Tumour Angiogeneis, Invasion And Metastasis

Question 1

What are characteristics of malignant tumours?

Answer 1

Growth
- unlimited growth as long as there’s a adequate blood supply is availability

Invasiveness
- migrational of tumour cells into surrounding stroma where they are free to disseminate

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

Question 2

Describe 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
3. Motility and invasion
   - epithelial to mesenchymal transition (invasive properties and extravasation from circulation to tissues)
4. Metastasis
   - colonisation of target organs (ability to expand from micro metastases)

Question 3

What is angiogenesis?

Answer 3

Formation of new blood vessels from pre existing vessels

Question 4

What is vasculogenesis?

Answer 4

Formation of new blood vessels from progenitor cells

Question 5

What are the 3 types of angiogenesis?

Answer 5

Developmental/vasculogenesis
- organ growth

Normal angiogenesis
- wound repair
- placenta during pregnancy
- cycling ovary

Pathological angiogenesis
- Tumour angiogenesis
- inflammatory disorders

Question 6

What are the three stages of angiogenesis?

Answer 6

1. Small tumour eventually gets large enough size where delivery of oxygen and nutrients from nearby capillaries becomes limiting
2. Tumour switches on expression of angiogenic genes/factors that initiate new blood vessel growth
3. New network of blood vessels grows in and around the tumour increasing the delivery of oxygen and nutrients that allows it to grow and provides routes for cells to shed off and spread.

Question 7

What is tumour hypoxia?

Answer 7

Hypoxia is a strong stimulus for tumour angiogenesis

Hypoxia is low oxygen tension < 1% and Increases with increasing distance from capillaries

This activates transcription of genes involves d in angiogenesis, tumour cell migration and metastasis

Question 8

What are the genes activated as a result of tumour hypoxia?

Answer 8

VEGF (vascular endothelial growth factor)

GLUT-1 (glucose transporter 1)

u-PAR (urokinase plasminogen activator receptor)

PAI-1 (plasminogen activator inhibitor 1)

Question 9

What are some examples of angiogenic factors?

Answer 9

VEGF (vascular endothelial growth factor)

FGF 2 (fibroblast growth factor 2)

PIGF (placental growth factor)

Ang 2 (Angiopoietin)

Question 10

What is the function of angiogenic factors?

Answer 10

To stimulate the directional growth of epithelial cells

They are stored and bound to components of the extracellular matrix and may be released by matrix mtelloproteinases

Eg. Matrix metalloproteinase 2 (MMP-2)

Question 11

Describe the VEGF signalling pathway

Answer 11

1. VEGF binds to VEGF receptor 2 on endothelial cells
2. The complex dimerises at the plasma membrane and recruits co factors
3. That subsequently activate 3 major signal transduction pathways
   - cell survival (PKB)
   - gene expression (Ras and Raf)
   - cell proliferation (PIP2 and DAG, IP3)
4. All of these pathways are essential for angiogenesis

Question 12

What are the 3 mechanisms of timeout cell motility and invasion?

Answer 12

Increased mechanical pressure caused by rapid cellular proliferation

Increased motility of the malignant cells

Increased production of degradative enzymes by both tumour cells and strolls cells

Question 13

What is lost during epithelial-mesenchymal transition (EMT)?

Answer 13

Epithelial shape and polarity is lost

Cyokeratin intermediate filament expression is lost

Epithelial adherents junction protein is lost

Question 14

What is acquired in epithelial mesenchymal transition (EMT)?

Answer 14

Fibroblast like shape and motility

Invasiveness

Vimentin intermediate filament expression

Mesenchymal gene expression

Protease secretion

Question 15

What are epithelial markers?

Answer 15

E-cadherin

Beta-catenin

Claudia-1

Question 16

What are mesenchymal markers?

Answer 16

N-cadherin

Vimentin

Fibronectin

Question 17

What are E cadherins in epithelial molecules?

Answer 17

Homotypic adhesion molecule (connects epithelial cells together)

Calcium-dependent

Inhibits invasiveness

Binds beta catenin

Without E cadherins cells would grow on top of eachother instead of being a mono layer of normal cells and cells become more motile.

Question 18

How do stromal cells contribute to tumour formation?

Answer 18

Factors released by stromal cells include angiogenic factors, growth factors, cytokines, proteases

Eg. uPA release by stromal cells bind to receptors on cancer cells and become activated.

Resulting in plasmin production.

Plasmin activates MMPs which permit invasion by degrading the extracellular matrix and releasing angiogenic factors.

Plasmin also activates growth factors

Question 19

What are the steps involved in cancer dissemination?

Answer 19

Primary tumour formation

Localisation invasion

Intravasation

Transport through circulation

Arrest in microvessels of various organs

Extravasation

Formation of a micro metastasis

Colonisation - formation of a macro metastasis

Question 20

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

Answer 20

Mechanical hypothesis

Seed and soil hypothesis

Question 21

What is the mechanical hypothesis?

Answer 21

Anatomical considerations: Blood and lymphatic systems, entrapment in capillary beds

Question 22

What is the seed and soil hypothesis?

Answer 22

Specific adhesions between tumour cells and endothelial cells in the target organ

Creating a favourable environment in the target organ for colonisation

Question 23

What is the success rates of targeting tumour angiogenesis to inhibit cancer?

Answer 23

Success with targeted therapy to angiogenic factors like vascular endothelial growth factor

Question 24

What is the success rates of targeting cell motility to inhibit cancer?

Answer 24

No success with targeting cell-cell adhesion molecules

Question 25

What is the success rates of targeting invasion to inhibit cancer?

Answer 25

All clinical trials with matrix metalloproteinases have been unsuccessful in reducing tumour burden

Question 26

What is Avastin?

Answer 26

First specific anti angiogenesis drug

Approved for colorectal, lung, kidney and ovarian cancers and eye disease.

It’s a monoclonal antibody

Question 27

Describe the mechanism of action of Avastin

Answer 27

1. Binds to VEGF
2. Prevents VEGF binding to VEGF receptors on endothelial cells
3. VEGF signal transmission inhibition (survival, angiogenesis, progression, metastasis)