CE L2 Proto-oncogenes

Question 1

3 e.g. of proto-oncogenes

Answer 1

EGFR
Ras
Src

Question 2

Until ……… discovery it was thought cancer was transmitted.

Answer 2

virus containing oncogene v-src identified.
but normal cells contain a v-src like genes.
So cancer is caused by action of near normal genes

Question 3

only human oncogenic retrovirus is

Answer 3

HTLV

Question 4

How does v-src containing virus cause cancer

Answer 4

Viral gene incorporation into host DNA, when it is excised it cuts out some host DNA (Src).

In normal cells with Src the C terminal is phosphorlated so tyrosine kinast is inactive and cannot interact with substrate. When active the C terminal gets dephosphorylated.

The C terminal is now cut off therefore constituatively active (cannot be phosphorylated to deactivate)

Question 5

V-src doesnt actually cause mutations by…

Answer 5

affects the function of key proteins

Question 6

V-src doesnt actually cause mutations by…

Answer 6

affects the function of key proteins

Question 7

How does HPV work?

Answer 7

Integretes viral DNA into host - permanently transforming host cells.
Doesn’t actually cause mutations but affects the function of key proteins.
Cause of cervical cancer.

Question 8

How does the HPV vaccine work?

Answer 8

Give the vaccine early on so the virus is identified as forgien

Question 9

3 hits that are caused by HPV?

Answer 9

E5 Prolonged activation of PDGFR

E6&7 Inhibit pRb and p53

Question 10

What is the basic function of epidermal growth factor (EGF) pathway?

Answer 10

Cells use this stimulation to stay alive.

At higher levels you get growth and proliferation

Question 11

Why is EGF receptors important in many cancers? (2)

Answer 11

1. EGF important - drives cell proliferation

2. Intrinsic kinase domain leading to down stream signalling pathways (Ras/MAPK and PI3K-PKB)

Question 12

Mutations in the EGF receptor can cause? (2)

Answer 12

Ligand independance (constituative dimerisation)
and
overexpression - gene amplification

Question 13

Explain the EGFR pathway…

Answer 13

…see pics.

EGFR -> Ras -> Raf -> MEK -> MEK -> ERK -> Regulation of transcroption

Question 14

3 types of proto-oncogene changes

Answer 14

1. Amplification of WT - when we copy gene to HER 2 the template slips and it gets copied twice (not a mutation, there is just more)
2. Val -> Gln - this is charged, unfavorable in the membrane therefore gets dimerised, consitutaively active HER2
3. Deletion - creates constituatively active tyrosine kinase (in EGF receptor)

Question 15

3 types of proto-oncogene changes

Answer 15

1. Amplification of WT - when we copy gene to HER 2 the template slips and it gets copied twice (not a mutation, there is just more)
2. Val -> Gln - this is charged, unfavorable in the membrane therefore gets dimerised, consitutaively active HER2
3. Deletion - creates constituatively active tyrosine kinase (in EGF receptor)

Question 16

2 Ways to target protooncogenes theraputically

Answer 16

1. Block the kinase domain

2. Block ligand binting

Question 17

E.g. of 2 drugs blocking the kinase domain

Answer 17

erlotinib and gifetanib (for NSCLC)

Small molecule inhibitors blocking ATP binding site on the kinase

Question 18

e.g. of drug blocking ligand binding

Answer 18

Herceptin

antibody (Ab can only be used for extracellular targets as huge)

Question 19

When do problems occur with herceptin

Answer 19

if the protein mutates again and the molecule cannot bind

Question 20

WT HER2 gene is also callled…..

and is amplified in …….. cases of breast cancer

Answer 20

ErbB2

25~30%

Question 21

HER2+ breast cancer is associated with

Answer 21

faster cell growth
tumour more likey to reoccur
more serious prognosis

Question 22

How do we detect HER2+ status? (2)

Answer 22

1. Immunohistochemistry
2. FISH (fluerescent in situ hybridisation) - more sensative than 1.
3. HER2-ECD-ELISA (detects cleavage product in serum)

Question 23

What is the basic action of herceptin?

Answer 23

binding and blocking the activity of HER2

Question 24

Herceptin is licenced…

Answer 24

originally only for final stage but now sooner.

Provides significant benefit

Question 25

Problems with herceptin (3)

Answer 25

Not a cure - just slower and remission
Cost
Patient will be on therapy the rest of their lives

Question 26

How does herceptin decease HER2 signalling? (5)

Need to know basic mechanism, not details

Answer 26

• may induce HER2 R down regulation
• Uncouples Src, Increases PTN
• Induces cell cycle arrest, increased p27
• may increase apoptosis/decrease angiogenisis
• promotes antibody dependent cellulate cytotoxicity (via Fcr and NK cells)

Question 27

Herceptoin is usaully given with combination of

Answer 27

doxorubicin and cyclophosphamide or paclitaxel

Question 28

Why give cancer drugs in combo?

Answer 28

Hit multiple pathways using lower doses so fewer sideeffects

Question 29

s/e problem of herceptin

Answer 29

cardiotoxicity

Question 30

Is resistance a problem with herceptin?

Answer 30

Yes- cells find other ways to get around the block or there are further mutations so the herceptin is not recognsed

(around 1 year of therapy)

Question 31

What us Pertuzumab?

Answer 31

A future treatment potentially inihibiting receptor dimerisation

Question 32

4 future directions for HER 2 breast cancer therapy?

Answer 32

1. Pertuzumab
2. Recombinant toxins
3. Immunotherapy: chimeric proteins - two antibody sights that cross link HER 2 and immune cells
4. Immunotherapy: HER 2 vaccines activating CD4+ T cell immunity

Question 33

Mutations in Ras create…

Answer 33

Ras proteins that are always active

Question 34

Discrive the ras pathway

Answer 34

**?????**

Question 35

Where is Ras in the cell?

Answer 35

attached the membrane via a fatty acid modification

Question 36

What do FTI do? (farnesyl transferase inhibitors)

Answer 36

Inhibit the tethering of Ras to the membrane

Question 37

Do FTIs work?

Answer 37

No - disappointing trials

because instead of useing farnesyl, geranylgeranyl is added and Ras is still active

But it has potential as a treatment with combination therapy

Question 38

3 alternative approaches to targeting oncogenes

Answer 38

1. Antisense oligonucleotides - HRas, c-Raf - but show little efficacy
2. MEK inhibitors - in trial for colon cancer
3. Raf inhibitors - approved for renal carcinoma

Question 39

e.g. of a Raf inhibitor

Answer 39

Nexavar

Question 40

how is herceptin made1

Answer 40

inserting murine cdr into human iGg