Inducing Angiogenesis Oct 31, 2017

Hallmarks of Cancer, 2011

Angiogenesis -the process of forming new blood vessels from pre-existing ones by growth and migration of epithelial cells -Common during embryogenesis but not in adults (wound healing) -diffusion limit of oxygen (100-200 um)

Necrosis Cells within the core of the tumor that do not receive oxygen or nutrients undergo cell death or necrosis

Blood Vessel Structure

Cancer vs. Wound Healing Cancer Wound Healing Neovasculature Leaky allowing cells Not leaky to enter Molecular markers Integrins are Normal level of upregulated Integrins Extracellular matrix Angiogenic markers Different markers

Angiogenic Switch Angiogenic Inhibitors Angiogenic Inducers

Angiogenic Switch Result: Angiogenesis Angiogenic Inhibitors Angiogenic Inducers Result: Angiogenesis

Angiogenic Inducers and Inhibitors Inhibitors Inducers Angiostatin VEGF Endostatin FGF Prolactin HGF p53 EGF Thrombospondins PDGF

Angiogenic Inducers VEGF and VEGF Receptor -Initiation of Angiogenesis Angiopoietins and Tie Receptor -Vessel Maturation Ephrins and Ephrin Receptor

VEGF Family -5 members -VEGF-A to D -PlGF (Placental Growth Factor) -3 Receptors -VEGFR-1, 2 and 3 -VEGF-A and VEGFR-2 are major players -VEGFR-1 acts as a decoy competing with VEGF-R2 -weak kinase activity -VEGFR-3 and VEGF-C are involved with development of the lymphatic system

VEGF-A -Secreted by tumor cells -Secretion by neighboring non-transformed cells -Induced by the tumor cells -Stores of VEGF-A in the Extracellular matrix released by metalloproteinases (MMP) -proteases whose catalysis involves a metal ion Functions of VEGF-A Promote endothelial cell proliferation Induce permeability and leakage in existing blood vessels -important for new blood vessel formation

VEGF-A Signaling Pathway

EGF Signaling Pathway

VEGF-A Responsive Genes EGFR ligand Epiregulin (EGF family member) COX2, a cyclooxygenase involved with prostaglandin formation MMP1 and MMP2

Metalloproteinases

Metalloproteinases

Angiogenic Inhibitors 1. Angiostatin 2. Endostatin 3. Thrombospondin-1

Angiostatin Stored as an inactive molecule within another molecule, Plaminogen Angiostatin binds to Annexin II to cause inhbition Cleavage

Angiostatin Stored as an inactive molecule within another molecule, Plaminogen Angiostatin binds to Annexin II to cause inhbition

Endostatin -Fragment of Collagen XVIII -Endostatin will block MMPs and MAPK

Concomitant Resistance A tumor is removed and dominant metastases are often activated Inhibition of micrometastases by Angiogenesis inhibitors from the tumor Once the tumor is removed the inhibitory signal is lost and there is also an increase in growth factors Angiostatin Endostatin

Angiogenic Switch Oxygen Sensor -HIFα and HIFβ are constitutively expressed -HIFα and HIFβ ativity is regulated by oxygen concentration -von Hippel-Lindau (VHL) tumor suppressor protein, a ubiquitin ligase Hypoxia Response Element

Oncogenic Proteins ~30 oncoproteins promote angiogenesis Growth factors -Stimulate growth of tumor cells, autocrine -Stimulate growth of endothelial cells, paracrine Receptor Tyrosine kinases (EGFR) Intracellular tyrosine kinases (Src) Intracellular transducers (Ras) Transcripition factors (Fos and Jun)

Tumor Suppressor Proteins Thrombospondin-1 prevents VEGFR Activation

Angiogenic Sprouting -Filopodia extend from endothelial cells towards the VEGF signal -VEGF-A/VEGFR-2 becomes activated -Signal is enhanced by Nrp1, a co-receptor

Angiogenic Sprouting -Filopodia extend from endothelial cells towards the VEGF signal -VEGF-A/VEGFR-2 becomes activated -Signal is enhanced by Nrp1, a co-receptor

Angiogenic Sprouting -Tip cells induce expression of Notch (DLL-4) and its release -Notch binds to its receptor on neighboring cells -Notch Receptor Intracellular domain (NICD) is released and is transported to the nucleus to repress VEGFR-2 and turns on VEGFR-1

Angiogenic Sprouting -Notch Receptor Intracellular domain (NICD) is released and is transported to the nucleus to repress VEGFR-2 and turns on VEGFR-1 -VEGFR-1 acts as a VEGF trap, reducing VEGF concentration and reducing VEGFR-2 activation -The growing sprout moves along the VEGF gradient

Angiogenic Sprouting

Angiogenic Sprouting -When 2 tips meet, they fuse, connecting the lumen and allowing blood flow