Angiogenesis

Question 1

What are the three ways of making blood vessels?

Answer 1

Vasculogenesis: formation of new blood vessels from bone marrow progenitor cells
Angiogensis: formation of new blood vessels by sprouting from pre-existing vessels
Arteriogenesis: collateral growth of blood vessels, dependent on shear stress + external factors like macrophages

Question 2

What is the main signal for angiogenesis?

Answer 2

Hypoxia

Question 3

What is the most important pro-angiogenic factor?

Answer 3

VEGF (Vascular Endothelial Growth Factor)

Question 4

Explain the mechanism by which hypoxia triggers angiogenesis.

Answer 4

HIF (hypoxia-inducible factor) is a TF responsible for expression of genes involved in angiogenesis
In normoxic conditions, HIF is bound to von Hippel Lindau protein (tumour suppressor), which inhibits HIF from promoting angiogenesis
In hypoxic conditions, HIF detaches so can go into nucleus, bind DNA + drive expression of genes involved in angiogenesis

Question 5

How many members are there in the VEGF family? List them.

Answer 5

5
VEGF-A, B, C, D
PlGF (placental growth factor)

Question 6

How many tyrosine kinase receptors are there for VEGF? List them.

Answer 6

3

VEGFR 1, 2 + 3

Question 7

How many coreceptors are there for VEGF? List them.

Answer 7

2

Neuropilin (Nrp) 1 + 2

Question 8

Which receptor is the major mediator in VEGF-dependent angiogenesis? What does it do?

Answer 8

VEGFR2

Activates signalling pathways that regulate endothelial cell migration, survival + proliferation

Question 9

What pathway is crucial for the selection of tip cells?

Answer 9

Notch signalling

Question 10

What happens when the notch ligand binds to the notch receptor?

Answer 10

The intracellular domain in the stalk cell is cleaved

This translocates to the nucleus, binds to RBP-J + regulates transcription

Question 11

What is another name for the notch ligand?

Answer 11

Delta-like ligand (Dll4)

Question 12

What effect does VEGF have on notch signalling?

Answer 12

VEGF activation increases expression of Dll4 on the tip cell
Dll4 drives Notch signalling, which inhibits expression of VEGFR2 in the adjacent cell
Dll4 expressing tip cells develop a motile, invasive + sprouting phenotype
Adjacent stalk cells form the base of the emerging sprout + proliferate to support sprout elongation

Question 13

How do macrophages participate in angiogenesis?

Answer 13

Carve out tunnels in ECM providing avenues for capillary infiltration
Tissue resident macrophages can be associated with angiogenic tip cells during anastomosis

Question 14

Which other cell type is recruited to help with the stabilisation of the newly formed vessel?

Answer 14

Pericytes

Question 15

Which cell adhesion molecules are essential for vessel stabilisation and quiescence? What else do they do?

Answer 15

VE-Cadherins (homophillic interaction)
Control contact inhibition of cell growth
Promotes survival of cell

Question 16

What growth factor do pericytes produce that is important for stabilisation of new blood vessels?

Answer 16

Angiopoietin 1

Question 17

Which important signalling pathway modulates the activation and return to quiescence of endothelial cells?

Answer 17

Angiopoietin-Tie2 signalling pathway

Question 18

Describe the actions of angiopoietin 1.

Answer 18

Promotes vessel stability

Inhibits inflammatory gene expression

Question 19

Describe the actions of angiopoietin 2.

Answer 19

Ang 2 antagonises Ang 1 signalling
Promotes vascular instability
Promotes VEGF dependent angiogenesis

Question 20

What is the name given to the point at which a tumour begins to initiate signals to generate new vasculature?

Answer 20

Angiogenic switch

Question 21

What are some of the issues with tumour blood vessels?

Answer 21

They are malformed because the signals are not physiological
Vessels can be irregularly shaped, distended, disorganised, tortuous, leaky + haemorrhagic etc
Haemorrhage is common in tumours.

Question 22

What is the aim of anti-angiogenic therapy in cancer?

Answer 22

To normalise tumour blood vessels to reduce hypoxia + improve efficiency of drug delivery

Question 23

What are the consequences of being too aggressive with anti-angiogenic therapy?

Answer 23

Can make tumour blood supply inadequate for delivery of drugs

Question 24

What is avastin?

Answer 24

Anti-VEGF humanised mouse antibody

Question 25

What are 6 side effects of avastin?

Answer 25

``` GI perforation Hypertension Proteinuria Venous thrombosis Haemorrhage Wound healing complications ```

Question 26

What are the 3 main mechanisms of resistance to VEGF blockade?

Answer 26

VEGF inhibition aggravates hypoxia increasing tumour's production of other angiogenic factors/ increases tumour invasiveness Tumour vessel cells may be less sensitive to VEGF inhibition Tumour cells that recruit pericytes may be less responsive to VEGF inhibition

Question 27

What did avastin start getting used for other than cancer?

Answer 27

Age-related macular degeneration (AMD)

Question 28

What slightly modified form of avastin became licensed by the FDA to treat AMD?

Answer 28

Lucentis (ranibizumab)

Question 29

List 3 physiological circumstances angiogenesis occurs in

Answer 29

Development Menstrual cycle Wound healing

Question 30

List 5 pathological circumstances angiogenesis occurs in

Answer 30

``` Cancer Chronic inflammatory diseases Retinopathies Ischemic diseases Vascular malformations ```

Question 31

Briefly describe the step by step sprouting angiogenesis process

Answer 31

Hypoxia stimulates angiogenic factor release VEGF binds to a receptor on a cell which becomes the Tip cell Cells adjacent become support "stalk cells" + proliferate Stalk elongation, tip cell fusion + lumen formation occur Then there is perfusion + vessel maturation

Question 32

When is Ang 2 released?

Answer 32

When the endothelium is activated e.g. in inflammation

Question 33

How are platelets involved in tumour angiogenesis?

Answer 33

Activated platelets are a source of pro-angiogenic + angiostatic factors Tumours cause platelet activation, aggregation + degranulation Overall they are pro-angiogenic

Question 34

Describe the limited efficacy of Avastin

Answer 34

No overall survival advantage over chemo alone | Sometime transitory benefit, then restoration of tumour growth + progression

Question 35

How may tumours become independent of VEGF for a blood supply?

Answer 35

Vascular mimicry Tumour cells organise themselves to form vessel like channels + allow blood to circulate Thus blocking VEGF will not be effective in stopping blood supply

Question 36

What is AMD?

Answer 36

Age-related macular degeneration Abnormal growth of choroidal blood vessels Leaky vessels cause oedema + visual impairment

Question 37

What new technique is being tested for cancer drug screening?

Answer 37

"tumour on a chip" in vitro models incorporating tumour cells + vasculature

Question 38

In which circumstances would pro-angiogenic therapy be useful?

Answer 38

Myocardial infarction | Peripheral ischaemia