Cancer Bio (Dan Lecture 2)

Question 1

What occurs on a cellular level to cause cancer?

Answer 1

• Changes in the chemical structure of DNA
• Can be base changes, deletions, translocations etc
• Mutations in oncogenes and tumour suppressor genes

Question 2

How can altered genes in cancer be identified?

Answer 2

• Cytogentics
• Chemical carcinogenesis
• RNA viruses and DNA viruses
• Transfection of tumour DNA into normal cells
• Identifiction of genes inherited in families that are associated with cancer predisposition
• Basic research on cell signalling, cell cycle control and apoptosis

Question 3

What is cytogenetics?

Answer 3

Study of inheritance in relation to the structure and function of chromosomes

Question 4

Give an example of how cytogenetics can be used to identify common cellular cancer features

Answer 4

Reciprocal translocation between chromosome 9 and chromosome 22 creating the BCR-ABL1 fusion genes
- Translocation present in 95% of all CML patients

Question 5

What is the study of chemical carcinogenesis?

Answer 5

Identification of carcinogenic agents and what changes they cause at the DNA level

Question 6

Explain how the Ames test tests for compound induced mutations

Answer 6

1) Rat liver is homogenised
2) Test compound is metabolically activated by rat liver enzymes
3) Added to Salmonella unable to grow without added histidine in culture medium
4) Count number of Salmonella colonies that grow on medium without histidine due to mutations

Question 7

Describe the early experiments using transfection of tumour DNA into normal cells that allowed identification of DNA as a causative cancer agent

Answer 7

• Transfection of tumour DNA into normal cells using calcium phosphate
• Cells plated as a monolayer
• When the plate is full of cells, normal cells stop dividing by contact inhibition
• Identification of cancr cells by uncontrolled growth
• Grow on top of eachother due to no space, no monolayer

Question 8

What oncogenes were discovered as a result of the transfection assays?

Answer 8

H-Ras and K-Ras (N-Ras found later by homology)

Question 9

What is the role of the Ras gene products and how often are these genes mutated in human cancers?

Answer 9

• 21kD proteins
• Have GTPase activity
• Involved centrally in signal transduction
• Found mutated in 40-50% of human cancers

Question 10

Give an example of an inherited gene associated with a predisposition to cancer?

Answer 10

Inheritance of the BRCA1 gene

- Associated with breast cancer

Question 11

What type of receptor is the Epidermal Growth Factor Receptor (EGFR) and where is it localised?

Answer 11

• Tyrosine kinase receptor
• Contains intracellular tyrosine residues that can be phosphorylated to control activation
• Membrane bound receptor

Question 12

Describe the EGFR signalling pathway

Answer 12

• Ligand binding, by multiple EGF family ligans, facilitates receptor dimerisation
• Dimerisation forces tyrosine kinase residues into close proximity leading to cross-phosphorylation of intracellular tyrosine residues
• Phosphorylated domains then bind to signalling proteins that initiate cascades
• Functional cascades include RAS-RAF, PI3K and STAT pathways
• Signalling regulates:
  > Proliferation
  > Differentiation
  > Motility
  > Survival

Question 13

What is the relation between the EGFR and cancer?

Answer 13

Mutations in EGFR render it constitutively active

• Promotes constant growth and division
• Anti-apoptosis via constant Ras signalling

Question 14

What part of the EGFR and the ligand could potentially be targeted to prevent cancer development?

Answer 14

1) Neutralising antibody (binds to ligand - prevents receptor binding)
2) Anti-heterodimerisation antibody (prevents dimerisation)
3) Kinase inhibitor

Question 15

What is a current EGFR targeted cancer drug?

Answer 15

Gefitinib - EGFR inhibitor

- Binds to ATP binding site of EGFR, removing phosphate sourse for tyrosine phosphorylation

Question 16

Where do mutations of the EGFR most commonly occur?

Answer 16

• Exons 18-24 of the tyrosine kinase domain of the gene

- Most common are deletion at exon 19 and point mutation at exon 21

Question 17

What is angiogenesis?

Answer 17

The formation of new blood vessels

Question 18

Why is angiogenesis crucial for cancer development?

Answer 18

• Cells require a supply of oxygen and nutrients
• Rapid cell growth means that cells often become isolated from vessels
• Formation of new vessels required to sustain cell growth

Question 19

How does angiogenesis occur?

Answer 19

• In response to angiogenic growth factors binding to endothelial cell receptors
• Outgrowths of new endothelial cells from existing vessels - called ‘chords’
• Chords fuse with neighboring vessels and develop lumens

Question 20

What occurs to tumours in the absence of angiogenesis?

Answer 20

• Will not grow beyond a small diameter
• Form ‘necrotic centres’ where cell growth is balanced by cell death
• May explain ‘dormancy’ of mcrometastases

Question 21

How is angiogenesis initiated?

Answer 21

• Tumour cells produce angiogenic factors, most potent being Vascular Endothelial Growth Factor (VEGF)
• VEGF binds to a 3 main types of tyrosine kinase receptor called VEGFR 1-3 or NP1/2

Question 22

What changes does VEGF bring about?

Answer 22

1) Initial effect - increases endothelial cell wall permeability allowing more nutrients to diffuse to cancer cells

2) Stimulates protease production by endothelial cells
- Allows remodelling of basement membrane and release of fibroblast growth factor (FGF)

3) Stimulates endothelial cells to secrete factors such as Insulin like growth factor (IGF) and Platelet derived growth factor (PDGF) which stimulate tumour growth

Question 23

Where is the VEGF gene located? How many proteins does it produce?

Answer 23

• On chromosome 6p
• Makes 5 different sized proteins
• VEGF A-D and placental growth factor (PGF)

Question 24

What is the structure of the growth factor?

Answer 24

A disulphide bonded homodimer

Question 25

What is the main treatment that targets the VEGF system?

Answer 25

Avastin

- Blacks VEGF binding to its receptor

Question 26

What type of molecule is Avastin? How is it administered? What cancers is it usually used to treat?

Answer 26

• Monoclonal antibody
• Usually given alongside chemo
• Mostly given to patients with advanced colorectal, breast and non-small cell lung cancers