Pathological angiogenesis is a hallmark of cancer and various ischaemic and inflammatory diseases Concentrated efforts in this area of research are leading to the discovery of a growing number of pro- and anti-angiogenic molecules, some of which are already in clinical trials The complex interactions among these molecules and how they affect vascular structure and function in different environments are now beginning to be elucidated This integrated understanding is leading to the development of a number of exciting and bold approaches to treat cancer and other diseases But owing to several unanswered questions, caution is needed

Angiogenesis in cancer and other diseases

Endothelial and smooth muscle cells interact with each other to form new blood vessels. In this review, the cellular and molecular mechanisms underlying the formation of endothelium-lined channels (angiogenesis) and their maturation via recruitment of smooth muscle cells (arteriogenesis) during physiological and pathological conditions are summarized, alongside with possible therapeutic applications.

Mechanisms of angiogenesis and arteriogenesis.

The maturation of nascent vasculature, formed by vasculogenesis or angiogenesis, requires recruitment of mural cells, generation of an extracellular matrix and specialization of the vessel wall for structural support and regulation of vessel function. In addition, the vascular network must be organized so that all the parenchymal cells receive adequate nutrients. All of these processes are orchestrated by physical forces as well as by a constellation of ligands and receptors whose spatio-temporal patterns of expression and concentration are tightly regulated. Inappropriate levels of these physical forces or molecules produce an abnormal vasculature--a hallmark of various pathologies. Normalization of the abnormal vasculature can facilitate drug delivery to tumors and formation of a mature vasculature can help realize the promise of therapeutic angiogenesis and tissue engineering.

Molecular regulation of vessel maturation.

The regulation of angiogenesis by hypoxia is an important component of homeostatic mechanisms that link vascular oxygen supply to metabolic demand. Molecular characterization of angiogenic pathways, identification of hypoxia-inducible factor (HIF) as a key transcriptional regulator of these molecules, and the definition of the HIF hydoxylases as a family of dioxygenases that regulate HIF in accordance with oxygen availability have provided new insights into this process. Here we review these findings, and the role of HIF in developmental, adaptive and neoplastic angiogenesis. We also discuss the implications of oncogenic activation of extensive, physiologically interconnected hypoxia pathways for the tumor phenotype.

Regulation of angiogenesis by hypoxia: role of the HIF system.

The role of macrophages in tumour growth and development is complex and multifaceted. Whilst there is limited evidence that tumour-associated macrophages (TAMs) can be directly tumouricidal and stimulate the anti-tumour activity of T cells, there is now contrasting evidence that tumour cells are able to block or evade the activity of TAMs at the tumour site. In some cases, tumour-derived molecules even redirect TAM activities to promote tumour survival and growth. Indeed, evidence has emerged for a symbiotic relationship between tumour cells and TAMs, in which tumour cells attract TAMs and sustain their survival, with TAMs then responding to micro-environmental factors in tumours such as hypoxia (low oxygen tension) by producing important mitogens as well as various growth factors and enzymes that stimulate tumour angiogenesis. This review presents evidence for the number and/or distribution of TAMs being linked to prognosis in different types of human malignancy. It also outlines the range of pro- and anti-tumour functions performed by TAMs, and the novel therapies recently devised using TAMs to stimulate host immune responses or deliver therapeutic gene constructs to solid tumours.

The role of tumour‐associated macrophages in tumour progression: implications for new anticancer therapies

Although tissue injury and inflammation are considered essential for the induction of angiogenesis, the molecular controls of this cascade are mostly unknown. Here we show that a macrophage-derived peptide, PR39, inhibited the ubiquitin-proteasome-dependent degradation of hypoxia-inducible factor-1alpha protein, resulting in accelerated formation of vascular structures in vitro and increased myocardial vasculature in mice. For the latter, coronary flow studies demonstrated that PR39-induced angiogenesis resulted in the production of functional blood vessels. These findings show that PR39 and related compounds can be used as potent inductors of angiogenesis, and that selective inhibition of hypoxia-inducible factor-1alpha degradation may underlie the mechanism of inflammation-induced angiogenesis.

http://www.angiogenesis-center.org/documents/Li%20et%20(NM).pdf?presentation_id=1404

PR39, a peptide regulator of angiogenesis

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PR39, a peptide regulator of angiogenesis