Molecular biology and the diagnosis and treatment of cancer Flashcards
Cancer can be caused by:
physical carcinogens
chemical carcinogens
biological carcinogens
physical carcinogens:
ultraviolet and ionizing radiation.
chemical carcinogens:
asbestos and tobacco smoke.
biological carcinogens:
infections from certain viruses, bacteria or parasites.
What does HER stand for?
Human Epidermal Growth Factor Receptors
What are HERs?
a family of structurally-related cell surface protein
4 HER families
HER1 (EGFR/ERB1)
HER2 (ERB2/NEU)
HER3 (ERB3)
HER4
What is the structure of HERs
Extracellular ligand-binding domain
Intracellular tyrosine kinase domain
What do HER proteins undergo? Which one if the exception?
HER proteins undergo a conformational change
upon ligand binding that is essential for dimerization and signaling
HER2 does not undergo this
What primes the receptor for activity?
The ligand
What happens once the ligand binds?
The receptor can either homo or heterodimerise.
This stimulates the receptor to signal.
Which pair has the strongest mitogenic signling?
HER2:HER3
Mitogenesis
The induction (triggering) of mitosis, typically via a mitogen.
Mitogen and mechanism of action
A mitogen is a peptide or small protein, that induces a cell to begin cell division: mitosis.
It triggers signal transduction pathways involving mitogen-activated protein kinase (MAPK), leading to mitosis.
Describe HER signalling pathway
Ligand binding causes a conformational change which leads to dimerisation.
Dimerisation activates the tyrosine kinase domain.
HER2 is in a conformation which promotes dimerisation.
Different combinations of receptors stimulate different signaling pathways.
HER pathways stimulate cell proliferation, survival and are anti-apoptopic.
Are HERs proto-oncogenes or tumor suppressor genes?
proto-oncogenes
How can HER become oncogenic?
Over expression
Mutation
What was published in 1984?
that a mutant form of HER2 (neu) promotes cancer in rats.
What is different about HER2 from the others and what can this lead to
HER2 doesn’t need a ligand – always in an active state, always ready to signal
why we get overexpression of protein and start to get cancer
Where is the HER2 gene frequently amplified?
in breast cancer samples
What can happen when DNA replication goes wrong?
The cell can
end up with hundreds of
copies of a gene (gene
amplification).
Normal
cells are diploid so 2n (2
copies of a gene).
What happens when DNA replication goes wrong in a proto-oncogene?
If the gene is a protooncogene like HER2 this
can promote cancer.
What technique can be used to determine copy number of a gene?
Fluorescence in situ
hybridisation (FISH)
Gene amplification of HER2 leads to
increased levels of the receptor
Difference in number of HER2 per cell in normal breast tissue and cancerous breast tissue
Normal breast tissue has approximately 20,000 copies of the HER2 per cell.
Cancerous tissue can have up to 2 million copies per cell.
HER2 as a marker
HER2 is a negative prognostic marker for several cancers
Over expression of HER2 correlates with.
Over expression of HER2 correlates with poor survival rates.
Median survival for breast cancer patients without treatment
(HER2 positive 3 years)
HER2 normal 6-7 years
What is HER2 positive cancer
25% HER2 overexpressed
can do little when HER2 positive compared to HER2 normal
How did Genetech target HER2 overexpression in breat cancer?
using therapeutic antibodies
Advantages of using antibodies
Antibodies can be raised against nearly any protein.
Antibodies are very specific.
Antibody binding can interfere with receptor signaling.
Antibody binding can target cells for destruction by the
bodies immune system.
First step in process of making therapeutic antibodies?
making a monoclonal antibody.
Monoclonal antibodies
Recognise a single epitope
on an antigen.
Disadvantage to monoclonal antibodies?
murine antibodies are not well tolerated in humans (Muromonab-CD3 1986).
How was the disadvantage to monoclonal antibodies solved?
This problem is solved by a process called humanisation.
What inhibits HER2 growth
Targeting HER2 over expressing cancer
cells with 4D5
Method of targeting HER2 over expression with 4D5
1) Treating HER2 over expressing cells with the monoclonal antibody
(4D5) which binds the extracellular domain of HER2 inhibits their proliferation.
2) Injecting mice with the anti-HER2 monoclonal (4D5) antibody suppresses tumor growth in mice.
3) Injected radio labeled 4D5 targets HER2 positive breast cancer cells in women.
humanised version of 4D5
Herceptin (Trastuzumab)
An IgG1 molecule consists
of 2 heavy chains and 2 light chains.
Hypervariable regions of the antibody
what are these regions also called?
Involved in antigen binding.
These regions are also called
complementary determining regions
(CDRs).
How many CDRs can be involved in binding an antigen?
Up to six CDRs can be involved in binding
an antigen.
Method of how humanised version of 4D5 Herceptin generated?
1) Clone the murine heavy and light chain cDNA encoding 4D5.
2) Clone the murine CDRs of 4D5 into human IgG1 heavy chain and light chain plasmids.
3) The humanised antibody is then made by transfecting CHO cells with light chain and heavy chain plasmids
Phase II clinical trials of Herceptin
Study shows that Herceptin is active on women with HER2 positive breast cancer.
However, it did not show any benefit on women who had normal levels of HER2.
Phase III clinical trials of Herceptin
Phase 3 clinical trial shows that women with HER2 positive breast cancer gain an
extra 5 months disease free survival. However, Herceptin can cause serious complications.
Cancer returns in the majority of the women.
in 1998 what does the FDA approve?
Herceptin for the treatment of women with metastatic
breast cancer who have tumors that over express HER2. In 2000 the European Commission
approve Herceptin.
More clinical trails performed two
- investigate the best way to use Herceptin
- Determine if Herceptin works on other HER2 positive cancers (indications)
Herceptin is most effective
if it is used in combination with surgery or chemotherapy (adjuvant therapy).
1 year of treatment.
What cancer is Herceptin also approved for?
Approved for use in metastatic gastric cancer.
Future directions
HER2 dimerisation inhibitors
Antibody drug conjugates
Targeting other HER family members
Drug combinations
Drug combinations
Giving Herceptin plus tyrosine kinase inhibitor (Tyverb) got rid of HER2 positive tumors within 11 days.
Women with normal levels of HER2 will respond to Herceptin? True or False
False
Cancer will come back in 15-25% of women treated with Herceptin?
True or False?
True
