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

Recent discoveries of endogenous negative regulators of angiogenesis, thrombospondin, angiostatin and glioma-derived angiogenesis inhibitory factor, all associated with neovascularized tumours, suggest a new paradigm of tumorigenesis. It is now helpful to think of the switch to the angiogenic phenotype as a net balance of positive and negative regulators of blood vessel growth. The extent to which the negative regulators are decreased during this switch may dictate whether a primary tumour grows rapidly or slowly and whether metastases grow at all.

Angiogenesis in cancer, vascular, rheumatoid and other disease

Patterns and Emerging Mechanisms of the Angiogenic Switch during Tumorigenesis

Matrix metalloproteinases (MMPs) have long been associated with cancer-cell invasion and metastasis. This provided the rationale for clinical trials of MMP inhibitors, unfortunately with disappointing results. We now know, however, that the MMPs have functions other than promotion of invasion, have substrates other than components of the extracellular matrix, and that they function before invasion in the development of cancer. With this knowledge in hand, can we rethink the use of MMP inhibitors in the clinic?

New functions for the matrix metalloproteinases in cancer progression

After the developing embryo has formed a primary vascular plexus by a process termed vasculogenesis, further blood vessels are generated by both sprouting and non-sprouting angiogenesis, which are progressively pruned and remodelled into a functional adult circulatory system. Recent results, particularly from the study of mice lacking some of the signalling systems involved, have greatly improved our understanding of the molecular basis underlying these events, and may suggest new approaches for treating conditions such as cancer that depend on angiogenesis.

Mechanisms of angiogenesis

Angiostatin: A novel angiogenesis inhibitor that mediates the suppression of metastases by a lewis lung carcinoma

Angiostatin: a circulating endothelial cell inhibitor that suppresses angiogenesis and tumor growth.

Medium conditioned by mouse sarcoma 180 cells stimulates the growth of capillary endothelial cells. The growth factor produced by mouse sarcoma 180 cells is heparin-binding, dithiothreitol-sensitive, endothelial cell specific, and secreted into the medium. The characteristics of this mouse sarcoma-derived growth factor are very similar to those of vascular endothelial growth factor (VEGF) first described by Ferrara and Henzel (1989). The N-terminal amino acid sequences of the two growth factors are similar. Since the amino acid sequence of vascular permeability factor (VPF) is essentially identical to that of VEGF, a Western blot of mouse sarcoma 180-derived endothelial growth factor was probed with a polyclonal antibody raised against human VPF. This antibody reacted with several proteins of approximately 23 kDa, suggesting the presence of multiple forms of a VEGF-like protein. A full length cDNA probe for bovine VEGF reacted strongly with RNA isolated from mouse sarcoma 180 cells. We conclude that an endothelial growth factor found in conditioned medium from mouse sarcoma 180 cells is VEGF.

Conditioned Medium from Mouse Sarcoma 180 Cells Contains Vascular Endothelial Growth Factor

We have previously shown that mouse sarcoma 180 cells produce vascular endothelial growth factor [VEGF; Rosenthal et al., 1990, Growth Factors, 4: 53-59], an endothelial mitogen that stimulates angiogenesis. Recent reports have implicated metalloproteinases and their inhibitors in the regulation of vascular morphogenesis, tumor invasion, and metastasis. We report here that mouse sarcoma 180 cells produce two collagenase inhibitors. These inhibitors were purified by heparin-Sepharose affinity chromatography, gel filtration, and C4 reverse phase h.p.l.c. Analytical gel electrophoresis of the purified inhibitors (MS-22 and MS-31) revealed molecular masses of 22,000 and 31,000 Da under reducing conditions, and 20,000 and 30,000 Da under nonreducing conditions, respectively. The NH2-terminal amino acid sequence of MS-22 was identical to that of tissue inhibitor of metalloproteinases type 2 (TIMP-2) produced by human melanoma cells [Stetler-Stevenson et al., 1989, J. Biol. Chem. 264: 17374-17378) over the first 30 amino acids. The NH2-terminal amino acid sequence of MS-31 was identical to that of murine TIMP-1 [Gewert et al., 1989, EMBO J 6:651-657]. Statistical analysis of the amino acid composition data of these two mouse sarcoma 180-derived collagenase inhibitors confirms the identification of MS-22 as TIMP-2 and MS-31 as TIMP-1.

Rosalind A. Rosenthal

Papers

Angiostatin: A novel angiogenesis inhibitor that mediates the suppression of metastases by a lewis lung carcinoma

Angiostatin: a circulating endothelial cell inhibitor that suppresses angiogenesis and tumor growth.

Conditioned Medium from Mouse Sarcoma 180 Cells Contains Vascular Endothelial Growth Factor

Purification and characterization of two collagenase inhibitors from mouse sarcoma 180 conditioned medium