VEGFs, receptors and angiogenesis

Kaposi's sarcoma-associated herpesvirus-encoded interleukin-6

Since the discovery of the virus in 1994, the rapid pace with which Karposi's sarcoma-associated herpesvirus (KSHV) research has progressed has quickly led to a broad understanding of the structure of the virus and its biology and pathology in humans. Molecular piracy of potentially useful cellular genes has emerged as a characteristic feature of this virus. The viral homolog of human IL-6, vIL-6 is an example in kind. Studies in vitro and in vivo have shown that vIL-6 can stimulate the growth of KSHV-infected primary infusion lymphoma (PEL) cells, can promote hematopoiesis, and act as an angiogenic factor through the induction of vascular endothelial growth factor (VEGF). It is not difficult to envision how vIL-6, through these properties and perhaps others yet to be identified, can contribute to KSHV survival and spread in the human population.

Current status of viral gene therapy for brain tumours

Malignant glial tumours represent the majority of primary brain tumours. Despite the use of many adjunctive treatment strategies in addition to surgery, the prospect of cure or even long-term survival is poor. In the last decade, there has been an explosion of interest in the development of delivery systems that will allow the expression of exogenous genes in the CNS. For the most part, these systems are based upon modified viruses. To date, the greatest experience has been with retroviruses, herpes simplex virus 1 (HSV), adenovirus and adeno-associated virus (AAV). This review will outline the biology of these viral vectors, modifications permitting in vivo administration and their respective advantages and disadvantages for the treatment of malignant brain tumours. The present obstacles to gene therapy strategies will also be described. To date, no convincing clinical trial has emerged that provides objective proof of the superiority of gene therapy strategies as compared to conventional treatment.

VEGFc and VEGFR3 expression in human thyroid pathologies

In vertebrates, vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) are major determinants of angiogenesis. In adults, the interaction between VEGFc and VEGFR3 (previously FLT4) is more specifically involved in the biology of lymphatics. Using PCR amplification of reverse-transcribed mRNA, we studied the expression of the VEGFR3 (including its short and long forms) and VEGFc genes in 38 samples of various human thyroid pathologies. VEGFR3 mRNA was detected in all samples of adenomas, nodular goiters and focal goitrogenic alterations; in all samples of thyroid tissue from patients with auto-immune diseases; and in some samples of adenocarcinomas. VEGFc mRNA was detected in most samples. We studied expression of the VEGFR3 and VEGFc proteins in thyroid tumors using appropriate antibodies. Co-expression of VEGFR3 and VEGFc was observed in most samples.

Angiogenesis in embryonic development--a review

Recent studies, particularly of genetically altered mice, have greatly improved our understanding of the molecular basis underlying the development of the vascular system. Endothelial signalling systems, such as the vascular endothelial growth factor (VEGF)/VEGF receptor system and the angiopoietin/Tie2 system, were identified as central regulators of embryonic angiogenesis. The complex interactions between these and other endothelial signalling systems are beginning to emerge. Placenta (2000), 21, Supplement A, Trophoblast Research, 14, S11-S15.

Tumor angiogenesis: past, present and the near future

The concept of treating solid tumors by inhibiting tumor angiogenesis was first articulated almost 30 years ago. For the next 10 years it attracted little scientific interest. This situation changed, relatively slowly, over the succeeding decade with the discovery of the first pro-angiogenic molecules such as basic fibroblast growth factor and vascular endothelial growth factor (VEGF), and the development of methods of successfully growing vascular endothelial cells in culture as well as in vivo assays of angiogenesis. However, the 1990s have witnessed a striking change in both attitude and interest in tumor angiogenesis and anti-angiogenic drug development, to the point where a remarkably diverse group of over 24 such drugs is currently undergoing evaluation in phase I, II or III clinical trials. In this review I will discuss the many reasons for this. These features, together with other recent discoveries have created intense interest in initiating and expanding anti-angiogenic drug discovery programs in both academia and industry, and the testing of such newly developed drugs, either alone, or in various combinations with conventional cytotoxic therapeutics. However, significant problems remain in the clinical application of angiogenesis inhibitors such as the need for surrogate markers to monitor the effects of such drugs when they do not cause tumor regressions, and the design of clinical trials. Also of concern is that the expected need to use anti-angiogenic drugs chronically will lead to delayed toxic side effects in humans, which do not appear in rodents, especially in short-term studies.

Prognosis of breast-carcinoma lymphagenesis evaluated by immunohistochemical investigation of vascular-endothelial-growth-factor receptor 3

Very few studies have yet addressed the question of the existence and role of lymphagenesis in tumor growth; it is generally overshadowed by the greater emphasis placed on the blood vascular system. Monoclonal antibodies against vascular endothelial-growth-factor receptor 3 (VEGFR3) have been shown to provide a specific antigenic marker for lymphatic endothelium. By comparison with the microvascular count (MVC), we investigated the prognostic value of the microlymphatic count (MLC) in a series of 60 cases of 2-cm-diameter breast carcinomas. The mean value of MVC was 72.5 and of MLC, 40.5. There was no quantitative correlation between these 2 parameters. The MVC but not the MLC had a prognostic value in overall survival. Neither the MLC nor the MVC had any correlation with axillary-lymph-node invasion.

Current biology of VEGF-B and VEGF-C

Endothelial growth factors and their receptors may provide important therapeutic tools for the treatment of pathological conditions characterised by defective or aberrant angiogenesis. Vascular endothelial growth factor (VEGF) is pivotal for vasculogenesis and for angiogenesis in normal and pathological conditions. VEGF-B and VEGF-C provide this gene family with additional functions, for example, VEGF-C also regulates lymphangiogenesis.

Signaling via vascular endothelial growth factor receptors

Angiogenesis, or development of blood vessels from preexisting vasculature, has important functions under both normal and pathophysiological conditions. Vascular endothelial growth factor receptors 1-3, also known as flt-1, KDR, and flt-4, are endothelial cell-specific receptor tyrosine kinases which serve as key mediators of the angiogenic responses. The review focuses on the signaling pathways that are initiated from these receptors and the recently identified VEGF coreceptor neuroplilin-1.

Pharmacological peroxisome proliferator-activated receptorgamma ligands: emerging clinical indications beyond diabetes

The discovery of peroxisome proliferator-activated receptor gamma (PPARgamma) as the molecular target for antidiabetic thiazolidinediones has heralded a new era in the approach to understanding the pathophysiology of insulin resistance and its relationship to cardiovascular disease. However, the subsequent discovery of PPARgamma-dependent modulation of immune function and the cell cycle has led to a new paradigm in the approach to treating proliferative, inflammatory diseases. Moreover, PPARgamma agonists can promote apoptosis, block angiogenesis and inhibit pathological remodelling in a variety of malignant and non-malignant pathological states. These findings imply that the pharmacological modulation of this key nuclear transcription factor and its co-factors could be important tools in understanding the relationships between multigenic diseases, and pave the way to a focused interventional approach in their treatment. With the availability of the PPARgamma protein crystal structure, the ligand binding domain co-ordinates and a better knowledge of the interaction of PPARgamma with co-factor assemblies, libraries of simple synthetic organic PPARgamma ligands can be constructed. High throughput screening can identify the best candidates for targeting cellular phenotypic transition, cell cycle control, inflammation and apoptosis. Instead of single agents for single pathologies, one can envisage the development of multifunctional therapeutic agents that target the multiple cellular processes that contribute to multifactorial diseases such as diabetes, hypertension, atherosclerosis, psoriasis and other inflammatory diseases, and carcinogenesis. The considerable potential of PPARgamma ligands in the treatment of diseases other than diabetes is the subject of this review.

Angiogenesis as a target for breast cancer therapy

Angiogenesis, the development of new blood vessels, is crucial for the growth of both primary tumors and metastases beyond a minimal size and the vasculature of tumors facilitates their metastatic spread. Inhibition of angiogenesis is thus seen as a potentially useful approach to anti-metastasis therapy, and is an area of active research and development. Here we discuss this therapeutic approach in the context of breast cancer. An overview of the contribution of angiogenesis to tumor development is provided and current treatment options for breast cancer are briefly summarized. Assessment of angiogenesis in primary breast tumors has been shown to provide independent prognostic information. There are opportunities for the application of anti-angiogenesis therapeutic strategies in the treatment of breast cancer. Clinical trial design must take into account the unique properties of anti-angiogenic agents to fully assess their potential clinical benefit.