1. Inducing Angiogenesis
Oct 31, 2017

2. Hallmarks of Cancer, 2011

3. 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 ( um)

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

5. Blood Vessel Structure

6. 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

7. Angiogenic Switch
Angiogenic Inhibitors
Angiogenic Inducers

8. Angiogenic Switch Result: Angiogenesis Angiogenic Inhibitors
Angiogenic Inducers
Result: Angiogenesis

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

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

11. 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

12. 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

13. VEGF-A Signaling Pathway

14. EGF Signaling Pathway

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

16. Metalloproteinases

17. Metalloproteinases

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

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

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

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

22. 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

23. 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

24. 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)

25. Tumor Suppressor Proteins
Thrombospondin-1 prevents VEGFR Activation

27. 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

28. 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

29. 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

30. 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

31. Angiogenic Sprouting

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