Angiogenesis

Angiogenesis

The Grandfather of Angiogenesis • Judah Folkman MD

• Folkman J. Tumour angiogenesis: therapeutic implications. New England Journal of Medicine 1971; 285: 1182-1186. • http://www.pbs.org/wgbh/nova/cancer/program.html#

What is Angiogenesis? • Survival and proliferation of cells is dependent upon an adequate supply of: – Oxygen – Nutrients – Removal of toxins

• Angiogenesis is the development of new capillaries from pre-existing blood vessels.

• For stimulated endothelial cells to form a new blood vessel they must proliferate, migrate and invade the surrounding tissue.

What is Angiogenesis? • Initial processes from blood vessels are known as capillary sprouts. • Must expand and undergo morphogenesis in order to form a mature capillary. • Without a blood supply, tumours can grow to about 2mm in size. • Without angiogenesis tumours with undergo regression, necrosis, apoptosis and will not be clinically relevant.

Angiogenesis is a normal Process • Angiogenesis occurs during foetal development during which a vast network of blood vessels must be created to support body development • Regeneration of the uterine wall following menstruation. • Wound healing requires development of new blood vessels • Walls of blood vessels are formed by vascular endothelial cells. These divide about once every 3 years. • When the situation requires, the process of angiogenesis stimulates endothelial cell division.

Angiogenesis

Theories of Angiogenesis

Stimulators of Angiogenesis  Acidic Fibroblast growth factor  Angiogenin

 Basic Fibroblast growth factor  Epidermal growth factor  Granulocyte colony-stimulating factor  Hepatocyte growth factor  Interleukin 8  Placental growth factor  Platelet derived endothelial growth factor  TGF, TGF  Tumour necrosis factor  Vascular Endothelial growth factor  Adenosine

 1-Butyryl glycerol  Nicotinamide

Angiogenesis Signaling Cascade

The Angiogenesis Signalling Cascade • The two most important angiogenesis factors are – VEGF (vascular endothelial growth factor). – BFGF (Basic fibroblast growth factor

• Activation of endothelial cells by VEGF or bFGF will lead toward the creation of new blood vessels. • Activated endothelial cells produce MMPs.

• These enzymes are then released from the endothelial cells into the surrounding tissue. • MMPs break down extracellular matrix. Breakdown of this matrix permits the migration of endothelial cells.

Angiogenesis Signaling Cascade • As endothelial cells migrate into the stroma, they organize into hollow tubes that evolve gradually into a mature network of blood vessels.

Other Genes associated with Angiogenesis • The process of angiogenesis is a radical molecular and cellular event and will require the up-regulation of genes controlling, for example – – – – –

Tissue architecture Cellular motility Cell division and DNA replication Extracellular matrix digestion Cell-to-cell junctions.

• Typical Genes classes – Cytoskeleton (-catenin) – Cell-to-cell interaction (CAMs – cadherins, Integrins) – MMPs

Angiogenesis Inhibition Natural Inhibitors of Angiogenesis

Angiostatin Endostatin Interferons Platelet factor 4 Prolactin 16kDa protein fragment TIMP-1 (Tissue inhibitor of MMP1) TIMP-2 (Tissue inhibitor of MMP2) TIMP-3 (Tissue inhibitor of MMP3)

Angiogenesis Inhibition • The discovery of angiogenesis inhibitors suggests such molecules might inhibit cancer growth. • Researchers have addressed this question in numerous experiments involving animals.

• In one striking study, mice with several different kinds of cancer were treated with injections of endostatin. • After a few cycles of treatment, the primary tumour formed at the site of the injected cancer cells regressed. • Mice did not develop resistance to the effects of endostatin after repeated usage.

Experimental Use of Endostatin

Angiogenesis Inhibitors Endostatin • Endostatin, 20kDa C-terminal fragment of collagen XVIII. • a potent antagonist of angiogenesis and inhibitor of tumor growth in mouse models. • At present, the mechanism of action of endostatin is unknown. • Recombinantly produced human endostatin interacts with 5- and vintegrins on the surface of human endothelial cells • Interaction of endostatin with integrins implicated in angiogenesis. M. Rehn et al., PNAS (2001), 98, 1024-1029.

Other Inhibitors • Thalidomide

• A sedative drug used in the 1950s that was subsequently taken off the market because it caused teratogenic birth defects when taken by pregnant women. • Although this drug clearly would not be suitable for pregnant women. • It functions by preventing endothelial cells from forming new blood vessels might make it useful in treating non-pregnant cancer patients.

Other Inhibitors • Angiogenesis inhibitors being tested in human clinical trials are molecules that interfere with steps in the angiogenesis signaling cascade. • Included in this category are anti-VEGF antibodies that block the VEGF receptor from binding growth factor. – Bevacizumab (Avastin), a monoclonal antibody, is the first of these antiVEGF antibodies to be FDA-approved. – This new drug has been proven to delay tumor growth and more importantly, to extend the lives of patients.

• Interferon-alpha, (naturally occurring protein) inhibits the production of bFGF and VEGF, preventing these growth factors from starting the signaling cascade.

Summary • Judah Folkman: The “grandfather” of angiogenesis research. • What is angiogenesis – definition. • Examples of angiogenesis as a normal process. • Theories of Angiogenesis. • Normal proteins and small molecules which stimulate angiogenesis. • Signaling and target genes associated with angiogenesis.

• Angiogenesis inhibitors. – Mechanisms of action. – Therapeutic potential.