Cancer 8 - Angiogenesis

Question 1

Give 3 examples of physiological angiogenesis

Answer 1

1. Embryonic development
2. Wound healing
3. Menstrual cycle

Question 2

What can insufficient angiogenesis cause?

Answer 2

Baldness
Ischaemia/MI
Limb fractures
Thrombosis

Question 3

What can vascular malformations (improper angiogenesis) cause

Answer 3

Angiodysplasia (HHT + VWD), cerebral malformations (AVM/CCM)

Question 4

What can excessive angiogenesis cause?

Answer 4

Retinal disease, cancers, atherosclerosis, obesity

Question 5

Name a pro-angiogensesis stimulus

Answer 5

VEGF - causes activated cell to change polarity + cytoskeleton which drives vessel sprouting —- forming TIP cell

Question 6

What do adjacent cells to the tip cell do?

Answer 6

Divide to stabilise the new vessel

Question 7

How is a balance of angiogenesis maintained

Answer 7

Balance between inhibitors and activators ensured

Question 8

What are the triggers for angiogenesis

Answer 8

Hypoxia - mediated by

1. HIF –> Hypoxia Inducible TF (controls regulation of gene expression by oxygen)
2. pVHL –> Von Hippel-Lindau TSG, controls HIF levels

Question 9

Explain how pVHL interacts with HIF

Answer 9

If sufficient oxygen - pVHL binds HIF - causing ubiquitination in HIF –> HIF degraded

If insufficient oxygen –> pVHL doesn’t bind HIF –> more HIF enters nucleus and binds HIF-beta —> drives transcription of genes promoting angiogenesis

Question 10

How many members are in the VEGF family

Answer 10

5

VEGF A/B/C/D
Placental Growth Factor (PIGF)

Question 11

What type of receptors bind the VEGF family and how many are there?

What is the coreceptor?

Answer 11

3 tyrosine kinase receptors - different dimer combinations

Co receptor is neuropilin 1/2

Question 12

Which is the major VEGFR that mediates VEGF-dependent angiogenesis

Answer 12

VEGFR2 - activates signal pathways that regulate endothelial cell migration, survival, proliferation

Question 13

Endothelial tip cells lead outgrowth of blood-vessel sprouts towards what gradient?

Answer 13

VEGF gradient

Question 14

How is it determined which endothelial cell becomes the tip cell?

Answer 14

Notch signalling

Question 15

How does a notch receptor and ligand bind

Answer 15

Notch receptor (stalk cell) and ligand (delta-ligand-4 on tip cell) are both membrane bound proteins —> they associate via extracellular domains

Question 16

What happens when the notch ligand binds the receptor

Answer 16

Intracellular domain (NICD) gets cleaved and translocates to the nucleus –> binds to TF RBP-J

Question 17

Explain how VEGF/notch signalling helps select the tip cells

Answer 17

1. DII4 and notch signalling stable in quiescent cells –> because signalling on both cells
2. VEGF activation - increased DII4 expression
3. Cell with more DII4 expression becomes the tip - DII4 expression drives notch signalling - inhibiting VEGFR2 expression in adjacent cell
4. The DII4 expressing tip cells acquire motile, invasive, sprouting phenotype
5. Adjacent cells form base of emerging sprout and proliferate to support sprout elongation

Question 18

Which 2 things are involved in sprout outgrowth?

Answer 18

1. Cytoskeletal reorganisation

2. Myeloid cell recruitment (e.g. in retina can help process)

Question 19

What is the role of VE-cadherin in sprouting angiogenesis

Answer 19

1. Constitutively expressed at junctions
2. Mediates adhesion between endothelial cells
3. Controls contact inhibition of cell growth
4. Promotes survival of endothelial cell

Question 20

What type of cancer can arise from loss of cadherin control

Answer 20

Epithelial cancers

Question 21

How do mural cells (e.g. pericytes) help stabilise me-vessels?

Answer 21

Pericytes normally wrap around capillaries - also produce Angiopoietin-1 (stabilising factor)

Question 22

Ang1 and Ang2 both bind to the Tie2 receptor. Explain their antagonistic effects

Answer 22

Ang1/Tie2 = vessel stability + anti-inflammatory gene expression

Ang2/Tie2 = antagonises Ang1 signalling, promotes vascular instability and VEGF dependent angiogenesis

Question 23

Which Ang is released more in inflammation as it helps the inflammatory response?

Answer 23

Ang2

Question 24

Plasma Ang2 is raised in disease. Name some diseases in which it is higher

Answer 24

1. Congestive heart failure
2. Sepsis
3. CKD

Question 25

What is Vascular Permeabiltiy Factor?

Answer 25

Same as VEGF

Question 26

What is avastin?

Answer 26

Anti-VEGF monoclonal antibody - used for advanced colorectal cancer but turned out to be ineffective

Question 27

Small tumours (<1 mm3) survive from oxygen and nutrients received how?

Answer 27

Via diffusion from host vasculature

Question 28

How do larger tumours survive?

Answer 28

They secrete angiogenic factors - creates a new vessel network that stimulates migration, proliferation + be-vessel formation by endothelial cels (in existing adjacent cells)

Question 29

What is the angiogenic switch

Answer 29

The point in the growth of a tumour where it now depends on angiogenesis for growth

Question 30

5 features of tumour blood vessels

Answer 30

1. Loss of balance of angiogenesis factors 2. Irregularly shaped, dilated, tortuous and fragile ---> meaning rupture-prone 3. Not organised well into venues, arterioles, capillaries 4. Leaky + haemorrhage (due to excessive VEGF)

Question 31

Give an example of an anti-VEGF humanised monoclonal antibody

Answer 31

Avastin (bevacizumab) | typically used in advanced stages of cancer

Question 32

What is Avastin used for in first line treatment of metastatic colorectal carcinoma?

Answer 32

Avastin + 5-fluorouracil

Question 33

What are the side effects of using Avastin in cancer therapy? No overall survival advantage over chemo alone

Answer 33

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

Question 34

What are the 2 modes of resistance to anti-angiogenic cancer therapy

Answer 34

1. Evasive resistance = adaptation to circumvent specific angiogenic blockade 2. Intrinsic/pre-existing indifference = if tumour more dependent on different GFs

Question 35

Give 6 cancers that bevacizumab (Avastin) may be used to treat

Answer 35

1. Cervical 2. Colorectal 3. Glioblastoma 4. Non-small cell lung cancer 5. Ovarian epithelial, Fallopian tube / primary peritoneal cancer 6. Renal cell cancer

Question 36

What are 2 ways to feed a tumour?

Answer 36

1. Angiogenesis - tumour secrete factors which stimulates vessel growth --> vessel grows into tumour 2. Tumour cell vasculogenic/vascular mimicry --> plasticity of aggressive cancer cells forming de novo vascular networks --> associated with malignant phenotype and poor prognosis

Question 37

What is the solution to the 2D in vitro tumour modelling problem currently being faced?

Answer 37

"Tumour on a chip" - in vitro disease model with vasculature also

Question 38

Give an example of antiangiogenic therapy in other diseases?

Answer 38

Abnormal retina vascularisation (e.g. diabetic retinopathy/ wet AMD)

Question 39

What causes age related macular degeneration

Answer 39

Abnormal growth of choroidal blood vessels ---> leaky vessels cause oedema causing visual impairment

Question 40

What is the main cause of blindness?

Answer 40

AMD

Question 41

How can therapeutic angiogenesis be used for coronary artery disease and PAD

Answer 41

Promote neovascularisation - to prevent ischaemic damage e.g. induce neo-angiogenesis in ischaemic myocardium using human GFs (may require proteins, stem cells, gene therapy)