Tumour Angiogenesis Invasion and Metastasis

Question 1

What are the characteristics of malignant tumours ?

Answer 1

Growth
Unlimited growth - if there is an adequate blood supply

Invasiveness-Migration of tumour cells into the surrounding stroma where they are free to disseminate via vascular or lymphatic channels to distant organs

Metastasis
Spread of tumour cells from the primary site to form secondary tumours at other sites in the body

Question 2

Summarise the key steps in cancer progression

Answer 2

1.Transformation
Extensive mutagenic and epigenetic changes followed by clonal selection

2.Angiogenesis
New blood vessel formation (overcomes limitations imposed by hypoxia
Nearby capillary will form more vessels

3.Motility and invasion
Epithelial to mesenchymal transition (invasive properties allowing intravasation into circulation and extravasation from circulation to tissues

Arrest in capillary beds through adhesion molecules

4.Metastais
Colonisation of target organs (ability to expand from micro metastases)

Question 3

Outline angiogenesis and the different types of angiogenesis

Answer 3

This is the formation of new blood vessels from pre-existing vessels

1.Developmental/Vasculogenesis
(Organ growth )

2.Normal angiogenesis
(Wound repair, placenta during pregnancy , cycling ovary

3.Pathologocial angiogenesis
(Tumour angiogenesis, ocular and inflammatory disorders

Question 4

What is Vasculogenesis

Answer 4

The formation of new blood vessels from progenitors

Question 5

Outline Neovascularisation of tumours

Answer 5

The natural formation of new blood vessels

Numerous blood vessels have infiltrated into the tumour tissue

Tumours will generally not grow beyond a size of about 1-2mm without their own blood supply

Question 6

Outline Tumour Angiogenesis

Answer 6

a) small tumour eventually gets to a large enough size when delivery of oxygen and nutrients from nearby capillaries become limiting
b) Tumour switches on expression of angiogenic genes/factors that initiate new blood vessel growth
c) New network of blood vessels grows in and around the tumour increasing the delivery of oxygen and nutrients that allows it to increase growth and provides a route for cells to shed off and spread.(Metastasis)

Question 7

Outline what tumour hypoxia is

Answer 7

This is the a strong stimulus for tumour angiogenesis

Hypoxia is low oxygen tension <1% O2

Increases with increasing distance from capillaries

Activates transcription of gene involved in angiogenesis , tumour cell migration and metastasis

The oxygen deprived cells will release growth factors:
Vascular endothelial growth factor (VEGF)
Glucose transporter 1( GLUT-1)
Urokinase plasminogen activator receptor (u-PAR)

Plasminogen activator inhibitor (PAI-1)

Question 8

What are the angiogenic factors ?

Answer 8

Tumour cells produce factors :

• Vascular Endothelial growth factor (VEGF)
• Fibroblast Growth factor 2(FGF2)
• Placental growth factor (PIGF)
• Angiopoietin 2(Ang 2)

These factors are secreted by tumour cells or are stored bound to components of the extracellular matrix + may be released by enzymes called matrix metalloproteinases

Matric Metalloproteinase 2 (MMP-2)

Question 9

How do these angiogenic factors then work ?

Answer 9

-VEGGF and Ang-2 are released by the tumour and bind to receptors on the blood vessel (endothelial cells)

The biological processes involved:

Proliferation
Migration
Invasion

Question 10

Outline the vascular endothelial growth factor (VEGE) signalling

Answer 10

(LOOK AT SLIDE)

VEGF binds to VEGF-R2 on endothelial cells

❶VEGF/VEGF-R2 dimerizes at the plasma membrane and recruits cofactors❷ that subsequently activate 3 major signal transduction pathways ❸

Ultimately, VEGF activates cell survival, vascular permeability, gene expression and cell proliferation

All of these pathways are essential for angiogenesis

Question 11

Outline the Epithelila-Mesenchymal Transition (EMT )

Answer 11

Loss of :

• Epithelial shape and cell polarity (beta-catenin,claudin-1)
• Cytokeratin intermediate filament expression
• Epithelial adherens junction proteins(E-cadherin)

Acquisition of :
•Fibroblast-like shape and motility
•Invasiveness
•Vimentin intermediate filament expression
•Mesenchymal gene expression (fibronectin, PDGF receptor, αvβ6 integrin)
•Protease secretion (MMP-2, MMP-9)

Question 12

Describe the E-Cadherins

Answer 12

Form homotypic dimers (two cells are adhered to each other )
Homotypic adhesion molecule (adhesion of cells with the same cadherin
Calcium dependent
Inhibits invasiveness
Binds beta-catenin

Question 13

What happens if there is a mutation on E-cadherin ?

Answer 13

Disrupted cell-cell adhesion
Mutation/loss of E-cadherin

Loss of contact inhibition cells grow on top of each other

Question 14

Describe a normal cell -Containing E-cadherin

Answer 14

Low density
Proliferation
Cell adhesion
Contact inhibition and monolayer of normal cells

Question 15

What is contact inhibition ?

Answer 15

When cells binds to another cell , there is a signal for them to not migrate /invade

Question 16

How do stromal cell contribute to tumour progression ?

Answer 16

Factors released by stomal cells (macrophages , mast cells , fibroblasts ) include angiogenic factors,growth factors and cytokines,proteases

Example :Urokinas-type plasminogen activator (uPA)activated by tumour cells -resulting in plasmin production

Plasmin activates matric metalloproteases (MMPS) which permit invasion by degrading extracellular matrix (ECM) and releasing matric-bound angiogenic factors such as transforming growth fasctors-beta 1.

Question 17

Outline the mechanism of action of Urokinase-type plasminogen activator (uPA)

Answer 17

Protease -Pro-uPA which will bind to a Urokinase plasminogen activator receptor on cancer cells. It will then activate it to active uPA which can activate plasminogen to plasmin which can also activate downstream enzymes such as pro-MMPs to MMPS which can break down ECM allowing cancer cell to move.
They can also activate latent growth factors
Latent TGF-beta 1 to TGF-B1 (activated)

Question 18

Outline the steps involved in cancer dissemination

Answer 18

Primary tumour formation 
Localised invasion 
Intravasation 
Transport through circulation 
Arrest in micro vessels of various organs 
Extravasation 
Formation of a micro metastasis 
Colonisation -formation of a macro metastasis

Question 19

What are the sites of tumour metastasis ?

Answer 19

Brain -Liver /lung/brain/bone 
Colorectal-Liver and lung
Gastric-Oesophagus/liver/lung
Lung-Adrenal gland ,brain, liver 
Pancreatic -liver /lung
Prostate-bone

Question 20

What are the two hypothesis of the pattern of tumour spread?

Answer 20

Blood /lymphatic systems ,
entrapment in capillary beds(20-30 um)

Seed and soil hypothesis
Specific adhesions between tumour cells and endothelial cells in the target organ creating a favourable environment in the target organ for colonisation
Genetic alteration acquired during progression allow tumour cells to metastasize

Question 21

What is the Angiogenesis hypothesis ?

Answer 21

Tumour growth is dependent on new blood vessel growth
If a tumour could be held indefinitely in the non-vascularised dormant state, it is possible that metastases will not arise.

e.g. Kidney cancer /renal cell carcinoma is a highly angiogenic and metastatic tumour

Question 22

Outline Avastin and what it can be used to treat .

Answer 22

This is the first anti-angiogenesis drug

Approved for colorectal ,lung ,kidney and ovarian cancers , eye diseases

Question 23

What is the mechanism of action of Avastin?

Answer 23

It is an anti-VEGF antibody , it binds to VEGF which has been secreted by the tumour.
It prevents it binding to the ligand binding site on the receptor of the endothelial cell.
No dimerization and no downstream phosphorylation.
Causes decrease in angiogenesis ,progression, metastasis and survival