The angiogenesis marker ED-B+ fibronectin isoform in intracranial meningiomas

Vascularity of meningiomas

Information on the vascular supply to meningiomas is critical to the neurosurgeon. Most meningiomas are supplied by the external carotid artery, though many get pial contribution as well. Angiogenesis is critical for these neoplasms to grow. Vascular endothelial growth factor (VEGF) has been a popular target of research to decrease angiogenesis. Peritumoral brain edema (PTBE) is occasionally seen in meningiomas, which makes surgical resection more challenging. The exact cause of PTBE remains unclear, but a number of factors have been postulated to contribute. Assessment of the vascularity of meningiomas is best carried out with angiography, but noninvasive techniques are improving, diminishing the need for more invasive imaging. Embolization of tumors can be performed to minimize perioperative blood loss and potentially lower surgical morbidity. However, it has not been shown to improve outcomes, and procedural risks exist. Higher grade tumors commonly have higher vascularity. Higher vascular meningiomas are more likely to recur and have higher levels of VEGF. The vascularity of meningiomas remains a topic of interest and is the focus of many research projects.

Multimodality Imaging in Tumor Angiogenesis: Present Status and Perspectives

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

Positron emission tomography tracers for imaging angiogenesis

Position emission tomography imaging of angiogenesis may provide non-invasive insights into the corresponding molecular processes and may be applied for individualized treatment planning of antiangiogenic therapies. At the moment, most strategies are focusing on the development of radiolabelled proteins and antibody formats targeting VEGF and its receptor or the ED-B domain of a fibronectin isoform as well as radiolabelled matrix metalloproteinase inhibitors or alpha(v)beta(3) integrin antagonists. Great efforts are being made to develop suitable tracers for different target structures. All of the major strategies focusing on the development of radiolabelled compounds for use with positron emission tomography are summarized in this review. However, because the most intensive work is concentrated on the development of radiolabelled RGD peptides for imaging alpha(v)beta(3) expression, which has successfully made its way from bench to bedside, these developments are especially emphasized.

Noninvasive tracer techniques to characterize angiogenesis

Great efforts are being made to develop antiangiogenesis drugs for treatment of cancer as well as other diseases. Some of the compounds are already in clinical trials. Imaging techniques allowing noninvasive monitoring of corresponding molecular processes can provide helpful information for planning and controlling corresponding therapeutic approaches but will also be of interest for basic science. Current nuclear medicine techniques focus on the development of tracer targeting the vascular endothelial growth factor (VEGF) system, matrix metalloproteinases (MMP), the ED-B domain of a fibronectin isoform, and the integrin alphavbeta3. In this chapter, the recent tracer developments as well as the preclinical and the clinical evaluations are summarized and the potential of the different approaches to characterize angiogenesis are discussed.

Endothelin-Mediated Oncofetal Fibronectin Expression in Chronic Allograft Nephropathy

BACKGROUND

Chronic allograft nephropathy is a sclerotic process characterized by an increased extracellular matrix (ECM) protein deposition. Fibronectin (FN) is a major component of ECM. FN has been reported to undergo alternative splicing and produce several isoforms including the extra domain-B (ED-B) containing embryonic isoform. In the present study, we investigated ED-B FN expression in chronic allograft nephropathy and its relationship with endothelins (ET).

METHODS

To establish chronic allograft nephropathy, allografts were performed between Fisher 344 --> Lewis rats. Allograft recipients were then randomly divided into two groups, allografts and allografts treated with ET receptor antagonist bosentan. Lewis --> Lewis recipients were used as isograft controls. Grafts were harvested at 30, 90 and 140 days for histological and gene expression analyses with respect to ED-B FN, ET-1 and transforming growth factor-beta1 (TGF-beta1) mRNA. ED-B FN protein levels were assessed by immunohistochemical analysis. Additionally, we analyzed human renal allograft biopsies.

RESULTS

Our data demonstrates that rat chronic allograft nephropathy is associated with progressive upregulation of ED-B FN mRNA and protein. ET-1 and TGF-beta1 mRNA were also upregulated. Treatment of allograft recipient rats with bosentan prevented upregulation of ED-B FN and TGF-beta1. We further show that total FN, ED-B FN, ET-1 and TGF-beta1 mRNA expression were upregulated in human chronic allograft nephropathy specimens.

CONCLUSION

Results obtained from both human and rat renal allograft tissues suggest that expression of ED-B FN is upregulated in chronic allograft nephropathy and such upregulation is mediated via ET-1 and its interaction with TGF-beta1.

Endothelin-mediated remodeling in aortas of diabetic rats

BACKGROUND

Smooth muscle cells proliferation and extracellular matrix (ECM) protein deposition are key features of diabetic macroangiopathy. In the present study, we have studied the role of endothelin(A) (ET(A)) receptor, the predominant receptor on smooth muscle cells, in diabetes-induced vascular hypertrophy and remodeling.

METHODS

Streptozotocin-induced diabetic rats were administrated a selective ET(A) receptor antagonist, TBC3214, for 26 weeks. Following treatment, aortas were harvested and subjected to gene expression and morphometric analyses. We quantified fibronectin (FN) and plasminogen activator inhibitor-1 (PAI-1) expression as indicators of increased ECM protein synthesis. ET-1, ET-3, transforming growth factor-beta1 (TGF-beta1) and angiotensinogen mRNA levels were measured to elucidate genes involved in FN expression. We have investigated an embryonic splice variant of FN, oncofetal FN, and nonmuscle myosin heavy chain (SMemb) as vascular remodeling indicators.

RESULTS

Our results show that diabetes leads to upregulation of FN, PAI-1, ET-1, ET-3, TGF-beta1 and angiotensinogen mRNA levels in association with increased medial thickness. Immunohistochemical analyses revealed concurrent protein level changes. Diabetes also upregulated oncofetal FN and SMemb mRNA levels. Treatment with TBC3214 attenuated the mRNA levels of several genes and prevented increased medial thickness.

CONCLUSIONS

These results indicate that diabetes-induced vascular hypertrophy and remodeling is associated with reexpression of embryonic forms of FN and myosin heavy chain. Such changes are ET-dependent and may be mediated via TGF-beta1 and angiotensin.

ED-B fibronectin as a target for antibody-based cancer treatments

Chemotherapeutic agents for the treatment of solid cancers do not discriminate between malignant and normal tissue, but rather depend on the increased proliferation of tumour cells versus benign cells. To reach therapeutically active concentrations in the tumour, large doses of these rather unspecific compounds have to be given to the patient, often resulting in severe side effects. Therefore, the goal of modern cancer research is the development of highly selective compounds which are able to discriminate between tumour tissue and normal tissue. One promising approach in this direction is antibody-mediated targeted cancer therapy which may either block an important receptor-ligand interaction or deliver a therapeutically active molecule to an otherwise nonfunctional target. A prerequisite for such an approach is the tumour-selective expression of the respective target structure. This review discusses extra domain-B fibronectin as a promising target which is associated with tumour angiogenesis and tumour growth for the development of novel antibody-mediated therapies.