8: Angiogenesis

Question 1

What is the main trigger for angiogenesis?

Answer 1

Hypoxia

Question 2

What molecules are involved in angiogenesis?

Answer 2

Hypoxia-inducible Transcription factor (HIF)
Regulates gene expression required in angiogenesis

pVHL tumour suppressor gene is bound to HIF and controls its levels by degradation

Question 3

What happens molecularly in hypoxia?

Answer 3

HIF no longer bound to pVHL
So HIF no longer degraded
HIF goes into nucleus and upregulates genes that promote angiogenesis

Question 4

What is VEGF?

Answer 4

Vascular Endothelial Growth Factor

Question 5

Which receptor is a major mediator of VEGF-dependent angiogenesis?

Answer 5

VEGFR-2

Question 6

What happens during sprouting angiogenesis?

Answer 6

Endothelial TIP cells lead the outgrowth of blood-vessel sprouts towards GRADIENTS OF VEGF.

Tip cell selection is controlled by Notch signalling
Notch receptors have extracellular domain that binds DLL4, and intracellular domain that goes into nucleus and binds to TF

1. In stable vasculature, DLL4 and Notch signaling maintain quiescence
2. VEGF activation increases expression of DLL4
3. DLL4 drives Notch signalling, inhibiting expression of VEGFR2 in adjacent cells. These become Stalk cells.
4. DLL4-expressing Tip cells become motile + invasive (sprouting phenotype)
5. Stalk cells form the base of the emerging sprout, proliferate to support sprout elongation.

Question 7

What happens during sprout outgrowth?

Answer 7

Tip cell communicates with ECM and myeloid cells for guidance

Question 8

What happens during stabilisation/quiescence?

Answer 8

Pericytes bind to outside of sprout and send stabilising signals
There is also barrier formation (cell junctions)

Question 9

Describe the structure of endothelial cell junctions in sprouts

Answer 9

VE Cadherin allows adhesion between the endothelial cells

Controls contact inhibition - allows formation of a SINGLE layer of cells

Question 10

What are pericytes?

Answer 10

Mural cells that wrap around the new vessels and produces the stabilising factor Angiopoietin-1

Question 11

Describe the angiopoietin-Tie2 pathway

Answer 11

Ang-1 binding to Tie2 promotes vessel stability

Ang-2 binding ANTAGONISES Ang-1 (i.e. vessel INstability) and promotes angiogenesis

Question 12

What diseases would you see an increase in plasma Ang-2?

Answer 12

Heart failure
Sepsis
Chronic Kidney disease

Question 13

What happens to angiogenesis in tumours

Answer 13

Tumours less than 1mm3 get oxygen/nutrients via diffusion from host vasculature

LARGE tumours (>1mm3) require angiogensis
Tumour secretes angiogenic factors
Newly vascularised tumour no longer relies solely on diffusion (oxygen + nutrients) from host vasculature
Facilitates progressive growth

Question 14

What is the angiogenic switch?

Answer 14

The point at which the tumour becomes dependent on NEW vasculature

Question 15

What is the angiogenic switch?

Answer 15

The point at which the tumour becomes dependent on NEW vasculature

Question 16

How are tumour blood vessels different?

Answer 16

Irregularly shaped
Dilated
Tortuous
Disorganised
Leaky/haemorrhagic (excessive VEGF)

Question 17

Example of drug targeting the VEGF pathway?

Answer 17

Avastin (Bevacizumab) - ANTI-VEGF monoclonal antibody

Question 18

Side effects?

Answer 18

GI Perforation
Hypertension
Thrombosis
Haemorrhage
No overall QOL or survival advantage
No overall survival advantage over chemo alone

Question 19

What are the mechanisms of resistance to anti-angiongenic therapy?

Answer 19

Other angiogenic factors can take over VEGF

Reduced blood supply to tumour means reduced access by chemotherapy drugs

Question 20

What is vascular mimicry

Answer 20

Tumour cells mimic endothelial cells and form de novo vasculature

Question 21

What diseases use angiogenic therapy?

Answer 21

ANTI-angiogenic: abnormal retina vascularisation (diabetic retinopathy), Age-related Macular Degeneration (AMD)

Pro-angiogenic: Ischaemic diseases (MI, Peripheral ischaemic disease)

Question 22

What is Age-related Macular Degeneration and how is it treated?

Answer 22

Main cause of blindness
Abnormal growth of choroidal blood vessels in the eye
‘Leaky’ vessels cause oedema leading to blindness

Anti-VEGF used for treatment
HIGH efficacy unlike for cancer

Question 23

What is tumor-on-a-chip?

Answer 23

New method for screening anti-angiogenic drugs

Tumours are complex 3D microenvironments
2D in vitro studies do not mimic interaction between tumour cells and extracellular environment. They also lack human vasculature supply
So drug screening with 2D models misleading

In vitro 3D models of cancer have tumour cells in a 3D ECM perfused by human vessels
May improve drug screening