Cancer: Angiogenesis

Question 1

Define angiogenesis

Answer 1

The formation of a new blood vessel from pre-existing blood vessels

(There are other ways to make new blood vessels)

Question 2

Define vasculogenesis

Answer 2

The differentiation of bone marrow progenitor cells (angioblasts) into endothelial cells as the formation of new vascular networks

Question 3

Define arteriogenesis

Answer 3

Collateral growth and increase in diameter that is dependent on shear stress and external factors e.g. macrophages

Question 4

Describe sprouting angiogenesis (5 stages)

Answer 4

Growth factors are released in response to hypoxia (most common cause) that activate endothelial cells in small vessels

Endothelial cells undergo a conformational change from a very organised monolayer to sending out filopodia, migrating towards growth factors

Tip cells lead the projection, being pushed by stalk-cells proliferating behind them

One tip cell meets a tip cell from a neighbouring capillary and fuses

Endothelial cells form a bridge and stabilise cell-cell adhesions to create a functioning vessel

Question 5

Which angiogenesis activator is essential for life?

Answer 5

VEGF

Loss of just one allele is incomaptible with life

The others are less important but developing vasculature still won’t be quite normal without them

Question 6

What is the transcription factor for hypoxia induced angiogenesis?

Answer 6

HIF (hypoxia-inducible transcription factor)

Question 7

Which tumour suppressor inhibits HIF under normal conditions?

Answer 7

Von Hippel-Lindau

Question 8

Name a target of HIF

Answer 8

VEGF gene expression

Question 9

Name the 5 members of the VEGF family

Answer 9

VEGF-A

VEGF-B

VEGF-C

VEGF-D

PIGF (placental growth factor)

Question 10

Name the 3 tyrosine kinase receptors for VEGF

Answer 10

VEGFR-1

VEGFR-2

VEGFR-3

Question 11

Name the 2 coreceptors for VEGF

Answer 11

Nrp1 (neuropilin-1)

Nrp2 (neuropilin-2)

Question 12

Which VEGFR is the major mediator of VEGF-dependant angiogenesis?

Answer 12

VEGFR-2

Question 13

Which pathway is responsible for selecting the tip cell?

Answer 13

Canonical Notch signalling pathway

Question 14

On what cells are Notch receptors present?

Answer 14

Stalk cells

Question 15

On what cells are Notch ligands present?

And what is the other name for Notch ligand?

Answer 15

Tip cells

Delta-like ligand 4 (Dll4)

Question 16

How does binding of the Notch ligand to the Notch receptor activate the signalling pathway?

Answer 16

Upon binding, the intracellular domain (NICD) of the notch receptor is clearved

NCID then translocates to the nucleus where it binds to the transcription factor RBP-J and regulates transcription

The stalk cells then begin to divide and push the tip cell towards the growth factor

Question 17

How does VEGF activation create tip cells?

Answer 17

VEGF activates an endothelial cell in a capillary and leads to an increased expression of Dll4 on its membrane (Notch ligand)

The Notch signalling in the adjacent cells results in decrased expression of VEGFR2 on their surfaces, stopping them from becoming tip cells themselves

Question 18

How do tip cells and stalk cells sprout forwards through the ECM?

Answer 18

The tip cell is responsible for guidance through the ECM via growth factors (e.g. VEGF and FGFs [fibroblast growth factors])

Macrophages carve the way through the ECM for the subsequent capillary infiltration (both physiolohically and pathalogically), aiding in eventual anastamosis

Question 19

Briefly describe the process of stabilisation during angiogenesis

Answer 19

It involves reforming the endothelial monolayer barrier

and recruiting pericytes

and switching off the active angiogenesis process

Question 20

Which adhesion molecule is essential for vessel stabilisation and quiescence?

and what is special about its interaction?

Answer 20

VE-Cadherin. It lines the junctions of endothelial cells

homophilic interaction (binds to the same receptor molecule on adjacent cell)

Note: cadherin interactions are also important in contact inhibition of cell growth

Question 21

What are mural cells?

Answer 21

The term generally refers to smooth muscle cells and pericytes, both of which are involved in the formation of normal vasculature

(responsive to VEGF)

Question 22

Why are pericytes so important in stabilisation of new blood vessels?

Answer 22

Because they produce proteins such as antiopoetin 1 (ANG1) which stabilise the endothelium

Question 23

Which system modulates the activation and quiescence of endothelial cells?

Answer 23

The angiopietin/Tie2 system

Question 24

What does angiopoetin 1 do?

and where is it released?

Answer 24

Binds to Tie2 and promotes quiescence

Pericytes

Question 25

What does angiopoeitin 2 do?

and where is it released?

Answer 25

It antagonises ang-1 signalling, and promotes vascular instability and VEGF-dependant angiogenesis

WPB (Weibel-Palade bodies)

Question 26

Define angiogenic switch

Answer 26

The key point in tumour development where the tumour gets to a certain size so that diffusion is no longer sufficient, and some cells within the tumour become hypoxic and send angiogenic signals

Question 27

Name 5 characteristics of tumour blood vessels resulting from pathalogical angiogenesis

Answer 27

Irregularly shaped

Not organised into definitive venules, arterioles and capillaries

Leaky and haemorrhagic

Perivascular cells often become loosely associated

Some may recruit endothelial progenitor cells from the bone marrow

Question 28

Why must anti-angiogenic drugs be balanced as to not be too aggressive?

Answer 28

It may damage healthy vasculature leading to the tumour, meaning inadequate delivery of further drugs

and oxygen which leads to hypoxia, causing the release of VEGF etc. which actively reverses the effects of the treatment you just prescribed

Question 29

What is avastin?

is it effective in cancer therapy?

Answer 29

An anti-VEGF humanised MAb (mouse antibody)

There are no survival advantages over chemotherapy alone

There are many significant side-effects because VEGF is essential for the homeostasis of the endothelium

Question 30

What was avastin eventually used to treat (being rebranded to lucentis)

Answer 30

Age-related macular degeneration (AMD)

Question 31

What might anti-angiogenic therapy later be used for? (4)

Answer 31

Combination therapy with other anti-cancer therapies

Combinatorial strategies with drugs targeting resistance mechanisms to anti-angiogenics

Novel non-VEGF targets

Pro-angiogenic therapy in ischemia, vascular repair and tissue engineering