterogeneities in tumor blood flow and to examine the reversibility of such phenomena. Data from all these techniques concurred to show that administration of an ET(A) receptor antagonist could reduce the extent of underperfused tumor areas, proving the key role of vessel tone variations in tumor blood flow heterogeneity. We also provide evidence that ET(A) antagonist administration could, despite an increase in tumor interstitial fluid pressure, improve access of cyclophosphamide to the tumor compartment and significantly influence tumor growth. In conclusion, tumor endogenous ET-1 production participates largely in the temporal and spatial variations in tumor blood flow. ET(A) antagonist administration may wipe out such heterogeneities, thus representing an adjuvant strategy that could improve the delivery of conventional chemotherapy to tumors.

Imaging of VEGF receptor kinase inhibitor-induced antiangiogenic effects in drug-resistant human adenocarcinoma model

Small molecule vascular endothelial growth factor (VEGF) receptor tyrosinase kinase inhibitors (VEGFR-TKIs) show great promise in inducing antiangiogenic responses in tumors. We investigated whether antiangiogenic tumor responses induced by an experimental VEGFR-TKI (AG013925; Pfizer Global Research and Development) could be reported by magnetic resonance imaging (MRI) during the initial phase of treatment. We used MRI and superparamagnetic nanoparticles for measuring relative vascular volume fraction (rVVF) in a drug-resistant colon carcinoma model. Athymic mice harboring MV522 xenografts were treated with VEGFR-TKI (25 mg/kg, p.o., with a 12-hour interval in between treatments) and were imaged after three consecutive treatments. Relative tumor blood volume fractions were calculated using deltaR2* maps that were scaled by the known VVF value of an in-plane skeletal muscle (1.9%). There was a pronounced and statistically significant (P < .001) decrease of tumor rVVF in treated animals (0.95 +/- 0.24%; mean +/- SEM, n = 66 slices, eight mice) compared to mice that received a placebo (2.91 +/- 0.24%; mean +/- SEM, n = 66 slices, nine mice). Tumor histology confirmed a three-fold decrease of vascular density and a concomitant increase of apoptotic cell index. Hence, we demonstrated that: 1) the VEGFR-TKI resulted in antiangiogenic effects that were manifested by a decrease or rVVF; and 2) iron oxide nanoparticles and steady-state MRI enable an early detection of tumor response to antiangiogenic therapies.

VEGF as a predictive marker of rectal tumor response to preoperative radiotherapy

BACKGROUND

Neoadjuvant radiotherapy for rectal cancer may result in tumor downstaging or complete tumor regression leading to greater sphincter preservation. The identification of molecular predictive markers of tumor response to preoperative radiotherapy would provide an additional tool for selecting patients most likely to benefit from treatment. The aim of this study was to determine whether VEGF expression in preirradiation tumor biopsies is a useful predictive marker of tumor response in patients with rectal cancer undergoing preoperative radiotherapy.

METHODS

Immunohistochemistry for VEGF was performed on 59 preirradiation biopsies from patients with completely responsive (ypT0) or nonresponsive tumors after preoperative radiotherapy. VEGF positivity was evaluated using several scoring methods and the association between VEGF and tumor response was compared. The distribution of VEGF scores was obtained as well as the mean VEGF expression in the two response groups.

RESULTS

The mean VEGF expression in nonresponsive tumors (NR) was significantly greater than in completely responsive tumors (CR) (P = 0.0035). Nearly half (47%) of all CR tumors had a VEGF expression of 10% or less. Eleven tumors were negative (0% immunoreactivity) for the protein and all of these (100%) were complete responders. Fifty-two percent of the NR tumors had VEGF scores of 80% or greater. The four scoring methods used to determine the association between VEGF and tumor response each produced significant results (P < 0.05).

CONCLUSIONS

The results of this study indicate that VEGF assessed immunohistochemically from preirradiation tumor biopsies may be a useful marker of rectal tumor response to preoperative radiotherapy.

Anti-angiogenic treatment of gastrointestinal malignancies

The scientific rationale to block angiogenesis as a treatment strategy for human cancer has been developed over the last 30 years, but is only now entering the clinical arena. Preclinical studies have demonstrated the importance of the vascular endothelial growth factor (VEGF) pathways in both physiologic and pathologic angiogenesis, and have led to the development of approaches to block its role in tumor angiogenesis. Bevacizumab is an antibody to VEGF and has been shown to prolong survival when given with chemotherapy in the treatment of metastatic colorectal cancer (CRC). Although this is the first anti-angiogenic treatment to be approved for the treatment of human epithelial malignancy, a number of other approaches currently are in development. Soluble chimeric receptors to sequester serum VEGF and monoclonal antibodies against VEGF receptors have both shown considerable promise in the laboratory and are being brought into clinical investigation. A number of small-molecule tyrosine kinase inhibitors that have activity against VEGF receptors also are in clinical trials. Although these novel treatments are being pioneered in CRC, anti-angiogenic approaches also are being tested in the treatment of other gastrointestinal malignancies. Anti-VEGF therapy has shown promise in such traditionally resistant tumors as pancreatic cancer and hepatocellular carcinoma. This review will examine the preclinical foundation and then focus on the clinical studies of anti-VEGF therapy in gastrointestinal cancers.

Angiogenesis in gliomas: imaging and experimental therapeutics

Much of the interest in angiogenesis and hypoxia has led to investigating diagnostic imaging methodologies and developing efficacious agents against angiogenesis in gliomas. In many ways, because of the cytostatic effects of these agents on tumor growth and tumor-associated endothelial cells, the effects of therapy are not immediately evident. Hence finding clinically applicable imaging tools and pathologic surrogate markers is an important step in translating glioma biology to therapeutics. There are a variety of strategies in the approach to experimental therapeutics that target the hypoxia-inducible factor pathway, the endogenous antiangiogenic and proangiogenic factors and their receptors, adhesion molecules, matrix proteases and cytokines, and the existing vasculature. We discuss the rationale for antiangiogenesis as a treatment strategy, the preclinical and clinical assessment of antiangiogenic interventions and finally focus on the various treatment strategies, including combining antiangiogenic drugs with radiation and chemotherapy.

Delivery of antiangiogenic agents for cancer gene therapy

The understanding that tumor growth and metastasis are angiogenesis dependent processes has led to interest in targeting tumor vasculature in anticancer therapy. Furthermore, recent insights into the molecular interactions that orchestrate physiologic and pathologic angiogenesis have resulted in a variety of antiangiogenic strategies. A gene therapy-mediated approach for the delivery of antiangiogenic agents has several advantages, including the potential for sustained expression. However, the choice of angiogenesis inhibitor, method of gene delivery, and target/site for transgene expression are important variables to be considered when designing this approach. Here we review the major alternatives within each of these categories and provide illustrative examples of their use in preclinical models.

Functional CT for Quantifying Tumor Perfusion in Antiangiogenic Therapy in a Rat Model

PURPOSE

To determine the histologic basis of perfusion parameters measured at functional computed tomography (CT) and to examine the relationship between changes in perfusion and changes in histologic parameters after antiangiogenic therapy in a rat model.

MATERIALS AND METHODS

This study had institutional animal care and use committee approval. Among 20 Fischer rats with implanted FN13762 tumors in the liver, 10 were treated with SU5416, a tyrosine kinase inhibitor of vascular endothelial growth factor receptor, and 10 were treated with the diluent only as control rats. Six rats chosen at random from each group underwent functional CT for the measurement of tumor blood flow, blood volume, mean transit time, and permeability-surface area product. Tumor tissue slides corresponding to functional CT sections were examined to measure tumor microvascular density, number of luminal vessels, vascular perimeter, and vascular area. Two-tailed Student t testing was used to determine differences in growth, numbers of metastases to major organs, vascularity, and perfusion between SU5416-treated and control tumors. Pearson correlation coefficients were used to investigate relationships between vascular parameters.

RESULTS

Mean tumor volume and number of metastases, respectively, were lower in SU5416-treated rats than in control rats (1580 mm3 +/- 830 [standard deviation] vs 2330 mm3 +/- 960 and 22.4 +/- 11.0 vs 35.2 +/- 17.3); however, these differences were not significant (P = .084 and P = .079). Mean tumor microvascular density was significantly lower in SU5416-treated rats than in control rats (6.4 vessels per field +/- 4.6 vs 17.2 vessels per field +/- 7.5, P < .001); however, vessel perimeter and vessel area, respectively, were significantly larger in treated rats than in control rats (470 microm per field +/- 320 vs 360 microm per field +/- 270, P = .02; and 4010 microm2 per field +/- 2990 vs 2230 microm2 per field +/- 1750, P = .001). Significant correlations were observed between microvascular density and vessel perimeter and area (r = 0.59 and r = 0.25, respectively; P < .01 for both) in SU5416-treated tumors but not control tumors. Blood flow, blood volume, and permeability-surface area product at functional CT were significantly higher in SU5416-treated tumors than in control tumors (P < .001 for all).

CONCLUSION

These results validate the idea that functional CT can help quantify the perfusion function of mature vessels but not changes in microvessel density in antiangiogenic therapy.

Metronomic low-dose chemotherapy as antiangiogenic therapeutic strategy for cancer. Metronomische niedrig-dosierte Chemotherapie als antiangiogene Therapiestrategie fur Tumorerkrankungen

New blood vessel formation is essential for the growth and metastasis of many cancers. As a result, antitumor activities of various angiogenesis inhibitors have been intensely explored in various tumors. Recent preclinical studies suggest that certain conventional cytotoxic agents can function as antiangiogenic drugs when administered at comparatively low doses on a continuous or very frequent schedule. Such antiangiogenic 'metronomic' scheduling of chemotherapy without extended rest periods has been shown to exert significant therapeutic antitumor efficacy with very limited toxicity in different tumor models. Combining metronomic low-dose chemotherapy regimens with specific angiogenesis inhibitors further increases efficacy. Based on the promising preclinical studies, it is anticipated that metronomic chemotherapy in combination with angiogenesis inhibitors will prove effective in clinical trials in terms of survival prolongation. While considerable progress may derive from larger randomized clinical studies, only joint efforts between basic and clinical research will ultimately advance the new paradigm of long-term metronomic antiangiogenic chemotherapy, which carries the prospect of turning cancer into a more controllable chronic disease at minimal toxicity.

Angiogenesis in colorectal cancer: therapeutic implications and future directions

This article discusses the therapeutic implications and future directions of angiogenesis in colorectal cancer.

Expression of angiogenic factors vascular endothelial growth factor and interleukin-8/CXCL8 is highly responsive to ambient glutamine availability: role of nuclear factor-kappaB and activating protein-1

Vascular endothelial growth factor (VEGF) and interleukin-8/CXCL8 (IL-8) are prominent pro-angiogenic and pro-metastatic proteins that represent negative prognostic factors in many types of cancer. Hypoxia is thought to be the primary environmental cause of VEGF and IL-8 expression in solid tumors. We hypothesized that a lack of nutrients other than oxygen could stimulate the expression of these factors and previously demonstrated that expression of VEGF and IL-8 is responsive to amino acid deprivation. In the present study, we examined the effect of glutamine availability on the expression of these factors as well as the role of transcription factors NFkappaB and activating protein-1 (AP-1) in the response of TSE human breast carcinoma cells to glutamine deprivation. VEGF and IL-8 secretion and mRNA levels were dramatically induced by glutamine deprivation. mRNA stabilization contributed to this response. Glutamine deprivation increased NFkappaB (p65/p50) and AP-1 (Fra-1/c-Jun+JunD) DNA-binding activities. Blocking NFkappaB and AP-1 activation with curcumin as well as expression of dominant inhibitors, inhibitor of nuclear factor-kappaB (IkappaB) super repressor (IkappaBM), and a mutant form of c-Fos (A-Fos) demonstrated that the activation of NFkappaB and AP-1 transcription factors was necessary for the induction of IL-8 expression but dispensable for the induction of VEGF expression. A macro-array containing 111 NFkappaB target genes identified a total of 17 that were up-regulated 2-fold or more in response to glutamine deprivation. These included growth regulated oncogene alpha (GROalpha/GRO1/CXCL1), another neutrophil chemoattractant implicated in tumor angiogenesis and metastasis.